The invasive, non-native slipper limpet Crepidula fornicata is poorly adapted to sediment burial

Hematodinium sp. infection does not drive collateral disease contraction in a crustacean host

Host, pathogen, and environment are determinants of the disease triangle, the latter being a key driver of disease outcomes and persistence within a community. The dinoflagellate genus Hematodinium is detrimental to crustaceans globally - considered to suppress the innate defences of hosts, making them more susceptible to co-infections. Evidence supporting immune suppression is largely anecdotal and sourced from diffuse accounts of compromised decapods. We used a population of shore crabs (Carcinus maenas), where Hematodinium sp. is endemic, to determine the extent of collateral infections across two distinct environments (open-water, semi-closed dock). Using a multi-resource approach (PCR, histology, haematology, population genetics, eDNA), we identified 162 Hematodinium-positive crabs and size/sex-matched these to 162 Hematodinium-free crabs out of 1191 analysed. Crabs were interrogated for known additional disease-causing agents; haplosporidians, microsporidians, mikrocytids, Vibrio spp., fungi, Sacculina, trematodes, and haemolymph bacterial loads. We found no significant differences in occurrence, severity, or composition of collateral infections between Hematodinium-positive and Hematodinium-free crabs at either site, but crucially, we recorded site-restricted blends of pathogens. We found no gross signs of host cell immune reactivity towards Hematodinium in the presence or absence of other pathogens. We contend Hematodinium sp. is not the proximal driver of co-infections in shore crabs, which suggests an evolutionary drive towards latency in this environmentally plastic host.

Natural dynamics overshadow anthropogenic impact on marine fauna at an urbanised coastal embayment

Understanding vulnerabilities of coastal ecosystems facing anthropogenic use is a precondition for management decisions and development planning. This can be challenging in urbanised areas with multiple activities affecting different faunal communities. The aim of this study was to provide a holistic understanding of the relative importance of anthropogenic and natural variables for macroinfauna, epifauna and fish in a heavily modified waterbody (HMWB) designated under the EU Water Framework Directive (WFD). The study area, Swansea Bay (Wales, UK), had two regularly dredged industrial ports, three estuaries, a wastewater discharge point and a dredge-spoil disposal site. Wave and tidal current models were constructed, and environmental data were gathered by field studies. Biota were assessed by grab sampling and dredging. Modelled and empirical data were combined in a Distance-based Linear Model (DistLM) that quantified how much of the faunal variation was explained by wave exposure and tidal currents, sediment characteristics and other environmental factors, and by anthropogenic usage. Wave and tidal current parameters explained over 50% of the variation in all biota. Infauna communities were further linked with sediment properties and epibenthos with distance to estuaries. Fish and epibenthos were affected by a dredge-spoil disposal site, but none of the faunal communities was affected by the wastewater outfall. Biota were predominantly driven by the natural hydrodynamic regime while anthropogenic factors had secondary influence. The study highlighted that ecosystems driven by a strong hydrodynamic regime can be relatively resistant to human activities.