NWA - Chapter 9.2

## Benthos Working Group Report

Chairman: Charles Peterson
Rapporteur: Robert Mohn

1. There was a consensus that processes affecting the larval life stage up to and including the time of settlement represent the largest gap in our understanding of population dynamics and quantitative demography of benthic invertebrates.

2. Principal attention should be focused on the larval (meroplanktonic) life stages.

3. The Working Group was pessimistic about the chances of being able to follow a cohort of scallop larvae in time and space sufficiently closely to draw inferences about what controls survivorship.

4. We debated over the rationale for choosing study species: although the sea scallop can be justified by the existence of a historical data base and ongoing prerogatives for continuing fisheries assessments and research, as well as an OPEN focus, it would be wise to choose a species on the grounds of selecting the best study system to address the problem. In this instance, that might be a highly localized, synchronous, predictably heavy spawner whose larvae were orange and naturally fluoresced. A proposal that discovered such a beast and proposed it as the focus of study would have much merit.

5. The best use of support to study the impacts of physical processes, direct and indirect, on larval ecology of benthic invertebrates would be to build a set of fundamental contrasts that could allow some extrapolation and prediction. Specifically, a) holoplankton vs. meroplankton; b) feeding vs. non-feeding larvae; c) phytoplanktivorous vs. zooplanktivorous larvae; d) long vs. short planktonic period (6 vs. 3 weeks); e) spawning season (spring vs. fall); f) strong vs. weak swimmers.

6. Field observations on how these types (from #5 above) compare in their responses to physical features and processes should be complemented by experimentation in situ, on shipboard, or in the laboratory to: a) test behavioral responses of larvae to changing stimuli; b) test for food limitations; c) address effects of predators.

7. Scallop larvae should be included in this group (#6) and a modest effort devoted to a population dynamics study of sea scallops, dovetailing with the studies of scallop settlement and early juvenile survival in OPEN.

8. Larval ecology field studies should be co-ordinated with the zooplankton and ichthyoplankton studies to set an appropriate sampling design as dictated by physical oceanographic considerations.

9. Specific physical processes and conditions of likely importance to population dynamics and likely to vary as a function of climate change should be explicitly identified. Explicit sampling, both physical and biological, with specific hypotheses, should be conducted, with emphasis on features and processes such as a) fronts of different types; b) stratification - mixing; c) advective regime and its forcing; d) tides; e) storms; f) wind field; g) temperature change; h) fresh water input; i) mediating variables of primary production, competitors, predators.

10. Critical need for technology development or device to quantify larvae of a few species by species (using perhaps immunology or some other biotechnological tool)

11. Equipment need for automatic larval sampler (fixed mooring)

12. Additional effort needed on benthic habitat (physical and biological) associated with juvenile cod, focusing on prey of cod, whether they are limited, etc.

13. In this connection, the Working Group recommends a study of how other groundfish (especially elasmobranchs) affect cod dynamics, including interactions mediated by their joint influences on benthic prey

14. Much interest exists among benthic biologists of Atlantic nations (especially US, Canada, France) in determining how benthic boundary layer dynamics influence growth and production of benthic animals, especially commercially important shellfish. If physical dynamics (bottom boundary currents, shear stresses, sediment dynamics, etc.) could be somehow related to global change with a sensible model, a major GLOBEC program could be generated addressing this issue.