Impact of microplastic on early life-history stages of seabream in the Atlantic Ocean

Abstract

Plastic litter has been entering the marine realm ever since the mass production of synthetic polymers began in the 1950’s, thereby potentially complementing and amplifying the effects of persistent stressors like ocean warming, acidification, overexploitation or habitat degradation. Despite the fact that first reports on plastic ingestion by marine fish date back to the 1970’s and that considerable scientific and public concern has been raised recently over the potential detrimental effects of micro-sized (i.e., < 5 mm) plastic items, research on the explanatory variables for uptake as well as on the physiological effects of exposure and ingestion is still at an early stage, impeding a thorough evaluation of the actual implications for living marine resources. The present thesis thus investigates the effects of microplastic exposure and uptake on growth, condition, and survival of early life-history stages of fish. It provides a critical analysis of the current state of the art on the extent of microplastic ingestion by marine fish, along with an examination of the effects and explanatory variables for plastic uptake based on a literature review of 90 in-situ studies published between 1972 and 2019 (Müller 2021). This review simultaneously lays the groundwork for an integrated research design, combining an in-situ (Müller et al. subm.) and an in-vivo (Müller et al. 2020) study, to determine the impacts of and driving factors for MP ingestion by nursery-dependent, omnivorous juveniles of a commercially and recreationally important fish species, the white seabream Diplodus sargus (Linnaeus, 1758) in the Ria Formosa lagoon, Portugal. The results obtained highlight the fact that larval and juvenile fish are underrepresented in scientific initiatives investigating the extent of microplastic pollution. Furthermore, the outcomes of the in-situ and in-vivo part of the thesis challenge the existing hypotheses that omnivores in general and early life-history stages of fish in particular are prone to elevated microplastic ingestion rates. Moreover, the notion of an inevitable deterioration of physiological condition upon uptake of synthetic polymers was refuted. The findings emphasise the need for a holistic integration of field and laboratory studies to determine species- and life-stage specific driving factors for and potential detrimental effects of plastic ingestion to enable a sound evaluation of the ecological and economic risk arising for coastal fish stock and fisheries.