Social-Ecological System of La Parguera
Social-Ecological System of La Parguera Bleaching events
Figure 29. Grounding on Margarita Reef, La Parguera and damage to coral September 2009 (photo credit M. Nemeth).
matter, González-Liboy (1979) reported intense impacts in the channel near Magueyes Island that caused significant patchiness of seagrass beds in this area. More recently, Otero and Carrubba (2006) documented major propeller scar impacts in various locations including shallow areas near Magueyes Island, Cayo Caracoles and Cayo Collado back reefs, where 43-74% of the area potentially affected by boat traffic showed damage due to propeller scarring. Uhrin and Holmquist (2003) found that shrimp and mollusk abundances were lower in scars compared to the undisturbed areas, although the impacts to the seagrass community at a larger scale were not determined. In addition, boating impacts are prevalent in the back reefs of keys and in shallow channels due to the heavy transit of vessels (Otero and Carrubba 2006). Some areas of La Parguera are consistently impacted by large numbers of vessels that anchor, scar the seafloor, and re-suspend sediments in shallow marine habitats (Figure 28). Over the years, several emergent coral reefs have been impacted by recreational vessel groundings. At least two recreational vessels grounded during the past 5 years in La Parguera. Part of one of these vessels hull was pushed onto the back reef zone of Corral reef and another was removed from Margarita Reef (Figure 29), both important fishing areas and perceived as having a high biodiversity. As a response to these events, an emergency restoration was conducted by the NOAA Restoration Center at the latter site to re-attach corals to the fore-reef. However the extent of groundings similar to these on the reefs of La Parguera is hard to determine due to the lack of reports and documentation. Quantification of the impacts of recreational use upon the habitats of La Parguera is essential for appropriate assessment of the ecosystem. 4.3 Global scale disturbances It is widely accepted that bleaching and coral reef infectious diseases are two factors that have become major players in the deterioration of coral reef condition over the last two decades (Weil 2004). CRES researchers devoted a considerable amount of effort studying the prevalence and distribution of these conditions in La Parguera. Coral diseases and syndromes generally occur in response to biotic stresses such as bacteria, fungi and viruses, and/or abiotic stresses such as increased seawater temperatures, ultraviolet radiation, sedimentation, and pollutants. The patchiness and irregular distribution of coral diseases and bleaching is related to differences in the distribution, composition, and abundances of susceptible species and the environmental conditions and susceptibility of hosts and/or pathogens to disturbed environments (Appeldoorn et al. 2009). 58
Bleaching is the whitening of corals and other endosymbiotic taxa due to the expulsion of photosynthetic symbiotic algae. The intensity and frequency of bleaching has increased during the last three decades in La Parguera, after the benchmark observations made by Goenaga et al. (1989). Although a number of environmental conditions may lead to bleaching, temperature is widely accepted as one of the primary causes (Hoegh-Guldberg et al. 2007). Data from La Parguera of 1966 to 1995 indicate that there is a strong relationship between severe bleaching and cumulative heat stress, but reports do not necessarily indicate the exact mechanisms correlating temperature to the onset or severity of bleaching (Winter et al. 1998). Mass bleaching events have occurred periodically worldwide, and in the Caribbean at least seven recent events have been reported. Puerto Rico had various bleaching events since 1985, four of which occurred between 1998 and 2006. Bleaching has been observed under slightly elevated sea surface temperatures, extended periods of calm seas, clears skies and high water transparency which increase the penetration of solar radiation (Goenaga et al. 1989, Winter et al. 1998). The assessment of the 2005 bleaching event in southwest and west Puerto Rico by Hernández-Delgado revealed that 65% of 4,000 corals examined exhibited bleaching, with highest occurrence of bleaching found in La Parguera of which 42% were fully bleached and 31% partially bleached (García-Sais et al. 2008). While most attention has been given to the coral species of the Scleractinian taxa, a number of studies in Puerto Rico and La Parguera have observed the physiology and behavior of octocorals, species that show a slightly different response to environmental stressors. Prada et al. (2009) surveyed La Parguera octocorals in in November of 2005, noticing that a number of them showed different levels of susceptibility to bleaching, suggesting differences in temporal patterns which implies a higher tolerance to thermal stress of octocorals compared to the other major cnidarian taxa. It follows that bleaching of octocorals was preceded by bleaching in scleractinian corals, hydrocorals, and the some zoanthid species (Prada et al. 2009). In La Parguera, the combined effect of the 2005 bleaching event and mortality due to subsequent disease, led to a failure of sexual reproduction in Acropora spp. and Montastraea spp. in 2006, as reported by Ballantine et al. (2008).That same year (2005) researchers conducted a survey to assess the extent of coral mass mortality after the bleaching event, to find out that La Parguera exhibited a higher percentage of partial mortality (5.4%) when compared to sites off the west coast 1.4 - 2.8% (García-Sais et al. 2008). Indeed, coral mortality was compounded by outbreaks of white plague type II (WP-II) and yellow band disease (YBD) that seemed to target the Montastraea species complex after the peak of the 2005-bleaching event. The colonies of Montastraea spp. experienced a massive loss of live tissue (an average of 50-60%) at the intermediate and deeper habitats of Turrumote Reef in that same period (García-Sais et al. 2008). These rather dramatic effects of bleaching on the coral reef communities are characterized by a suite of physiological responses that include: (1) death, (2) increased vulnerability to disease, (3) reduced reproduction and (4) shifts in community structure (Edmunds 2000, Harvell et al. 2002, Weil et al. 2009). Diseases Since the mid 1990’s, coral reef disease research in Puerto Rico has yielded important information on the number, distribution, prevalence, and impact of the most common diseases. 59
