U.S. GLOBEC: Field Studies of Predation Mortality of Copepods and Fish Larvae on Georges Bank

Co-PIs: Laurence P. Madin (WHOI) and Stephen M. Bollens (SFSU)


Our overall goal is to measure directly predation mortality on the target species on Georges Bank, and to compare this source of mortality to all other loss and gain terms (i.e., growth, reproduction, starvation, immigration, emigration) in the population dynamics of the target species. As with our results from Phase I, we will combine rate information and distributional data to estimate predation mortality on target species over the whole Bank throughout the winter and spring. Several additional goals are specific to Phase II, including 1) relate predator distribution to the physical environment, particularly advective forces; 2) estimate the abundances of predators that come onto the Bank from external source regions; 3) determine regions of loss from the Bank, and numbers of predators lost; 4) estimate numbers of predators retained on the Bank by physical forces. We will continue to work closely with Barbara Sullivan and Grace Klein-MacPhee (University of Rhode Island) whose emphasis is on smaller invertebrate predators and experimental work in mesocosms, and with NOAA's Coastal Ocean Program effort led by Mike Fogarty (Northeast Fisheries Science Center, NMFS, NOAA) on predation by pelagic fishes.


Given the reduction of our funding by over 50% in year 1 and about 30% in years 2 and 3, we cannot realistically expect to complete all the work set out in the original proposal; we have therefore substantially reduced the effort committed to this project. Also, Steve Bollens will be moving from WHOI to San Francisco State University (SFSU) in September, 1996, and our original budget has therefore been split into separate budgets for each institution. This Work Statement applies to both PIs, but we have provided separate budget justifications.


Although the BSS is supported by separate grants to other investigators charged with obtaining samples for the program as a whole, the critical importance of the BSS samples to our work requires that we involve ourselves in the collection and analysis of part of the sample set. Specifically, we will take on much of the responsibility for use of the 10 m2 MOCNESS trawl net, which is used to collect vertically- stratified samples of the larger (>3mm) invertebrates and juvenile fish in 4 discrete depths per tow. All aspects of the BSS work (1.1 -1.4 below) will proceed during all three grant years.

1.1. Preparation of MOC-10 system.
Our group will prepare the MOC-10 net system for use before each BSS cruise, including transportation of the net to the port of embarkation, loading and assembly of the net frame and components, installation of the nets and cod-ends, connection and testing of the mechanical and electrical systems, and consultation with the BSS Chief Scientist on operation of the net. We will provide sample jars and labels as needed. At the end of each cruise we will be responsible for disassembly and unloading of the MOC-10 if necessary, including arrangements for storage or transport between cruises, and storage of samples until they are sorted.

1.2. Analysis of Broad Scale MOC-10 samples.
We will be responsible for sorting BSS MOC-10 samples collected in 1997, 1998 and 1999. Samples will be sorted and counted, but appropriate subsamples will be taken from particularly dense samples. Invertebrates will be identified to species (and sex or stage where possible), counted and measured. Measurements will be used to estimate biomass as carbon weight, using published or newly derived relationships. These results will be tabulated in a spreadsheet format we are currently using, which can be added to the general GLOBEC database.

1.3. Additional sampling for gelatinous predators.
It is expected that a 1 meter, large-cod end "Reeve" net will be added to the BSS station plan to allow better sampling of ctenophores and other gelatinous predators. We will provide the nets and cod-ends and train members of the BSS scientific party to make these tows and counts.

1.4. Collaboration with NOAA's Coastal Ocean Program
Intensive net and hydroacoustic collections on the southern flank of Georges Bank are planned by COP ("Predation and the Structure of the Georges Bank Ecosystem"; M. Fogarty, project coordinator) for the spring and summer of 1997, with less intense sampling scheduled for 1998. We will continue our collaboration with Fogarty et al. by providing technical assistance in the processing of the copepod component of the pelagic fish predator stomachs collected by the COP, as well as collaborating on the comparison and synthesis of results.


