Comparative Raman Spectroscopy Study of the Coelomic Fluid of Grazing Sea Urchins and Their Native Seawater: Prospect for A Potential Indicator of Environmental Aggression

Abstract

Sea urchins have limited ability to move, and they use the watervascular circulation system to pump surrounding sea water in order to set body parts in motion. It is therefore thought that coelomic fluid, a body fluid of sea urchins which acts as its internal transport and immune system, contains metabolised pollutants. In the present study, we developed a method for detection of carotenoids in the coelomic fluid by Raman spectroscopy. Carotenoids were obtained from the coelomic fluid by ethanol extraction and their selective resonance Raman signal was enhanced employing the surface enhanced Raman scattering (SERS) technique. Carotenoids are ingested by sea urchins through their plant-based diet, metabolised and transported into the coelomic fluid, where they were detected for the first time via SERS. We further investigated the correlations of carotenoids signalling from the coelomic fluid with the local sea water to prospect a potential linkage with changes under environmental aggression. The antioxidative and immunomodulatory role of carotenoids, especially of β-carotene, was extensively studied in vertebrates (Chew and Park, 2004). Biological defence and increased antioxidant activity is associated with an increased carotenoids level and/or change in their species balance in native sea urchins. Additionally, we compared relative sulfate concentration of sea urchin coelomic fluid with local sea water using FT-Raman technique. We discuss the possibility for development of methods for rapid and cost effective monitoring of the native environmental waters via sea urchin carotenoids. Other co-existent pollutants which may enter the coelomic fluid via the digestive system or through water-vascular system of sea urchins are expected to correlate with the animal response via an increased antioxidant activity due to carotenoids. Thus, sea urchins may prove to be good sentinels of environmental water changes via their carotenoids signalling.