The effect of habitat and herbivory on an intertidal alga: Potential impacts of climate change on algal distribution

The processes that shape species distributions are particularly crucial to understand, as global warming is altering the earth’s climate, and species distributions are shifting in response.  Species’ distributions are often limited by propagule dispersal, biotic, and abiotic factors. This study used experimental manipulations of herbivory and habitat to examine the factors that determine the propagule survival of a marine alga, Pelvetiopsis limitata, common in the rocky intertidal between Vancouver Island, British Columbia, and Point Conception, California.  This Fucoid alga occupies the zone at the highest tidal elevation on the shore and is likely to experience increased desiccation stress due to climate change. Plastic settling plates were deployed in the intertidal area of the Bodega Marine Reserve in a factorial design in sites that differed in wave exposure, tidal height, and aspect (north-facing or south-facing slopes). Grazing herbivores were excluded from half of all treatments using barriers of copper paint. A standardized mass of reproductive adult tissue was held on top of each plate by a piece of plastic mesh, and established embryos were counted one month later.  Our results indicate that embryo survival depends on habitat characteristics and accessibility to herbivores. Determining the factors that limit species distributions is crucial in predicting species response to climate change.