“Allow me the use of
Four species of oysters are grown commercially in
Each geographic area has traditional, even unique, methods for cultivating, maintaining and harvesting its shellfish resources and Chesapeake Ray is no exception. Generally colorful phrases and local jargon are associated with these operations to the extent that the newcomer to this area is often quite taken by them.
Unlike the European or Dutch flat oyster, Ostrea edulis, and other members of the genus Osirea members of the genus Crassostrea have separate sexes. In the summer during periods of spawning, both eggs and sperm. produced literally by the millions, are shed into the water where fertilization takes place by chance contact. Fertilized eggs, or embryos, develop into free-swimming, plankionic larvae called veligers and are carried by currents. Development continues as the bivalve shells form through the straight hinge and into the umbo stage. By the end of 10-25 days, depending on genetic proclivities and environmental factors, baby oysters are ready to set into nonmotile stages for the rest of their lives.
By means of secretions from a “Cement gland”
oyster larvae attach themselves to various materials called clutch and the
newly settled oysters are called spat; a term both singular
or plural. A set of spat is called a strike, a heavy set is a “wrap up
set” or “wrap up strike.” Oysters in
It takes about 3 years for oysters to reach the
harvestable size of 3 inches in
Oysters that can be transplanted from one location
to another are called seed. Seed oysters can be of almost any size or age, but the are usually under 1½-inches long and 6 months to 1 or
even 1½-years old at the time of transplantation. Seed oysters are usually
transplanted along with the clutch material to which they have become attached.
Cultch, as used in
There are some privately owned and managed oyster
beds in Chesapeake Bay (more in
These methods largely involve a hunting approach and ostensibly are carryovers from olden days. However, it should be noted that each of these methods is technologically primitive, and fuel and other energy expenditures are smaller than for other mechanized, more sophisticated fishing practices. Recently, scuba diving has been introduced as a method of harvesting in the Bay, and has created a considerable amount of concern (and even animosity), among those engaged in the traditional pursuits.
Man, one of nature’s most aggressive and
persistent predators as well as polluters and despoilers, has managed to reduce
the harvest of oysters from
Infectious disease agents such as viruses, bacteria, fungi, and protozoa contribute to fluctuations and declines in oyster recruitment and productivity. Parasites and predators such as oyster drills, flat worms, and crabs, as well as other plants and animals that compete for space and food also contribute. Similarly, natural events such as storms, hurricanes, drought, and abnormal temperatures can affect the health and even accessibility of oysters. The 1973 summer hurricane Agnes is a good example of a natural event causing catastrophic consequences. Large amounts of fresh water run-off from the storm, carried chemicals and sediments into the Bay and over shellfish beds, dropping shellfish populations dramatically. Only recently has the Bay recovered from this natural phenomenon.
Fishery management agencies involved with the Bay try to keep abreast of new developments in oyster and shellfish culture. Furthermore, using the best council available, they devise new strategies to enhance recruitment, conserve, and if necessary, protect growing stages and increase production of this economically important renewable resource.
Some of the oyster culture techniques used in
Probably foremost is the difficulty in overcoming
tradition in the multiple use of waterways in the
culture systems, could probably be used effectively to
enhance recruitment of early life history stages of oysters. Suspended or
elevated off-bottom structures could be placed in broodstock
areas to capture seed for later transplant. Mechanized systems are used
oyster hatcheries have been built in the
Pond culture of oysters along the edges of the Bay and sea also hold promise even to the extent of using them in polyculture systems in which more than one species or type of animal and plant can be grown simultaneously. Environmental conditions (salinity, pH, dissolved oxygen. and temperature), type of food, and nutrients, diseases, and predators can be more easily controlled or regulated in these systems.
Culture of oysters in vertical systems such as
silos and in other systems such as tank farms and raceways are also being
attempted in some parts of the world all with possible future application to
To return to our original question:
Would our Japanese
colleague still feel he could use
II THE MUSSEL
— A Bivalve for All Seasons
Of all the marine animals that the beach walker
might observe, the mussel and its colleague in the intertidal
environment, the barnacle, are by far the most common in those coastal habitats
that have pilings, rock outcroppings, and other hard surfaces where these
animals can attach. The common mussel, often referred to as the blue mussel,
is a medium size bivalve which can grow to three or four inches long. It has an
elongated foot which can be extended from between the two shells and can
actually be used to allow the animal to move about. This foot has a special
modification called the byssus, made up of several
threads which are produced by a gland in the foot. These threads are used to
attach the mussel to hard surfaces. The mussel is a highly social animal and
generally occurs in aggregations of hundreds or thousands where extensive rocky
coastlines occur, as in
The mussel is extremely adaptable, found
throughout the intertidal and sublittoral
zones. In areas which receive heavy wave spray, the mussel will occur high in
the intertidal environment. Moreover, because of its
adaptability, the blue mussel is circumboreal in its
distribution, i.e., it is found in temperate waters throughout the northern
hemisphere. The blue mussel occurs on the west and east coasts of the
Two other mussels are common to the east coast.
The horse mussel is a much larger species, most often found in deeper waters
and to the north of
The other common mussel on the East coast is the ribbed mussel, a common denizen of marshes. It can be observed nested between stalks of marsh grass in most of the common east coast wetlands. Neither the horse mussel nor the ribbed mussel is regarded as suitable for human consumption. They often have a bitter taste, and the ribbed mussel frequently lives in environments which receive wastes or natural organic debris and is therefore not considered fit to eat.
The blue mussel is, however, an important food organism. It also functions within an important ecological niche in terms of other marine animals. As previously mentioned, the blue mussel will often form dense beds on rock surfaces or pilings, creating a habitat for many smaller species of marine life. Polychaete worms, amphipods or small shrimplike animals, snails, hydroids, small brittle-stars, and other forms requiring protection from predation will often live within and beneath the dense mussel beds. These small animals can move about under the layer of mussels and thus receive considerable protection from predators and from strong wave action and currents which might sweep them from their preferred habitat. Because of the strong byssal attachments, the mussels themselves are difficult to remove and are able to withstand all but the strongest waves that pound exposed shorelines.
