Diversity and Distribution Patterns in High Southern Latitude Sponges

Rachel V Downey,Huw J Griffiths,Dorte Janussen,Katrin Linse,Simon Thrush

doi:10.1371/journal.pone.0041672

Abstract

Sponges play a key role in Antarctic marine benthic community structure and dynamics and are often a dominant component of many Southern Ocean benthic communities. Understanding the drivers of sponge distribution in Antarctica enables us to understand many of general benthic biodiversity patterns in the region. The sponges of the Antarctic and neighbouring oceanographic regions were assessed for species richness and biogeographic patterns using over 8,800 distribution records. Species-rich regions include the Antarctic Peninsula, South Shetland Islands, South Georgia, Eastern Weddell Sea, Kerguelen Plateau, Falkland Islands and north New Zealand. Sampling intensity varied greatly within the study area, with sampling hotspots found at the Antarctic Peninsula, South Georgia, north New Zealand and Tierra del Fuego, with limited sampling in the Bellingshausen and Amundsen seas in the Southern Ocean. In contrast to previous studies we found that eurybathy and circumpolar distributions are important but not dominant characteristics in Antarctic sponges. Overall Antarctic sponge species endemism is ∼43%, with a higher level for the class Hexactinellida (68%). Endemism levels are lower than previous estimates, but still indicate the importance of the Polar Front in isolating the Southern Ocean fauna. Nineteen distinct sponge distribution patterns were found, ranging from regional endemics to cosmopolitan species. A single, distinct Antarctic demosponge fauna is found to encompass all areas within the Polar Front, and the sub-Antarctic regions of the Kerguelen Plateau and Macquarie Island. Biogeographical analyses indicate stronger faunal links between Antarctica and South America, with little evidence of links between Antarctica and South Africa, Southern Australia or New Zealand. We conclude that the biogeographic and species distribution patterns observed are largely driven by the Antarctic Circumpolar Current and the timing of past continent connectivity.

Highlights

Sponges play a key role in Antarctic marine benthic community structure and dynamics [1,2,3]
The number of unidentified sponge records gathered in this study means that there is a large amount of data that could not be included in our analyses (Table 1)
Our analyses support the recognition of a single Antarctic demosponge biogeographic zone, which includes the subAntarctic regions of Iles Kerguelen and Macquarie Island

Summary

Introduction

Sponges play a key role in Antarctic marine benthic community structure and dynamics [1,2,3]. All four classes of Porifera (sponges), Hexactinellida, Demospongiae, Homoscleromorpha and Calcarea, are represented in the SO; the first two classes ( the demosponges) have been found in higher diversity and abundances, whereas the latter two are comparably rarer. Glass sponges (Hexactinellida) are an ecologically important group and are more common in the SO than in any other ocean [16], [17], with a few endemic genera dominating shelf communities, most notably the Weddell and Ross seas [13]; whereas the diversity of hexactinellid sponges in is notably higher in the Antarctic deep-sea [18]. Representatives have been recently found at great depths in the Weddell Sea [19]

Methods

Results

Discussion

Conclusion