Low abundance and high species richness: the structure of the soft-bottom isopod fauna of a West Antarctic glacial fjord

Abstract

Isopods belong to the most speciose groups of the Antarctic benthic fauna, although the knowledge on their diversity and small-scale distribution patterns is still limited. Here we analyze the diversity of the isopod fauna in the Admiralty Bay, a glacial fjord on the King George Island. The basin is located in the region of the Antarctic Peninsula, the fastest warming area of the Southern Ocean. The study provides important baseline data for future research, particularly with respect to temporal fluctuations in benthic fauna, associated with global changes observed in that part of the world. Forty species of isopods representing 19 families were recorded on the soft bottom of the Admiralty Bay. The analyses were based on 99 quantitative samples collected, within the 20-502-m depth range, with a 0.1 m 2 van Veen grab. The materials for the analyses were obtained in the austral summer seasons of 1984/1985 and 1985/1986. The data revealed a high number of isopod species occurring at a low abundance, the mean abundance amounting to 4.8 ± 8.6 ind./0.1 m 2 . Most of the species occurred at low abundances, 25% of the species being represented by singletons. Caecognathia polaris, the most abundant species, showed the mean abundance of merely 1.2 ± 4.2 ind./0.1 m 2 . Species richness, diversity and abundance of the isopod fauna were much higher in the central basin of the Admiralty Bay than in the Ezcurra Inlet, an area affected by a strong disturbance of glacial origin.

New records of isopod species of the Antarctic Specially Managed Area No. 1, Admiralty Bay, South Shetland Islands

“…Only Cryosignum incisum (Richardson 1908) was found in the shallowest sublittoral and it seems that this species is generally associated only with the shallower sublittoral zone (Doti et al 2005). Most of the species found in our study were singletons, doubletons and tripletons, which supports earlier results from the Admiralty Bay soft bottom (Zemko et al 2017) and other studies showing low densities of the Antarctic isopods (Richardson and Hedgpeth 1977;Brandt 2001), although it is worth mentioning that van Veen grab is not a perfect tool for isopod sampling. A higher number of individuals was found only for Eurycope crassiramis Golovan, 2008 and Coulmannia australis Hodgson, 1910, however both species were found in two samples only.…”

“…It was already suggested that the high diversity of habitats (including different types of soft and hard bottom, macroalgae forests) and dynamic set of environmental properties can be a reason of high diversity of the Admiralty Bay macrofauna in many taxonomic groups . High diversity of habitats can be vitally important in the case of isopods, because their distribution in the Admiralty Bay is very patchy and most of the species were rare (Zemko et al 2017). Therefore, there is a need for further studies based on large sampling effort, and exploration of different types of habitats.…”

“…However, recent studies of the soft-bottom isopod communities demonstrated that despite the very large sampling effort the species accumulation curves are still steep and a comprehensive evaluation of the isopod species richness in this basin is still far from being complete (Zemko et al 2017). Our study provides new data on species richness of the isopod fauna of Admiralty Bay, which will enhance future biodiversity assessments of this basin.…”

“…Isopods are among the most speciose groups of benthic macrofauna of the Southern Ocean (De Broyer et al 2011) and third most speciose group of benthic macrofauna of Admiralty Bay (Arnaud et al 1986;Presler 1986;Teodorczyk and Wägele 1994;Zemko and Brix 2012;Siciński et al 2012;Zemko and Kaiser 2012;Zemko et al 2015Zemko et al , 2017. However, recent studies of the soft-bottom isopod communities demonstrated that despite the very large sampling effort the species accumulation curves are still steep and a comprehensive evaluation of the isopod species richness in this basin is still far from being complete (Zemko et al 2017).…”