U.S-GLOBEC: NWA Georges Bank—Processes Controlling Abundance of Dominant Copepod Species on Georges Bank

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Figure 1. Broadscale survey results. A. Mean GB copepod abundance from 1995. B. Salinity anomaly 1992-2002 (dashed lines bracket GLOBEC years), C. phytoplankton vs salinity, D. larval fish growth vs prey abundance, E. larval fish mortality vs year, F. larval fish mortality vs salinity anomaly.

Figure 2. (Left Panel) The Arctic’s Beaufort Gyre can accumulates or releases low-salinity melt water depending on the phase of the Arctic Oscillation. (Right Panel) The transit time for Arctic melt water to travel from Baffin Bay to the GB-GoM region is 2 years.

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Figure 3. Local and remote forcing on plankton by hydrography, currents, and nutrient input into the GB-GoM region. (upper left) Local forcings include tides, winds, mean flows, and mixing. (other panels) Remote forcing include surface and deep intrusions of water from the Labrador Sea. Deep Labrador Slope Water is relatively poor in nitrate and its intrusion is NAO – related.

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Figure 4. Model schematics for physical (left) and biological (right) models.

Figure 5. Example of 3D, NPZD-FVCOM output (right). This model was run through the GLOBEC years from 1995-1999. The model was used to compute the N-budget for Georges Bank (below) and effects of LSW intrusions.

Figure 6. Example of copepod model output. The mean-age copepod model was coupled with the NPZD-FVCOM model and run during the first GLOBEC year, 1995. The model was able to reproduce the 3D distribution of Pseudocalanus observed in the field data.

Dec 1, 2005 through June 30, 2008

Dr. Cabell Davis
Woods Hole Oceanographic Institution, Woods Hole, MA 02543

Dr. Robert Beardsley
Woods Hole Oceanographic Institution, Woods Hole, MA 02543

Program Manager: Dr. Elizabeth Turner, NOAA/NOS

Related NOAA Strategic Plan Goal:
Our research has implications that are relevant to NOAAs goals:
Goal 1. Protect, restore and manage the use of coastal and ocean resources through ecosystem-based management.
Goal 2. Understand climate variability and change to enhance society’s ability to plan and respond.
Goal 3. Serve society’s needs for weather and water information.
Goal 4. Support the Nation’s commerce with information for safe, efficient, and environmentally sound transportation.

Project Overview
A fundamental goal of Biological Oceanography is to understand how underlying biological-physical interactions determine abundance of marine organisms. For animal populations, it is well known that factors controlling survival during early life stages (i.e., recruitment) are strong determinants of adult population size, but understanding these processes has been difficult due to model and data limitations. Recent advances in numerical modeling, together with new 3D data sets, provide a unique opportunity to study in detail biological-physical processes controlling zooplankton population size. We are using an existing state-of-the-art biological/physical numerical model (FVCOM) together with the recently-processed large 3D data set from the Georges Bank GLOBEC program to conduct idealized and realistic numerical experiments that explore the detailed mechanisms of how local dynamics and remote forcing control lower food web dynamics and dominant zooplankton species in the Georges Bank-Gulf of Maine region. Remote forcing being studied include low-salinity surface water intrusions from the Scotian Shelf (due Arctic ice melt) and NAO-dependent intrusions of deep Warm Slope Water versus Labrador Slope Water through the Northeast Channel into the GB-GoM region. The effects of this remote forcing together with realistic local forcing (from tides, winds, heat flux, local advection and mixing) on nutrient-phytoplankton-microzooplankton-detritus (NPZD) dynamics and population dynamics of dominant copepod species are being studied. Self-sustainability of each species population on the bank itself and in the Gulf of Maine is being examined by controlling immigration from source regions. This modeling study is providing new insights into the role of local and large-scale processes controlling zooplankton abundance in the ocean. The modeled copepods include small species that are the dominant prey for larval cod and haddock in this region, thus providing critical information for concurrent larval fish modeling studies. This detailed, process-oriented, regional-scale modeling with boundary forcing lays the groundwork for integration with models of the entire ocean basin. The resulting model provides a powerful new tool for understanding how local and large-scale forcing interact to control plankton production in the sea.

