Environmental impact of recreational diving
During the 20th century recreational scuba diving was considered to have generally low environmental impact, and was consequently one of the activities permitted in most marine protected areas. Since the 1970s diving has changed from an elite activity to a more accessible recreation, marketed to a very wide demographic. To some extent better equipment has been substituted for more rigorous training, and the reduction in perceived risk has shortened minimum training requirements by several training agencies. Training has concentrated on an acceptable risk to the diver, and paid less attention to the environment. The increase in the popularity of diving and in tourist access to sensitive ecological systems has led to the recognition that the activity can have significant environmental consequences.
Scuba diving has grown in popularity during the 21st century, as is shown by the number of certifications issued worldwide, which has increased to about 23 million by 2016 at about one million per year. Scuba diving tourism is a growth industry, and it is necessary to consider environmental sustainability, as the expanding impact of divers can adversely affect the marine environment in several ways, and the impact also depends on the specific environment. Tropical coral reefs are more easily damaged by poor diving skills than some temperate reefs, where the environment is more robust due to rougher sea conditions and fewer fragile, slow-growing organisms. The same pleasant sea conditions that allow development of relatively delicate and highly diverse ecologies also attract the greatest number of tourists, including divers who dive infrequently, exclusively on vacation and never fully develop the skills to dive in an environmentally friendly way. Low impact diving training has been shown to be effective in reducing diver contact.
Types of impact
Research on the effects of divers on tropical coral reefs has shown reduced coral cover on heavily dived sites and a change in coral structure, with more resilient corals becoming dominant and a loss of species diversity over time. These reefs may be less resilient to other stressors like disease outbreaks and severe weather damage.
There is persuasive evidence that reefs can be damaged and the amenity value of dive sites compromised by badly planned or over-intensive tourist use. Marine tourism affects reef communities directly through disturbance such as structural damage to corals, boats grounding on reefs and damage by anchors, and indirectly through alteration of water quality by nutrient enrichment and pollution by toxic substances, waste water and increased turbidity. The level of degradation depends on the intensity, frequency, time and type of use and the specific environment.
Diver impact damage to corals includes skeletal breakage of branching species, tissue abrasion, possibly leading to infection by coral diseases, and an overall reduction of hard coral coverage on reefs. Diving related activities may also reduce the reef's resilience to reef stressors like climate change and bleaching events.
In some frequently dived tropical coral reef sites recreational divers have caused negative ecological impacts by inadvertent impacts with live corals causing physical damage at a rate faster than compensated for by natural recovery. The long term result is reef degradation. One of the common challenges for local policy and management is maximising tourism benefits while also reducing environmental degradation to long-term sustainable levels.
In the soft sediment bottomed "muck diving" environment, it was observed that photography causes greater environmental disturbances than effects caused by diving experience, certification level, gender or age. Divers came into contact with the substrate more often on soft sediment than on coral reefs, but environmental damage was not greater. Divers tend to touch animals more frequently when observing or photographing cryptobenthic fauna, and spent up to five times linger in interactions when using dSLR-cameras. Long-term impacts of this behaviour on cryptobenthic fauna and soft sediment habitats are unknown.
The impacts of photographer behaviour and photographic flashes on a small sample of benthic fish species was investigated. The study showed negligible effects beyond those caused by human presence alone. Flash photography caused no discernible ocular changes in seahorses and feeding success was not affected. Physical handling of animals produced strong stress responses.
Diver impact on subtropical, and particularly temperate reefs is less researched than tropical reefs. The perception is that these reefs are less vulnerable than tropical reefs and the sessile species are less exposed to diver impact. Research in the Mediterranean in Spain indicates that sessile organisms with fragile and brittle calcareous or corneous skeletons are not resilient to frequent disturbances by divers.
Diver contact with the bottom is also prevalent on temperate reefs. One of the main forms mentioned is fin contact with the bottom sediment, raising particulate material into the water column and degrading visibility.
Reasons for impact
Repetitive contact by divers and their equipment on the benthos is the general mechanism of reef degradation by recreational divers. Factors correlating with frequency of reef contact were found to be:
- Interval since the previous dive
- Experience in terms of number of dives to date
- Location of certification training
- Awareness of marine park zoning
- Use of photographic equipment - photographers are more likely to contact the reef while their attention is focused on taking a photo.
- Depth of the dive
- Large groups of divers gathering at the beginning of a dive before they establish neutral buoyancy
Fin impacts have been identified as contributing the most to damage to reef biota, erect and branching hard corals are the most sensitive taxon to contact damage, and the severity of damage is influenced by habitat complexity. This indicates that better diver trim, buoyancy and finning techniques, situational awareness of position relative to the reef, and awareness of the damage done by contact with corals in habitats where close proximity of fins to sensitive organisms is likely, are priorities for reducing damage. Training in low impact diving skills appears to significantly reduce contact with the benthos in divers of all certification and experience levels. This result can be extrapolated to other diving environments as a method to protect the environment and help to make recreational scuba diving more ecologically sustainable, and may enhance the diving experience.
