A sea urchin. An unnatural low number of predator fish leads to an increase in sea urchins that feed on and erode the coral reef. PHOTO | A ROCHA KENYA
What you need to know:
Corals are living organisms and are affected by climate change, erosion, human exploitation such as over-fishing, and coral and deep sea sand harvesting. This makes it imperative to monitor them so as to understand the reef’s resilience against such disturbances, and to come up with the strategies to apply in managing the ocean ecosystem.
The tide is ebbing and the water calm. It makes for a beautiful morning for snorkelling in the Watamu Marine National Park.
Two marine biologists from A Rocha Kenya (ARK) dive into the coral beds to check on sea urchins and starfish (also called sea stars).
They are assessing the population of sea urchins, starfish, fish, molluscs, sea cucumbers and other echinoderms. The biologists are also noting down the state of sea grasses and coral.
The last such inventory was done in 1937, leaving an enormous gap in research and poor understanding of the reef, both vital for an informed management of the ocean ecosystem.
At the turn of the millennium, ARK embarked on a baseline study to ascertain what was in the reef in Watamu. The organisation’s scientific programme includes research in neighbouring threatened habitats and species in the Arabuko-Sokoke forest, Mida Creek, Dakatcha woodland and the general local marine ecosystem.
“The reef is a very complex ecosystem,” said Jaap Gijsbertsen, ARK’s scientific director. “It is much more than rocky formations surrounded by fish. In our biodiversity study we are trying to unravel some complexity and monitor change for successful conservation of the sites in the marine park.”
Coral reefs
That the world’s coral reefs — like every other ecosystem on the planet — are under threat is no secret. According to research, around one third of the world’s coral, which build the reef, are threatened with extinction.
Corals are living organisms and are affected by climate change, erosion, human exploitation such as over-fishing, and coral and deep sea sand harvesting. This makes it imperative to monitor them so as to understand the reef’s resilience against such disturbances, and to come up with the strategies to apply in managing the ocean ecosystem.
The health of the coral reef is important since it is the first line of defence against the open seas. Once this “wall” collapses, there’s little to keep the waves at bay, not to mention the rising sea levels.
“We’ll drown,” said Peter Musembi, ARK’s marine researcher.
Already parts of Kenya’s 536-kilometre long coastline are experiencing the consequences of an eroded shoreline in areas like Ng’ombeni, a few kilometers north of Watamu. Villages have had to recede to higher ground.
Watamu Marine National Park
The Watamu Marine National Park and Reserve was established in 1968, one of the first protected marine areas in Africa. It encompasses the coral gardens around Whale Island, has amazing array of fish species, animated polyps that sway in the gentle current, and sea urchins and starfish anchor on the reefs.
“We’re monitoring echinoderms and more especially sea urchins because they are indicators of the state of the reef,” explained Gijsbertsen.
According to the monitoring results that go back to 2011, the sea urchin population has increased while that of the starfish has decreased.
An explosion of sea urchins is a serious threat to coral reefs as they gnaw on the latter incessantly, eroding the reef foundation.
“Increasing numbers of sea urchins could mean that there is an unnatural low number of predator fish (that eat the sea urchins) in the coral reef. Removal of large molluscs is another factor contributing to the uncontrolled growth of the sea urchin population,” said the marine scientist.
“Some species of fish are an important predator of sea urchins. When there is no control of sea urchins, they increase in numbers potentially leading to the collapse of entire reef system,” he added.
Overfishing
Overfishing is a serious threat to coral reefs. Working with ARK, the Wildlife Conservation Society marine researchers in Kenya found reefs in areas closed to fishing grew more in size and structure than those in areas open to fishing.
The two-decade study shows how proper fisheries management encourages healthy coral ecosystems and sustainable fishing economies.
The researchers found that without predators like fish that feed on sea urchins, the latter multiply and overgraze on the reefs – which is a more serious and persistent threat than the El Niño swells that devastated coral reefs throughout the tropics in 1998.
“This study illustrates the cascading effects of predator loss on a reef system and the importance of maintaining fish populations for coral health,” said Tim McClanahan, head of WCS’s coral reef research and conservation programme.
In response to this situation, the WCS team is working with local fishing communities to stop the fishing of the orange-striped triggerfish (Balistapusundulatus) called kikandemistari in Kiswahili and the tripletail wrass (Cheilinustrilobatus) locally called stefue or badu. Both are known to feed on sea urchins.
The WCS will print and distribute posters in fish landing sites to educate residents on the importance of conserving the species.
