Evaluating Macrobenthic Process Indicators in Relation to Organic Enrichment and Hypoxia

Adopting macrobenthic process indicators with clear connections to ecosystem function should facilitate assessments of inherently variable estuarine ecosystems. Most current macrobenthic indicators do not directly reflect ecosystem function because they rely on taxonomic based metrics including diversity and the occurrence of indicator taxa. The goal of the present study was to evaluate prospective macrobenthic process indicators in relation to organic enrichment and hypoxia. Organic enrichment combined with hypoxia typically engenders depauperate macrobenthic communities consisting mostly of small short-lived opportunistic organisms. Thus, indicators predicated upon body-size descriptors potentially concur with effects of eutrophication. In the present study, two orthogonal complex indicators, or benthic functions (BFs), comprised a suite of eight macrobenthic metrics from 133 sampling events representing 29 sites over four years within three central Gulf of Mexico (GoM) estuarine systems. Benthic Function 1 (BF1) exemplified community maturity, whereas BF2 conveyed secondary production potential. Three complex macrobenthic indicators, including the two BFs and the benchmark Benthic Index (BI) for the Gulf of Mexico (GoM), were related to four environmental functions (EFs) comprising a suite of 15 environmental variables. The two BFs related more robustly to the EFs than the BI. Moreover, BF2 related strongly to the dissolved oxygen (DO) driven EF2. Notwithstanding a somewhat nonlinear relationship between BF2 and EF2, monotonic variation in BF2 relative to DO-driven EF2 ensured the interpretability of the relationship. A significant correlation between BF1 (i.e., community maturity) and the BI implied a link between benthic function and biodiversity. Other significant relationships involving the complex macrobenthic indicators and trophic structure underscored the ecological relevance of functional diversity. Implementing macrobenthic process indicators to gauge estuarine condition offers a compelling approach to coastal ecosystem management. (C) 2011 Elsevier Ltd. All rights reserved