Dvoretsky A.G.1, Britayev T.A.2 2010. Population biology of symbiotic amphipods Ischyrocerus spp. and their relationships with the host, the red king crab, in the Barents Sea // Invertebrate Zoology. Vol.6 (for 2009). No.2: 89–102 [in English].

1 Murmansk Marine Biological Institute KSC RAS, Vladimirskaya Str. 17, 183010 Murmansk, Russia. E-mail: vdvoretskiy@mmbi.info

2 A.N. Severtsov Institute of Problems of Ecology and Evolution RAS, Leninsky pr. 33, 119071, Moscow, Russia. E-mail: britayev@yandex.ru

KEY WORDS: red king crab, symbionts, amphipods, population biology, Barents Sea.

ABSTRACT: The relationship between two amphipod species of the genus Ischyrocerus and the alien species, the red king crab, and the population structure of these amphipods were studied in the Barents Sea. In 2004, 58.4% and 21.5% of crabs were colonized by I. commensalis and I. anguipes respectively. For both species of amphipods proportion of crabs with amphipods increased with the increase of the host size. All crabs with carapace width (CW) more than 140 mm were infested by I. commensalis. For I. anguipes prevalence never exceeded 50 %. Small crabs with CW less than 56 mm were never infested. The amphipods I. commensalis were located on the mouth appendages, gills, pereiopods between basiopodite and ischiopodite as well as between meropodite and carpopodite. Less frequently they were located on the abdomen, carapace, and eggs of crab females. Specimens of I. anguipes were located on the same sites but they were rarely found on the mouth appendages, gills and female eggs masses. The two species co-occurred on 47 crabs out of 132, other crabs were hosts of I. commensalis only. In smaller crabs with 60–120 mm CW, the ratio between amphipod species was 50:50. In larger crabs with CW > 120 mm, more than 80% of symbiotic amphipods were I. commensalis. In populations of both species, females were more abundant and larger than males. In both amphipod species, the proportion of females at later stages of maturity increased as crab size increased. There were marked differences in the diameter of the embryo at the first maturity stage and mean individual fecundity between the two amphipod species. These values were 0.40±0.05 mm and 23.0 eggs on average in I. commensalis, and 0.28±0.06 mm and 7.0 eggs on average in I. anguipes. Our results demonstrated that I. commensalis is more closely associated with the host than I. anguipes. The relationships of both amphipods with the red king crab are discussed.

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