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Boletín de Investigaciones Marinas y Costeras - INVEMAR

Print version ISSN 0122-9761

Bol. Invest. Mar. Cost. vol.47 no.1 Santa Marta Jan./June 2018

https://doi.org/10.25268/bimc.invemar.2018.47.1.740 

Research Articles

Coral cover decline on La Chola reef (Eastern Tropical Pacific)

Mateo López-Victoria1  0000-0002-7307-8680

Fernando A. Zapata2  0000-0001-8989-4458

1 Departamento de Ciencias Naturales y Matemáticas, Facultad de Ingeniería, Pontificia Universidad Javeriana Cali, Calle 18 # 118-250, Cali, Colombia; malov@puj.edu.co

2 Departamento de Biología, Facultad de Ciencias, Universidad del Valle, Calle 13 # 100-00 Cali, Colombia; fernandozapata@correounivalleedu.co


ABSTRACT

La Chola Reef is located at the easternmost sector of the Eastern Tropical Pacific. This coral formation of 11 ha is dominated by branching corals of the genus Pocillopora. The main goal of this study was to evaluate changes in coral cover over time, by comparing data collected in 2002 and 2013, implementing the chain transect methodology. Additionally, we generated an up-to-date map of this reef using field data collected with a GPS and present the first in-situ water temperature data. The reef exhibited a 20% coral cover decline during the study period, with associated increases in algal cover (mainly coralline algae). Total extension of the reef seems to have remained stable during the last 30 years. Besides the usual stressors commonly associated with limitations in coral reef development in this region of the Pacific, seasonal decreases in temperature are proposed as a potential cause of coral cover loss on the deeper sectors of the reef.

KEY WORDS: Reef dynamics; Temporal changes; Colombian Pacific; Coral cover; Low water temperature

RESUMEN

En el extremo oriental del Pacífico Oriental Tropical se encuentra el arrecife de La Chola. Esta es una formación coralina de 11 ha de extensión, dominada por corales ramificados del género Pocillopora. El objetivo de este estudio fue evaluar los cambios en la cobertura coralina de este arrecife en el tiempo, mediante comparaciones entre datos tomados en 2002 y en 2013, usando transectos fijos. Adicionalmente, se generó un mapa actualizado de este arrecife, a partir de datos de campo tomados con un GPS, y se presentan los primeros datos de temperatura del agua. El arrecife experimentó una reducción cercana a 20% en la cobertura coralina viva durante el período evaluado, con un incremento en la cobertura de algas (principalmente algas coralinas). La extensión del arrecife parece haberse mantenido estable durante los últimos 30 años. Además de los tensores habituales asociados con las limitaciones en cobertura coralina de esta región del Pacífico, se proponen los descensos estacionales en la temperatura como potencial causa de las pérdidas de cobertura coralina en los sectores más profundos del arrecife.

PALABRA CLAVE: Dinámica arrecifal; Cambios temporales; Pacífico colombiano; Cobertura coralina; Temperatura fría

INTRODUCTION

The coral reefs of the Eastern Tropical Pacific are few and poorly developed (Cortés, 2003), among which La Chola Reef is the best developed on the coast of the Colombian continental Pacific (Zapata and Vargas-Ángel, 2003). This reef is located on the eastern side of the Utría cove, in the department of Chocó, a region of the Colombian Pacific that has few inhabitants and is far from urban centers. Despite the relative importance of this reef, its remote location has kept it away from the attention of researchers. Additionally, the social instability of the region, a product of the internal conflict that Colombia has endured for decades, has prevented visits by researchers to this reef for many years, further limiting their knowledge. Prahl and Erhardt (1985) were the first to note the existence of this reef, and they described it in a general way. Vargas-Ángel (1988, 1996) published detailed descriptions of this coral formation, as well as others of lesser coverage and development in the vicinity of the same cove. Díaz et al. (2000) and Zapata and Vargas-Ángel (2003) published some general notes on the coral reef cover of La Chola, also providing an approximate map (based on Vargas-Ángel, 1996), which showed the distribution of the main ecological units of this reef. Vargas-Ángel (2003) compared several biotic and abiotic variables of two coastal reefs (La Chola and Tebada) with those of an insular reef (La Azufrada, Gorgona Island), to identify the determinants of the structure of the coral communities in the Colombian Pacific. More recently, Vargas-Ochoa and Ramírez-Gallego (2008) gave a general description of the state of the reef, mainly focusing on the coverage of corals and algae. Although these studies offer a good approximation of the shape and size of the reef, as well as the coverage of its main benthic components, an analysis of the temporal dynamics of this reef is difficult because all those studies were based on the same sampling method (chain transects), but the studies were located in different sectors of the reef at different times of the year, which makes direct comparisons difficult.

