Estimating secondary production and benthic consumption in monitoring studies: A case study of the impacts of dredged material disposal in Galveston Bay, Texas

We examined the effects of dredged material disposal on benthic macroinvertebrates in Galveston Bay, Texas, USA, while investigating the utility of estimating secondary production with estimation methods that have less rigorous data requirements than most classical techniques. Production estimates were compared to estimates of benthic consumption by blue crabs, shrimp, and epibenthic fish. There was no evidence that dredged material disposal had a detrimental impact on benthic production; however, production was low throughout the entire bay the year following dredged material disposal, which may have obscured an assessment of the impact of disposal. In fact, disposal sites yielded both the highest production estimates and species richness in both the upper and lower bay areas 2 yr after disposal. Of the five estimation methods used, two that incorporated environmental parameters (temperature and depth) yielded similar and moderate results, ranging from 1.1 g ash-free dry weight m(-2) yr(-1) to 26.9 g ash-free dry weight (AFDW) m(-2) yr(-1) over the 4 yr studied. Daily food ration estimates applied to fishery-independent trawl-survey data yielded overall benthic consumption estimates ranging from 1.1 g AFDW m(-2) to 1.7 g AFDW m-2. A second method of estimating consumption, which used transfer efficiency estimates and annual fisheries statistics produced slightly lower benthic consumption estimates (0.72-1.13 g AFDW m(-2)). The average consumption estimate exceeded benthic production in the upper bay in one of the 4 yr for which benthic production was estimated. In years with high benthic production, the estimated benthic food requirement of epibenthic predators was roughly 10-15% of benthic production. Variation in annual benthic production estimates was two to three times greater than the variation in consumption estimates