Density and biomass of two copepod size fractions and various species obtained during Almirante Irizar cruises to the Drake Passage and Scotia Sea (2000-2003)

The relative importance of small forms of copepods has been historically underestimated by the traditional use of 200-300-µm mesh nets. This work quantified the distribution and abundance of copepods, considering two size fractions (<300 µm and >300 µm), in superficial waters (9 m deep) of the Drake Passage and contributed to the knowledge of their interannual fluctuations among three summers. Four types of nauplii and eleven species of copepods at copepodite and adult stages were identified, with abundance values of up to 13 ind/L and 28,300 µg C/m**3. The <300-µm fraction, composed of Oithona similis, small cyclopoids and nauplii, dominated the copepod communities in the 3 years; it accounted for more than 77% of the total number and for between 40 and 63% of the total biomass. Changes in density and biomass values among the three cruises differed according to copepod size fraction and water mass; the >300-µm fraction showed no changes among the 3 years, both in Antarctic (density and biomass) and in Subantarctic waters (density), whereas the <300-µm fraction showed higher (density and biomass) values in 2001 both in Subantarctic and in Antarctic waters. Sea surface temperature and its anomaly accounted for the largest proportion of variability in copepod density and biomass, particularly for the <300-µm fraction.

长期以来，传统采用200-300微米网目渔网的采样方法，曾低估了小型桡足类（copepods）的相对重要性。本研究针对德雷克海峡（Drake Passage）9米深的表层水域，按<300微米与>300微米两个粒径组分量化了桡足类的分布与丰度，并为解析三个夏季期间桡足类的年际波动提供了数据支撑。本次研究共鉴定出4类无节幼体（nauplii）以及11种处于桡足幼体（copepodite）和成体阶段的桡足类，其丰度最高可达13个/升，总生物量可达28300微克碳/立方米。由微刺角水蚤（Oithona similis）、小型剑水蚤类（cyclopoids）与无节幼体组成的<300微米粒径组分，在三年调查中主导了桡足类群落：其个体数量占总丰度的77%以上，生物量占总生物量的40%至63%。三次航次中桡足类的密度与生物量变化，因粒径组分与水团类型而异：>300微米粒径组分在三年内无显著变化，无论是南极水域的密度与生物量，还是亚南极水域的密度均无明显波动；而<300微米粒径组分在2001年的亚南极与南极水域中，其密度与生物量均显著更高。海表温度及其异常值是解释桡足类密度与生物量变异的最主要因素，尤其对<300微米粒径组分而言更为突出。