Doctor of Philosophy (Ph.D.)
Virginia Institute of Marine Science
Distribution patterns of the Atlantic menhaden Brevoortia tyrannus) have been evaluated in respect to the feeding ecology of the species. Feeding experiments, functional morphology, and field distribution studies with young postmetamorphic fish were conducted to differentiate the feeding dynamics of different size menhaden, and to define the relationship between feeding and distribution. Feeding experiments were conducted with 138 mm fork length menhaden to determine their particle size-specific feeding abilities. The minimum size of particles filtered, the minimum size threshold, was 7 to 9 (mu)m. Phytoplankton larger than the minimum size threshold and smaller than 20 (mu)m upper limit for nanoplankton, were filtered at efficiencies averaging 21% (n = 24). Prey particles exceeding the size limits of nanoplankton, were filtered at average efficiencies ranging from 22% to 84%. The mean filtration efficiency for Artemia sp. nauplii of 36% (n = 7) was lower than for smaller phytoplankton prey. as menhaden grown, their feeding repertoire shifts to larger planktonic organism. Surface ultrastructure, epithelial organization, and gross morphology of the branchial basket in menhaden were analyzed with respect to food particle capture, transport of food from the point of capture to point of ingestion, and potential gustatory reception. Branchiospinules, sites of small particle capture, lacked mucous cells, suggesting that food is captured primarily by mechanical sieving. Taste buds on the glossohyal are thought to be mechanoreceptors, whereas taste buds on the crest of the fifth branchial arch are thought to be chemoreceptors. Concurrent synoptic observation of the relative abundance of menhaden and parameters relevant to characterizing primary production along transects in estuarine creek ecosystems have been used to interpret the factors governing the fishes' local distribution. The strongest associations were between catch and chlorophyll-a, catch and microflagellates, and catch and diatoms. Fish often distributed with a gradient of one phytoplankton taxa over another based on selectivity for large phytoplankton cell size. Menhaden are optimal foragers displaying kinesis selecting for areas of optimally sized prey, chemosensory preference for plant versus detrital particles, and possibly taxa specific avoidance. Comparison of latitudinal distribution patterns of menhaden with the latitudinal trends in plankton community size frequency suggest that fish stratify by size at latitude to maximize the efficiency with which they filter-feed.
© The Author
Friedland, Kevin David, "Menhaden distribution as mediated by feeding (filter-feeding, phytoplankton)" (1984). Dissertations, Theses, and Masters Projects. Paper 1539616649.