Coral Reefs in Honduras: Status After Hurricane Mitch
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S3©^=-^i* -^"i^^^? °»"a.~ » "* ' USGS L??=*F-vC? » science for a changing world Coral Reefs in Honduras: Status after Hurricane Mitch Introduction: Reef corals from around the world were severely affected from bleaching by the large El Nifio event in 1997-1998. Mass bleach ing events occur when prolonged high sea-surface temperatures stress corals, causing the expulsion of symbiotic zooxanthellae (plant- like organisms living within the coral tissue). Extended periods of bleaching may lead to an increase in coral mortality. It is estimated that -16% of the world's corals were destroyed from this single bleaching event in 1998 (Wilkinson, 2000). Unfortunately, coral reef environments along the north coast of Honduras were about to face additional problems. On October 25, 1998, Hurricane Mitch (Figure 1) had formed into the fourth strongest Atlantic hur ricane on record; a category 5 hurricane with 180+ mph wind speed and estimated wave heights of 50 feet. Mitch turned out to be the deadliest hurricane since the great hurricane of 1780 (http:// www.ncdc.noaa.gov). Figure 2. Index map (top) showing location of Cayos Cochinos and Roatan, Honduras and path of Hurricane Mitch. Aerial photograph of Cayos Cochinos (bottom) showing location of monitoring stations (red dots) and distribution of fringing coral reefs. 'r - Mitch lost energy and became Cochinos on October 27 & 28 ''"'" Cayos Cochin"S os ^*vfei^ a category 4 hurricane on October (Figure 2) with 130-mph winds 27 as it began to interact with and caused severe damage to build the mountainous terrain on the ings and onshore habitats. Mitch Figure 1. Satellite image of Hurricane Mitch on Honduras mainland. Mitch passed dropped over 6 ft of rain on the October 27,1998 showing a very well developed cen tral eye. Mitch was positioned just to the northeast of over Roatan, Guanaja, and Cayos mainland causing severe flooding, Guanaja, Honduras. Image provided by NOAA. U.S. Department of the Interior USGS Open File Report 01-133 U.S. Geological Survey June 2001 economy, supplemented by suste nance fishing for the indigenous people. Though the reefs of Roatan and Cayos Cochinos share many similarities, there are important dif ferences. Historically, Roatan has been bathed in clear water (100+ ft visibility), which is a result of relatively strong oceanic cur rents that sweep past the island. However, during the past decade poor land-use practices and devel opment have resulted in increased runoff and sediment deposition on the reefs (Mehrtens, C.J. and others, in press). Cayos Cochinos, on the other hand, is located on the shallow continental shelf and is persistently influenced by Figure 3. Photographs depicting various diseases observed throughout the Cayos region. (A) Black band disease on a brain coral (Diploria sp). This disease typically begins at one location and spreads out very quickly runoff from mainland rivers that killing the coral as it grows and leaving only bare skeleton in its path. (B) Bleached Meandrina sp. coral. result in salinity, temperature, tur (C) Montastrea sp. that has been partially killed by white plague or white band disease and the remaining skeleton colonized by red algae. bidity and water-quality fluctua tions. Land clearing and defores landslides, and mudflows. In its the coral reef systems of Cayos tation on the Honduras mainland wake, Mitch left about 11,000 Cochinos and Roatan, Honduras. has probably accelerated sediment people dead and 2 million people loading, nutrient content, and fre homeless throughout the countries Study Location: quency of flood events that even of Honduras, Nicaragua, El Four site visits were made tually impact the marine envi Salvador, and Guatemala. In between October 1999 and April ronments around Cayos Cochinos, response to this devastation, 2001 to investigate and monitor and to a minor extent, other Bay funding for the project was pro the coral reefs around Cayos Islands. vided through the U.S. Agency Cochinos and Roatan, Honduras for International Development (Figure 2). Cayos Cochinos Purpose of Study: (USAID), from a supplemental Biological Reserve served as the Investigation of coral reef Congressional budget allocation to primary study site with secondary damage from Mitch involved: 1) provide assistance to Mitch- efforts in the Roatan Marine assessing the amount of coral affected countries. USAID also Reserve. Cayos Cochinos is breakage and displacement that earmarked funds for use by the located on the continental shelf occurred as high waves and strong U.S. Geological Survey (USGS) approximately 12 miles off the currents impacted the reef and 2) to establish a network of early northern coast of Honduras and identifying the effects of increased detection systems (stream gauges, 18 mi south of Roatan in the coastal sedimentation and nutri maps of landslide-prone areas, etc), Caribbean