Coral Reef Restoration Handbook - Chapter 2 pptx

26 Coral Reef Restoration Handbooksedimentation rates, have received great attention from the scientific community.4,7–11 However, there is comparatively little information on direct ant

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of Small-Boat Grounding Damage to Shallow Corals of the Florida Keys

Steven J Lutz

CONTENTS

2.1 Introduction 25

2.2 Materials and Methods 26

2.3 Results 29

2.3.1 Geographic Distribution 29

2.3.2 Reef Sites 30

2.3.3 Head/Cluster Size 31

2.3.4 Depth of Head/Clusters 32

2.3.5 Mooring Buoys 32

2.4 Discussion and Conclusions 32

2.4.1 Geographic Distribution 33

2.4.2 Reef Size 33

2.4.3 Head/Cluster Size 33

2.4.4 Depth of Head/Clusters 33

2.4.5 Mooring Buoys 34

2.4.6 Impacts to Individual Coral Heads 34

2.4.7 Trend in High User Pressure 34

2.4.8 Management Considerations 34

2.5 Conclusion 36

Acknowledgments 36

References 36

2.1 INTRODUCTION

For thousands of years coral reefs have survived natural impacts, such as storms, diseases, and predation What they cannot withstand is the combination of these natural impacts with severe or repeated anthropogenic damage, such as overfishing, sedimentation, and excess nutrients Reefs around Jamaica and San Andres have been devastated by this combination,1,2 and Florida reefs are widely reported to decline.3,4 Indeed, according to Wilkinson (1992),5 South Florida’s reefs are so

“threatened” that they may disappear in 20 to 40 years

Anthropogenic impacts to corals can be divided into direct and indirect effects.6 Indirect anthropogenic impacts throughout the Florida Keys, which include poor water quality and high 2073_C002.fm Page 25 Friday, April 7, 2006 4:36 PM

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26 Coral Reef Restoration Handbook

sedimentation rates, have received great attention from the scientific community.4,7–11 However, there is comparatively little information on direct anthropogenic damage, such as broken or over-turned corals, on Florida coral reefs Much of this research has been related to the damage and rehabilitation of larger vessel groundings, which are highly visible and well documented.12–14

In contrast, little or no information on direct physical damage to corals caused by smaller vessels is available Previous studies and reports have noted this form of damage,12,15–20 also referred

to as “orphan groundings” by Florida Keys National Marine Sanctuary staff However, the amount

of damage caused by small vessels that are able to leave grounding incidents under their own power

is unreported and may be vast; certainly, such incidents are much more numerous than large vessel groundings In the Florida Keys small-vessel grounding damage may be particularly widespread because many of the reefs that attract visitors have shallow-water corals Assessing the extent, amount, and impact of this form of anthropogenic damage to coral is essential for reef management This report is the first estimate of the geographic distribution and severity of small-vessel grounding damage on shallow-water massive corals of patch reefs throughout the Florida reef tract

In this assay 315 shallow-water massive coral colonies from 49 reef sites within the Florida reef tract were examined for signs of boat grounding damage

2.2 MATERIALS AND METHODS

This study was conducted from August 1996 to January 1997 on 49 reef areas with high-profile shallow-water coral heads or clusters of heads in the Florida Keys reef tract (Figure 2.1 and Figure 2.2) All but one of the reef sites surveyed were patch reefs; the exception was Carysfort Reef, a bank-barrier reef Patch reefs occur throughout the Florida reef tract They are particularly abundant in the waters off northern Elliot Key and south Key Largo, which include over 5000 patch reefs.21 Patch reefs typically occur in water 2 to 9 m deep and vary from 30 to 700 m in diameter.22 In the Florida Keys, the framework builder coral species of patch reefs include Siderastrea siderea, Diploria strigosa, D labyrinthiformis, Colpophyllia natans, Montastraea annularis, and M faveolata. These corals have been termed boulder or massive corals.23Montastraea annularis (senso lato) is partic-ularly important as it has been described as a “keystone” species24 and can exhibit lateral growth

as it approaches sea level This massive coral can be found growing in individual colonies, or heads, and in groups of amalgamated colonies, or clusters, growing together They can grow to be up to

