Meiofauna and microphytobenthos of Martel Inlet (Admiralty Bay, King George Island, Antarctica)

Abstract

Studies on the meiofauna community in Admiralty Bay started in 1991, when samples were collected through SCUBA diving in front of the Brazilian Station “Comandante Ferraz” (Martel Inlet) at depths ranging from 6 to 25 m. The dominant groups were Nematoda and Harpacticoida, followed by nauplii and Polychaeta. The density of meiofauna in Martel Inlet, excluding the ice scour affected areas, was high, and varied from 3,523±2,117 to 7,641±388 ind.10 cm-2 (mean ± SD) at 6-11 m depth, and from 3,479±1,205 to 8,216±3,030 ind.10 cm-2 at 18-25 m depth (Skowronski et al., 1998). Further samplings, including measurement of microphytobenthic biomass, were done at 15-20 m depth in seven areas of Martel Inlet: in front the Brazilian Station (CF), Yellow Point (YP), Rock O Connor (RO), Ullman Point (UP), Botany Point (BP), Hennequin Point (HP) and Plaza Point (PP) (Figure 1). The sampling was undertaken during two consecutive summers (1996/97 and 1997/98) and the results revealed that high meiofaunal densities are characteristic of this whole inlet, varying between 1,952±326 and 6,738±1542 ind.10 cm-2 and were correlated with the percentage of gravel, silt and clay (Skowronski & Corbisier, 2002). In both summers, the areas with the highest densities were CF and UP and also HP in the first summer and PP in the second (Figure 1). There was no significant difference in the densities between the two summers, although the higher value of microphytobenthic biomass, the potential food for the meiofauna, was recorded in the first summer. Horizontal differences were found in the microphytobenthic biomass throughout the inlet and seemed to be more related to the sediment characteristics, but no clear pattern of microphytobenthic distribution could be distinguished. An inter-summer variation was observed: the first summer showed the highest microphytobenthic biomass apparently related to more hydrodynamic conditions, which causes the deposition of allochthonous material (Skowronski et al., 2009). A positive correlation between the microphytobenthos biomass and the meiofaunal densities was observed during the second summer, when the microphytobenthos biomass was approximately 25% lower than in the first summer (Skowronski et al., 2009). This might have acted as a limiting factor to the meiofauna in some of the areas (Skowronski & Corbisier 2002). It may be supposed that the stronger hydrodynamic conditions of the first summer led to a high deposition of phytodetritus (phaeopigments), which masked the interaction between the meiofauna and the microphytobenthos. The bathymetric variation of the meiofauna and the microphytobenthos was also evaluated along transects (10 to 60 m depth) in five areas (CF, YP, RO, UP and BP) in Martel Inlet during the summer of 1997/98 and 2004/05 (Gheller, 2007; Skowronski et al., 1998; 2009). Concerning the microphytobenthos, mean biomass values were inversely related to the depth gradient. The highest values were found at 10 to 20 m (mean ± SD: 136.2±112.5 mg Chl a.m-2, 261.7±455.9 mg Phaeo.m-2), 6