Bunting Imogen, Bornemann Santamaría Laura, Kok Yun Yi, Krieger Erik C, Mullarney Julia C, D'Archino Roberta, Cornwall Christopher E
School of Biological Sciences, and Coastal People Southern Skies Centre of Research Excellence, Victoria University of Wellington Te Herenga Waka, Wellington, New Zealand.
National Institute of Water and Atmosphere Research Taihoro Nukurangi, Wellington, New Zealand.
J Phycol. 2025 Jul 18. doi: 10.1111/jpy.70054.
Coastal regions are complex habitats, where multiple natural and anthropogenic drivers can interact to affect the survival and growth of marine organisms. The giant kelp Macrocystis pyrifera is sensitive to increasing seawater temperatures and susceptible to marine heatwaves. Light availability and hydrodynamics can also affect the growth, morphology, and resilience of this species. In this experiment, juvenile sporophytes of M. pyrifera from Scorching Bay, Wellington, Aotearoa, New Zealand, a were exposed to a combination of simulated marine heatwaves at one of four different temperatures (20, 22, and 24°C compared to a 16°C control), one of two irradiance levels (shaded: 0.9 mol photons · m · d or ambient: 1.4 mol photons · m · d), and one of two flow speeds (5.3 cm · s or 6.1 cm · s) in a fully factorial design. Simulated heatwaves lasted for 21 days, with temperatures ramped by 2°C · d, followed by a 21-day recovery phase. The heatwave treatments represented severe heatwaves in present day or hypothetical future conditions, whereas the control represented historical average summer sea temperatures in Wellington, and 21 days represented a realistic duration for heatwaves in this region. Temperature was the main driver of negative physiological impacts, with 100% of sporophytes dying within 42 days of exposure to a 24°C heatwave. Sporophytes experienced 44% mortality at 20°C and 81% mortality at 22°C, and growth rates declined significantly with increasing temperature. However, survival rates were modified by light and water velocity, with 56% of sporophytes surviving under a combination of ambient light and fast water velocity, compared with less than 50% under each of the other light-velocity combinations. Light limitation also reduced sporophyte survival, growth rates, and effective quantum yield. Water velocity alone did not significantly affect sporophytes, but flow speeds had interactive effects with temperature and light. The findings of this experiment suggest that M. pyrifera at sites with optimal environmental conditions, including low sediment loads and fast tidal flows, could be more resilient to marine heatwaves, as long as temperatures do not exceed critical thresholds for survival.
沿海地区是复杂的栖息地，多种自然和人为驱动因素可能相互作用，影响海洋生物的生存和生长。巨型海带巨藻对海水温度升高敏感，易受海洋热浪影响。光照可用性和水动力也会影响该物种的生长、形态和恢复力。在本实验中，来自新西兰奥特亚罗瓦惠灵顿炽热湾的巨藻幼年孢子体，在完全析因设计中，被暴露于四种不同温度（与16°C对照相比，分别为20、22和24°C）之一的模拟海洋热浪、两种辐照度水平（遮荫：0.9摩尔光子·米·天或环境：1.4摩尔光子·米·天）之一以及两种流速（5.3厘米·秒或6.1厘米·秒）之一的组合条件下。模拟热浪持续21天，温度以每天2°C的速度上升，随后是21天的恢复阶段。热浪处理代表当今或假设未来条件下的严重热浪，而对照代表惠灵顿历史平均夏季海温，21天代表该地区热浪的实际持续时间。温度是负面生理影响的主要驱动因素，100%的孢子体在暴露于24°C热浪的42天内死亡。孢子体在20°C时死亡率为44%，在22°C时死亡率为81%，生长速率随温度升高而显著下降。然而，存活率受到光照和水流速度的影响，在环境光和快速水流速度的组合下，56%的孢子体存活，而在其他光照 - 速度组合下，存活率均低于50%。光照限制也降低了孢子体的存活率、生长速率和有效量子产率。单独的水流速度对孢子体没有显著影响，但流速与温度和光照有交互作用。本实验结果表明，只要温度不超过生存的临界阈值，处于包括低沉积物负荷和快速潮汐流等最佳环境条件地点的巨藻，可能对海洋热浪更具恢复力。
