No abstract

Physical and biological data were gathered over the Campeche Canyon area, Gulf of Mexico, in summer 1999. These include hydrographical and meteorological parameters, and oxygen content, as well as, at some oceanographic stations, suspended particulate matter (SPM), chlorophyll‐a, and in vivo natural fluorescence profiles. Dry air from the east set up a latent heat flux that ranged from 50 to 300 Wm−2. The wind mixed layer (ML) was isothermal and averaged 40 m thick, but with a noticeable increase of oxygen supersaturation toward the northwest. Temperature and dynamic height structure reveal an anticyclone‐cyclone eddy pair. At the southeastern part of the study area a noticeable thermal gradient was observed toward the shelf break of the Campeche Bank, which corresponded to a tilting up (doming) of low oxygen saturation midwater to near the base of the ML. This doming of isotherms along the margin of the Campeche escarpment is likely an upper‐ocean response to the sharp gradient in water depth between the canyon and outer continental shelf. It is suggested that the doming of midwater on to the Campeche escarpment and at the head of the Canyon, as denoted by locally low values of oxygen saturation, plays an important role in the biological patterns. Throughout the field area, the values of total SPM were higher than reported previously for subtropical open ocean environments. The impact of autotrophic‐heterotrophic biogeochemical processes on chlorophyll was reflected in the local deepening of the deep of chlorophyll maximum (DCM) and the depth of the euphotic zone within the anticyclonic eddy.

Eddies and fronts created by geostrophic balance between counter-rotating currents are hydrodynamic processes that concentrate or dilute plankton and suspended material by physical processes of accumulation, retention, or dispersion. Over Campeche Canyon, in the southern Gulf of Mexico, observations revealed an anticyclonic eddy, a cyclonic current off the continental shelf, and an associated thermal front in their common boundary. Along this front there was high Trichodesmium spp. occurrence. Three water masses were found in the upper 120 m layer: Caribbean Tropical Surface Water (CTSW), Caribbean Subtropical Underwater (CSUW), and Gulf Common Water (GCW). The frontal zone between the warm core and cyclonic circulation was observed below the hot summertime mixed layer. The presence of Trichodesmium spp. was associated with the front, indicating its influence on the distribution of this diazotrophic cyanobacterium that enters the Campeche Canyon region via modified CTSW. The associated phytoplankton was dominated by tropical oceanic species of diatoms and dinoflagellates, especially species of Ceratium.

Studies on metabolic balance in hermatypic corals have been unable to separate the analysis of animal’s respiration from that of plant. The objective of this research was to determine the metabolic balance in the mutualistic symbiosis polyp-algae through incubations in respirometric chambers of twelve fragments of coral. The species studied Porites panamensis (Scleractinia: Poritidae), Verrill, 1866 was collected near La Paz, Baja California Sur, México. Experiments were performed during fall 2009 and winter 2010. Water temperature, salinity, dissolved oxygen, pH, irradiance and photosynthetic pigments were measured every two hours during the incubation times. The concentration of pigments was determined through spectrophotometry. The maximum primary production was at 12:00 h, with 3.80 mg O2∙l-1∙h-1 for fall and 4.92 mg O2∙l-1∙h-1 for winter. According to the P : R (Production : Respiration) ratio of 1.90 for fall and 2.07 for winter, the mutualistic symbiosis in P. panamensis showed a predominantly autotrophic behavior. The relative quotients of chlorophyll concentrations (mg∙polyp-1), Chl a : Chl c2, were 1.0 : 0.69 for fall and 1.0 : 1.22 for winter; while ratio of concentrations chlorophyll a : carotenes , Chl a : carotenes (both in mg∙polyp-1), were 1.0 : 2.13 for fall and 1.0 : 1.88 for winter. The high relative concentrations of Chl c2 and carotenes with respect to Chl a is explained as an adaptive response to high irradiance. Balance metabólico en la simbiosis mutualista pólipo-alga en el coral hermatípico Porites panamensis en La Paz, Baja California Sur, México Estudios del balance metabólico en corales hermatípicos han sido incapaces de separar el análisis de la respiración animal y vegetal. El objetivo en este trabajo fue determinar el balance metabólico en la simbiosis mutualista alga-pólipo a través de incubaciones en cámaras respirométricas en doce fragmentos de coral. Los experimentos se realizaron en otoño del 2009 e invierno del 2010. La especie estudiada fue Porites panamensis (Scleractinia: Poritidae), Verrill, 1866, recolectada en La Paz, Baja California Sur, México. La temperatura del agua, salinidad, oxígeno disuelto, pH, irradiación y pigmentos fotosintéticos fueron registrados cada dos horas durante los tiempos de incubación. Los pigmentos fotosintéticos se determinaron mediante espectrofotometría. La producción primaria máxima fue a las 12:00 h, con 3.80 mg O2∙l-1∙h-1 para otoño y 4.92 O2∙l-1∙h-1 para invierno. De acuerdo con el cociente P : R (Producción : Respiración) con valor de 1.90 para el otoño, y 2.07 para el invierno, la simbiosis mutualista en P. panamensis muestra un comportamiento predominantemente autótrofo. Los cocientes relativos de concentración de clorofilas (mg ∙polyp-1), Cl a : Cl c2, fueron 1.0 : 0.69 para otoño y 1.0 : 1.22 para invierno, mientras que la relación de clorofila a : carotenos, Cl a : carotenos (ambos en mg∙polyp-1), fueron de 1.0 : 2.13 para otoño y 1.0 : 1.88 para invierno. Las altas concentraciones relativas de Cl c2 y carotenos con respecto a Cl a se explican como una respuesta adaptativa a una mayor irradiancia.