Durbin#1 Report

### US GLOBEC: Zooplankton Counting Technical Group

    INVESTIGATORS:

    Dr Edward Durbin
    Graduate School of Oceanography
    University of Rhode Island
    South Ferry Rd
    Narragansett, RI, 02882
    (401) 792-6695
    (401) 792-6240 fax
    email: edurbin@gsosun1.gso.uri.edu

    Dr Ann Durbin
    Graduate School of Oceanography
    University of Rhode Island
    South Ferry Rd
    Narragansett, RI, 02882

    GRANT PERIOD:  September 1, 1994 - April 30, 1996

#### STATEMENT OF OBJECTIVES:

- To determine the abundance and distribution of zooplankton on Georges Ban and adjacent waters,

- To determine the age structure of the target species of copepods Calanus finmarchicus and Pseudocalanus spp. as the basis for understanding their demographics, and to provide input for modelling studies of the species.

#### STATEMENT OF WORK:

A Zooplankton Technical Group has been established at the Graduate School of Oceanography, URI. The major responsibility of this group is to enumerate zooplankton samples from the broad scale survey and to analyse the data. In addition, they form part of a distributed Technical Group which is responsible for participating in the regular cruises and collecting the samples.

Six Broad Scale survey cruises are planned per year. The cruise dates for 1995 are:

    Date			Days
    Feb 10-21		10
    March 13-24		11
    April 11-23		12
    May 8-19		11
    June 5-17		12
    July 11-22		11

Additional samples have been collected during the Albatross IV training cruise to Georges Bank (AL 9410) between 7 Nov and 18 Nov 1994, and on the first process cruise (EN259) 10 Jan - 22 Jan 1995. These additional samples help provide a better seasonal coverage of the population dynamics of the target zooplankton species on Georges Bank. During 1996 a similar series of cruises are planned. However, during this year we are planning to move the July cruise to January to provide information on the early winter recruitment of zooplankton on the bank.

On each survey cruise 38 stations are occupied. At each station zooplankton and ichthyoplankton samples are collected with a 1m2 MOCNESS net tow. At 18 stations a pump cast is also made for smaller zooplankters (this is funded as a separate component). Depths for the MOCNESS sampling are 0-15 m, 15-40 m, 40-100m or bottom if it is less than 100 m, and 100-bottom where the depth is greater than 100 m. The MOCNESS is towed through two oblique hauls. The first five nets are 150 um for zooplankton and the second five 333 um for ichthyoplankton. Zooplankton are preserved in buffered formalin for later counting.

In the laboratory the displacement volume and wet weights are determined after separating the mesozooplankton and the macrozooplankton (euphausids, juvenile fish, gelatinous zooplankton). Wet weight/dry weight ratios are determined from a subsample taken from the first (down) net. For enumeration the samples are split with a Folsom splitter to provide a subsample of about 1000 animals. The two target species (Calanus and Pseudocalanus)are enumerated to stage while other zooplankton are identified to species. Copepods are grouped as copepodites and adults. Nauplii are not counted since, with the possible exception of the last two Calanus naupliar stages, they are not quantitatively sampled.

The data for each cruise will be presented in a cruise report when all samples for each cruise are completed. In addition as individual samples are completed they will be available on the data base management system. This has not yet been set up but will be done by the end of July.

#### SUMMARY OF KEY FINDINGS:

The first five cruises have been successfully completed with one remaining to be carried out. The technical group has been trained in zooplankton identification and are presently spending time between cruises enumerating samples. It is still too early in the project to provide many results. However, initial results show a much earlier initiation of reproduction by Calanus finmarchicus on the bank than expected. A few animals were reproducing on the bank in November while by mid January about half the Calanus were present as females and a cohort of young nauplii were developing. Surveys in future years will show whether this observation in 1995 is a normal occurence.