Date of Award

Fall 1996

Project Type

Dissertation

Program or Major

Zoology

Degree Name

Doctor of Philosophy

First Advisor

Larry G Harris

Abstract

Tenellia adspersa is a small (5-7 mm) estuarine nudibranch. Tenellia lives in a highly variable environment and feeds on many gymnoblastic and calyptoblastic hydroids. I undertook a field study at four sites in the Great Bay Estuary (Durham, New Hampshire) to assess the amount of variability in abiotic and biotic factors. Environmental parameters (temperature and salinity) and the availability of hydroid prey (Cordyolophora lacustris and Obelia spp.) varied within the generation time of Tenellia and could affect its life history.

Laboratory studies compared the growth rate of the hydroid, Cordylophora to the growth rate and predation rate of Tenellia. The results suggested that Tenellia could exhaust its food supply within a single generation, depending on initial colony size. Demographic studies comparing nudibranch life history reared on two common hydroids (Cordylophora and Obelia) found that Tenellia could vary its life history (age and size at maturity) in response to differences in hydroid species.

Tenellia displays poecilogony (more than one developmental mode). Proximate environmental sources were investigated in an examination of the effect of adult nutritional state on reproductive output, offspring development, survival and growth. I compared nudibranchs provided with an ad libitum diet of Cordylophora to individuals starved up to four days. Development was plastic; eggs from the same spawn produced veligers that either hatched as non-feeding swimming larvae or metamorphosed within the capsule, hatching as benthic juveniles. This strategy was dependent on egg size, with eggs larger than 125 $\mu$m hatching as benthic juveniles. Adult nutritional state affected egg size and the frequency at which the two developmental modes were expressed. Five to 20 percent of the eggs within a spawn hatched as benthic juveniles under well-fed conditions. In contrast, all of the eggs within a spawn hatched as swimming larvae and metamorphosed into smaller juveniles under starvation conditions. However, adult starvation did not affect juvenile growth and survival, suggesting that any cost associated with maternal investment were confined to the pre-metamorphic stages. Furthermore, these results suggested that the plastic developmental strategy employed by Tenellia may represent a bet-hedging strategy allowing Tenellia to survive and reproduce in an unpredictable estuarine environment.

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