The Effects of SCUBA Diving on Coral Reefs

Raychelle Marsman, Undergraduate Student, Dalhousie University

Abstract Coral reef habitats are in danger of destruction due to the carelessness of divers. Stony coral, the foundation from which coral reefs are built, have proven to be the most easily damaged by SCUBA divers in the Caribbean and Red seas. Through observation of the behaviour of divers around coral habitats over ten minute intervals, researchers were also able to determine that the dive frequency of an area and the level of experience of the SCUBA divers are extremely important factors influencing how much damage is being done to corals. Overall, it is the areas of high dive intensity and the diving groups with the least experience that cause the most damage to all coral types. Aside from improving education of divers, it is important to monitor them and lessen the frequency at which certain sites are being dived in order to preserve the fragile balance of diversity within these habitats.

1. Introduction

Coral reefs, renowned internationally for their beauty and colour, are being threatened by our desire to observe them. Americans spend 1.2 billion dollars annually on tourism, much of which goes towards Caribbean isle vacations (Camp & Fraser 2012). Here, they have the chance to dive in one of the most spectacularly diverse ecosystems in the ocean. Coral communities are not solely for recreation, however, as they provide shelter, food and breeding grounds for many coral- dependant and independent species (Hawkins et al 1999; Glynn 2004). Millions of humans are also dependant on coral reefs. Coral reefs buffer thousands of miles of inhabited coastline from the full brunt of ocean waves as well as bring in billions of dollars annually through tourism and fisheries (Hoegh-Guldberg et al 2007). The loss of these corals would not only upset the fragile coral community food chain (Glynn 2004) but could also cause an economic breakdown in countries whose income is dependent on reefs.

Reefs also offer a unique opportunity to study a diversity of species in a relatively concentrated area (Glynn 2004; Hoegh-Guldberg et al 2007). SCUBA (Self-Contained Underwater Breathing Apparatus) became a means for scientists to study coral and their importance to the ecosystem more closely. With advancements in technology, SCUBA also became a leisurely venture by which tourists could see firsthand the majesty of coral reef communities. In order to dive with SCUBA, however, training is required (Camp & Fraser 2012). According to the Professional Association of Diving Instructors (PADI), almost one million people are certified every year for recreational diving. With interest in coral reefs growing and almost 250,000 dives per year within only 12 km of Red Sea coast alone (Zakai & Chadwick-Furman

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2002), the damage being done to coral reefs is becoming extensive. All of the reviewed studies, focusing on SCUBA and corals, observed the physical activity of unsuspecting divers during 10 minute intervals, taking note of the extent of damage being done to corals through contact.

They found that damage to coral reefs varies based on the intensity at which a certain site is being dived (Hawkins et al 1999), the type of coral (Rouphael & Inglis 1997) and the experience of divers (Zakai & Chadwick-Furman 2002). Although some may argue that the extent of damage to corals by individual divers is not enough to affect the overall health of local coral reefs (Rouphael & Inglis 1997), the data collected by Hawkins et al (1999) and Zakai & Chadwick-Furman (2002) suggest that the impact of coral diving on a large scale is far too great to be ignored. It is important to note the difficulty in determining a coral environment’s carrying capacity, which is an ecosystem’s specific ability to support itself without environmental degradation, with respect to diving activity. This is mainly due to the scientists’ inability to differentiate influences from factors such as climate change, ocean acidification and over-fishing, which all compromise the strength of coral reefs, from diving. Regardless, it is known that diving can weaken coral communities, lowering the carrying capacity and destroying entire areas in as few as 4000 dives per year (Hawkins et al 1999).

In order to protect coral reefs while still being able to profit from tourism, many researchers have proposed strategies to limit human contact with corals. The effects of diving on coral reefs is a well researched and reviewed topic but there is still conflict regarding whether diving is harmful enough to affect whole coral populations. Therefore, through the compilation of various research studies, this paper will investigate the impacts of SCUBA diving on coral reef communities of the Caribbean and Red seas and offer a definitive answer as to whether diving is a threat to coral habitats.