2.1. Sampling Bank-edge transects on two process cruises during spring of 1997.
Our main goal is to sample transects that cross the Bank margin, from well off-Bank in toward the central plateau, at locations and during times of year when advective events are thought to affect the transport of water and organisms on and off the Bank. Our proposed cruise plan is for repeated occupation of a transect 1) across the Northeast Peak (NEP) into Scotian Shelf waters in April and 2) across the southeast flank into the Slope water in May. We will use several different gear types (MOC-1, MOC-10, SCUBA, LAPIS - see below, Reeve net) to sample a broad range of predator types. In addition to sampling for distribution, abundance and diet, we expect to continue ship-board experiments and incubations for additional data on predation rates and gut clearance (see below). Each cruise would include repeated sampling along a transect of 100-200 km total length, with ca. 10 stations 10-20 km apart, defined by bathymetric and hydrographic criteria. We expect to share shiptime on these cruises with other GLOBEC investigators involved in "vital rates" work (Durbin, Gifford et al.).

2.2. Development and use a Large-Area Plankton Imaging System (LAPIS).
This sampler is similar in concept to the Video Plankton Recorder (VPR), but designed to image larger gelatinous and micronektonic organisms (>10 mm) within a much larger field of view (1-4 m2). Video and data (flowmeter and CTD) signals are transmitted to the ship via fiber-optic cable, where they are recorded on High Definition and conventional recorders. LAPIS would be deployed in transect mode on each of the two 1997 process cruises. The principal goal will be to obtain horizontal and vertical distributions, abundance and size-frequency information for large gelatinous predators and other zooplankton or fishes in the 5 - 50 mm size range, which can be compared to catches with the MOCNESS nets. Funding for construction of this device has been cut to 1/3 of what was requested. We therefore are seeking additional matching support to build and use the instrument. While we consider the LAPIS a valuable tool for our work, we cannot at this time guarantee that these efforts will succeed and that LAPIS will be available for this project.

2.3 Diet of predators collected on Process cruises.
Gut contents from a sub-sample (10-20 individuals per species per sample) of different predators sampled with the MOC-10 during the 1997 process cruises will be examined, identified to the lowest taxa possible and quantified as total wet weight. MOC-1 samples will processed by our collaborators B. Sullivan and G. Klein-MacPhee via a sub-contract to URI. We do not expect to have enough time or personnel to examine guts from BSS samples routinely, but will apply rates generated from Process samples to distributional data from the BSS. This work will be undertaken primarily in grant years 2 and 3.

2.4. Development of a polyclonal probe for Pseudocalanus in predator gut contents.
Our first GLOBEC grant included a subcontract to Hydros Inc. (Falmouth, MA) for development of polyclonal antibody reagents for the detection of Calanus finmarchicus and Pseudocalanus spp. in the guts of predators. The objective was a specific, colorometric test that could detect the presence of the target species of copepods even when macerated and partially digested in the guts of crustaceans or fishes. The subcontractors have succeeded in isolating a protein that occurs only in Calanus finmarchicus, producing antibodies to it, and using these to create a sensitive, color-change test for the presence of C. finmarchicus. However, the subcontractor could not obtain enough Pseudocalanus spp. in 1994 to do the same thing for this species. Therefore we are proposing a continuation of the subcontract to allow them to produce a test for Pseudocalanus also. We expect that the new antibody will be developed in the same way as the previous one and detailed in our proposal. Positive and negative control assays will be run with all predators from Georges Bank which might feed on Pseudocalanus. The probes will be used for the detection of Pseudocalanus remains in the guts of predators collected on Process cruises in 1997, along with our existing polyclonal probe for Calanus. The budget allocation for this work represents the minimum amount which the subcontractor considers necessary to support the work.

2.5. Continue determination of feeding rates from gut contents.
During 1995 we worked on estimation of in situ feeding rates based on gut contents analysis and rates of gut clearance or passage time measured in shipboard incubations. During the 1997 process cruises we will concentrate on the medusae (Mitrocomella, Laodicea, Cyanea), ctenophores (Bolinopsis), siphonophores (Nanomia, diphyids), amphipods (Themisto), isopods (Cirolana), euphausiids, mysids, and any other common predators for which we do not yet have sufficient data on gut passage rates. Where possible, we will feed predators colored and uncolored prey alternately and time the appearance of colored fecal pellets. For species that won't feed in the lab, or in which gut mixing obscures the passage time, we will carry out incubations without food to measure decline in gut fullness and production of fecal pellets. For these experiments we will collect predators in short tows at times when we expect them to be feeding in-situ, and rapidly transfer groups of 20 or more to incubations. Initial gut fullness will be measured from a subsample taken at time 0, subsequent samples will be taken at intervals (based on the species of predator) for analysis of fullness as a percent of initial. Fecal pellets will be collected at the same intervals. This approach may be the only option for some species, but results are likely to be quite variable, and we will use the data cautiously.