Elsevier

Continental Shelf Research

Volume 157, 1 April 2018, Pages 20-31
Continental Shelf Research

Macrobenthic patterns at the shallow marine waters in the caldera of the active volcano of Deception Island, Antarctica

https://doi.org/10.1016/j.csr.2018.02.005Get rights and content

Highlights

  • Invertebrate assemblages based on sediment characteristics.

  • Rich suspension feeder community associated to hard-bottom substrates.

  • Soft-bottoms favoured a community dominated by infauna and mobile deposit feeder.

  • Huge densities of echinoderms and infauna.

Abstract

Deception Island is an active volcano located at the southern end of the South Shetland Archipelago, in the Antarctic Ocean. After the last eruption in 1970, benthic recolonization took place within the bay, with echinoderms being the dominant epifauna (e.g., the ophiuroid Ophionotus victoriae, the echinoid Sterechinus neumayeri and the sea star Odontaster validus), together with dense infaunal communities (mostly composed by oligochaetes, polychaetes, and bivalves). Here, we aim to describe the actual status of the marine benthic ecosystems inhabiting the shallow subtidal areas of this volcanic island. Benthic species were qualitatively scored as presence versus absence, considering the different sampling effort between localities done over the years. A total of 139 species of macroorganisms, belonging to 16 phyla were found, including fauna and flora, increasing the species richness values previously reported in all sites surveyed within the volcano caldera. Moreover, a dramatic increase in biodiversity was found towards the entrance of the bay. We suggest, however, that recolonization from external waters may not be the only reason for this pattern. In fact, sediment flux rates and substrate instability are common disturbances within the bay, probably being among the major factors determining benthic community assemblages. These processes probably favour deposit feeding communities at the innermost locations of the bay. This study provides a remarkably increased and updated species inventory from previous reports, altogether with a description of the main communities inhabiting the bay and the abiotic factors regulating this, mainly the bottom type.

Introduction

Deception Island (DI) is an active volcano at the southwest end of the South Shetland Archipelago. Its central flooded caldera (i.e., Port Foster) connects with the Bransfield Strait through a narrow channel named Neptune's Bellows. This large protected bay (10 × 7 km2), has a maximum depth of 160 m (Smith et al., 2003). The characteristics of the surface water masses (< 30 m) of Port Foster are similar to those along the Bransfield Strait. However, deeper areas have been described to be significantly different. Bottom water temperatures in the central and northern sector of Port Foster are about 2–3 °C, suggesting geothermal warming (Ortiz et al., 1992). Indeed, DI harbours one of the warmest sites -albeit patchy- in the Southern Ocean as a result of its volcanic activity (Sturz et al., 2003, Meredith and King, 2005). Methane concentrations also indicate venting of hydrothermal fluids (Tilbrook and Karl, 1994), along with high concentrations of diluted Fe, Mn, and Si (Elderfield, 1972). On seasonal timescales, the water temperatures experience stratification during the summer and full-depth mixture in fall/winter (Lenn et al., 2003). These circumstances suggest that at the sill of Neptune's Bellows there is limited water exchange below 30 m in the summer months (Sturz et al., 2003). Neptune's Bellows is approximately 150 m wide at the narrowest point with a sill depth of 11 m, which minimizes the number of icebergs entering from outside, therefore limiting one of the most important disturbance factors affecting benthic Antarctic communities in other areas, i.e., ice-scouring (Gutt, 2001).

The Antarctic benthos has been categorized as a relatively homogenous biological unit (Barthel and Gutt, 1992, Sarà et al., 1992; Smale 2008; Downey et al., 2012). Many species share the same evolutionary constraints (Clarke and Crame, 1992, Clarke et al., 2004, Arntz et al., 2005) and some large-scale ecological conditions are similar around most parts of the continent, i.e., low and relatively stable temperature, seasonality of primary production, and low terrigenous input (Bullivant, 1959, Clarke and Leakey, 1996). Some authors indicate that identical conditions can support similar faunal assemblages in Antarctic sea bottoms (Dayton et al., 1994). However, other studies show that similar faunal assemblages can be found under different physical drivers (Barnes and Conlan, 2007, Angulo-Preckler et al., 2017b). Gutt (2007) proposed two types of core macrobenthos assemblages at community level. The first one would be dominated by sessile and sedentary suspension feeders, while the second one would consist in mobile deposit feeders and infauna. In both communities, this pattern can be overlaid by a second gradient ranging from very high to extremely low abundances.

