Laboratório de Microalgas Marinhas, Departamento de Ecologia e Recursos Marinhos, Instituto de Biociências, Universidade Federal do Estado do Rio de Janeiro (UNIRIO), Rio de Janeiro, Brazil.
Laboratório de Echinodermata, Museu Nacional/Universidade Federal do Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil.
Mar Environ Res. 2018 Apr;135:11-17. doi: 10.1016/j.marenvres.2018.01.014. Epub 2018 Feb 2.
Blooms of the benthic dinoflagellate Ostreopsis cf. ovata have been recorded with increasing frequency, intensity and geographic distribution. This dinoflagellate produces potent toxins that may cause mortality of marine invertebrates. Adults of sea urchins are commonly affected by O. cf. ovata exposure with evidence of spines loss and high mortality during periods of high dinoflagellate abundances. Here, we report on the effects of the toxic dinoflagellate O. cf. ovata on fertilization and early development of the sea urchin Lytechinus variegatus, a key ecological herbivore. Lytechinus variegatus eggs and sperm were experimentally exposed to different concentrations of Ostreopsis cf. ovata (4, 40, 400, and 4000 cells ml) to test the hypothesis that fertilization success, embryonic and larval development of the sea urchin are negatively affected by the toxic dinoflagellate even at low abundances. Reduced fertilization, developmental failures, embryo and larval mortality, and occurrence of abnormal offspring were evident after exposure to O. cf. ovata. Fertilization decreased when gametes were exposed to high O. cf. ovata abundances (400 and 4000 cells ml), but just the exposure to the highest abundance significantly reduced fertilization success. Sea urchin early development was affected by O. cf. ovata in a dose-dependent way, high dinoflagellate abundances fully inhibited the early development of L. variegatus. Ostreopsis cf. ovata significantly increased the mortality of sea urchin eggs and embryos in the first hours of exposure (∼1-3 h), regardless of dinoflagellate abundance. Abundances of 400 and 4000 O. cf. ovata cells ml induced significantly higher mortality on sea urchin initial stages in the first hours, and no egg or embryo was found in these treatments after 18 h of incubation. The early echinopluteus larva was only reached in the control and in treatments with low Ostreopsis cf. ovata abundances (4 and 40 cells ml). The exposure to O. cf. ovata led to significantly higher occurrence of skeletal anomalies in the early larva of L. variegatus. Interactions of sea urchin gametes and Ostreopsis cells may naturally occur in coastal areas due to the match between O. cf. ovata blooms and L. variegatus reproductive period. Reduced larval density and increased larval abnormalities were observed even at low abundances (4 and 40 cells ml) frequently found in tropical environments all year round. The chronic exposure to O. cf. ovata could significantly impact larval fitness, thus compromising recruitment success, and highlight the negative effects of benthic HABs on sea urchin populations and its possible broader ecological implications.
底栖腰鞭毛虫属（Ostreopsis）中的塔玛亚历山大藻（Ostreopsis cf. ovata）的大量繁殖已越来越频繁，其分布范围也越来越广。该腰鞭毛虫会产生强效毒素，可能导致海洋无脊椎动物死亡。在塔玛亚历山大藻大量繁殖期间，海胆的成年个体通常会受到影响，表现为棘刺脱落和高死亡率。在这里，我们报告了有毒腰鞭毛虫塔玛亚历山大藻对棘皮动物海胆 Lytechinus variegatus 的受精和早期发育的影响，海胆是一种关键的生态草食动物。实验中将海胆 Lytechinus variegatus 的卵子和精子暴露于不同浓度的塔玛亚历山大藻（4、40、400 和 4000 个细胞 ml）中，以检验受精成功率、胚胎和幼虫发育是否会因低丰度的有毒腰鞭毛虫而受到负面影响的假设。暴露于塔玛亚历山大藻后，明显观察到受精率降低、胚胎和幼虫发育失败、胚胎和幼虫死亡以及出现异常后代。当配子暴露于高塔玛亚历山大藻丰度（400 和 4000 个细胞 ml）时，受精率降低，但仅最高丰度的塔玛亚历山大藻显著降低了受精成功率。海胆的早期发育受到塔玛亚历山大藻的剂量依赖性影响，高浓度的腰鞭毛虫完全抑制了 Lytechinus variegatus 的早期发育。塔玛亚历山大藻显著增加了海胆卵和胚胎在暴露最初几小时（约 1-3 小时）的死亡率，而与腰鞭毛虫丰度无关。丰度为 400 和 4000 个塔玛亚历山大藻细胞 ml 在最初几小时内会显著增加海胆初始阶段的死亡率，在 18 小时的孵化后，这些处理中没有发现卵或胚胎。只有在对照组和低浓度塔玛亚历山大藻（4 和 40 个细胞 ml）的处理中才出现早期的幼体。暴露于塔玛亚历山大藻会导致海胆 Lytechinus variegatus 的早期幼虫骨骼异常的发生率显著增加。由于塔玛亚历山大藻的繁殖期与海胆的繁殖期相匹配，因此海胆配子和塔玛亚历山大藻细胞可能会在沿海地区自然相互作用。即使在全年热带环境中经常发现的低丰度（4 和 40 个细胞 ml）下，也观察到幼虫密度降低和幼虫畸形增加。慢性暴露于塔玛亚历山大藻会显著影响幼虫的适应能力，从而影响繁殖成功，并强调底栖赤潮对海胆种群及其可能更广泛的生态影响的负面影响。
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