Coral Reef Reconstruction and Management

introduction

On 12 January, 1996, a cruise ship struck portions of Soto's Reef off George Town, Grand Cayman Island, British West Indies. The ship's hull struck portions of the reef mass, dislodging and crushing reef formations as it maneuvered out of the harbor. A survey by the Cayman Islands Department of the Environment (DOE) quantified the damage at approximately 967 m2 (planar aspect, based on aerial photogrammetry). The damage was in the depth range of 4.6 to 15.2 m. Damages included abrasion from the ground tackle, dislodged coral formations, and a large crushed area where the hull came down hard on the reef.

Soto's Reef, one of the better known dive sites on Grand Cayman, lies within the Cayman Islands Coral Reef Park. The area is visited by thousands of divers and snorkelers annually, because the relatively shallow depth (less than 10 m) provides an excellent dive site for novices to view coral reef marine life.

Jack Morelock and Walter Jaap were retained by the Holland America Line to develop and supervise restoration of the damaged reef habitat. Both individuals have extensive expertise in coral reef biology, ecology, and geology and have been actively working in coral reef restoration projects resulting from vessel groundings. After a reconnaissance of the grounding site, the consultants met with the DOE to propose and develop a restoration plan that included removing rubble, salvaging and transplanting dislodged corals, and moving large coral formations back onto the reef. The DOE and the Holland America Line came to an agreement resulting in restoring the damaged reef. Work began in late January, within weeks of the incident. To facilitate an orderly restoration and record keeping, the area of damage was divided into three work zones. Approximately 15 large reef boulders, more than 50 medium sized boulders, and about 100 small boulders were moved back onto the cleared reef platform using "lift bags" . These reef boulders and smaller pieces of limestone that were salvaged were used to construct three-dimensional relief in areas where the vessel's hull had flattened the reef profile.

The movement of large blocks was accomplished using the buoyant force of air within lift bags to raise the mass and move it to a position that we deemed most appropriate. Some structures were moved into position in the large scarred areas. Very large structures were turned to their upright orientation, but were not moved.

Rubble not required for construction was used to construct structural modules off the reef, on the sand bottom. Approximately eight artificial structures were created. The largest was 18 m long, 4 m wide, and 1.5 m high.

The most time-consuming effort was re-attaching salvaged coral colonies back onto the reef or to the boulders. Recovered coral were stored in crates . More than 4,500 coral colonies were cemented to the damaged areas of the reef. The base of the coral and the substrate was cleaned with a wire brush. We used an underwater epoxy material (Liquid Rock 500) with an applicator that mixes and dispenses the epoxy . In wave surge areas, we used a pneumatic drill to drill a 1/4 inch hole in the bottom of the coral and the substrate, (one to two inches deep). Stainless steel rod was used with epoxy to serve as an anchor to keep the coral in place. Epoxy was applied to the base of the coral and or the reef substrate, and the coral was pressed onto the substrate. The coral cover in undamaged areas was estimated at 20 to 30 percent living coral (surveys reported here give more information) and in the restoration, we tried to achieve 15-20% cover in critical areas as shown in the vista of a restored reef area.

This project was the largest attempt ever made to restore a reef immediately following a vessel grounding and monitoring the results is important for future considerations. The monitoring project is intended to answer the following questions:

monitoring program

Status and trends monitoring Likens 1988, Swanson and Sparks 1990 is the best way to determine the success of any restoration. We firmly believe that this approach should provide answers to the questions previously posed. Monitoring coral reefs through time is a proven method to document the dynamics of community structure. Davis, 1982; Done, 1992, Hughes and Jackson, 1985; Jaap et al., 1988 In this case, monitoring will evaluate the success of transplanting corals, building structures, and replacing the large masses that were dislodged by the accident.

After discussing the monitoring project with the DOE, a schedule was accepted that includes four sampling periods: a baseline, six months, one-year, and two-year observations (each return subject to approval of HAL). The DOE has agreed to be a collaborative participant in the monitoring by providing logistic support, certain equipment, and staff.

Damage and restoration by zones : in zones one and two is characterized as spatially separated patches. Zone three was a large relatively uniform scarified area; most of the damage occurred in zone three. We divided the monitoring into tasks relating to specific restoration.

Coral health and vitality: Photographic analysis of individual coral colonies

A 35 mm Nikonos camera, with a 35 mm lens, Ikelite M-50 strobe (50 Watt seconds of power), and the Nikonos "close-up" accessory lens were used to photograph corals in the areas where the transplanting occurred and in adjacent undamaged areas (zones one, two, and three). The photos were taken haphazardly in order to have several photographs of the typical species found in the local area. We used ISO 100, Kodacolor Gold print type film. The F stop was between 16 and 22. Photographs were developed upon return to St. Petersburg using standard processing. The photograph print size is four by six inches (152 cm2) and the actual coverage area of the coral in the photo was reduced by a magnification ratio of 0.93 based on a reference scale in a photograph. Thus the coverage in a photo was approximately 141 cm2. Corals were the principal focus of this photographic sampling.