100 m2 in area and have up to 5 m of relief.25 Shallow-water massive coral heads and clusters of shallow massive coral heads are termed head/clusters for the purposes of this study The geographic location of each reef site was recorded with a hand-held global positioning system

The exact depth and diameter of each coral head/cluster found within 2 m of the surface was recorded for each reef site The survey depth of 2 m was chosen to accommodate for tidal range (~1.5 m) and the maximum depth of typical hulls and/or propellers for small vessels (~1 m) The Northern Florida Keys tidal range was determined by inspection of tide tables.26,27 To account for tidal variation, all in situ depth measurements were standardized to depth below spring mean low water tide level Standardized depths ranged from 0.1 to 1.0 m According to vessel registration records, the majority of registered vessels in Miami-Dade and Monroe Counties are pleasure craft from 16 to 26 ft in length In the two counties, 36,312 such vessels were registered in 1994, accounting for 56% of all registered vessels.28 Miami-Dade and Monroe Counties are the closest counties to the northern Florida reef tract All of the corals in this survey were potentially susceptible

to small-vessel grounding damage

Reefs surveyed contained from one to 28 shallow-water head/clusters with the majority, 75%, containing from one to five head/clusters In total, 315 coral head/clusters were measured Head/clusters ranged in size from less than 1 m (a singular head) to 18 m in diameter (a large cluster of amalgamated heads) The majority, 79%, were less than 5 m in diameter Tidal range corrected depth of the top surfaces of head/clusters ranged from 25 cm to 1 m in depth; 39% from 0 to 0.25 m deep, 51% from 0.25 to 0.75 m deep, and 10% from 0.75 to 1 m deep 2073_C002.fm Page 26 Friday, April 7, 2006 4:36 PM

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A Thousand Cuts? 27

Of the 315 shallow-water head/clusters surveyed, 312 were Montastraea spp and three were

S siderea Montastraea spp were identified according to the classifications of Weil and Knowlton (1994).29Montastraea annularis and M faveolata were the only Montastraea spp recorded in the survey These two coral species commonly co-occur.30

FIGURE 2.1 Approximate locations of reef sites surveyed (North Florida reef tract).

South Florida

Lower

Keys

Middle Keys

Upper Keys

N

Caesar Creek

Bache Shoal patch reef Patch reef east of channel marker 11 Patch reef east of channel marker 13

Patch reef east of channel marker 19

Patch reefs southeast

of channel marker 17

Patch reefs east of channel marker 21

East Basin Hill Shoals patch reefs

Carysfort reef

Basin Hill Shoals patch reefs

North Sound

South Sound

Cannon patch reef

Mosquito Bank patch reefs

Dry Rocks patch reef

25 10'

25 20'

Land Reef area with shallow head/cluster corals, undamaged

Reef area with shallow head/cluster corals, damaged

Broad Creek

Ha

wk Ch ann el

(appr

ox r out e)

Ell iot K

ey

Ke y L arg o

2073_C002.fm Page 27 Friday, April 7, 2006 4:36 PM

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Although Acropora palmata is commonly found growing close to the surface, this coral was not included in the survey This coral species is particularly vulnerable to natural fragmentation during storms, which renders it difficult to distinguish between natural and anthropogenic damage.31,32 For underwater observations of direct physical damage a meter rule marked in 2- and 10-cm increments was used Damage was recorded in squarecentimeters and as the extent of surface area destroyed Two forms of physical damage were identified, collision damage and scarring damage Collision damage occurs when a coral is crushed and split by a vessel’s hull into multiple fragments Hull paint is often driven into the coral skeleton (Figure 2.3A and Figure 2.3G) Scarring damage, from boat propellers, tears off live coral, exposing the skeleton In propeller scarring, typical scarlike striations are seen (Figure 2.3B, Figure 2.3C, Figure 2.3D, Figure 2.3E, Figure 2.3F, and Figure 2.3I), and large fragments of coral can be chipped off (Figure 2.3E, Figure 2.3G, Figure 2.3H, and Figure 2.3I) Any damage whose source was not readily identifiable, for example when the surfaces were completely overgrown by turf algae and the corallites were not exposed or identifiable, was not included in the survey

Statistical analysis was performed with the t-test and analysis of variance (ANOVA) where applicable

FIGURE 2.2 Approximate locations of reef sites surveyed (Middle and South Florida reef tract).

South Florida

Upper Keys

25 58'

80 34'

81 24'

24 38'

24 36' Munson Heads patch reefs Newfound Harbor Keys

81 28'

Loggerhead Key

Monkey Head patch reef

Hawk Channel (approx route)

Approach to Newfound Harbor Channel

Hawk Channel to the southeast

The Rocks patch reefs

Lower

Keys

Land

Reef area with shallow head/

cluster corals, undamaged

Reef area with shallow head/

cluster corals, damaged

Middle Keys

B

A

N

A

Pl ant ation K ey

Ne

w Snake Cre ek

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A Thousand Cuts? 29

2.3 RESULTS

2.3.1 G EOGRAPHIC D ISTRIBUTION

The results indicate that boat damage was widespread Most (57.1%) of the shallow-water reef sites surveyed showed signs of damage Of the 315 coral head/clusters found on those reefs, 79 (25%) had been damaged The total estimated area of destroyed coral found was 37,675 cm2 The area of damage to individual head/clusters ranged from 25 to 5800 cm2 Most damage found on

FIGURE 2.3 Damage to various head/clusters A Patch reef southeast of channel marker 17, Biscayne National Park (BNP) Arrows indicate boat hull paint embedded in coral B Patch reef east of channel marker

21, BNP Arrow indicates small propeller scar C Mosquito Bank patch reef, John Pennekamp Coral Reef State Park (JPCRSP) D East Basin Hill Shoals patch reef, Florida Keys National Marine Sanctuary (FKNMS).

E Basin Hill Shoals patch reef, JPCRSP F Patch reef area southeast of channel marker 17, BNP G Bache Shoal patch reef, BNP Arrows indicate crushed coral and boat hull paint H Munson Heads patch reef, FKNMS I East Basin Hill Shoals patch reef, FKNMS.

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individual head/clusters was under 250 cm2 (illustrated in Table 2.1) Two reefs, Bache Shoal and Mosquito Bank (see Figure 2.1), had much more severe extent of damage than all other reef sites (3366 +/– 1570 cm2 (n = 6) on Bache Shoal and Mosquito Bank compared to 775 +/– 109 cm2 (n = 22) on all other reef sites, P = 0.0017) These two reefs accounted for 60.2% of all damage found (20,200 cm2) However the occurrence of damage incidents to head/clusters was not statis-tically significantly higher than at other reef sites (48.5 +/– 12.3% of head/clusters damaged on Bache Shoal and Mosquito Bank compared to 28.9 +/– 5.98% damaged on all other reef sites)

2.3.2 R EEF S ITES

Reef sites surveyed contained from one to 28 shallow-water massive coral head/clusters The total amount of damage found on head/clusters per each reef site ranged from 25 to 10,925 cm2 coral destroyed

For a comparative assessment of reef size damage, reef sites were divided into three size categories: small (zero to five head/clusters per reef); medium (six to 15 head/clusters per reef);

(I)

FIGURE 2.3 (Continued.)

TABLE 2.1

Percent of Damaged Head/Clusters by Area of Coral Destroyed

Area of Coral Destroyed (cm 2 )

Percent of damaged

head/clusters

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A Thousand Cuts? 31

and large (>15 head/clusters per reef) (illustrated by Table 2.2) Damage among these reef size

classes was distributed in the following proportions: 17 of the 36 (47.2%) small reefs, four of the

six (66.6%) medium reefs, and seven of the seven (100%) large reefs had signs of damage

A significant correlation was found between the number of shallow-water head/clusters per

reef site and the amount of damage (mean total area in square centimeters per reef site): large reefs

= 2557 +/– 1414 cm2 (n = 7); medium reefs = 700 +/– 375 cm2 (n = 6); small reefs = 421 +/–

117 cm2 (n = 36), P = 0.0055 A significant correlation was also found between the number of

shallow-water head/clusters per reef site and the mean number of damaged head/clusters per reef

site: (large reefs = 5.0 +/– 0.976 (n = 7); medium reefs = 2.5 +/– 1.147 (n = 6); small reefs = 0.806

+/– 0.19 (n = 36), P = 0.0001 (illustrated by Table 2.2)

However, the number of shallow-water head/clusters per reef site did not appear to influence

mean damage incidence or wound size: large reefs = 431 +/– 158 cm2 (n = 17); medium reefs =

218 +/– 68 cm2 (n = 4); small reefs = 528 +/– 125 cm2 (n = 7) (illustrated in Table 2.2)

2.3.3 H EAD /C LUSTER S IZE

In order to determine whether head/cluster size influenced damage incidence, the 315

shallow-water massive coral head/clusters were divided into three size categories: small (< 5 m diameter);

medium (5 to 10 m diameter); and large (>10 m diameter) (illustrated in Table 2.3) No connection

was found concerning damage incidence; 54 of the 240 (22.5%) small head/clusters, 17 of the 47

(36.1%) medium head/clusters, and eight of the 28 (28.5%) large head/clusters were damaged

TABLE 2.2

Reef Size and Damage

Reef Size Class (Number of Head/Clusters)

Number of head/clusters

per reef size class

damage

Mean number of

damaged head/clusters

TABLE 2.3

Head/Cluster Size and Damage

Head/Cluster Size Small (<5 m

Diameter)

Medium (5 to 10 m Diameter)

Large (>10 m Diameter)

Number of head/clusters per

head/cluster size class

Percent of damaged

head/clusters

per head/cluster size class

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However, it was found that head/cluster diameter did influence the extent of damage (mean area

in square centimeters per head/cluster size class) Medium and large head/clusters had more damage than did those in the small size class: small head/clusters = 77 +/– 15 cm2 (n = 240); medium

head/clusters = 282 +/– 131 cm2 (n = 47); large head/clusters = 194+/– 109 cm2 (n = 28), P = 0.0087.

2.3.4 D EPTH OF H EAD /C LUSTERS

The depth below mean low-water level of the top surfaces of the shallow-water head/clusters ranged from 0 to 1.0 m In order to investigate the effect of depth on damage, the head/clusters were divided into three depth categories: 0 to 0.3, 0.4 to 0.6, and 0.7 to 1.0 m depth (illustrated in Table 2.4) Damage incidence among the depth classes was distributed in the following proportions: 37 of the

123 (30%) 0- to 0.3-m deep head/clusters had signs of damage, as did 37 of the 161 (22.9%)

0.4-to 0.6-m deep head/clusters and five of the 31 (16.1%) 0.7- 0.4-to 1.0-m deep head/clusters Damage extent (total squarecentimeters of coral damaged per head/cluster) among the depth classes was distributed in the following proportions: 15,200 cm2 of the 0- to 0.3-m deep head/clusters coral was destroyed, 21,775 cm2 of the 0.4- to 0.7-m deep head/clusters coral was destroyed, and 700 cm2 of the 0.7- to 1.0-m deep head/clusters coral was destroyed The three depth categories do not signif-icantly differ from each other in either damage incidence or extent Neither, when damage occurs, does the depth of the top surfaces of shallow-water head/clusters affect the area of coral destroyed (mean areain square centimeters per damaged head/clusters) (0 to 0.3 m depth = 578 +/– 171 cm2

(n = 37); 0.4 to 0.6 m depth = 410 +/– 76 cm2 (n = 37); 0.7 to 1 m depth = 140 +/– 67 cm2 (n = 5).

