Madin Report

### Effects of Predation by Fish and Invertebrates on Target Species of Fish and Copepods on Georges Bank.

    INVESTIGATORS:

    Laurence P. Madin
    Woods Hole Oceanographic Institution
    Woods Hole, MA 02543
    508-289-2739
    lmadin@whoi.edu

    Stephen M. Bollens
    Woods Hole Oceanographic Institution
    Woods Hole, MA 02543
    508-289-3213
    sbollens@whoi.edu

    Barbara K. Sullivan
    Graduate School of Oceanography
    University of Rhode Island
    Narragansett, RI 02882
    401-792-6132
    bsull@gsosun1.gso.uri.edu

    Grace Klein-MacPhee
    Graduate School of Oceanography
    University of Rhode Island
    Narragansett, RI 02882
    401-792-6695
    gracemac@gsosun1.gso.uri.edu

    Grant Period: July 1, 1993 - January 31, 1996

#### STATEMENT OF OBJECTIVES

The overall objective of our research is to describe and quantify the effect of predation on the population dynamics of the four target species on Georges Bank. Our specific focus is on invertebrate predators ranging from cnidarians to crustaceans. Predation by fishes is the subject of research conducted by our collaborators Mike Fogarty and Bill Michaels at the Woods Hole Northeast Fisheries Science Center, with funding from the NOAA Coastal Ocean Program. Our research goals are to:

1. Determine the broad-scale (10-100 km) horizontal and fine-scale (10 m) vertical distributions and abundances of the vertebrate and invertebrate predators over Georges Bank during 1994 and 1995. (In collaboration with Broad Scale Survey and Coastal Ocean Program).

2. Use gut contents analysis to determine the diet and diel feeding cycles of the principal invertebrate predators over Georges Bank during 5 process-cruises in 1994 and 1995.

3. Develop polyclonal antibody techniques (in collaboration with Hydros Inc.) for the detection of Calanus remains in the guts of predators.

4. Determine gut evacuation rates or digestion times of the principal invertebrate predators during the 5 process-cruises.

5. Determine feeding rates of selected invertebrate predators on larval cod and haddock in laboratory aquaria, ranging up to 13 m3 experimental enclosures.

6. Combine the above data to determine the predation mortality inflicted by invertebrate predators on the target species of copepods and fish.

7. Compare estimates of predation mortality measured at different times of year and under contrasting physical conditions of the water column (i.e., stratified vs. mixed).

8. Compare our estimates of invertebrate predation mortality with other loss terms (e.g. predation by fishes, starvation, advection) estimated by other GLOBEC investigators to determine the overall importance of predation as a factor controlling population abundance of target species on Georges Bank.

#### STATEMENT OF WORK

Our group has participated in Process Cruises in May 1994, March 1995, April 1995, May 1995 and June-July 1995. Sampling on these cruises included 1/4 m2, 1 m2 and 10 m2 MOCNESS nets fished from the bottom to the surface in replicated day/night pairs (when possible) at both stratified and well-mixed stations. Additional sampling was done with Bongo nets and by SCUBA diving. Subsamples of invertebrate predators were removed at sea for special fixation in preparation for analysis of gut contents with polyclonal antibodies.

MOCNESS samples are being sorted, identified and enumerated by members of our group at WHOI (10 m2 MOCNESS) and URI/GSO (1 m2 MOCNESS). Subsamples of predators are being examined microscopically for gut contents.

Shipboard experimental work has included incubations to determine digestion or gut passage times of predators eating copepods and copepod eggs. Feeding experiments were also done to provide samples of predators with known target species as prey for antibody analysis.

The pelagic hydroids which were abundant components of the plankton at the well-mixed site were brought back to WHOI and GSO and maintained in continuous culture. A number of observations and experiments on feeding behavior, feeding rates, and growth responses to food supply and mixing were conducted with these cultures.

With supplemental grant support from NURC/UCAP in Connecticut, we used a ROV on two Process cruises in 1995 to survey bottom habitats for the presence of attached hydroid colonies that might be the source of the suspended fragments. Videotape, suction samples and grab samples are being analyzed from 4 sample regions on the Bank.

Our group has worked with a subcontractor, Hydros Inc., to develop a polyclonal antibody method for the detection of Calanus finmarchicus in the guts of predators. This is particularly important for predators like crustaceans which chew the prey into pieces too small to identify microscopically.

During 1995, we have provided support and set-up assistance to get the 10 m2 MOCNESS system installed and operating on the ships conducting the Broad Scale survey. Samples with the MOC-10 have been included in all Broad Scale cruises in order to provide distribution and abundance data for the larger predators. These samples will be sorted and identified in our labs.

#### SUMMARY OF KEY FINDINGS

Analysis of MOCNESS samples has been completed for the 1994 Process cruise, and is in progress for the 1995 cruises. So far it has revealed strong diel variations in abundance and composition of the invertebrate zooplankton. Major predatory species identified and quantified include chaetognaths, amphipods, isopods, decapod shrimp, medusae, ctenophores and suspended colonies of hydroids. A manuscript summarizing historical (MARMAP) data on invertebrate predator distribution on Georges Bank has been submitted.

Feeding studies on the process cruises included gut contents analysis and digestion time measurements for ctenophores (Pleurobrachia, Bolinopsis) collected by divers, gut passage time determinations for decapod crustaceans (Crangon, Dichelopandalus) isopods (Cirolana) and amphipods (Themisto), and preparation of predators with known prey in their guts for tests of the antibody methods.

The suspended hydroid colonies which dominated the plankton at some stations in 1994 were also found on all cruises in 1995, though in lower numbers. Observations and experiments conducted on process cruises and in our laboratories at WHOI and URI demonstrated that the hydroids (principally Clytia gracilis) were able to feed effectively on eggs and nauplii of Calanus finmarchicus and other copepods, and on larval cod. A short manuscript concerning the occurrence of the hydroids and their potential predatory impact has been prepared and submitted to Deep- Sea Research.

Other laboratory experiments with the hydroids have demonstrated the effect of food supply and mixing rate on growth rate and colony structure of the hydroids. These results will help us interpret the life history of Clytia on Georges Bank.

Sampling conducted with the NURC/UCAP ROV in May and June-July revealed large numbers of Clytia colonies on the bottom in the Northeast Peak region of the bank, upstream from the well-mixed central region where the suspended hydroids mainly occur. Some of the ROV data have been analyzed by a WHOI Summer Student Fellow, and will be prepared for publication this fall.

Development of the polyclonal antibody for Calanus finmarchicus has progressed to the point where we now have large quantities of an antibody to a protein that appears to be specific to Calanus. Tests of cross-reactivity have been conducted with all the principal predators that might consume Calanus. A protocol for fixing predator samples at sea has been developed to allow us to use the antibody on preserved samples on shore, and we have approximately 700 such samples, representing 18 species of predators. Final details of the laboratory protocol for washing and analyzing these samples are being worked out.

#### PUBLICATIONS RESULTING FROM THIS GRANT:

Sullivan, B.K. and C.J. Meise. Spatial and temporal patterns in abundance of invertebrate predators of zooplankton on Georges Bank, 1977-1987. Deep-Sea Res. (submitted)

Madin, L.P., S.M. Bollens, E. Horgan, M. Butler, J. Runge, B.K. Sullivan, G. Klein-MacPhee, E. Durbin, A. Durbin, A. Bucklin and M.E. Clarke. Voracious planktonic hydroids: Unexpected predatory impact on a coastal marine ecosystem. Deep-Sea Res. (submitted)