The environmental impact of recreational diving is the effects of recreational scuba diving on the underwater environment, which is largely the effects of diving tourism on the marine environment. It is not uncommon for highly trafficked dive destinations to have more adverse effects with visible signs of diving's negative impacts due in large part to divers who have not been trained to sufficient competence in the skills required for the local environment, an inadequate pre-dive orientation, or lack of a basic understanding of biodiversity and the delicate balance of aquatic ecosystems. There may also be indirect positive effects as the environment is recognised by the local communities to be worth more in good condition than degraded by inappropriate use, and conservation efforts get support from dive communities who promote environmental awareness, and teach low impact diving and the importance of respecting marine life. There are also global coral reef monitoring networks in place which include local volunteer divers assisting in the collection of data for scientific monitoring of coral reef systems, which may eventually have a net positive impact on the environment.
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. 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 and resilient due to rougher normal 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. Various strategies for environmental management are being tested, in an attempt to achieve a sustainable balance between conservation and commercial exploitation.
Active avoidance of benthos contact requires appropriate motivation, and successful avoidance requires appropriate competence. Low impact diving training has been shown to be effective in reducing diver contact in suitably motivated divers. Experience appears to be the most important factor in explaining divers' underwater behaviour, followed by their attitude towards diving and the environment, and personality type.
Affected environments All underwater environments frequented by recreational divers are potentially affected, but the impact is observed to be greater where there are large numbers of dives or the environment has fragile slow-growing organisms or delicate structures. The more obvious examples are tropical coral reefs and flooded caves with fragile speleothems. Relatively large numbers of studies have been done on tropical coral reefs as the pressure on them has been perceived to be highest. Coral reefs are to some extent self-repairing, and also sustain damage from non-anthropogenic causes, so an acceptable level of continuous diver induced degradation is theoretically possible, which would be matched by the natural recovery rate. Underwater speleothems, once broken, do not regenerate at all while the cave remains flooded, and remain broken forever, if human timespans are considered. Underwater cultural heritage in the form of historically important wrecks and archaeological sites are also susceptible to irreversible damage, but they are usually constantly deteriorating in any case. Diver impact mainly accelerates the inevitable.
Subtropical, temperate, and polar marine reef environments vary considerably in their ability to recover from damage, and have historically been considered less impacted by diving, consequently fewer studies are available on diver damage, reef recovery and sustainable carrying capacity. These areas are emerging as diving destinations, as is research on diver impact on their environments.
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 longer 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, in freshwater environments, and in caves. One of the main forms mentioned is fin contact with the bottom sediment, raising particulate material to into the water column and degrading visibility, but disturbance of sediment and delicate benthic biofilms by fin wash without direct contact is also a concern.
The impact of recreational scuba diving on recreational dive values and the cultural heritage of shipwrecks has been found to comprise four basic types: The removal of artifacts and associated disturbance to wreck sites, Direct contact with wrecks and the benthic biota living on them by divers and their equipment, Exhaled air bubbles trapped inside the wreckage, Impact damage by anchors of dive boats, considered by some researchers to be the most damaging form of impact associated with recreational wreck diving. Shot line weights can also damage relatively fragile wreckage by impact and snagging, but usually to a lesser extent as the shot is generally lighter than an anchor or and there is less lateral load on it. This type of damage can be avoided completely by installing permanent moorings at frequently dived wrecks.
Gender distribution of diver impact on reefs is inconclusive, different studies have produced contradictory findings.
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 – A longer interval correlates with skill loss and poorer buoyancy control and trim. Experience in terms of number of dives to date – A lower number of dives correlates with poorer buoyancy control and trim. Location of certification training – Training in easy conditions does not develop more advanced skills, but experience in ecologically similar environments produces some familiarity with delicate and fragile organisms. 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 – divers were observed to make fewer contacts at greater depth. The reasons are not clear, but may be related to less water movement or less buoyancy variation with depth. Large groups of divers gathering at the beginning of a dive before they establish neutral buoyancy A considerably higher rate of impacts has been observed during the initial phase of dives and has been attributed to divers taking some time to get their buoyancy correct and to get themselves orientated, particularly when entry points are directly over shallow coral formations, or the divers are unfamiliar with the environment.
Observations that experience does not predict frequency of impacts is not necessarily incompatible with findings that practical training reduces frequency of impacts, as experience is not always an indicator of competence.