Marine biodiversity-ecosystem processes under uncertain environmental futures

海洋沿海生态系统是地球上最多产和最多样化的群落之一。海洋生态系统内的生物和地球化学过程对于调节气候、营养循环和食物链非常重要。海洋生态系统为人类提供了许多资源，如饮用水、食物和氧气，以及吸收二氧化碳(CO2)等气体。从大气中去除二氧化碳很重要，因为它是一种与全球变暖有关的温室气体。许多人类活动，如运输和取暖，都涉及燃烧化石燃料，向大气中释放二氧化碳，这些二氧化碳最终将被海洋吸收。这正在造成河口和海岸水域的化学变化，影响海洋生物本身、水的化学缓冲能力以及大气吸收二氧化碳的潜力。迄今为止的所有证据都表明，在可预见的未来，我们将经历全球气温和大气二氧化碳水平的进一步上升，以及生物多样性的减少。因此，重要的是要了解生物多样性和生态系统过程之间的关系在不同的温度和二氧化碳条件下可能会发生怎样的变化。最近的研究集中在找出生态系统过程如何随着生物多样性的减少而变化。已经在实验室中进行了模拟生物多样性丧失的实验，方法是在水族馆中聚集不同数量的物种，并在受控的环境条件下测量每种物种的混合物对生态系统过程的影响。通过比较物种较多的水族馆和物种较少的水族馆，可以确定物种从一个系统中消失的影响。该项目将采用类似的方法，将生活在河口沉积物中的小动物暴露在不同的环境制度(二氧化碳和温度)下。这些生物在海洋生态系统中特别重要，因为它们从底部搅动沉积物--这一过程被称为生物扰动--导致营养物质返回水柱。然后，这些营养物质就可以用来支持浮游植物的生长，浮游植物是海洋食物网的大部分食物能量的来源。在我们的实验中，我们将记录由于生物扰动而从沉积物释放到水中的各种营养物质的水平。我们还将使用被称为发光体的颜色鲜艳的沉积物颗粒直接测量生物扰动的程度。随着动物的生物扰动，它们会将其中一些颗粒移动到沉积物中更深的地方。在实验结束时，可以通过从水族馆的不同深度提取沉积物并计算发光体的数量来恢复这些发光物质。通过这些实验，我们将能够确定不同物种混合物移动沉积物的模式、速度和幅度，并确定这对营养循环的影响。通过将营养和生物扰动数据与物种数量和环境条件相匹配，我们将能够预测未来生物多样性丧失对生态系统过程的可能后果。在预测未来模式时，包括与预测相关的不确定性水平的信息也很重要。我们的实验将使我们能够量化这种不确定性(通过在一组特定条件下获得的值的范围)，从而识别我们可以对预测最有信心和最不自信的温度和二氧化碳的组合。这类研究的结果将对评估和管理海洋系统的变化具有直接意义，并为决策者提供有关未来环境变化的潜在影响的重要信息。

Marine coastal ecosystems are among the most productive and diverse communities on Earth. Biological and geochemical processes within marine ecosystems are important for regulating climate, nutrient cycling and the food chain. Marine ecosystems provide humans with many resources such as drinking water, food and oxygen, as well as absorbing gases, such as carbon dioxide (CO2). Removal of CO2 from the atmosphere is important because it is a greenhouse gas that is linked to global warming. Many human activities, such as transportation and the heating of our homes, involve the burning of fossil fuels that release carbon dioxide into the atmosphere, which will eventually be absorbed by the oceans. This is causing chemical changes in the waters of our estuaries and coasts that affect marine organisms themselves, the chemical buffering capacity of the water, and the potential for atmospheric CO2 absorption. All evidence to date suggests that, for the foreseeable future, we will experience further increases in global temperature and levels of atmospheric CO2, combined with decreases in biodiversity. Therefore it is important to understand how the relationship between biodiversity and ecosystem processes may change under different temperature and CO2 conditions. Recent research has focussed on finding out how ecosystem processes alter with decreasing biodiversity. Experiments have been performed in the laboratory which mimic biodiversity loss by assembling different numbers of species in aquaria and measuring the effect each species mixture has on ecosystem processes under controlled environmental conditions. By comparing aquaria with many species to those containing fewer species, the impact of species loss from a system can be determined. This project will adopt a similar approach, by exposing small animals that live in the sediments of estuaries to different environmental regimes (CO2 and temperature). These organisms are particularly important within marine ecosystems because they churn up sediments from the bottom - a process referred to as bioturbation - which results in nutrients being returned to the water column. These nutrients are then available to support the growth of phytoplankton, which are the source of food energy for much of the ocean's food web. In our experiments, we will record the levels of various nutrients that are released into the water from the sediment as a result of bioturbation. We will also measure the extent of bioturbation directly using brightly coloured sediment particles called luminophores. As the animals bioturbate, they will move some of these particles deeper into the sediment. These can be recovered at the end of the experiment by taking sediment from different depths of the aquarium and counting the number of luminophores. From these experiments, we will be able to define the pattern, rate and magnitude with which different species mixtures move sediments and determine the impact of this on nutrient cycling. By matching the nutrient and bioturbation data with the number of species and environmental conditions, we will be able to predict the likely consequences of future biodiversity loss on ecosystem processes. When predicting future patterns, it is also important to include information on the level of uncertainty associated with the predictions. Our experiments will enable us to quantify this uncertainty (through the range of values obtained under a specific set of conditions), and therefore to identify those combinations of temperature and CO2 for which we can be most and least confident in our predictions. The outcomes of such research will have immediate relevance for assessing and managing change in marine systems, and provide important information for policy makers concerning the potential impacts of future environmental change.