The mussel is an important prey for many species of marine fish and invertebrates. Mouths of the temperate water cunner and tautug are specially equipped to tear smaller mussels from their substrate. Other fish, such as dogfish and rays, also actively prey on mussels. In turn, as the mussels are gradually removed through grazing, other prey species are exposed and different forms of fish and invertebrates can then feed on them. In addition to fish, sea-stars, lobsters, and crabs, other invertebrates may use mussels for food. Thus, this important marine bivalve, which itself obtains food by filtering water for tremendous quantities of particulate foods, is able to grow very rapidly and, as a population, serves as an important element of intertidal and sublittoral food chains.
In many instances, mussels in some parts of the world have been avoided during the summer months because of the possible toxic seafood poisoning which can develop. Traditionally, it has been held that mussels, along with other filter-feeding shellfish, should be collected or eaten only during a month with an “r” in its name. Marine scientists now understand that seafood poisoning develops when some species of single-celled phytoplankton are present in the water. Toxic forms of these phytoplankters produce a poisonous substance which is distributed throughout the tissues of bivalves when ingested. Scientists now are able to detect the presence of such phytoplankton species and in many parts of the world waters are routinely analyzed to determine if they are free of toxic substances. This allows the mussels to be collected and prepared for consumption without undo concern for mussel poisoning.
The ecological requirements for mussel recruitment and growth, as previously noted. are extremely broad. For this reason many cultures throughout the world have for more than a century had commercial operations in which floats, ropes, and other devices are used to collect the early larval stages of the bloc mussel in shallow coastal waters and embayments. By properly placing such collecting devices, the mussel “farmer” is able to gather crops of mussels numbered in the millions. Because the mussel tends to reproduce most of the year, there is often a steady supply of larvae, and it is possible to have a more or less continuous crop of mussels developing within a given area all year long. Through the management of such extensive natural systems it becomes possible to provide food for large segments of the world’s populations. As previously noted, mussels are extremely nutritious and even one or two individual animals eaten several times a week would provide the minimal protein allocations necessary for normal body maintenance and growth. Because the mussel can be grown in extensive numbers in compact areas, it becomes possible to provide food to extensive populations near mussel growing areas, cutting transportation and processing costs. It also ensures that the nutrients from runoff from the land are picked up as they pass through estuaries and before they are carried into the open oceans where they are effectively lost from a food web which culminates in man.
mussel has not only provided food for other forms of marine life, but has also been a delicacy in the diet of
many human cultures. Romans regarded mussels as highly appetizing. Today,
people throughout much of
To ensure that mussels are suitable for use, however, it is essential that their environment be free of sewage and industrial wastes. As is true for many bivalves, mussels can take up sewage wastes, including pathogenic microorganisms, and transfer them to the ultimate consumer, man. Mussels are also capable of biomagnification of industrial wastes. For instance, toxic levels of heavy metals and organic substances such as DDT and PCB's can accumulate in bivalves.
Given the foregoing, and the benefit of seafood easily grown in coastal waters, it is obvious that we must preserve water quality in estuaries not yet polluted and, further, we must upgrade the water quality of major urban estuaries that are already burdened with pathogenic microorganisms and industrial wastes. This can and should be done. It will require recognition that coastal waters and estuaries are suitable for purposes other than waste disposal and industrialization. It will take a concerted effort by scientific and federal and state agencies to identify problems, the sources of contaminants, and solutions. It will require massive amounts of money to upgrade the sewage treatment and industrial waste treatment systems within such areas. The alternative, however, is to allow continued degradation of coastal waters and to allow areas that are already heavily polluted to remain relatively unproductive. Since estuarine and coastal water areas are limited, it is obvious that mankind must make the best use possible of habitats that are available to it for the production of seafoods. The mussel is one of the more productive organisms available, a relatively inexpensive seafood which has not only luxury connotations, but can also he a staple in the diet of mankind.
III Common Chitons of
by JAMES DUGGAN in Naturalist
The second largest and most familiar group of invertebrates is the mollusca (“soft-bodied”). Members of the group. which include snails, slugs, clams, oysters, octopuses, and squids are widely used as food for man. Some typical anatomical features of mollusca are variously modified, or even lost in the more specialized forms, like the clam. Less common than their more conspicuous and economically valuable relatives, chitons display the molluscan body plan in its most typical form.
belong to the class Amphineura,, known to exist for about 570 million
years, long before the first fish swam the seas. There are about 600 species of
chitons existing around the world, sonic 140 of which
thrive along the coasts of
Chitons are sluggish animals, and most browse on the algal growth of rocks near the seashore. They move very slowly and may remain in one area for long periods. The body is bilaterally symmetrical. At the anterior end is an inconspicuous head. The bottom surface is mostly taken up by a broad flat, muscular foot, abundantly supplied with a slimy secretion. The foot functions for adhesion as well as locomotion. Over the foot lies the visceral mass (containing most organs) covered by a heavy fold of tissue extending around over the foot. This fold is the mantle, and its peripheral area is called the girdle. This girdle may be smooth and marked or covered with scales, bristles, or calcareous spicules, depending on species.
On its upper surface, the mantle secretes a shell, which in most chitons consists of eight separate plates, overlapping from front to rear. The digestive system is simply a tube extending from a mouth in the head to the anus. The mouth leads to a muscular chamber in which is found the radula. This is a horny ribbon with 17 chitonous teeth, some of which are capped with magnetite (iron) and is used to rasp off algal fragments. A subradula organ in the mouth area is used to locate food. Not all molluscs have radulas, but nothing like it exists anywhere else in the animal kingdom.
A chiton’s nervous system is primitive, a ring of nervous tissue around the esophagus, connected to two pair of long nerve cords which go to muscles in the foot and mantle. There are no sensory organs except for the subradula organ and aesthetes. Aesthetes, unique to chitons, are mantle sensory cells in the upper part of the calcareous plates. They provide dorsal sensory reception to light. Most chitons are negatively phototactic and live under rocks and ledges during the day and feed mostly at night or on cloudy days.
During May of 1982, while working for the National Oceanic and Atmospheric Administration (NOAA) aboard the Hydrographic Survey Ship, DAVIDSON, I was able to collect, identify and observe four different species of chiton thriving in the cold waters of Southeast Alaska. The locality was a rocky, fiord-like environment called the Bay of Pillars, located near Kuiu Island about 110 miles SSW of the state capitol, Juneau.
To collect chitons for study one must remove the animal from its substrate. This is not always easy but can be accomplished successfully by inserting a thin bladed knife under the foot of the animal and gently prying it oft the rock. A 10% buffered formalin solution is a good preservative. To prevent the animal from curling up you can secure the chiton to a thin board with strong thread before immersion in the fixative and leave it in the solution for about two weeks. The chiton can then be removed from the board and left to dry in a shady spot.
The most abundant chiton
I observed was the Black Katy Chiton (Katharina tunicala).
This chiton has a thick, black girdle that covers
about two thirds of each plate. It lives on rocks exposed to heavy wave action
and full sunlight. Its range stretches from
I found a colorful, smaller chiton, the Lined Chiton (Tonicalla lineala), very abundant in tidal pools encrusted with a
pink corallinc algae, its primary food source. The
colors of the plates vary greatly, enabling it to camouflage itself against the
rocks surface. This chiton has a smooth brownish
girdle and ranges from
Chiton (Mopalia muscosa), tolerates
large changes in environmental conditions (i.e. salinity, temperature). This
animal has many stiff mossy hairs on its girdle, with dark brown to olive green
plates. It lives in protected areas where heavy wave action is absent. Its diet
consists of animal and plant matter
and can be found along the coast from
least common of the chitons collected was the Mottled
Red Chiton (Tonicella njarmorea), a chiton with very beautifully sculptured bright red-orange
and white lined plates. Its girdle is smooth with a leathery consistency. I
found this chiton in tidal pools along with the Lined
Chiton, feeding on coralline algae. This species
also ranges widely along the
The chitons are of interest in the persistence of their primitive body plan and their success in survival. The success of the molluscan plan, a compromise of a protective shell with some degree of mobility, is proven by the existence of over 70,000 species of molluscs.
Sea shell collections have made the phylum Mollusc the most familiar group of animals in the sea. Collectors travel to all parts of the world to find new molluscs. For example, there was a 32 year old man who journeyed to a remote Indo-Pacific island to skin-dive and collect shells. Having picked up a uniquely decorated shell to examine, he was stung lightly on the thumb before he could drop it. He did not feel the pain at first, but soon discovered difficulty in breathing and although the wound was a little more than a puncture mark, he died within three hours. What is the fascination with this group of animals that would cause a man to travel halfway around the world and eventually meet his death?
Over 100,000 living species of the phylum Mollusca have been described. Forty thousand of these are found in the sea making this phylum the most abundant marine animal group. There is great diversity within the phylum to which both clam and octopus belong. This large group is subdivided into six classes, five of which are described below:
1. Amphineura (Polyplacophora) - the chitons
2. Scaphopoda - tusk shells
3. Pelecypoda (Bivalvia) -clams and oysters
4. Gastropoda - snails, slugs, nudibranchs, limpets etc.
5. Cephalopoda - the octopuses and squids
6. Monoplacophora - Neopilina (Q1)
Octopus, clams, snails, and squids certainly do not look very much alike. Why have biologists placed these different animals in the same group? In placing animals into groups, taxonomists look for similarities in development as well as similarities in appearance. Animals classified as mollusks go through a stage of larval development in which they look the same. The larval forms of marine mollusks are drifting zooplankton called trochophores. The trochophore larva (see picture) is typical of marine mollusks. The hairlike cilia propel the larva and also sweep food into their mouths. (Q2)
The body of an adult mollusk has a head, a foot, and a visceral (VISS-uh-rul)hump. Inside the visceral hump are the digestive organs, excretory organs, and the heart. The visceral hump is covered by the mantle. This is a thin skin that in most species secretes the calcium carbonate shell. The mantle hangs down over the sides and back of the body, forming a space called the mantle cavity. The gills are in this cavity. The are the respiratory organs of the aquatic mollusks. Undigested materials go from the anus into the mantle cavity before passing out of the animal. (Q3)
In most mollusks a current of water flows through the mantle cavity. The water carries in oxygen and food, and carries away carbon dioxide and other wastes. You might think that mollusks with a shell have a problem disposing of wastes. They do not. Water flows into the cavity through an opening called the incurrent siphon. The water circulates over the gills, where it picks up the carbon dioxide and wastes, and exits through the excurrent siphon. (Q4)
The type of shell or shells or the absence of shells and the type of muscular foot are also characteristics used to divide the mollusks into the classes mentioned above.
The class Amphineura
includes the chitins with a "shell" made up of eight partially overlapping
plates lining the dorsal (back) surface of the body. The muscular foot of these mollusks is broad
and well adapted for clinging to rocks.
Most chitins are unable to keep their gills free of debris. The animals are therefore obligated to live in
clear water such as is common to rocky shores.
Food is obtained using a rasp-like radula to
remove algae, detritus etc. encrusted on the roks. Most species are light sensitive and are most
frequently found under rocks in tide pools.
Adult chitins seldom reach a length longer than two inches. The Gumboot chitin, found on the west coast
The class scaphopoda contains about 200 species of burrowing marine mollusks. These are the tooth or tusk shells. The shell is an enlogated cylinder shaped much like an elephant's tusk. The attractive appearance of the shell and its relatively scarcity are witnessed by the fact hat Northwest coast Indians use to use these shells as money or wampum.
