CORAL REEF & REEF FISH

CORAL REEF & REEF FISH

Coral reef and reef fish surveys were carried out on the south of Tikus Island on April 2014. These three sites were chosen in order to find out the coral reef coverage, while also taking a close look at the abundance of the reef fish within the area (Picture x). The survey was conducted using a 50 meter line transect to assess the percentage cover of all major benthic organisms, including hard corals, soft corals and others such as seagrass, sponges and others associated reef organisms. For reef fish, the study was conducted only in the last 2 stations because of limited time and inability to identify the species.

There were a similar pattern of coral coverage recorded in Tikus Island, with all three stations seemingly dominated by sand (Picture xx) and rubbles, with a small portion of other fauna (mostly seagrass). Only a small percentage of hard corals were found. Station 1 is dominated by sand (87%) and other fauna (10% seagrass), with a small portion of hard coral (2%). Station 2 is also dominated by sand (57%) with a minor cover of dead coral and rubble (both 18%), only 7% of hard coral cover were found. Station 3 is significanly different than the first two stations. It is dominated by rubble (48%) and other fauna (34% seagrass). Sand, surprisingly, was much less dominant (9%) and only 4% of hard coral cover were recorded. Coral family composition among individual sites is relatively similar, with most of the corals found was from the poritidae family.

A total of 104 fishes from 7 families were observed among all stations, namely Gobiidae, Labridae, Mullidae, Nemipteridae, Pomacentridae, Scaridae and Lutjanidae. Among these that are regarded as target species were Labridae, Mullidae, Nemipteridae and Lutjanidae; while the rest is a major species (Dartnall & Jones 1986 in Adrim 2007). There were a significant differences on the number of fish recorded on each sites. A total number of 70 fishes were recorded in station 2, with a high number of pomacentridae and labridae recorded from this station, whereas there are only a total of 34 fishes from station 3, dominated by Lutjanidae. In station 2, there were 6 families of fishes recorded, whereas in station 3 only 4 families were found. The family of Lutjanidae, known as a popular target species for fishermen, was only found in station 3.

Coral community around Tikus Island has long been exposed to various factors such as high water temperature and anthropogenic activities. But the best possible explanation on the low percentage of the hard coral cover is the substrate domination. Sand was recorded as a dominant substrate exist in all three stations, with the exceptions of station 3, where rubbles are more dominant. This kind of substrate is not suitable for the coral to grow, because corals need solid basis in order to support their growth. Instead, other organisms could take advantages from this sandy bottom environment. Seagrass was evident in station 1 and 3, while sand-burrowing organisms thrives in the area. Turbidity is also a reason why the corals are scarce in this area. Fine sediments would often block the corals surface and limit their photosynthesis activities (Rodríguez 2006) and could eventually die, as is evident on the relatively high number of rubbles found in station 3. Most of the rubbles were the products of Acropora spp., a vulnerable species of corals in terms of facing significant changes in water environment (Estradivari et al 2011).

The Pari Islands Aggregation have become a famous tourism destinatoins in recent years, with most of the tourists flocking from the nearby city of Jakarta. These tourists often don’t have adequate knowledge of coastal ecosystem and what they are capable of doing in terms of bringing negative impacts to the surrounding environment. The low percentage of hard coral cover found in the sites along with a number of rubbles and dead corals, more or less, supports this theory. Rubbles are far more less popular than sand, as it brings bad effects to the surrounding environment. They are a perfect place for the algae to grow, and when the number of algae explode uncontrollably, it could potentially damage the ecosystem as a whole.

Fishes that were found in Tikus Island are relatively scarce. They are so low in number that we have to adjust the units into individual/hectare. The fish was dominated by algae eater of Pomacentridae and benthic organisms eater of Labridae (Dhahiyat et al 2003). These two families are the most observed reef fish in coral reef ecosystem (TERANGI 2004; Quenouille et al 2004; Sale 1991; Estradivari et al 2011). Pomacentridae would often feed on plankton and algae (TERANGI 2004; Sale 1991). The possibility of nutrient abundance from surrounding islands is high, therefore increasing the food supply for this family of fish. Labridae are benthic eater (Sale 1991), they would eat all sorts of small invertebrates that found in the sand, which is abundant in Tikus Island. Some even formed a schooling.

Generally, reef fishes are territorial, but because they are mobile as well, their existence in ecosystem would be greatly influenced by their environmental condition. If it is suitable for the reef fish to live in, then huge number of fishes would flocked into the area, but if the area is not suitable, the opposite will occur. The coverage of coral is one of the main factor of reef fish abundance (Bell & Galzin 1984).

Other supporting factor of the low cover of hard coral in Tikus Island is the absence of indicator fish species, widely known as Chaetodontidae. The existence of this family of reef fish is integral in the coral reef ecosystem. They feed on corals (Allen 2000), therefore they are often used as an indicator species. If the reef ecosystem in an area is healthy, then this family of fish would be commonly found. 

 

References

Adrim M. 2007. Komunitas ikan karang di Perairan pulau Enggano, Propinsi Bengkulu. Oseanologi dan Limnologi di Indonesia 33:139-158.

Allen GR. 2000. Reef and shore fishes of the Calamianes Islands, Palawan Province, Philippines. In TB Werner, GR Allen, eds. A rapid marine biodiversity assessment of the Calamianes Islands, Palawan Province, Philippines. RAP Bull. Biol. Assess. 17: 31-44.

Bell JD, Galzin R. 1984. Influence of Live Coral Cover on Coral Reef Fish Communities. Marine Ecology Progress Series 15: 265-274.

Dhahiyat Y, Sinuhaji D, Hamdani H. 2003. Struktur Komunitas Ikan Karang di Daerah Transplantasi Karang Pulau Pari, Kepulauan Seribu. Jurnal Iktiologi Indonesia 3(2): 87-94.

Estradivari, Setyawan E, Yusri S, Timotius S. 2011. Terumbu Karang Jakarta: Pengamatan Jangka Panjang Terumbu Karang Kepulauan Seribu (2005-2009). Jakarta: Yayasan Terumbu Karang Indonesia (TERANGI).

Quenouille B, Bermingham E, Planes S. 2004. Molecular Systematics of Damselfishes (Teleostei: Pomacentridae): Bayesian phylogenetic analyses of mitochondrial and nuclear DNA sequences. Molecular Phylogenetic Evo 31(66): 66-88.

Rodríguez IB. 2006. Relationships between reef fish communities, water and habitat quality on coral reefs. [Thesis]. University of Puerto Rico, Puerto Rico.

Sale PF. 1991. The Ecology of Fishes on Coral Reefs. Academic Press, San Diego: 564-598.

[TERANGI]. 2004. Panduan Dasar Untuk Pengenalan Ikan Karang Secara Visual Indonesia. Yayasan Terumbu Karang Indonesia.