The Existence of the Halmahera Walking Shark (Hemiscyllium Halmahera), How are Coral Reefs as the Primery Habitat in Maitara Small Island Sea. North Maluku. Indonesia?

In the warm, shallow waters of the Indonesian archipelago, a unique evolutionary experiment is taking place. While most sharks are built for speed and open-ocean cruising, a small group of relatives has adapted to life on the ocean floor, using their fins to "walk" across the sand and weave through coral branches. Among these is the Halmahera walking shark, a species found only in the waters of North Maluku. These creatures rely heavily on healthy coral reefs, which provide not just shelter from predators but also a complex landscape where they can hunt for small fish and crustaceans. However, coral reefs are fragile ecosystems, often threatened by human activity and changing climate. Understanding how the health of these underwater gardens directly affects the growth and survival of such specialized animals is crucial for protecting them. If the coral dies, the walking shark loses its home, but the exact relationship between a thriving reef and a healthy shark has remained a question for scientists to answer in the field.

A team of researchers from Khairun University and Bogor Agricultural University traveled to Maitara, a small island nestled between the larger islands of Ternate and Tidore, to investigate this connection. Maitara is known for its stunning white-sand beaches and clear waters, but it holds a deeper secret: it is one of the few places where the Halmahera walking shark is found. The scientists chose three specific coastal areas around the island to study: the waters near Doe Doe Village in the north, Akebay Village also in the north, and Pasimayou Village in the south. These locations were selected because they represent different types of marine environments, ranging from popular tourist spots to areas with a history of fishing. The team's goal was simple yet vital: to measure the condition of the coral reefs, observe the physical size and weight of the sharks living there, and see if a link existed between the quality of the reef and the health of the shark.

To gather their data, the researchers dove into the water at a depth of about three meters, a depth where sunlight penetrates easily and coral thrives. They laid out long measuring lines along the seabed and took hundreds of photographs of the coral within square frames. Using these images, they calculated exactly how much of the ocean floor was covered by living coral versus dead rock or sand. They also collected samples of the sand on the ocean floor to see what size the grains were, as the type of sediment can affect how well the sharks can move and hide. Simultaneously, the team searched for the walking sharks themselves. When they found one, they gently brought it to the surface to measure its length from snout to tail and weigh it, recording details like the size of its fins and head before carefully releasing it back into the water. This process was repeated for every shark they encountered across the three sites.

The results painted a clear picture of how the environment shapes the life of the shark. At the first two sites, Doe Doe and Akebay, the coral reefs were in good shape. The ocean floor was covered with living hard coral, particularly branching types that create a dense, three-dimensional forest. In these areas, the researchers found larger, heavier sharks. The sharks here were fully grown adults, with some reaching lengths of over 70 centimeters and weighing nearly 800 grams. In contrast, the third site, Pasimayou, told a different story. The coral there was largely dead, with more than half of the reef covered in decaying skeletons rather than living tissue. The few sharks found here were significantly smaller and lighter than their counterparts in the healthier waters. The data showed a direct correlation: where the coral was lush and complex, the sharks were bigger and heavier. Where the reef was degraded, the sharks were smaller.

The researchers also looked at the water itself to ensure that other factors weren't the cause of these differences. They measured the temperature, saltiness, and clarity of the water at all three sites. They found that the water quality was generally good and consistent across the board, with clear visibility and temperatures suitable for coral growth. This suggested that the difference in shark size was not due to the water being "bad" in one place and "good" in another, but rather due to the physical structure of the habitat. The type of sand on the ocean floor was also consistent, dominated by medium-sized grains that are stable and easy for the sharks to navigate. The only major variable that changed between the sites was the health of the coral.

The study concluded that the Halmahera walking shark is deeply tied to the health of its coral home. The analysis indicated that the amount of living coral cover directly influences how big and heavy the sharks grow. In the areas where the reef was thriving, the sharks had access to better shelter and likely more food, allowing them to reach their full potential size. In the damaged areas, the lack of complex structure meant the sharks could not grow as large. This finding is significant because it highlights that protecting the coral reef is not just about saving the plants and fish that live on it, but is essential for the survival of unique species like the walking shark. The local community on Maitara already holds a traditional belief that disturbing these sharks brings bad luck, which has helped protect them from overfishing. This scientific evidence supports those local traditions, showing that when the reef is healthy, the sharks thrive, and when the reef is damaged, the sharks suffer. The future of this endemic species depends on maintaining the integrity of the coral reefs that serve as their primary home.