The shells, which are open at both ends, average 25-50 mm (1-2 inches) in length. The body is greatly elongated and the head and foot project from the larger opening of the shell. These animals burrow head down in sand or mud leaving only the posterior tip of the shell above the sand. Water is drawn in and expelled through the opening in the posterior tip of the shell. Oxygen and some food is drawn in with the water. Using thread-like tentacles, scaphopods capture microcopic food organisms from the sand surrounding them.
The majority of scaphopods live burrowed in sand under water ranging in depth from 6 to 1830 meters (20-5,500 feet). As a result the living animals are not frequently encountered. Judging from the number of shells washed up on beaches, however, scaphopods are not to be considered rare animals. (Q6)
Mollusks like clams, oysters, scallops, and mussels are called bivalves because their shells have two halves or valves. Bivalve mollusks belong to the class Pelecypoda or Bivalvia (new one). A hinge connects the two shells so they can be opened and closed by the animal. The shells are chalky structures made of calcium carbonate (lime) and other materials secreted by the mantle. There are 3 layers: an inner, pearly layer next to the mantle; a central chalky layer: and a thin outer layer made of the same material as the hinge. (Q7)
Pelecypoda means "hatchet footed". the hatchet shaped, muscular foot helps the mollusks quickly dig into mud or sand. Many members of this class spend most of their lives partly buried. The valves are kept slightly apart and two siphons are extended into the water. Water flows into the mantle cavity through the incurrent siphon. The water flows through the gills before it is expelled through the excurrent siphon. The gills remove dissolved oxygen from the water and release carbon dioxide. They also serve another important function. The gills are covered with a thin layer of mucus which traps small food particles. Cilia on the surface of the gills carry the food-bearing mucus to the mouth. These mucus-feeders feed on dead and decaying organic matter and many microscopic plankton found in the siphoned water. (Q8)
Many bivalve mollusks are important as food. Clams, oysters, scallops and mussels are all harvested in great numbers. Many of these species are cultivated by man and serve as the basis for thriving industries.
The most successful group of marine mollusks is the gastropods; sails, slugs, nudibranchs, limpets and abalones. There are over 28,000 species of marine gastropods. Most of these animals have only one shell (univalves). Some have no shells.
All gastropods possess a flat, muscular foot used for creeping. Most gastropods are slow travelers with a top speed of about 3 miles per hour. Gastropods also have a head, usually with tentacles and eyes.
This group of mollusks possess a rasping, tongue-like structure called a radula. The word radula comes from a Latin word meaning scraper. The ribbonlike oral structure contains rows of serrations or teeth which the gastropod uses to file its food apart. Sometimes during the development of all gastropods torsion occurs. Torsion is a 180 degree rotation of the internal organs. This rotation results in the anus, gills, and mantle cavity (all originally in the rear) all being located immediately behind the head. The most widely accepted theory to explain the survival importance of torsion was advanced many years ago by the biologist Garstang. Garstang maintained that torsion allows the head to be rapidly retracted into the mantle cavity. This offers the gastropod protection from attack. (Q9)
Octopus, squid, cuttlefish, and chambered nautilus belong to the Cephalpoda, or "head-footed" mollusks. Cephalopods are he most highly developed mollusks and may even be the most highly developed invertebrates.
The head of these headfooted mollusks is well developed and contains a large, differentiated brain. This complex nervous system allows the animals to be extremely active and provides for an effective control of the activity. Well developed eyes, similar to the human eye, are present. With the notable exception of the chambered nautilus, most cephalopods have no external shell. Instead, they have an internal pen which supports the body.
Cephalopods possess a siphon through which water can be expelled with great force. This stream of water propels the animal forward or backward in a jet-like manor. Some members of this group have fins which enable the animal also to swim in a fish-like fashion.
The mouth is surrounded by eight or ten sucker-bearing tentacles used for gathering food and for reproduction. A strong, parrot-like beak, frequently covered with a poisonous slime, is present in the mouth for grasping food. Immediately behind the beak is a file-like radula which is used to grind through shells.
Effective protection is obtained via an ink sac. The cephalopod can discharge a cloud of black, inky fluid that hides its escape from enemies. The high degree of development of this group is also seen in its behavior. Females frequently watch over their young, which develop directly (no larval stage), as they grow in "nest".
The giant squid is probably the largest
invertebrate in the world. It may grow
to be 18 meters long (58') and weigh 1,800 Kg (3,960 lbs). Sucker marks from these giants are often seen
on the skin of deep diving whales. In
spite of its reputation, the octopus is usually a timid animal. The largest octopus is found along the
Mollusks play a variety of ecological roles in the life of the sea: from scavenger to predator. Their diversity, abundance and large range (where they are found) make mollusks one of the most important groups of sea animals. Mollusks also play a large role in man's interactions with the sea. This group provides the "shell fish" which are widely harvested: clams, oysters, mussels, abalone, squid, octopus, etc. It also provides the most realistic hopes for "sea farming" or mariculture. The many members of the phylum Mollusca are both ecologically and economically important.
V Red Gilled Nudibranch of the Old Sow by Robert Leahy UW v19 #3 p7
Along Fundy’s western shoreline are several island communities known as the Quoddy Loop. The area features rugged coasts that include deep water coves, inlets, bays, and three islands (Moose, Deer, and Campobello) which collectively border Old Sow.
The deep waters of the
The inhabitants of this underwater wilderness have not been photographed extensively, primarily because of the cold water (average temperature is 48 degrees F.) and the false assumptions that the marine life here is not as colorful as in the warmer latitudes, nor is the water as clear.
