Influence of body size and environmental conditions on parasite assemblages of the black-spotted croaker (<i>Protonibea diacanthus</i>) (Teleostei: Sciaenidae) in northern Australia

The functioning and richness of marine systems (and biological interactions such as parasitism) are continuously influenced by a changing environment. Using hierarchical modelling of species communities (HMSC), the presence and abundance of multiple parasite species of the black-spotted croaker, Protonibea diacanthus (Sciaenidae), was modelled against environmental measures reflecting seasonal change. Protonibea diacanthus were collected in three seasons across 2019–2021 from four locations within the waters of the Northern Territory, Australia. The length of P. diacanthus proved to have a strong positive effect on the abundance of parasite taxa and overall parasitic assemblage of the sciaenid host. This finding introduces potential implications for parasitism in the future as fish body size responds to fishing pressure and climate changes. Of the various environmental factors measured during the tropical seasons of northern Australia, water temperature and salinity changes were shown as potential causal factors for the variance in parasite presence and abundance, with changes most influential on external parasitic organisms. As environmental factors like ocean temperature and salinity directly affect parasite–host relationships, this study suggests that parasite assemblages and the ecological functions that they perform are likely to change considerably over the coming decades in response to climate change and its proceeding effects.