Bivalve Biology

1/30/2020

BIVALVE BIOLOGY

Matt Griffin Adapted from Dale Leavitt 2019

PHYLUM MOLLUSCA

• Invertebrates – no backbone - Millions of years old

• High diversity > 85,000 living species > 60,000 species in fossil record

• Habitat - Te rre s t r i a l - Freshwater -Marine

• Represents 23% of all named marine organisms

PHYLUM MOLLUSCA

• Bilaterally symmetrical

• Majority have a hard shell - exp: Nudibranchs & Cephalopods

• Three distinct areas - head area - visceral mass -mantle

• Primarily herbivorous

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PHYLUM MOLLUSCA Highly diverse - 7 classes

Oyster drill Channel whelk Moon snail

PHYLUM: MOLLUSCA CLASS: GASTROPODA

• Spiral coiled shells – body can be withdrawn • Carnivorous – some predatory on bivalves

PHYLUM: MOLLUSCA CLASS: CEPHALOPODA

• Reduced shells - beak • Rival mammals in terms of complexity and function

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PHYLUM: MOLLUSCA CLASS: BIVALVIA

• Two laterally compressed shells • Hinged together by elastic ligament and teeth • Head greatly reduced • Fleshy mantle encasing the visceral mass • Muscular foot • Loss of radula • Large gills used for feeding & respiration • Mostly sedentary

BIVALVE • Lifestyles BIOLOGY • Anatomy

• Growth

• Respiration • Feeding and digestion • Nervous system • Circulatory system What do you need • Locomotion to know as a farmer? • Reproduction

HABITAT - LIFESTYLES

Epifaunal - Byssal attached (blue mussel) - Reclining (Giant clam) - Cemented (oyster) - Swimming (scallops)

Semi-Infaunal - Byssally attached (ribbed mussel)

Infaunal - Burrowing (quahog) - Boring (piddock)

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EPIFAUNAL - CEMENTED

EPIFAUNAL – BYSSAL ATTACHMENT

EPIFAUNAL - RECLINING

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EPIFAUNAL - SWIMING

SEMI-INFAUNAL – BYSSAL ATTACHMENT

INFUANAL - BURROWING

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INFUANAL - BURROWING

Beak Bill

EXTERNAL ANATOMY - OYSTER

EXTERNAL ANATOMY - QUAHOG

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QUAHOG – TWO VARIETIES

• Mercenaria mercenaria alba - White color - 98% of wild

• Mercenaria mercenaria notata - “Charlie brown clams” - 1% - 2% of wild catch - May be common in hatchery stock

BIVALVE SHELL LAYERS

• Periostracum - thin - mostly made of protein - may or may not be present

• Prismatic layer - thick layer - provides structure

• Nacreous layer - AKA “pearly layer” - very smooth - protects bivalve soft tissue

INTERIOR OF AN OYSTER

resilium SHELL

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INTERIOR OF A QUAHOG SHELL

WAMPUM (SUCKÁUHOCK)

Shell beads of Eastern Woodland Tribes Mostly used in exchange in rights of honor and ceremonial gifts

• Wampum – white beads • Suckáuhock – purple beads

What is the purple from?? - slow growing - metabolic waste product deposited in shell

BIVALVE CROSS SECTION

Bilateral Symmetry

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SCALLOP QUAHOG OYSTER

OPENING SHELLFISH

OPENING AN OYSTER

HINGE SHUCK

OPENING AN OYSTER BILL SHUCK

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OPENING THE QUAHOG

Gills

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BIVALVE MANTLE

• First layer of tissue next to shell • Very thin (2 cells thick in some cases) • Muscles for movement (retraction)

• Primary functions - Seals bivalve - Locomotion (in some cases) - SHELL FORMATION

MANTLE FUNCTION

Seals valves Locomotion

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MANTLE FUNCTION

SHELL GROWTH

Mantle controls chemistry within the extra pallial fluid 1. Mantle exeats periostracum to seals off extra pallial cavity 2. Protein matrix on leading edge 3. Calcium carbonate crystals deposited into protein matrix

PEARL FORMATION

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PEARL FORMATION

QUAHOG PEARLS

SHELL GROWTH

• Growth forms on leading edge - primarily linear growth - can force deeper cup

• Ecotherms - metabolism depended upon water temperature - seasonal growth patterns

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HOW OLD IS THAT SHELLFISH?

