The ecological and economic value of sandy shoals off the Louisiana coast is not well understood. During three years of comprehensive benthic sampling and environmental measurements I studied the Ship, Trinity, Tiger Shoal Complex (STTSC), which comprises changing and discrete benthic habitats including high relief sandy shoals, and muddier, mostly deeper off-shoal areas, prone to hypoxia. Benthic macrofaunal assemblages of shoals included endemic species, and shoal communities were significantly different from each other and the muddier offshoal habitat, contributing to northern Gulf of Mexico (GoM) regional biodiversity. Sand percentage was the most influential environmental parameter shaping macrofaunal community composition across the region. My study revealed several more potential shoal-based functions such as providing a conduit for GoM sandy-habitat metapopulations, serving as an oxygenated benthic refuge from seasonal bottom water hypoxia, and functioning as offshore blue crab (Callinectes sapidus) spawning grounds. I discovered unexpectedly high concentrations of spawning female blue crabs, greatly expanding what was previously understood about blue crab reproductive migrations. Blue crab abundances were significantly higher on Ship and Trinity Shoals than the surrounding muddier and deeper seafloor. STTSC blue crabs compared favorably with those from nationally recognized spawning grounds in terms of condition factor (an index of health), abundance, and fecundity. This work is the first to use an ecological field study to predict the number of days (~21) between successive spawns for blue crabs, suggesting STTSC blue crabs produce at least seven broods per spawning season (~April October). My morphometric predictors of crab weight were 12 to 16% better than the traditionally used method. In addition, I used natural abundance isotopes (δ13C, δ15N) to link blue crabs from the STTSC to the inshore blue crab fishery. I analyzed isotopic variations in crab muscle and ovary tissue and found relationships with salinity and proximity to the Atchafalaya River, indicating that crabs predominately migrate directly offshore from their home estuary, including from low salinity environments. Isotopic analysis also suggests that crabs utilize offshore prey resources and do not re-enter inshore estuaries during the spawning season but rather remain offshore for the season, continually spawning and hatching their eggs.
| Identifer | oai:union.ndltd.org:LSU/oai:etd.lsu.edu:etd-04202012-133757 |
| Date | 24 April 2012 |
| Creators | Gelpi Jr., Carey George |
| Contributors | Xu, Zhimin, Dubois, Stanislas, Carman, Kevin, Fleeger, John, Condrey, Richard, Gambrel, Robert |
| Publisher | LSU |
| Source Sets | Louisiana State University |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lsu.edu/docs/available/etd-04202012-133757/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached herein a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to LSU or its agents the non-exclusive license to archive and make accessible, under the conditions specified below and in appropriate University policies, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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