Congratulations to Lis Cordner and Cara Simonsen! These ladies are the Sandin Lab’s newest BS/MS alums! We are so proud of their accomplishments and can’t wait to see what they bring to the science community in the future.

 

Lis Cordner focused her studies on various factors that could influence the diet composition of fish.  From food availability to habitat composition and predation risk, Lis conducted her research in the Northern Line Islands to determine how these factors influenced fish diets in a natural coral reef system.

Lis Cordner at her thesis celebration

Lis Cordner at her thesis celebration

Thesis abstract:
Food availability and predation risk are the primary factors that influence an individual’s diet composition. Reduced food availability will result in populations with broader diet breadths due to individual diet specialization. This effect can be enhanced when predators limit foraging movement of prey. Predators can also force prey to forage in lower-risk habitats. An opportunity for us to study these influences on fish diets in a natural system exists in coral reefs. The reefs of the Northern Line Islands vary in their predator biomass and the amount of food available to each trophic guild. To determine the effects of changing food availability and predator densities on the diets of fishes we quantified the diets of species from three trophic guilds from the Northern Line Islands. Populations experiencing higher predation pressure and/or lower food availability are expected to have wider diet breadths. Trends in diet breadth varied across species. The results do not offer a clear indication that fish are shifting their foraging habitats to be closer to reef refuges in response to increased predation pressure. So, changes in predator density and the amount of food available seem to influence shifts in diet breadth, but the influences vary across species. There are two factors that may also influence diets: habitat complexity and resource patchiness.

 

Cara Simonsen focused her Master’s thesis on the factors that influence the foraging behavior of herbivorous fish in Caribbean reefs, primarily in Curaçao. In an observational study, she quantified preferred bite rates, species abundances and diversity, and food availability to determine how these factors influenced foraging behavior. Understanding the impacts of herbivory can help determine how herbivorous fish affect benthic reef composition and coral reef functionality.

Cara Simonsen at her thesis celebration

Cara Simonsen at her thesis celebration

Thesis Abstract:
Coral reefs have undergone major phase shifts in the past three decades resulting in algal dominance. Herbivorous fish are the main force removing algae from Caribbean reefs since the die-off of Diadema antillarum. This study looks to determine the elements controlling herbivorous fish populations on Caribbean coral reefs and their ability to remove turf and erect macroalgae. We asked whether the foraging rates and behaviors at a species, family and guild level changed with context. Over a three-month period, focal observations were conducted on five common herbivorous fish species, three Scarids and two Acanthurids, at nine sites on Curaçao that varied in benthic  xi composition and fish populations. Bite rates, benthic composition and fish assemblages were quantified at each site. The three driving forces of foraging behavior of reef fishes are preferred bite rates, species abundances and diversity, and food availability. An increase in any of these factors increases the foraging intensities. I also found that herbivores have an overwhelming preference for turf algae at every site, regardless of the benthic makeup. Variations of density, estimated bite rates and selectivity all decreased along an inverse taxonomic gradient. These findings suggest that analyzing foraging behavior and intensity at a guild level is the most beneficial to understanding impact of herbivory on coral reefs. The total amount of bites taken on a reef can determine how the herbivorous fish guilds affect both the overall benthic composition and coral reef functionality.