Lagoon / Marine life

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  • 29 November 2022
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Lagoon / Marine life

The lagoons of New Caledonia and in particular that of Ouvéa, are inscribed on the UNESCO World Heritage List, and form one of the most varied, largest, and best-preserved coral ecosystems on the planet.

To understand marine life in the Loyalty Islands, it is essential to keep in mind that the islands were formed by the ocean, carried by the Loyalty ridge, and separated from the Grande Terre, New Caledonia’s main island, by the basin of the same name, more than 2,000 metres deep. In the islands, the sea is always present and numerous clans have marine animals as their totem: sharks, fish, snakes, crabs, turtles, etc. Fragile balances are found here where white-sand beaches often give way to precipitous cliffs guarding hidden mangrove swamps, as on Ouvéa. A wide range of habitats coexist thanks to a fragile balance.

Reef formation

The full extent of the beauty of the Loyalty Islands is best appreciated during a dive. When you enter this living sanctuary, you must always keep in mind its great vulnerability. The reefs are exposed to human activity, but can also be threatened by natural causes, such as diseases or parasites.

Reefs originate from reef-building corals that are capable of fixing limestone. These corals are very particular and require very strict living conditions: water with constant salinity, well-oxygenated and with a temperature of between 20°C and 30°C. Give them a hard substrate as well, and magic occurs. The majority of coral species reproduce sexually, during a mass spawning that occurs for only a few days each year. Reef corals are also very colourful, thanks to the unicellular algae, the zooxanthellae, nestled in their tissues.

Apart from Ouvéa, the Loyalty Island seabeds present single facies, lined with sheer drops and caves along the limestone cliffs. Only Ouvéa and Beautemps-Beaupré retain a central lagoon. Coral reefs are among the richest ecosystems on the planet. Those in the Loyalty Islands are certainly no exception to the rule. They offer optimum comfort for life, providing habitat and food to all species that have chosen to live there.

Pinnacles and flats

Reef formations are rich and varied. Pinnacles are certainly among the most poetic. These underwater reliefs in the form of mounds are more or less rounded and set on a flat floor. Here and there they rise above the water’s surface, and some can reach several dozen metres in height. They are veritable little reef residences, home to numerous species that seem to squeeze in haphazardly, but in reality, are selected based on the lighting! Pinnacles offer perfect refuges for many fish and crustaceans.

On the reef flats, life is just as intense. The flats are exposed to the surface of the sea, and surviving there requires the development of grand strategies. The reef flats are subject to the swell on the Loyalty Islands, and also to the tides, leaving the flats exposed for some hours.

Passes, caves and cliffs

The Pacific Ocean is not a tractable child. The reef learns this each day to its cost. The strength of the swell combined with the fragility of the structures has led to the formation of caves and overhangs, where the deepest species have chosen to live. The dim light also favours their settlement. Groupers, moray eels, slipper and other lobsters and crabs find shelter there. They share this very particular space with orange corals, and especially with magnificent gorgonian coral.

Life on the cliffs is even more difficult. While the upper part, far too battered by the surf, is deserted by most species, the slopes are the preferred site of the gorgonian coral and the puffer fish.

As its name indicates, a pass in the reef breaks its continuity, to the great good fortune of pelagic species and the great predators. Rays, sharks, turtles, bulbnose unicornfish, barracudas, etc. For some species, the passes are the preferred location to reproduce. The larvae then colonise the reefs and lagoon areas.

Life in the reefs

According to a well-established order, life within the reefs varies both in space and time and depending on the environmental conditions and the food available. The diurnal and nocturnal populations cross paths and mix in a ballet that has gone on since time immemorial.

In the daytime, from the first light of dawn, the diurnal species wake up the reef! The tomato rockcod races after its breakfast, seeking small fish, crustaceans or molluscs. The angel fish and butterflyfish engage in well-practised choreography and parade a thousand nuances of blue, silver and yellow. The hermit crab goes its way looking for little living prey or, not being too fussy about freshness, makes do with carcasses.

The big pelagic fish, such as trevally, will take advantage of the light to slide between the corals in a group or alone, while bands of several hundred yellowfin goatfish parade along the reef.

Life is not a bed of roses for the reef species. Each one is trying to feed itself, stay away from its predators and ensure that it reproduces. To manage this, they have used gems of imagination and adaptation.

At night, the predators reign! While the diurnal species are looking for a place to hide for the night, the crustaceans attack the reef. Lobsters, crabs, prawns and hermit crabs wave their antennae around to find the best spots for zooplankton and invertebrates. They have to share their dinner with the squirrelfish and soldierfish.

More astonishing, some fish choose the dark waters of the night to change their pigment distribution, so they can pass unnoticed. This is true in particular of the bicolor goatfish and the bluestripe snapper. Others have developed strategies involving the environment. Thus some parrotfish secrete a cocoon of mucus which surrounds them and masks their odour!

All means are good for surviving and ensuring progeny. The famous clownfish live in the heart of the sea anemones’ stinging tentacles. The clownfish share this defence system with numerous prawns, which are also immunised against the stinging cells. The sea urchins have taken the spirit of hospitality as far as hosting prawns, fish or flatworms on their spines. Numerous crustaceans swear only by gorgonian coral, using it to camouflage themselves.

Life on the reef is not only a question of prey and predators. The strategies implemented to live together are numerous: parasitism, symbiosis, sharing food, protection, etc. All species participate in a fairy-tale world of colours heightened by the crystalline waters of the Loyalty Islands.

I take the plunge

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