2. Investigating the Impacts of SCUBA diving on Corals 2.1 What are Corals?

Corals are classified under the class Anthozoan containing over 6000 species of invertebrate marine animals. According to Cole et al (2008), coral communities are highly self-sustaining and diversity dependent. They live symbiotically with many organisms but are also consumed for food. The species directly dependent on corals for food have their populations controlled by larger carnivorous organisms who are in turn controlled by top predators. This diversity is what sustains a healthy balance of life within the habitat. The foundations of coral reefs are stony corals (Scleratinians) whose thick CaCO3 shells provide shelter, protection and mating grounds for a diversity of marine life (Glynn 2004). These branching forms of coral have proven to be the most at risk of being damaged by SCUBA divers (Hawkins et al 1999). Damage to these corals, such as broken branches, does not always kill the organism but rather exposes their softer internal structure making them more susceptible to predators and disease (Hawkins et al 1999) (see Figure 1).

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Destruction of stony and other corals undermines the entire coral community through loss of essential diversity (Cole et al 2008). The threat to coral reefs is therefore apparent as without corals the entire ecosystem collapses. It is the fragility of these harmonious habitats that influence many researchers to investigate the exact cause of their widespread destruction.

Figure 1: Elkhorn coral (Acropora palmata), a stony coral, suffering from white band disease. The disease is characterized by large white patches and eventual loss of living tissue, exposing the skeleton beneath. Diseases such as this are irreparable. [Image from http://celebrating200years.noaa.gov/visions/coral/image11_220.jpg].

2.2 Methods used for observing divers and corals

The papers reviewed here focused on corals from regions that are immensely popular with tourists: the Caribbean islands (Hawkins et al 1999; Rouphael & Inglis 1997; Tratalos & Austin 2001) and the Red Sea (Zakai & Chadwick-Furman 2002). In order to study how divers interact with corals and the potential damage being done, it was important that the study sites were secluded enough to not be impacted by urban development or pollution (Hawkins et al 1999). This is, of course, so that any results collected are only reflective of divers. Wave height, depth of water and reef structure were also crucial factors in determining the perfect location to study SCUBA. As a control, Hawkins et al (1999) used reserved coral communities that were similar in terms of topography (Figure 2).

Determined to be the most effective time period through extensive testing by Rouphael & Inglis (1997), all studies used 10 minute interval observations of

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anywhere from 251 individual divers per site to over 9000 separate dives per site within a three month period (Zakai & Chadwick-Furman 2002; Figure 3).

Figure 2: Stylistic representations of the general reef topography at the three types of dive sites used in the study. (From Rouphael & Inglis 1997)

Figure 3: Estimated number of dives per 3 month period at 12 coral sites of the northern Red Sea in Eilat, Israel (January 1st-March 31st 1996). It is important to note that all bars in this bar graph are straight. (From Zakai & Chadwick-Furman 2002)

Since divers ascend and descend from mooring buoys, studies by Hawkins et al (1999), Rouphael & Inglis (1997) and Tratalos & Austin (2001) analyzed their data based on the distance that damage was found from the mooring. The study by Zakai & Chadwick-Furman (2002) factored in diver experience when observing the

R. Marsman \ Oceans First, Issue 2, 2015, pgs. 33-41. 36 Disclaimer: This is exemplary work from a first-year science writing class. The views expressed herein are not necessarily endorsed by Dalhousie University.

susceptibility of different coral types. Damage done by guided dives, introductory course dives and open water dives (one star being the lowest level) were recorded separately (Figure 3). As seen in Figure 4, damage to corals was differentiated into being skeletal (pertaining to the outer shell of stony corals), tissue abrasive (pertaining to the softer, more life-sustaining parts of the coral) or loss of coverage (pertaining to the loss of entire sections of reefs) in order to determine the severity of damage being done by each group.

