Spatial and Seasonal Patterns of Salinity in a Large and Shallow Tropical Estuary of the Western Caribbean Laura Carrillo & Emilio Palacios-Hernández & Mario Yescas & Ana María Ramírez-Manguilar Received: 22 August 2008 / Revised: 26 June 2009 / Accepted: 30 June 2009 / Published online: 21 July 2009 # Coastal and Estuarine Research Federation 2009 Abstract Salinity profiles and meteorological data were analyzed during February, May, and September 2006 in Chetumal Bay, a large, shallow estuary of the Western Caribbean. Local meteorological conditions revealed three seasons: (1) a dry season (March–May); (2) a wet season (June–October); and (3) the nortes season, with northerly wind events (October–February). During the nortes and wet seasons, salinity ranged between 13 and 16 psu, and salinity was highest in the dry season, ranging between 18 and 22 psu over most of the area; a strong stratification and a significant contribution of salty water characterized this season. Strong horizontal gradients were observed near Rio Hondo during the three seasons. Deep and narrow peculiar bathymetric features called the pozas showed a strong stratification and a relatively high salinity. The northern part of Chetumal Bay and probably the entire system are far from being homogeneous. Keywords Tropical estuary . Seasonality . Western Caribbean . Mesoamerican reef system . Chetumal Bay . Caribbean . Belize . Chetumal Introduction Chetumal Bay is a large and shallow tropical estuary of the Western Caribbean coast that is part of the Mesoamerican reef system. This estuarine system is shared between Mexico and Belize; it has an area of approximately 2,560 km 2 . The northern part of Chetumal Bay (Fig. 1) is a shallow basin with depths ranging between 2 and 5 m. It has several fresh water inputs such as the inflow of Rio Hondo, a flooded geological fracture, small creeks, and underground springs; it is connected to several adjacent lagoon systems such as Guerrero Lagoon. The bay supports one of the largest populations of manatees of the Caribbean, about 150 individuals of the endangered species of West Indian manatee (Trichechus manatus; Morales-Vela et al. 2000; Morales-Vela, personal communication). In addition, marine protected areas sur- round this bay. However, several water quality studies in the northern area of the bay indicate severe pollution problems mainly near the margin of the Rio Hondo and close to the coast of Chetumal City where there is an important urban population growth (Alvarez-Legorreta 2002; Alvarez-Legorreta 2008; Ortiz-Hernández and Sáenz-Morales 1997; Zapata-Pérez et al. 2000). Further- more, Chetumal Bay is subject to both extensive use and protection policies. Recently, there has been an increased interest in developing tourism infrastructure along the coastal zone. Despite the importance of this estuary, the local salinity fields remain unstudied. Indeed, relevant questions about its seasonality as a response to atmospheric forcing and precipitation are still unanswered. Hitherto, strong salinity horizontal gradients have been observed near the Rio Hondo (Herrera-Silveira et al. 2002; Morales-Vela et al. 1996); however, a detailed description of the salinity fields during different seasonal atmospheric forcing and L. Carrillo (*) : M. Yescas : A. M. Ramírez-Manguilar Depto. Ecología y Sistemática Acuática, El Colegio de la Frontera Sur, Av. Centenario km. 5.5, Col. Pacto Obrero, 77014 Chetumal, Quintana Roo, Mexico e-mail: lcarrillo@ecosur.mx E. Palacios-Hernández Depto. de Física, Universidad de Guadalajara, Revolución 1500, Col. Olímpica, Sector Reforma, 44840 Guadalajara, Jalisco, Mexico Estuaries and Coasts (2009) 32:906–916 DOI 10.1007/s12237-009-9196-2