DEVELOPMENT RATES AND HABITAT SHIFTS IN THE ANTARCTIC NERITIC EUPHAUSIID EUPHAUSIA-CRYSTALLOROPHIAS, 1986-87

Dynamics of distribution and growth were studied in the coastal Antarctic euphausiid Euphausia crystallorophias in the western Bransfield Strait region during the 1986-87 summer. The life phases showed differences in distribution. After the start of reproduction, which was well underway in December across shelf and open waters of the straits, the January distribution of larvae expanded with concentrations near the Peninsula, along the main Bransfield Current, and, to a lesser extent, around the South Shetlands. In February the distribution retracted toward the Peninsula as abundance diminished greatly. By March, larvae were found only north of the South Shetlands and in Gerlache Strait area where highest numbers had been observed through the season. Juveniles, believed to be 1 year old, and subadults, 2 years old, appeared to be randomly dispersed across the region at all times. Our few specimens of the adult class were from within or near embayments. Most December larvae were nauplii, metanauplii and Calyptopis 1. In January, older calyptopis stages were dominant. Latest observed eggs and nauplii were in January inside the Deception Island caldera. During February to March, development progressed from the calyptopis phase to the furcilia phase, and mean abundance of larvae declined from the > 100 m-2 level of January to < 10 m-2. Most late March larvae were furcilia stages 2 and 3, averaging one stage less than the more rapidly growing E. superba which had begun reproduction about a month later than E. crystallorophias. The Year-1 cohort was recognized in December as 12-16 mm juveniles, dispersed across the strait at mean abundances like those of the Year-0 larval class in March. The juveniles were about 15-21 mm by February, and there was no apparent growth through March. Subadults and adults were sparse in these open waters. Based on earlier year-round data on older E. crystallorophias from Poland's research station at Admiralty Bay, there seem to be two post-juvenile year classes. Our subadults fit into that pattern and are considered Year-2. Late in Year-2 and during Year-3 (maturity), females grew to a larger size than males and were more numerous.