Meiofauna communities from the Straits of Magellan and the Beagle Channel

G C Chen,R L Herman,M Vincx

doi:10.3989/scimar.1999.63s1123

Abstract

Meiofauna from 20 stations (ranging between 8 and 550 m) in the Magellan Straits and the Beagle Channel revealed 28 small sized taxa of higher categories including the temporary meiofauna. Nematoda, Copepoda Harpacticoidea and Polychaeta occurred in all samples; Turbellaria, Bivalvia, Kinorhyncha and Ostracoda were regularly present. Nematodes represented between 68% and 94% of the meiofauna at each station, followed by the copepods (2.3% to 14.5%) and polychaetes (1.1% to 11.5%). Maximal total density, 9700 individuals 10 cm -2 , was found in the surroundings of Picton Island, while the mean abundance per station was 3374 individuals 10 cm-2. The vertical pattern within the sediment showed that 87% of meiofauna components concentrated in the upper 0-5 cm sediment layers and 13% in the lower ( > 5cm) layers. More than 95% of copepods, as well as the temporary meiofauna occurred in the top 5 cm layers. The proportion of nematodes and copepods shows opposite trends in the vertical distribution. Multivariate analysis using the total density and the 10 `true´ meiofauna taxa densities discriminates between communities in the Straits of Magellan and the Beagle Channel area. Meiofaunal density was much higher in the Beagle Channel, but the diversity was lower than that in the Straits of Magellan. The Southern Magellan meiofauna communities are compared with those found at the Antarctic Peninsula and in the Weddell Sea (high Antarctic). It is considered that hydrodynamic features (tidal currents with strong winds), geographical characteristics, together with sediment composition are the key parameters structuring the meiofauna community in the Straits of Magellan and in the Beagle Channel.

Highlights

During 17 October to 25 November 1994 the Chilean-German-Italian R.V
Meiofaunal samples were collected from 20 sta tions, of which 11 stations were located in the Straits of Magellan and 9 stations in the Beagle Channel, during the R.V. 4Victor Hensen’ Joint Magellan Campaign 1994 (Table 1, Fig. 1)
Copepods and polychaetes were found at all sites; the relative abundance of these three main taxa represented about 97.0 % in total of the meiofauna community

Summary

Introduction

‘Victor Hensen’ Cam paign was carried out in the Straits of Magellan and the Beagle Channel. The Straits of Magellan is a narrow channel, about 500 km long which crosses the Sub-Antarctic region of the South American continent, separates Patagonia from Tierra del Fuego and connects the Atlantic and Pacific Oceans (Brambati and Colantoni, 1991). Tides are the most significant hydrodynamic feature in the Straits of Magellan, the highest spring amplitudes in the Atlantic entrance are about 9.0 m; in the central and western basins, tides are of a mixed type, predomi nantly semidiurnal and mean amplitudes are 1.1 m (Medeiros and Kjerfve, 1988). The mean annual air temperature is 6°C on the Pacific side, 2°C in win ter season. (Brambati et al, 1991; Panella et al, 1991). The Straits of Magellan is close to the Antarctic and the exchange between the southern tip and the Antarctic is supposed to have been more fre quent and longer lasting than between other frag ments of Gondwana (Arntz and Gorny, 1996)

Methods

Results

Discussion

Conclusion