Matthias Gorny

Shrimp (Decapoda, Natantia) occurrence and distribution in the eastern Weddell Sea, Antarctica

Summary108 successful ground and Agassiz trawl catches were taken between 155 and 2031 m depth in the eastern Weddell Sea on board RV Polarstern in spring and summer (October–February) 1985–1989. In addition, 7 hauls were taken with a semipelagic trawl. Only 19 hauls (16.5%) contained no shrimps. The others yielded large numbers of Notocrangon antarcticus, Chorismus antarcticus, and Nematocarcinus lanceopes as well as 20 Lebbeus antarcticus and 11 specimens of an Eualus species new to science. 8 Pasiphaea scotiae were caught in a pelagic krill trawl. No reptant decapod crustaceans were detected in the study area. Shrimp densities determined from trawl catches were lower than estimates derived from underwater photography but in the same order of magnitude. Although yields of the three common shrimp species in some cases exceeded 20 kg per 0.5 h haul, shrimp stocks in the area cannot be considered to be of commercial significance. A wider geographical distribution and greater frequency of shrimps in high Antarctic waters was found than described hitherto. There was considerable variation in numbers, sex composition, occurrence at different depths, and size-frequency distributions. C. antarcticus and N. antarcticus grow to a larger size compared with individuals from the Antarctic Peninsula area. Within the area of investigation, length frequency distributions are skewed towards larger sizes at higher latitudes. In the eastern Weddell Sea larger specimens of the three common species live at greater depths than smaller individuals. Potential reasons for these differences are discussed.

Spatial distribution of Antarctic shrimps (Crustacea: Decapoda) by underwater photography

Three species of shrimps ( Notocrangon antarcticus, Chorismus antarcticus, Nematocarcinus lanceopes ) were investigated in the south-eastern Weddell Sea using of underwater photography. Maximum densities of c. 100 specimens per 100 m 2 were found for N. antarcticus on the continental shelf (200–600 m) and for N. lanceopes on the slope (800–1200 m). Small-scale dispersion patterns and size-frequency distributions were analyzed within dense concentrations. These direct observations indicate that the behaviour of the three species is adapted to different habitats with Chorismus distribution correlated with that of sponges and Notocrangon with base sediment.

Gonopore development and sex change in the Antarctic shrimp Chorismus antarcticus (Caridea: Hippolytidae)

Chorismus antarcticus is the only protandrous hermaphrodite decapod species found on the Antarctic continental shelves. The morphological structures of the male and female gonopores were described and used to determine sex and to fix the size range at which the transition from male to female takes place. The parallel occurrence of male and female gonopores was found in all specimens. The presence of open gonopore flaps at both the third and fifth pair of pereiopods in individuals between 9 and 12 mm of carapace length (CL) is discussed as the morphological indicator of sex change. Few females occurred from 9 mm CL onwards, whereas all shrimps larger than 13 mm CL only had open female gonopores. This size corresponds exactly with the CL at which onset of oocyte development and female gonad production starts. Secondary sexual characters, the gonopore structures, seem to allow an accurate prediction of the size range at which hermaphrodite caridean decapods change sex.

Oocyte development and gonad production of Nematocarcinus lanceopes (Decapoda: Caridea) in the eastern Weddell Sea, Antarctica

Abstract Nematocarcinus lanceopes Bate 1888 is the only decapod that occurs in large numbers on the continental slope of the Weddell Sea, Antarctica. Histological examination of the female gonads and analyses of oocyte growth indicate a biannual reproduction cycle with seasonal occyte maturation in this species. Vitellogenic development is estimated to take 2 years and culminates during summer. Females spawn three times, every 2nd year, while they grow from 27 to 34 mm carapace length. Based on these results the calculated female gonad production is 184 g wet mass (70.5 g dry mass)/total catch, which is high compared to shrimp populations on the continental shelf of the Weddell Sea. Seasonal reproductive patterns of N. lanceopes seem to reflect oscillating food conditions in the Antarctic Weddell Sea. This mode of reproduction differs from all other Nematocarcinidae, which release eggs the whole year round. The ability to adapt the reproductive cycle to a seasonal productivity pattern may have been an important factor in extending the distribution range of the deep-water genus Nematocarcinus into Antarctic waters.