Manatee grazing impacts on a mixed species seagrass bed

Marine Ecology Progress Series
InoMedic Health Applications, Inc;National Oceanic and Atmospheric Administrationmahon
By: , and 

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Abstract

The endangered manatee Trichechus manatus is one of few large grazers in seagrass systems. To assess the long-term impacts of repeated grazing on seagrasses, we selected a study site within Kennedy Space Center in the northern Banana River, Brevard County, Florida, that was typically grazed by large numbers of manatees in spring. Two 13x13 m manatee exclosures and 2 paired open plots of equal size were established at the study site in October 1990. Shoot counts, biomass, and species composition of the co-dominant seagrass species, Syringodium filiforme and Halodule wrightii, were sampled 3 times per year in all 4 plots between October 1990 and October 1994. We used a Bayesian modelling approach, accounting for the influence of depth, to detect treatment (exclosed vs. open) effects. S. filiforme shoot counts, total biomass, and frequency of occurrence significantly increased in the exclosures. By July 1993, mean biomass values in the exclosures (167 g dry wt m-2) greatly exceeded those in the open plots (28 g dry wt m-2). H. wrightii decreased in the exclosures by 1994. Initially, both S. filiforme and H. wrightii responded positively to release from manatee grazing pressure. As S. filiforme continued to become denser in the exclosures, it gradually replaced H. wrightii. Our findings may be helpful to biologists and managers interested in predicting seagrass recovery and manatee carrying capacity of repeatedly grazed seagrass beds in areas of special significance to manatees and seagrass conservation.

Additional publication details

Publication type Article
Publication Subtype Journal Article
Title Manatee grazing impacts on a mixed species seagrass bed
Series title Marine Ecology Progress Series
DOI 10.3354/meps11986
Volume 564
Year Published 2017
Language English
Publisher Inter-Research
Contributing office(s) Wetland and Aquatic Research Center
Description 17 p.
First page 29
Last page 45