Hydroacoustics evaluation of zooplankton in the Department of Magdalena, Colombian Caribbean

Zooplankton is one of the main components of biological communities in the marine ecosystems, these have been traditionally studied through net-sampling methods, but in recent years new technologies such as hydroacoustics have been implemented allowing improved estimates. The present study was used as a general model to correlate the hydroacoustic backscatter and dry weight biomass of zooplankton estimated from net tows. Samples were obtained during oceanographic cruise in May of 2016. Zooplankton biomass values were between 0.06 g / m
²
and 1.04 g / m
²
, with average 0.53 g / m
²
± 0.23 g / m
²
, Nautical Area Scattering Coefficient (NASC) between 1.10 m
²
/ n.mi and 3.98 m
²
/n.mi
²
(average 2.54 m
²
/n.mi
²
± 0.71 m
²
/n.mi
²
); The stations with highest acoustic density were those located more offshore (western sector of the gulf), while those with lower density were located closer to coastline, between the western and central sector of the gulf, the biomass coincided respectively with the hydroacoustic information. The relationship between zooplankton dry weight and backscatter was significant (p <0.001) and explained 78% of the variability in the dry weight data. To analyze the mean and the variance a geostatistical analysis was applied ordinary kriging to create a spatial zooplankton community map. The spatial average density was 1,160 g / m
²
. The mean zooplankton dry weight biomass estimates from plankton net tows and hydroacoustics were not significantly different (p = 0.99). The maps of zooplankton distribution illustrated the spatial trends of aggregations that could not be distinguished by general means. It was possible to determine that a general model can be a simple and effective method to convert the hydroacoustic backscatter to zooplankton dry weight biomass in a specific area of the Colombian Caribbean like Gulf of Salamanca.