Vista desde la Isla San JoséThe biological station is located on San José island in the Muerciélago archipelago, located south of the Santa Elena Peninsula within the 43,000 ha Marine Protected Zone of the ACG. it includes various near shore islands and islets (uninhabited except for the ACG biological station and visitors), open ocean, rocky coasts, and beaches, including approximately 20 km of sea turtle nesting beaches. More specific surface habitats include coral reefs, rocky reefs, sandy bottoms, rock fields, deep water, algal beds and upwelling currents. 

Sector Marino is the only place so far where we have found two rare corals, Pocillopora inflata and Leptoseris scabra. The first was described as recently as in 2000 and its distribution in the eastern Pacific is quite restricted, Clipperton Atoll, Murcielagos, Isla Uva in Panama, and Galapagos. Its abundance at the mentioned sites is about 50 colonies. The other coral occurs only in Coco Island and the ACG Sector Marino. The presence of this coral in our waters is very important because it may have been a new arrival which was taken by the El Nino warm currents. Its scarcity and distribution make it an excellent subject for biogeographical studies.

Also Sector Marino contains the healthiest and largest of the Pocilopora reefs in Costa Rican waters. It shelters a large healthy population of “rolling stones” - hemispherical colonies detached from the bottom - of the coral Pavona varians. This coral occurs elsewhere in Costa Rica only at Cano Island (Parque Nacional Corcovado), where the population is very small.  Pocillopora inflata is intermingled with other coral colonies in the reef.

The Sector Marino is located on the margin of the Papagayo Upwelling, which makes it an extremely important site for comparative studies of corals and numerous other marine organisms.  It contains an exceptionally high diversity of octocorals.

The best Black coral population of the near shore sites of the Costa Rican coast are located at Sector Marino. Again, their scarcity and rareness at other sites of the coast, makes Sector Marino an extremely important place to protect. This coral takes decades to reach a size of 30 cm and at Sector Marino we have seen colonies of one and a half meters. We don't know how these colonies were missed by the commercial divers, but it is probably due to  the dangerous currents and unpredictable winds on the end of the Santa Elena Peninsula.

In 1997 a marine researcher  observed one specimen of the highly toxic and very colourful Alicia mirabilis anemone. He found another isolated specimen at Cahuita National Park in the Caribean The observation at Sector Marino is rather puzzling for A. mirabilis is regarded as a Caribbean anemone.

The most incredible groups of Gardineroseris found so far in Costa Rican waters are in Sector Marino.  There is a small patch reef built entirely by this coral, with colonies surpassing 1.20 m height and 0.8 m diameter. About 60 colonies are located in a small cove at Cocineras Island, near the Biology Station on Isla San José. Just two colonies of similar size are known from Panama. This Gardineroseris population is the most dense for this species in the entire eastern Pacific region, and the size of the colonies indicates individuals older than 50 years.

The few research projects that have been done in Sector Marino show the presence of many unique species as well as a large amount of fish, starfish, sea urchins, sea cucumbers, sharks, sponges, mollusks, turtles and many other organisms that were once commonly found throughout the Pacific coast of Central America, but have generally been severely depleted by many kinds of fishing.  Porpoises are common and whales occasionally pass through.

The marine scientists belive that Islas Murcielagos is a rare combination of island reef organisms and coastal ones. While the area merits many more underwater observational hours, all evidence points to a very important area of marine diversity for Costa Rica and the Eastern Pacific.
The region’s marine biodiversity is has long been harvested as traditional products (snapper mainly, sometimes crabs, octopus, lobster, and other species) by local fisherman and is showing decreases in sizes of individual animals and increases in effort required for the same catch (but the Sector Marino has largely escaped  this because of the dangerous currents and winds). Moreover, outside fishing interests (mainly shrimpers for Puntarenas, Costa Rica) are causing damage by passing through the outer edge of Sector Marino with small-mesh nets and dumping the abundant bycatch. Sport fishermen from south of the ACG have used the area, but are proving to be excludable by explaining that it is a national park. Conflicts between outside fishing interests and local fishermen are growing. The ACG has established good relations with local fishermen and has started a program of applied research and participation with them, so as to gradually wean them from the use of the Sector Marino for any fishing. However, these are complex social-economic-ecological problems and trends, and we estimate many more years before absolutely all fishing has been excluded.