Biology of mussels & Camps

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Biology of Mussels & Clamps
Introduction:
Mussel is the common name used for members of several families of clams or bivalvia
mollusca, from saltwater and freshwater habitats. These groups have in common a shell
whose outline is elongated and asymmetrical compared with other edible clams, which
are often more or less rounded or oval.
They have two shells connected by a hinge-like ligament. Around the world, mussels live
in a variety of freshwater habitats but are most prevalent in stream and rivers. They
vary in their adult sizes from those as small as a thumbnail to others as big as a pie
plate.
The common name "mussel" is also used for many freshwater bivalves, including the
freshwater pearl mussels. Freshwater mussel species inhabit lakes, ponds, rivers,
creeks, canals, and they are classified in a different subclass of bivalves, despite some
very superficial similarities in appearance.
Fig: Marine blue mussel, Mytilus edulis,
Importance:
By dooing this assignment we can know about:
 The internal anatomy of mussels
 The external feathers

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 The reproductive system
 The distribution
 The life cycle
 The food & feeding behavior
Classification:
Kingdom: Animalia
Phylum: Mollusca
Class: Bivalvia
Subclass: Pteriomorphia (marine mussels), Palaeoheterodonta (freshwater
mussels), Heterodonta (zebra mussels)
Order: Mytiloida
Family: Mytilidae
Subfamily: Mytilinae
Genus: Mytilus
Species: M. edulis (Blue mussel)
Three key characteristics of Mussels:
1. These include a two velvet shell to contain soft body.
2. A muscular foot often seen extended from between the two velvet.
3. Its aids the mussels in locomotion, burrowing & positioning in the river bottom.
General Anatomy:
 The mussel's external shell is composed of two hinged halves or "valves".
 The valves are joined together on the outside by a ligament, and are closed when
necessary by strong internal muscles.
 Mussel shells carry out a variety of functions, including support for soft tissues,
protection from predators and protection against desiccation.

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The shell has three layers. In the pearly mussels there is:
 An inner iridescent layer of nacre (mother-of-pearl) composed of calcium
carbonate, which is continuously secreted by the mantle;
 The prismatic layer, a middle layer of chalky white crystals of calcium carbonate
in a protein matrix; and the periostracum, an outer pigmented layer resembling a
skin.
 The periostracum is composed of a protein called conchin, and its function is to
protect the prismatic layer from abrasion and dissolution by acids (especially
important in freshwater forms where the decay of leaf materials produces acids).
Fig: External Morphology of Mussels
Different organs:
Fluting – repeated ridges and valleys alternately arranged
Hinge – the edge of the shell where the two valves are physically connected

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Lateral teeth – the elongate, interlocking ridges on the hinge line of each valve
Mantle – the fleshy tissue that is attached to the nacre and envelops a mussel’s soft
parts
Nacre – the pearly interior of a mussel shell that may vary in color
Pallial line – the indented groove on the inner shell surface, roughly parallel to the
ventral edge, that marks where the mantle was formerly attached
Periostracum – the outermost external layer of a shell
Pseudocardinal teeth – the interlocking tooth-like structures located near the umbo
Pustule – a small bump or knob
Rays – a solid or broken stripe on the periostracum that usually radiates from the umbo
Sculpture – raised portions on the shell exterior that form lines, ridges or pustules
Sulcus – a narrow shallow shell depression extending from umbo to ventral margin
Umbo – the area of the shell first to form (sometimes called the beak)
Valve – one of the halves of a shell
Wing – a thin posterior extension of the shell most notable on heelsplitters
Internal Morphology:
 This simplified illustration shows the arrangement of the soft tissue body parts
of a freshwater mussel.
 The adductor muscles function to close the two halves of the shell.
 The mantle surrounds the visceral mass and covers the interior surface of the
shell. The mantle also manufactures the shell itself, which is mostly composed of
calcium carbonate. Water enters the mantle cavity through the incurrent siphon.
 Mucus secreted by the gills traps food which moves to the palps, is passed to
the mouth and is digested in the stomach.

