Variación a largo término (2002-2016) en la densidad y composición del mesozooplancton indica cambio de régimen en isla Margarita (Venezuela)

Abstract

In the east of Margarita Island (Venezuela), the composition and density of mesozooplankton were studied for 15 years (2002 to 2016) in two fixed stations five miles from the coast. Samples (total 655) collected biweekly by hauls using net with a diameter of 1.7 m and a length of 3.5 m (mesh size of 400 microns) towed horizontally at a depth of 10 to 15 m for 20 minutes. The abundance of the main planktonic groups (21) was estimated by their density (ind/m3) by direct counting. In 13 groups: copepods, cladocerans, sergestoids Lucifer, brachyurans zoea, chaetognaths, mollusk larvae, cirripede larvae, penaeid mysis, pteropods and in the gelatinous plankton (salps,appendicularians, jellyfish, siphonophores) during the periods 2002-2004 and 2014-2016, lower values of annual density and representation were found, while in 2005-2013 the values were notoriously higher. The sardine eggs deviate from the indicated trend, since they were more abundant in years 2002-2004 and 2014-2016 and were lower in density between 2005 and 2013. This trend was more notable in its representation (%) in mesozooplankton. Due to the greater abundance of 13 zooplankton groups and their total density, it is confirmed that a regime shift occurred affecting ecosystem services such as sardine fishing, generating an approximately 10-year long crisis.