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A Key tool for Saving our Oceans

Over the past 20 years, scientists have been assembling compelling data that show the world’s oceans are in deep trouble. Once-abundant species are disappearing, habitats are being destroyed, and fisheries are collapsing across the globe (Jackson et al. 2001, Lotze et al. 2006). For example, studies estimate that biomass of tunas and billfish have decreased...

Over the past 20 years, scientists have been assembling compelling data that show the world’s oceans are in deep trouble. Once-abundant species are disappearing, habitats are being destroyed, and fisheries are collapsing across the globe (Jackson et al. 2001, Lotze et al. 2006). For example, studies estimate that biomass of tunas and billfish have decreased by over 90 % lower than in preindustrial fishing levels (Myers & Worm 2003).

English: Menhaden fishing - menhaden in the hold of the mother vessel. These fish are used for fertilizer and pet food. Photo: Bob Williams. Wiki Commons


A growing number of studies are also showing that marine protected areas (MPAs) can safeguard habitats from destructive fishing, and well-located and strongly protected MPAs increase species diversity, abundance and average size in many species.  The benefits of MPAs include restoring the essential services that functioning marine ecosystems provide and improving fishing by enhancing fish populations outside MPAs (Norse 2010).

A dolphin swims in the azure waters of the Bahamas. Photo: Neil Hammerschlag

“In the short term, there are two kinds of benefits from protecting marine areas,” says Elliott Norse, Founder and Chief Scientist of the Marine Conservation Institute.  “First, within MPAs, the diversity of species, average size of many groups of organisms and total biomass generally increase.  Second, MPAs export eggs, larvae, young and adults of living things into surrounding areas.  But these effects are seen primarily in strongly protected areas, such as no-take marine reserves.  Less-protected areas show far fewer benefits, if any,” he added.

A recent report to the UN Meeting of Biodiversity in Hyderabad, India found that   roughly 2.3% of the ocean is designated as a Marine Protected Area (MPA)(Spalding et al. 2012). Moreover, the report suggested that at the current rate of MPA implementation, global coverage would reach about 10 % in 10 years.

The most recent rise in MPAs is largely attributed to the establishment or expansion of several colossal ones, including:

  • UK-controlled Chagos archipelago – 545 thousand sq km MPA
  • Australia – 2.7 mil sq km increase in Great Barrier Reef MPA
  • Cook Islands plan for a 1.1 million sq km MPA
  • New Caledonia plan – 1.4 million sq km MPA

These areas range from strongly protected to existing only on paper.  Paper parks are not MPAs.

Other analysts that filter out bad data (e.g., MPAs that are on land or in freshwaters) or don’t include MPAs that don’t meet even the weakest definition of “protected” have lower estimates of MPA coverage (e.g.  But overestimating MPA coverage is not the most important reason why people overestimate adequacy of the world’s MPAs.  A bigger reason is that many of the world’s MPAs do not actually protect against the greatest threat facing marine species: fishing! For example, many MPAs prevent oil and gas exploration, but do not prevent the removal of wildlife from the ocean. This issue is highlighted in a study by Mora et al. (2006) that examined the effectiveness of MPAs on coral reefs. They found that about 18.7 % of the world’s coral reefs fell within an MPA; but less than 0.1 % of the reefs were managed in a way that prevented fishing or poaching within MPA boundaries. Although these figures are outdated, the message is still clear – although MPA numbers and area are on the rise, the great majority of MPAs don’t prevent fishing or habitat damage caused by fishing. And that’s crucial because fishes (from the sharks, tunas and groupers at the top of the ecological pyramid to the small fishes near the bottom) are major drivers of marine ecosystem processes.  Remove them and you’ve started and uncontrolled experiment that quite probably will dangerously alter marine ecosystem services we humans need.

MPAs are the way we save fishes, which are the oceans’ version of seed corn.  MPAs allow us to save the life forms that will everything evolution has shaped them to do to keep the world’s oceans hospitable for humankind.

Marine reserves (= no-take marine reserves) are a type of MPA that prohibits all extractive activities, including fishing. Reserves significantly rebuild fish biomass in overfished areas. A great example is Cabo Pulmo National Park (CPNP) in the Gulf of California, Mexico. In 2011, Aburto-Oropeza and colleagues published a paper that compared fish biomass among no-take reserves, MPAs that permitted some fishing) and open access areas.  The study found that  four years after establishment of the reserve, there were no significant differences in fish biomass between the most-protected and least-protected areas. However, ten years after establishing the reserve, there was a 463% increase in total fish biomass at the CPNP reserve, including an 11-fold increase in the biomass of top predators! Moreover, fish biomass did not significantly change in other MPAs or open access areas. Not surprisingly, the study also found that the recovery of fish biomass inside CPNP generated significant economic benefits for the local community.

So what about creating a global system of strongly protected MPAs that saves marine life and improves fishing?   There are lots of models.  For example, a growing number of studies suggest that establishing a no-take marine reserve surrounded by an MPA buffer is a useful place-based management strategy.

For those interested in keeping tabs on MPAs, the world’s most comprehensive online map of MPAs was just released ( The new interactive mapping tool, called MPAtlas, allows users to see the global scope, scale and distributions.

Marine Protected Areas increase species diversity, abundance and average size in many species. Photo: Neil Hammerschlag

Reference Cited:

Aburto-Oropeza O, Erisman B, Galland GR, Mascareñas-Osorio I, Sala E, Exequiel Ezcurra. (2011) Large Recovery of Fish Biomass in a No-Take Marine Reserve. PLoS ONE 6(8): e23601. doi:10.1371/journal.pone.0023601

Jackson BC, Kirby MX, Berger WH, Bjorndal KA, Botsford LW et al. (2001). Science 293 (5530), 629-637.

Mora C, Andrèfouët S, Costello MJ, Kranenburg C, Rollo A, Veron J, Gaston KJ, Myers RA. (2006). Ecology. Coral reefs and the global network of Marine Protected Areas. Science 23; 312(5781):1750-1

Myers, R.A. and B. Worm (2003). Rapid worldwide depletion of predatory fish communities. Nature 423:280–283

Norse E. (2010) Ecosystem-based spatial planning and management of marine fisheries: why and how? Bulletin of Marine Science 86(2): 179–195

Spalding MD, Meliane I, Milam A, Fitzgerald C, Hale LZ.The Nature Conservancy – Policy Brief – October 2012 – Aichi Target 11 – Reshaping the global agenda for MPAs





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Meet the Author

Neil Hammerschlag
Research Associate Professor at the University of Miami, Rosenstiel School of Marine & Atmospheric Science Dedicated to advancing marine conservation through research, education and outreach Views my Own