Contributions of macroalgae in the diets of herbivorous benthic invertebrates

Abstract

The purpose of this research was to quantify the contributions of macroalgae in the diets of two major herbivorous benthic invertebrates (sea urchin, Mesocentrotus nudus and sea snail, Turbo sazae) in the southern (Tongyeong) and eastern (Uljin) coasts of the Korean Peninsula. Benthic invertebrates and macroalgal samples, and surface seawater were collected from two sites (Tongyeong and Uljin), and during the colder (May) and warmer (July-August) seasons. Dietary contributions between macroalgae and other prey sources were accessed using stable isotope analyses and stomach contents analyses. In both regions, benthic invertebrates showed higher stable carbon and nitrogen isotope values than macroalgae and particulate organic matter (POM) as well as co-occurring macro-benthos, indicating that the two species were top predators in the benthic food webs of the study areas. According to the isotopic mixing model, in the eastern coast site, the macroalgae and POM showed higher contributions to the diet of M. nudus and T. sazae respectively. While the contributions of macroalgae and POM were similar between the diets of T. sazae and M. nudus in the southern site, except during the warmer season for T. sazae. Stomach contents analyses of M. nudus revealed that macroalgae were the primary prey items, making up a substantial volumetric proportion. The volumetric contributions of macroalgae to the stomach of M. nudus caught from Tongyeong were slightly higher than that in Uljin. Both stable isotope and stomach content analyses can strengthen our understanding the contributions of prey types to the major benthic herbivorous invertebrates and enhance our ability to assess the impact of benthic herbivorous grazing on the abundance of benthic macroalgae in Korea.