Intraspecific variation in muscle growth of two distinct populations of Port Jackson sharks under projected end-of-century temperatures.

Although pervasive, the effects of climate change vary regionally, possibly resulting in differential behavioral, physiological, and/or phenotypic responses among populations within broadly distributed species. Juvenile Port Jackson sharks (Heterodontus portusjacksoni) from eastern and southern Australia were reared at their current (17.6 °C Adelaide, South Australia [SA]; 20.6 °C Jervis Bay, New South Wales [NSW]) or projected end-of-century (EOC) temperatures (20.6 °C Adelaide, SA; 23.6 °C Jervis Bay, NSW) and assessed for morphological features of skeletal muscle tissue. Nearly all skeletal muscle properties including cellularity, fiber size, myonuclear domain, and satellite cell density did not differ between locations and thermal regimes. However, capillary density was significantly influenced by thermal treatment, where Adelaide sharks raised at current temperatures had a lower capillarity than Jervis Bay sharks raised at ambient or projected EOC temperatures. This may indicate higher metabolic costs at elevated temperatures. However, our results suggest that regardless of the population, juvenile Port Jackson sharks may have limited acclimatory potential to alter muscle metabolic features under a temperature increase, which may make this species vulnerable to climate change.

Foraging preferences influence microplastic ingestion by six marine fish species from the Texas Gulf Coast.

This study evaluated the influence of foraging preferences on microplastic ingestion by six marine fish species from the Texas Gulf Coast. A total of 1381 fish were analyzed and 42.4% contained ingested microplastic, inclusive of fiber (86.4%), microbead (12.9% %), and fragment (<1.0%) forms. Despite a substantial overlap in diet, ordination of ingested prey items clustered samples into distinctive species groupings, reflective of the foraging gradient among species. Orthopristis chrysoptera displayed the lowest overall frequency of microplastic ingestion and the most distinctive ordination grouping, indicating their selective invertebrate foraging preferences. Cluster analysis of O. chrysoptera most closely classified microplastic with the ingestion of benthic invertebrates, whereas the ingestion of microplastic by all other species most closely classified with the ingestion of vegetation and shrimp. O. chrysoptera, as selective invertebrate foragers, are less likely to ingest microplastics than species exhibiting generalist foraging preferences and methods of prey capture.