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A great global ribbon, representing the land-to-sea continuum, is an emerging frontier in conservation biology. Some 60% of humanity dwells in the coastal zone, the setting for the richest and most complex system for life on Earth and the place where most human cultural interaction with the sea occurs. This is where the unreconciled solitudes of terrestrial and marine conservation present at once both critical challenges and sterling opportunities. What a fertile area for conservation biology this could be, yet conservation biology and management continue to ignore this ecological reality by separating land and sea into different arenas.

The concept of a “coastal zone,” developed in the 1970s, spoke of a heterogeneous portion of Earth, where land, sea, and atmosphere interact with great intensity through exchanges of energy and materials, which underscores connectivities that influence biotic distributions and interactions. This zone may be considered either transitional or a system in its own right, by virtue of its linking terrestrial and marine habitats via watersheds and estuaries. In either case this zone deserves recognition as a complex, interactive realm, a term that celebrates its high biogeographic rank. For example, almost half of all fishes and marine mammals live primarily in this realm and depend on land–sea interactions for support. From an ecosystem perspective, although the coastal realm occupies only 18% of Earth's surface (both land and sea), 8% of ocean surface, and 0.5% of ocean volume, it provides about 50% of global denitrification, 80% of global organic matter burial, 90% of sedimentary mineralization, 75–90% of the global sink of suspended river load and associated elements and pollutants, in excess of 50% of global carbonate deposition, about a quarter of global primary production, about 14% of global ocean production, and more than 90% of the global fish catch.

The land–sea interface is an area of great uncertainty in conservation, which is characterized by piecemeal responses to known threats due to many ecological and jurisdictional boundaries and intense political intervention that often overwhelms science-based management approaches. Humanity has fragmented coastal zone management among local, state, national, and international needs and responsibilities. Critical challenges for coastal conservation are, first, that coastal resources have been exploited by humanity for millennia, altering the distribution and abundance of many organisms. Human exploitation and physical alteration have sharply reduced the productivity of many coastal systems, such as estuaries, deltas, coral and oyster reefs, and mangroves. Exacerbating this is the crush of coastal humanity and the reality that much future human population growth will occur there—particularly in developing countries. The greatest challenge may be the rate and magnitude of climate change, the most intense effects of which are already being felt along coasts. These include community and habitat transformations and sea level rise, with a host of cascading effects. For example, rapid environmental change provides opportunities for introduced species to flourish, which in coastal systems are almost impossible to control. In addition, burgeoning human populations along coasts are at risk—witness Hurricane Katrina.

How can conservation biologists help meet these challenges? Foremost, we must become more ecosystem-oriented and focused toward promoting management policies that better link watersheds to coastal seas and oceans. This requires a new approach to conservation planning and ecological connections, including a shift from protection and preservation of species and individual habitats to ecosystem restoration of depleted large-scale coastal systems. One example of thinking connectedly is offered by the United States Ocean Action Plan of 2004: “Approaching the management of our ocean, coastal, and Great Lakes resources from a watershed perspective allows impacts from both coastal and upland activities to be taken into account, providing a more comprehensive basis from which to protect, restore, and conserve the Nation's waters” (http://www.oceans.ceq.gov; accessed January 2007).

Conservation biologists also must become increasingly interdisciplinary to address transboundary marine, terrestrial, and freshwater realms. The concept of a connectedness that includes watersheds in coastal marine conservation is matched by ideas of whole-catchment management that extends into seascapes. What use, then, is it to designate conservation zones in coastal oceans unless the contiguous lands and watersheds are also a functional part of the area?