Several studies have found the main reason for contact by inexperienced divers to be poor buoyancy control. There appears to be little correlation between site topography and coral damage, but damage is related to coral morphology and structural strength. Most damage is to branching species which are inherently weaker against bending loads.
Studies on recreational divers on tropical coral reefs have shown that the rate of contact between diver and environment varies significantly between divers who are able to maintain neutral buoyancy and those who are deficient in the skill, with divers who do not maintain neutral buoyancy contacting the reef more often. Briefing divers on the effects of contact with the reef reduced contact in divers with good buoyancy skills, but not in divers who lacked those skills. The problem appears to be one of competence. Without the necessary competence, divers are unable to modify their behaviour appropriately, and cannot produce the skills merely by being made aware of their necessity. The solution to reducing reef contact is in requiring the diver to have the skill before allowing them to dive in the environment where it is needed.
There is evidence that the ability of dive guides to positively influence diver behaviour relating to reef contact is less for larger groups of divers, but the implementation of programmes which focus on dive industry operations can contribute to the reduction of anthropogenic reef damage.
Some MPAs in the Mediterranean have prohibited scuba diving completely, or have restricted it to reefs near the boundaries of the MPA. Others have established diving trails which keep divers away from vulnerable areas. Another conservation strategy identified potentially vulnerable species and based the determination of sustainable numbers of visitors on this.
Several studies have found that damage to coral reefs by divers can be minimized by modifying the behavior of those divers.
Strategies for reducing diver impact
- Correct weighting - a prerequisite for good buoyancy control
- Good buoyancy control - needed for level trim
- Level trim - brings fins higher above benthos on most reefs
- Reduction of dangling equipment - reduces risk of low-hanging items contacting reef when in close proximity
- Awareness of proximity to surroundings - allows avoidance of movements which will result in reef contact, particularly high impact contact
- Appropriate finning technique - finning technique should reduce risk of reef impact - select to suit lateral or vertical proximity
- Understanding of ecological effects of reef contact - allows avoidance of particularly vulnerable organisms
- Adjusting proximity to suit sea conditions - clearance between diver and benthos can be adjusted to allow acceptable risk of contact for variations in surge and current.
Low impact diving training
Low impact diving training has been shown to be effective in reducing diver contact. The specific PADI Low Impact Diver training program takes 2 days and appears to be effective for a large range of pre-existing skill and certification levels. Similar training from other providers should have similar results. Many of the skills are included in technical diver training, particularly cave and wreck diving, where they are also important for safety.
Strategies for sustainable use management
Several methodologies have been developed with the intention of minimising the environmental impact of divers on coral reefs
- Carrying capacity approach. where the number of divers is restricted. This also limits tourism income from the region. Sustainable diver carrying capacity is influenced by factors which vary between sites. These include coral morphology, presence of vulnerable species, environmental awareness and competence of the divers, presence of other stressors,size of the dive site, reef topography, and sea conditions. Continuous adjustment may be necessary to account for changes, unknowns and inaccurate models.
- Limits of acceptable change. This model uses quantitative limits on change defined in specific management objectives for a site using an established baseline. It does not handle natural variation well if this is unknown, and cannot distinguish between causes of change, some of which may be unrelated to diving. In some cases an undisturbed baseline may not be available.
- Percentile approach: This method considers a need for multiple reference sites and establishes trigger values quickly by comparing the extent of coral damage between dived sites and similar non-dived control sites. The trigger for management action is if the median abundance of damage to coral equals or exceeds the 80th percentile of damage at the reference sites. Limitations to this system include sensitivity to initial conditions - it does not work well if the reference sites are already significantly degraded, permanent moorings tend to concentrate damage to the region near the mooring, it may pick up false positives from damage from non-diver causes, and it is sensitive to conditions at the control sites.
- Restricting recreational divers to delimited locations, which usually concentrates divers and damage along diving trails. This creates paths of degraded reef through the more pristine areas, and will cause customer dissatisfaction as the trail degrades further.
- Regulating the type of diving equipment allowed, generally accessories which are thought to increase reef contacts, such as gloves and cameras. These restrictions are understandably unpopular with photographers, and may be applied to both divers who manage to avoid contact and those who do not.
- Changing the methods by which the industry provides services: Closer supervision and intervention by dive guides can reduce diver contact rates where the divers are sufficiently skilled to modify their behaviour during the dive. It does not address basic incompetence, which is common. A pre-dive briefing on responsible behaviour, regulations and environmental values can reduce the rate of diver impacts where the divers are sufficiently competent to avoid contact. Experience was not found to be a strong indicator of competence. More effective interventions occur when the ratio of divers to guide is low.
- Scuba diving tourism – Industry based on recreational diver travel
- Environmental issues with coral reefs – Factors which adversely affect tropical coral reefs
- Coral reef protection – Modifying human activities to reduce impact on coral reefs.
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