Zooplankton biomass and species composition and abundance in the southeastern Caribbean Sea (Cariaco Basin, October 2001 – January 2017) collected by the CARIACO Ocean Time-Series Program

Study Extent

The CARIACO Ocean Time-Series study area is the Cariaco Basin, located on the continental shelf of Venezuela, in the southeastern Caribbean Sea. The Cariaco Basin is a large (∼160 km long, 70 km wide) and deep (∼1,400 m) basin, located on the Venezuelan continental shelf, with an area of approximately 11.200 km2; bound to the north by a sill connecting Margarita Island to Cabo Codera, at a mean depth of about 100 m with two channels breaching this sill (La Tortuga: ∼135 m and Centinela: ∼146 m). The basin is divided into two sub-basins, one eastern and one western, separated by a saddle of approximately 900 m deep. The Cariaco Basin region is between 10-11 degrees N and 64-66 degrees W. The Cariaco Basin shows marked seasonal and interannual variation in hydrographic properties and primary production (carbon fixation rates by photosynthesis of planktonic algae) due to the seasonal coastal upwelling. The Cariaco Basin hydrography is affected by North-Atlantic gyre-scale processes, including dispersal of Subtropical Underwater and western boundary current variability, cross-equatorial flow of water masses, wind-driven upwelling compounded by geostrophic circulation, ventilation forced by Caribbean Sea eddies, and river discharge. Due to its restricted circulation and high primary production, the basin is anoxic below ~250 m.

Sampling

Zooplankton samples were collected during each monthly CARIACO time-series cruise from October 2001 to January 2017 (cruises 71-232). It was used a BONGO type net with two receptacles of 60 cm opening diameter and two different mesh sizes of 200 and 500 microns. A flowmeter was set at the opening of the 500 microns’ net to calculate the volume of water filtered. An oblique tow was made for ~15 minutes during the day (between 9 and 10 AM) from between 200 m deep to the surface. During the entire tow, the cable was maintained at an angle of 40-45 degrees with a clinometer. The ship’s speed during the tows was maintained around 1-1.5 knots, and the net was pulled upwards at a speed of 1 m/s. Once at the surface, the nets were washed with seawater, and the collecting jars contents were emptied in labeled glass bottles that were kept refrigerated until returning to the lab. Zooplankton taxonomy was performed at Fundación La Salle de Ciencias Naturales, Estación de Investigaciones Marinas de Margarita (EDIMAR), Isla de Margarita, Venezuela. When zooplankton samples were returned to the lab (~12 hours later), formalin (5%) neutralized with borax was added to each sample for preservation. For processing, each sample was split in two aliquots with a Folsom splitter, one for biomass and the other for taxonomy. The aliquot for biomass calculation was washed with DI water to eliminate salt excess, dried in pre-weighted crucibles for 48 hours in an electric oven at a constant temperature of 60°C, and it was kept in a desiccator until measuring the Dry Weight (biomass). Afterwards, the dry sample was calcined in a muffle furnace at 450°C for 4 hours and weighted to measure Ash (inorganic remains). For taxonomy, aliquots were extracted and placed in a 10 ml Bogorov chamber in order to count and identify taxonomic groups present. Identification and counts were made using a stereomicroscope Baush & Lomb (7x). Processed taxonomy samples were stored in the collection maintained at the Museo Oceanológico Hermano Benigno Román (MOBR - EDIMAR). The manuals used for zooplankton identification were Newell & Newell (1977), Tregouboff & Rose (1978), and Boltosvkoy (1981).

Method steps

1. See Sampling Description