The Mutualist Life of Bivalves Wendy Stickel EVPP

The Mutualist Life of Bivalves Wendy Stickel EVPP Seminar on Mutualism March 4, 2010

Some Basic Facts • Belong to bivalvia class of molluscs • 30, 000 species • Include clams, oysters, mussels, scallops • Very ancient and successful taxonomic group

Bivalve Anatomy • Two-part shell operated by adductor muscles • Mantle covering soft body • Siphons pull in and release water • Gills take oxygen out of water, filter food and detritus, and circulate water • Two palps extend from mouth collect and sort incoming particulates

Distribution • • Marine All depths All latitudes Most substrates-rock, sand, compacted mud • Often dominant on coasts and estuaries, also offshore sediments • Tolerate extreme environments (deep sea vents)

Ecological Roles • • Filter-feeder Bioturbator Bioengineer – reef and mat builder Mutualist ØZooxanthallae ØSeagrasses ØEpibionts ØAnemones

Cockles and Zooxanthallae • Fragum erugatum • Hypersaline waters in Shark Bay, Australia • Densities >4, 000/m 2 • Photosynthetic zooxanthallae provide nourishment in return for stable environment and access to CO 2 and N wastes • Light-harvesting and lightfiltering services (in some species) Source: Hickman 2003

Mussels and Seagrasses • Spartina alterniflora – perennial deciduous grass, salinetolerant, builds up land at seaward edge of marsh • Grass height, biomass, and flowering correlate with mussel (Conkensia demissa) density • Experimental evidence: – Manipulated mussel density to observe effect on Spartina biomass – Nutrient enrichment of sediment was important on marsh flats but stabilization of substrate more important at marsh edge Source: Bertness 1984

Source: Bertness 1984

More on Seagrasses • Broadened findings to mussels (Mytilus edulis) and eelgrass (Zostera marina L) • Western Baltic • Sediment porewater concentrations of ammonium and phosphate doubled from mussels fertilization • Fertilization affected eelgrass growth (largest fraction of nutrient demands met via roots) Source: Reusch 1994

Some limitations on seagrassbivalve mutualisms • Interference competition of eelgrass by mussels squeezing roots – space limitations? (Ruth 1991; Kobarg 1993) • Interaction variable with non-native mussel (Musculista senhousia) – Effects ranged from facilitation to interference – Consistently impaired eelgrass rhizome elongation rates (Reusch and Williams, 1998)

Another benefit to seagrasses • Bivalves increase structural complexity of habitat • Spaces between shells offer refuge for small epiphytic grazers (gastropods, etc. ) • Reduced predation on grazers increased grazing from seagrass leaves=>increased light absorption • Tested with Thalassia testudinum (turtle grass) and Modiolus americanus (tulip mussel) Source: Peterson and Heck 2001

Bivalve-seagrass mutualism Source: Peterson and Heck 2001

Clams and Epibionts • Chama pellucida lives attached to shallow rock surfaces • Covered by dense growth of sessile plants and animals • Removal of epibionts increases predation on chama • Chama likewise offers low-mortality habitat to diverse sessile biota • Hypothesis that epibiont larvae preference for rough vs. smooth-surfaced substrates is selected for, increasing likelihood of interaction Source: Vance 1978

Some common themes • Habitat alteration is central • Conditional and dynamic – Contingent on broad processes rather than particular species-specific characteristics – Powerful force in shaping community structure • Need to look at in community context • Factor in restoring/preserving ecosystem function

How applicable to PRV? • Species common to coastal conditions • Bring ecosystem services which are needed for very disturbed environment – – – Filter-feeding Increased rate of nutrient cycling Reef and marsh building Grazing of epiphytes Light-harvesting and filtering • Ability to manage environmental changes – Increased nutrient loading – Climate change impacts: sea level rise, erosion from storm events

Partial List of References • PETERSON, BRADLEY J. AND KENNETH HECK, JR. Positive interactions between suspension-feeding bivalves and seagrass—a facultative mutualism MARINE ECOLOGY PROGRESS SERIES, Vol. 213: 143– 155, 2001. • BERTNESS, MARK D. RIBBED MUSSELS AND SPARTINA ALTERNIFLORA PRODUCTION IN A NEW ENGLAND SALT MARSH' in Ecology, 65(6), 1984, pp. 1794 -1807 6 c) 1984 • VANCE, Rl. CHARD R A MUTUALISTIC INTERACTION BETWEEN A SESSILE MARINE CLAM AND ITS EPIBIONTS, in Ecology, 59(4), 1978, pp. 679 -685 Cv) 1978.