Collaborative Research: The tropicalization of Western Atlantic seagrass beds

温带海洋群落的变暖正在成为一种全球现象，产生了新的生物相互作用，可能导致对生态系统结构的一系列级联效应。例如，食草动物种群向极地扩张可能导致形成栖息地的植被消耗，从而改变沿海环境提供的生态服务（一种被称为热带化的现象）。许多处于危险中的栖息地，如海带林和海草床，提供了支持复杂食物网的基础栖息地。墨西哥湾沿岸的海草草甸目前正经历着热带食草动物的涌入，然而，对这些群落最终可能如何应对的综合理解却缺乏。这个项目描述了第一个量化热带化对广泛分布的海草生态的破坏性影响的实验。该项目的一个主要贡献将是发展一个海草研究合作网络，作为更广泛的科学探究和未来合作的平台。这项合作涵盖了总共11个机构，这个网络将促进初级和高级科学家以及许多本科生和研究生之间的广泛合作。鉴于这项工作的地理范围，研究小组将通过举办一系列公开讲座和科学讲座活动，进一步寻求在整个网络上推广海洋生态和保护主题的机会。这项研究将在加勒比海地区开展大规模的操纵实验，以15个海洋站点的比较网络为前提，量化温度和光线如何与食草动物对主要热带海草——海草的影响相互作用。研究人员沿着纬度梯度（从百慕大到巴拿马）选择了地点，这样光照和温度就会发生变化，从而使研究人员能够测试非生物因素对增加放牧的生态效应的影响（通过人工剪叶模拟热带化）。在15个海洋试验点中，放牧处理将与营养处理相交叉，在因子设计中进行18周，之后将通过测量面积生产力、芽密度、地上生物量和碳水化合物储量来评估海草的结构和功能。实验将分别在非生物梯度最弱和最强的夏季和冬季进行。分层混合模型和结构方程模型中的新兴统计技术将进一步允许实验和观测数据的整合。

The warming of temperate marine communities is becoming a global phenomenon, producing new biotic interactions that can result in a series of cascading effects on ecosystem structure. For example, the poleward expansion of herbivore populations can lead to the consumption of habitat-forming vegetation, which alters the ecological services provided by coastal environments (a phenomenon known as tropicalization). Many of the habitats at risk, such as kelp forest and seagrass beds, provide foundational habitat that supports complex food webs. Seagrass meadows along the Gulf of Mexico are currently experiencing an influx of tropical grazers, however a integrated understanding of how these communities might ultimately respond is lacking. This project describes the first experiment to quantify the disruptive effect of tropicalization on the ecology of a widely-distributed seagrass. A major contribution of this project will be the development of a seagrass research collaborative network to serve as a platform for broader scientific inquiry and future collaboration. The collaboration spans a total of 11 institutions, and this network will foster extensive collaborations among junior and senior scientists, as well as many undergraduate and graduate students. Given the geographic scope of this work, the research team will further pursue outreach opportunities across the network by hosting a series of public lectures and science café events promoting topics in marine ecology and conservation. This study will develop a large-scale manipulative experiment across the Caribbean, premised upon a comparative network of 15 marine sites, which will quantify how temperature and light interact with grazer effects on the dominant tropical seagrass, Thalassia testudinum. Sites have been selected along a latitudinal gradient (from Bermuda to Panama), such that light and temperature vary, allowing the investigators to test for the effects of abiotic factors on the ecological effects of increased grazing (tropicalization simulated via artificial leaf clipping). At each of the 15 marine sites, grazing treatments will be crossed with nutrient manipulations in a factorial design for 18 weeks, after which seagrass structure and functioning will be assessed via measurements of areal productivity, shoot density, aboveground biomass, and carbohydrate storage. Experiments will be conducted both in the summer and winter seasons, when abiotic gradients are at their weakest and strongest, respectively. Emerging statistical techniques in hierarchical mixed modeling and structural equation modeling will further allow for integration of experimental and observational data.