Comparisons of morphology and neritic distributions of Euphausia crystallorophias and Euphausia superba furcilia during autumn and winter west of the Antarctic Peninsula

摘要

Euphausia crystallorophias and E. superba larvae often overlap in distribution in Antarctic coastal regions. Here, we describe the morphology and ecology of E. crystallorophias furcilia stages F3-F6, with emphasis on characteristics that distinguish them from E. superba, based on samples collected west of the Antarctic Peninsula during autumn and winter 2001 and 2002. During autumn most E. crystallorophias occurred as F4s (53%) and F5s (35%), while E. superba occurred in all furcilia stages (F1-F6). During winter, F6 was the dominant stage ( >67%) for both species. On average, body lengths of E. crystallorophias larval stages were significantly greater than those of E. superba. During autumn, densities of the two species were similar (range: 0.003-11.8 m~(-3)) at many on-shelf stations, with lower densities during winter. Where both species occurred, > 58% of E. crystallorophias furcilia were collected between 50 and 100 m depth, while 82% of E. superba were shallower (25-50 m). Younger stages of E. crystallorophias occurred more frequently (54% of F3s) in water > 100 m than older stages (11% of F6s). Thus, many larval E. crystallorophias were vertically segregated from E. superba, thereby reducing grazing competition between the young of these morphologically similar species.