Benthic Macroinvertebrates

Benthic macroinvertebrates are macroscopic invertebrates (predominantly insects) that live on the bottom of lakes and rivers and provide an important food source for fish. Alpha diversity of lake littoral (near-shore) habitats showed strong regional differences, with the lowest alpha diversity in remote areas and islands (e.g., Greenland, Iceland, Faroe Islands, Wrangel Island) and the highest taxonomic richness in Fennoscandia and the coastal regions of Alaska. Similarity in diversity estimates for the most taxonomically poor ecoregions suggests that barriers to dispersal, such as proximity to mainland and presence of mountains, limit biodiversity in these northern lakes. Beta diversity within ecoregions was variable, with a higher importance of species loss evident in remote island ecoregions. Macroinvertebrate diversity in the lake profundal (deep water) zone habitat was lower and less variable than littoral zone observations; nevertheless, circumpolar trends showed a similar pattern.

Alpha diversity of river macroinvertebrates was lowest at the highest latitudes and on remote islands (e.g., Canadian high Arctic, Svalbard, Greenland, Iceland, Wrangel Island). Diversity also appeared to be lower in mountainous ecoregions. Conversely, the highest alpha diversity was observed at the lowest latitudes on the mainland where connectivity does not affect dispersal of taxa from southern regions and thermal regimes are the warmest. Beta diversity for rivers was high within all ecoregions, and taxonomic nestedness (loss of species) contributed more to beta diversity in high latitude, high altitude, and remote island ecoregions.

Further analysis of alpha diversity in lakes in rivers in relation to latitude indicated a strong latitudinal decline in both rivers and lake littoral zones above 68°N. Declines were likely a result of high-Arctic environments exceeding the thermal tolerances of taxa. In rivers, variability in this pattern at the mid-latitudes was associated with a west-east temperature gradient that exists in North America and colder thermal regimes in the eastern Canadian Arctic relative to similar latitudes in Fennoscandia. Lower diversity was also evident where dispersal was limited. This was particularly evident in lakes located on islands, where diversity was consistently lower than mainland stations, even at similar latitudes.

Monitoring gaps for benthic invertebrates of lakes and rivers are largely related to the need for harmonized sampling design and method. River benthic macroinvertebrate data were among the most extensive of all FECs with good spatial coverage across the circumpolar region, and with a relatively standardized sampling method. However, single-event sampling of riverine macroinvertebrates was common, and with the exception of Sweden, time series data were scarce. In lakes, there were large gaps in the spatial coverage of benthic invertebrate data due to a lack of routine monitoring in many areas, and because the sampled habitats (e.g., near-shore vs. deep-water zones, which have different assemblages of benthic macroinvertebrates) and sampling methods varied by country. To support future macroinvertebrate assessment in lakes, countries need to standardize the sampling approach, ideally including sampling of the taxonomically rich littoral habitat. An additional limitation to the strength and scope of diversity assessment for both rivers and lakes is the current inconsistency in the taxonomic resolution, particularly for midges (chironomids), which are predominant in the Arctic. Future assessments should continue to make use of the strong spatial coverage of data and accessibility of data from national databases, but monitoring activities must include higher taxonomic resolution of the Chironomidae (i.e., to sub-family using microscopic techniques or to species-level using genetic barcoding) and schedule regular re-sampling of areas to establish the time-series data required to assess the impacts of climate change and development.