“A land ethic,” the great naturalist writer Aldo Leopold observed toward the end of his famous Sand County Almanac, “reflects the existence of an ecological conscience, and this in turn reflects a conviction of individual responsibility for the health of land.” This philosophy of care for the earth’s ecosystems and species provides one of the core foundations of modern conservation and has catalyzed a movement that has helped to protect more than 14 percent of the world’s lands.

Today, our oceans are in need of a similar conservation ethic. Only 3 percent are protected on paper (with a far smaller area effectively conserved). The global community agreed in 2010 under the Convention on Biological Diversity’s Aichi Targets to set aside a full 10 percent of the earth’s oceans as “ecologically representative and well connected systems of protected areas” by 2020. While, recent efforts have secured greater protection for ocean areas adjacent to remote islands, still remaining is the challenge of effectively conserving our coastal waters, where the vast majority of marine biodiversity, productivity and threats are found.

One means of ocean protection that could address that challenge if scaled up systematically is the extension of coastal land parks out to sea. The political obstacles to successfully declaring a marine park can be considerable. By contrast, marine extensions in some cases fall within the management arrangement of an existing land-based park. In an era where there is great concern over “paper parks” – those that sit on the books but remain unenforced – many terrestrial parks already have enforcement staff, a regulatory framework and a management plan in place. Great cost savings can be found by taking advantage of these existing resources.

Though not all waters adjacent to existing terrestrial protected areas have a high conservation value, the potential to leverage existing conservation and park management infrastructure warrants deeper consideration. Moreover, inland activities are increasingly recognized as among the greatest threats to near-shore ecosystems. Already-protected terrestrial habitat can thus provide considerable ecological and environmental benefits to coastal marine conservation.

Tests of the impact of this approach have revealed something remarkable. A global GIS analysis of the World Database of Protected Areas found that extending existing land-based protected areas seawards to the limits of the territorial sea (12 nautical miles) would lead to a 50 percent expansion of marine protected area (MPA) coverage globally – 6 million square kilometers. Extending the areas across Exclusive Economic Zones could result in coverage that exceeds global MPA targets. In an encouraging sign, governments are increasingly demonstrating a willingness to use this approach for major advances in marine conservation.

In November, Gabon announced a significant expansion of its protected areas system into the sea, increasing its ocean protection from less than 1 percent to greater than 23 percent – an outstanding accomplishment. Critical to the plan was an expansion of the boundaries of near-shore protected zones such as Mayumba National Park. There, the world’s largest group of nesting leatherback sea turtles is threatened by trawlers at sea during the 10-day interval between laying eggs. By significantly expanding Mayumba and other coastal parks further into the sea, Gabon will protect this globally important sea turtle population and other marine wildlife.

Like many countries Gabon started first with terrestrial protected areas in a sweeping announcement of “Gabon Verde” in 2002 to protect some of Africa’s most intact rainforest from emerging challenges of poaching and logging. The recent announcement to protect its offshore waters was driven by a similar initiative, “Gabon Blue”, to sustainably manage its seas and protect them from illegal fishing. While the experience in Gabon has demonstrated the utility of this approach, it has also demonstrated that this is not a simple quick fix to the challenges of ocean conservation.

Proposing seawards extension to coastal parks on paper is easy, but not all extensions make ecological and conservation sense. Over a decade of scientific discovery and several years of systematic conservation planning and outreach have been required to build the case for these parks in Gabon. Just as we did in association with the creation of Gabon’s terrestrial parks, Wildlife Conservation Society (WCS) over the years has provided significant scientific rationale for park expansion into the sea, this time in collaboration with the Waitt Institute and National Geographic.

Gabon is the most recent example but not the only one. Argentina has for several years been expanding a number of its coastal protected parks for penguins, sea lions, and elephant seals to the limits of its territorial sea, contributing to significant fisheries and habitat protection in the process. And in California the Marine Life Protection Act has in some cases significantly expanded marine protections using the same approach, for example in Año Nuevo State Park, which protected land first in the 1950s, then leveraged that success to protect the adjacent sea nearly 50 years later in 2007.

A half-century is too long to wait to protect the worlds’ oceans. Due to a dramatic asymmetry in funding and political support, conservation of near-shore terrestrial habitat has far exceeded that for adjoining coastal areas. Our predecessors may have been correct in their day to halt conservation efforts at the high water mark for reasons of limited data, political expediency or – in some cases – the lack of a pressing threat. That restraint has now created an obligation of global proportion. The responsibility to seize this opportunity to protect our oceans and their marine life now lies with the rest of us.

The next time we sit in a protected public park gazing towards the sea we should ask (first ourselves, and then the relevant authority) if those waters are as ecologically secure as the land. If not, why not? And what can be done to extend our conservation effort? It’s time that we learn from Leopold and commit ourselves to expanding global ocean protection by half in a new interpretation of his thinking for an “ocean ethic” that recognizes the innate value of life and ecosystems in the waters that cover nearly three-quarters of our planet.