Antarctic zooplankton community in the Bransfield Strait and Elephant Island

January 2006. Peru ANTAR XVI

Abstract

Two analyzes, one spatial and other temporal zooplankton community structure, from 44 samples (22 for each analysis) collected with Bongo net (300 and 500 μm mesh) and oblique tows (0-200 m), were carried out in the Strait Bransfield and around Elephant Island during the cruise ANTAR XVI 0601 BIC Humboldt. In the first analysis, the total zooplankton abundance showed values between 485 and 8947 ind/1000 m3 for 300 μm mesh, and between 33 and 8821 ind/1000 m3 for 500 μm mesh. A total of 15 groups were identified and Copepods were the most abundant and frequent, followed by Euphausiids (Thysanoessa sp.) and Chaetognaths (Eukhronia hamata). Salps showed low frequencies (27.27%) and abundance (33 ind/1000 m3). Also, two species were recorded in the ichthyoplankton, Nototheniops larseni, that was the most abundant and frequent (36.36%) than Pleuragramma antarcticum (27.27%). Total volumes fluctuated between 1.10 and 39.73 mL/1000 m3, and between 0.04 and 33.82 mL/1000 m3 for 300 μm and 500 μm mesh, respectively. Diversity (H ‘) values ranged from 1.09 to 3.76 bits, and from 0.93 and 3.19 bits to 300 μm and 500 μm mesh. Community analysis showed three biologically established groups. Group 3 was located north of the Bransfield Strait, Group 2 was in the center and the Group 1 closer to the Antarctic Peninsula and Weddell Sea. Calanus propinquus (Group 1: 54.01%), Metridia gerlachei (Group 2: 33.81%) and C. propinquus and Ctenocalanus sp. (Group 3: 43.04%) were the major contributors to this grouping. Finally, total values of zooplankton abundance and volumes were recorded, especially in coastal areas, and copepods and euphausiids dominated throughout the study area, with high abundance of small copepods (M. gerlachei and Ctenocalanus sp.). In the second analysis, a total of 11 groups was obtained. The highest abundance was found at 00:14 and 4:04 pm. Copepods not show any pattern in their timing within 200 meters, except for M. gerlachei, with higher abundance at 00:14. Euphausiids were only found overnight, indicating a daily migration to greater depths.