Qualitative assessment of vitality

Each photo was assessed based on color, signs of bleaching, algal competition, and coral disease. If the coral appeared to be of a normal color, it was scored as a five, if the color was faded or blotchy, it was scored 4 to 1, based on the condition ( 1 being the worst condition). In a similar manner, we scored bleaching conditions, algal competition, and disease. Sponge-coral competition was not seen in any of the photographs.

Point counting cover analysis

A transparent overlay with ten random points was superimposed over each photograph. The overlay had a border that defined the perimeter of the photograph and ten random points were positioned within the overlay border. The points were determined by the Quattro Pro spreadsheet random procedure.

We tabulated the attributes in the photograph lying directly under the points (Curtis 1968, Bohnsack 1979). The number of points superimposed on an attribute divided by the total number of points multiplied by 100 is the percent contribution for that particular attribute. We computed the means and the standard deviation for each attribute by control and transplant site. We included coral, bleached corals, diseased corals, algae, sponges, and other (other includes bare rock, poorly illuminated areas in the photos, and micro-caverns). Results were compared statistically and graphically.

The statistical approach is that there is no difference in the survival and health of the transplanted corals compared to the adjacent populations. We will use univariate, non-parametric tests and multivariate trend analyses to evaluate the status: Mann Whitney U-test, Bray Curtis Community classification analyses, and Multi-dimensional scaling, ordination (Boesch, 1977; Bloom, 1981; Field, Clark and Warwick, 1982; Lambshead, Platt and Shaw, 1983; Warwick and Clarke, 1991).

Evaluating coral cover using photo and video analytical methods

Coral cover is an important index of recovery. It is recognized as an important parameter in coral reef quality (Weinberg, 1981; Bak and Luckhurst, 1980; Done, 1992). We define cover as the percentage of a unit area that is occupied by living coral. The corals that we transplanted replaced the corals lost due to the accident. By comparing the values of cover in the three damaged areas with adjacent undamaged areas, we can compare damaged versus non-damaged and evaluate recovery.

The photo-video, transect sampling technique has been employed for a number of years. It is rapid, providing cover by species or the cumulative contribution by all species. Photographic assessment is rated as a good method to evaluate coral reef status (Weinberg, 1981, Dodge, et al., 1982; Morelock, 1990). The method utilizes a 35 mm Nikonos camera with a 28 mm lens mounted on a vertical apparatus that has a fixed distance of 1.2 m from the reef surface. At this distance, each photo covers an area of 0.7 m2 . We use 200 ISO print type color film and four by six inch prints. Following development, we measure the planar area (two-dimensional) of the living coral. The photograph is scanned into the computer and planimetry (digitizing the outline of the coral polygon using Jandel Sigma Scantm) defines the perimeter of the coral. Data are imported to a spreadsheet for statistical and graphic analyses.

Stability of large reef boulders that were moved

Approximately 15 large (greater than two meters in diameter) and more than 50 medium-sized boulders were lifted and moved from the sediment beds back onto the reef. The stability of the living coral surfaces that were shaded or partially buried were monitored by visual inspection and were documented with video recordings.

Fate of the rubble piles that were created off site

We created approximately eight rubble structures on the sediment bed away from the reef. The material is concentrated in mounds, piles, and long drifts. In time, the structures should stabilize by natural cementing and growth of binding organisms. We used video documentation and visual observations to monitor these structures for stability and recruitment of invertebrates and fish, with special emphasis on corals.

Recruitment of corals on the damaged area

Each of the monitoring stations (photo quadrat) was visually and photographically studied for settlement of juvenile corals. Settled corals are small, inconspicuous, and enigmatic to identify. We identified the juvenile corals to the best taxonomic resolution based on our experience and ability (species, genera, and family).

results

During our initial dives, we marked potential sampling stations with flagging tape. At the same time, we made general notes on the reconstruction and a video record of the three restored areas. We also took test photos and a video transect on the control station and across the large rubble pile. Following discussions with the DOE principals, we installed permanent sampling stations in the respective zones (restored and controls).

Installation included drilling a hole in the reef framework and cementing a reference stake in the hole. The stake serves as an index mounting for the camera system (photo-quadrats) and a reference marker for the recruitment study.

