&lt;i&gt;Mycale (Aegogropila) magellanica&lt;/i&gt; (Porifera: Demospongiae) in the southwestern Atlantic Ocean: endobiotic fauna and new distributional information

Laura Schejter,Brenda L Doti,Ignacio L Chiesa,Claudia Bremec

doi:10.3989/scimar.03490.21a

Abstract

The composition of endobionts in the sponge Mycale (Aegogropila) magellanica at the shelf-break, near 100 m depth, in the Argentine Sea was studied. We also provide new information on the distribution of M. (A.) magellanica , extending its northern limit to 38o36.02’S and 55o44.68’W, 91 m in the SW Atlantic Ocean. The main Patagonian scallop fishing grounds are located in the shelf-break frontal area of the Argentine Sea. In this area, M. (A.) magellanica plays an important role in providing habitat for at least 23 taxa of small invertebrates, mostly crustaceans (66% to 96% of the total number of individuals). On average, this sponge hosted 348 individuals per litre; Aristias cf. antarcticus (Amphipoda) was the most frequent and abundant species. Other organisms commonly found were the isopod Caecognathia sp., the amphipod Leucothoe cf. spinicarpa , the bivalve Hiatella meridionalis and the ophiuroid Ophiactis asperula . As previously demonstrated for other sponges, our study suggests that M. (A.) magellanica enhances benthic biodiversity, as it shelters a variety of invertebrate species. In areas of soft and flat substrate, erect and sessile epifauna usually acts as an ecosystem engineer, structuring the architecture of the habitat by increasing the sea-bottom complexity. Mass removal of this fauna due to intense trawling activities on Patagonian scallop beds could have devastating effects on local biodiversity.

Highlights

The sponge Mycale (Aegogropila) magellanica (Ridley, 1881) is distributed in Antarctic, sub-Antarctic, Chilean and Argentine waters
In spite of its wide distribution, relatively frequent finding and easy identification compared with other sponges in the shelfbreak frontal area of Argentina (Schejter et al 2006, Bertolino et al 2007), no studies have been performed on this species, besides the original description and subsequent faunistic records
Samples for ecological purposes are collected as a routine procedure during Patagonian scallop Zygochlamys patagonica stock assessment cruises performed yearly by the Instituto Nacional de Investigación y Desarrollo Pesquero (INIDEP)

Summary

Introduction

The sponge Mycale (Aegogropila) magellanica (Ridley, 1881) is distributed in Antarctic, sub-Antarctic, Chilean and Argentine waters (van Soest et al 2011). In spite of its wide distribution, relatively frequent finding and easy identification compared with other sponges in the shelfbreak frontal area of Argentina (Schejter et al 2006, Bertolino et al 2007), no studies have been performed on this species, besides the original description and subsequent faunistic records. The relation between sponges and their associated organisms ranges from accidental or intentional commensalism to predation, mutualism or parasitism (Sará and Vacelet 1973, Pawlik 1983, Wendt et al 1985, Wulff 2006, Winfield and Ortiz 2010, and references therein). The most common endobionts are protozoans, diatoms, cnidarians, polychaetes, crustaceans, echinoderms and other invertebrates such as pycnogonids, platyhelminths, sipunculids and nemertins, but they include fishes (see Supplementary material Appendix 1 for examples; and Wulff 2006 for review). Klitgaard (1995) suggested that the majority of the fauna associated with sponges in temperate/cold waters is

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