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 The intestines continue to the anus, where waste is carried out the excurrent
siphon. Water circulation also provides oxygen exchange in the gill tubes and on
the gill’s outer surface.
 Mussels have two pairs of gills; one pair rests in each shell valve.
 Other organs of the mussel include the hepatopancreas, gonad, kidney and a 2-
chambered heart.
 The nervous system consists of ganglia. The foot extends from between the two
shell halves and is used for movement and to anchor the animal in the substrate.
Fig: Internal Morphology of Mussels
Distribution:
Marine mussels are abundant in the low and mid intertidal zone in temperate seas
globally. Other species of marine mussel live in tropical intertidal areas, but not in the
same huge numbers as in temperate zones.
Certain species of marine mussels prefer salt marshes or quiet bays, while others thrive
in pounding surf, completely covering wave-washed rocks. Some species have colonized

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abyssal depths near hydrothermal vents. The South African white mussel exceptionally
doesn't bind itself to rocks but burrows into sandy beaches extending two tubes above
the sand surface for ingestion of food and water and exhausting wastes.
Freshwater mussels inhabit permanent lakes, rivers, canals and streams throughout the
world except in the Polar Regions. They require a constant source of cool, clean water.
They prefer water with a substantial mineral content, using calcium carbonate to build
their shells.
The diversity of freshwater mussels in the United States is unmatched. Of the estimated
1,000 species worldwide are found. In comparison to other countries and continents
like Africa with 96 species, China with 60 species, and Europe with a paltry 12 species,
the wealth of the U.S. becomes truly impressive. The lion's share of this diversity is
found in the southeastern drainages of the Ohio, Tennessee, Cumberland, and Mobile
rivers.
Habitat:
 Mussels generally live half-buried in gravel, sand, or mud on the bottoms of
streams and lakes.
 Some species prefer to live in large rivers, while others are adapted to small
creeks or to ponds or lakes with standing water.
 Mussels that live in moving water often have shells that are heavy or are
sculptured on the outside. Weight and sculpturing help anchor mussels in river
beds and prevent them from being washed away.
 Mussels that live in lakes or ponds tend to have thin, unsculptured shells.
Food & Feeding Habit:
 Mussels are efficient suspension feeders. They feed by actively filtering particles
from the water, which passes into and out of the mantle cavity through the frilled
siphons. Breathing also occurs as this stream of water passes over the creature's
gill.

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 Feeding both marine and freshwater mussels are filter feeders; they feed on
plankton and other microscopic sea creatures which are free-floating in
seawater.
 Phytoplankton cells both living and dead constitutes the main source of food, but
other sources of carbon such as decomposed macrophytes or resuspended
detritus may also supplement their diet. As stocking density increases, the
demand for food eventually exceeds the supply, ultimately resulting in food
limitation, which in turn could reduce growth.
 A mussel draws water in through its incurrent siphon.
 The water is then brought into the brachial chamber by the actions of the cilia
located on the gills for ciliary-mucus feeding.
Lifecycle of Freshwater mussel:
Freshwater mussels belonging to the order Unionoida (also called naiads) are large
bivalves which live in the sediment of lakes and rivers around the world. The lifecycle of
freshwater mussels is unique among bivalves: larvae (called glochidia) are released into
the water where they attach to the gills and fins of fish. The glochidia remain attached to
the fish for between one week and several months, developing into juvenile mussels
before detaching from the fish host and dropping off into the sediment to grow. In this
way the mussels can be transported upstream by the host fish
Fig: Life cycle of M. eduli

