Stabilized coral ranged from 15 cm to 3.4 m in length; all detached fragments larger than 1 m, 80% of the fragments between 0.5 and 1.0 m, FIGURE 14.1 Location of the Fortuna Reefer rest
Trang 1at Mona Island, Puerto Rico
Andrew W Bruckner and Robin J Bruckner
CONTENTS
14.1 Introduction 257
14.2 Initial Restoration 258
14.3 Approach to Evaluate Fragment Survivorship 260
14.3.1 Early Patterns of Fragment Survival 260
14.3.2 Midcourse Correction 261
14.3.3 Patterns of Survival and Recovery over 6 Years 261
14.3.4 Causes of Mortality 262
14.3.5 Effects of Size, Orientation, and Attachment Site 262
14.3.6 Effect of Depth 264
14.4 Efficacy of the Restoration 267
14.5 Conclusions 268
Acknowledgments 268
References 269
14.1 INTRODUCTION
On July 24, 1997, the M/V Fortuna Reefer ran aground on a fringing reef located off the southeast coast of Mona Island (18°02'N; 67°51'W), 65 km west of mainland Puerto Rico (Figure 14.1) The 326-foot freighter remained grounded for 8 days within the island’s largest remaining Acropora palmata (elkhorn coral)stand Although the Fortuna Reefer was not carrying any cargo at the time
of the grounding, some of the approximately 100,000 gallons of fuel oil and 33,000 gallons of marine diesel were removed to prevent a spill and lighten the vessel prior to removal Steel cables were attached between the stern of the Fortuna Reefer and two tugboats to stabilize and extract the vessel During removal, the extraction path did not follow the original collision path and the steel cables dragged across the reef surface, further expanding the area of injury
The grounding and subsequent removal of the Fortuna Reefer impacted 6.8 acres of shallow fore reef habitat.1 The reef substrate was crushed and fractured along the inbound track of the vessel, with additional damage occurring while the ship remained grounded as a result of waves and swell that caused the hull to rise and fall and shift sideways (Figure 14.2C) Total coral destruction occurred along the inbound and outbound paths of the vessel, extending from the reef crest approximately 300 m seaward (2 to 4 m depth) and up to 30 m in width Collateral injuries from the steel cables extended beyond the perimeter of the vessel tracks, to 6 m depth Entire 2073_C014.fm Page 257 Friday, April 7, 2006 5:09 PM
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colonies of A palmata, many that were several meters in diameter, were crushed or dislodged and fractured by the boat, and the cables sheared off hundreds of additional A palmata branches (Figure 14.2E) Brain corals (primarily Diploria strigosa) and other benthic organisms were also abraded, shattered, or detached from the reef
14.2 INITIAL RESTORATION
A team of experts from the Commonwealth of Puerto Rico and the National Oceanic and Atmo-spheric Administration (NOAA) Damage Assessment and Restoration Program (DARP) conducted
a natural resource damage assessment of the grounding site and determined that an emergency repair of damaged corals was warranted Coral fragments were scattered across the reef, and many had collected in sand channels The surge continued to shift and overturn fragments, abrading their coral tissue and minimizing the likelihood of reattachment (Figure 14.2D) Without intervention,
a high percentage of fragments may have died due to sand scouring or been removed from the site during periods of high wave action; securing coral fragments was predicted to accelerate recovery
of the injury to the reef.1 Under the Oil Pollution Act (OPA) of 1990, NOAA expedited a settlement with the responsible party amounting to U.S $1.25 million for primary and compensatory resto-ration, including $650,000 to conduct an emergency restoration of coral resources injured as a result of the incident.2
The objectives of the emergency restoration were to reestablish the structural relief of the coral reef community and reduce coral mortality by reattaching loose A palmata branches.1 Between September 24, 1997, and October 14, 1997, a team of 19 marine engineers and biologists stabilized 1857 A palmata coral fragments Stabilized coral ranged from 15 cm to 3.4 m in length; all detached fragments larger than 1 m, 80% of the fragments between 0.5 and 1.0 m,
FIGURE 14.1 Location of the Fortuna Reefer restoration site off the southeast coast of Mona Island, Puerto Rico.
FR
Mona Island
20 m Contour
Reef Crest
Puerto Rico
Puerto Rico Mona 67° W 18 ° N
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FIGURE 14.2 (See color insert following p 240.) Impacts of the M/V Fortuna Reefer to shallow reefs A The ship grounded in the reef crest Steel cables were attached between the vessel and tugboats to facilitate removal Photo courtesy of the NOAA Restortation Center B Undamaged elkhorn coral thicket adjacent to the grounding C The condition of the substrate after removal of the vessel The reef substrate was crushed
palmata fragments sheared off by the cables Photo courtesy of Dr Jack Morelock F Example of a fragment attached to nails inserted into the reef substrate Blue scale bar is 15 cm G Example of a fragment oriented
H Example of a fragment that was reattached in 1997 and had overgrown the wire but was secured with additional wire during the midcourse correction in July 2000 Blue scale bar is 15 cm.
