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The Mutualist Life of Bivalves

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.

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The Mutualist Life of Bivalves

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

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

  3. 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

  4. 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)

  5. Ecological Roles • Filter-feeder • Bioturbator • Bioengineer – reef and mat builder • Mutualist • Zooxanthallae • Seagrasses • Epibionts • Anemones

  6. Cockles and Zooxanthallae • Fragum erugatum • Hypersaline waters in Shark Bay, Australia • Densities >4,000/m2 • Photosynthetic zooxanthallae provide nourishment in return for stable environment and access to CO2 and N wastes • Light-harvesting and light-filtering services (in some species) Source: Hickman 2003

  7. Mussels and Seagrasses • Spartina alterniflora – perennial deciduous grass, saline-tolerant, 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

  8. Source: Bertness 1984

  9. 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

  10. Some limitations on seagrass-bivalve 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)

  11. 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

  12. Bivalve-seagrass mutualism Source: Peterson and Heck 2001

  13. 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

  14. 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

  15. 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

  16. 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 6c) 1984 • VANCE, RlCHARD R A MUTUALISTIC INTERACTION BETWEEN A SESSILE MARINE CLAM AND ITS EPIBIONTS, in Ecology, 59(4), 1978, pp. 679-685 Cv) 1978.

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