Work

Testing and improving the usefulness of invertebrate indicators of multiple freshwater stressors

Year: 2025

Type: article

Abstract: Ecological indicators may provide information about multi‐stressor impacts, but they are often applied under hidden and untested assumptions, such as the number of stressors the indicator is sensitive to, the identity of those stressors, and the sensitivity of the indicator to individual stressors. Indicators used under false assumptions lead to perverse outcomes like failure to identify and regulate polluters. We analyzed the sensitivity of New Zealand macroinvertebrate community indicators (macroinvertebrate community index and its quantitative variant and average score per metric, hereafter, collectively, NZMCIs) to multiple stressors. We tested three assumptions: (1) NZMCIs exhibit a negative relationship with dissolved nutrients and suspended fine sediment (SFS). (2) Taxon‐specific “tolerance values” (TVs), upon which NZMCIs are based, accurately characterize invertebrates' tolerances of nutrients and SFS. NZMCI TVs have been derived using professional opinion and studies with narrow spatial and temporal domains. We determined whether these TVs are positively correlated with alternative measures of tolerance—“critical tolerances” (TT crit s)—developed using national, long‐term datasets and rigorous statistical models. (3) Macroinvertebrate taxa are positively co‐tolerant to nutrients and SFS, such that the order of taxon‐specific TT crit s for nutrients is positively correlated with that of SFS. We found little support for these assumptions. Although NZMCIs declined with increasing nutrients and SFS, the magnitude of decline was negligible, spanning only 7% of the NZMCI range observed in the data. NZMCI TVs were poorly correlated with TT crit s, so a factor contributing to the low sensitivity of NZMCIs to nutrients and SFS may be TVs that poorly reflect taxon‐specific tolerances. Taxa tolerant of nutrients were not necessarily tolerant of SFS; hence, the assumption of positive co‐tolerance was unsupported. Given our data and models, NZMCIs appear to be poor indicators of nutrient and SFS effects. Decision‐makers concerned with nutrients and SFS impacts should interpret NZMCI data cautiously. Macroinvertebrate communities can tell us a lot about ecosystem health, but how we use them for that purpose should be more critically assessed and matched to the specific water resource problems we are trying to solve. We present suggestions for improving the means by which we use macroinvertebrate communities as ecological indicators.

Source: Ecosphere

DOI: 10.1002/ecs2.70446

Authors: R. S. A. White, T. Stephens, T. Kpodonu, R. J. Stoffels

Institutions: Earth Sciences New Zealand, Auckland Council

Language: English

Topic: Freshwater macroinvertebrate diversity and ecology

Subfield: Ecology

Field: Environmental Science

Domain: Physical Sciences

SDGs: Clean water and sanitation, Life below water

Open Access status: gold

Estimated APC paid: $2,430