Relative abundances of sessile species (seaweeds and sessile invertebrates) in subtidal communities.

<p>North and south refer to the biogeographical barrier at Cape Cod, Massachusetts. Species listed comprised 80% of the overall community, and data are means ±1 At each site, a 20 m transect was haphazardly placed in the subtidal zone, at approximately the mid point of the species’ typical depth range (mean depth = 2.0±0.11 m). We placed a 0.0625 m² quadrat every 2 m along the transect. Within each quadrat, the percent cover of each macroalgal and sessile invertebrate species was recorded. When present, a subsample of <i>Heterosiphonia</i> individuals was collected from each site. Upon collection, specimens were returned to the laboratory, where field identifications were confirmed under a compound microscope (100X) using characteristics from Schneider <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0062261#pone.0062261-Schneider1" target="_blank">[8]</a>. All individuals collected were either vegetative or tetrasporic. No fertile gametophytes were found during our sampling. At an additional 12 sites within our subtidal survey range, we examined the intertidal and/or shallow subtidal zone for evidence of drifting <i>Heterosiphonia</i> individuals. At each of these sites, individuals were collected and identified under a field microscope (40X) or laboratory microscope (100X). Due to logistical constraints, we clustered all crustose coralline algal species together, as <i>in situ</i> identifications to the species level proved impossible for this group. When possible, a subsample of <i>Heterosiphonia</i> individuals from most locations was pressed and deposited in the University of Rhode Island (KIRI) or Northeastern University (HNUB) herbarium collections.