To solve the problem of limitations in the comparisons, in 2002 the Coral Reef Monitoring System of Colombia [Sistema de Monitoreo de Arrecifes Coralinos de Colombia, SIMAC (Garzón-Ferreira and Rodríguez-Ramírez, 2010)] established six fixed monitoring stations on the La Chola reef, opening the possibility of rigorous and periodic monitoring of the state of the reef. However, for the reasons already explained, this follow-up had not been possible. The initial results of that first evaluation in fixed stations were presented in unpublished technical reports (Garzón-Ferreira et al., 2002, 2003). Almost a decade after that first systematic and standardized evaluation of the state of the La Chola reef, a sampling of these stations was made, using exactly the same method used in 2002, to establish the following: a) the coverage of the main components of benthos in the reef, and b) the main changes that have occurred in this coverage in the last decade. In addition, the contour of the reef was completely examined to produce an updated map of its extension, and an automatic temperature measurement device was recovered, whose data provided temperature variations occurring over a year. This paper presents the results of this assessment and proposes scenarios that help explain the changes in the benthic coverage of La Chola reef.

STUDY AREA

La Chola reef (also known locally as La Aguada) is located on the eastern margin of the entrance of the Utría inlet (6°00'40"N-77°20'48"W), a small, elongated, fjord-type bay, which is located in the northern half of the Colombian Pacific (Fig. 1). This area is an extremely rainy region (more than 5000 mm of rainfall per year), with an average annual temperature of 25.7 °C and average relative humidity of approximately 80% (data from a meteorological station located in Bahía Solano, 24 km to the north of La Chola reef, in a straight line, IDEAM, 2005). The region is characterized by two climatic periods, one dry at the beginning of the year and the other rainy, starting in April-May (IDEAM, 2005). The reef has a moderately developed coral framework, with shallow sectors dominated by Pocillopora spp. and intermediate sectors with the presence of some scattered colonies of massive corals in a matrix of Pocillopora spp. and Psammocora stellata Verrill (Vargas-Ángel 1988, 1996; Díaz et al, 2000; Zapata and Vargas-Ángel, 2003; Vargas-Ochoa and Ramírez-Gallego, 2008). The coral formations do not reach more than 6-8 m in depth, and the reef zonation is not clear, but obvious shallow sectors with good coral development and deep sectors with poor coverage are present. Previous data on the water temperature in the Utría cove is scarce or derived from satellite measurements (Vargas-Ángel et al, 2001; Vargas-Ángel, 2003). During the rains, copious run-off of sediment-laden waters occurs (Vargas-Ángel, 1988, 1996). The tides in this sector are semidiurnal, with a maximum amplitude of 5.4 m (IDEAM, 2014).

