new or full moon. Equinoctial spring tides, those that are of greater than average range and flow, occur near the equinoxes in March and September, at new and full moon. Neap tides, those of minimum range and least flow, occur twice a month at or near the first and last quarters of the moon. These are best for wreck diving and photography. The word spring (an outflow of water) and the word neap (Anglo-Saxon for scanty) are both from Old English. Local tide tables enable divers to calculate incoming flood tides, (sea level rising), outflowing ebb tides (sea level falling) and slack water, the time of least flow when tides are changing from flood to ebb or vice versa.
The shape of the shoreline has an effect on the height of the tide. Where stretches of water are enclosed by a shoreline with a funnel shape, tides are amplified as the funnel narrows. The upper parts of Nova Scotia’s Bay of Fundy have the world’s highest tidal range – 16m (52ft).
THE MARINE ENVIRONMENT
Viewed from space the oceans dominate the earth, covering 70 per cent of our planet. They provide us with food, a large area for recreation and they regulate the climate. Mankind has treated the oceans as a rubbish pit for centuries. However, modern agricultural and industrial pollution is much more damaging and is accompanied by prodigious overfishing, often by detrimental methods. The combined effect has been threefold: huge plankton blooms (that suffocate organisms below), damaged reefs and depleted fish stocks. Ships taking on seawater as ballast in one region and discharging it in another, and aquariums emptying exotic fauna and flora into seas where they have no natural predators, have severely upset the ecology, often with disastrous results. We are slowly learning that there is a limit to the way in which we can treat the oceans.
Storm-driven wave action will occasionally damage coral reefs. However, some human activities, such as blast and cyanide fishing, coral mining, landfill, dredging, siltation caused by dredging or logging, and the indiscriminate collection of corals to sell as curios, are just as destructive. Similarly, overfishing depletes fish life, upsets the food chain and, in the case of herbivorous fish, leads to the corals becoming overgrown with algae. Corals found deep down in temperate waters are also being damaged by destructive fishing methods.
As diving becomes more popular, environmentalists are becoming increasingly concerned by the damage done by careless divers to live corals. Some diving operators in warm waters have banned the use of gloves, except on wrecks, in an effort to stop divers from holding on to live coral. If divers have to settle on the seabed to practise diving exercises or adjust equipment, they should do so only on dead sand to avoid killing live coral.
The growing awareness of environmental issues has given rise to ecotourism – tourism with an ecological conscience. Ecotourism is often summed up as ‘take nothing but photographs, leave nothing but footprints,’ but even footprints, as indeed any form of touching, is a problem for corals. It may be better to manage tourism, and the tourists themselves, in such a way as to be ecologically sustainable. The capital investment necessary to develop ecotourism is minimal, much-needed employment becomes available to the local population and in the long term the profits exceed those of logging or overfishing.
Although many divers, dive operators and diving resorts lead the field in protecting marine ecosystems, we all require somewhere to eat and sleep. If a small resort is built without a waste-treatment system, the nearby reefs may not be damaged irreparably. However, if those same reefs attract increasing numbers of tourists and more resorts, then controls on the resorts, visiting divers from nearby areas, and visiting live-aboard boats, become necessary.
Coral reefs are not the only places affected by divers, but that is where concentrations of divers are found. There is also concern over some divers’ behaviour in places where annual congregations of larger animals occur, but this can be controlled by educating divers and operators.
It has been suggested that in a few cases environmentalists have gone too far. If rules in one area are too strict, divers and snorkellers will lose interest in that area and either give up entirely or go elsewhere. Either way, if divers and snorkellers are not around regularly to keep an eye on the animals or coral reef, and the local people do not gain employment from tourism, there is more chance of unscrupulous fishermen wiping out the animals or using damaging fishing methods on reefs.
ECO-FRIENDLY DIVING
Ecological sustainability of the marine environment depends as much on individual divers as on dive operators and resorts.
■ Do not touch living marine animals or organisms with either your body or your diving equipment.
■ Control your fins. Their size and the force produced by the fin-stroke can damage large areas of coral. Do not use deep fin-strokes next to the reef, the surge of water can disturb delicate organisms.
■ Master good buoyancy control. Much damage is caused by divers descending too rapidly or crashing into corals while trying to adjust their buoyancy. Be properly weighted and if you have not dived for a while, practise your skills where you can do no damage.
■ Do not kick up sand. Clouds of sand settling on the reef can smother corals. Snorkellers should be careful not to kick up sand when treading water in shallow reef areas.
■ Do not stand on corals. Living coral polyps are easily damaged by the slightest touch. Similarly, never pose for pictures or stand inside giant basket or barrel sponges.
■ Do not collect or purchase shells, corals, sea stars, turtle shells or any other marine souvenirs.
■ If you are out of control and about to collide with the reef, steady yourself with your fingertips on a part of the reef that is already dead or covered in algae. If you need to adjust your diving equipment or mask, try to do so in a sandy area away from the reef.
■ On any excursion, whether with an operator or privately organized, make sure you take your garbage back for proper disposal on land.
■ Take care in underwater caverns and caves. Avoid several people crowding into a cave, and do not stay too long, because your air bubbles collect in pockets under the roof of the cave and delicate creatures living there ‘suffocate’ in air.
The endearing Dusky Anemonefish or Clownfish (Amphiprion melanopus) in a Heteractus crispa anemone at Pulau Redang.
A colourful Gorgonian with its polyps retracted on the reef edge at Calusa Island in the Philippines Sulu Sea.
Close-up of a Humphead or Napoleon Wrasse (Cheilinus undulatus) at Taytay Bay, Philippines. One of the largest of reef fish.
■ Before booking a dive trip on a boat, ask about the company’s environmental policy – particularly on the discharge of sewage and anchoring. Avoid boats, both live-aboard and day, that cause unnecessary anchor damage, have bad oil leaks, or discharge untreated sewage near reefs.
■ Do not participate in spear-fishing for sport, selectively killing the larger fish upsets the chain of reproduction. If you are living on a boat and relying on spear-fishing for food, make sure you are familiar with all local fish and game regulations and obtain any necessary licenses.
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