Seaweed - epiphyte - mesograzer communities were tested for their responses to moderate nutrient enrichment and combined elevated seawater temperature and [CO2] in benthic mesocosm experiments in Kiel during summer

Coastal marine ecosystems have been under high anthropogenic pressure and it can be assumed that prevalent local perturbation interacts with rising global stressors under proceeding climate change. Understanding their effective pathways and cumulative effects is of high relevance not only with regard to future risk assessment, but also for current ecosystem management. In benthic mesocosms, we factorially tested the effects of one global (combined elevated seawater temperature and CO2 concentration) and one local (nutrient enrichment) stressor on a common coastal Baltic seaweed system (Fucus vesiculosus). Both treatments in combination had additive negative impacts on the seaweed-epiphyte-mesograzer system by altering its regulatory mechanisms. That is, warming decreased the biomass of two mesograzer species (weakened top-down control), whereas moderate nutrient enrichment increased epiphyte biomass (intensified bottom-up control), which ultimately resulted in a significant biomass reduction of the foundation seaweed. Our results suggest that climate change impacts might be underestimated if local pressures are disregarded. Furthermore, they give implication for local ecological management as the mitigation of local perturbation may limit climate change impacts on marine ecosystems.

近岸海洋生态系统长期承受高强度的人为干扰压力，且可以推测，在气候变化持续推进的背景下，普遍存在的局部扰动会与日益加剧的全球环境压力因子产生交互作用。厘清这些交互作用的有效传导路径与累积效应，不仅对未来生态风险评估具有重要意义，同时也可为当前的海洋生态系统管理提供科学支撑。本研究在底栖中型实验生态系统（benthic mesocosms）中，采用析因实验设计，探究了两类环境压力因子对波罗的海常见海藻群落——泡叶藻（Fucus vesiculosus）的影响：一类为全球尺度压力因子（海水温度与二氧化碳浓度协同升高），另一类为局地尺度压力因子（营养盐富集）。两类压力因子的联合作用通过改变该海藻-附生藻类-中小型底栖消费者系统的调控机制，对其产生了叠加性负面影响。具体而言，海水升温会降低两种中小型底栖消费者的生物量（削弱了下行调控作用）；而适度的营养盐富集则会提升附生藻类的生物量（强化了上行调控作用），最终导致作为建群种的泡叶藻生物量出现显著下降。本研究结果表明，若忽略局地环境压力，可能会低估气候变化对海洋生态系统的实际影响。此外，本研究结果也为局地生态管理提供了启示：缓解局部人为扰动，或可有效降低气候变化对近岸海洋生态系统的负面影响。