Effects of mussel farming on macrobenthic community structure in Southeastern Brazil

Abstract

Mussels cause the deposition of great amounts of suspended matter as faeces and pseudofaeces, which can impact on surrounding communities. The effect of mussel farming on the macrobenthic community under mussel ropes was assessed at Anchieta, Southeast Brazil. Bimonthly samples of sediment were collected with a Petersen dredge at four sites: beneath the mussel ropes, at 50 m, 200 m and 500 m (reference site). The sediment samples were washed through a 0.5-mm mesh and all retained organisms were preserved in 10% formalin and ethanol after the trial. A sub-sample of sediment from each sample was separated for organic matter contents and granulometric composition. The organic matter in the sediment varied from 4.9% to 9%, with no spatial or temporal differences ( P > 0.05). The sediment was a distinct mud–sand in the majority of samples. Quantitative and qualitative community analyses of the four sites revealed 103 taxa and 12,962 individuals, consisting of Crustacea (78.7%), Polychaeta (15.4%), Mollusca (4.5%) and Echinodermata (1%). The most abundant organisms were the tanaid Kalliapseudes schubartii, representing 72% of total individuals, the amphipod Ampelisca pugetica (5.9%), the polychaetes Lumbrineris sp. (3.8%), Goniada sp. (3.6%) and Owenia fusiformis (3.3%). Polychaete was the most speciose group, with 51 taxa. The reference and farming sites recorded the highest number of species with 64 and 62 taxa, respectively, without significant differences among sites (P > 0.05). On average, the diversity was higher under the cultivated site (1.97), significantly different from the reference site (1.38) (ANOVA: F = 8.22; df = 3; P < 0.05). The abundance of individuals was significantly higher in the reference site (4378 individuals) compared to the farming site (2270 individuals) (ANOVA: F = 4.43; df = 3; P < 0.05). The macrobenthic community abundance varied significantly over the months (ANOSIM: R = 0.618, P < 0.001) and between sites (ANOSIM: R = 0.457, P < 0.001). Ovigerous females of K. schubartii were found throughout the year. These results suggested that the mussel culture had no negative impact on the macrobenthic community.