Sow drops to over 450 feet but the
underwater rim of this turbulent whirlpool appears to attract much of the
beautiful and prolific marine life which can be photographed during slack tide
in this “North Atlantic Caribbean.” Its near vertical
walls help provide a rich biosphere which has created an exceptional environment for growth and reproduction
of the red gilled nudibranch. Although their habitat
extends from the Arctic to
The red gilled nudibranch is a member of the sea slug family — class Gastropoda, phylum Mollusca. These gastropods don’t have true gills, but breath through their skin or projections on the dorsal surface. They vary in size, shape and color and are of two types: the oval dorids, which have gills on their backs, one pair of tentacles and feed on sponges and bryozoa; and the aeolids, which have cerata or fleshy protuberances from the main body which are not gills and two pairs of tentacles. Gastropods are small animals. The adults rarely exceed two inches in length and a half inch in width. They are translucent white, with an opaque white strip down the middle of the back and a tapered tail.
The red gilled nudibranch is a member of the aeolid group which feeds on hydroids and anemones. This shell-less mollusk appears defenseless, but like most aeolids, utilizes ingested nematocysts (stinging cells) of its hydroid prey to defend itself from predators.
Up to 100 long finger-like extensions protrude in rows on each side of its back. These finger-like projections have a bright red (occasionally brown) core and an opaque white ring near the tips.
These extensions are not gills but extensions of the nudibranchs gut. The ingested nematocysts are directed to the gut extensions and become a part of its defense. The head has two pair of long
antennae, and the front end of the foot has a sharp hook-like extension on each side.
These animals are found mostly among seaweed and hydroids, their favorite dining entrees. Reproduction takes place at any depth; however most egg ribbons observed and photographed, were in 6 feet of water (at high tide) or deeper. Thr red gilled nudibranch spins a spiral egg casing containing hundreds of tin embryos. The developmental period of one to two weeks (depending on water temperature). Few predators have been identified that seek out and feed on these eggs. Larva are free swimming and have small shells. The young resemble adults and have large secretory glands which may provide a defense similar to the distastefulness of butterflies. Their color acts as a warning to shallow water fish that this morsal does not taste good; thus increasing their safety on the run of Old Sow. Winter flounder and cod appear to be the chief predators of this colorful aeolid.
Although prevalent along the entire coast of Maine, the red gilled nudibranch as well as the northern red tetia sea anemones appear in larger numbers adjacent to the rim and in the bore of Old Sow. The rich biosphere including a Field of hydroids created by the Fundy tidal flow promotes astonishing growth an reproduction for this and many benthic animals of the area. I also observed a low diversity of predators in this region. This combined with the fact that nudibranch are brightly colored and conspicuous during the day and may have a noxious defense to compliment the ingested nematocysts, contributes to the large populations.
There are 32 species of nudibranchs
in the southern
VI Hermit Crabs--THE SHELL GAME by DAVID K. BULLOCH
Unlike other knights of the order Decapoda (prawns, shrimp, crabs, and lobsters), the hermit crabs do not come equipped with full suits of armor. They lack any hard parts aft of their cephalothorax, which leaves their soft and defenseless hindquarters exposed to easy assault.
Their evolutionary response to nature which provided only plated gloves and jackets but no pants has been to employ empty snail shells as leggings. Among a few species in odd parts of the world, other items have been pressed into service — bamboo joints, half a coconut shell, and even a concavity in a bryozoan colony — but most stick to gastropod attire.
Since hermits of various species come in different size ranges, each must habituate the haunts of a similarly sized snail host to find a custom fit. In the shallow waters of mid-Atlantic shores, Pagurus longicarpus (the long-clawed hermit), the commonest of the small tideline hermits, inhabits the shells of the periwinkle, Littorina littorea; the mud snail, Alectrion trivittata; and the little moon snail, Natica pusilla.
A larger cousin, P. pollicaris (the flat-clawed hermit), abundant in deeper waters from Maine to Florida, suit themselves in the carbonate remains of the whelks, Busycon; the sand collar snail, Natica; and moon snails,Polinices, or any other large shell it can find.
On the west coast, the tidepool hermits, P. samuelis and P. granosimanus, have an overwhelming fondness for Tegula shells; whereas P. hfrsuriusculus, more plentiful in deeper water, prefer Acanthina or Olive/la.
Ten or more common species of hermits in the tropics use the wide variety of shells found in warmer waters. The tropics are also home to a land hermit, the soldier crab, Coenobita clypeatus, that leaves the sea when just out of the larval stage, returns often when young, but wanders further afield as an adult, returning only to procreate. The adult has a fondness for the West Indian top snail, Cittariunz pica, and is the reason these shells are often found deep in the rainforest and at relatively high altitudes.
Hermits often share both the inside and the outside of their chosen mobile home with others. The slipper shell, Crepidula, finds the interior lip of a whelk a good place to live, and its presence doesn’t seem to bother a hermit one bit. Deep inside, the polynoid worm, Halo.sydna, or a polychaete, Nenes, may set up housekeeping practically in the bosom of the hermit. Whether these worms arrive before or during occupancy by the hermit is unclear.
The outside of the shell can be cluttered with a long list of life — anything from the lightweight fuzz of Htydractinia or a coat of bryozoa, to a substantial load of barnacles or anemone that add serious wciglit to the total load the hermit must haul.
Irrespective of the burden, having an anemone on one’s shell is something of a status symbol in the hermit’s world. A have-not, especially if it is bigger, will boldly approach a have, grab the anemone around its midriff with its large claw, and give it a squeeze, at which point the anemone will let go its hold on its former home and, upon positioning, attach itself to the shell of its new conpanion.
shelled, the hermit has enemies. The octopus, for one, and shccpshead, spotted kelpfish, and perch for others.
Sex has its dangerous moments as well. Somehow the females growing receptiveness is sensed by the male which will seize her shell and carry it (and her) with him occasionally banging their two shells together. When both have reached the necessary level of stimulation, they simultaneously pop out of their shells, mate in a flash, and pop back into their respective quarters.
Aside from the daily grind of searching for food and occasional sexual forays, the hermit finds house hunting a consuming preoccupation. Although there have been a few reports to the contrary, most species have the common decency to wait until the original occupant passes on its legacy via natural causes. This is probably due more to the impervious defense the snail can muster by withdrawing its foot
and blocking an attack than any altruism on the part of the hermit.
