MYSIDS IN NEARSHORE FOOD WEBS OF CHESAPEAKE BAY TRIBUTARIES

Abstract

Mysids, particularly Neomysis americana and Americamysis spp., are abundant crustaceans in the nearshore Chesapeake Bay that are important for connecting the microscopic and macroscopic portions of food webs. However, the effects of fish predation on mysid communities and prey of mysids are not well understood in these habitats. Our objectives were to 1) estimate the effect of predation of mysids by fishes in a shallow nearshore habitat of the Patuxent River in Chesapeake Bay and 2) determine the diet of mysids in situ in the St. Marys and Patuxent rivers. For objective 1, we conducted nighttime fish sampling using a 30×1.2 m beach seine, and mysids were sampled during the day using a 500 ?m-mesh epibenthic sled approximately weekly during August–September, 2023. Consumption of mysids was quantified by enumerating mysids found in the stomachs of each species of finfish and comparing estimates of consumption to estimates of mysid abundance. Only Americamysis spp. were observed during the study period, and estimated abundance fluctuated across sampling days. Estimated daily consumption varied among fish species, and the aggregate daily predation mortality rate of the local mysid population was estimated to be 1.1% d-1. We used DNA metabarcoding of the stomach contents of mysids sampled using an epibenthic sled and zooplankton nets from the St. Marys and Patuxent rivers to characterize mysids’ diets in situ. Dual-indexed amplicon-based high throughput sequencing was used to generate meta barcode libraries from the small subunit gene (18S) from pooled mysid stomachs. A small portion (0.18%) of our metabarcoding sequences were identified as non-mysid taxa, including copepods, fungi, macroalgae, microalgae, protists, segmented worms, tunicates, terrestrial plants, hydrozoans, and fish. Length of consumer mysid and time of sampling best predicted abundance of putative prey sequences. There was not a significant relationship between the length of consumer mysids and the putative prey they consumed. The results of this thesis are useful for building our knowledge of the Chesapeake Bay food web and of trophic niche of mysids.