Spatial subsidies often occur from highly productive donor ecosystems to recipient systems with low productivity, but little is known about subsidies between highly productive ecosystems. Here, we investigated whether the kelp Ecklonia radiata, which is frequently dislodged from reefs, provides spatial subsidies in adjacent seagrass meadow where in situ productivity is already high. We clarified the pathways of the allochthonous kelp as a spatial subsidy by adding ¹⁵N-enriched kelp to Posidonia sinuosa seagrass meadows, tracing the uptake of kelp-derived nitrogen by seagrass epiphytes and epifauna. We observed a 32.5–52.2% loss of kelp biomass (wet weight), representing almost 13,000 μg of ¹⁵N from the labelled kelp. This corresponded with an increase in δ¹⁵N and ¹⁵N biomass of detritivores and epiphytes, showing either a direct or indirect (via epiphytes) assimilation of kelp-derived nutrients. The densities and biomass of the gastropod Strigosella lepidus and shrimps were higher in seagrass plots with input of E. radiata, but not for amphipods or the biomass of epiphytes. We estimate that the detritivores and epiphytes in the seagrass plots assimilated about 3% of the ¹⁵N released from the labelled kelp, and based on a data from previous study, the seagrass itself could have assimilated up to a further 6% of the released kelp ¹⁵N. Our findings show that in a highly productive seagrass ecosystem, where autochthonous food sources are available, the input of allochthonous resources such as kelp can supplement those resources and appears to play an important a role as a vector for a spatial subsidy.

从高生产率的捐助者生态系统到低生产率的接收者系统通常会获得空间补贴，但对于高生产率生态系统之间的补贴知之甚少。在这里，我们调查了经常从礁石上移走的海带Ecklonia radiata是否在原位生产力已经很高的相邻海草草甸上提供了空间补贴。我们通过向中华s海藻草地中添加¹⁵个富氮海藻，追踪海藻附生植物和附生动物对海藻来源的氮的吸收，阐明了异体海带作为空间补贴的途径。我们观察到的生物质海带（湿重）的32.5-52.2％的损失，几乎代表了13000微克的¹⁵N来自标记的海带。这相当于与增加δ ¹⁵ N和^15个食碎屑和附生N个生物量，示出海带衍生的营养物质中的任一个直接或间接（通过附生植物）同化。密度和生物量的腹小号trigosella莱皮杜斯和虾海草地块较高与输入E.辐射，但不能用于片脚或附生植物的生物量。我们估计海草样地中的有害生物和附生植物吸收了标记海带释放的¹⁵ N中的约3％，并且根据先前研究的数据，海草本身可能吸收了多达6％的海藻吸收了¹⁵N.我们的发现表明，在拥有高产海藻食物资源的高产海草生态系统中，海藻等异源资源的输入可以补充这些资源，并在空间补贴中起着重要作用。