Stoichiometry, growth, and fecundity responses to nutrient enrichment by invertebrate grazers in sub-tropical turtle grass (Thalassia testudinum) meadows
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Although the effectiveness of herbivores in mitigating the effects of nutrient enrichment is well documented, few studies have examined the effects of nutrient enrichment on components of consumer fitness. Enclosures were deployed in shallow turtle grass (Thalassia testudinum) beds in Florida Bay, Florida in fall 2003, spring 2004, and fall 2004 to measure the effects of nitrogen and phosphorous enrichment on the growth, fecundity, and stoichiometry of three invertebrate epiphyte grazers commonly associated with T. testudinum. The gastropod Turbo castanea exhibited significantly greater wet weight gain and lower C:P and N:P in enriched than in ambient treatments. Although nutrient enrichment did not have any significant effects on the growth of caridean shrimp (treatment consisted of several different caridean shrimp species), their C:N was significantly lower in enriched treatments. The final size and stoichiometry of the hermit crab Paguristes tortugae was not significantly affected by nutrient enrichment, nor did nutrient enrichment significantly affect the fecundity of P. tortugae, the only grazer in which gravid individuals or egg masses were present. Our study demonstrated that nutrient enrichment of primary producers can positively affect the growth of marine invertebrate grazers and alter their stoichiometry; however, these effects were species-specific and may be dependent upon the life stage, specific diets, and/or compensatory feeding habits of the grazers.
KeywordsNutrient Enrichment Submerged Aquatic Vegetation Carapace Length Hermit Crab Grazer Treatment
This research was made possible by grants from the Alabama Center for Estuarine Studies (ACES Project # R-83065101-3-05), the Everglades National Park under cooperative agreement 1443CA528001022, and the Florida Coastal Everglades Long Term Ecological Research Program funded by the US National Science Foundation (Cooperative Agreement # DEB-9910514). D. Morrison and B. Perry facilitated permit issuance and the use of ENP facilities. We are grateful to the following people for their hard work and assistance with the field experiments: From the DISL: R. Adams, D. Booth, D. Byron, B. Furman, J. Koeppel, L. Kramer, K. Merkins, R. Shiplett, T. Spitzer, C. Steeves, and K. Young. From Florida International University: B. Dewsbury, C. Furst, M. Gil, S. Ruiz, T. Thyberg, and P. William. We thank L. Linn of DISL for her assistance with elemental analysis, and S. Bosarge of DISL for creating Fig. 1. This is the contribution number 408 from the Dauphin Island Sea Laboratory and 569 from the Southeast Environmental Research Center at Florida International University.
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