Sea. A deep trough ent-enrichment, which resulted collection of water-quality infor (1400 ft) separates Cayos and from flooding after Mitch moved mation, and assessment of post- Roatan. onshore. Monitoring and evaluat Mitch damage to coastal resources Fringing coral reefs line the ing the damage to the reefs from such as coral reefs, seagrass beds, coasts of all the Bay Islands, pro Hurricane Mitch involved install and mangrove forests. This study viding protection from storms. This ing instruments around Cayos focuses on the impact of Mitch on protection allows a tourism-based Cochinos (Figure 2) and Roatan, Status of Coral Reefs: Utila, and Cayos Cochinos) during Physical damage to coral reefs the fall of 1998. Upwelling of deep from Hurricane Mitch may have oceanic water lowered the surface been kept to a minimum because temperatures by 4°F as Hurricane the reefs in this area are composed Mitch passed over the Bay Islands of robust head coral species such (Jennifer Keck, pers. comm.). The as brain coral (Diploria sp.) and drop in surface temperature most star coral (Montastrea sp.). likely had a positive effect by Sedimentation and freshwater reducing the severity of coral runoff from the mainland most bleaching, thereby preventing fur likely caused more damage to ther coral mortality. In addition, corals than did waves and currents. during the past two years Divers observed widespread coral (1999-2000), summertime sea-sur disease such as black band, white face temperatures throughout the pox, and bleaching and an abun dance of algae during the initial Figure 4. Color-enhanced satellite image (SeaWiFS) visit to Cayos in October 1999, one from November 1, 1998, showing the extent of the freshwater plume (yellow) that was induced by intense year after Mitch (Figure 3). The rainfall from Hurricane Mitch. SeaWiFS image pro occurrence of these diseases and vided by University of South Florida, St. Petersburg, Florida. algae are thought to be a result of stress induced from a combi as well as photo documentation nation of pre-hurricane high sea- of coral disease, algae abundance, surface water temperatures, and Oct/29/99 Feb/5/00 May/16/00 Aug/24/00 physical damage to corals, and post-hurricane high sedimentation overall reef health. Very little coral and nutrient influx from the reef data exist for Cayos (e.g., mainland. SeaWiFS (Sea-viewing Guzman, 1998), so the data pre Wide Field-of view Sensor) sat -2 feet water depth sented here are considered to be ellite imagery (Figure 4) taken -17 feet water depth the first to be collected throughout November 1, 1998, shows a large the region. plume of sediment-laden, high- Apr/8/00 May/24/00 Jul/9/00 Aug/24/00 Two instruments recording nutrient river water flowing from water salinity, temperature, and the engorged Aguan River Valley 2000 light intensity were installed on directly to Guanaja. Portions of a shallow (-17 ft) reef at Cayos this large plume eventually inun and Roatan. In addition, three sites dated the Cayos Cochinos region. throughout Cayos (Lions Head, Coral reef communities typically Pelican Point and a shallow reef thrive in clear, low-nutrient oce near the field station; red dots on anic water and therefore are Figure 2) were selected to house affected when subjected to water instruments measuring temperature that has lower-than-normal salinity, only. These temperature loggers increased sedimentation, and addi 30 were placed on the reef in 17-ft tional nutrients. Cayos Cochinos is Aug/12/00 Aug/14/00 Aug/16/00 Aug/18/00 and 66-ft water depths to measure regularly influenced by all of these Figure 5. Examples of data collected at Cayos upwelling events that might occur factors, especially during the rainy Cochinos. (A) 11-month record of sea-surface tem peratures taken in a water depth of 5 ft. (B) Surface as a result of meteorologic or season (August - February). salinity recorded approximately once a week at the oceanographic changes and to mea biological field station dock (-2 ft) on Cayos Pequeno It is probable that Hurricane and from the reef (-17 ft) at Pelican Point, which was sure extreme sea-surface tempera Mitch prevented further bleaching collected at 15-minute intervals during the summer of tures on a shallow reef (-3 ft). 2000. (C) Light (PAR) record for a seven-day period damage to the corals throughout showing decreasing light intensities with pulses of the Bay Islands (Roatan, Guanaja, 'fresher' water. Caribbean have receded below surface temperatures (Figure 5A). is essential to understanding the coral bleaching threshold temper In October 1999 there was a long-term impacts that sedimen atures (~86°F) (Hoegh-Guldberg, brief period of high temperature tation, nutrification and low-salin 1999). Temperature data at Cayos (88°F) that did not cause severe ity events may have on coral confirms a trend of lowered sea- widespread bleaching. A recovery reef health within the Cayos period was continuing in 2000 as Cochinos Biological Reserve.