Infantes Eduardo, Crouzy Caroline, Moksnes Per-Olav
Department of Marine Sciences, University of Gothenburg, Gothenburg, Sweden.
PLoS One. 2016 Dec 15;11(12):e0168128. doi: 10.1371/journal.pone.0168128. eCollection 2016.
There is an increasing interest to restore the ecosystem services that eelgrass provides, after their continuous worldwide decline. Most attempts to restore eelgrass using seeds are challenged by very high seed losses and the reasons for these losses are not all clear. We assess the impact of predation on seed loss and eelgrass establishment, and explore methods to decrease seed loss during restoration in the Swedish northwest coast. In a laboratory study we identified three previously undescribed seed predators, the shore crab Carcinus maenas, the hermit crab Pagurus bernhardus and the sea urchin Strongylocentrotus droebachiensis, of which shore crabs consumed 2-7 times more seeds than the other two species. The importance of shore crabs as seed predators was supported in field cage experiments where one enclosed crab caused 73% loss of seeds over a 1-week period on average (~ 21 seeds per day). Seedling establishment was significantly higher (14%) in cages that excluded predators over an 8-month period than in uncaged plots and cages that allowed predators but prevented seed-transport (0.5%), suggesting that seed predation constitutes a major source of seed loss in the study area. Burying the seeds 2 cm below the sediment surface prevented seed predation in the laboratory and decreased predation in the field, constituting a way to decrease seed loss during restoration. Shore crabs may act as a key feedback mechanism that prevent the return of eelgrass both by direct consumption of eelgrass seeds and as a predator of algal mesograzers, allowing algal mats to overgrow eelgrass beds. This shore crab feedback mechanism could become self-generating by promoting the growth of its own nursery habitat (algal mats) and by decreasing the nursery habitat (seagrass meadow) of its dominant predator (cod). This double feedback-loop is supported by a strong increase of shore crab abundance in the last decades and may partly explain the regime shift in vegetation observed along the Swedish west coast.
在全球范围内鳗草持续减少之后，恢复鳗草所提供的生态系统服务的兴趣日益浓厚。大多数使用种子恢复鳗草的尝试都面临着极高的种子损失挑战，而这些损失的原因并不完全清楚。我们评估了捕食对种子损失和鳗草定植的影响，并探索了减少瑞典西北海岸恢复过程中种子损失的方法。在一项实验室研究中，我们确定了三种先前未描述过的种子捕食者，即滨蟹（Carcinus maenas）、寄居蟹（Pagurus bernhardus）和海胆（Strongylocentrotus droebachiensis），其中滨蟹消耗的种子比其他两个物种多2至7倍。在野外网箱实验中，滨蟹作为种子捕食者的重要性得到了证实，在为期1周的时间里，一只封闭在网箱中的滨蟹平均导致73%的种子损失（每天约21颗种子）。在8个月的时间里，排除捕食者的网箱中的幼苗定植率（14%）显著高于未设网箱的地块以及允许捕食者但阻止种子传播的网箱（0.5%），这表明种子捕食是研究区域种子损失的主要来源。在实验室中，将种子埋在沉积物表面以下2厘米可防止种子被捕食，在野外也能减少捕食，这是一种在恢复过程中减少种子损失的方法。滨蟹可能通过直接食用鳗草种子以及作为藻类中食草动物的捕食者，充当阻止鳗草回归的关键反馈机制，使藻垫过度生长在鳗草床上。这种滨蟹反馈机制可能通过促进自身育苗栖息地（藻垫）的生长以及减少其主要捕食者（鳕鱼）的育苗栖息地（海草草甸）而自我强化。过去几十年滨蟹数量的大幅增加支持了这种双重反馈循环，这可能部分解释了瑞典西海岸观察到的植被状态转变。
