The microbial and metazoan community associated with colonies of Trichodesmium spp,.: a quantitative survey

J van Montfrans
CH Ryer
RJ Orth

Abstract

Various marine and estuarine species utilize chemical cues during settlement. We investigated responses by megalopae and first juvenile (J1) blue crabs to common Chesapeake Bay substrates in mesocosm and field experiments. Mesocosm trials examined responses of megalopae or J1 crabs to sand, marsh mud, live oysters Crassostrea virginica, sun-bleached oyster shell, eel grass Zostera marina and artificial seagrass in replicate 160 l tanks. Either 10 megalopae or J1 crabs isolated in each of 6 substrates were allowed total access after acclimation to test the null hypothesis of equal distribution among substrates after 13 h. Thirty-five percent of megalopae were recovered from Z. marina, with the remaining substrates containing fewer than half that many. In contrast, 30 % of J1 crabs (with only 17 % recovered from Z. marina) were found in live C. virginica. A field experiment quantified responses of ingressing megalopae to Z, marina, marsh mud, and C. virginica. Overnight settlement was significantly higher in Z. marina ((x) over bar = 3.3 ind.; 60 % of total) when compared to mud ((x) over bar = 0.9; 16 %) or C. virginica ((x) over bar = 1.3; 24 %). Likewise, J1 crabs were significantly more numerous in Z. marina ((x) over bar = 3.7 ind.; 55 % of total) than in C. virginica ((x) over bar = 1.8; 27 %) and mud ((x) over bar = 1.2; 18 %). J1 crab distribution in field plots likely reflected habitat selection by megalopae; laboratory results were equivocal and probably due to artifacts associated with density-dependent agonism. The initial non-random distribution of blue crabs in Chesapeake Bay may be deterministic and due to habitat-selection behavior by megalopae. Selection for seagrass assures the greatest likelihood of maximal survival and accelerated growth. Similar relationships may also exist in estuarine-dependent species with comparable habitat requirements and life-history characteristics.