Presented with a cluster of empty shells, the hermit ritually repeats an elaborate inspection of each one, turning the shell over and over, probing its passages, and if eminently suitable, popping out of its old home into its new. Even a new shell home does not stop it from going through the same routine with every encounter. If it comes across a shell it has recently examined, the normal riganiarole will be duly abbreviated as it somehow senses it is going over ancient history.
If a new shell is already occupied by a hermit, neither is deterred from the shell game. If the bigger of the two decides it wants to try out the shell of its smaller acquaintance, it is sure to get its way. The vanquished, forced to withdraw from the shell, is not molested by the victor and will usually pop into the victor’s hand-me-down or, if that’s not possible, quickly burrow into the sand to get out of harm’s way before some other predator comes along to take a snap at its hindquarters.
The hermit’s house hunting is entirely innate, unlearned, and hard-wired into its genotype. That is not to say the hermit is incapable of adaptive behavior. It is, but the presence of an empty shell automatically sets off a foreordained response that is present from the very first time it sets eyes on a shell.
The ethologist, Konrad Lorenz, calls this behavior a “species-characteristic drive-action” (the term in German “arteigene triebhandlung” doesn’t translate into anything more succinct). It is a set of neurophysiological sequences in which a selective response to a specific stimulus releases a fixed motor pattern. Put another way, a pattern of movements is evoked by an impulse internally produced but held in check until externally released by what has come to be called an “innate releasing mechanism”
This pattern of movement and its trigger, the IRM, is similar from one species of hermit to another, indeed from one genus to another within the suborder Paguridea, with as much constancy as their common physical characteristics.
These motor sequences have a phylogenetic origin and are part and parcel of the hermit’s inheritance. As such, hermits are highly resistant to individual modification. However, all animals have a feedback circuit that interprets the consequences of their behavior; specifically whether it is useful or not under prevailing circumstances. If you were to partly fill some shells with plaster of Paris or, more challenging, lightweight plastic foam, the hermit will learn by examination that the shells are useless.
Because they are ceaselessly active, hermits make good aquarium additions. They are easy to maintain. Feed them brine shrimp and, occasionally, a bit of seaweed. Forget hunks of meat that might entice other crabs. Hermits eat only small fragments and will not tear big pieces apart.
If, by chance, you want to entice a hermit crab out of its shell to temporarily get a better look at it, give up all thoughts of pulling it out. It will hold fast with two claw-like uropods affixed to its hindquarters and you will only break it in two.
The best way to get a hermit out of its shell is to tempt it with a new shell with a hole drilled in an appropriate rear whorl. When the hermit takes up residence in the shell with the back door open, you have only to prod into the hole with something pointed to elicit its departure. In fact, one marine biologist so acclimated a pet Pagurus that it immediately dropped out of its shell without a poke whenever it was lifted out of the water. Put back in the aquarium, it would await the return of its shell, and instantly resume residence when the shell was dropped back into the water.
VII Suspension Feeding by Bivalves: The Inside Story
The ocean is clouded with small particles of many types, defying a careful and complete description. Large rivers empty specks of degraded leaves, clay and silt particles, and detritus of many other types into an ocean already filled with phytoplankton, smaller zooplankton, and a plethora of animal and plant degradation products and exudates that collide in the water column, to eventually form what is often termed marine snow. A typical coastal water column has all this complexity, but even deep waters may be surprisingly rich in suspended particles.
Suspension-feeding animals must face this complexity and eek out a living by collecting particles, ingesting them, and absorbing nutrients. Many of the particles in the water, however, have no nutritive value, Of course one might imagine a suspension feeder ingesting all particles indiscriminately, digesting only those that are palatable, but this strategy would have two important disadvantages. First, the gut would be filled with large amounts of indigestible material. This would waste opportunities to digest perfectly good food. Second, materials might enter the gut that have negative physiological effects and even are poisonous. For example, the saxitoxin-bearing dinoflagellate Alexandrium has strong negative effects on bivalve function, so why would a bivalve want to ingest it? Why not reject the toxic substance beforehand?
Long ago, a simple observation demonstrated that bivalves could reject particles and even discriminate among different particle types. If you placed an oyster in a dish and fed it a high concentration of phytoplankton or a large amount of silt particles, you would soon see diffuse material at the bottom of the dish, emanating usually from the incurrent siphon or from between the shells. Flow did this happen? The internal space of a bivalve, its mantle cavity, contains a series of structures that transport and potentially reject particles before they cuter the mouth. Ibis process is known as preingestive selection. Particles enter a siphonlike entrance and then are drawn toward the surfaces of the gills. The water movement within the mantle
is stimulated by a complex set of ciliated tracts that heat continuously, creating a pressure differential that moves water and particles through the incurrent siphon and toward the gill surfaces. It appears that particles hit ciliated surfaces by inertial impaction, whereupon they become subject to selectivity (see Box Figure 13.2b), are moved by ciliary beating to more centralized ciliary tracts, and may then be transported to another main structure known as the palp (Box Figure 13.2b). The bivalve palp varies in structure depending upon species, but it is typically highly ridged, and the ridges and valleys are also ciliated. The palp moves particles along its own ciliated systems and eventually transfers some to the mouth.
To investigate this type of feeding, particles could be placed upon both gills and palps that have been surgically removed and mounted on slide, If the ciliated tracts were “smart,” they could reject bad particles before the palp had transferred them to the mouth. The rejected material that is never ingested is known as pseudofeces; this is the stuff mentioned earlier that was found in a dish with a bivalve, as opposed to true feces, which is matter that is egested from the gut. Pseudofeces production may occur by the gill sloughing off material directly or passing it to the palp, which can also form and pass pseudofeces outside the mantle cavity.
