In previous work, Dr. Heck and collaborators assessed the importance of short-term grazing by sea urchins, and bioturbation by sand dollars in a seagrass habitat in the northern Gulf. Based on results of this effort and newly published information, they will now initiate additional field experiments in the northern Gulf of Mexico, as well as studies at a south Florida site, to identify more precisely the densities of sea urchins and the duration of herbivory required to permanently create unvegetated sand flats. Together these two sites represents the northern and southern extents of some of the most extensive seagrass habitats in the United States, encompassing some 14,000 Km2. Additionally, they will continue assessing the role of bioturbation of the seagrass rhizosphere by sand dollars, and the potential interaction between sand dollar bioturbation and sea urchin herbivory in limiting the distribution of seagrass habitats. They will carry out the first experimental examination of the ability of stringrays and burrowing crabs to create and maintain unvegetated sand flats within otherwise suitable habitat for seagrasses. The work will improve our understanding of the variables involved in maintaining habitat and mosaics, and those that facilitate changes between alternative community states (e.g. seagrass meadows and sand flats) which in turn can lead to drastic shifts in primary and secondary productivity.
