Dissolved organic matter influences the timing of embryonic development of the purple sea urchin, Strongylocentrotus purpuratus.

摘要

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 (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 the experiments, all studies in the literature that examine the realized effects of DOM transport were analyzed to ascertain when the manifestation of DOM uptake is most likely to occur. From these results, it appears that the effects of DOM transport are most likely to manifest after the life stage in which the majority of uptake occurred. If DOM transport has an affect within a life stage it is most likely to manifest as moderation of biomass loss or maintenance of endogenous reserves. With the addition of the experimental results from this study to the information already in the literature we begin to more fully grasp the importance of DOM transport to S. purpuratus. DOM influences the time of hatching, biomass, arm length, and stomach size of the species; results that highlight the importance of examining multiple affects of DOM transport for a single species. In conclusion, future research should look for multiple effects of the presence of DOM both within and across life stages (for a single species) to better understand the importance of DOM to marine invertebrates.