Photo-quadrat stations were established in the three damage zones, with nearby control stations for comparison. Each quadrat consisted of two photographs covering a planar area of 0.65 m2 taken 180o from each other and about 70 cm between the two photograph edges; the photo-quadrat composite area was 1.3 m2. Identification of coral species was made in the field, and that information was transferred to the prints when they were digitized. More than 600 coral colonies were measured from the 15 double photo quadrat stations in this study.

Sets of two companion stakes were installed in the restored and undamaged areas as terminal points for the video transects. The transects pass or bisect across the area of the photo stations. A tape measure was laid between the reference markers, and an 8 mm video camera was used to record a path along the tape measure. This provides a record for an area that is approximately 0.5 m wide for the length of the transect.

We attached brass tags to the reference stakes to designate the station. The following provides GPS coordinate fixes for the permanent sampling stations. The GPS coordinates for sampling stations were collected mid-way between the reference markers. Code letters CW are used for controls and HW for the restored sites. The depth is the nominal range in feet, determined with a digital depth gauge with plus or minus one percent accuracy from 0 to 200 ft. This accuracy is 0.2 ft at 20 ft, 0.3 ft at 30 ft, and 0.4 ft at 40 ft. Bearings were taken with a divers compass and metric measuring tapes from stake to stake. We estimate a five percent accuracy for the compass, and the distance measurements. Table 2 and Figures 13 , 14, 15 exhibit areas and station locations.

Mean coral cover in the photographs ranged from 38.9 percent to 58.5 percent. Figures 16, 17, 18 and Table 3 summarize the results of point-count analysis. With the exception of zone two, the corals in the control and restored areas were very similar in all categories. The zone two control photographs exhibited a relatively higher percentage of coral and lower percentage algae compared to zones one and three. Perhaps the explanation is that the control for this area was in somewhat shallower depths and the corals generally were larger.

We scored the corals on a gradient of one to five in the photographs for color, bleaching, algal competition, and disease. A score of five was good to excellent, and a score of one was poor. Figures 19, 20, 21 and Table 4 summarizes the results for the qualitative analysis. The conditions for the corals all scored relatively high, implying good vitality. All areas have statistical equivalency except for zone two control which had significantly higher coral cover than the other zones. The percentage of coral cover was about twenty percent higher in area two compared to the other areas The corals we transplanted are in similar condition to those that were not influenced by the grounding.

The black wool-ball blue green algae and Schizothrix alga was also very common. These were equally abundant in reconstructed areas and in undamaged areas.

Evaluating coral cover using photo and video analytical methods

Restored stations have less cover than the control stations. The results indicate that the coral cover is twofold greater in the control stations in area one; it is relatively similar in area two stations; and there is approximately a threefold difference in the control and restored stations (mean value) for area three. These results are not unexpected. We did not attempt to locate lush areas in the restored areas for sampling stations.

The measurements of total cover, diversity, and evenness were calculated. The species and diversity values imply that these areas have low species richness and that the relative abundance is biased toward a few species (low evenness). The values of diversity and evenness were consistently lower in the restored areas compared to the control areas.

The photogrammetric planar measurements of the two most abundant species of coral that were seen in the photographs (Montastraea annularis and Agaricia agaricites) document that the mean size of M. annularis was greater in control stations for all areas. However, for A. agaricites, the mean size was greater in the restored station.

Photo-quadrats also provide the ability to track individual corals and to follow recruitment. In the quadrats from zone 1, eleven transplanted corals and eight corals from the control quadrats were selected and will be specifically followed in subsequent surveys. These same quadrats will be examined for recruitment in the next surveys. In the quadrats from zone 2, nine transplanted corals and four corals from the control quadrats were selected. In the quadrats from zone 3, thirty transplanted corals and 13 corals from the control quadrats were selected.

We recorded video transects and general video views over the areas of rubble removed from the reefs, and over areas where major reconstruction was done with large to medium sized coral boulders. Video provides a visual record which can be compared to later surveys, but, if necessary, we can obtain individual stills from the video. This was not considered part of the monitoring, and equipment is not presently available for this, but the video tape is available for any future analyses desired. We reviewed the video, and it has the qualitative value of showing algal abundance and coral vitality from larger scale or perspective.

The large reef boulders moved were examined visually and are present in the video. We did not see evidence that structures had moved or broken. Rubble piles appear to be stable. Fish and small mobile invertebrates have colonized these structures thanks to the variety of refuge habitat. The surfaces of the fragments are heavily encrusted with algae of numerous species, which is a good sign, since in the sequence of ecological succession, algae are a pioneer group. The rubble piles do not appear to be subsiding into the sediments.

Although not enough time has passed since completion of the work to expect major recruitment of corals on the damaged areas of reef (coral spawning usually occurs eight to twelve days after the August Full Moon), we did see a few juvenile corals. Notes were made of small recruits, and their fate will be followed in subsequent surveys.

return to top