Cetaceans as a potential indicators of microand macroplastic impact in the marine environment: Trend topic and emerging gaps

How can 5 mm plastic debris (microplastics) affect filter feeder baleen whales? How can kilograms of plastic debris affect sperm whales? Here, we report the scientific evidence and the emerging gaps of the interaction between the charismatic megafauna (filter feeder baleen whales and deep divers) and micro- and macroplastics studying their impact and their related toxicological effects. We also propose these species as candidate indicators for micro- and macro-plastic pollution, respectively, at global scale. Regarding the interaction between whales and microplastics the first warning was reported for Mediterranean fin whales (Balaenoptera physalus) since 2012, and confirmed later (high concentrations of PBTs, plastic additives and specific biomarker responses, detected in skin biopsies) in the same species and for other filter feeders (basking and whale sharks). Filter-feeding megafauna are susceptible to high levels of microplastics ingestion and exposure to associated toxic compounds due to their feeding strategies and for habitat overlap with microplastic hot spots. For these reasons, this whale species has been proposed as a candidate indicator of microplastics pollution in semi-enclosed basins. On the other hand, deep divers such as the sperm whale and the Cuvier's beaked whale, are exposed to the ingestion of marine litter (ML), including large plastic fragments, due to their feeding in marine canyons. High occurrence of ML (75%) has been reported in Mediterranean sperm whales. This species was recently proposed as a candidate indicator the presence of ML in the Mediterranean (IMAP indicator 24). As these megafauna species are charismatic and iconic indicators that serve as flagship species for marine conservation, this research field became recently a “trend topic”. However, several gaps must be resolved, such as the investigations of new plastic tracers in the tissues and the identification (through omics techniques) of the toxicological effects caused to plastic debris ingestion in these species.