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Spawning:
When sperm and eggs are fully ripe they are released from the follicles in each gonad
into a series of genital canals that gradually combine into a common gonoduct that
opens on the genital papill . Eggs and are liberated via the exhalent siphon directly into
the water column, where fertilization occurs. About 10,000 spermatozoa are shed for
each ovum spawned
Gametes and Fecundity :
The eggs are spherical and 68-70 pm in diameter; each possesses a vitelline coat 0.5- 1.0
pm thick, and contains numerous lipid droplets and yolk granules. Accurate
measurements of fecundity are difficult to obtain due to the experimental difficulties of
assessing an individual female's output over the entire breeding period. Estimates
obtained by inducing females to spawn in the laboratory suggest that a large adult
mussel (4-5 cm long) weighing 1 (tissue dry weight) may liberate about 8 x 10 6 eggs .
Spermatozoa swimming freely in the water column react on contact with the egg by
extruding an acrosome filament (Bayne 1976b) that enables the sperm to penetrate the
vitelline coat and initiate meiosis. At 18 OC the eggs hatch about 5 h after fertilization to
produce a ciliated embryo.
Reoproductive Strategy:
The large number and small size of eggs produced by the blue mussel are typical of the
planktotrophic reproductive strategy in which output is maximized but nutrient
investment per egg is small (for review see Bayne 1976b). This strategy is generally
considered to aid dispersal as it allows mussels to produce the maximum number of
larvae which require a prolonged pelagic development period. However, such a strategy
produces an egg with the barest minimum of nutrient reserves to enable the larva to
develop sufficiently to start feeding on plankton.

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Larval Development and behavior:
The stages of larval development and their durations are summarized in Table 1. It must
be emphasized that the larval stage may anywhere from 15 to 35 days and that the
duration is dependent on prevailing environmental conditions. Larvae of blue mussels
from Connecticut developed normally only within the temperature range of 15-20 OC;
at 15 OC they developed normally in salinities ranging from 15 to 35 ppt, whereas at 20
OC they could only developnormallybetween 20 and 35 ppt (Hrs-Brenko and Calabrese
1969). Bayne (1965) reported that the trochophore could develop successfully only in a
salinity of 30-40 ppt and at temperatures of 8-18 OC, and that within this temperature
range, the development rates were fastest at the highest temperatures. Larvae from an
oceanic blue mussel population grew fastest at 30-32 ppt and did not grow well at
salinities below 24 ppt .
Reproductive behavior:
The life cycle of the freshwater mussel is
one the most complex and interesting in the
animal world. Unlike other animals that can
actively search for a mate, the sedentary
mussel depends on the river current to
reproduce. The process begins with the
male releasing sperm, and the female
located downstream drawing it in through
her incurrent siphon. Numbering in the
100's to hundreds of thousands, the
fertilized eggs develop into glochidia within
her gills.
Once mature, they are released into the water column to begin the second part of their
lives-attaching to the gills, fins, or scales of freshwater fishes. At this point, the process
is further complicated because not only do the glochidia have to find a fish, but it has to
be one of a few specific fish species for the life cycle to continue. If a glochidium attaches

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to the correct fish species, it encysts into the fish's tissue and undergoes a short life as a
parasite.
Over several weeks, it begins to develop gills, a foot, and other internal structures to
become a juvenile mussel. The now fully transformed, but still microscopic, juvenile will
drop off the fish and begin its life on the stream bottom. Unbeknownst to the fish, it has
just served as a taxi transporting the young mussel into new habitat away from its'
parent. If the mussel is lucky enough to grow into an adult, it may live 20-100 years or
more depending on the species.
Fig: Lampsilis' display attracts host fish - Paul L. Freeman, The Nature Conservancy
Lampsilis ornata (Pocketbook) from Coosa River, Alabama

