Report of working group 2

Present: Pershing (Rapporteur),Mountain, Gangopadhyay, Bisagni, Brunner

For the discussion, we considered the six thematic questions listed in Section 4. Our discussion ranged across these questions, but we've attempted to categorize the main points according to the six themes.

1. What are the key mechanisms controlling recruitment success in the target species? e.g. bonanza year classes of haddock (1998, 2003)

The general consensus was that the field program has provided good evidence linking feeding conditions with good larval recruitment, especially in haddock. The naupliar and early copepodid stages, especially in Psuedocalanus, were identified as the most important food items. Independent of food limitation, good recruitment years also coincided with years of reduced off-Bank transport and low egg mortality.

2. Ecosystem indicators

First, there was a general discussion of what a valuable indicator would be, with general agreement that simpler is better. We focuses manly on physical indices, as biological indices (for example, target copepod species) had been covered during the presentations and in the discussion of (1). Ideas for physical indicators that could be useful included:

simple wind product for GB
salinity (indicator for productivity)
frontal positions (SSF, GS front)
NAO--use as an integrated index, lagged
maybe replace with windstress info from Lab Sea
NEC slope water index, for long-term system production a la Steele
need flux, not just TS
Gulf Stream rings impinging on Bank
Zooplankton indices: Calanus, Ctyp, Oithona

3. What are the physical and biological processes that link global/basin and the GB/GOM region?

Many of our "big ideas" (e.g. 5) touched on this issues. We did address one link to the basin scale that was not covered during the presentations or other discussion. Specifically, the group was interested in David Townsend's observations on the silica cycle on Georges Bank and wondered how remineralization, which is important for continuing some diatom production in the summer, would be altered in a warmer world.

4. What are the relative importance of top-down vs. bottom-up forcing of GOM/GB ecosystem?

difference between mean state and variability
copepod models are entirely bottom up (no variability in predation)
this is an area for theory, definition

First off, we recognized the need to distinguish between forcing of the mean state vs. forcing of the variability and agreed to consider the later. The general tone of the discussion was that bottom-up processes were more important drivers on Georges Bank, in contrast with Frank et al's assertions for the Scotian Shelf. We noted that the copepod models being employed in Phase IVb only allow for bottom-up variability (e.g. changes in production) as mortality is assumed to be fixed. Finally, we concluded that this is a topic that would benefit from future theoretical treatment.

5. What are the big ideas to come out of GLOBEC NWA?

We were able to identify several ideas emerging from our program that were especially novel or that would apply to a wide range of ecosystems. First, we noted that the we've established important linkages between GOM/GB and the basin scale. These include the NAO-Calanus relationships, the impact of low salinity intrusions on phytoplankton and zooplankton, and Wiebe's "three gyres" hypothesis for Calanus biogeography. Modeling is an important component of all GLOBEC studies, but the GLOBEC NWA program is unique in its development and use of models using unstructured grids (e.g. Quoddy, FVCOM). Related to question 4, we thought that Steele's identification of a strong bottom-up signal in Georges Bank despite intense fishing pressure was especially noteworthy. The group also thought that the possibility of alternate "regimes" in the GOM/GB ecosystem could be especially useful for management.

We also considered whether there were any conventional wisdoms that were disproved during our program. A major hypothesis at the start of the program was that stratified environments would provide better feeding conditions for larval fish (e.g. the Lasker hypothesis). Our program showed that other factors were more important, such as the duration of light required for efficient feeding. A major theme at the beginning of the program was the central importance of Calanus in the Georges Bank food web. Although Calanus is certainly important, it appears that variability in Calanus is of secondary importance for larval fish compared with smaller species such as Pseudocalanus. Due to the interest in early life history of cod and haddock, the program concentrated on the winter-spring period. However, recent work suggests that processes in autumn can lead to substantial variability in zooplankton abundance, and there is evidence that this variability can persist through winter and affect larval fish recruitment. Our group suggested that a fall study would be a good follow-up to the Georges Bank program.

6. What are the products/transitions of GLOBEC NWA? e.g. operational products, lead-ins to new scientific programs

Following from the last point above, there was considerable support for an intensive field program focusing on the fall-winter period in the Gulf of Maine. The group was also very interested in ensuring that the legacy of the NWA program be preserved and that it be communicated to the general public. We suggested a brochure capturing some of the main results would be an attractive option, as would a documentary of some kind. Along these lines, there was considerable enthusiasm for a COSEE program to bring GLOBEC and even JGOFS results into the K-12 curriculum.