Figure 4: Extent of damage done (%) to different types of coral (A-D) at four different sites in the northern Red Sea of Eilat, Israel (From Zakai & Chadwick-Furman 2002).

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2.3 Results of SCUBA diving with coral

The frequency and intensity at which a certain site is dived was of significant importance to the results of all studies. Hawkins et al (1999) discovered that more partially dead corals were found at heavily used diving sites when compared to sites with low usage. This study also observed that heavily dived sites had 1/5 less coral coverage and significantly more loose coral fragments when compared to the reserved control group. Tratalos & Austin (2001) saw very similar results. The study done by Rouphael & Inglis (1997), whose objective was to explore the effects of diving on different topographies (Figure 2), found that whilst topographies had no effect on the amount of damage being done, dive frequency plays a much larger role. Rouphael & Inglis (1997) observed that, within a 10 minute observation period, a diver could touch corals with either their hands or fins 5-41 times. Thirteen percent (13%) of these divers caused visible damage to corals, but the amount of damage varied significantly across sites. At one particular site, 45% of observed divers broke corals (see Figure 5). However, Rouphael & Inglis (1997) found no relationship between the frequency of dives in their six sites and the average percentage of broken or damaged colonies, which is in stark contrast to all other reviewed studies. Tratalos & Austin (2001), whose study was conducted in a very similar way to the study of Rouphael & Inglis (1997) found a 3.66% cover of dead coral fragments at areas of high frequency dives compared to only 1.80% and 1.69% at low and no frequency dive sites (respectively). At high frequency dive sites in the Red Sea, up to 100% of corals were damaged in some areas (Zakai & Chadwick- Furman 2002). Little correlation was found by any study between diver frequency and the damage done to soft corals.

Figure 5: The proportion of divers observed at each site who (a) made physical contact with or (b) broke corals during a 10min observation period, and the (c), mean (+ SE) number of contacts and (d) damaging incidents per diver per 10min interval (n = 25; Rouphael & Inglis 1997).

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All the studies agreed regarding the types of coral most susceptible to damage. Tratalos & Austin (2001) found a much higher percentage of broken hard corals in high intensity dive sites when compared to low intensity sites and reserves. This is supported by Zakai & Chadwick-Furman (2002), who observed that branching stony corals are the most likely to become damaged but, thanks to their CaCO3 shells (Glynn 2004), they sustain mostly reparable skeletal damage (Figure 4). As seen in the same figure, non-stony corals are much more likely to sustain severe tissue abrasion. Similar results were collected by Hawkins et al (1999) and Rouphael & Inglis (1997), who concluded that if damage were to occur to corals, it is most likely to be sustained by stony corals.

Though the distance of divers from the mooring buoy does not correlate to the amount of damage being done to corals (Hawkins et al 1999; Rouphael & Inglis 1997; Tratalos & Austin 2001), Zakai & Chadwick-Furman (2002) found that diver experience is of much more significance. Referring to Figure 4 and comparing it with the results of Figure 3, a visible pattern emerges: The more introductory dives there are at a specific site, the more damage is being done to corals. The Caves and Central reserve, both of which are classified as high use locations, were the two locations which suffered the most observed damage. These locations also had more introductory and guided tours (which take uncertified tourists out diving) than any other dive group type. This strongly suggests the need for better pre-dive education regarding the safety and importance of corals as well as better care by instructors.

All of the reviewed studies provide similar evidence showing that SCUBA divers do indeed significantly damage corals, but that the amount of damage depends on how frequently a certain site is dived at, the type of coral and the level of experience of the divers. The long-term implications of this, however, are still in need of research. The study by Rouphael & Inglis (1997) concludes that damage being done by individual divers is not enough to have a large impact on entire coral ecosystems, however the study does not take into account the increasing amount of tourists who dive every year (Camp & Fraser 2012). Zakai & Chadwick-Furman (2002) and others show that individuals within groups can be extensively destructive, damaging an average of 1.70±4.90 corals per 60 minute dive. When accounting for how many dives there are per year, the reality and danger of SCUBA diving is obvious.