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Fig: Glochidia of Lampsilis encapsulated on the gills of largemouth bass. Glochidia are
parasites but they usually do no harm to the host. The glochidium clamps on, and the
epithelial cells of the gill then migrate to form a capsule around it. This structure is
often erroneously called a cyst, but technically cysts are structures made by a parasite,
while capsules are made by a host.
Mussels and nutrient mitigation:
Marine nutrient bioextraction is the practice of farming and harvesting marine
organisms such as shellfish and seaweed for the purpose of reducing nutrient pollution.
Mussels and other bivalve shellfish consume phytoplankton containing nutrients such
as nitrogen (N) and phosphorus (P). On average, one live mussel is 1.0% N and 0.1% P.
When the mussels are harvested and removed, these nutrients are also removed from
the system and recycled in the form of seafood or mussel biomass, which can be used as
an organic fertilizer or animal feed-additive. These ecosystem services provided by
mussels are of particular interest to those hoping to mitigate excess anthropogenic
marine nutrients, particularly in eutrophic marine systems. While mussel aquaculture is
actually promoted in some countries such as Sweden as a water management strategy
to address coastal eutrophication, mussel farming as a nutrient mitigation tool is still in
its infancy in most parts of the world. Ongoing efforts in the Baltic Sea (Denmark,
Sweden, Germany, Poland) and Long Island Sound and Puget Sound in the U.S. are

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currently examining nutrient uptake, cost-effectiveness, and potential environmental
impacts of mussel farming as a means to mitigate excess nutrients and compliment
traditional wastewater treatment programs.
Factors affecting Mussel biology:
Temperature:
The adults are incapable of surviving in the waters, where summer water temperatures
exceed 27 0C (Wells and Gray 1960). Lethal temperature response of the blue mussels
depends on the animal's previous thermal history. In mussels acclimated to an
intermediate temperature (20 OC) and transferred to water at 27.5 OC, the "time to 50%
mortality" was 350 h, which was about 8 times as long as that of mussels acclimated to
10 OC.
Salinity:
The blue mussel is a euryhaline species that occurs in environments ranging from full
oceanic salinities (34 ppt) to mesohaline (5- 18 ppt) estuarine conditions (Bayne et al.
1976a). If the tidal variation in salinity is small (< 10 ppt), the blue mussel remains
active throughout the salinity fluctuation (Widdows 1985). In response to a rapid drop
in ambient salinity, such as may occur with the ebb tide in estuaries with a large input of
fresh water, the blue mussel first closes its exhalent siphon to stop the ventilation of the
mantle cavity, and then closes its shell if the salinity change is large enough (reviewed
by Davenport 1982). It can thus effectively isolate its tissue from up to half the change
in ambient osmotic concentration (Shumway 1977). Shell closure cannot be maintained
longer than about 96 h (Gilles 1972) because the animal must rely on stored nutrient
reserves and anaerobic metabolism to sustain energy demands.
Substrates and Current:
The mussel is an epibenthic species that as an adult lives in areas with substrates
ranging from rock to coarse gravel; even areas with mud and sand substrates can be
colonized provided that there is a firm surface, such as a stone or another mussel shell,
to which the byssus threads can be attached. The blue mussel requires sufficient water
flow to ensure larval dispersal and carry suspended food particles. It tends to attain a
larger size in sheltered environments than in more exposed open coast conditions (Seed

