Marine dissolved organic matter (DOM) comprises one of the largest carbon reservoirs on earth and has long been considered a potential energy source for marine invertebrates. The importance of DOM transport has been adequately demonstrated for unicellular organisms, where DOM can meet 100% of an organisms energy needs, but the effects of DOM uptake for marine metazoans are less well understood. In this study, three general areas involving the influence of DOM transport to marine invertebrates were explored. First, we assessed the effects of using seawater exposed to high intensity ultraviolet radiation (UVR) on the study organism; embryos of the purple sea urchin, Strongylocentrotus purpuratus. This was important because we used seawater treated in this way to create water types used in the experiments. Exposing seawater to high intensity UVR oxidizes (and functionally removes) DOM in the seawater. Second, the influence of the presence of DOM on the timing of embryonic development was examined for embryos of S. purpuratus. Specifically, the time of cell division and the time of hatching were determined for embryos in seawater with and without DOM.Finally, the ability of DOM to moderate the negative effect of UV-exposure on time of cell division was assessed. To make these comparisons experiments were performed using three water types: FSW (0.22 micron filtered seawater), DOM-depleted seawater v (UV oxidized 0.22 micron filtered seawater), and DOM-enriched seawater (UV oxidized 0.22 micron filtered seawater enriched with labile DOM). In the first experiment, batches of embryos in the three water types were either exposed or not exposed to ultra-violet radiation and the time of first cell division was compared for embryos across the six treatments. In the second experiment, batches of embryos were placed in the same three water types and the time of first cell division and the time of hatching were quantified.From these experiments several results were generated. First, seawater exposed to high intensity UVR did not influence the timing of development of embryos of S. purpuratus.Embryos in water exposed to high intensity UVR (DOM-enriched and DOM-depleted seawater) hatched at similar times and completed first cell division at times similar to embryos in water not exposed to high intensity UVR (FSW). Next, we found that the influence of the presence of DOM on the development timing of S. purpuratus embryos depended on the event that was examined. The time of first cell division was not affected by the presence of DOM but the time of hatching was. Embryos in water with dissolved organic matter hatched on average 86 minutes later than embryos in water without DOM.Potentially, embryos in seawater without DOM speed up development to more quickly reach the point that they can feed on particulates. Lastly, the presence of DOM did not influence UVR-induced cleavage delay. The percent cleavage delay was not significantly different for embryos in seawater with (DOM-enriched) and without (DOM-depleted) DOM. In addition to th...
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