The Mutualist Life of Bivalves
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Transcript of The Mutualist Life of Bivalves
The Mutualist Life of Bivalves
Wendy StickelEVPP 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
• MutualistZooxanthallaeSeagrassesEpibiontsAnemones
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
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
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 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)
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 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.