The benthic community of Lake Superior: Analysis of spatial and temporal trends from 1973 to 2022

Abstract

Biotic interactions and environmental changes due to increasing water temperatures, nutrient enrichment, and other factors can affect species diversity, abundance, and distribution. Lake Superior is the deepest and one of the most oligotrophic lakes in the Laurentian Great Lakes system. While considered the least affected by cultural eutrophication, Lake Superior is among the world’s fastest-warming freshwater bodies, having already exhibited resulting physical and ecological changes over the past three decades. We used data from current and historical surveys to identify spatial patterns and provide an assessment of the status and temporal trends of the Lake Superior benthic community over the last 50 years. Our study indicated that the dominance structure of the community remained quite stable, with the highest proportion of community comprised by the deepwater amphipod Diporeia hoyi, followed by Oligochaeta, Sphaeriidae, and Chironomidae. Benthic community structure differed spatially, with higher species diversity found in the shallow zone (≤30 m), the highest Diporeia densities at intermediate depth zones (30–50 and 50–90 m), and the lowest densities of all taxa in the deepest zone (>90 m). Lakewide benthos densities increased in the 1990s–2000s, most likely due to reduced fish predation, but are now stabilized. Although current benthos densities are still higher than in the 1970s, nearshore surveys indicated declines in Diporeia and other major taxa in the last decade. These changes may indicate a return to levels observed in the 1970s or reflect a long-term trend of decline in populations, reinforcing the importance of frequent monitoring that could foretell lakewide changes.