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and 50% of the fragments up to 0.5 m in length were restored Fragments were secured to the relict reef substrate (reef) or to dead, standing A palmata skeletons (skeleton) Fragments attached
to skeletons were expected to exhibit enhanced survivorship associated with a reduction in scouring, improved water circulation, increased light exposure, and possibly a reduced exposure
to pathogens and benthic predators
To secure fragments to the reef, stainless steel wire was extended across each fragment and then wrapped around stainless steel nails that were cemented into holes drilled in the reef (Figure 14.2F) Plastic cable ties were used initially to secure fragments to skeletons, with subsequent stabilization using wire that was wrapped around the fragment and skeleton.2,3 Fragments were reattached either
in an upright or downward position (with respect to their original orientation) such that the live, unbleached tissue faced upwards (Figure 14.2G) They were firmly anchored to withstand normal surge and wave action typical of shallow, exposed reef environments Due to the high wave exposure observed during the restoration effort, cement or epoxy was not used, as the amount of time required for these materials to harden was not feasible.1
14.3 APPROACH TO EVALUATE FRAGMENT SURVIVORSHIP
Fragment survival and patterns of coral recovery were evaluated approximately 2 years after the grounding, and in May and August 2000, 2001, and 2003 The initial survey involved an assessment
of the number, size, and condition of fragments that remained attached, and the number of fragments that were broken loose and displaced or missing Detached fragments were estimated by:
1 Tallying groupings of nails within the reef to which fragments were no longer attached
2 Counting remnant wire on skeletons that was not associated with fragments
3 Counting detached fragments with remnants of attached wire
For each remaining fragment, measurements of the size (maximum length to nearest centimeter), orientation (up, down, or sideways with respect to their orientation prior to breakage), location
of attachment (reef or skeleton), and condition (live or dead) were recorded Dead fragments were marked with numbered aluminum tags to avoid recounting these on subsequent surveys Live fragments were examined and evaluated for tissue growth over the wire, presence of protobranches, natural cementation (fusion) to the reef or skeleton, and growth onto the substrate
or skeleton
Estimates of remaining tissue and percent mortality were made from a planar perspective For each fragment, a 1-m bar (divided into 1-cm increments) was oriented along the center of the long axis of the fragment to measure length, tissue survivorship, and tissue loss Partial mortality was recorded as the percent loss of tissue from the upper surface of the reattached branches and does not include mortality to branch undersides All fragments were presumed to have 100% of their upper surface covered with tissue when first reattached in 1997 Causes of partial or total mortality were identified as disease (white-band disease [WBD] or other syndromes); growth abnormalities (e.g., neoplasia or hyperplasia); overgrowth by boring sponges (Cliona
spp.); predation by snails (Coralliophila abbreviata), polychaete worms (Hermodice caruncu-lata),orparrotfish(Sparisoma viride); macroalgal competition; or presence of three-spot dam-selfish(Stegastes planifrons) territories If a cause of mortality could not be determined, it was recorded as unknown
14.3.1 E ARLY P ATTERNS OF F RAGMENT S URVIVAL
More than half (57%) of the fragments were alive 2 years after the restoration effort, while the remainder had died (26%) or became detached and removed from the site (17%).4 Fragments secured to the reef had lower rates of early mortality (27%) and a higher rate of detachment due 2073_C014.fm Page 260 Friday, April 7, 2006 5:09 PM
Trang 5Restoration Outcomes of the Fortuna Reefer Grounding at Mona Island, Puerto Rico 261
to wire breakage (24%) than fragments attached to skeletons Surviving fragments had tissue covering a mean of 50% of the original upper branch surface, with 23% of the fragments exhibiting little (<5%) or no partial mortality In addition, 19% of the live fragments exhibited vertical growth features in the form of small protobranches that were 2 to 5 cm in length
Interim monitoring reports from 1999 indicated a fairly good retention of wired fragments (esti-mated loss of 17%) even though the site had been affected by a category 5 storm (Hurricane Georges) and several severe winter storms.4 However, broken wire was noted throughout the site, and only a small proportion of the fragments had successfully fused to the reef (10%) or to standing skeletons (7%) Between August 1999 and May 2000, another 8.3% of the fragments were detached and overturned or removed from the site The wire continued to corrode and break, suggesting that sustained wire failure during periods of high wave action could hinder long-term recovery A midcourse correction was conducted in July 2000 to prevent additional fragment loss The mid-course correction primarily involved further stabilization of fragments with Monel 400, a more durable wire consisting of a copper–nickel alloy (Figure 14.2H) This wire was chosen because of its noncorrosive features, good flexibility, and excellent strength