2.3.5 M OORING B UOYS

Of the seven reef sites with mooring buoys that were surveyed, all but one had signs of damage

Of the 42 reefs without mooring buoys surveyed, 22 had signs of damage However upon statistical evaluation, it was found that whether or not a reef had a mooring buoy did not affect the frequency

of damage incidence (37.3 +/– 16.5% for reef sites with buoys [n = 7] compared to 30.3 +/– 5.9% for reef sites without buoys [n = 42]) Similarly, the extent of damage (mean areain square centimeters) found on reef sites is not affected by the presence or absence of mooring buoys (1415 +/– 485 cm2 [n = 22] on reefs without buoys compared to 1021 +/– 485 cm2 on reef sites

with buoys [n = 6]) The presence or absence of mooring buoys on a reef did not significantly

affect the degree of damage caused by small-boat groundings

2.4 DISCUSSION AND CONCLUSIONS

Most damage found on individual head/clusters was under 250 cm2 Although this category of damage appears widespread throughout the study range, it does not suggest that it is a cause of any specific decline in the health of corals throughout the Florida Keys reef tract Additionally, the Florida Keys

TABLE 2.4 Depth of Head/Clusters and Damage

Head/Cluster Depth

head/cluster

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A Thousand Cuts? 33

reef tract is a vast natural structure, most of which remains submerged out of smaller-vessel impact range during tidal fluctuations While the direct damage from small-boat contact does not pose a serious threat to its overall survival, the accumulated damage can degrade and destroy the structure

of localized areas of shallow-water corals and coral clusters, demonstrating this impact’s importance

to the health of localized head/clusters and contributing to the stresses these corals already experience

2.4.1 G EOGRAPHIC D ISTRIBUTION

The total amount of damage found at Bache Shoal and Mosqutio Bank was substantial, 60.2%

of all damage found Indeed, these reefs show impact levels significantly higher than those of all other reefs Bache Shoal is one of the closest shallow reefs with mooring buoys to metro-politan Miami and is directly adjacent to a major boating channel, Hawk Channel (see Figure 2.1) To prevent vessel impacts, it is marked by a triangular reef warning tower and channel marker at its north tip It is significant to note that all shallow head/clusters surveyed at Bache Shoal were damaged, suggesting that its level of use or boat traffic (and related impacts) exceeds the safety methods used Mosquito Bank, located adjacent to Hawk Channel and directly in the line of boat traffic coming from slips on Key Largo and South Sound, also has a high percentage (42.6%) of head/clusters damaged, indicating a high level of use or traffic and the need for additional protection Results also suggest that these reef areas may be experiencing collisions by vessels that are larger and/or going much faster than on other reef sites Mosquito Bank’s high percentage of damage supports the Florida Department of Environmental Protec-tion’s findings.33,34 Farther south, navigation channels and boater access may also play important roles in boat grounding damage, as The Rocks and Munson Heads are both adjacent to boating routes (see Figure 2.2)

2.4.2 R EEF S IZE

It appeared that reefs with five or more shallow-water head/clusters were more susceptible to small-boating damage than were reefs with fewer than five water head/clusters The more shallow-water head/clusters that a reef has, the more damage incidents or wounds, but the mean wound size remained the same, regardless of reef size Larger reefs may receive more damage because the likelihood of collision with a larger reef area is greater, even though smaller reefs are more numerous However, smaller reefs may also not be as attractive to small-boat traffic from tourists because they have less relief, smaller associated fish populations, and a smaller amount of live coral

