Changes in Shell and Soft Tissue Growth, Tissue Composition, And
Journal of Experimental Marine Biology and Ecology 313 (2004) 75–104 www.elsevier.com/locate/jembe Changes in shell and soft tissue growth, tissue composition, and survival of quahogs, Mercenaria mercenaria, and softshell clams, Mya arenaria, in response to eutrophic-driven changes in food supply and habitat R.H. Carmichael*, Andrea C. Shriver, I. Valiela Boston University Marine Program, Marine Biological Laboratory, Woods Hole, MA 02543, USA Received 2 February 2004; received in revised form 4 April 2004; accepted 4 August 2004 Abstract Eutrophic-driven changes in the composition of near-bottom seston and surface sediment potentially affect food resources and habitat of commercially important bivalves like quahogs, Mercenaria mercenaria, and softshell clams, Mya arenaria. To define how land-derived nitrogen loads and resulting eutrophication affect bivalves, we compared estuarine features to growth and survival of clams across estuaries receiving different N loads. The major effects of nitrogen enrichment on near-bottom seston and surface sediment were to (1) increase microalgal concentrations and reduce carbon to nitrogen ratios, increasing quantity and quality of available foods, and (2) reduce oxygen content in sediments, potentially reducing habitat quality. Shell growth of juvenile and native clams increased with increasing food supply, driven by N enrichment. Growth of soft tissue followed growth of shell, and %N content of soft tissue increased across N loads, providing direct evidence of a link between N loads and growth responses in clams. In some locations, low salinity limited growth and low oxygen concentrations may have reduced survival. * Corresponding author. Now at: University of Maine at Machias, 9 O’Brien Avenue, Machias, ME 04654, United States.
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