Do bivalves manage to select against nutritionally poor or even toxic particles before ingestion? A simple experiment suggests that they do. One can make a mixture of silt and phytoplankton and feed the particles to the bivalves. Presumably the phytoplankton are suitable food and the silt is not. One can measure the organic content of the food by sampling the experimental water and compare the results to measurements made of pseudofeces. Such experiments generally show that the pseudofeces are proportionally depleted in organic material, suggesting that selective rejection of nonnutritious material is occurring.
But where is the site of selectivity? This has been a mystery for many years. It has been possible to surgically removed structures such as gills and palps to trace the directions of ciliary beating, but this precludes observing the entire mantle cavity organ system as an integrated unit and disrupts any special hydrodynamic conditions that might occur in the intact mantle cavity.
Enter (literally) the surgical endoscope, which is a tubular lens that may be made of a Fiber-optic bundle or may be a single glass lens. For bivalves, endoscopes of as little as I mn in diameter are available, which allows for easy insertion into the mantle cavity, especially of larger bivalves. The endoscope can be attached to a video monitor and video tape recorder, allowing recordings of the movements of particles within the mantle cavity.
Another instrument aids us greatly in studying particle selectivity. The flow cytometer is an instrument adapted
From medical uses to marine biology. The principle is fairly simple. A small volume of water is drawn into a tube and as particles pass through the tube, they are struck by a laser beam. Particles reflect the laser light and can be counted and even sized, because the larger the particle cross section, the greater the reflection. Phytoplankton cells have a variety of photosynthetic pigments, many of which fluoresce when bombarded by blue light. For example, when chlorophyll is bombarded with ultraviolet Iight it fluoresces a vivid red color.
The flow cytometer reads the light reflected and fluoresced from each particle by means of a series of detectors. The combined signal of each particle allows us to discriminate among a variety of different particle types. Flow cytometers are extremely useful in analyzing marine water samples, but they also can be used to tell if a suspension feeder is selecting among different particle types. For example, one could feed a series of phytoplankton species and tell if some are being selectively ingested merely by comparing counts in the water column with particles in the pseudofeces. If there are proportionally more particles in the suspended food than in the pseudofeces, then the bivalve must be selectively ingesting those particle types because they are depleted in pseudofeces.
A simple experiment demonstrated an interesting result. Sandra Shumway and colleagues’ pioneered in using the flow cytometer to study selective feeding by bivalves. They fed mixtures of algal cultures to see whether species of algae were preferentially ingested, which could be told by comparing available food particles in the water with the material rejected in the pseudofeces. On comparing samples of algal mixtures, it was clear that a variety of bivalves were selectively rejecting certain phytoplankton species and preferentially retaining others for ingestion.
But where did the selection occur? Roger Newell and Stephen Jordan did an experiment that set the stage for the problem. After feeding the eastern American oyster Crassos!rei virguzica, a mixture of silt and the alga Tetraselmis sp., they found that the pseudofeces were strongly enriched with silt relative to the mixture in the water. This suggested that oysters are able to ingest organic rich particles and reject nonliving particles in the pseudofeces. Not only was the selectivity clear, but it worked in favor of excluding indigestible material (i.e., the silt) from ingestion. Because this study compared food in the water and in pseudofeces, it was nut possible to demonstrate where selection had occurred in the mantle cavity. Newell and Jordan followed the popular wisdom that oysters selected particles on the palp, maintaining that the gills had no role.
The use of a surgical endoscope clarified this problem definitively. J. Evan Ward and colleagues’ examined the feeding of Crassslna virginica by placing the tip of an endoscope between the open valves. The structure of oyster gills is rather different from those of many other bivalves. The gill is folded, or plicate, and the valleys are lined with cilia that beat dorsally. The “hills” also are covered with cilia and can either transfer particles or ventrally. If particles were transported dorsally, they arrived at a basal ciliated tract that transferred particles in a slurry toward the palp and were ingested. Particles transported ventrally, however were moved to a so-called ventral groove and were either rejected from the gill or transported to the palp and rejected from there as pseudofeces. The bidirectional option of particle transport immediately suggested the gill as the possible site of particle selection, rather than the palp, which was the standard belief of bivalve researchers for many decades.
A simple experiment performed by J. Evan Ward and colleagues combined observations using the endoscope with sampling directly from various ciliated tracts in the mantle cavity. While the endoscope was focused on various parts of the gill, a fine pipette was located to sample material from the dorsal and ventral ciliated tracts. It was already known that the dorsal tract carries particles that will be ingested and the ventral ciliated tract carries particles that are to be rejected. Therefore, one could sample these two tracts and compare them with the particles in the water, representing the available food. A flow cytometric analysis could then determine whether the gills were sorting the good from the bad particles.
Ward and colleagues used an approach similar to that of Newell and Jordan. They fed the oysters Crassostrea inginica and C. gigas with aged cord-grass (Spartina alterniflora) detritus, which they had ground to match an alga (Rhodonzonas) in particle size. The detritus was very poor in nutrients, much like the silt used by Newell and Jordan. The results were immediately apparent, especially because Rhodonzonas is a vivid red. The particles in the dorsal tract were clearly red and the ventral tract was tan, the color of the cord grass detritus. This demonstrate that it was the gill doing the sorting, not the palp.
Not all bivalves work this way. Mussels mainly transport particles ventrally and these particles are usually transported to the palps. Here the structure of the gill (much simpler) precludes sorting at this stage, and it is the palp that does the job. Indeed, the palp sorts among the cord grass detritus and Rhodonzone way to get the job done, apparently.
This research opens tip of the “black box” and allows us to mechanism is completely unknowm. No chemosensory cells have yet been found on bivalve gills. Yet the impact of good and bad Particles is literally spread all over the gill, so there must be a general system of detection. We also have no idea why different bivalves have such different gill architectures. Mussels do not select particles on the gills, yet oysters do this routinely. Both types of bivalve often live in near shore estuaries with complex arrays of particle types, nutritionally poor as well as appropriate. The results thus far therefore just scratch the surface..
