IOV - Distribución espacial y temporal del fitoplancton en el Golfo de Cariaco

Study Extent

The Gulf of Cariaco is located in the northeastern region of Venezuela, between 10° 36' 00" - 10° 26' 20" N and 64° 13' 40'' - 63° 38' 20" W (Caraballo, 1982a). Its general characteristics are described in Caraballo (1982a, 1982b). The Gulf is a water body that is influenced by the Northeast trade winds during the first part of the year and, is influenced by the Intertropical Convergence Zone (ITCZ) during the second half of the year (Quintero et al., 2004, López-Monroy and Troccoli- Ghinaglia, 2014). Considering its high productivity, this study proposes to evaluate the spatio-temporal variation in phytoplankton composition, abundance and, diversity in the Gulf of Cariaco.

Sampling

Samples were taken monthly at seven stations (georeferenced, using a Garmin GPS), on the surface and at 10 m depth using a Niskin bottle (5L) from February to july 2014

Method steps

1. Water transparency was measured in situ with a Secchi disc (m), and salinity (UPS) and temperature (ºC) were measured with a multiparameter probe (Jenway 970 DO2 Meter). Measurements of chlorophyll a (chlor. a) and phaeopigments was performed according to the Lorenzen method, described and improved by Parsons et al. (1984), whereas the determination of microalgal abundance was carried out according to the Utermöhl sedimentation method that is described by Edler and Elbrächter (2010). Phytoplankton species were identified according to the works of Cupp (1943), Tomas (1997), Berard- Thierrault et al. (1999) and Rivera-Tenenbaum (2006).
2. In addition, species diversity was calculated with the Shannon index (Krebbs, 1999). Wind speed data (average of the sampling day and the three previous days) were supplied by the meteorological station of the Antonio José de Sucre Airport, Cumaná, Sucre State. Oceanographic periods were established by modifying the periods proposed by Rivas-Rojas et al. (2007). Samples corresponding to the upwelling period (February-May) presented a temperature of ≤ 24 °C, nitrite + nitrate concentrations between 1 and 7.5 μmol L-1 and phosphate concentrations between 0.5 and 1.2 μmol L-1. Samples from the transition period (June- August) were characterized by temperature values in the range 24 < X ≤ 26 °C, nitrite + nitrate concentrations from 0.5 to 4 μmol L-1 and phosphate concentrations from ND to 0.8 μmol L-1. Finally, during the calm season (September-January) the temperature was ≥ 26 °C, approximate nitrite + nitrate concentrations varied between 0.5 - 1 μmol L-1 and phosphate concentrations ranged from 0.3 to 1 μmol L-1. The transition period corresponds to the secondary upwelling period that is described by Rueda-Roa et al. (2018).

Efforts were made to identify the phytoplankton to species, in some cases even genus were identified.

1. Cylindrotheca closterium
   rank: species
2. Nitzschia longissima
   rank: species
3. Dinophysis acuminata
   rank: species

The Gulf of Cariaco is located in the northeastern region of Venezuela, between 10° 36' 00" - 10° 26' 20" N and 64° 13' 40'' - 63° 38' 20" W (Caraballo, 1982a). Its general characteristics are described in Caraballo (1982a, 1982b).