Benthic macroinvertebrate and fish communities of submerged sinkhole groundwater vents in Lake Huron

Researchers have recently documented the presence of several groundwater vents in Lake Huron. They are characterized by intruding groundwater that is physico-chemically different from surrounding lakewater which creates benthic gradients of nutrients, dissolved oxygen, and temperature. We studied two vents: (1) a shallow water site in a protected embayment, and (2) an offshore open-water site. We analyzed the distribution and composition of benthic macroinvertebrate and fish communities surrounding the vents and compared them to lake-water control sites. Groundwater sites exhibited differences in the benthic macroinvertebrate community composition relative to control sites, although the shallow groundwater site had higher mean individuals/m² (1527 +/- 702 vs. 513 +/- 276) while the offshore groundwater site had lower individuals/m² (1662 +/- 3117 vs. 4650 +/- 2423) compared to the controls. There were no differences in benthic fish community composition, although groundwater sites had lower CPUE (fish/net-hour) and fish from the offshore site had lower average condition factor. Stable isotope analysis (¹³C, ³⁴S) also shows distinct isotope signatures of the benthic fish and invertebrate communities in the groundwater sites. The data suggest that unique physico-chemical gradients created by the groundwater affect the community composition, distribution, and physiological condition of organisms in the local ecosystems.