ecology of Jellyfish Lake

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Posted by on June 29, 2004 at 09:10:43:

This Jakarta Post article is a very interesting description of the ecology of Jellyfish Lake.

Seawater species adapt to survive in wondrous lake

Tantri Yuliandini, Berau, East Kalimantan

As we began our descent into Kakaban Island's jellyfish lake, silt from the lake bottom rose up and muddied the otherwise clear water of this prehistoric, brackish wonder.

A natural process of over millions of years has created a lagoon on an atoll in the middle of the ocean, the like of which can be found at only one other place on earth -- Palau Island in Micronesia, about 750 kilometers southeast of the Philippines.

Lake Kakaban was created through a geological uplifting over a period of two million years, raising an atoll from 300 meters below the sea and trapping five square kilometers of seawater within a 50-meter-high ridge.

This effectively created a landlocked marine lake that -- because of the filtering effect of the coral and years of dilution by rainwater -- has lower salinity than that of the ocean.

The organisms found in the lake are originally seawater species such as marine algae, sea anemones, jellyfish, sponges, sea cucumbers, clams, and several small fish, which over thousands of years have adapted to their unusual surroundings.

Christien Ismuranty, the Indonesian Biodiversity Foundation's (Kehati) information, education and research program manager, said that since no connecting caves between the lake and the ocean have been discovered, no larger animals have been able to enter or leave the lake for thousands of years.

"The existing marine life had to adapt to brackish water, poor mineral content, small biota variation, a simple food chain and stagnant water.

"The resulting ecosystem is totally unique," she said during a recent trip to the islands.

Upon entering the warm water with snorkel and fins, one is immediately welcomed by the graceful dance of a thousand jellyfish.

Four species of endemic jellyfish lives in this lagoon: the Cassiopeia ornata, which has a habit of lying on its back and exposing its symbiotic algae to the sunlight to produce food, Mastigias papua, Aurelia aurita and Tripedalia cystophora.

It was a good thing that the Mastigias and Aurelia have lost their sting, for jellyfish were swimming all around us and were not at all timid in their welcome.

The lake is surrounded by a narrow mangrove belt, whose roots provide a habitat for tunicates, sponges, tube worms, bivalves, crustaceans, sea anemones, sea cucumbers, several species of sea snakes, cardinal fish and at least five species of gobies.

Another interesting inhabitant of Lake Kakaban is the jellyfish-eating anemone (Actinaria), whose symbiotic green algae, or zoocanthellae, has been lost so that it appears white in color. The anemone's tentacles are not poisonous but it catches its prey by excreting sticky fluid.

Instead of a coral bottom, the lake is covered with the green algae, halimeda. About three species of this calcium carbonate-producing green algae covers the bottom of the shallow areas of the lake, so dense that the lake is often referred to by scientists as "halimeda Lagoon".

Kakaban's unique ecosystem is a natural wonder for biologists; a place where scientists can directly observe the result of an ecological process in a naturally isolated environment.

"Kakaban's ecosystem is an example of the basic principle of ecology, showing a unique pyramid of primary producer, consumer and predators, fighting for their lives in a world completely shut off by the walls of the atoll rocks," senior research associate of Oxford University's Institute of Biological Anthropology and Department of Zoology, Jonathan Kingdom, said in the book Merintis Konservasi Pulau Kakaban (Pioneering the Conservation of Kakaban Island), published by Kehati.

Kakaban Island's current-swept sloping reefs, creating a wall decorated with gorgonian fans and twisted sponges, is also a wonderland for drift dives.

One of several dive centers catering for Kakaban is the Sangalaki Dive Lodge, about a one-hour boat ride from Kakaban on Sangalaki Island.

The lodge offers dives at Barracuda Point, one of the many favorite sites at Kakaban, which features schooling barracudas, jacks, leopard sharks, gray reef sharks and the hammerhead, "all in a ripping current that lets you fly along the wall like Superman," the lodge's website said.

Another highlight of the Kakaban experience is a dive at Blue Light Cave, for experienced divers. The system starts on a reef flat at two meters deep and descends through a narrow chimney to a massive, pitch-black room at 30 meters. There are two exits onto the wall, one at 44 meters and another at 60 meters.

However, Kakaban's ecosystem is so fragile that it could never support a large-scale tourism industry. Instead the area must be managed with an exclusive tourism approach based on precautionary principles to keep its unique ecosystem intact and therefore able to generate more tourism revenue for a long time.

One recommendation from Kehati was to keep tourism focused on the island's marine areas and leave the lake to scientific purposes because of its more fragile state.

So far, the island's remote area and the little information available about Kakaban have protected this unique ecosystem; however, attempts to generate more tourist interest in early 2000 have already had some impact.

Trees have been cut down from the southwest of the island to make cottages, facilitate the construction of walkways and also cater for construction needs on neighboring Maratua Island.

People have even brought in the omnivorous hawksbill sea turtle (Eretmochelys imbricata) into Lake Kakaban, a mistake that has caused the demise of the lake's mollusks, crustaceans, sponges, algae and jellyfish, all of which are on the hawksbill's dinner menu.

Various environmental non-governmental organizations have since worked to build awareness among both local communities and the Berau administration on the importance of Kakaban.

On May 31 a memorandum of understanding was signed between the Ministry of Maritime Affairs and Fisheries, the Berau Administration, World Wide Fund for Nature, Kehati, The Nature Conservancy and Berau Lestari and Mitra Pesisir, to develop the Derawan Islands, including Kakaban Island, as part of a large-scale marine conservation area.

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