3. Conclusion

As emphasized throughout the review, SCUBA diving is causing the destruction of coral reefs en masse. The goal of this review paper was to compile various studies in an attempt to definitively and informatively determine the effect of SCUBA diving on corals. There has been extensive research on this topic and the information reviewed provided the clear answer that SCUBA diving is a risk for coral communities. Although unintentional, with the amount of tourists visiting coral areas, the cumulative damage is something of concern to the scientific and touristic community (Hawkins et al 1999). Coral reefs provide one of the largest habitats to

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species in the world (Hoegh-Guldberg et al 2007) as well as physical protection from ocean swells and billions of dollars of income to dependant coastal areas. Preserving coral reefs is of benefit to not only the environment but to the global economy which thrives on touristic spending.

The reviewed papers observed the behaviours and impacts of divers during ten minute intervals, recording their activities and contact with reefs. Hundreds of thousands of dives happen each year in the Red Sea alone, accumulating the effects of high frequency diving before corals have the chance to recover. The study by Rouphael & Inglis (1997) claims that the small amount of damage being done by individual divers is not enough to affect local populations, but the collective data of all reviewed papers suggests a different conclusion. With up to 100% of divers making contact with reefs during each dive and thousands of introductory tours being conducted during every three month period (Zakai & Chadwick-Furman 2002), the amount of damage being done is no longer something that can be considered small scale enough to not destroy entire areas of coral reefs (Hawkins et al 1999).

It is important to note that research on the carrying capacity of coral reefs is still lacking and could be essential in determining exact limits at which to stop divers before damage becomes irreparable. Until more research on this is conducted, however, the reviewed papers share a common suggestion that coral reefs must be better surveyed and divers better educated in order to slow the further degradation of these beautiful communities. The personal suggestions of this review are best summed up by Zakai & Chadwick-Furman (2002) which states that proper management of coral areas should reduce the number of dives per site per year, mandate that all dives be guided, transfer all introductory courses to less fragile coral areas, divert recreational diving away from areas becoming highly dived and improve the education of divers concerning damage being done to corals (pre-dive). These recommendations have been implemented in coral areas before but have not been managed strictly enough to be effective (Zakai & Chadwick-Furman 2002). Successful application of these suggestions as well as further research into the carrying capacity of reefs is the only way to sustainably continue the well-loved practice of SCUBA diving with corals.

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R. Marsman \ Oceans First, Issue 2, 2015, pgs. 33-41. 40 Disclaimer: This is exemplary work from a first-year science writing class. The views expressed herein are not necessarily endorsed by Dalhousie University.

Hawkins JP., Roberts CM, Hof VT., De Mayer K., Tratalos J., Aldam C. 1999. Effects of recreational SCUBA diving on Caribbean coral and fish communities. Conservation Biology. 13(4): 888-897.

Hoegh-Guldberg O., Mumby PJ., Hooten AJ., Steneck RS., Greenfield P., Gomez E., Harvell CD., Sale PF., Edwards AJ., Caldeira K., et al. 2007. Coral reefs under rapid climate change and ocean acidification. Science. 318: 1737-1742.

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Tratalos JA., Austin TJ. 2001. Impacts of recreational SCUBA diving on coral communities of the Caribbean island of Grand Cayman. Biological Conservation. 102: 67-75.

Zakai D., Chadwick-Furman NE. 2002. Impacts of intensive recreation diving on reef corals at Eilat, northern Red Sea. Biological Conservation. 105: 179-187.

R. Marsman \ Oceans First, Issue 2, 2015, pgs. 33-41. 41 Disclaimer: This is exemplary work from a first-year science writing class. The views expressed herein are not necessarily endorsed by Dalhousie University.