Comparison of epipelagic mesozooplankton samples obtained from WP-2 and MOCNESS nets

Abstract

Extensive studies on zooplankton biomass, abundance, and taxonomy were conducted around the Canary Islands and the Azores Islands using different sampling gears. Thus, comparing the results from different studies can be challenging. Here, we compared the epipelagic (0-200 m layer) mesozooplankton community sampled using two types of zooplankton sampling nets, the WP-2 and the MOCNESS, during day- and nighttime in two stations of the North Atlantic Ocean. Data obtained by MOCNESS provides detailed information at stratified depth layers of the water column, while the WP-2 sampled the entire 0-200 m water column. Chlorophyll a concentration values were slightly higher close to the Azores Islands compared to the southern oligotrophic open waters. The mesozooplankton community sampled using both gears were similar between stations, with Copepoda being the dominant group in both nets. However, we found differences in the biomass values obtained. The MOCNESS net collected more mesozooplankton biomass in the epipelagic zone in the oligotrophic waters, while the WP-2 net captured more biomass near the Azores Islands. In terms of diversity, the MOCNESS trawl tended to capture larger zooplanktonic organisms such as Euphausiacea, whereas the WP-2 net was more effective in collecting smaller and more delicate organisms, such as Appendicularia.