Accomplishments
Although the start date for this project is listed as 12/1/2005, funds were not received at WHOI until late July 2006, and work did not begin until this time. Over the past year, we have made considerable progress toward our goals. We know from the broadscale survey data (Fig. 1) that copepods abundance increased during the GLOBEC years (1995-1999), and that this increase was associated with an intrusion of low salinity water from the Scotian Shelf, the latter being identified from oxygen isotope analysis to originate from the Labrador Sea. The low salinity water had higher chlorophyll concentration (Fig. 1C). The higher copepod concentrations also were associate with higher growth rate and survival of larval cod and haddock (Fig. 1D-E). We believe that the low-salinity water may have been caused by a melting Arctic (Fig. 2), which releases fresher water through the Canadian archipelago that continues on through the Labrador Sea and Scotian Shelf to the GB-GoM region. We hypothesize that this low salinity surface water causes an early spring phytoplankton bloom, leading to early growth of copepods and better feeding environment for larval fish on Georges Bank. In addition, we hypothesize that the NAO induced intrusion of nutrient-poor deep Labrador Slope Water into the GB-GOM through the Northeast Channel will lead to reduced nutrients on Georges Bank and reduced productivity (Fig. 3). To test these hypotheses on remote forcing, together with other hypotheses on local forcings and population sustainability, we developed a biological-physical model (Fig. 4), and are using it in idealized and realistic forcing scenarios. We have completed a full 5-year run for the NPZD-FVCOM coupled model and can generate the seasonal evolution of 3D patterns in nutrients and phytoplankton that are consistent with the field data. We have used this model to conduct the first high-resolution N-budget for Georges Bank water column including scenarios of low-nutrient LSW intrusions (Ji et al., in press). We also examined satellite and field collected data to determine the effects of low-salinity intrusions from the Scotian Shelf on the timing of the spring phytoplankton bloom (Ji et al., accepted). We have completed development of a new “mean-age” copepod population model that is concentration-based and minimizes the effects of artificial numerical diffusion. This development is significant as it allows for the use of concentration-based population models in complex 3D models. We completed a model run for the copepod Pseudocalanus for the first GLOBEC field year, 1995 (Fig. 6). During the next phase of this project we will complete the model runs for Pseudocalanus for 1995-1999 and will model the other dominant copepod species (Calanus finmarchicus, Centropages typicus, Centropages hamatus).

Publications
Hu, Q., C. Davis, and C. Petrik. A simplified age-stage model for copepod population dynamics. Mar. Ecol. Prog. Ser. (accepted with revision)
Hu, C., and C. S. Davis. Normal versus Gamma: Stochastic model of copepod molting process. J. Plankton Res. (accepted with revision)
Ji, R., C. Davis, C. Chen, R. Beardsley. Influence of local and external processes on the annual nitrogen cycle and primary productivity on Georges Bank: A 3-D biological-physical modeling study. J. Mar. Systems (in press)
Ji, R, C. Davis, C. Chen, D W Townsend, D G Mountain, R C Beardsley. Influence of ocean freshening on shelf phytoplankton dynamics. Geophys. Res. Let. (accepted)
Ji, R., P. J. S. Franks. 2007. Vertical migration of dinoflagellates: model analysis of strategies, growth, and vertical distribution patterns. Mar. Ecol. Prog. Ser., 344, 49–61.

Summary of Interaction with NOAA
Davis has made several presentations on the progress of this project to NOAA personnel on the US GLOBEC Scientific Steering committee at their semiannual meetings (10/2006 and 5/2007). He also presented part of this work during an overview presentation for the Pan-Regional GLOBEC meeting in Boulder, CO, 11/27-30/2006 and to Drs. Steve Murawski and Elizabeth Turner (NOAA) following the CAMEO meeting in Falmouth, MA (June 2007). Davis presented a portion of this work to the ICES WGZE meeting in Riga, Latvia (March 2007) and to the IMBER modeling meeting in Cadiz, Spain (March, 2007). Davis and Ji also presented this work at the Zooplankton Symposium in Hiroshima, Japan (May-June 2007) and at the Gordon Conference on Coastal Ocean Modeling in New London, NH June 2007 Chen and Ji also made presentations on their subcomponents of the project to NOAA personnel at national meetings and at the SSC meetings.

Summary of Education and Outreach Activity
We have developed websites for the project for access by the educational (K-College) and public sectors:
http://www.whoi.edu/sbl/liteSite.do?litesiteid=5935
http://fvcom.smast.umassd.edu/research_projects/GB/index.html
Davis has made presentations on this project and GLOBEC NWA program in general to public audiences (e.g., business professionals at the Harvard Club breakfast, Dec 2006). Chen’s lab at UMASSD SMAST is linked to the SEA LAB Marine Science Education Center, a part of the New Bedford public school system. As our research progresses we will work with SEA LAB and the NSF-funded Center for Ocean Sciences Education Excellence– New England (COSEE-NE) staff to disseminate this material to the larger educational community.

Last updated: August 19, 2008