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1976). This differential size is probably due to differences in food availability between
habitats and the stunting effect of the extensive disturbance of feeding and exposure to
air in open coastal populations (Seed 1976). In addition, predation may be so severe in
the exposed sea coast populations that few mussels survive into their third year (Seed
1969).
Oxygen:
Oxygen diffuses into the blue mussel across the gill, where there is close contact
between the water and the hemolymph pumped through the gill filaments by the heart.
There are no oxygen-carrying pigments in the blood (Newel1 1979). Theede et al.
(1969) reported that under laboratory conditions the blue mussel survived 35 days in
water at 10 OC containing only 0.15 ml 0 2 . I-', but survival was reduced to 25 days
when hydrogen sulfide was present. In response to a gradual decline in oxygen content,
the blue mussel can increase its extraction efficiency for oxygen.
PH:
The upper pH tolerance limit of the zebra mussel (Dreissena polymorpha) has not been
established experimentally. This study was designed to test the effect of elevated pH on
the health and survivorship of zebra mussels. All zebra mussels acceptable ph level is
9.3 to 9.6 . The zebra mussels in the high-NaOH treatment moved and formed byssus
attachments less often and had lower mean dry body mass than zebra mussels in other
treatments. Dishes that contained zebra mussels had more algal genera than control
dishes. In this experiment, the upper pH tolerance limit of zebra mussels was between
9.3 and 9.6 and may have been dependent on the rate of pH change.
Economic value:
Freshwater mussels have a high ecological value. They are an important food source for
many other animals including muskrats, minks, otters, fishes, and some birds. More
importantly, they serve as indicators in that they are sensitive to pollutants such as
heavy metals, pesticides, agricultural nutrients, heavy loads of fine silts. These
pollutants will kill mussels and thus provides a warning of the particular waters
infested with these pollutants. It is inevitable that mollusks are going to be exposed to
water born chemicals. Once exposed uptake is very rapid and very easy. Examples of

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these compounds include benzene hexachloride, chlordane, DDT, dieldrin, and
toxaphene. There are other unnoticeable pollutants that are found in commercial
plastics such as Phthalate esters. Since mollusks are not very good at biodegrading these
pollutants pose a threat to their lives.
Uses of mussel as food:
Humans have used mussels as food for thousands of years and continue to do so. About
17 species are edible, of which the most commonly eaten are Mytilus edulis, M.
galloprovincialis, M. trossellus and Perna canaliculus.
Freshwater mussels nowadays are generally considered to be unpalatable, though the
native peoples in North America ate them extensively. During the second World War in
the United States, mussels were commonly served in diners. This was due to the
unavailability of red meat related to wartime rationing.
In Belgium, the Netherlands, and France, mussels are consumed with french fries
("mosselen met friet" or "moules-frites") or bread. In Belgium, mussels are sometimes
served with fresh herbs and flavorful vegetables in a stock of butter and white wine.
Frites/Frieten and Belgian beer sometimes are accompaniments. In the Netherlands,
mussels are sometimes served fried in batter or breadcrumbs, particularly at take-out
food outlets or informal settings. In France, the Éclade des Moules is a mussel bake that
can be found along the beaches of the Bay of Biscay.
Recommendation:
Due to chemical pollutants and zebra mussels, many of the unionids are declining in
population or becoming endangered. Conservation efforts have begun by two main
methods. Ecologists are focusing on mussel relocation to separate the native mussels
from the zebra mussels, or polluted body of water. While those in the gaming industry
are focused on killing the zebra mussels by a variety of different methods including
electrical. Nonetheless many of the native mussels are endangered and must be
protected, by mainly not polluting our freshwaters. In terms of species domination by
the zebra mussel, perhaps that plays in the role of natural selection, and unless there
are severe consequences, should be left alone.

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Conclusion:
Freshwater mussels are an essential component of our rivers and streams. By their
siphoning actions, mussels filter bacteria, algae, and other small particles, which make
them one of the few animals that improve water quality. Mussels also serve as a food
source to many species of fish, reptiles, birds, and mammals. So as a student of fisheries
we have to give more emphasis on it.
References:
Links:
http://en.wikipedia.org/wiki/Mussel
http://www.gpnc.org/shells.htm
http://www.museum.state.il.us/intro_habitat.html
http://molluskconservation.org/MUSSELS/Reproduction.html
http://www.museum.zoo.cam.ac.uk/bivalve.molluscs/bivalve.research/freshwater.mus
sels
http://www.dgif.virginia.gov/wildlife/freshwater-mussels.asp
http://www.bio.umass.edu/biology/conn.river/reproduction.html
http://www.inhs.uiuc.edu/cwe/wwwtest/mussel/Pages/introduction.html