Date Awarded

Summer 2018

Document Type


Degree Name

Master of Science (M.Sc.)




Jonathan D Allen

Committee Member

S. Laurie Sanderson

Committee Member

Paul D Heideman


The supply of new individuals into a population is one of the most important factors impacting species distributions and ecological interactions within a community. For marine invertebrates with complex life cycles, the supply of new individuals into a population can be influenced by factors experienced throughout their life history—before, during, or after metamorphosis. In recent years, scientists have begun to take a more holistic approach to understanding marine population assemblages by considering links between early life stages. When experiences in the pre-metamorphic life stages impact post-metamorphic life stages, this is known as carry-over effects. Because carry-over effects impact fitness of individuals, they could determine which individuals are recruited into the population and ultimately influence adult population structure. Using the keystone sea star Asterias forbesi, I tested how carry-over effects of larval food environment influence post-metamorphic performance in juveniles. I also tested whether carry-over effects could be compensated for if juvenile sea stars are fed juvenile mussels. Larvae were reared to metamorphosis under high larval food concentration and low larval food concentration. to test for carry-over effects of larval food concentration, my response variables at metamorphosis were survival, age, juvenile area, and juvenile spine number. to test if carry-over effects could be compensated for, each juvenile sea star was reared for 2-3 weeks on a juvenile feeding treatment of unfed, 1 juvenile mussel week-1, 3 juvenile mussels week-1, or 6 juvenile mussels week-1. My main response variables for the juvenile feeding experiment were mussel mass consumed and juvenile growth rate. I predicted that juveniles that settled early would experience the most severe carry-over effects, so I conducted the juvenile feeding experiment on the first settlers (“early”) and settlers that delayed their metamorphosis relative to the first settlers (“late”). Overall, I found that A. forbesi larvae reared under low food concentration took longer to reach metamorphosis and settled as smaller juveniles with fewer spines compared to those juveniles reared on high larval food concentration. For early settlers, juveniles from low larval food background metamorphosed at smaller sizes, so they reduced feeding and had lower mean growth rates compared to juveniles from high larval food background. Therefore, carry-over effects significantly impacted early settler performance, and this could not be overcome through juvenile feeding. However for late settlers, there was no significant difference in area at settlement between juveniles reared from high versus low larval food background. Therefore, carry-over effects of larval food environment were not present among late settlers, and thus there were no differences observed in juvenile performance. The differences observed between early and late settlers suggest that there may be a trade-off between larval duration time (i.e. delaying metamorphosis) and post-metamorphic performance.




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