The knotted wrack (Ascophyllum nodosum) is a common seaweed along North Atlantic coastlines. In wave‐sheltered intertidal habitats, A nodosum fronds can reach up to 1.6 meters in length. At high tide, the fronds stay upright in the water column, owing to their gas bladders. When emerged during low tide, the flexible fronds form dense canopies that protect understory organisms like mussels (Mytilus spp) from desiccation and thermal extremes. However, by permanently attaching to the fronds with their byssal threads, mussels might also use the fronds as a high‐tide refuge from benthic predators. In that way, mussels would be relatively safe from predatory crabs, mollusks, and echinoderms during high tide.

Surveying wave‐sheltered locations along the Atlantic coast of Nova Scotia in 2015 and 2016, I repeatedly observed mussel patches (composed of juveniles and adults) attached to the center (left) and the tip (right) of A nodosum fronds. In the benthic zone at nearby locations, I also detected green crabs (Carcinus maenas), dogwhelks (Nucella lapillus), and sea stars (Asterias rubens and Asterias forbesi).

Mussel larvae are known to respond to waterborne cues. For instance, lab experiments have demonstrated that larvae are repelled by cues from benthic predators (indicating predation risk) but attracted to cues from conspecific mussels (indicating suitable habitat for settlement and growth). It would be interesting to determine whether the detected mussel patches resulted from such chemical‐mediated interactions and whether the A nodosum fronds provide a high‐tide refuge facilitating mussel survival from benthic predators.

打结的沉船（Ascophyllum nodosum）是北大西洋沿岸的常见海藻。在波浪遮蔽的潮间带生境中，结节叶的长度可达1.6米。在涨潮时，由于气囊，叶状体在水柱中保持直立。当在退潮时出现时，柔软的叶状体会形成致密的冠层，从而保护诸如贻贝（Mytilus spp）之类的地下生物免受干燥和极端温度的影响。但是，贻贝通过其附生线永久附着在叶状体上，也可能会将叶状体用作底栖食肉​​动物的高潮避难所。这样，贻贝在涨潮时相对免受掠食性螃蟹，软体动物和棘皮动物的危害。

我在2015年和2016年对新斯科舍省大西洋沿岸的避浪地进行了调查，我反复观察到结节叶的中心（左）和尖端（右）附着的贻贝斑块（由少年和成年鸟组成）。在附近位置的底栖地带，我还发现了绿蟹（Carcinus maenas），dog类（Nucella lapillus）和海星（Asterias rubens和Asterias forbesi）。

贻贝幼虫对水基线索有反应。例如，实验室实验表明，幼虫被底栖捕食者的线索击退（表明捕食风险），但被同种贻贝的线索吸引（表明适合定居和生长的栖息地）。确定检测到的贻贝斑块是否是由这种化学介导的相互作用引起的，以及结节叶是否提供高潮庇护所以促进贻贝从底栖捕食者的生存，这将是很有趣的。