Gulf of Nicoya

• Category: Marine and Oceanic Biomes.
• Geographic Location: Central America.
• Summary: Costa Rica’s largest gulf supports diverse habitats and the country’s fishing industry, both of which are threatened by pollution and overfishing.

The Gulf of Nicoya represents an ecologically and economically invaluable asset of Costa Rica. Located on the Pacific coast of the country on the Nicoya Peninsula, it contains a remarkably diverse collection of landscapes, habitats, and organisms. It is vital to the fishing industry and is a popular destination for national and international tourists. Development, overfishing, and pollution threaten the wealth of resources offered by the Gulf of Nicoya.

The funnel-shaped gulf lies within the curve created by the Nicoya Peninsula and the western shore of Costa Rica. The geological history of this gulf lends to its unique shape and varied landscapes. Once a hilly terrain, it plunged below sea level thousands of years ago due to volcanic activity along a fault line. Only the hilltops remain above water and form small islands located throughout the gulf. At 50 miles (80 kilometers) in length and 31 miles (50 kilometers) across at its widest point, Nicoya is Costa Rica’s largest gulf. At the gulf’s narrowest point, a ferry serves as the primary form of transportation between the mainland port city of Puntarenas and the southern part of the Nicoya Peninsula.

The Nicoya Peninsula has two seasons: dry, which runs from the end of November until May, and the rainy season, which is September to November. The intervening months between the two seasons, known as “little summer,” experience periods of rain and showers. During the rainy season, the peninsula turns into a rainforest. Temperatures during this period—considered winter—may sometimes drop to 63 degrees F (17 degrees C). During the summer dry season, the temperature may reach 100 degrees F (38 degrees C). Rainfall during the rainy season exceeds 10 inches (250 millimeters) per month.

The Tempisque River drains fresh water into the northern, or upper, part of the gulf, creating a rich estuarine habitat. Organic material carried in by the river builds up on the floor of the relatively shallow upper gulf, which is 13–39 feet (4–12 meters) deep.

The lower section of the gulf has much deeper water than the upper regions, roughly 98–591 feet (30–180 meters) in depth, and lacks the other estuarine characteristics. However, this part of the gulf has two rivers, the Río Grande de Tárcoles and the Barranca, emptying into it. Rocky shores and steep bluffs border the gulf and connect the sparsely populated land with the water. Small fishing villages dot the shorelines. The deepwater here is rich with fish species, but supports relatively few mollusks or shrimp.

Biodiversity

Gulf waters have a high nutrient content, allowing algae to bloom profusely, which supports many fish and mollusks. Zooplankton supports large schools of sardines and anchovies, which then feed the larger fish. Present are sharks, dolphins, turtles, manta rays, tuna, snappers, groupers, dorado, roosterfish, jacks, trevallys, sea bass, mackerel, catfish, porgy, bonito, and sailfish. Between August and December, humpback whales visit the gulf.

The upper Nicoya gulf contains the gulf’s largest island, Islá Chira. Wading birds such as roseate spoonbills (Platalea ajaja) and herons (Ciconiiformes spp.) feed and nest on Chira, which also attracts tourists and bird watchers to its banks. Other birds of Nicoya include grooved-billed ani (Crotophaga sulcirostris), scissor-tailed flycatcher (Tyrannus forficatus), hummingbird (Trochilidae spp.), brown pelican (Pelecanus occidentalis), magnificent frigatebird (Fregata magnificens), fiery-billed and collared aracari (Pteroglossus frantzii and P. torquatus), and bananaquit (Coereba flaveola).

This estuary also serves as prime habitat for mangrove trees. Their roots grow down into the water, creating a web of underwater structures that protects many species of fish, shellfish, shrimp, and other marine life. The biodiversity found in the mangroves is protected by the Costa Rican government. There are seven species of mangrove trees in Costa Rica including red mangroves (Rhizophora mangle and R. harrisonii, Rhizophoraceae), black mangroves (Avicennia germinans and A. bicolor, Verbenaceae), tea mangrove (Pelliciera rhizophorae, Theaceae), white mangrove (Laguncularia racemosa, Combretaceae), and the buttonwood mangrove (Conocarpus erectus, Combretaceae).

The gulf features many mammal, reptile, amphibian, and insect species. Monkeys are some of the most visible inhabitants of the rainforests surrounding the gulf, including white-faced or capuchin (Cebus capucinus), squirrel (Saimiri), howler (Alouatta monotypic), and spider monkeys (Ateles). Other local animals include mantled howler monkey (Alouatta palliata), fishing bulldog bat (Noctilio leporinus), black ctenosaur (Ctenosaura similis), house gecko (Hemidactylus frenatus), paca (Agouti paca), and milk frog (Phrynohyas venulosa).

Environmental Threats

There are many threats to the gulf, including overfishing, industrial runoff, red tide, conversion of mangroves for energy uses, threats from overgrazing and cattle ranching, and climate change. Overfishing has caused the Costa Rican government to implement periodic mandatory fishing bans, although with limited success.

The Nicoya has been compromised by runoff from industry, agriculture, and urban areas. In fact, the most polluted river in Costa Rica, the Río Grande de Tárcoles, empties water and toxins into the gulf. Although habitat destruction such as the removal of mangrove forests was once popular, many of the gulf’s most important habitats are now under government protection. Boat traffic and development continue to take a toll on the marine life within the gulf and tidal zones.

Red tides—single-cell organisms called dinoflagellates—bloom in the early rainy-season months of April and May. Dinoflagellates use the sun to photosynthesize and grow, and can secrete toxins absorbed by shellfish such as mussels and oysters that can have deadly effects on humans who consume them. While this is not often the case, there have been isolated deaths. Red tide is naturally occurring but can be exacerbated by pollution, fed by agricultural runoff and raw sewage that provide the nutrients for the algae to grow.

The mangrove forests are being destroyed to convert their areas to fish pens, rice paddies, salt-drying ponds, cattle pastures, tourist developments, and human settlements. Mangrove wood makes good fuel and charcoal, and red mangrove is an important source of tannin, used in processing leather. Stripping the bark to get the tannin kills the tree. In 2021, Costa Rica pledged to protect and restore coastal wetlands including mangrove forests.

Climate change is likely to aggravate these human-induced disruptions of the waters here, forcing changes to the natural habitats on which the terrestrial and marine species depend.

Bibliography

Almeyda, Angelica M., et al. “Ecotourism Impacts in the Nicoya Peninsula, Costa Rica.” International Journal of Tourism Research 12, no. 6 (2010).

Baez, Stacy. "Costa Rica Ensures Future for Its Mangrove Forests." Pew Charitable Trusts, 26 July 2021, www.pewtrusts.org/en/research-and-analysis/articles/2021/07/26/costa-rica-ensures-future-for-its-mangrove-forests. Accessed 18 Nov. 2024.

Fosmo, Joaquín Swett, and Patricia Slump-Mulder. “The Nicoya Peninsula Faces a Dire Threat as Deforestation Escalates.” Karen Mogensen Reserve, 15 Sep. 2023, www.karenmogensenreserve.org/blog/deforestation-crisis. Accessed 18 Nov. 2024.

Voorhis, Arthur D. “The Estuarine Character of the Gulf of Nicoya, an Embayment on the Pacific Coast of Central America.” Hydrobiologia 99, no. 3 (1983).

Whelan, Tensie. “Environmental Contamination in the Gulf of Nicoya, Costa Rica.” Ambio 18, no. 5 (1989).