In Deception island, several studies have documented the impact of eruptions and the posterior recolonization in benthic communities (Angulo-Preckler et al., 2017b, Arnaud et al., 1998, Barnes et al., 2008, Cranmer et al., 2003, Gallardo et al., 1999, Gallardo, 1975, Gallardo and Castillo, 1968, Gallardo and Castillo, 1970, Gallardo et al., 1977, Lovell and Trego, 2003, Moya et al., 2003, Pellizzari et al., 2017, Retamal et al., 1982, Sáiz-Salinas et al., 1997). Remarkably, an intense repopulation of flora and fauna has been observed in Port Foster since the last eruptions in 1967, 1969, and 1970 (Lovell and Trego, 2003), even though it seems clear from these studies that impacts and their effects on the communities lasted several years. The first surveys revealed that the opportunistic annelid Echiurus antarcticus Spengel, 1912 colonised the area in 1972 (Gallardo et al., 1977), although it seems to be absent now (Lovell and Trego, 2003, Barnes et al., 2008). In 1981, the area showed a significant enrichment in polychaetes and cumaceans as the dominant infaunal taxa, while the echinoderms Ophionotus victoriae Bell, 1902, Sterechinus neumayeri (Meissner, 1900), and Odontaster validus Koehler, 1906 became the dominant epifauna within the caldera to the present day (Angulo-Preckler et al., 2017b, Arnaud et al., 1998, Cranmer et al., 2003, Lovell and Trego, 2003, Retamal et al., 1982). Arnaud et al. (1998) considered the benthic system of Port Foster different from the rest of the South Shetland Islands (SSI) and described a lower taxonomic richness (6 species) but a higher biomass. A depth zonation of the dominant benthic fauna was described, with Ascidiacea dominating between 40 and 50 m, Echinoidea from 100 to 150 m, and Ophiuroidea below 150 m (Arnaud et al., 1998). This faunal zonation is dependent on sediment type, from gravels at the shallow stations to sandy and muddy sediments at the deepest areas (Gray et al., 2003). A later study, in which sampling was performed in deeper waters throughout the year, reported higher diversity, with up to 13 phyla, 16 classes, and 68 species (Lovell and Trego, 2003). These authors found a predominance of O. victoriae, along with a poor representation of sponges and ascidians in the deeper mid-bay. A scuba diving study reported 10 phyla, 13 classes, and 35 species at the entrance of the bay (Barnes et al., 2008) describing a declining biodiversity gradient. Barnes et al. (2008) described a strong decrease of species richness from the entrance to the internal caldera at subtidal depths, with remarkably low species richness within the bay. In summary, up to 2008, a total of 163 faunal species had been reported for DI (Barnes et al., 2008 and references therein). Moreover, in a recent study of the infauna, we reported the highest densities of organisms found so far for Antarctica, within the sediment of the shallow waters of DI (Angulo-Preckler et al., 2017b). Concerning macroalgae in DI, in a catalogue of benthic algae from the Brandsfield Strait, Gallardo et al. (1999) cited 26 algal species (7 Chlorophyta, 6 Ochrophyta and 13 Rhodophyta), 23 of them were found after the last eruption in 1970. Overall, and despite all these previous studies, the biodiversity of the shallow waters of Port Foster (< 40 m) has never been adequately assessed.

While most studies on shallow-water Antarctic benthic communities focus on the fauna, algal communities have never been included, even if it is well known that synergies between benthic macroalgae and invertebrates are crucial. These effects may be “positive” (richer macroinvertebrate communities or populations with increasing macroalgae) or “negative” (poorer macroinvertebrate communities or populations with increasing macroalgae; Mattson, 2009). Furthermore, DI has been and still is a centre of interest for non-indigenous species (NIS) establishment. DI is one of the Antarctic areas most likely to be colonized by both, natural means due to its close proximity to South America and its relatively mild and locally geothermal influenced climate, and by substantial human activity, such as tourist ships and research activity (IAATO (International Association of Antarcti Tour Operators), 2016, COMNAP (Council of Managers of National Antarctic Programs), 2017). For instance, ship borne transport is probably the main driver for NIS algae arrived at DI (Clayton et al., 1997, Barnes et al., 2008).

The current study aims to provide an updated comprehensive description of the shallow benthic assemblages of DI (fauna and flora), while providing a baseline information for reconstructing the historical community shifts from the entrance to the inside of the caldera to be compared with future studies. Considering the threats of climate change and anthropogenic impacts, an updated description of the current macro- and megabenthos communities and their spatial distributions in this vulnerable area of the planet is essential to assist in building tools to predict potential future environmental changes.

Section snippets

Sampling

Surveys were carried out inside Port Foster's Bay (except for Peter's Pilar) by scuba diving at different depths during the austral summers of 2008–10, 2011–13, and 2015–16 (Table 1, Fig. 1). Samples were randomly collected by scuba diving down to a maximum of 25 m depth, during the projects ACTIQUIM-I, ACTIQUIM-II, and DISTANTCOM. Samples were collected by hand in plastic bottles or bags. Each dive was performed by two-three divers for 25–35 min. Dives on soft-bottoms were done in parallel to

Results

A total of 139 species belonging to 16 phyla and 26 classes were collected at shallow waters in more than 150 dives at DI and identified to species level, when possible. Among the macroalgae reported, 31 different species were found, being the rest different invertebrates. Overall, more than one-third of the species recorded are new cites for DI (48/139). New records include 14 molluscs, 10 sponges, 6 echinoderms, 4 bryozoans, 3 cnidarians, 2 nemerteans, 2 tunicates, 1 annelid, 1 platyhelminth,

Discussion

The shallow waters of Port Foster are characterized by a rich biodiversity, with higher species richness than recorded in previous studies, accounting for a total of 139 species belonging to 16 phyla. This is thus the widest study carried out so far at the shallow waters of DI inner bay. Nonetheless, different methodologies and sampling efforts make the comparison between our data and those of the literature difficult (Cranmer et al., 2003, Lovell and Trego, 2003, Barnes et al., 2008,

Acknowledgments

Thanks are due to Dr F.J. Cristobo, Dr S. Taboada, Dr A. Riesgo, and M. Bas for their help during the fieldwork and species identification. Special thanks are due to Dr. Tuya for statistical advice. Thanks are also due to the crew of BAE Gabriel de Castilla for their logistic support during diving. This work was developed within the frames of the ACTIQUIM-I (CGL2007-65453/ANT), ACTIQUIM-II (CTM2010-17415), and DISTANTCOM (CTM2013-42667/ANT) research projects. Dr C. Angulo-Preckler was funded by

Ethical statement

The research reported here has been conducted in an ethical and responsible manner and comply with all relevant legislation.

  • 1.

    We have no potential conflict of interest.

  • 2.

    All procedures performed in this study involving animals were in accordance with the ethical standards of the institution or practice at which the study was conducted.

Contributors

All authors contributed extensively to the work presented in this paper. Design of the work; C.A.P. and C.A. Data collection; C.A.P., B.F., L.N.P., J.M., and C.A.

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