IMIS - Marine Research Groups

The Mochima National Park (PN. Mochima) is subject to an active center of coastal upwelling, this phenomenon presents a seasonal behavior; therefore, with the present work it is intended to have quantitative information on the species of the Temoridae family, analyzing the seasonal and spatial variations of their abundance and the age structure of the population, during the periods of upwelling and relaxation. This in relation to the environmental variables. Significant differences were found in the temperature during the months of study. Furthermore, zooplankton biomass showed significant spatial differences in the two depths studied. The zooplankton density registered the highest average values ​​in April 2016, 335 and 551 ind.m-3 at 10 and 50 m respectively. We found significant spatial differences in the two sampling periods and in both sampling depths, T. turbinata was more abundant and dominant than T. stylifera. The abundance of T. turbinata did not vary over time, nor for distance from the coast; however, the highest values ​​were recorded in the internal stations. For T. stylifera, the highest abundances were recorded 50 m from the coast and at external stations. The highest abundance found for T. turbinata is due to its short life cycle and high number of generations per year, a reproductive advantage over other species. Study Extent: The study was conducted in the Mochima National Park, located in the northeastern region of Venezuela, between the states of Anzoátegui and Sucre, between latitudes 10°9'50″ and 10°26'0″ North and longitudes 64°13 '20″ and 64°47'32″ West (Figure 1). The bay is surrounded by mountains and open to the north by a channel 1.7 km wide by 60 m deep that communicates directly with the Cariaco basin (Okuda et al., 1968; Kato, 1972). The external stations include the Caracas Islands, a system of islets located in the extreme north of the NP. Mochima, Sucre zone, considered oceanic stations, with sandy beaches with shallow profiles and limited by shallow coral reefs in the coastal part and octocoral formations in its deepest part. The internal stations are located within the Mochima bay, in three relatively well-differentiated zones: station 4, the innermost one, called sac, is characterized by a smooth and regular topography with a maximum depth of 20 m; station 5, in the central area, limited by steep slopes, including the central channel, whose maximum depth is 27 m, and station 6, in the outermost area of ​​the bay, the mouth, at the which is dominated by gently sloping slopes, where the maximum depth is 60 m (Okuda et al., 1968; Méndez et al., 1988). Method step description: Sampling was carried out bimonthly for a year, from December 2015 to October 2016. A Bongo-type net with a diameter of 30 cm and a mesh opening of 300 µm for mesozooplankton (Boltovskoy , 1981), equipped with a torpedo-type flowmeter at the mouth of the net to measure the volume of filtered water, and a zooplankton collector at the end of the net. The sampling was made from a peñero-type boat, obliquely, at a speed of 2 knots for 15 min at 10 and 50 meters from the coast, in 6 stations, distributed in the NP. Mochima: 3 external stations (stations 1, 2 and 3) and 3 internal (stations 4, 5 and 6). Once the sampling was finished, the zooplankton nets containing the biological material were emptied into previously identified plastic containers and fixed in a 4% formaldehyde solution with seawater, neutralized with sodium tetraborate (Smith and Richardson, 1979) and transferred to the Zooplankton Laboratory of the Oceanographic Institute of Venezuela. Temperature, salinity, and surface dissolved oxygen were measured at each station using a multiparameter probe (YSI). Zooplankton components were quantified using a Bogorov chamber, three aliquots of 5 ml were taken with a Stempel pipette, from a 400 ml stock. This was taken under a stereoscopic magnifying glass to determine the different groups that make up the zooplankton and then the copepods of the Temoridae family were separated to determine the species and sex of each organism. The identification of the Temora species was carried out through specialized taxonomic keys.