1 2 3 4 5 6 7 8 9 10 11 12 13

SHELL CROSS SECTIONS

“MING”

WORLDS OLDEST ANIMAL

507 YEARS OLD

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OYSTER LENGTH AT AGE

• Highly dependent upon - location - food flux - husbandry

• Market Oysters (3”) ~ 18 – 36 months in SNE

 Understand growth cycles on your farm

SHELL LENGTH VS. SOFT TISSUE MASS

• Diploids - 2 sets of chromosomes - spawn in summer months - reduced condition

• Triploids - 3 sets of chromosomes - increased growth (sometimes) - consistent condition - more expensive - harder to handle

Always in season!

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RESPIRATION & FEEDING

OYSTER RESPIRATION & FEEDING

• Pumps up to 50 gallons of water a day • Filters down to 2-3 microns

NUTRIENT CYCLING & REMOVAL

N - removal by a single oyster 0.77 g N/yr. (if harvested)

N - removal of 1-acre farm 231 kg N/yr. = 509 lbs.

N - removal from RI oyster sales in 2018 = 14,500 lbs.

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RESPIRATION & FEEDING

dorsal EXHALENT CURRENT

ventral INHALENT CURRENT

posterior

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QUAHOG

SOFT SHELL CLAM

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BLUE MUSSEL FEEDING – E. WARD

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LABIAL PALPS

Crystalline Style

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DIGESTION

• Free floating crystalline style

• Cilia rotate crystalline style

• Food ground against gastric shield

• Digestive enzymes released

• Food particles moved to digestive glands and intestine

• Heart • Veins and arteries • No capillaries OPEN • Open sinus that blood (hemolymph) moves through CIRCULATORY SYSTEM

OYSTER CIRCULATORY SYSTEM

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CLAM CIRCULATORY SYSTEM

CIRCULATORY SYSTEM BLOOD CELLS

• Ameboid phagocytic blood cells • Tr anspor t oxygen • Can ingest bacteria

Normal cell morphology

Abhorrent cell morphology

HEMATOPOIETIC NEOPLASIA (AKA CLAM LEUKEMIA)

• Proliferation of abhorrent blood cells • Displace tissue • Interfere with normal functioning of circulatory system

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NERVOUS SYSTEM

No centralized nervous system Comprised of ganglia and nerves Mostly associated with mobile parts of the bivalve - Foot - Siphon

SIMILAR ANATOMY THROUGHOUT BIVALVES

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LOCOMOTION

• Swimming • Walking • Digging 1. Push foot into substrate 2. Balloon distal end of foot (anchor) 3. Retractation – liquifies substrate 4. Valves move toward foot

JELLYBEAN CLAM (SOLEMYA)

PISMO CLAM

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QUEEN SCALLOP

RAZOR CLAM RACES

SWIMMING AND BURROWING

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WALKING

REPRODUCTION

• Dioecious - separate sexes (mostly) • External fertilization • Free swimming planktonic larval stage • Settlement • Recruitment

 Temperature & chemical ques

Clam Life Cycle

Infuanal

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fertilized egg

early cell division pediveliger D-stage larvae umboned larvae

adult males & females

Spat attached to substrate

Epifaunal Cemented

PROTANDRIC HERMAPHRODITISM

• Development of male organs first • Switch sex to female • Females occur in larger (older) animals - energetics - avoid self-fertilization • Can switch sex back to female • E.g. oysters and quahogs

SIMULTANEOUS HERMAPHRODTISM ripe unripe

• Male and female gonads occur at the same time • Release of eggs or sperm is often delayed

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SEX DETERMINATION

GONAD INDEX

Size of gonad relative to the size of other soft tissue • Increase (March – Jun/Jul) • Decrease (Jul – Aug/Sep) • Increase (Sep – December) • Steady or slight decrease (Jan – March)

 Direct impact on meat quality

SHELLFISH TERMINOLOGY

Larvae (babies) • Free-swimming during first 2 – 3 weeks of life Metamorphosis • When larvae transform to their adult body shape Settlement • When metamorphosing shellfish occupies its adult-type of habitat Recruitment • When current cohort of larvae settle into a population Spat/Seed (Juveniles) • Spat: Juvenile bivalve after settlement • AKA Seed: terminology used in aquaculture