Short-Term Effects of the Cessation of ShrimpTrawling on Texas Benthic Habitats

摘要

We compared sediments and benthos of two adjacent zones of the middle Texas coast, one of which was closed to shrimp trawling for 7 months. We hypothesized that the no-trawling zone would experience accumulation of fine surficial sediments, leading to increased proportions of silt, clay, and organic matter and decreased proportions of rubble and sand. We also hypothesized that cessation of trawling would affect benthic community structure, directly or indirectly leading to altered types and densities of dominant taxa between zones. During June 2001, divers collected benthos and sediment cores from 32 sites in each zone, using random stratified sampling based on previously mapped sediments. Benthic organisms were identified to family or higher taxonomic levels, counted, and weighed. Our study indicated that the predicted accumulation of fine materials over the 7-month closure did not occur, as we found no sedimentary differences that could not be referenced to sampling design. This lack of change was likely due to the short closure period and to the shallow, sand-dominated nature of the study zones, wherein winter storms, summer tropical cyclones, and seasonally reversing coastal currents more likely influence long-term sediment structure than does presence or absence of shrimp trawling. Densities and biomasses of most abundant taxa and major taxonomic groups were similar between zones, although there were significant differences between zones for nemerteans, amphipods, mactrid clams, and spionidpolychaetes. Our data indicate that ambient shrimp trawling effort during winter and spring off the middle Texas coast had little impact on small benthic organisms. A better way to determine whether community and ecosystem structure (and function) might be different from what we now see is to make comparisons between areas closed to all extractive uses for an extended period of time (years to decades) and areas open to all maritime users.