UC Davis

Batoids are animals of the Chondrichthyan group comprising stingrays, skates, and guitarfishes. InCalifornia coast, batoids, such as bat-rays, shovelnose guitarfish, and round stingrays, inhabits coastal areas that can be impacted by overfishing, habitat degradation, and pollution. These animals play the role of mesopredators and can have a large effect on the structure and function of benthic communities. Paradoxically, habitat use and feeding ecology of batoid species are poorly understood as well as their exposure risk and accumulation patterns of contaminants, such as Hg. Considering that most batoids have a life cycle strongly associated with the bottom sediments of benthic habitats, which is an important site deposition and partitioning processes for many pollutants, these animals might be at risk of higher exposure to these pollutants and exposed to deleterious effects. This research aims to describe the habitat use of batoids species occurring in San Diego Bay, Southern California, and Tomales Bay, Central California, and assess their exposure levels to pollutants. In chapter 1, I present an extensive systematic review of the scientific literature on the fate of trace metals and POPs in batoids with the goal of describing the current state of environmental contamination in batoids. In chapter 2, I describe trophic interactions of three sympatric batoid species inhabiting an urbanized estuary using carbon (δ13C) and nitrogen (δ15N) stable isotopes and total Hg (THg) as ecological tracers. I also assess THg accumulation in two populations of Myliobatis californica while accounting for changes in trophic structure, diet sources, and contamination background. In chapter 3, I describe and compare Hg bioaccumulation and biomagnification between two estuarine food webs in California coast assessing temporal and spatial variation in Hg levels, and which factors best explain these variations.