Growth of juvenile predators feeding on benthic infaunal populations from natural sediments and dredged materials in Galveston Bay, Texas

The objective of this study was to compare growth of juvenile nekton predators and removal of benthic infaunal prey from natural sediments and dredged-material sediments in Galveston Bay. Sediments were examined from three plots in the upper bay and three plots in the lower bay. One plot in each of these groups was covered with new-work dredged material from the Houston Ship Channel in the winter and spring of 1992. In summer and fall of 1993, sediments were collected from plots in 20-cm diameter experimental chambers and transported to laboratory raceways. Predators were enclosed in the chambers for a period of 11 days. Growth was measured at 7 days and at the end of the experiment, and infaunal abundance and biomass in predator chambers were then compared with initial values and with control chambers. The infauna was dominated by polychaete worms. Juvenile brown shrimp and spot were used as predators in the summer, while juvenile white shrimp and lesser blue crabs were used in the fall. Growth of spot was negative, and these predators lost biomass over the experimental period. Crustacean growth was positive, however, and biomass increased over the first seven days of experiments. Mean growth rates of spot and crab generally declined from the lower bay plots and to the upper bay plots, but only growth of brown shrimp varied significantly between natural sediments and dredged-material sediments. In the lower bay, brown shrimp growth was higher on dredged material while in the upper bay growth was lower on dredged material. Thus, the location of the dredged material deposition may be important, but overall, there was little difference in growth of predators on these two sediment types. However, if the value of sediments as foraging habitat is determined by the number or biomass of prey removed by predators, dredged material sediments appeared to be relatively poor foraging habitats for most predators.