Utilization of submerged aquatic vegetation habitats by fishes and decapods in the Galvestion Bay Ecosystem, Texas

Abstract

Fish and decapod densities in shoalgrass, Halodule wrightii, wigeongrass, Ruppia maritima, and adjacent non-vegetated sand or mud habitats in Galveston Bay, Texas were compared to determine the relative value of each habitat in terms of faunal utilization and species richness. Physical, environmental and other biological variables for each habitat were examined in relation to faunal density. Fish and decapod densities were quantitatively sampled during fall, spring and summer using a lm2 throw trap. Totals of 48 taxa and 8,163 individuals were collected from 204M2 throw trap samples (equally divided between vegetated and non-vegetated habitats) taken during the period 30 September 1993 to 28 November 1994. Vegetated habitat (Halodule and Ruppia) contained 89% of the total fauna by number (83% decapods; 17% fishes), with nonvegetated substrate (sand and mud) containing 11% (55% decapods; 45% fishes). The dominant species in vegetated habitats were daggerblade grass shrimp, Palaemonetes pugio, 40%; blue crab, Callinectes sapidus, 15%; and white shrimp, Penaeus setiferus, 12%. Dominants in non-vegetated habitats included Penaeus setiferus, 21 %; Callinectes sapidus, 16%; and gulf menhaden, Brevoortia patronus, 14%. The amount of submerged aquatic vegetation (SAV) cover appeared to be the most important variable related to total fish and decapod densities. Significant differences in faunal densities indicated that SAV habitat was more valuable to fishes and decapods than non-vegetated substrate. Non-vegetated substrate adjacent to SAV, however, was utilized by some species including commercially important Penaeus setiferus. Total faunal densities were similar between Halodule and Ruppia each season, but there were seasonal variations in use of each habitat at the species level, particularly by some commercial and recreational species. Halodule and Ruppia appear to function as "essential fishery habitat", as defined by the Magnuson-Stevens Fishery Conservation Act of 1996, and should be conserved to maintain fishery productivity.