School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand.
Department of Biological and Environmental Sciences and Technologies, University of Salento, Lecce, Italy.
Glob Chang Biol. 2024 Aug;30(8):e17417. doi: 10.1111/gcb.17417.
Marine heatwaves (MHWs) are increasing in frequency, duration and intensity, disrupting global marine ecosystems. While most reported impacts have been in tropical areas, New Zealand experienced its strongest and longest MHW in 2022, profoundly affecting marine sponges. Sponges are vital to rocky benthic marine communities, with their abundance influencing ecosystem functioning. This study examines the impact of this MHW on the photosynthetic sponge Cymbastella lamellata in Fiordland, New Zealand. We describe the extent, physiological responses, mortality, microbial community changes and ecological impact of this MHW on C. lamellata. The Fiordland MHW reached a maximum temperature of 4.4°C above average, lasting for 259 days. Bleaching occurred in >90% of the C. lamellata Fiordland population. The population size exceeded 66 million from 5 to 25 m, making this the largest bleaching event of its kind ever recorded. We identified the photosynthetic symbiont as a diatom, and bleached sponges had reduced photosynthetic efficiency. Post-MHW surveys in 2023 found that over 50% of sponges at sampling sites had died but that the remaining sponges had mostly recovered from earlier bleaching. Using a simulated MHW experiment, we found that temperature stress was a driver of necrosis rather than bleaching, despite necrosis only rarely being observed in the field (<2% of sponges). This suggests that bleaching may not be the cause of the mortality directly. We also identified a microbial community shift in surviving sponges, which we propose represents a microbial-mediated adaptive response to MHWs. We also found that C. lamellata are key contributors of dissolved organic carbon to the water column, with their loss likely impacting ecosystem function. We demonstrate the potential for MHWs to disrupt key marine phyla in temperate regions, highlighting how susceptible temperate sponges globally might be to MHWs.
海洋热浪（MHWs）的发生频率、持续时间和强度都在增加，正在扰乱全球海洋生态系统。虽然大多数报告的影响都发生在热带地区，但新西兰在 2022 年经历了其最强和最长的 MHW，这对海洋海绵产生了深远的影响。海绵对岩质海底海洋群落至关重要，其丰度影响生态系统功能。本研究调查了这种 MHW 对新西兰 Fiordland 的光合作用海绵 Cymbastella lamellata 的影响。我们描述了这次 MHW 对 C. lamellata 的范围、生理反应、死亡率、微生物群落变化和生态影响。Fiordland MHW 达到了平均温度 4.4°C 的最高温度，持续了 259 天。在 C. lamellata Fiordland 种群中，超过 90%的海绵出现了白化现象。该种群在 5 到 25 米的范围内超过 6600 万只，这是有史以来记录到的最大规模的白化事件。我们确定光合作用共生体是一种硅藻，并且白化海绵的光合作用效率降低。2023 年的 MHW 后调查发现，在采样点超过 50%的海绵已经死亡，但其余海绵已经从早期的白化中大部分恢复。通过模拟 MHW 实验，我们发现尽管在野外很少观察到坏死（<2%的海绵），但温度应激是导致坏死而不是白化的驱动因素。这表明白化可能不是直接导致死亡率的原因。我们还在幸存的海绵中发现了微生物群落的转变，我们认为这代表了微生物对 MHWs 的适应反应。我们还发现，C. lamellata 是水柱中溶解有机碳的主要贡献者，其损失可能会影响生态系统功能。我们证明了 MHWs 有潜力在温带地区扰乱关键的海洋门，突出了全球温带海绵可能对 MHWs 有多么敏感。
