Aquatic invertebrate diversity in Apostle Islands and Isle Royale waters: Comparison among habitats and sampling gears and to open Lake Superior

Abstract

Aquatic invertebrate composition in Great Lakes nearshore regions is known to differ from offshore, but studies representing the closest-to-land end of this gradient are primarily from estuaries and rivermouths having substantial watershed connectivity and anthropogenic influence. Here, we present data from aquatic invertebrate surveys conducted in two Lake Superior parks that are distanced from such watersheds and pressures, namely Apostle Islands National Lakeshore (APIS) and Isle Royale National Park (ISRO). Our intensive, multi-gear surveys from 99 APIS stations in 2017 and 165 ISRO stations in 2012 reveal a broad diversity of zooplankton and benthic/littoral macroinvertebrate taxa. Park samples yielded 29 zooplankton and >300 benthic/littoral taxa, with richness exceeding that of comparable nearshore datasets, especially for aquatic insects, leeches, and mites. Station depth was a major factor structuring invertebrates, and benthic/littoral densities were highest and composition most diverse at shallow stations having aquatic vegetation. Species composition and taxa accumulation patterns differed considerably among sampling gears, highlighting the value of multi-gear surveys. Several park mollusk and insect species matched ‘special concern’ listings, and two non-native cladocerans were very abundant. These two surveys added 11 new species to the aquatic macroinvertebrates known from Lake Superior, highlighting the importance of these parks in harboring biodiversity and the importance of individualized assessments of places not well represented in more routine lakewide biological monitoring. Our data are available as baselines for future biological surveys and trend assessments.