Seasonal changes in the species composition of mesozooplankton in the Beagle Channel, southern tip of South America

AGUIRRE, GASTON; CAPITANIO, FABIANA; LOVRICH, GUSTAVO A.; ESNAL, GRACIELA

Hiroshima, Japón

Simposio; 4th International Zooplankton Production Symposium; 2007

North Pacific Marine Science Organization

<!-- /* Style Definitions */ p.MsoNormal, li.MsoNormal, div.MsoNormal {mso-style-parent:""; margin:0cm; margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:"Times New Roman"; mso-fareast-font-family:"Times New Roman";} @page Section1 {size:612.0pt 792.0pt; margin:70.85pt 3.0cm 70.85pt 3.0cm; mso-header-margin:36.0pt; mso-footer-margin:36.0pt; mso-paper-source:0;} div.Section1 {page:Section1;} --> The Beagle Channel (54º50’S, 66º50’-69ºW) is an area of great interest due to the mixing of Atlantic, Pacific and Antarctic waters.  However, little information is available on zooplankton distribution patterns in this area.  Therefore, this work aims to study the diversity and seasonal changes of the mesozooplankton community in the channel.  Twelve coastal stations were sampled during spring, summer and autumn (November 2005, March 2006 and June 2006 respectively), and surface temperature, salinity and chlorophyll-a concentration were measured.  Salinity amplitudes were higher during spring and summer (21.7-32.0 and 23.9-31.6 psu respectively) than in autumn (30.3-31.7 psu) due to continental runoff, ice melting from glaciers and precipitations.  Temperatures ranged between 7.5-10.3ºC in spring-summer and between 4.8-6.8ºC in autumn.  The highest chlorophyll-a concentration was registered in spring (mean 1.23±0.74 mg m-3) in coincidence with the maximum densities of copepods and appendicularians. Copepods assemblages were mainly composed by Acartia tonsa, Oithona similis, Ctenocalanus citer, Drepanopus forcipatus Calanus australis, Centropages brachiatus, Clausocalanus brevipes and Oncaea curvata.  Among appendicularians, the eurihaline and cosmopolitan Fritillaria borealis and Oikopleura dioica were the most abundant, although O. fusiformis was also recorded.  During summer, the cold water cladocerans Podon leuckarti and Evadne nordmanni were abundant.  The subantarctic chaetognath Sagitta tasmanica and the circumpolar amphipod Themisto gaudichaudii were found mainly in autumn.  A great abundance of meroplanktonic larvae was registered in spring, suggesting a strong plankton-benthos coupling during this season.