Data for Symplegma manuscript

The global increase in frequency and severity of marine heatwaves (MHWs) is highlighting the impact these extreme climatic events can have on marine ecosystems. Throughout the summer of 2021/2022 northeastern Aotearoa/New Zealand suffered an unprecedented MHW. Worst impacted areas, such as the semi-enclosed Te Moananui-ā-Toi/Hauraki Gulf, experienced more than three continual months of temperatures at or above the climatological mean maximum (20.7°C). During this period, we observed a rapid increase in the abundance and cover of the invasive, warm-affinity colonial ascidian Symplegma brakenhielmi on temperate rocky reef. Population expansion of this species has not previously been linked to MHW events. Benthic monitoring as water temperatures cooled showed a sharp decrease in S. brakenhielmi abundance, but not complete disappearance, and the coverage of individually monitored colonies also declined. There was no observed increase in abundance or cover throughout the summer of 2022/2023, a potential consequence of cooler water temperatures and multiple cyclones. Observed impacts included the growth of S. brakenhielmi over other sessile invertebrate and macroalgal species, as well as on highly mobile spiny lobster, suggesting that this species can have a variety of impacts on temperate rocky reefs. These findings highlight how MHW can facilitate the rapid expansion and integration of non-native, warm-affinity species into temperate reef ecosystems and provide insight into what we can expect in the future as ocean temperatures continue to warm.

全球海洋热浪（MHWs）频率与强度的不断上升，凸显了此类极端气候事件对海洋生态系统可能产生的影响。在2021/2022年的整个夏季，新西兰东北部地区遭受了一场史无前例的海洋热浪。受影响最严重的区域，如半封闭的Te Moananui-ā-Toi/Hauraki海湾，经历了连续超过三个月的气温高于或等于气候学平均最高温度（20.7°C）的情况。在此期间，我们观察到入侵性、喜暖性的丛生海鞘Symplegma brakenhielmi在温带岩石礁上的数量和覆盖度急剧增加。该物种种群扩张与之前未曾关联的MHW事件。随着水温的降低，底栖生物监测显示S. brakenhielmi的数量急剧下降，但并未完全消失，且单独监测的种群覆盖度也有所下降。在2022/2023年的整个夏季，未观察到数量或覆盖度的增加，这可能是由于水温较低和多次气旋活动的潜在后果。观察到的后果包括S. brakenhielmi在多种固着性无脊椎动物和大型藻类物种，以及高度移动的棘龙虾上的生长，这表明该物种可以对温带岩石礁产生多种影响。这些发现突显了MHW如何促进非本地、喜暖性物种在温带珊瑚礁生态系统中快速扩张和融合，并为未来随着海洋温度持续变暖我们可能期待的情况提供了洞见。