Physical and Biological Determinants of Population Connectivity: Are Perceived Temperate-Tropical Differences Real?

The proposed working group, co-chaired by RR Warner and JM Leis, will address the perceived vs. real differences in connectivity of marine metapopulations through larval dispersal in temperate and tropical environments. Space-based management of coastal oceans, including no-take marine reserves, is being developed worldwide. Proper design of marine reserve networks depends on knowing the extent to which the changes inside a protected community are reflected in the connections to other communities (e.g., supplying larvae to fished areas, or connecting to other reserves in a network). There are few differences between temperate vs. tropical areas in the positive response within reserves to protection, but at this point we do not know if there are fundamental differences in connectivity associated with different coastal environments. Managers and designers are unsure if lessons learned about connectivity in one realm are applicable to another. The working group will establish the critical determinants of geographical variation in connectivity, with an aim of providing clear guidelines for spatial design and management. There are a number of reasons to expect that the scale and processes of connectivity might differ geographically; some arise from contrasts in species composition and community structure, some from temperature influences on physiology and development, and others from differences in physical processes. We will explore these perceived differences to determine which are real, which may be due to the different perceptions, perspectives, and research agendas of those working in the different environments, and which require further research. The working group will bring together scientists with expertise in marine community ecology, conservation genetics, larval biology, physical oceanography, and fisheries to consider the critical factors affecting geographical variation in connectivity. Many of the factors that may affect the scale and processes of connectivity on a geographical basis are also projected to be themselves affected by global environmental change. Therefore, we will use the findings of this working group to explore how connectivity might change over time in any particular geographical area due to climate change. In addition to a major synthetic review, the working group will produce a practical guide to the factors that might affect connectivity in marine systems, with special attention paid to how these factors might vary on a geographic basis or over decades of environmental change. The second meeting of the group will integrate our findings into marine spatial planning criteria, with explicit acknowledgement that a single-minded approach is simply inappropriate for places as complex as the coastal ocean. Background and Rationale Marine spatial planning generates opposition from some stakeholders whose objections usually focus on the science behind marine reserve planning. Even when the science is sound, some claim that evidence gathered from one geographic area (say, temperate coastal waters) is not applicable to geographically distinct areas (such as coral reefs). The extent to which these are valid objections is unclear. For example, it has been suggested that the responses of organisms to protection in reserves may differ between temperate and tropical areas (Laurel and Bradbury, 2006). In contrast, Lester et al. (2009) demonstrated that temperate and tropical communities responded similarly to protection. Most marine organisms have a pelagic propagule stage that poses a further challenge to spatial planning. Although the positive demographic responses of marine organisms to protection inside reserves are clear, we know much less about the fate of the increased SCOR Working Group Proposal: Temp-Trop Connectivity 2 reproduction that occurs inside of reserves. This question is critical, because it addresses both the service function of reserves (e.g., export of larvae to fished areas) and the design of reserves (e.g., networks connected through larval exchange; Warner and Cowen, 2002; Sale et al., 2005). Evidence is accumulating about the extent of larval export from reserves (Pelc et al., 2010), and the degree to which larvae may be able to influence their settlement location (Leis, 2007, 2010). However, at this point we have little ability to respond to the suggestion that connectivity between marine populations might vary geographically (e.g., as a function of temperature or underlying demography; Laurel and Bradbury, 2006; O‟Connor et al., 2006). As estimates of connectivity and dispersal are important criteria in marine spatial planning (Botsford et al., 2003; Roberts et al., 2003), this limits the confidence of designers and managers to apply general criteria to local problems. This working group will examine and evaluate the potential importance of geographically varying physical and biological factors in affecting dispersal and connectivity in coastal marine environments, and will produce clear guidelines for the practical application of our findings. A recent symposium convened by Leis and Warner on this theme (Larval Fish Conference, 2009) confirmed this is a problem of general interest, particularly to managers. A SCOR working group is the ideal vehicle to complete this process. Connectivity demands a multi-disciplinary approach, and because we seek to examine regional differences, and must involve workers from different perspectives and with different goals, a SCOR working group is the best way to go. Workers and funding agencies have tended to focus on their own discipline or region, often both, but the question demands a broader, more integrated approach. We have identified scientists whose depth of knowledge and strong interactive ability make them ideal participants in an SCOR working group setting. Two advantages accrue from developing a working group out of a symposium: 1st, many of the data required to address the problem have already been organized, allowing us to work efficiently; 2nd, we are much more aware of critical information gaps. On the biological side, information on connectivity comes from studies in genetics, tagging, otoliths, larval biology, oceanographic sampling, and physiology (Leis et al 2011). Data are rather sparse and the methods used vary from study to study. On the physical side, data from drifters, oceanographic models, and direct or remote measurements are more standardized, but the datasets can be enormous.