O'Connors, H.B., Jr. (1974). The feeding behavior of two populations of the estuarine copepod Acartia clausi. Ph.D. Dissertation, Oregon State University, Corvallis, Oregon, USA. 69 pp.

105724

O'Connors, H.B., Jr.

1974

69 pp. 

Publication

https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/fj2365032

Available for editors   [request]

The feeding behavior of adult females of two spatially separated populations of the Yaquina Bay, Oregon copepod Acartia clausi was studied. The copepod populations, one centered near the mouth and the other centered further up the estuary were distinguished on the basis of cephalothorax lengths, carbon and nitrogen content, and in vivo pigmentation differences, The down-bay females were longer, contained more carbon and nitrogen, and possessed fewer ventral pigment patches. Animals with intermediate cephal.othorax lengths or other characteristics were not found, Females collected during the spring and summer reproductive season of 1971 and 1972 were fed separately unialgal suspensions of the chain-forming, neritic, planktonic diatoms Thalassiosira nordenskioldii and Thaiassiosira gravida over a range of diatom biomass concentrations, The volume of an average-sized T, nordenskioldii particle was about half that of the average-sizedT. gravida particle. During the one-to-two year culturing period, the volume size class frequency distribution of both diatoms continuously shifted toward a higher frequency of smaller particles in non-grazed suspensions. The grazing activity of females from both populations of A. clausi also produced a higher frequency of smaller particles (single cells and two-cell chains) when fed T. gravida, but not when fed the smaller, shorter chained T, nordenskioldii, Suspensions of both diatoms were observed to be nearly free of cell fragments, with or without grazing. Observations made on feeding animals suggested that the scoop net activity of the maxillipeds and the clearance of particle accumulations on the setae of the feeding appendages might be the ways in which copepods dismembered long diatom chains into shorter chains and single cells. Comparisons of ingestion rates obtained for each copepod population fed separately on both diatoms were made. The data showed that at low food concentrations, the ingestion rates of both population& females fed T, nordenskioidii overlapped the ingestion rates of females fed T. gravida. At comparable higher food concentrations, T. gravida-fed females achieved higher ingestion rates than did T. nordenskioldii-fed animals. This trend was exhibited by both copepod populations. At very high food concentrations of T. nordenskioldii the ingestion rates of both populations appeared depressed. Comparisons of ingestion rates for both populations fed T. nordenskioldii showed that the rates determined for the larger downbay females were, on the whole, higher over the experimental range of food concentration than the ingestion rates determined for the smaller up-bay females. Ingestion rates determined for both upbay and down-bay females fed the larger diatom, T. gravida, were nearly the same over the entire range of food concentration. These data suggested that the larger down-bay females could obtain greater amounts of food over a wider range of food particle size than could the smaller up-bay females. The up-bay animals perhaps could obtain more food biomass from T. gravida than from T, nordenskioldii however, because they could break up the larger diatom particles into smaller ones. The down-bay animals also broke large T. gravida. particles into smaller ones during grazing. Specific ingestion rates were determined as amounts of carbon and nitrogen eaten per copepod carbon and nitrogen per day, expressed as percent. Animals ingested several times their body carbon and nitrogen content when fed either diatom. Specific ingestion rates were probably the result of severa. 1 factors, including the "starved" condition of the copepods, and their reproductive state.

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