Ecological subsidies and ecosystem function: the role of dislodged seaweeds in the energy flow between coastal habitats

生态系统可以通过它们之间的能量和物质流动连接起来，这是捐助国和受援国之间的一种生态补贴。在海洋沿海地带，从高产地区（如岩石海岸、盐沼）到生产力极低的地区（如沙滩、泥滩）的生境形成了一个相互关联的马赛克，其能量是由沿海洋流搬运的被移走的植物（如海藻、沼泽草）传递的。一般来说，波浪，尤其是在风暴期间发生的波浪，是造成植物移位的干扰因素，但在高纬度地区，海冰的冲刷可能同样重要，甚至更重要。这种增加的生态因素可以改变生态补贴过程的动态，可能对依赖这种资源的较高营养水平产生影响。

Ecosystems can be connected by the flow of energy and material between them a form of ecological subsidy between donor and recipient areas. In marine coastal zones, habitats ranging from highly productive areas (e.g., rocky shores, salt marshes) to ones with extremely low productivity (e.g., sandy beaches, mud flats) form an interconnected mosaic with energy transferred by the transport of dislodged plants (e.g., seaweeds, marsh grass) by coastal currents. Typically waves, especially those occurring during storms, are the disturbance agents responsible for dislodging plants, but at higher latitudes scouring by sea ice can be equally or even more important. This added ecological factor can alter the dynamics of the process of ecological subsidies with possible consequences for the higher trophic levels that depend on this resource. Although such subsidies have been well recognized and frequently observed in coastal ecosystems, the variation in the temporal and spatial dynamics over which this energy transfer occurs remains largely undocumented. Moreover, the role of disturbance from ice scouring is entirely unknown. Preliminary work in the St. Lawrence maritime estuary has, however, shown a dramatic shift in the timing of the accumulation of dislodged seaweeds on the shore (known as “wrack”) with the dominant pulse occurring in the spring. The general objective of this proposal is to determine the spatio-temporal dynamics of this ecological subsidy, including specific objectives that assess (1) the local seaweed production in source areas and the contrasting disturbance processes dislodging seaweeds; (2) the transport of dislodged seaweeds from these sources areas and their accumulation in sink areas; and (3) the impacts on animal assemblages (e.g., invertebrates, birds) exploiting this resource. The first aspect of this study will be addressed using time series that map seaweed beds in tandem with high-resolution measures of wave forces and ice scouring within the beds. The second aspect will be explored first using the particle-tracking capacities of existing circulation models to predict the likely connections between source and sink areas, and then by the release and recovery of drift cards to empirically validate the model's predictions. The final aspect will be investigated by descriptive and experimental work aimed at documenting the patterns of the deposition of seaweed wrack and manipulating its abundance to determine how the spatial and temporal availability of wrack influences the population dynamics of the detritivores (i.e., invertebrates such as insects, worms, crustaceans) and the predators (e.g., spiders and birds) that depend on this resource. Overall, the proposed research will provide a cradle-to-grave perspective that will allow us to predict how subsidies will respond to environmental change, especially climate-induced changes to sea ice dynamics.