Abstract

This paper examines how community-level facilitation by macroalgal foundation species changes with environmental stress. In rocky intertidal habitats, abiotic stress (mainly due to desiccation and thermal extremes during low tides) increases sharply with elevation because of tide dynamics. A previous study done on the Atlantic coast of Nova Scotia (Canada) showed that, at low elevations, where conditions are benign because low tides are brief, fucoid algal canopies (Ascophyllum nodosum and Fucus spp.) do not affect the structure of benthic communities. However, at middle and high elevations, where low tides last longer, fucoid canopies limit abiotic extremes near the substrate and, in that way, increase the richness of benthic communities. Richness was measured as the number of benthic algal (except fucoids) and invertebrate species found in replicate quadrats. Using the published data from that study, the present study compares the intensity of facilitation and its importance (relative to all other sources of variation in richness) between middle and high elevations, which represent intermediate and high stress, respectively. Facilitation intensity was calculated as the percent increase in benthic richness between quadrats with low canopy cover and quadrats with high canopy cover, while the importance of facilitation was calculated as the percentage of observed variation in richness that was explained by canopy cover. Data for a total of 688 quadrats surveyed along 350 km of coastline were used. The analyses revealed that both the intensity and importance of facilitation were greater at middle elevations than at high elevations. As canopies were previously found not to affect benthic communities at low elevations, this study indicates that the facilitation-stress relationship viewed at the community level is unimodal for this marine system. Such a trend was already found for some terrestrial systems involving canopy-forming plants as foundation species. Thus, this unimodal pattern may be ubiquitous in nature and, as further studies refine it, might help to predict community-level facilitation depending on environmental stress.

Talk to us

Join us for a 30 min session where you can share your feedback and ask us any queries you have

Schedule a call

Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.