Geology topics

W.C. Sharp

Publications and source records attributed to W.C. Sharp.

2 recordsLinked to original sources

USGS2000

The use of coded microwire tags mark-recapture studies of juvenile Caribbean spiny lobster, Panulirus argus

To evaluate the suitability of using coded microwire tags (CWTs) to mark early-benthic-stage Caribbean spiny lobster, Panulirus argus , we compared the survival, growth, and feeding of tagged and untagged lobsters held in the laboratory through the first five juvenile molts. We also examined the growth of 65 microwire-tagged lobsters released into the wild as early-benthic-stage juveniles. Tag retention rates of lobsters held in the laboratory were 86% for those tagged as first-stage juveniles and 96% for those tagged as second-stage juveniles; virtually all tag loss was confined to the first post-tag molt. Survival and growth rates of tagged second-stage juveniles in the laboratory did not significantly differ from those of untagged lobsters, but first-stage-tagged juveniles had lower growth rates than untagged lobsters did and a 25% post-tagging mortality rate. The mean growth rate of juveniles released into the wild was 0.82 mm CL/wk, but growth differed by season; no sex- or habitat-specific differences in growth were observed. Data obtained from these recaptured lobsters provide the first detailed estimates of growth of P . argus under natural conditions during the earliest part of their benthic life and illustrate the potential usefulness of coded microwire tags in mark-recapture investigations of juveniles for this and other species.

Florida↗

USGS1999

Overgrazing of a large seagrass bed by the sea urchin Lytechinus variegatus in Outer Florida Bay

Unusually dense aggregations of the sea urchin Lytechinus variegatus overgrazed at least 0.81 km2 of seagrass habitat in Outer Florida Bay (USA) between August 1997 and May 1998. Initially, sea-urchin densities were as high as 364 sea urchins m-2, but they steadily declined to within a range of 20 to 50 sea urchins m-2 by December 1998. Prior to this event, sea-urchin densities were <1 sea urchin m-2 in this area of Outer Florida Bay. Seagrasses in Outer Florida Bay consist primarily of manatee grass Syringodium filiforme, of which 82% or 390 g dry weight m-2 of total seagrass biomass and > 95% of the short-shoot apical meristems were removed by sea-urchin grazing in our study area. Such extensive loss may severely limit recovery of this seagrass community by vegetative reproduction. Effects of the removal of seagrass biomass have already resulted in the depletion of epifaunal-infaunal mollusk assemblages and resuspension of fine-grained (<64 ??m) surface sediments - which have caused significant changes in community structure and in the physical properties of the sediments. These changes, coupled with the loss of essential fishery habitat, reductions in primary and secondary production, and degradation of water quality, may lead to additional, longer-term, indirect effects that may extend beyond the boundaries of the grazed areas and into adjacent coastal ecosystems.

Marine Ecology Progress Series↗