Macrobenthos - organisms larger than 2 mm. These are higher crustaceans, echinoderms, polychaetes, large mollusks, etc.

The marine macrobenthos community is a critical component and reliable indicator of the biotic integrity of marine ecosystems, especially tidal ecosystems. Macrobenthos plays a vital role in maintaining ecosystem functions such as material cycling in sediments and energy flow in food webs. It is relatively sedentary and reflects the environmental conditions in the sediments where many pollutants (e.g. heavy metals and organic enrichment) are ultimately distributed.

Macrobenthos consists of numerous taxa, and different species tolerate environmental pressures in different ways. The polychaetes Capitella capitata and Heteromastus filiformis are naturally tolerant of environmental disturbances and can live well in areas with high organic matter content or heavy metal contamination. And some taxa (e.g., the polychaete Magelona dakini and the amphipod Perioculodes longimanus) are inherently sensitive to environmental disturbance and cannot survive in such highly polluted areas.

Visual inspection of macroorganisms at the bottom of an aquatic ecosystem can be a good indicator of water quality.