This emphasis on connectedness is no less pertinent for place-based coastal-zone conservation, wherein we need to better understand interactions between land and sea so that integrated approaches that straddle ecological realms at multiple scales can be developed. A small-scale conservation focus is concerned with areas between marine and terrestrial systems that might otherwise be ignored, such as the intertidal zone. A mesoscale focus is on critical transition zones, for example, within estuaries and coastal wetlands. Yet another focus emphasizes connectedness that can extend to all scales from local to global. We must also recognize that applying terrestrial research and planning methods to coastal conservation can be an awkward fit. Perhaps the greatest difference between marine and terrestrial ecosystems is the relatively open movements of nutrients, materials, and species' propagules in the sea.

A few examples will serve to illustrate scales of connectedness that must be incorporated into coastal-realm conservation. Various Pacific salmon (Oncorhynchus spp.) play a totemic role throughout the temperate North Pacific and for many people resonate as bellwethers for coastal ecosystem health. A key feature of salmon in the ecological integrity of coastal ecosystems is their return as adults from the sea to their natal freshwater streams to terminally spawn, which provides relatively stable, cyclical nutrient inputs for riparian forest ecosystems, and the foundation of salmonid genetic diversity. Transferred marine nutrients from spawning salmon cast into riparian areas is a key characteristic of temperate North Pacific coastal forests and is becoming the leading topic in fish–forestry interactions and management.

Salmon and the riparian habitat they affect are central to the forthcoming mountaintop-to-sea-bottom conservation envisioned for an integrated terrestrial and marine protected area (Gwaii Haanas) in the Queen Charlotte Islands, British Columbia. Conservation will span alpine to deep-sea ecosystems in which the extent of the combined area of 5000 km2 includes 3400 km2 of proposed marine area. The breadth and completeness of the watershed coverage draining into the ocean will be globally unique for a temperate coastal rainforest protected area. In anticipation of seamless data management for Gwaii Haanas, a coastal-base mapping convention will be needed because mapped coastal features are represented differently on terrestrial topographic maps and marine hydrographic charts. This fundamental coastal mapping discontinuity is an example of problems that arise from different human technical (e.g., mapping) and administrative (e.g., jurisdictional) cultures across the land-sea continuum. These problems can be solved by embracing a systems approach.

Another coastal connectivity example involves management of coral reefs, which are shallow-water phenomena and as such are particularly vulnerable to climate change. They are intimately connected functionally to sea grass, mangrove, and other adjacent ecosystems, and are almost always near the shore, even in open-ocean regions (e.g., Fiji, Hawaiian Islands). Thus, managing land runoff is a key consideration in reef conservation. Furthermore, because of the large scale of whole seas, the need for a systems approach has long been obvious. The Black, North, Bering, and Mediterranean seas illustrate the futility of small-scale measures restricted to individual species and biotopes.

But it is not enough for conservation biologists to do good transboundary science and then hand their findings over to decision makers. We need no further incentives to do good science, but the conservation implementation framework requires concrete attention and revision. If we want our work to connect with actual coastal-zone conservation, we must engage in transdisciplinary collaboration with our colleagues from the social sciences, within research and planning frameworks designed to foster conservation. To be effective, our coastal-realm projects must unfold strategically from conservation science and in a way that recognizes local and regional mechanisms for conservation management.

Implementing coastal-realm conservation requires conservation biologists not only to “think system,” but to collaborate with social scientists. Social scientists can articulate the strong cultural links with the sea among aboriginal and nonaboriginal people—an essential facet of effective conservation. They can examine critical questions about who is responsible, who benefits, and who pays for conservation. They can help reveal the power structure of decision making and aid coordinated conservation management across terrestrial and marine authorities and from international to local levels of citizen initiative. They also can advise us if decision makers at all levels understand our science and help us communicate more effectively. As conservation biologists, we need to step outside our comfort zones to communicate with the public and policy makers in our study areas in terms they will understand, making it perfectly clear that the beautiful, rich, priceless coastal realm must be protected now and holistically.

But the first step is to get our ecology and biogeography right. With respect to the Society for Conservation Biology, is it realistic, or just tradition, to pursue terrestrial and marine initiatives independently by creating separate sections? If not, then what “connectedness” do we see for ourselves?