Quantitative analysis of macrobenthic soft-bottom assemblages in South Shetland waters (Antarctica)

Abstract

Macrobenthic assemblages were investigated at 26 stations located around Livingston Island, Deception Island and the Bransfield Strait at depths ranging from 42 to 671 m. Representatives of 30 major taxa were found. The maximal density was 5,260 specimens · m\ at Livingston Island; the mean abundance per station ranged from 160 to 4,380 specimens · m\. The total biomass of the macrozoobenthos declined with depth, with mean values of 3,201 g · m\ at shallower depths ( (100 m) and 210 g · m\ further down ( '100 m). After multivariate analysis (cluster analysis, MDS) based on Bray-Curtis dissimilarities, most stations could be assigned to one of three groups on the basis of distinct biomass differences between sites. The first cluster with a rich Ascidiacea biomass is common on shallower bottoms. The second, with Ophiuroidea as a characteristic group, is common on deeper bottoms. The absence of an 'indicator' taxon is characteristic of the remaining cluster of those stations with the lowest biomass values. No significant correlations were detected between macrobenthic biomass and any sediment parameters measured, probably because part of the benthos (i.e. the epifauna) could be better explained by the coupling with a highly productive water column. The role of the epi-infauna sensu Gallardo as the main factor structuring benthic assemblages in the investigated area is discussed.

The megazoobenthos of the Scotia Arc islands

“…Dense suspension-feeder communities are absent in the Magellan channels , as well as in other extensive areas of the Scotia Arc archipelagos, such as the vast southern shelf of the South Orkneys (Ramos and Sobrino, 1991), west of Elephant Island, the shallow bays of the South Shetlands (Gallardo, 1992;Jazdzewski et al, 1986;Sáiz-Salinas et al, 1997;Arnaud et al, 1998) and in Bransfield Strait (Mühlenhardt-Siegel, 1988Ramil and Ramos, 1997). This could be due, among other factors, to their location, close to glacial fronts or in the frequent passage of large icebergs.…”

“…As they seem to grow faster than other invertebrates, particularly during some years (Kühne, 1997, cited by Arntz, 1997), they are probably more opportunistic, and could take over the ecological niche of other, much more demanding suspension feeders. This hypothesis could explain the ascidian dominance in zones with strong glacial influence, such as some bays of the South Shetlands, on bottoms less than 100 m depth (Jazdzewski et al, 1986;Kowalke, 1989;Sáiz-Salinas et al, 1997;Arnaud et al, 1998), or those subject to active volcanic conditions, such as the South Sandwich archipelago or inner and outer Deception Island (Retamal et al, 1982;Sáiz-Salinas et al, 1997;Arnaud et al, 1998;Ramos, unpubl. data).…”

“…Studies on the South Orkneys and South Shetlands are somewhat more numerous, mostly focusing on Signy Island (Hardy, 1972;Barnes, 1995a, b) and some of the South Shetlands shallow bays (Gallardo, 1992), especifically those of Greenwich (Gallardo and Castillo, 1969;Gallardo et al, 1977) and Deception islands (Retamal et al, 1982). During the last decade, this information has been expanded by the work of Jazdzewski et al (1986), Sáiz-Salinas et al (1997) and Arnaud et al (1998) in the South Shetland area, as well as that of Mühlenhardt-Siegel (1988 in the South Orkneys, South Shetlands, Elephant Island, and the Antarctic Peninsula. Since the methodology used in all those projects was aimed at studying the infauna, they offer little information on the characteristic components of the megabenthos, particularly regarding the distribution of the rich three-dimensional communities of suspension feeders that are so characteristic of the Antarctic epifauna (Arntz, 1997;.…”

Assemblages and habitat preferences of soft bottom Antarctic Amphipoda: Admiralty Bay case study

“…Even though Amphipoda play a very important role in the Southern Ocean benthic communities, in the majority of ecological studies they are identified only to the order level (e.g. Sáiz-Salinas et al 1997;Gambi and Bussotti 1999;Barnes et al 2006;Rehm et al 2006Rehm et al , 2011Glover et al 2008;Saiz et al 2008;Cummings et al 2010). Taxonomical studies are time consuming and difficult, which led several authors to search for Abstract Amphipoda belong to enormously diverse benthic invertebrate groups in the Southern Ocean, playing a very important role in the Antarctic communities.…”

Estructurada de las comunidades bontónicas en tres sitios de las islas Shetland del sur (Antártida): Patrones de diversidad, composición y tamaños corporales

“…Estudios recientes sugieren que la distribución espacial y la zonación trófica del bentos antártico en las Islas Shetland del Sur están principalmente determinadas por un factor dependiente de la profundidad (Sáiz-Salinas et al 1997;Piepenburg et al 2002); habiéndose además realizado evaluaciones de abundancia y biomasa tanto en Islas Shetland del Sur como en la Península Antártica (Arnaud et al 1998). Además, cabe destacar que la alta biomasa de muchas comunidades bentónicas está probablemente relacionada con adaptaciones a los bajos y oscilantes niveles de alimento (Brey & Clarke, 1993) Los objetivos del presente trabajo son: (1) caracterizar y comparar la estructura de las comunidades bentónicas antárticas en tres sitios de las Islas Shetland del Sur con distintas características topográficas y (2) evaluar si la relación entre la abundancia y biomasa de los distintos grupos de invertebrados es un buen indicador para detectar casos de gigantismo y enanismo.…”