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Efficient biodiversity monitoring programs are essential to assess the ecological status of marine ecosystems. In the context of the European Marine Strategy Framework Directive (MFSD), coastal rocky reef fish assemblages are most often surveyed using underwater visual census (UVC). While UVC is well-suited to monitor conspicuous fish, it underestimates hidden, vagrant and/or elusive fishes. Hence, complementary methods are needed to survey the whole fish assemblage. Environmental DNA (eDNA) metabarcoding is increasingly used in this context. Here, we evaluated the effectiveness of eDNA metabarcoding collected from water to provide sound and complementary diversity data to UVC in support of the MFSD. Both methods were used to examine coastal rocky reef fish assemblages in one bay of Brittany (France), along an inshore-offshore gradient and during two seasons. eDNA metabarcoding was carried out following different water sampling strategies: small water volumes (2L) from stationary sampling at the surface and bottom and large water volume (30L) filtered at the surface while moving in close vicinity of the sampling site. A total of 93 (including 57 species) and 33 (including 27 species) taxa were detected with eDNA metabarcoding and UVC, respectively. Eleven species were only recorded by UVC, a result explained for nine of them by a lack of taxonomic resolution of the markers used (12S and 16S) and/or the unavailability of reference sequences. eDNA metabarcoding allows to recover species expected to be present, such as demersal rocky specialist fishes, at a similar species richness level than UVC (14 species for UVC and 12 species for eDNA). It however also unveiled other taxa (pelagic, bentho-pelagic and others demersal fishes) inhabiting the bay and rarely reported through UVC (18 species for UVC and 45 species for eDNA). Despite these differences in species identified by UVC vs. eDNA, both survey methods were consistent in characterizing spatio-temporal variabilities of fish assemblages, highlighting strong site fidelity of eDNA to the source communities. In a well-mixed water column, the eDNA signal was very homogeneous, allowing the use of the cost-effective small water volume eDNA sampling method. eDNA metabarcoding is thus particularly promising to study coastal rocky reef assemblages, and when coupled with UVC, it improves monitoring surveys. • Fishes are crucial to monitor in biodiversity surveys, but this is challenging. • eDNA metabarcoding outperforms UVC when assessing fish assemblages of rocky habitats. • eDNA metabarcoding reveals spatio-temporal community patterns at fine scale. • Lacks of resolution at species level can limit fish detection by metabarcoding. • Combining eDNA metabarcoding and UVC improves coastal fish monitoring. [ABSTRACT FROM AUTHOR]

Despite the importance of estuarine nurseries in the regulation of many fish stocks, temporal and spatial movements and habitat use patterns of juvenile fish remain poorly understood. Overall, combining several movement metrics allowed us to characterize dispersal patterns of juvenile flounder, Platichthys flesus, along an estuarine seascape. Specifically, we investigated otolith microchemistry signatures (Sr:Ca and Ba:Ca ratios) and stable isotope ratios (δ13C and δ15N) in muscles of these juveniles, during three consecutive years to assess inter-annual fluctuations in their home range and isotopic niches. The morphological condition and lipid content of individuals were lower in years of high as compared to low dispersal along the estuarine gradient. We discuss these results in relation to the ecosystem productivity and intra- and inter-specific competition level, which in turn affects movements and foraging behaviors of juvenile flounders. • Otolith chemistry and muscle isotope ratios varied congruently across the estuary. • Home range and quantitative movement metrics were derived from biological tracers. • Juvenile condition fluctuated annually in line with spatial and trophic niches. • Foraging specialization was related to higher body condition and lipid content. • Fine-scale movements highlighted inter-annual variations of nursery quality. [ABSTRACT FROM AUTHOR]

