Effects of variable maternal diet conditions on the reproductive success and development of the California sea cucumber (Parastichopus californicus)

Abstract

Anthropogenic and natural climate change is altering the biology and ecology of marine organisms, which can be reflected in the supply of primary production that provides food for consumers. Primary producers differ in their biochemical composition, and marine food webs are thus based on specific combinations of producers that provide key nutrients such as dietary fatty acids (FA). Some FA cannot be synthesized by marine invertebrates, and must be acquired directly from diets. Reproductive processes in marine invertebrates are often timed to correspond with seasonal patterns in primary production, such that dietary FA and other nutrients can be partitioned to eggs to provide energy for cell division and biomolecules needed for membrane development. My dissertation investigates the consequences of changing patterns in primary production by examining the effects of maternal diet on reproductive fitness of a deposit feeder, and provides information to support the management and continued captive culturing of the commercially harvested Parastichopus californicus (California sea cucumbers). In chapter 1, I describe a novel live-spawning method and quantify basic reproductive parameters for P. californicus. Peak spawning in the Southeast AK population was about two months earlier and three times smaller than previously observed in British Columbia, Canada. Live-spawned captive females produced more viable eggs and strip-spawned females produced higher fecundity rates. These findings are relevant for the management of commercially harvested populations of P. californicus because they more accurately define spawning seasons, and provide a reliable method to spawn captive animals for further aquaculture development. In chapter 2, I present the results of feeding experiments that explore the effects of two mono-specific algal feeds with different FA profiles on female reproductive output and pre-feeding larval fitness. Females fed with the green alga Tetraselmis sp. had higher fecundity, but there was reduced larval survival relative to females that were fed the diatom Thalassiosira sp. Similar rates of larval development were recorded in both feed treatments. Significant differences were observed in the abundance of FA 20:5ɷ3 (EPA), 22:3ɷ6 (DHA), 12:0, 16:0, and 18:0 FAs in eggs and female gonads between the two feed treatments. In chapter 3, I used field collections in Southeast AK to assess temporal patterns feeding behavior and diet, and examined tissue-specific patterns in total lipid and FA storage and utilization, in in situ populations of P. californicus. All tissue ratios (percent of each tissue relative to the total body mass) varied significantly among collection dates. Tissue and gut content total lipid content also varied significantly among collection dates, except for muscle tissue. Shell debris and terrestrial debris were abundant in all guts regardless of collection date. FA composition differed significantly among females with different gonad maturation periods in skin, viscera, and gonads, suggesting the use of lipids stored in skin and viscera for gonad development. These results further the understanding of dietary factors affecting reproductive fitness in deposit feeders by demonstrating the importance of diet and lipid storage to gonad development.