2.4.3 H EAD /C LUSTER S IZE

It appeared that the larger, in diameter, a shallow-water head/cluster, the more damage, but the frequency of damage remains the same, regardless of diameter It is possible that small-vessel impact damage is infrequent overall and occurs at random However, when such damage occurs, the larger in diameter a head/cluster, the greater the chance that a single damage incident will result

in substantial damage

2.4.4 D EPTH OF H EAD /C LUSTERS

It was interesting to find that within the 1-m depth range from spring low tide, the depth of the top surfaces of shallow-water head/clusters did not significantly influence either the degree or extent of damage caused by small-boat groundings Therefore, all corals within a 1-m depth range from spring low tide are susceptible to small-vessel grounding damage If the sample depth range of this survey had been extended to 2 or 3 m, frequency and extent of damage might have significantly correlated with depth; this, however, would have greatly lengthened survey time

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2.4.5 M OORING B UOYS

One would expect to find higher levels of damage to shallow-water massive corals at reef sites with mooring buoys since mooring buoys tend to attract more recreational boaters However, the presence

or absence of mooring buoys on a reef did not significantly alter the frequency or extent of damage caused by small-boat groundings More recreational boaters may be drawn to reefs with mooring buoys, but they appear to avoid any significant additional damage to shallow-water massive corals

2.4.6 I MPACTS TO I NDIVIDUAL C ORAL H EADS

It might be expected that small-vessel groundings are an important cause of damage on localized cluster-heads Because boating damage tends to occur on the top surfaces of coral colonies, their detrimental effects may be more substantial than those of other types of lesions Damage caused by storm rubble, in contrast, tends to occur more often on the sides of large colonies, rather than the tops Large lesions may not completely heal, although partial regeneration may occur at the edges.35,36 It has been found that within a week of a scarring event, filamentous algae colonize exposed skeleton and inhibit coral regeneration Turf algae or other reef organisms may be well established by the time the healing margin of live coral reaches them The encrustation of some organisms (e.g., boring sponges, encrusting zoanthids) can lead to further bioerosion of the colony Meesters (1995),36 in a study regarding damage and regeneration on scleractinian corals, showed that many lesions on the top surfaces

of bleached coral colonies enlarged to numerous times their initial size, occasionally resulting in the

death of the entire colony Indeed, it appears that M annularis may be very sensitive to bleaching.36–38 Herbivorous fish pecking at the edge of a scar can consume turf algae and coral at the same time.39 In addition, coral scarring may affect the total health of the colony by forcing the coral to reallocate resources to regeneration, and away from growth, reproduction, and combating disease

Additionally, the cumulative effect of this form of damage to individual coral heads may have negative tourism consequences As impacts are to the shallowest and most accessible area of reefs, they are easily within snorkeling range Figure 2.3 clearly illustrates the diminished aesthetic value

of damaged coral heads

2.4.7 T REND IN H IGH U SER P RESSURE

The increasing trend of recreational use of South Florida marine habitat is evidenced by the 40.8% increase in registered vessels in 10 years in Miami-Dade and Monroe Counties (from 62,274 in

1993 to 87,699 in 2003).40,41 Indeed, it appears almost certain that continued high user pressure on the most frequented reefs will, in a short time, degrade the aesthetic and recreational qualities of the reefs Additionally, the continued high and relentless incidence of damage to these colonies will result in loss of the larger and older massive coral colonies For these reasons it is imperative that management deal with the small-boat problem as a priority

2.4.8 M ANAGEMENT C ONSIDERATIONS

This study indicates that the cumulative effect of small-vessel groundings presents a serious threat

to localized coral eco-health and contributes significantly to other reef stresses Marine parks and management in the Florida Keys are charged with the protection of the natural resources, especially coral reefs, under their jurisdictions Table 2.5 illustrates coral damage on shallow water reef sites

by management authority for reefs surveyed A comprehensive management plan is needed in order

to reduce the number of small-vessel groundings

Management’s options for minimizing this type of anthropogenic damage would vary according

to available manpower and funds In order to present a scientifically based management plan, the author suggests that, first, localized shallow-water reef areas with high levels of user impact must be identified For “real time” observations, this type of survey should be carried out on an annual basis,

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