The Occurrence of Intersex in Different Populations of the Marine Amphipod Echinogammarus marinus in North-West Brittany - A Longterm-Study.

In the past two decades, an increasing body of studies has been published on the intersex phenomenon in separate-sexed crustaceans from marine and freshwater ecosystems. Various causes are being considered that could have an influence on the occurrence of intersex. Besides genetic factors, environmental conditions such as photoperiodicity, temperature, salinity and parasitism, but also environmental pollution with endocrine disrupting chemicals (EDCs) are discussed. As part of a long-term monitoring (2012 - 2020) in north-west Brittany, we recorded the occurrence of intersex in the marine amphipod Echinogammarus marinus. We quantified the intersex incidence at marine and estuarine sites and analyzed the incidence in relation to the endocrine potential of the sediments. Intersex occurred with mean frequencies between 0.87% and 12%. It was striking that the incidence of intersex increased with increasing distance from the sea. Since the highest incidence was observed at the range boundary of this stenohaline species, we assume that intersex is triggered by endocrine potential and increasing stress due to increasing freshwater content - and thus an interplay of different environmental factors.

Pesticides are the dominant stressors for vulnerable insects in lowland streams.

Despite elaborate regulation of agricultural pesticides, their occurrence in non-target areas has been linked to adverse ecological effects on insects in several field investigations. Their quantitative role in contributing to the biodiversity crisis is, however, still not known. In a large-scale study across 101 sites of small lowland streams in Central Europe, Germany we revealed that 83% of agricultural streams did not meet the pesticide-related ecological targets. For the first time we identified that agricultural nonpoint-source pesticide pollution was the major driver in reducing vulnerable insect populations in aquatic invertebrate communities, exceeding the relevance of other anthropogenic stressors such as poor hydro-morphological structure and nutrients. We identified that the current authorisation of pesticides, which aims to prevent unacceptable adverse effects, underestimates the actual ecological risk as (i) measured pesticide concentrations exceeded current regulatory acceptable concentrations in 81% of the agricultural streams investigated, (ii) for several pesticides the inertia of the authorisation process impedes the incorporation of new scientific knowledge and (iii) existing thresholds of invertebrate toxicity drivers are not protective by a factor of 5.3 to 40. To provide adequate environmental quality objectives, the authorisation process needs to include monitoring-derived information on pesticide effects at the ecosystem level. Here, we derive such thresholds that ensure a protection of the invertebrate stream community.