Alexei I. Pinchuk

Climate-related differences in zooplankton density and growth on the inner shelf of the southeastern Bering Sea

Abstract Zooplankton abundance and biomass were measured during spring and late summer on the inner shelf of the southeastern Bering Sea in years of climate extremes. Samples were taken during late spring and late summer of three years: 1997, a year of moderate spring ice cover and unusually warm, calm summer conditions; 1998, a year of warm, but stormy summer conditions with very little spring ice cover; and 1999, a year of extensive spring ice cover, cold spring conditions and storms during spring and summer. Mean water column temperature was significantly lower during June 1999 than June 1998 and 1997. Copepod abundance and biomass during June were correlated with mean water column temperature and mean temperature below the thermocline. Mean calanoid abundance during June 1999 was 8–52% of the mean abundance during 1998 and 1997. Significantly lower abundances during June 1999 were observed for Calanus marshallae , Acartia spp., Pseudocalanus spp. and calanoid nauplii. Significant interannual differences in mean water column temperature and calanoid abundance during late summer (late July–early September) were not detected. The Hirst–Lampitt equations were used to estimate the mean daily copepod production during the warm and cold years. The mean production estimate during warm conditions was 13 mg C m −2 d −1 , with a range of 3–37 mg C m −2 d −1 , similar to previous estimates. Production estimates during the cold spring, 1999, were 3–4% of the production during warm periods. Assuming a 35% gross growth efficiency, calanoids could consume an average of 37 mg C m −2 d −1 during warm periods, but only about 2.6 mg C m −2 d −1 during a cold spring. Comparison of the above estimates to concurrent measures of primary production indicate that during warm, calm seasons, calanoids could remove most or all of the available water column primary production, thus indicating that calanoids may have been food limited. During cool conditions, the calanoids could remove only about 3% of the estimated daily primary production. Lower post-bloom primary production rates and higher calanoid grazing rates may result in substantially lower annual carbon flux to benthic communities on the inner shelf during warm calm years relative to cold years with extensive spring ice cover.

The abundance and distribution of euphausiids and zero-age pollock on the inner shelf of the southeast Bering Sea near the Inner Front in 1997–1999

Abstract Acoustic data and net samples were collected during late spring and early fall 1997–1999 to assess zooplankton and micronekton abundance and distribution relative to the Inner Front at three sampling grids (Port Moller, Cape Newenham and Nunivak Island) on the inner shelf of the southeast Bering Sea. Epibenthic scattering layers were observed during May–June and August–September in all three years. Acoustic data were scaled to euphausiid biomass using target strength models. Mean euphausiid biomass determined acoustically for each transect line was 0.7– 21 g m −2 , with most values below 5 g m −2 . There was no consistent relationship between the distribution and biomass of euphausiids and the location of the Inner Front. Zero age pollock were observed on the inner shelf in August–September during all years, but were confined primarily to the stratified side of the Inner Front and to the frontal regime. The acoustic data for pollock were scaled to biomass using laboratory measurements of gas bladder dimensions and target strength models. Acoustic determinations of mean transect biomass for euphausiids did not differ from literature values for the inner shelf of the southeast Bering Sea, and pollock biomass on the inner shelf did not differ from that around the Pribilof Islands. Despite recent anomalies in climate and oceanographic conditions on the inner shelf, and high mortality of shorttail shearwaters during 1997, we found no evidence of significant interannual differences in the biomass of euphausiids or zero-age pollock on the inner shelf of the southeast Bering Sea.

Alliance for Coastal Technologies: Advancing Moored pCO2 Instruments in Coastal Waters

The Alliance for Coastal Technologies (ACT) has been established to support innovation and to provide the information required to select the most appropriate tools for studying and monitoring coastal and ocean environments. ACT is a consortium of nationally prominent ocean science and technology institutions and experts who provide credible performance data of these technologies through third-party, objective testing. ACT technology verifications include laboratory and field tests over short- and long-term deployments of commercial technologies in diverse environments to provide unequivocal, unbiased confirmation that technologies meet key performance requirements. ACT demonstrations of new technologies validate the technology concept and help eliminate performance problems before operational introduction. ACT’s most recent demonstration of pCO2 sensors is an example of how ACT advances the evolution of ocean observing technologies, in this case to address the critical issue of ocean acidification, and promotes more informed decision making on technology capabilities and choices.

NAUPLIAR DEVELOPMENT OF METRIDIA PACIFICA (COPEPODA: CALANOIDA) REARED IN THE LABORATORY

All 6 naupliar stages of Metridia pacijica are described. Naupliar development is compared within the genus Metridia and external morphological characters are discussed with respect to previous studies on co-occurring nauplii of Calanus, Neocalanus, and Pseudocalanus. A key to the identification of the naupliar stages is provided. Knowledge of naupliar morphology is very important for studies of stage-dependent biological and ecological phenomena. Larval walleye pollock (Theragra chalcogramma Pallas) in the southeastern Bering Sea are very selective in the species of copepods and developmental stages that they eat. They prefer nauplii of Metridia, although these nauplii are relatively rare (Hillgruber et al., 1995). As part of a study of biological and physical variability that influences recruitment of walleye pollock in the southeastern Bering Sea, I describe the naupliar stages of Metridia pacifica Brodsky, 1950, and those diagnostic features that facilitate their identification.

Eastern Gulf of Alaska Ecosystem Assessment, July through August 2017

The goal of the Gulf of Alaska Ecosystem Assessment is to characterize ecosystem function and status in the eastern Gulf of Alaska. This survey is a coordinated research effort, conducted by the Recruitment Processes Alliance within the Alaska Fisheries Science Center. The scientific objectives of the survey are to assess age-0 groundfish, juvenile salmon, zooplankton, and oceanographic conditions in the coastal, shelf, slope, and offshore waters of the eastern Gulf of Alaska. This information is used to describe species distributions, ecosystem processes, marine productivity, and recruitment processes in response to changes in climate patterns and temperature anomalies (i.e., “The Blob”, and El Niño).