Trophic functioning of macrobenthic fauna in a tropical acidified Bornean estuary (Southeast Asia)

The trophic structure of a community is used to infer ecosystem functioning (e.g. energy transfer and nutrient cycling). Here the trophic structure of the benthic infaunal and epifaunal communities in the Brunei Estuary are characterized, and their distribution along an estuarine pH gradient is analyzed using univariate and multivariate techniques. This analysis revealed that surface deposit feeders (e.g., polychaetes) were numerically dominant within the infaunal communities whereas in the epifaunal communities filter feeders (e.g., bivalves) were highly abundant. Species richness for almost all trophic groups increased toward the lower estuary, except for omnivores in the epifaunal communities, which decreased markedly. Both Analysis of Variance (ANOVA) and Analysis of Similarities (ANOSIM) detected significant differences in the density of respective trophic groups among stations. Within infaunal communities, both Biological and Environmental procedure (BIO-ENV) and Canonical Correspondence Analysis (CCA) showed that trophic shifts were associated with environmental gradients. Surface-deposit feeders and omnivores were the most abundant macrobenthos of the upper estuary characterized by low salinity, low pH, and a higher percentage of mud particles. The proportion of filter feeders and carnivores increased with salinity/pH and sand. A more uniform distribution of trophic structure was found in the lower estuary, with high salinity and pH over sandy habitat. In contrast, within epifaunal trophic groups, the percentage of surface deposit feeders and omnivores declined, but filter feeders remarkably increased toward the sea. The proportion of carnivores remained similar at all stations. Non-Metric Multidimensional Scaling (nMDS) ordination for epifaunal trophic groups clearly demarcated higher salinity/pH stations from lower salinity/pH stations, suggesting different trophic compositions along the estuarine pH gradient.

Hossain M. B., in press. Trophic functioning of macrobenthic fauna in a tropical acidified Bornean estuary (Southeast Asia). International Journal of Sediment Research. Article (subscription required).

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