Activities and Findings report for NSF award OPP0125004 to Sharon Smith and Jack Fell

Submitted to the National Science Foundation, October 2004

Shelf-Basin Exchange of Large-Bodied Zooplankton [Copepods] in the Chukchi and Beaufort Seas

Year 1

Activities for year 1 of this project focused on field work conducted during summer 2002 aboard the USCGC HEALY. This work included MOCNESS, Bongo, and ring net tows for the collection of mesozooplankton. Due to mechanical damage to the MOCNESS resulting from collisions with ice floes early in the cruise, we had very limited stratified sampling success. Vertical Bongo net tows were successfully completed at nearly all stations. Non-quantitative vertical ring net samples were collected in cooperation with the Ashjian zooplankton group for collection of live animals that were selected for dry weight analyses, egg production experiments or for later molecular analyses. Underway sampling of surface plankton was conducted throughout the cruise for the specific purpose of mapping the distribution of copepod larvae. These samples were collected from the outflow of a thermosalinograph system utilizing a 35 µm mesh sieve.

Although most of the samples collected during summer 2002 were still on the USCGC HEALY at the writing of the year 1 report, a qualitative assessment was made of samples collected and scanned microscopically during the cruise. Only the deeper tows contained the copepods Euchaeta and Microcalanus for example, while the 0-100m tows usually contained Calanus hyperboreus, Calanus glacialis and chaetognatha. The onshore-offshore gradients in taxa were quite confused to the east of Barrow Canyon, with each station often seeming to have an assemblage not fully present at adjacent stations. Coastal species (e.g., Acartia) were collected offshore and Arctic Ocean taxa (e.g., C. hyperboreus) were collected on the shelf. Many taxa we expected to see were absent; some stations were fairly diverse, others were nearly monocultures. The clearest pattern was the absence of deep Bering Sea copepods in the study area in general. They were collected only at two nearshore stations in the Alaska Coastal Water (ACW). All other stations, including Herald Valley where they were supposed to be found in the Bering Sea inflow to the Chukchi shelf and slope, lacked Bering Sea species totally. The slope stations in the Herald Valley area (western-most part of the study area) contained a zooplankton assemblage that was typical of the deep waters of the Arctic Ocean. Based on earlier zooplankton collections during warm and cold years in this region, this warmest summer on record should have been accompanied by widespread distribution of large-bodied copepods coming from the deep Bering Sea. This was definitely not the case.

Year 2

Activities for year 2 of this project focused primarily on laboratory analyses of samples collected in year 1. Approximately 40 Bongo net and MOCNESS collections were enumerated for 38 species and taxonomic groups. The data from these samples have been entered into Excel worksheets and the abundance of selected data plotted in a variety of formats. In addition to taxonomic enumeration, portions of all zooplankton samples collected during the summer 2002 SBI cruise, which were size fractionated and dried at sea, have been weighed for biomass estimates. The biomass data were plotted and presented at the SBI meeting held in March 2003 at the Rosenstiel School/University of Miami. Molecular analyses consisted of selecting adult specimens of relatively common copepod species, identifying the species based on morphological characteristics, extracting the DNA and amplifying and sequencing the D1/D2 domains of the large (28S) subunit rDNA (circa 700 bp). In several species the mitochondrial 16S RNA (circa 400 bp) region was also amplified and sequenced (see Findings section). In addition to laboratory studies conducted in year 2, field collections of zooplankton were again made during a summer survey cruise on the R/V N.B. PALMER. These collections consisted of vertical Bongo net tows made by L. Llin·s while assisting Dr. James Swift of the Scripps Institution of Oceanography in CTD operations on the summer 2003 SBI survey cruise.

Laboratory analysis of Bongo net samples suggested that the mesozooplankton community was numerically dominated by copepod nauplii and small-bodied juveniles, including Pseudocalanus spp. and Oithona similis. We observed very few large-bodied copepods from the Bering Sea. However, much of the shelf region surveyed included relatively numerous large-bodied Calanus spp. juveniles and adults, suggesting that these copepods were reproducing over the shelf. The large-bodied copepod Calanus hyperboreus was rare over the shelf east of Hannah Shoal but relatively numerous over the outer shelf near Herald Canyon and Herald Valley. These observations suggest that large-bodied, deep-water species from the basin may be advected onto the Chukchi Shelf where they could significantly impact the food chain there and at downstream locations.

