Mid-term coral-algal dynamics and conservation status of a Gorgona Island (Tropical Eastern Pacific) coral reef

Fernando A Zapata,Alberto Rodríguez-Ramírez,Carlos Caro-Zambrano,Jaime Garzón-Ferreira

doi:10.15517/rbt.v58i1.20025

Abstract

Colombian coral reefs, as other reefs worldwide, have deteriorated significantly during the last few decades due to both natural and anthropogenic disturbances. The National Monitoring System for Coral Reefs in Colombia (SIMAC) was established in 1998 to provide long-term data bases to assess the changes of Colombian coral reefs against perturbations and to identify the factors responsible for their decline or recovery. On the Pacific coast, data on coral and algal cover have been collected yearly during seven consecutive years (1998-2004) from 20 permanent transects in two sites at La Azufrada reef, Gorgona Island. Overall, coral cover was high (55.1%-65.7%) and algal cover low (28.8%-37.5%) and both exhibited significant changes among years, most notably on shallow areas. Differences between sites in both coral and algal cover were present since the study began and may be explained by differences in sedimentation stress derived from soil runoff. Differences between depths most likely stem from the effects of low tidal sub-aerial exposures. Particularly intense sub-aerial exposures occurred repeatedly during January-March, 2001 and accounted for a decrease in coral and an increase in algal cover on shallow depths observed later that year. Additionally, the shallow area on the Northern site seems to be negatively affected by the combined effect of sedimentation and low tidal exposure. However, a decrease in coral cover and an increase of algal cover since 2001 on deep areas at both sites remain unexplained. Comparisons with previous studies suggest that the reef at La Azufrada has been more resilient than other reefs in the Tropical Eastern Pacific (TEP), recovering pre-disturbance (1979) levels of coral cover within a 10 year period after the 1982-83 El Niño, which caused 85% mortality. Furthermore, the effects of the 1997-98 El Niño, indicated by the difference in overall live coral cover between 1998 and 1999, were minor (< 6% reduction). Despite recurrent natural disturbances, live coral cover in 2004 was as high as that existing before 1982 at La Azufrada, and one of the highest observed on healthy coral reefs in the TEP region.

Highlights

Pandolfi et al 2003)
Mean percent live coral cover varied danudrin6g5.7th±e23s.t2u%dy(Xp–e±rSioDd) between 55.1±30.0% while algal cover did between 28.8±15.1% and 37.5±24.2%
Assessing stability and resilience on coral reefs has been difficult for at least two reasons: 1) there is a lack of adequate long-term data to provide a basis for assessments, in lessdeveloped countries where most coral reefs are located, and 2) different criteria have been used to determine the degree of stability and resilience of coral reef communities

Summary

Introduction

Pandolfi et al 2003). Signs of deterioration include a progressive reduction in live coral cover and a shift to dominance by benthic algae (Hallock et al 1993, Ginsburg 1994, Hughes 1994, Gardner et al 2003), massive mortalities of functionally important organisms (Gladfelter 1982, Lessios et al 1984, Carpenter 1990, Garzón-Ferreira & Zea 1992, Liddell & Ohlhorst 1992, Hughes 1994), depletion of fisheries resources (Rogers 1985, Hughes 1994) and an increase in the frequency, intensity and geographic distribution of coral bleaching events (Williams & Bunkley-Williams 1990, Glynn 1993, Brown 1997b, Glynn et al 2001, McWilliams et al 2005). Detailed quantitative assessments of the impacts of natural and anthropogenic perturbations on most Colombian coral reefs have been hampered by the lack of adequate baseline data on the natural variability of their major physical and biological components. A number of studies have described many of Colombian coral reefs and documented their most significant changes (Garzón-Ferreira & Kielman 1994, Díaz et al 1995, 1996, 2000, Zea et al 1998, Zapata et al 2001, Zapata & Vargas-Ángel 2003); only in 1998 a monitoring program was established to evaluate the status and dynamics of such reefs. We focused on temporal and spatial variation in abundance of corals and algae because they are major benthic components of coral reef communities and serve as primary indicators of coral reef “health” (Brown 1997a)

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Results

Conclusion