Integrating multiple indices based on heavy metals and macrobenthos to evaluate the benthic ecological quality status of Laoshan Bay, Shandong Peninsula, China

Many different indices have been developed to evaluate habitat quality status (EcoQs) in marine ecosystems; however, few studies have concurrently considered both abiotic and biotic indices in their assessments of benthic EcoQs. Here, we propose and test a framework for integrating heavy metal pollution-related indices and macrobenthos-based indices to assess the benthic EcoQs of Laoshan Bay (Yellow Sea, China). This bay is exposed to urbanization, construction, heavy metal pollution, and land-and marine-based culturing operations for commercially valuable species like fish, scallop, and laver (seaweed). We first assessed the EcoQs of Laoshan Bay using four heavy metal pollution-related indices, i.e., the geo-accumulation index (Igeo), potential ecological risk index (RI), pollution load index (PLI), and Nemerow pollution index (Pn) and four macrobenthos-based indices, i. e., AZTI's Marine Biotic Index (AMBI), the multivariate AMBI (M-AMBI), BENTIX, and the feeding evenness index (jFD). All indices (except Igeo) were then reclassified and combined to assess the overall EcoQs of Laoshan Bay. Our results show that, while some sites in Laoshan Bay have relatively high levels of heavy metal (Hg and Cd) pollution, the benthic EcoQs is acceptable across 88.90% of the bay. Kappa analysis showed that the agreement between any two indices was very low, which suggests that the composite index used here may be more robust for assessing EcoQs and more closely represent the actual status of benthic habitats than assessments based on single indices. In addition, the assessment framework proposed here is relatively flexible and can serve as a useful tool for evaluating the benthic EcoQs of similar marine ecosystems.

Automated summary

This study proposed and tested a framework for integrating heavy metal pollution-related indices and macrobenthos-based indices to assess the benthic ecological quality status of Laoshan Bay. The results showed that the benthic ecological quality status was acceptable across most of the bay, although there were high levels of heavy metal pollution. The agreement between different indices was low, suggesting that the composite index used in this study may be more reliable for assessing the ecological quality of benthic habitats.