MATERIALS AND METHODS

Following the protocols of SIMAC (Garzón-Ferreira et al., 2002, 2003), sampling was conducted February 22-25, 2013, at the six monitoring stations established in 2002 (three shallow, 2-3 m at high tide, and three deep, 5 m. At each station, all pairs of rods placed by SIMAC (n = 18) were searched for; at each station, six rods were originally present, indicating the starting and ending points of three transects, each 10 m long. However, only eight pairs of rods were found (Appendix 1), so the comparative analyses between 2002 and 2013 refer exclusively to those eight transects (for descriptive purposes of the current coverage of the reef, all transects were used, nine shallow and nine deep). In cases where the one rod of a pair was not found, a provisional location was established by calculating the approximate placement of the original rod (according to the location maps of the transects of Garzón-Ferreira et al., 2002). To quantify the coverage of live coral, dead coral, and algae, the chain-transect method was used (Garzón-Ferreira et al., 2002). In each transect, a chain with links of ~1 cm was extended on the substrate between each pair of rods. The number of links for each type of substrate category was recorded: live coral, discriminating by coral species; algae, discriminating between coralline and non-coralline algae (i.e., fleshy algae, turf algae); dead coral; and sand. For the comparison between the coverages of 2002 and 2013, paired Student t tests were performed, with percentage data undergoing arc-sine transformation (Zar, 2010). Figure 2 shows the original values of coverage percentages, and Appendix 2 shows all original data, which were complete for both years of sampling.

The contour of the reef was followed by a diver, who dragged with a rope a GPS Garmin® that operated at the surface and automatically recorded the track data, which were used to develop a detailed map of the contour of the reef; the total surface of coral formations with relevant coverage was derived from this map. These routes were incorporated into a geographical information system (ArcGIS®) and the map contours were refined with the help of an oblique aerial photograph taken from a commercial aircraft.

To obtain the reef temperature data, an automatic data storage device (HoboTemp® H01-001-01), installed at 6 m depth at one of the reef stations by SIMAC in 2002 was recovered (the device remained submerged for 11 years). This device recorded temperature data every 5 hours for a period of one year, so the data correspond to the period between March 2002 and March 2003. The temperature data were plotted placing the months January-March 2003 before April 2002 to illustrate the pattern of annual seasonal variation.

RESULTS

According to the detailed map developed by georeferencing La Chola reef, the extension of this coral formation was estimated to be approximately 11 ha. The reef has an irregular shape and its maximum dimensions are 600 m long x 350 m wide (Fig. 1).

Figure 1 Up-to-date map of La Chola Reef (Utría cove) indicating its relative position in Choco and Colombia. 

A significant reduction of approximately 20% occurred in the live coral coverage between 2002 and 2013 [t (7) = 3.53; p = 0.009; Fig. 2], and a significant increase of 9% occurred mainly in the coverage of coralline algae during the same period [t (7) = - 4.28; p = 0.003; Fig. 2]. The fleshy algae and the turf algae mats, on the other hand, did not show significant temporal variation in their coverage [t (7) = 0.65; p = 0.533].

Figure 2 Average cover (±1 SE) of the main benthic components of La Chola Reef in 2002 and 2013, based on data from all the original transects (2002) found in 2013 (n = 8). Data from 2002 provided by the data base of SIMAC (INVEMAR), based onGarzón-Ferreira et al.(2002, 2003). 

Figure 3 La Chola Reef landscapes in 2013: (a) Shallow habitat dominated by Pocillopora damicornis. (b) Deep habitat dominated by coral rubble and disperse colonies of Psammocora stellata and P. damicornis. 

The dominant coral species in the shallow stations was Pocillopora damicornis (Linnaeus), with an average coverage of 54.3% of the substrate (n = 9 transects), whereas Psammocora stellata was codominant on some deep stations of the reef, with an average coverage of 10% (vs. 15% reached by P. damicornis in this sector, n = 9 transects) (Fig. 3).

Figure 4 Annual temperature variation, at 6 m depth, at La Chola Reef. Data collected with a data-logger, between March 2002 and March 2003. Data were organized in the sequence of months for a calendar year, starting in January. 

The temperature data of the reef water showed two contrasting periods in the year (Fig. 4). One period, beginning at the end of January and ending at the beginning of May, with cold water (as low as 22 °C) and marked daily variation, and a second period, corresponding to the months of May to January, with warm water (average temperature of approximately 28 °C) and little daily variation.

DISCUSSION

The extension of La Chola reef has remained constant since 1988-1989, when Vargas-Ángel (1996) estimated it, for the first time, at 10.5 ha (vs. the 11 ha estimated during the present study). On the other hand, the coral cover seems to have decreased during recent decades, according to the different averages recorded by different authors (Vargas-Ángel, 1996, 2003; Garzón-Ferreira et al., 2002, 2003; Vargas-Ochoa and Ramírez-Gallego, 2008). Although all of these studies used equivalent methods to estimate the coverage (Table 1), the transects were established in different places, which makes it difficult to draw rigorous conclusions about trends over time. However, from these different estimates, in the last decade, a decrease in live coral coverage of approximately 20% can be concluded.