Abstract: Male responses to risk of sperm competition play an important role in sexual selection, sexual conflict, and the evolution of mating systems. Such responses can combine behavioural and physiological processes, and can be mediated through different components of the ejaculate such as sperm numbers and seminal proteins. An additional level of ejaculate complexity is sperm heteromorphism, with the inclusion of non-fertilising parasperm in the ejaculate. We now test the response to rivals in a sperm heteromorphic species, Drosophila pseudoobscura, measuring the behavioural response and sperm transfer and, crucially, relating these to short-term fitness. Males respond to exposure to conspecific rivals by increasing mating duration, but do not respond to heterospecific rivals. In addition, after exposure to a conspecific rival, males increased the transfer of fertilising eusperm, but not non-fertilising parasperm. Males exposed to a conspecific rival also achieve higher offspring production. This suggests that the evolution of parasperm in flies was not driven by sperm competition and adds to the increasing evidence that males can make extremely sophisticated responses to mating competition. [Copyright &y& Elsevier]

In a 10-month experimental study, we assessed the combined impact of warming and acidification on critical life stages of small-spotted catshark (Scyliorhinus canicula). Using recently developed frameworks, we disentangled individual and group responses to two climate scenarios projected for 2100 (SSP2-4.5: Middle of the road and SSP5-8.5: Fossil-fueled Development). Seasonal temperature fluctuations revealed the acute vulnerability of embryos to summer temperatures, with hatching success ranging from 82% for the control and SSP2-4.5 treatments to only 11% for the SSP5-8.5 treatment. The death of embryos was preceded by distinct individual growth trajectories between the treatments, and also revealed inter-individual variations within treatments. Embryos with the lowest hatching success had lower yolk consumption rates, and growth rates associated with a lower energy assimilation, and almost all of them failed to transition to internal gills. Within 6 months after hatching, no additional mortality was observed due to cooler temperatures. • Summer temperatures revealed embryo vulnerability to seasonal fluctuations. • Hatching success ranged from 82% in control and SSP2-4.5 to 11% in SSP5-8.5. • The death of embryos was preceded by distinct individual growth trajectories. [ABSTRACT FROM AUTHOR]

The temporal asynchronies in larvae production from different spawning areas are fundamental components for ensuring stability and resilience of marine metapopulations. Such a concept, named portfolio effect, supposes that diversifying larval dispersal histories should minimize the risk of recruitment failure by increasing the probability that at least some larvae successfully settle in nursery. Here, we used a reconstructive approach based on otolith chemistry to quantify the larval dispersal portfolio of the European seabass, Dicentrarchus labrax , across six estuarine nursery areas of the northeast Atlantic Ocean. The analysis of natal and trajectory signatures indicated that larvae hatch in distinct environments and then dispersed in water masses featured by contrasting chemical signatures. While some trace elements appeared affected by temporal changes (Mn and Sr), others varied spatially during the larval stage but remained poorly affected by temporal fluctuation and fish physiology (Ba, Cu, Rb and Zn). We then proposed two diversity metrics based on richness and variations of chemical signatures among populations to reflect spatio-temporal diversity in natal origins and larval trajectories (i.e., estimates of dispersal portfolio). Along the French coast, the diversity estimates were maximum in nurseries located at proximity of offshore spawning sites and featured by complex offshore hydrodynamic contexts, such as the Mont St-Michel bay. Finally, our findings indicate that the dispersal portfolio was positively related with the local abundance of seabass juveniles, supporting the assumption that heterogeneity in dispersal history contributes to promote recruitment success in nurseries. [Display omitted] • Larval dispersal portfolio of seabass was quantified based on otolith chemistry. • Otolith signatures reflect spatio-temporal changes of marine environment. • Larvae hatch and disperse in distinct environments between estuarine nurseries. • Diversity in natal origins and larval trajectories depends on hydrodynamic context. • Heterogeneity in dispersal history promotes juvenile abundance in fish nurseries. [ABSTRACT FROM AUTHOR]

The animal gut contains a large reservoir of symbionts. Whilst these microbes have obvious physiological functions in, for example, digestion and immune defence, they can also affect their host's behavior. Increasing evidence suggests that gut microbiota alters the scent of an individual, thereby affecting mate choice and kin recognition. [ABSTRACT FROM AUTHOR]