MACROBENTHIC COMMUNITIES - ASTEROID AND POLYCHAETE DIVERSITY

Americo Montiel¹, Laura Alonso-Sáez², Harald Bohlmann³, Pablo López-González⁴, Elisabet P. Sañé Schepisi²

1 Universidad de Magellanes, Punta Arenas, Chile

2 Institut de Ciènces del Mar, Barcelona, Spain

3 ISITEC, Bremerhaven, Germany

4 University of Sevilla, Spain

Objectives

Macrobenthic communities in the Larsen A/B area. Studies of recolonization processes in benthic communities after ice disturbance are scarce in Antarctic areas. The recent collapse of two huge pieces of continental ice shelf, Larsen A and B, created large ice-free areas. This presents a unique opportunity to study the structure of macrobenthic communities in shelf areas having been covered by permanent ice for hundreds to thousands of years, to compare these communities with other shelf communities from areas being covered by seasonal sea ice and to follow changes in the biodiversity after the disintegration. Since 1986, studies with multibox corers (MG) contribute to our understanding of distribution, diversity and recolonization patterns of macrobenthic organisms in high Antarctic shelf areas, such as Auståsen and Kapp Norvegia on the south-eastern Weddell Sea shelf. The main objectives were

- to complement former benthos studies of the EASIZ and LAMPOS expeditions with a study in a new and pristine Antarctic area, which until 2002 (Larsen B) and 1995 (Larsen A) has been covered by thick and permanent ice, thus allowing comparisons with former work, and - to enlarge the quantitative benthos data base for the Weddell Sea

obtained during several previous Polarstern cruises (e.g. EASIZ, LAMPOS and BENDEX expeditions).

Polychaete and asteroid diversity. Polychaetes and asteroids are important components of the Antarctic benthos. They contribute considerably to the overall biodiversity, occurring with 645 polychaete and 108 asteroid species.

The species are widely distributed in the Weddell Sea, along the Antarctic Peninsula and up to the Magellan area. They seem to be successfully adapted to extreme environmental conditions, such as austral cooling and the last maximum glaciations in South America. Recently, morphological and

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taxonomical results have shown the presence of species–complexes, i.e., groups of species with slight morphological differences; this may suggest occurring in cryptic and/or sibling species. The combination of molecular-genetics and the traditional taxonomical approaches has produced substantial progress in Antarctic science, although such studies are lacking in polychaetes and asteroids.

The main objectives of this project were:

- to collect as many polychaete and asteroid species as possible in order to initiate a bank of key species to be fixed and prepared for genetic analyses.

- to combine this molecular approach with traditional taxonomic work in order to obtain further insights into the similarity/dissimilarity of the community structure and species distribution of polychaetes and asteroids in high and subantarctic waters.

Work at sea

During ANT-XXIII/8, the multi-grab (MG) with attached underwater and digital cameras was successfully deployed on the eastern Peninsula shelf in the Larsen A and B areas. A total of 74 cores from 10 stations were obtained, covering a depth range from 202 to 850m depth. Besides the benthic samples, additional samples for sediment analyses and digital photos and videos were taken for better evaluation of the communities and habitats in these areas. For the first time, two 70W Xenon Lamps and a UV Flash (45) were used to improve digital photos from a Kongsberg 3.2 Mp digital camera.

All quantitative samples obtained were sieved on 500 micron screens and preserved in 10% formalin - sea water solution, buffered with borax. Further sorting of the benthic samples will take place at the home lab of the Alfred Wegener Institute for Polar and Marine Research (AWI), Bremerhaven, Germany. Sediment analyses will be done in the Institut de Ciènces del Mar, CSIC Barcelona, Spain.

A census of polychaetes and asteroids was collected from the by-catch of 31 bottom (BT) and 4 Agassiz trawls (AGT), taken on the shelf areas of Elephant, South Shetland and Joinville Islands in water depths between 94 to 353m. For the determination of the asteroids we used the “Fauna der Antarktis” and the catalogue of the British Antarctic Survey. The polychaete determinations were performed using “the interactive identification guide”. The similarity among the three groups of islands was analysed with PRIMER software based on presence/absence data of the polychaetes and asteroids in the catches.

Specimens of both groups were preserved in 10% buffered formalin - sea water solution for later taxonomical and stomach content analyses. Additional specimens were preserved in 96% ethanol or frozen at -30 °C for genetic/molecular studies, for biomass estimations and size distribution measurements.

ANT-XXIII/8, Scientific reports

Preliminary results

Macrobenthos communities in the Larsen A & B areas. More than 85% of the total samples reached core length > 20cm depth, which will be considered for the further quantitative analysis in the AWI (Fig 2.3). Our preliminary descriptions of the surface sediment composition and the visible macrofauna base on 274 UW-pictures and 3 hours of UW-video material. Most of the stations showed a high frequency of big sized stones in a matrix of silt and clay, except in the station 722-2, which was dominated by silt and very well sorted sediment, which decreased the efficiency of the gear to only 4 corer samples. The faunal composition was dominated by 3 species of holothurians and several species of ophiuroids. Sponges were only observed at one station in Larsen A and one in Larsen B (Table 2.1).

