Marine life at wreck dive sites
Malta – a diving mecca! Fortunately, this is how scuba divers and snorkellers view the Maltese Islands. But according to divers who practise their sport here, fish and other marine life are not abundant locally, which makes dives “less interesting”, at least compared to some other parts of the Mediterranean and exotic diving destinations such as those in the Red Sea.
There are scientific reasons for this. One concerns nutrients – substances in the environment that provide essential nourishment for living organisms. Marine biologists classify the Mediterranean Sea as oligotrophic, meaning this sea has a low amount of nutrients. The waters surrounding the Maltese Islands have even lower amounts of nutrients compared to other Mediterranean coastal areas.
This results from: (i) the relatively distant location of the islands from the continents, and hence from important nutrient input via rivers into the sea, and (ii) the archipelago’s small size and high exposure to sea currents that disperse and dilute the nutrients.
Since nutrients are important for plants, which support other marine organisms including animals that depend on them, an indirect consequence of the low amounts of nutrients in our coastal waters is a low abundance of marine life, including fish.
Another reason for the low numbers of fish is Malta’s high population density and consequent high levels of disturbance to the marine environment, including overfishing.
One way to increase the attractiveness of a coastal dive site, while also enhancing the abundance of fish and other marine life, is to introduce an underwater artificial structure. There are several such structures, including artificial reefs designed to enhance marine life.
A more attractive category of underwater artificial structures are wrecks of airplanes or vessels which have been scuttled at sea intentionally or not. Wrecks that have been unintentionally scuttled around the Maltese Islands include airplanes and vessels that sank during the two world wars. Four such wrecks – two airplanes and two vessels – are located in waters that are less than 40 metres deep, and hence within reach of the recreational diver. Another eight wrecks – all vessels – have been intentionally scuttled to enhance dive sites.
When scuttled at an appropriate site, for example, a sandy bottom that supports no plants and few associated fauna, and where no species or habitat of conservation importance are present, a wreck will serve as a habitat for many species, particularly fish fauna.
Marine life is primarily attracted to wrecks because the animals find refuge in the nooks and crannies, and food on the surfaces on the structure and around it. The increased marine life associated with wrecks, their aviation and maritime history, as well as the many associated parts and machinery that are not normally closely observable on working airplanes or floating vessels, makes the structures very attractive to divers. Furthermore, wrecks often have an exciting or tragic history, and present a different challenge to the diver.
During the past 14 years or so, the Professional Diving Schools Association, with the support of the Malta Tourism Authority, has successfully promoted new wreck dive sites around the Maltese Islands by intentionally scuttling vessels at suitable locations. As a result, Malta has become one of the most popular wreck dive destinations in Europe.
Identifying and assessing a new wreck dive site is a long and detailed planning process that requires consultations with several authorities, in particular the Malta Environment and Planning Authority and Transport Malta, which also needs to grant the necessary permits.
Often, the scuttling of a vessel entails an Environmental Planning Statement, which involves studies and assessments, including detailed descriptions of the project (including justification for the project and waste management aspects) and of the identified site and surroundings (including land and sea uses, environmental aspects, archaeological features and cultural heritage), assessment of environmental impacts and risks, and formulation of mitigation measures and an environmental monitoring programme.
When the permits are obtained, a vessel destined for scuttling is cleaned of potential pollutants and towed to the targeted site, where it is scuttled according to a well-planned and detailed operation that can take several hours.
The sinking of the vessel takes a short time, sometimes only a few minutes, but is crucial for the success of the project. Improper positioning of the structure may result in the vessel capsising and resting upside down on the seabed, in which case it loses much of its appeal to divers or may even be dangerous for diving.
Alternatively, the vessel may end up at a site that is distant from the intended location, which may be unsuitable for recreational diving (as when the water depth exceeds the safe limit for recreational diving), or where the seabed supports a habitat or species of high conservation importance, which may be adversely affected by the presence of the structure.
Part of the Environmental Impact Statement involves detailed studies of the marine environment at the identified site. Such studies include collecting physical environmental data (such as the type and state of seabed, sea currents and wave action), characterisation and mapping of the seabed habitats, and assessment of the species associated with the bottom and the water column, in particular plants and animals of high ecological value and/or conservation importance.
The studies also involve collection of data on the fish fauna at the site – this information will eventually be compared with data collected after the vessel has been scuttled to enable assessment of whether the presence of the wreck on the seabed has resulted in an increased or decreased abundance of fish.
Monitoring studies are also carried out after the wreck has been scuttled. This is an essential requisite and forms parts of the conditions of the Mepa permit. The Malta Marine Foundation, which has lately been responsible for promoting and managing wreck dive sites where vessels have been scuttled for use as a diving attraction, has been regularly commissioning the necessary studies on the marine environmental monitoring of wreck dive sites.
The necessary funding for such monitoring services is provided by the MTA, which commissions such studies through a call for tenders. The most recent monitoring studies, undertaken during the past two years, are those concerning the P29 wreck located off Cirkewwa and the P31 wreck off west Comino.
The reports indicate that the surfaces of these two wrecks, which have been scuttled on a sandy seabed, serve to mimic a natural hard bottom habitat, and support several species of flora and fauna. But the diversity of flora and fauna found attached to the metal surfaces of the wrecks appears to be lower compared to that found on rocky bottoms.
One reason for this is that marine flora and fauna are capable of recognising the chemical composition of a hard surface to which they may attach, and most species tend to prefer natural surfaces such as rocky bottoms and large boulders, on which they seem to grow and survive better. Another reason is that the metal surface tends to deteriorate slowly but steadily; this makes the surfaces generally less stable for the attached marine life.
On the other hand, the findings from the monitoring studies indicate that wrecks greatly enhance the abundance and diversity of fish fauna, and that the fish that select wrecks as their new habitat are often very similar to those found associated with rocky bottoms.
Many different species of flora and fauna are found attached to the surfaces of wrecks in local waters, mostly on the exterior parts of the vessel, namely the hull, deck and cabin. The typical fauna comprise sponges, hydroids, fan worms (polychaetes), small hermit crabs and other crustaceans, sea stars and marine snails.
The fish fauna is usually very abundant and comprises comber, large shoals of damselfish, bogue and spicarel, several species of wrasse and bream, grouper and wreck fish. Marine flora and fauna is therefore certainly not lacking at local wreck dive sites.
The efforts of local diving associations, in particular the Malta Marine Foundation and the Professional Diving Schools Association, supported by the MTA, have been very fruitful. Divers who practise their sport around the Maltese Islands can visit various wreck dive sites, all of which support a diversity of marine life, while scuttling of the vessels at such sites has been carefully planned to ensure good access, as well as safe and interesting dives.
Joseph Borg is head of the University’s Department of Biology, and a marine ecologist.