A pearl is unique. It is the only gem created by a living creature! A pearl is formed when a foreign particle enters the body of an oyster (or other mollusk) along with some of the special cells which secrete nacre - the pearly substance of the pearl. For centuries, divers have searched the seas hoping to find an oyster with a pearl!
Today man has formed a partnership with the
mollusk which has resulted in the fabulous CULTURED PEARL INDUSTRY. The center
of this industry is in
The mollusks are collected and opened and the pearls are separated from the bodys. The lovely harvest is sorted according to size, weight and color. The pearl industry recognizes 7 colors as acceptable: white, cream, pink, green, blue and black. The Japanese Ministry of International Trade has enacted very strict regulations which govern the growing, sorting and selling of the pearls. This guarantees that all Japanese cultured pearls will be of highest quality.
IX About Octopi ....
Octopi are the phylum Mollusca which includes chitons, snails and clams. Their closest relatives are the chambered nautilus, cuttlefish and squids.
largest and smallest octopi are found off the
often encountered on the west cost of
Octopi have the most complex brain of the invertebrates (animals with out backbones). They have long term and short-term memories as do vertebrates. The octopus learns to solve problems by trial-and-error and experience. Once the problem is solved, the octopus remembers and is able to solve it and similar problems repeatedly.
Sense of touch is acute in the suckers. The rim of the cups are particularly sensitive. A blindfolded octopus can differentiate between objects of various shapes and sizes as well as a sighted octopus.
The octopus has highly complex eyes which compare to human visual acuity. Focusing is done by moving the lens in and out rather than by changing its shape as the human eye dose.
When threatened, the octopus will often try to escape by releasing a cloud of purple-black ink to confuse the enemy. It will change color and jet away to safety. Several blotches of ink can be released before the ink sac is empty. The ink is toxic to the octopus who will become ill or perhaps die if released in a confined area where the octopus can't escape the ink.
Color change is initiated by the eyes. If the octopus is disturbed, cells in the skin (chromatophores) will be active in an attempt to blend in with the surroundings. The chromatophores consist of three bags containing different colors which are adjusted individually until the back ground is matched. Coloration reflects mood, white for fear, red for anger, brown is the usual color.
Many octopi produce venomous secretions. In members of the Octopus genre, this venom is fatal to crabs and lobsters, their main food source.
Octopi have separate sexes (male and female) and fertilization is internal. In some species, the male can be distinguished by greatly enlarged sucker discs on the tentacles, which is used to remove a mass of spermatophore from within his mantle cavity and insert it into the mantle cavity of the female. Within two months after mating the female attaches strands of clustered eggs to the ceiling of her lair. More than 200,000 eggs may be laid. She shields the eggs, oxygenates them with streams of water from her syphon and cleans them with her suction cups. Most females will not eat after laying eggs and die soon after they hatch. Young octopi are carried about in water currents for about a month before they settle to the bottom. Only one or two out of 200,000 eggs will survive to become adult.
1. What species
of oyster is grown in the
2. Why are exotic species not grown there?
3. What happens to eggs from fertilization until attachment?
4. What do oysters use to attach themselves?
5. What sex are most oysters during their first 3 years of life..What happens later in life?
6. What is a clutch? a seed? a spat??
7. What do the
watermen do in the
8. How much has the harvest declined....what has caused it?
9. How did hurricane Agnes affect the population?
10. Why is
off-bottom culture not useful in the
11. How does off bottom culture system work?
12. What type of culturing is being tried?
13. Will oyster cultivation in the
1. What is a byssus
2. Where, geographically (range) are mussels found?
3. What are the three types of mussels listed....What use is each for food for man?
4. How do mussels benefit other organisms in a mussel bed?
5. What organisms feed on mussels?
6. What can cause poisoning in mussels?
7. What is the nutrition value of mussels?
8. What is the main drawback of raising mussels in coastal waters?
9. What is the main idea of the last paragraph?
"Common Chitons of
1. To what class do chitons belong?
2. How many species are there and how old is this group?
3. What percentage of the known chitons lives along the coasts of
4. How big is the largest chiton and what is it called?
5. What kind of symmetry do these animals exhibits?
6. What is the function of the muscular foot?
7. What layer secretes the shell?
8. Describe the chiton's digestive system.
9. Describe the chiton's nervous system.
10. What do they eat?
11. Who first discovered the chitons?
12. Why is the molluscan body plan so successful?
1. Which one of the five classes mentioned above do you think has the greatest number of species?
2. Which is one observation taxonomists use to place animals in the phylum Mollusca?
3. What are two functions that the mantle performs?
4. What substances of importance to the mollusk does the incoming water carry?
5. Since chitons can only live in clear water, how might we use them as an indicator of environmental pollution?
6. Considering the way scaphopods capture their food, do you think more scaphopod species would be found living in the mud or sand? Why?
7. Shells play a number of different roles in the life of marine mollusks. What are two ways in which shells are used to help marine animals survive.
8. What is the path of water flowing through a pelecypod mollusk?
9. How has torsion increased the survival chances of gastropods?
10. List three structures and behaviors that make marine scientists think that cephalopods are the most highly developed molluscs:
11. Describe the BEAK in Cephalopods.
12. Which organisms best provide hope in mariculture?
5 "The Red Gilled Nudibranch of the Old Sow"
1. Where does the red-gilled nudibranch live?
2. Describe the place called "Old Sow".
3. How high is the tidal range and what is the speed of water movement in and out?
4. What is the family, class, and phylum for the nudibranch" A)
5. What does the red-gilled nudibranch eat?
6. What does it use to protect itself7
7. What animals are the chief predators?
6. Hermit Crabs
1. What can be found outside the shell?
2. How would you get a hermit crab out of its shell?
3. What does the presence of an empty shell do to a hermit crab?
4. What is meant by the analogy "provided only plated gloves and jackets but no pants"?
5. To what Order do hermit crabs belong?