Temperature drives benthic macroinvertebrate distributions across lotic & lentic ecosystems, but responses vary among shared taxa

Communities of invertebrates are notably shaped by temperature, driving trends in composition and diversity. Yet few studies have examined how thermal niches of taxa may vary across distinct ecosystems, such as lakes and streams. The U.S. Environmental Protection Agency’s National Aquatic Surveys (NARS) offers a unique opportunity to compare how the influence of temperature on benthic macroinvertebrates varies between ecosystem types across the conterminous U.S. Multivariate random forest (MVRF) models of taxon (genus-level) distributions within each ecosystem type allowed us to assess the relative importance of temperature in structuring assemblages as well as characterize the variation in thermal niches among shared genera. To examine thermal niches, we used accumulated local effect plots of MVRF predictions of genus probabilities of occurrence to assess how genera responded to temperature, while removing the influence of non-temperature factors used in the MVRF models. Modeled summer water temperature was a top predictor in lotic and lentic ecosystems for macroinvertebrate genera relative to other watershed factors. Several genera, such as the mayfly Caenis, have similar thermal response curves between lentic and lotic ecosystems, but thermal optima were, on average, 2°C higher in lentic ecosystems relative to lotic ecosystems. Some genera, such as the caddisfly Mystacides, have response curves that differ somewhat between the ecosystem types, suggesting different aspects of the complete thermal niche may be captured by samples in each ecosystem type (lower vs upper thermal limits). Other genera have thermal response curves that differ completely between lentic and lotic ecosystems, which may reflect sub-genus level variation and/or local adaptation. Thermal niches may be conserved across ecosystem types for many macroinvertebrate genera, but substantial variation among some genera suggests the thermal gradient of a single ecosystem type, even at a large spatial scale, may not adequately capture the full niche of many genera.

Impact/Purpose

It is not well understood how temperature varies in influence on stream and lake biological conditions. Understanding the impact of temperature relative to watershed factors on these different ecosystem types could improve the way we prioritize management of these systems at the national scale. Further, this understanding will help support current work by EPA economists to improve the way EPA captures the existence value of freshwater ecosystems and our understanding of the factors influencing this value. In this talk, we describe work to assess the relative importance of temperature in structuring macroinvertebrate assemblages as well as characterize the variation in thermal niches among shared genera. We found that modeled summer water temperature was a top predictor in lotic and lentic ecosystems for macroinvertebrate genera relative to other watershed factors. We also found that while many shared genera have similar thermal response curves for lakes and streams, thermal optima were often higher in lakes. In addition, other shared genera had curves that somewhat differed in shape between the two ecosystems, suggesting different parts of the niche are captured in each ecosystem type as well as potential variation at the sub-genus level. The results of this work will support efforts by NCEE economists to improve national valuation of freshwater ecosystems when conducting analysis of proposed Clean Water Act regulations and contributes to StRAP subproduct SSWR.401.3.2.2 – Empirical models to interpolate benthic macroinvertebrate observed/expected ratios, or other biological indicator(s) of aquatic ecosystem health, from NARS stream and lake condition to HUC12 or HUC8 units over CONUS under Product SSWR.401.2.2 – Interpolation and stressor-response analyses that extend the use of NARS data to support regulatory program needs.

Citation

Jansen, L., R. Hill, D. Kopp, S. Rumschlag, AND L. Yuan. Temperature drives benthic macroinvertebrate distributions across lotic & lentic ecosystems, but responses vary among shared taxa. Annual Meeting of the Society for Freshwater Science, San Juan, PR, May 18 - 22, 2025.