Ampelisca eschrichtii are among the most important prey of the Western North Pacific gray whales, Eschrichtius robustus. The largest and densest known populations of this amphipod occur in the gray whale’s Offshore feeding area on the Northeastern Sakhalin Island Shelf. The remote location, ice cover and stormy weather at the Offshore area have prevented winter sampling. The incomplete annual sampling has confounded efforts to resolve life history and production of A. eschrichtii. Expanded comparisons of population size structure and individual reproductive development between late spring and early fall over six sampling years between 2002 and 2013 however, reveal that A. eschrichtii are gonochoristic, iteroparous, mature at body lengths greater than 15 mm and have a two-year life span. The low frequencies of brooding females, the lack of early stage juveniles, the lack of individual or population growth or biomass increases over late spring and summer, all indicate that growth and reproduction occur primarily in winter, when sampling does not occur. Distinct juvenile and adult size cohorts additionally indicate growth and juvenile production occurs in winter through spring under ice cover. Winter growth thus requires that winter detritus or primary production are critical food sources for these ampeliscid populations and yet, the Offshore area and the Eastern Sakhalin Shelf ampeliscid communities may be the most abundant and productive amphipod population in the world. These A. eschrichtii populations are unlikely to be limited by western gray whale predation. Whether benthic community structure can limit access and foraging success of western gray whales is unclear.

No abstract

BackgroundAmpelisca eschrichtii Krøyer, 1842 of the Sakhalin Shelf of the Okhotsk Sea, Far Eastern Russia, comprise the highest known biomass concentration of any amphipod population in the world and are a critically important prey source for western gray whales. Growth and reproduction in this population has not been apparent in summer. However, they are not accessible for sampling in winter to test a previous default conclusion that they grow and reproduce in winter.MethodsWe tested the default winter growth and reproduction hypothesis by detailed comparisons of the brood and gonad development among 40 females and 14 males and brood sizes among females observed since 2002. Our test included six predictions of reproductive synchrony that would be apparent from gonad and brood morphology if active reproduction occurs in summer.ResultsWe found high prevalences of undersized and damaged oocytes, undersized broods, a lack of females brooding fully formed juveniles, atrophied ovaries, and males with mature sperm but lacking fully developed secondary sex morphologies required for pelagic mating. All of these conditions are consistent with trophic stress and starvation.DiscussionThese A. eschrichtii populations therefore appear to starve in summer and to grow and reproduce in winter. The Offshore A. eschrichtii populations occur in summer below water strata bearing high phytoplankton biomasses. These populations are more likely to feed successfully in winter when storms mix phytoplankton to their depths.

The activity of acid and alkaline phosphatases, glucose-6-phosphatase. ~g~+ -~T P a s e and glucose-6-phosphate dehydrogenase was investigated in embryos and larvae obtained from gametes of the sea urchin Strongylocentrotus nudus exposed for 30 d to increased zinc, copper and cadmium concentrations (100, 25 and 50 ltg 1-l. respectively). Exposure of parent sea urchins to zinc resulted in increased M g 2 + -~T P a s e activity and decreased glucose-6-phosphate degydrogenase activity in larvae at the stage of 2 d pluteus, followed by their death. Exposure of parents to copper resulted in accelerated development of larvae at the stage of early pluteus; exposure to cadmium led to no visible changes in larval development.