Fig 2.3 Penetrations depth of the corer samples from the MG in Larsen A and B area.

At the Larsen “B_Seep” station (709), one complete shell and several fragments of the genus Calyptogena, three specimens of holothurians and two different specimens of ophiuroids were collected. The shells of Calyptogena sp. will serve for growth analyses to be performed by O. Heilmayer, AWI.

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Table 2.1 List of stations, numbers of corers and photographs per station. Information on sediments and occurrence of macrobenthic organisms bases on the UW-photographs (* = samples for granulometry analysis).

Comparison of the macrofauna communities in Larsen A and B suggests at a first glance that in general the shallow stations in both areas were very similar of sediment environment and macrofaunal inventories. However, this has to be confirmed after more detailed sorting of samples and analysis of data.

Fig. 2.4 Species richness per catch at the Antarctic Peninsula. Columns in black: Elephant Island, in white: South Shetland Islands and in grey: Joinville Island.

Station corer Photogr. Sediment Macrobenthos

PS 693-3 4 34 gravel & clay Octocorallia / Ascidiacea / Bryozoa PS 700-1 9 * 19 stone & clay Ophiuroidea / Serpulidae

PS 701-1 9 * 14 gravel & clay Ophiuroidea / Porifera / Crinoidea PS 703-4 6 * 19 clay & stone Ophiuroidea / Holothuroidea / Asteroidea PS 704-1 7 * 31 clay & stone Holothuroidea / Ophiuroidea

PS 706-3 9 * 42 clay & stone Holothuroidea / Ophiuroidea

PS 709-6 9 * 22 clay & stone Holothuroidea / Ophiuroidea / Echiuridae PS 715-3 9 * 25 gravel & clay Holothuroidea / Ophiuroidea

PS 718-7 4 * 23 gravel & clay Holothuroidea / Ophiuroidea PS 722-2 4 * 23 silt & clay Ophiuroidea / Ascidiacea PS 725-4 9 * 22 gravel & clay Ascidiacea / Porifera / Crinoidea

ANT-XXIII/8, Scientific reports

Polychaete and asteroid diversity. The species richness in both groups varied between 2 and 9 species per trawl. The most diverse stations were 641-1, 666-1 and 668-1 with 9 species per trawl. All other stations showed less than 7 species per trawl (Fig 2.4). The species richness of the both taxonomical groups was slightly higher in the South Shetland area as compared to the Elephant and Joinville Islands. In comparison with previous findings obtained by the same methods species richness in polychaetes was lower than the reported information from the Peninsula area. Nevertheless, as in the EASIZ I, II, and III expeditions, Laetmonice producta was the most frequent polychaete occurring at 66% of all stations, followed by Aglaophamus macroura and Maldane sarsi occurring at 20 and 11%, respectively.

A total of 21 asteroid species were found seven of which remained undetermined, whereas nine polychaete species were determined (Table 2.2).

The most frequent asteroids species was Notasterias armata (23%), followed by Diplasterias brucei (23%), Cryptaster turqueti and Labidiaster annulatus.

The remaining species constituted less than 14% to asteroid diversity.

Although biomass was not considered in this study, a big catch (3.5kg) of L.

annulatus and the presence of some large specimens of L. magnificus (1.5 kg) are worth mentioning.

Table 2.2 Preliminary list of identified polychaete and asteroid species from 35 catches of bottom trawl and AGT. The percentages of frequency of occurrence in all samples are included.

Asteroids Frequency (%) Polychaetes Frequency (%)

Notasterias armata 66 Laetmonice producta 66

Diplasterias brucei 57 Aglaophamus macroura 20

Bathybiaster loripes 54 Malde sarsi 11

Cryptaster turqueti 43 Pista spinifera 9

Labidiaster annulatus 43 Paraonuphis sp. 6

Odontaster validus 37 Hartmothoe sp. 6

Acodontaster conspicuus 20 Barrukia sp. 6

Leptychaster magnificus 17 Ophelina sp. 3

Psilaster charcoti 14 Perkinsiana sp. 3

Porania antarctica glabra 14

Perknotaster fuscus 14

Asteroidea indet. 5 14

Cuenotaster involutus 11

Odontaster meridionalis 6

Crossaster fuscus 6

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According to ANOSIM analysis slight significant differences exist among the three groups of islands (R = 0.235; P = 0.001). These have to be confirmed after more detailed analyses of the biological and environmental data sets obtained.

2.1.3 BENTHIC-PELAGIC COUPLING IN POORLY KNOWN