Although trophic cascades-the effect of apex predators on progressively lower trophic level species through top-down forcing-have been demonstrated in diverse ecosystems, the broader potential influences of trophic cascades on other species and ecosystem processes are not well studied. We used the overexploitation, recovery and subsequent collapse of sea otter (Enhydra lutris) populations in the Aleutian archipelago to explore if and how the abundance and diet of kelp forest fishes are influenced by a trophic cascade linking sea otters with sea urchins and fleshy macroalgae. We measured the abundance of sea urchins (biomass density), kelp (numerical density) and fish (Catch per unit effort) at four islands in the mid-1980s (when otters were abundant at two of the islands and rare at the two others) and in 2000 (after otters had become rare at all four islands). Our fish studies focused on rock greenling (Hexagrammos lagocephalus), the numerically dominant species in this region. In the mid-1980s, the two islands with high-density otter populations supported dense kelp forests, relatively few urchins, and abundant rock greenling whereas the opposite pattern (abundant urchins, sparse kelp forests, and relatively few rock greenling) occurred at islands where otters were rare. In the 2000, the abundances of urchins, kelp and greenling were grossly unchanged at islands where otters were initially rare but had shifted to the characteristic pattern of otter-free systems at islands where otters were initially abundant. Significant changes in greenling diet occurred between the mid-1980s and the 2000 although the reasons for these changes were difficult to assess because of strong island-specific effects. Whereas urchin-dominated communities supported more diverse fish assemblages than kelp-dominated communities, this was not a simple effect of the otter-induced trophic cascade because all islands supported more diverse fish assemblages in 2000 than in the mid-1980s.

It has been assumed that strategies for estuarine and marine conservation must be substantially different than those for terrestrial conservation because the seas are all publicly owned. This is an unfortunate misconception. We explored the leasing and ownership of submerged lands as tools for marine conservation and provide examples of the implementation of these tools from The Nature Conservancy's work in Texas, Washington, and New York (U.S.A.). We found that the leasing and ownership of submerged lands are viable new tools for marine conservation. There is a significant amount of submerged land available for lease and ownership in the United States and other countries that includes a diverse array of ecosystems (e.g., kelp forests, marshes, seagrass meadows, oyster reefs, tidal flats, clam beds, scallop beds, sponge, and coral reefs). From our review of policy and experience in practice, we have identified some key benefits and considerations for the use of these tools. Conservation benefits for the leasing and ownership of submerged lands include opportunities to restore ecologically and economically important species, protect diversity in sanctuaries, draw on substantial terrestrial experience in leasing and ownership, buy land cheaply, develop ecologically sustainable harvest practices, partner with fishers and local communities to improve water quality, create control areas for research, and partake in local management forums as a direct stakeholder. Bivalve shellfish are particularly amenable to conservation with these tools because existing policy is well established for leasing and ownership rights to sessile animals that exist on the sea floor. Conservation buyers need to consider that community sentiment does not always favor private rights to submerged lands, conservation interest in submerged lands could affect prices, association with incompatible aquaculture practices will be detrimental, enforcement of restrictions can be difficult, and there may be concerns about setting the precedent of paying for conservation of submerged lands. Policy makers should be encouraged to include more opportunities for conservation and not just exploitation of natural resources on submerged land leases. Nuevas Herramientas para la Conservación Marina: El Arrendamiento y Propiedad de Tierras Sumergidas Resumen: Se ha asumido que las estrategias para la conservación estuarina y marina deben ser sustancialmente diferentes de las de conservación terrestre porque los océanos son propiedad pública. Está es una imprecisión desafortunada. Exploramos el arrendamiento y propiedad de tierras sumergidas como herramientas para la conservación marina y proporcionamos ejemplos de la aplicación de estas herramientas a partir del trabajo de The Nature Conservancy en Texas, Washington y New Cork (E. U. A.). Encontramos que el arrendamiento y la propiedad son nuevas herramientas viables para la conservación marina. En Estados Unidos y otros países hay una cantidad significativa de tierras sumergidas disponibles para el arrendamient...