Dataset: Copepod abundance - bongo net tows
Deployment: TT054

Bongo net. Bongo net collections covering the upper 200 meters were made at all intermediate stations and at some hydrographic stations, but not at the 48-hour time-series stations. Bongo net frames were 60cm diameter and were fitted with 153 and 335um mesh nets. Only the 153um mesh samples were analyzed. General Oceanics model 2030R flow meters were placed in the net mouth openings for the determination of volume filtered. The nets were towed obliquely from the side of the ship at approximately 1.5 to 2 knots (2.8-3.7 km h-1) through the water. Winch speed was generally 30m min-1 during deployment and 20m min-1 during recovery. The net was allowed to settle for about 30 seconds while at maximum wire out. The target depth for all Bongo tows was 200m, unless the sonic depth was less than that, and the wire out was adjusted during each tow, depending on the wire angle, to attain that depth. The maximum sampling depth of each tow was determined from a Wildlife Computers Mk3e Time Depth Recorder (TDR) attached to the net frame. Elapsed sampling time versus depth was plotted from TDR data for representative tows from cruises TN050 (August 18, 1995 - September 15, 1995) and TN 054 (November 30, 1995 - December 29, 1995). These comparisons showed that retrieval of the net was reasonably steady in both monsoon seasons so that all depth intervals were sampled uniformly. In the worst weather (TN 050; SW Monsoon), the rate of vertical ascent of the net was 11m min-1 (+/- 3; n=4), while in the better weather (TN054; NE Monsoon) ascent rate was 14m min-1 (+/-2; N=4).

The samples from the 153um Bongo net were split in a modified Folsom splitter, which split the sample into four parts consisting of 50%, 20%, 20% and 10%. In general, 10% was used for dry weight measurements (Lane and Smith, 1997;), 20% was preserved for collaborating scientists, and 70% was preserved for displacement volume measurements and taxonomic analysis.

Laboratory analysis. The samples reported here were split one to four times, depending on the amount of plankton present, in a Folsom splitter at the Rosenstiel School of Marine and Atmospheric Science (RSMAS), University of Miami. Subsamples were concentrated to 20 to 100ml and were transported to Ukraine (Russia) for enumeration and identification at the Institute for Biology of the Southern Seas (IBSS) in Sevastopol. Treatment of the samples at IBSS depended on the amount of plankton present in each sample. When the sample contained only a small amount of plankton, the entire split was analyzed for all species. In most cases, however, organisms smaller than ~1.5mm were identified and counted in smaller subsamples collected with a 1, 2 or 5ml Stempel pipette. Two replicate subsamples were withdrawn and counted and the data were averaged for calculation of abundance; generally 1-40 individuals per taxon were identified and sometimes more when a taxon was particularly abundant. Organisms ranging in size from ~1-2mm were counted in another part of the subsample collected with a 5ml Stempel pipette or by splitting the subsample into two or four equal parts. The entire subsample originating at RSMAS was then analyzed for abundance of organisms larger than 2mm, including copepods, euphausiids, amphipods, fish larvae, ostracods and any rare, large organisms. A total of 300 to 500 organisms per entire split were identified and counted.  The identifications were performed with the aid of Leningrad Optic-Mechanics Company (LOMO) binocular microscopes using various magnifications depending on the sizes of the individuals being identified. Copepod species are listed in alphabetical order. All copepod adult stages, copepodite stages and nauplii found in each sample are listed. The taxonomic notations are: c1 = copepodite stage I of the species; c2 = copepodite stage II of the species; c3 = copepodite stage III of the species; c4 = copepodite stage IV of the species; c5 = copepodite stage V of the species; c = undetermined copepodite stage of the species; m = adult males of the species; f = adult females of the species. Total length of the copepods is the average length in mm measured microscopically for that taxon.