Zooplankton biomass around marine protected islands in the tropical Atlantic Ocean

Abstract

ooplankton biomass (as wet weight) was studied around marine protected islands in the tropical AtlanticOcean.Thestudywasbasedon96zooplanktonsamplescollectedduringa3-yearperiod;specifically,2010wasconsidered a year of thermal stress, and 2012 and 2014 were considered years without thermal stress. Theanalysis showed that zooplankton biomass varied significantly among protected areas, where the smallest andmost isolated archipelago among the tropical islands, Saint Peter and Saint Paul Archipelago (SPSP), hadapproximatelytwicethebiomassofFernandodeNoronhaArchipelago (FN)andthreetimesthatofRocasAtoll(RA). The position of SPSP near the equatorial divergence zone, the seasonal occurrences of phytoplanktonblooms eastofthe Equator,the contributionofthe productivewaters thatSPSPreceivesfromthe Africancoastunder theinfluence oftheSouthEquatorial Current(SEC)system andthelocalupwelling effectinduced bythepresence of the island were considered to be the factors responsible for the high pelagic productivity in thisremote archipelago. Differences between day and night were also recorded. The high nocturnal biomass wasconsidered an effect of the capture of larger-sized animals, which are considered to be strong migrators. Thelowestzooplanktonbiomasswasrecordedin2010andwasconsideredanapparenteffectofthehighseasurfacetemperature observed in that year. However, the interaction between spatial and interannual factors showedthat,inFNandSPSP,thezooplanktonbiomasswaslowerintheyearunderthermalstress(2010).Incontrast,RApresented a higher biomass value in this period. We suggest that this increase in zooplankton biomass is theresult of the contribution of autochthonous sources (e.g., as a consequence of local physical events, such ascurrent wakes, recorded during this period at RA and responsible for the increase in local planktonic pro-ductivity) and allochthonous sources (e.g., organisms supplied by FNviathe zonal current.