Parasite assemblages as indicators of stability in stock structure of Cynoscion guatucupa (Sciaenidae) after a quarter of century of exploitation in a marine warming hotspot

Climate change is impacting marine species, leading to shifts in their distribution to higher latitudes and to deeper locations. Parasite communities are dynamic systems influenced by biotic and abiotic factors, making them valuable tools for studying ecological processes of their hosts. This work aims to assess possible changes in parasite structure that occurred in the northern stock of Cynoscion guatucupa in the Argentine Sea, over approximately 25 years, by using parasites as tags in a region characterized as a hotspot of significant warming in recent decades. Parasite assemblages of adult and juvenile fish from two periods caught at two regions of the Argentine Sea were analyzed. Species richness remained relatively constant across samples, although four of the eight compared species from juvenile fish showed significant increases in prevalence, while for adults three species decreased. Differences in parasite assemblages were significant between periods, but not between regions, indicating that the stock structure has apparently remained stable in recent years, even under a warming process that, in turn, seems to have affected its parasite assemblages which however, continue showing homogeneous parasitological attributes throughout the habitats. Most results indicate that changes in parasite burdens are not related to the population density or geographic distribution of C. guatucupa, but to changes in temperature, salinity or in the density of top predators. Parasites seem to have felt the impact of global change before their host, thus, they can be considered early sentinels to monitor the stability and distribution of this important resource.