Home

Methods

Data

COOA

OPAL

Pictures

METHODS

At each station a full suite of measurements were made, including: CTD casts, collection of water samples at five depths, and vertically-stratified plankton tows using a 1/4-m MOCNESS equipped with a light sensor and fluorometer. Data and sample analysis will yield hydrographic structure and current flow, full nutrient analysis, chlorophyll concentration, identification and quantification of phytoplankton functional groups, toxic dinoflagellate (Alexandrium sp.) cell counts, counts of copepod species' abundances, including molecular discrimination of two cryptic sibling species of Pseudocalanus.

CTD (Conductivity, Temperature, Depth)

At each station a Sea Bird SBE25 was lowered to within 8m of the bottom. The SBE25 recorded depth, temperature, conductivity (salinity), flourescence, PAR (Photosynthetically Active Radiation), transmissivity, and disolved oxygen. Sampling rate was 4Hz. Data was processed using SBE Data Processing software from Sea Bird.

Water Samples

Niskin bottles collected 5L of water from depths of 2, 10, 20, 40m, and 10m off the bottom. From these water samples the following analyses were performed:

Chlorophyl: 100mL of seawater were filtered through a 25mm GF/F filter. The filter was folded in half and placed in a 15mL conical tube and wrapped in foil. Once in the lab, 10mL of 90% acetone were added to the tube and the filter was allowed to steep for 24 hours. The tube was then agitated for 30 seconds. Some of the acetone/chlorophyll mixture was then pipetted into a glass tube and flourescence measurements were taken in a flourometer.

Phytoplankton: 250mL of water from 2m only were preserved with Lugol's solution.

Nutrients: 250mL of water were collected from each depth and preserved with two drops of chloroform. Samples were kept on ice for transport back to the lab, where they were filtered and run through a Lachat nutrient analyzer.

Alexandrium: 2L of water were filtered through a 20 micrometer mesh sieve. Filtered material was preserved with a few drops of formalin. Cell counts were performed by Dave Townsend's lab at the University of Maine in Orono.

Zooplankton

Zooplankton samples were collected using a ¼ m square Multiple Opening Closing Net and Environmental Sensing System (MOCNESS), with 150 micrometer mesh nets and integrated CTD. The volume of water sampled by each net was determined using a flowmeter mounted on the net frame and an on-board inclinometer to record the area of the net opening. Real-time CTD data relayed to the ship as the MOCNESS was lowered were used to locate the pycnocline (defined as a sharp gradient in temperature and/or salinity separating two depths of different densities) and thus to select the depths of three discrete samples taken during the uphaul. Samples were taken within 5m of the bottom to 5m below the pycnocline, through the pycnocline, and from 5m above the pycnocline to the surface. If no pycnocline existed, the water column was equally divided between the three samples. On average, the surface net sampled down to 19m, the midwater net sampled between 19m and 42m, and the deep sample was from 42m to within 5m of the bottom. Zooplankton samples were preserved in 95% ethanol immediately after retrieval and the ethanol was changed after 24 hr.

A Folsom plankton splitter was used to divide an aliquot of approximately 200 adult copepods from the original sample (mean aliquot size = 212 copepods, SD = 97.0), requiring splits of 1/8 to1/1024. All adult copepods in this aliquot were identified to species and counted. Species count data were transformed into densities (number per cubic meter) using the dilution factor of the subsample and the volume of water sampled by that net.

SS-PCR (Species-Specific Polymerase Chain Reaction)

Pseudocalanus moultoni and Pseudocalanus newmani were identified to species utilizing a multiplexed, competitive species-specific polymerase chain reaction (SS-PCR, Bucklin et al. 2001). Female Pseudocalanus were sorted from the subsample and 24 individuals were randomly chosen for identification by SS-PCR. At least 20 successful PCR identifications were done for samples in which Pseudocalanus spp. comprised at least 5% of adult copepods. Densities for each species were determined by the proportion of SS-PCR identified P. moultoni and P. newmani in each aliquot multiplied by the total number of Pseudocalanus spp. counted in the original subsample.