Mexico's coast covers 5,800 miles and is impacted by the Pacific Ocean, Caribbean Sea and the Gulf of Mexico. Sea floor topography, the circulation of winds and oceanic currents are the underlying mechanism that generated the incredible diversity of marine life along Mexico's expansive coast.

The cold California current, which runs southwards along the coast, is deflected westwards by the rotational movement of the Earth. The deflected surface layers are replaced by an upwelling of deeper water which is transported from the nutrient-rich layers of the ocean floor, bringing fertility to the surface. Local currents produce similar upwelling phenomena in the Sea of Cortez. Thus, the cold oceanic currents are a product of the ocean's upwelling and are the major cause of the great productivity of the regional seas.

The southern region of Pacific Mexico abuts the Middle America Trench where the ocean floor drops off very close to shore. It is here that the continental shelf is narrow and steep, and extreme ocean depths are reached very near the coast. This area benefits from the northerly bend of the Equatorial Countercurrent as the flow pushes along the Central American coast and then west as it joins the North Equatorial Current.

Mexico's Gulf and Caribbean coast are a major western borders for the Atlantic Ocean systems. The Caribbean Current flows into the Yucatan Current which forms the Mexican and Loop Currents in the Gulf of Mexico. The Gulf Loop flows in through the straits of Yucatan and exits through the straits of Florida. At times it flows along a long loop to the North before turning south and eventually exiting through the straits of Florida. This elongated loop is unstable and pinches off large eddies that spin clockwise as they drift westward above the Campeche Bank. The eddies eventually spin down in the western Gulf. They sweep over the bottom and may have a great influence on the marine ecosystem.

TRAVEL ADVISORY:

Entry Requirements:
Passport/Visa: Photo identification and proof of citizenship are required for entry by all U.S. citizens. A passport is the best document. A visa is required only for stays exceeding 180 days.

Insects: All travelers should take measures to prevent both daytime and nighttime insect bites. Insect-bite prevention measures include a DEET-containing repellent applied to exposed skin, insecticide (permethrin) spray applied to clothing and gear, and use of a permthrin-treated bednet at night while sleeping.

Marine Hazards:

• Swimming related hazards include jellyfish, spiny sea urchins, and coral.
• Ciguatera poisoning is prevalent and can result from eating coral reef fish such as grouper, snapper, sea bass, jack, and barracuda. The ciguatoxin is not destroyed by cooking.
• Scuba Diving-Hyperbaric Chamber Referral: Divers' Alert Network (DAN) maintains an up-to-date list of all functioning hyperbaric chambers in North America and the Caribbean. DAN does not publish this list, since at any one time a given chamber may be non-functioning, or its operator(s) may be away or otherwise unavailable. Through Duke University, DAN operates a 24-hour emergency phone line for anyone (members and non-members) to call and ask for diving accident assistance. Dive medicine physicians at Duke University Medical Center carry beepers, so someone is always on call to answer questions and, if necessary, make referral to the closest functioning hyperbaric chamber. In a diving emergency, or for the location of the nearest decompression chamber, call 919-684-8111.

Onchocerciasis: This blackfly-transmitted disease is limited to areas along rivers between 600 and 1,500 meters elevation in Chiapas and Oaxaca States. Highest risk is from October through April. Travelers should take measures to prevent insect (blackfly) bites.

Seabather's Eruption: Reported in and near Cancun. This condition is caused by sea anemone larvae trapped under the bathing suit. Released toxin causes skin irritation, rash, and fever.