Indian Point, St. Andrews,. New Brunswick. Page 4. In Passamaquoddy Bay,. NB, Canada, mussel predators include: -Common Eiders. (Somateria mollissima).
Interactions between invertebrate predators in an intertidal mussel bed community
Yamada 2001
Brady K. Quinn, Melanie R. Boudreau, Diana J. Hamilton Department of Biology Mount Allison University
The Blue Mussel, Mytilus edulis • Forms dense beds on the rocky intertidal • Mussels important food for a wide variety of animals • Predation affects mussel abundance, causing changes to the community
http://www.thefreedictionary.com/Mytilus+edulis
Study Site Indian Point, St. Andrews, New Brunswick
http://www.sunrisebirding.com/07NEweb/index.htm
In Passamaquoddy Bay, NB, Canada, mussel predators include: -Common Eiders (Somateria mollissima) - green crabs (Carcinus maenas) -dogwhelks (Nucella lapillus) -sea stars (Asterias spp.)
http://www.gastropods.com/5/Shell_1175.shtml
http://www.sunrisebirding.com/07NEweb/index.htm
In Passamaquoddy Bay, NB, Canada, mussel predators include: -Common Eiders (Somateria mollissima) - green crabs (Carcinus maenas) -dogwhelks (Nucella lapillus) -sea stars (Asterias spp.)
http://www.gastropods.com/5/Shell_1175.shtml
Research Questions • What are the effects of intraspecific and interspecific interactions between invertebrate predators on mussel predation? – Prediction: Predators inhibit each other’s feeding, leading to non-additive predation
• How do interactions affect selection of mussel prey by predators? – Prediction: Predators shift to less profitable mussel sizes in the presence of other predators
Experimental Design
Predation Treatments Low and high natural densities of predators used, with predator species alone or in combination Average predator sizes surveyed: whelks 23-28 mm, crabs 33-38 mm Natural densities of mussels (186/0.09m2) allowed to settle on tiles and placed in cages Predators collected, starved for three days, then placed in enclosures with mussels
Mussel Sorting • Mussels separated by cause of death and measured • Some mussels found eaten by both crab and whelk – Communal feeding – Biomass divided up according to per individual consumption by crabs vs. whelks (6:1)
• Biomass and mean size eaten by each predator species determined
Statistical Analysis • Mixed model ANOVA design used to analyze foraging rates and mean sizes eaten: – Treatment = fixed factor – Round, Block(Round) = random factors – Initial mean size as covariate where appropriate
• Observed foraging rates in high density and mixed-species treatments compared to additive expectations – Differences compared between treatments, and compared to zero
Foraging Rate of Whelks
Significant effect of predator treatment on whelk foraging rate (p < 0.001)
Additive Predation - Whelks Deviation varied between treatments (p < 0.001) Whelk feeding depressed in presence of crabs Whelks also depressed by conspecifics
Foraging Rates of Crabs
Significant effect of treatment on crab feeding (p = 0.020)
Additive Predation - Crabs Significant differences between treatments (p < 0.001) Crab feeding depressed by conspecifics Depression nonsignificant in presence of whelks
Size Selection by Whelks
Sizes of mussels eaten by whelks not significantly different between treatments (p = 0.084)
Size Selection by Crabs Treatment significant (p = 0.003) Mussels eaten by crabs in LC were smaller than those eaten in all other treatments Larger mussels eaten in the presence of whelks (at low densities) and other crabs
Communal Feeding Communally eaten mussels significantly larger than those eaten by crabs alone (p < 0.001), but not significantly different from those eaten by whelks alone (p = 0.086)
Kleptoparasitism • Communally-eaten mussels represent kleptoparasitism by crabs on whelk-drilled mussels • Allows smaller crabs to feed on relatively large mussels without added handling costs • May be an important interaction between crabs and whelks in nature
Conclusions Prediction: Predators inhibit each other’s feeding, leading to non-additive predation • • •
Crabs Whelks: whelk foraging inhibited by crabs Whelks Crabs: crab foraging positively influenced by whelks Conspecifics: inhibition observed among whelks and crabs
Prediction: Predators shift to less profitable mussel sizes in the presence of other predators Whelks
Crabs
Implications • Multiple predators exist in natural systems • Predators moderate each other’s impact on prey • Future research should examine – Effects of additional predators (sea stars) – Role of kleptoparasitism by crabs on whelks in nature
http://www.narragansettbay.info/shellfish.cfm
http://www.lukemiller.org/journal/journal.html
Acknowledgements • Dr. Ron Aiken • Andrew Taylor, Mike Coffin, Laura Bursey, Cindy Ochieng, Jillian Craig • Mount Allison University • NSERC • NB Wildlife Trust Fund
