Natural variation of carotenoids in the eggs and gonads of the echinoid genus, Strongylocentrotus: implications for their role in ultraviolet radiation photoprotection

Abstract

We examined variability in carotenoid concentration in the gonads and eggs of four sea urchin species ( Strongylocentrotus purpuratus, Strongylocentrotus franciscanus, Strongylocentrotus pallidus and Strongylocentrotus droebachiensis) to explore the possible role of carotenes as photoprotectants. Carotene concentrations were measured in gonads and gametes of each species, while in eggs the ultraviolet radiation (UV-R) sensitivity and self-shading capacity by carotenes were calculated. Mean concentrations of carotenes in gonads ranged from 0.13±0.017 mg g −1 dw ( S. purpuratus), 0.14±0.019 mg g −1 dw ( S. franciscanus), 0.29±0.079 mg g −1 dw ( S. pallidus) to 0.36±0.06 mg g −1 dw ( S. droebachiensis). In eggs, concentrations ranged from 0.026±0.003 to 0.09±0.034 mg g −1 dw. UV-R sensitivity in eggs was quantified by measuring UV-R induced first-cleavage delay. Intra-specifically, cleavage delay varied significantly between individuals, and could be correlated with carotene concentration. Interspecific differences in cleavage delay and carotene concentrations were not correlated. Using the observed concentration of β, β-echinenone (which makes up between 82.4% and 94.9% of the total carotene concentration in the eggs) and a molar extinction coefficient of ε=13.7×10 3 mol −1 cm −1 at 334 nm, we calculated self-shading efficiency in the eggs. Self-shading capacity ( J 334) indicated that the eggs could only screen from 4.6% ( J 334=0.046) down to 1.5% ( J 334=0.015) of UV-R at 334 nm. While not sunscreens, we suggest that carotenes can photoprotective in echinoid eggs, probably by mitigating the effects of reactive oxygen species.