Download The Mutualistic 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
• 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
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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
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Filter-feeder
Bioturbator
Bioengineer – reef and mat builder
Mutualist
Zooxanthallae
Seagrasses
Epibionts
Anemones
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 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
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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.