M.S. Marine Biology
Richard E. Spieler
David S. Gilliam
The 3-dimensional structural complexity of coral reef environments is positively correlated with measurements of biodiversity and biomass. EcoReefs are a type of artificial reef that resemble branching corals, such as Acropora cervicornis, which provide an environment of high structural diversity, and that are effective at recruiting and sustaining fish populations. Little is known, however, about the effects of EcoReefs on the surrounding environments in which they are deployed, so this study examined the results after installing Ecoreef modules in a seagrass environment. The installation occurred in March 2009 at Coco Cay in the Berry Island chain in the Bahamas and data was taken over the next two years to compare changes on Ecoreef deployment sites (experimental sites) to sites with no EcoReefs (control sites) and also an older and larger installation with both EcoReefs and Reefballs (Old Reef) that dates back to 2004. Two main categories of information were collected: at the same time (a) the changes in growth of two types of seagrass, Thalassia testudinum and Syringodium filiforme, and (b) the changes in fish populations in and around the EcoReef installations. Experimental sites consisted of 3 groups, 30-35 metres apart, each of 12 EcoReef modules in seagrass beds off the east side of the island. Both seagrass and fish data were collected within the module groups and also for the area 1 metre around the installation to see if there were any “halo” effects, i.e. where seagrass around a reef is cleared by resident fish populations. Seagrass measurements including direct measurements of blade length, width, percentage of epiphytic fauna, and the percentage of dead tissue on each blade were collected. Seagrass coverage was also estimated using a photographic technique. Fish counts were performed using a modified Bohnsack-Bannerot visual survey method, and augmented with transect counts. The results for seagrass indicated that there were some seasonal changes in growth and coverage. Fish populations accumulated rapidly on the Ecoreef modules: at the first-post installation collection data period 4 month later the experimental site fish populations were between 30 and 153 individuals, and remained at this level throughout the study, with a mean population per site of 84.4 individuals over the length of the study. Over the study period it was found that the majority of the fish (67%) on the experimental sites were haemulid, and scarid juveniles of less than 5 cm in length, in contrast to the older and larger mixed reef that had 73% above 5cm, including a stable population of 184 (+/- 24.5) grunts. The older site also had a distinct halo zone of cleared and cropped seagrass, whereas no halo zone was visible at the experimental or control sites, suggesting that the abundance and size of the fish establish and maintain this zone. The results from this study suggest that EcoReefs modules foster fish populations and cause changes in seagrass length, but do not result in the formation of a halo zone directly; the formation of this zone, where present, is likely the result of the fish species that settle on these structures.
Joseph M. Penta. 2013. Changes in a Tropical Seagrass Environment After Installation of Small Artificial Reefs. Master's thesis. Nova Southeastern University. Retrieved from NSUWorks, Oceanographic Center. (157)