ESTIMATING SECONDARY PRODUCTION AND BENTHIC CONSUMPTION IN MONITORINGSTUDIES - A CASE-STUDY OF THE IMPACTS OF DREDGED MATERIAL DISPOSAL INGALVESTON BAY, TEXAS

We examined the effects of dredged material disposal on benthic macroi nvertebrates in Galveston Bay, Texas, USA, while investigating the uti lity of estimating secondary production with estimation methods that h ave less rigorous data requirements than most classical techniques. Pr oduction estimates were compared to estimates of benthic consumption b y blue crabs, shrimp, and epibenthic fish. There was no evidence that dredged material disposal had a detrimental impact on benthic producti on; however, production was low throughout the entire bay the year fol lowing dredged material disposal, which may have obscured an assessmen t of the impact of disposal. In fact, disposal sites yielded both the highest production estimates and species richness in both the upper an d 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-fr ee 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 f ishery-independent trawl-survey data yielded overall benthic consumpti on 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 esti mates and annual fisheries statistics produced slightly lower benthic consumption estimates (0.72-1.13 g AFDW m(-2)). The average consumptio n estimate exceeded benthic production in the upper bay in one of the 4 yr for which benthic production was estimated. In years with high be nthic production, the estimated benthic food requirement of epibenthic predators was roughly 10-15% of benthic production. Variation in annu al benthic production estimates was two to three times greater than th e variation in consumption estimates.