Benthic cyanobacterial mats (BCMs) are becoming increasingly abundant on coral reefs worldwide. High growth rates and prolific toxin production give them the potential to cause widespread coral recruitment failure through allelopathic effects, but few studies have made the link between their toxicity for coral larvae and in situ toxin concentrations. Here we investigated the allelopathic effects of the benthic cyanobacterium Anabaena sp.1 on larvae of the coral Pocillopora acuta. This cyanobacterium produces several non-ribosomal cyclic lipopeptides of the laxaphycin family with cytotoxic properties. Therefore, we measured the concentration of laxaphycins A and B in Anabaena mats and in the water column and tested their effects on coral larvae. We found that Anabaena crude extract reduces both larval survivorship and settlement and that laxaphycin B reduces settlement. When larvae were exposed to both laxaphycins, there was a reduction in both larval survival and settlement. In the natural reef environment, laxaphycin A and B concentrations increased with increasing proximity to Anabaena mats, with concentrations being consistently above LC₅₀ and EC₅₀ thresholds within a 1 cm distance of the mats. This study demonstrates that laxaphycins reduce the survival and inhibit the settlement of coral larvae at concentrations found near Anabaena mats in situ. It further shows a combined effect between two cyanobacterial metabolites. As BCMs become more common, more of their secondary metabolites might be released in the water column. Their occurrence will lead to a reduction in coral recruitment rates, contributing to the continuing decline of coral reefs and shift in community structure.

全球珊瑚礁上的底栖蓝藻垫 (BCM) 正变得越来越丰富。高生长率和大量的毒素产生使它们有可能通过化感作用导致广泛的珊瑚招募失败，但很少有研究将它们对珊瑚幼虫的毒性与原位毒素浓度之间的联系联系起来。在这里，我们研究了底栖蓝藻Anabaena sp.1 对珊瑚Pocillopora acuta幼虫的化感作用。这种蓝细菌产生拉沙霉素家族的几种具有细胞毒性的非核糖体环状脂肽。因此，我们测量了鱼腥藻垫和水柱中拉沙霉素 A 和 B 的浓度，并测试了它们对珊瑚幼虫的影响。我们发现鱼腥藻粗提物可降低幼虫的存活率和沉降，而拉沙霉素 B 则可减少沉降。当幼虫暴露于两种拉沙霉素时，幼虫的存活率和定居量都会减少。在天然珊瑚礁环境中，拉沙霉素 A 和 B 浓度随着距离鱼腥藻垫的距离的增加而增加，在距离垫 1 厘米的范围内，浓度始终高于 LC ₅₀和 EC _50阈值。这项研究表明，在鱼腥藻垫附近发现的拉沙霉素会降低珊瑚幼虫的存活率并抑制其定居。它进一步显示了两种蓝藻代谢物之间的联合作用。随着 BCM 变得越来越普遍，更多的次生代谢物可能会释放到水体中。它们的发生将导致珊瑚补充率下降，导致珊瑚礁持续减少和群落结构发生变化。