14.3.3 P ATTERNS OF S URVIVAL AND R ECOVERY OVER 6 Y EARS
Six years after the restoration, 20.3% (377) of the restored fragments were living (Figure 14.3) Fragments had an average of 60% live tissue (Figure 14.4), although 33% had little or no mortality, and 22% showed signs of resheeting over previously denuded skeleton (Figure 14.5D) In addition, 30% (114) had solidly fused to the substrate (reef and skeletons) and exhibited new growth that was expanding outward, onto the reef or dead branches More than half (58%) of the fragments had developed multiple branches that resembled the typical treelike morphology typical of adult colonies (Figure 14.5C) On average, fragments had four protobranches (maximum of 30) each, ranging in size from a mean of 21 to a maximum of 73 cm (Figure 14.6) Larger fragments appeared to have a greater number of protobranches (r2 = 0.58, p< 0.01), and these were larger in size than those observed on small fragments, as estimated by regression (r2 = 0.60, p< 0.01) Partial loss of tissue appeared to have less of an effect on the number of protobranches produced (r2 = 0.12, p< 0.0001) While protobranch size was highly variable between fragments, protobranches on individual frag-ments were similar in size, suggesting that most protobranches on a single fragment formed at the same time
FIGURE 14.3 Proportion of fragments that were living (white bars), dead (black bars), or missing (spotted bars) during surveys in 1999, 2000, 2001, and 2003.
0 10 20 30 40 50 60 70
1999 2000 2001 2003 1997–2003
Live Dead Missing
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14.3.4 C AUSES OF M ORTALITY
Some of the most important factors contributing to fragment mortality were overgrowth by the
brown boring sponge Cliona spp., predation by corallivorous gastropods, diseases, algal
competi-tion, and abrasion from the wire (Figure 14.7) Over the 6-year study, 20% of all fragments were
killed by Cliona spp., and 5% of the remaining live fragments were affected by this sponge in
August 2003 (Figure 14.8C) The sponge was most abundant on those fragments attached to dead
standing colonies, advancing from the skeleton to the fragment Many of these colonies were
colonized by the sponge prior to the restoration effort, as evidenced by video documentation of
the restoration Disease was observed throughout the site at a low prevalence until 2003, when an
outbreak of WBD was recorded on both restored fragments and unrestored colonies within and
outside of the grounding site (Figure 14.8E) In August 2003, 4% of the living fragments and 15%
of the standing colonies were affected by WBD
The wire used in the initial restoration effort often negatively affected fragments Tissue abrasion
associated with wire and/or fragment movement during periods of surge was noted under and
adjacent to the wire in 73% of the live fragments during initial surveys (Figure 14.8A) However,
this was not always the case, as 22% of restored fragments had completely or partially overgrown
the wire Conversely, the wire used during the midcourse correction (July 2000) did not appear to
negatively affect fragment survivorship, as tissue overgrew the wire within 30 to 45 days Most
wire breakage and fragment loss occurred prior to the midcourse correction (23%), with detachment
of <0.5% of the remaining fragments occurring between August 2000 and August 2003
14.3.5 E FFECTS OF S IZE , O RIENTATION , AND A TTACHMENT S ITE
Fragment length, attachment site, and orientation appeared to affect patterns of survival over 6 years
The highest rates of mortality were recorded between 1999 and 2001 (20 to 38% per year); these
were primarily small fragments (mean = 59 cm) and fragments attached to skeletons Additional
fragments that died between August 2001 and August 2003 (5.4%) were larger than those that died
in the first 3 years (t-test, p< 0.01), but they were still smaller than the remaining fragments
FIGURE 14.4 Size and condition of remaining live fragments in August 2003 The bars illustrate the percent
of fragments in each size class oriented upright (white bars) and oriented down (spotted bars) The diamonds
refer to the mean percent partial tissue mortality for each size class Standard error is presented for partial mortality.
0
10
20
30
40
50
15–24 25–49 50–74 75–99 100 125 150 175 >200
Size class (cm)
0
10
20
30
40
50
Up, n = 248
Down, n = 129
% mortality
60
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FIGURE 14.5 ( See color insert following p 240.) Signs of recovery among restored A palmata fragments Ruler is 15 cm A Growth of tissue over the wire B Fusion with the substrate C Fragment secured to the reef with numerous protobranches as of 2002 D Growth of a fragment onto an elkhorn skeleton (2003).
