The climatology of the Alaska Beaufort Sea shelf told by brittle star population dynamics

Brittle stars are a key component of Arctic benthic shelf systems due to their high standing stock, dominance in abundance over all other epibenthic organisms, and as prey for higher trophic organisms. On the Alaskan Arctic shelves, the circumboreal species Ophiura sarsii and Ophiocten sericeum are the dominant brittle stars with densities of up to 260 ind. m^-2 and 20 ind. m^-2, respectively. Although present across all Alaska Arctic shelves these specie have a segregated distribution; O. sarsii dominates the more productive Chukchi and western Beaufort Sea shelves and O. sericeum dominates the more river influenced Beaufort Sea shelf east of 150°W. Despite the pervasiveness of these species, little is known of their population parameters, the stability of their respective distribution patterns over time, or the factors that contribute to their geographic distribution. The objective of this study was to analyze the population size structure, growth, productivity, and distribution of the two species. Our results indicate that O. sarsii grows faster and lives longer than O. sericeum, and at equal body size, O. sarsii has significantly higher organic mass compared to O. sericeum. Compared to early records, we observed a shift in the distribution of the two species on the Alaska Beaufort Sea shelf over the past 40 years. Changes in intensity and frequency of easterly wind events over the western Beaufort Sea may be a key factor driving the distribution expansion of O. sericeum and the retreat of O. sarsii towards the west in this region. Considering the significant difference in these species’ growth rate and organic mass content, the consequences of this distribution shift for brittle star predators and benthic community remineralization may be substantial.