Table 1 Comparisons of coral cover estimates at La Chola reef based on several studies with similar methods, but on transects located at different 

Not enough information is available to attribute this decline in live coral coverage to a particular factor, but at least some possible causes can be suggested based on previous (Vargas-Ángel, 1996, 2003) and current observations. The most obvious cause would be excessive sedimentation because it is one of the rainiest regions in the world (Poveda and Mesa, 2000), where deforestation and the associated sediment load in the rivers have increased, all due to an increase in illegal activities (Dávalos et al., 2011); in the reef, sedimentation in the water was evident after heavy downpours. Another cause could be the excess of fresh water from the stream that flows directly into the reef, with significant flows occurring during and after the downpours. In both cases, these stressors have existed for a long time, and the reef developed and remains under these conditions (the fresh water forms a superficial layer that affects, above all, the shallow part of the reef, which is the sector that presented minor changes in coverage, see Appendix 2).

In addition to the two above mentioned factors, Vargas-Ángel (1996) suggested that El Niño phenomena and extreme low tides may be responsible for changes in coral cover at La Chola reef. However, between 2002 and 2013 no major effects of El Niño were observed and extreme low tides are a frequent disturbance in Colombian Pacific coral reefs. In addition, the extremely low tides affect especially the shallow sectors, and those were the ones that presented fewer changes in the living coral cover between the two periods evaluated (the most affected were the deep ones, where the effect of extreme low tides does not operate). For example, in the reefs of Gorgona Island coral mortality is notorious in the shallow sectors, attributable to sub-aerial exposure during extreme low tides (Zapata et al., 2001, 2010; Zapata, 2017), but in La Chola reef the deep sectors (and not the shallow ones) showed a reduction in coverage over the last decade (see Appendix 2).

From the limited observations and temperature records, another scenario is proposed that could explain these changes in coverage. The coral reef of La Chola presented a marked seasonality in terms of water temperature, as it occurs in the reefs of the Gulf of Panama (D'Croz et al, 1991; D'Croz and Robertson, 1997), Gorgona (Diaz et al, 2001), and Malpelo (Zapata et al, 2011), where temperatures can fall at the beginning of the year to as low as 16°C. These temperature drops in the Colombian Pacific basin are due to seasonal upwelling, generated by masses of cold water that move south from Panama, pushed by the trade winds (Rodríguez-Rubio and Giraldo, 2011). In the coral formations of Malpelo, for example, these low temperatures have been associated with coral bleaching and mortality (Zapata et al, 2011). The marked daily variation in the temperature of La Chola reef can be attributed to the entry and exit of cold-water masses caused by tidal fluctuations.

Fronts of particularly cold water masses, for example, during La Niña years, could be the main cause of the reduction in coral cover in the deepest sectors of the reef, in addition to being the main stressor limiting coral reef development at greater depths, not only on this reef but in this region of the eastern Pacific. Although a marked seasonality was observed in terms of temperature, because these are the first data collected and are based on a single year of sampling, these results must be taken with caution, and circumstantial or experimental evidence of low temperatures as a limitating factor for the development of these reefs must be sought.

ACKNOWLEDGEMENTS

We thank the staff of the Utría Natural National Park for logistical suport and the Marine and Coastal Research Institute (Invemar) for sharing the 2002 SIMAC sampling data from La Chola reef. Our special thanks are given to J. L. García, K. Mejía, and C. G. Muñoz for their assistance during the field work and to J. Olaya for supplying the oblique aerial photography of La Chola reef. The reviewers made accurate comments and corrections, which helped us revise and improve the manuscript. This research was supported by the Natural Heritage Fund (Fund for Biodiversity and Protected Areas).

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Received: July 12, 2017; Accepted: February 20, 2018

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