ARE ALL FISH NURSERIES EQUAL? DETERMINING HOW FOOD WEB DYNAMICS AFFECT FISH NURSERY HABITAT

"The fish nursery habitat concept has been used to define important habitat for larval and juvenile fish throughout coastal and estuarine areas. Nursery habitat has been defined as an area that produces more fish biomass , in the form of recruits to the adult population , compared to other habitat types. Management agencies and scientists have used this definition to identify nursery habitats; however , how nursery habitats function has remained a ""black box."" The complex mechanisms that make a particular habitat a nursery remain unknown. Many authors have explored these mechanisms in an attempt to open and describe the ""black box."" One such mechanism hypothesizes that food quantity and quality are linked to enhanced larval fish growth and survival. The objective of this dissertation was to investigate this particular hypothesis by focusing on the planktonic food web that supports larval and juvenile fish. This hypothesis predicts that abiotic and biotic factors that play a role in determining food quantity and quality and therefore help explain how a nursery habitat may function. In North Carolina , strategic habitat areas (SHAs) are defined as areas that contribute most to the integrity of the system and for fish as ""locations of individual fish habitats or systems of habitats that have been identified to provide exceptional habitat functions or that are particularly at risk due to eminent threats , vulnerability or rarity , "" but did not incorporate river herring nursery habitat in designations. In particular , the quality of strategic habitat areas was explored on two rivers in North Carolina that have been designated strategic habitat areas and have spawning anadromous fish populations especially river herring. River herring were an important commercial fishery in North Carolina and throughout the eastern seaboard , but a decline in populations resulted a moratorium on river herring harvest being implemented at the state level in 2007 yet the population has not recovered. Chapter 2 examined the percent total lipids and fatty acid profiles of tissue and ovaries from river herring. The goal was to determine if maternal effects on the offspring are a potential contributor to population decline. Results demonstrated that female river herring had increased percent total lipids , and a fatty acid profile that represents both a marine and freshwater diet. The ovaries had increased percent of DHA , which was similar to other herring species , and used for development and growth of larval fish. River herring female tissue and ovary total lipids and fatty acid profiles are at a quality that would result in successful migrations , spawning , and lipid storage for larval river herring to survive to first feeding. The goal of Chapter 3 and 4 was to determine if species and fatty acid composition of the lower food web varied in relation to abiotic factors of the sampling site in an estuarine fish nursery. In order to achieve this goal , the spatial and temporal variability of abiotic factors , phytoplankton pigments , zooplankton species composition , as well as the fatty acid composition of the seston , zooplankton , and larval fish were examined. The main findings were that phytoplankton biomass was correlated to changes in nutrient dynamics , and there were differences seen in the overall phytoplankton pigment composition differed within and between the two river systems. This study identified the seston fatty acid profiles correlated to the phytoplankton pigments , but some caution needs to be taken since there were low chlorophyll a levels , which is indicative of fatty acids that are indicators of detritus or other microplankton. The zooplankton in the Chowan River and tributaries was a mix of cladoceran and copepods in 2016 , but communities were mainly composed of cladoceran especially Bosmina spp. and Daphnia spp. in 2017. This change in zooplankton community composition resulted in decreased percent DHA and increased EPA for the zooplankton fatty acid profiles. The zooplankton in the Tar/Pamlico River and tributaries was a 50/50 mix of cladoceran and copepods both years in the freshwater , and Acartia spp. was the dominant species in the brackish water reaches. The zooplankton fatty acid profiles in freshwater had a similar percent of EPA and DHA but had an increase in DHA in the brackish water sites. The larval river herring from the Chowan River and tributaries had a similar fatty acid profile with increased DHA over space and time , which could have been a result from bioaccumulation or bioconversion. My dissertation research resulted in an assessment of nursery habitat areas that included the important component of the lower trophic food web. All of my research sites are considered strategic habitat areas in North Carolina , and this research could result in suggestions to improve the model for defining important fish habitats that are not listed as primary nursery habitat. For example , fatty acids of the plankton could be monitored to determine if changes are occurring in the food quality for zooplankton and larval fish. The answer to the question ""Are all fish nursery areas equal?"" is no. This answer informs management and researchers that including more factors than habitat alone is needed to fully and better predict possible future effects on important nursery habitat that could link to river herring recovery in the future or the lack thereof river herring recovery.