Rock pool ecosystems provide opportunities to test metacommunity theory and to evaluate the importance of disturbance to community structure and diversity. They offer discrete, niche habitats for many terrestrial and aquatic species. Plants and algae are quick to establish themselves in these pools, and for many egg-laying species, these habitats are important havens in which their offspring can hatch and develop. They are also highly dynamic systems. As the height of the river changes, pools can become completely submerged or exposed, in turn disturbing the micro-ecosystems established in the affected rock pools. According to the intermediate disturbance hypothesis, occasional flooding disturbances help reduce the populations of dominant species and allow other species the chance to establish themselves, leading to an increase in local species diversity. These flooding events are likely to increase in frequency and/or intensity as climate changes. To gain a better understanding of the role these disturbances have on shaping the ecological community, we studied a river rock system along the James River in Richmond, Virginia. The frequency of pool disturbance was determined using data collected on site from field surveys and drone imagery in addition to USGS river gage data for the past 25 years. Biodiversity data were collected using dip net sampling of the pools from 2012 to 2017. The flooding frequency for each of nearly 300 pools was then compared to the Simpson's Index value for species diversity of the pool as a test of the intermediate disturbance hypothesis.
Results/Conclusions
The frequency of flooding varied among the rock pools from over 50 times per year to once every few years. Species richness ranged from 1 to 14 species per pool with Simpson’s Diversity Indices ranging from 0 to 0.89. Annual variability in community composition for pools sampled in multiple years was nearly equivalent to the variability among pools. For a given year, pool diversity was associated with flood frequency peaking at pools with intermediate flood recurrence intervals. The findings were consistent with theory that suggests that intermediate disturbance frequencies increase diversity by opening up resources and introducing or removing organisms from the pool. Should flood frequency increase due to climate change, certain species may not have enough time between events to establish themselves, causing significant shifts in the community structure and overall diversity of the rock pool.