Molecular analyses completed during year 2 allowed the sequencing of several genera of copepod (see year 2 activities section). Sequences from the D1/D2 domains of the large (28S) subunit rDNA (circa 700 bp) were determined for 22 species belonging to the genera Augaptilus, Calanus, Centropages, Eucalanus, Metridia, Microcalanus, Neocalanus, Oithona, Oncaea, Paraeuchaeta, Pseudocalanus, Scaphocalanus and Spinocalanus. The rD1/D2 domains discriminated among most copepod species, with important exceptions such as the morphologically distinct species Calanus marshallae and C. glacialis which were identical in the mitochondrial 16S RNA (circa 400 bp) and in the rD1/D2 domains.

Year 3

Molecular studies have been ongoing in year 3 in an attempt to discriminate between the closely related Calanus species C. marshallae and C. glacialis; the Neocalanus species N. plumchrus and N. flemingeri; and the Pseudocalanus species P. acuspus, P. minutus, and P. mimus. Extraction and amplification techniques were partially modified in order to improve the quality of the amplicons obtained and reduce time. Beside the D1/D2 domains of the large (28S) subunit rDNA and the mithocondrial 16s DNA, also the Lsub ITS rDNA regions (circa 700 bp) and the mithocondrial cytochrome oxidase I region (COI) (circa 600 bp) were explored for potential differences among the above mentioned species. Based on the sequences obtained in Year 2, 3 alternative species-specific probes were designed and tested for each of the 12 species that showed acceptable difference in the Lsub D1D2 rDNA domains. We have also utilized specimens of C. marshallae collected for us by William Peterson off the Oregon coast and C. glacialis collected for us by StÈphane Plourde and Pierre Joly from the Gulf of St. Lawrence, where presumably C. glacialis and C. marshallae do not overlap. This experimental work is continuing. This year was also an intensive field study year, with four of us participating in two 40-day research cruises in May, June, July and August, and one of us participating on a 30-day cruise in September. The field work included use of the new HydroBios MultiNet plankton sampler, acquired in March. This system worked very well for collecting vertically stratified samples over five depth intervals in heavy ice-covered conditions. The MultiNet sampler was deployed 82 times during the 2004 cruises. Over one thousand surface samples were collected for mapping naupliar distribution. Analyses of taxonomic data from the 2002 field year have also continued this year and will be included in a manuscript in preparation.

Molecular analysis of the mithocondrial cytochrome oxidase I region (COI) of Calanus marshallae and C. glacialis showed potential differences between the two species allowing the design in this region of species-specific probes. This molecular work is ongoing. During our field work this year we made several coarse observations of the zooplankton community from various net collections. During the spring 2004 cruise we found the large, typically Arctic copepod Calanus hyperboreus predominantly in the upper 300 meters in stratified samples in slope water. Deeper samples contained predators (chaetognaths, Paraeuchaeta) and the omnivore Metridia longa. The vertical distribution of the actively reproducing copepod Calanus glacialis could not be discerned with the naked eye, but was common in live tows from 100 meters to the surface. Preliminary observations of surface fluorescence voltage from the SCUFA fluorometer used with our surface-mapping system suggested that the highest chlorophyll during the spring cruise was observed near Pt. Hope. Surface fluorescence on a section that ran offshore over Barrow Canyon was highest near the 200 m isobath, and lower both offshore and near the coast. During the summer 2004 cruise we were able to sample at much deeper stations in the Canada Basin than on our previous cruises. The basin station at the northeast corner of our study area, the offshore end of the East Barrow section, was dramatically different from all other stations sampled previously. Particles were so sparse that the acoustic Doppler current profiler was unable to record currents except in the upper-most, surface layers. The dominant pelagic fauna were the large-bodied copepod C. hyperboreus, a pteropod, and the predatory copepod Paraeuchaeta. An additional three basin stations did not appear to have the clearcut Arctic Ocean zooplankton assemblage observed at the offshore end of the East Barrow section. Further south, in slope waters, and on the Chukchi shelf near Bering Strait, we found large-bodied copepods typical of the deep Bering Sea. Surface fluorescence measured by the SCUFA fluorometer suggested that the highest chlorophyll values were again in the region of Pt. Hope and over the slope on the East Barrow sampling line. Over Barrow Canyon, surface chlorophyll concentrations were relatively low. In general, high surface fluorescence values in our study area were associated with warmer waters regardless of salinity.