Seawater species adapt to survive in wondrous 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 www.sangalaki.net 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.