E Fragment attached to a standing elkhorn skeleton (2003) The fragment has grown over the skeleton and produced multiple branches F Planar view of a restored fragment secured to the reef The fragment is firmly
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(Table 14.1) Fragments attached to the reef and oriented upright exhibited the highest rate of survival
(33.7%), while fragments attached to skeletons and oriented down had the highest rate of mortality
(85%) (Table 14.2) A significant relationship was observed between size and survival, with larger
fragments surviving better than small fragments over 6 years In contrast, there did not appear to be
any interaction between attachment site and orientation (Table 14.3) Survival was also related to
attachment site and orientation (Table 14.4); however, this may be due to variations among treatments, as:
1 A greater number of restored fragments were originally attached to the reef (56%)
2 Fragments attached to the reef were larger in size (75 cm) than fragments attached to
skeletons (53 cm)
14.3.6 E FFECT OF D EPTH
Restored fragments were reattached throughout the grounding site from about 2 to 6 m depth
Fragments attached to the reef in the shallow depths were detached more frequently than were
fragments in deeper water and fragments attached to skeletons.4 Fragments at intermediate
depths (3 to 4 m) exhibited the highest survivorship, with losses in excess of 85% in areas
deeper than 4 m
FIGURE 14.6 Relationship between fragment length and length of protobranches (rectangles) and number
of protobranches (diamonds).
FIGURE 14.7 Prevalence of disease (open diamonds), the gastropod Coralliophila abbreviata (squares), and
sponge (Cliona spp.) overgrowth (solid circles) during semiannual surveys.
0
2
4
6
8
10
0 20 40 60 80 100 120 140 160 180 200 220
Fragment length (cm)
0
10
20
30
40
50
Protobranch length r2 = 0.58 Protobranch number r2 = 0.60
0
1
2
3
4
5
6
8/99 5/00 8/00 5/01 8/01 5/03 8/03
Cliona
Snails wbd
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FIGURE 14.8 ( See color insert following p 240.) Factors contributing to fragment mortality A Partial tissue mortality associated with abrasion from the wire used to secure fragments B Fragment attached to a
the presence of nails and wire E Restored fragment with white-band disease F Large fragment that has experienced 99% partial mortality but continued to hang on The insert in the upper right is a close-up of the
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TABLE 14.1 Condition Fragments in August 2003
Attachment Orientation
No
Live
Length of Live Fragments
Percent Old Mortality
Percent Recent Mortality
Percent Dead Fragments
Length
of Dead Fragments
Reef Up 134 93 (3.5) 36.4 (2.9) 1.0 (0.5) 66.3 68 (1.9)
Down 55 80 (5.0) 39.8 (3.9) 0.8 (0.3) 74.8 68 (2.5) Skeleton Up 149 65 (3.2) 40.5 (2.3) 0.4 (0.1) 70.0 49 (1.4)
Down 34 62 (4.9) 48.6 (6.0) 0.3 (0.3) 85.0 48 (1.5)
Note: The total number, mean length (cm), and degree of partial mortality are shown for live fragments attached to the reef or skeletons and oriented up or down, followed by the percent of dead fragments and their length (cm) Standard error is in parentheses.
TABLE 14.2 Extent of Growth and Partial Mortality for Live Fragments in 2003
Attachment Orientation No.
Length (cm)
Percent w/Protobranches
No Proto-branches
Size of Proto-branches (cm)
Percent Mortality
Reef Up 134 93 (3.5) 66 4.9 (0.4) 24 (1.6) 37.4 (2.9)
Down 55 80 (5.0) 49 3.8 (0.4) 19 (2.2) 40.6 (3.9) Skeleton Up 149 65 (3.2) 59 4.3 (0.4) 20 (1.4) 40.9 (2.3)
Down 34 62 (4.9) 38 3.5 (0.6) 18 (0.6) 48.9 (6.0)
Note: The amount of partial mortality and extent of new growth (protobranches) are shown for the remaining live fragments that were attached to the reef or skeleton and oriented up or down with their original orientation on the source.
TABLE 14.3 Three-Factor Analysis of Variance (ANOVA) Testing for Relationships between Fragment Length and Orientation (up or down),
Attachment Site (Reef or Skeleton), and Survival (Live or Dead)
Source of
A Orientation 10.631 1 10.631 3.353 0.067
B Attachment 344.444 1 344.444 108.630 < 0.0001
C Survival 196.488 1 196.488 61.968 < 0.0001
A × B 6.555 1 6.555 2.07 0.151
B × C 0.897 1 0.897 0.28 0.595
A × C 0.048 1 0.048 1.6 0.2
A × B × C 6.759 1 6.759 2.132 0.145 Error 419 1323 0.983
Note: Length (cm) data were log transformed.
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