Between a rock and a soft place: surfgrass colonizes sediments without attachment to rock

The complex coastline that stretches from Southeast Alaska to the Salish Sea hosts an expansive and verdant bathtub ring of seagrasses. Their presence is facilitated by the geographic complexity of the region, which promotes a variety of suitable substrates that are appropriate for seagrass recruitment (mud to sands to rock within small spatial scales). Seagrasses are marine flowering plants that have evolved at least three times from land plants back to the sea (Les et al. 1997). Although several adaptations have allowed for them to recolonize marine environments, they still rely upon rhizome and root structures for nutrient uptake and storage, gas exchange, and anchoring to substrates. These structures are reminiscent of their terrestrial ancestors, by which the rhizomes and roots of most species form belowground networks in soft-sediments but sometimes exhibit plasticity in anchoring strategy, where a minority of species can also colonize rocky substrates. In such instances, attachment is secured via the secretion of an adhesive, mucilage from the plant's roots (see Appendix S1: Table S1). Of the 72 species of seagrass, there are only five (genus Phyllospadix) described to use rock as an obligate substrate (summarized by Balestri et al. 2015). Their niche is further differentiated from other seagrasses in that they prefer habitat with higher wave exposure and, as such, they are commonly referred to as "surfgrasses". This article is protected by copyright. All rights reserved.