First results on zooplankton community composition and contamination by some persistent organic pollutants in the Gulf of Tadjoura (Djibouti) G. Boldrocchi a , Y. Moussa Omar b , D. Rowat c , R. Bettinetti a, ⁎ a Department of Theoretical and Applied Sciences, University of Insubria, Via Valleggio 11, 22100 Como, Italy b Centre d'Etude et de Recherche de Djibouti Route de l'aéroport, Djibouti, Djibouti c Marine Conservation Society, Seychelles, PO Box 389, Victoria, Seychelles HIGHLIGHTS • Zooplankton composition, density and biomass were investigated in Djibouti during whale shark aggregation season. • A temporal trend in zooplankton biomass concentration was shown. • PCB and DDT were measured for the first time in zooplankton samples from the Gulf of Tadjoura. • Analysis revealed the consistent presence of both DDT and PCB residues in zoo- plankton samples. GRAPHICAL ABSTRACT abstract article info Article history: Received 9 November 2017 Received in revised form 26 December 2017 Accepted 28 January 2018 Available online xxxx Editor: Kevin V. Thomas The Gulf of Tadjoura is located in the Horn of Africa and is widely recognized as an important site where the zooplanktivorous whale sharks seasonally aggregate from October to February. The surface zooplankton commu- nity (0–3 m) was weekly sampled from November 2016 to February 2017 in two sites during the whale shark aggregation period. A total of 12 phyla were identified. Copepoda represented the most abundant and diverse group with 29 different genera, and contributed with an average of 82% of the mean zooplankton density of ap- proximately 6600 ind m -3 . During the sampling period, copepods were dominated numerically by Calanoida (3600 ind m -3 ), followed by Poicilostomatatoida (1300 ind m -3 ). Within the copepods, Paracalanidae, Calanidae, Oncaeidae and Miraciidae were the most common families. The temporal trend in zooplankton bio- mass at both stations revealed the highest peak in December (41.3 ± 36.4 mg m -3 ), and the lowest in February (6.6 ± 3.3 mg m -3 ). As no information is available on the occurrence of legacy contaminants use and release in this area, analysis revealed the consistent presence of both DDT and PCB residues in zooplankton samples in the Gulf of Tadjoura. Total PCB ranged from approximately 110 to 637 ng g -1 d.w., while total DDT from 21 to 80 ng g -1 d.w. The proportion of primary DDT in the total residue was higher than DDE and DDD, which strongly suggests that the area might actually be subjected to DDT inputs of the parent compound. © 2018 Elsevier B.V. All rights reserved. Keywords: Copepods Biomass Density DDT PCB 1. Introduction Zooplankton constitutes the largest ecological group of organisms in the sea and, even if regarded as a homogeneous constituent, it is composed by organisms which differ substantially from each other, not only in their taxonomy but also in body size, metabolic rates and ecological roles (Bettinetti and Manca, 2013; Goswami et al., 2000). Zooplankton plays an important role in regulating patterns and mecha- nisms through which matter and energy are transferred from the base to the upper levels of food webs (Bettinetti and Manca, 2013). It serves as a primary food source for fish, fish larvae, cephalopods and other Science of the Total Environment 627 (2018) 812–821 ⁎ Corresponding author. E-mail address: Roberta.bettinetti@uninsubria.it (R. Bettinetti). https://doi.org/10.1016/j.scitotenv.2018.01.286 0048-9697/© 2018 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv