What Does The Science Say?

Scientist measuring

Marine Protected Areas can be a smart investment to recover and maintain marine resources that provide benefits for people, today and in the future.

Scientific research shows that MPAs consistently produce ecological, economic, and social benefits when they include fully protected areas and are well-designed and well-managed. These benefits are realized in and around MPAs all over the world.

Marine protected areas (MPAs) are places in the sea designed to protect marine species and ecoystems, while sometimes allowing for sustainable uses of marine resources within their boundaries. We define 2 primary levels of protection - 1) partially protected, where some uses are prohibited but some extractive activities are allowed and regulated, and 2) fully protected, where all extractive and destructive activities are forbidden, except as need for scientific monitoring. Fully protected areas are also called no-take areas.


One key goal of MPAs is to protect the abundance and diversity of marine life. Scientists have studied more than 150 fully protected MPAs around the world and monitored biological changes inside their borders. A global review (see graph at right) revealed that marine fishes, invertebrates, and seaweeds show significant average increases in biomass, density, size, and diversity inside fully protected areas compared to unprotected areas.

  1. Biomass, or the total weight of animals and plants, increased an average of 446%.
  2. Density, or the number of plants or animals in a given area, increased an average of 166%.
  3. Body size of animals increased an average of 28%.
  4. Species diversity, or the number of species, increased an average of 21%.

Global graph with picture

MPAs can help restore the natural range of individual ages and sizes of many species, and they can boost the recovery of top predators and heavily fished species (i.e. groupers). These changes can make these ecosystems more resilient to environmental changes and bring tangible fishery, biodiversity, and tourism benefits.


MPA uses and shrimp photo

Scientific research can also guide the design of MPAs to balance trade-offs between protecting habitats and species, supporting local economies, and preserving social wellbeing. Effective MPAs can sustain fisheries, improve local livelihoods, and promote sustainable tourism. For example, the Medes Islands MPA in Spain, with a fully protected area less than 1 km2, generates revenues of about 10 million euros annually. Almost 85% of these economic benefits are generated by SCUBA diving and glass-bottom boats (see pie chart at left). The recovery of marine life, especially large fishes, attracts thousands of tourists every year from all over the world. In some well-designed MPAs the income generated can be 2-3 times greater than the management costs. The involvement of stakeholders and communities is key to the success of MPAs. Their engagement increases compliance, improves decision-making, reduces management efforts and costs, and ensures MPAs deliver benefits.