Sunflower sea star predation on urchins can facilitate kelp forest recovery

The recent collapse of predatory sunflower sea stars (Pycnopodia helianthoides) due to sea star wasting disease (SSWD) is hypothesized to have contributed to proliferation of sea urchin barrens and losses of kelp forests on the North American West Coast. We used experiments and a model to test whether restored Pycnopodia populations may help recover kelp forests through their consumption of nutritionally poor purple sea urchins (Strongylocentrotus purpuratus) typical of barrens. Pycnopodia consumed 0.68 S. purpuratus day−1, and our model and sensitivity analysis shows that the magnitude of recent Pycnopodia declines is consistent with urchin proliferation after modest sea urchin recruitment, and even small Pycnopodia recoveries could generally lead to lower densities of sea urchins that are consistent with kelp-urchin coexistence. Pycnopodia seem unable to chemically distinguish starved from fed urchins and indeed have higher predation rates on starved urchins due to shorter handling ti..., 1) Sea urchin conditioningData: gonads.xlsxCode: Gonad Index Analysis.RMethod: Our interest was in whether Pycnopodia will prey on S. purpuratus that exist in sea urchin barrens, which have minimal gonad content and low nutritional value to predators. However, S. purpuratus are rare in the San Juan Islands and do not currently form urchin barrens. We therefore used a conditioning protocol to create urchin-barren analog urchins by starving and spawning out urchins and kelp forest analog urchins by feeding the urchins with kelp ad libitum prior to the predation trials, summarized in Supplementary Table 1. We conducted 3 collection dives over July 18-20 at known populations of purple urchin sites near Cattle Pass, Lopez, and San Juan Islands. We collected 300 S. purpuratus from rocky subtidal habitat with healthy bull kelp forests and high flow, in roughly the interquartile range of the sizes we observed in the field; we avoided the largest and smallest of the urchins. The sizes of the ur..., R and R studio近期，捕食性向日葵海星（Pycnopodia helianthoides，sunflower sea star）因海星消瘦病（sea star wasting disease, SSWD）大规模消亡，这一事件被推测是推动北美西海岸紫海胆荒（sea urchin barrens）扩张、海藻林（kelp forests）衰退的关键诱因之一。本研究结合实验与模型模拟，验证了恢复的向日葵海星种群是否可通过捕食营养匮乏的紫海胆（Strongylocentrotus purpuratus，purple sea urchin，这类海胆常见于海胆荒生境），助力海藻林的修复。 研究测得单只向日葵海星的日捕食量为0.68只紫海胆；模型与敏感性分析结果显示，向日葵海星近期的种群衰减幅度，与海胆幼体适度补充情况下的海胆种群扩张特征相吻合；且即便仅实现小幅的向日葵海星种群恢复，通常也可降低海胆种群密度，从而实现海藻与海胆的共存。 此外，向日葵海星似乎无法通过化学信号区分饥饿与饱食的海胆，且由于处理时长更短，其对饥饿海胆的捕食率更高。1）海胆驯化实验 实验数据：gonads.xlsx 代码：Gonad Index Analysis.R 研究方法：本研究旨在探究向日葵海星是否会捕食海胆荒生境中的紫海胆——这类海胆的生殖腺含量极低，对捕食者而言营养价值匮乏。但圣胡安群岛（San Juan Islands）本地的紫海胆种群较为稀少，当前并未形成海胆荒生境。因此，我们采用驯化方案构建两类海胆模型：通过饥饿诱导排精产卵的方式制备海胆荒类似型海胆，通过不限量投喂海带的方式制备海藻林类似型海胆，相关细节详见补充表1。 我们于7月18日至20日期间，在洛佩斯岛（Lopez）的卡特尔通道（Cattle Pass）附近以及圣胡安群岛的已知紫海胆种群分布点开展了3次采集潜水作业。从健康巨藻林且水流充沛的岩质潮下带生境中，采集了300只紫海胆，所选个体的体型处于野外观测到的四分位距范围内，避开了体型过大与过小的个体。海胆体型相关数据……以及R与R Studio软件。