Conserving Tubbataha Reef National Marine Park
    and World Heritage Site

Micaela C. Ledesma and Manuel N. Mejia

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Introduction

       Tubbataha Reef lies in the middle of the Sulu Sea and is one of the last marine frontiers of the region. Because of its globally significant biodiversity, UNESCO declared it a natural World Heritage Site in December 11, 1993. The total area of the Park covers 33,200 hectares including surrounding waters. Tubbataha Reef consists of two coral atolls, separated by an eight-kilometer channel.

      The coral reefs of Tubbataha Reef National Marine Park have been surveyed since 1982 (White and Arquiza, 1999). Many different organizations and academic agencies have visited and collected data in these two remote atolls in the Sulu Sea. Hypothesized to populate neighboring reefs with fish and coral larvae due to the prevailing currents in the Sulu Sea (Alcala, 1993), Tubbataha Reef is a valuable resource to the country. Tubbataha is one of the last few reefs in the Philippines that is relatively intact and harbors an abundant and diverse association of organisms. In one survey alone, more than 300 coral species and at least 379 species of fish were recorded ( White and Arquiza, 1999).

      The Park, despite its remoteness, was still affected by illegal fishing practices commonly found all over Southeast Asia. Tubbataha experienced the highest levels of destruction in the 1980’s and by 1989 the reefs were no longer in pristine condition (White and Arquiza, 1999). The stresses on the reef eased when it was designated as National Marine Park in 1988 and was closed off to fishing. However, due to lack of surveillance equipment, illegal fishers still continued to exploit the Park.

      A Tubbataha Protected Area Management Board (TPAMB) was established in July 1999 and as a result, the rules of the Park are now fully and strongly enforced by a composite team of Park rangers, using a new radar system and more chase boats. This had led to many improvements in the Park and has kept illegal fishers out.

      Given the critical levels of over-exploitation of many coral reefs, marine reserves may be the only viable option available to maintain levels of spawning stock biomass necessary to sustain reef fisheries (Russ et al, 1992). Hence, the goals of our monitoring efforts are to expand knowledge of the unique ecosystem of Tubbataha and to provide technical information that will improve and facilitate the management of this Marine Park.

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Methods

Survey of Bethnic Communities

      In 1997, seven (100-meter) permanent transects were set parallel to the reef crest at an average depth of 10 meters around the two atolls of Tubbataha. These sites were to be monitored annualy from 1997 to 2000. However, due to technical difficulties that prevented the collection of data in some sites, only three of the sites were considered in the change through time analysis. Change in percentage cover of benthic communities through time was recorded using the video technique, modified from English et al (1997) except for 1999 when the benthos point-intercept transect method was used. A separate benthos point-intercept transect survey was done in year 2000 to compare the results obtained by the two methods. A paired T-test showed that there was no significant difference between the two methods (T = 0.012, P = 0.990), therefore data obtained from 1999 was included in the change through time analysis. Coral mortality indices were calculated based on Gomez et al (1994). A one-way ANOVA was used to test for changes through time. Data sampling for benthic cover was conducted within the summer months of March to May.

Fish Visual Census

      Fish populations were surveyed from 1998 to 2000 using the visual fish census modified from English et al (1997) in all seven (100-m) permanent transect sites. For each variety of fish encountered, the numbers and sizes were estimated. Biomass of fish assemblages were calculated based on Kulbicki et al (1993) and ICLARM Fishbase and was standardized to metric tons per square kilometer. Data on fish density were standardized to density per square meter. A one-way ANOVA was used to test for changes between years. Biomass data was log transformed prior to analysis to ensure normality. Data sampling for the fish census was conducted also within the summer months of March to May.

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Results

      Mean live coral cover in the tree sites (sites N1, N3 & S5) decreased by 24.9% from 1997 to 1999. However, there was a recorded 3.3% increase in live coral cover from 1999 to 2000. Results from the one-way ANOVA, however, show that both hard coral and soft coral did not differ significantly over time. There were no significant differences in the abiotic component and other live benthic components (OT). Algal cover, however, significantly increased (F = 15.585, P = 0.001) between 1998 and 1999, and dead coral with algae (DCA) (F = 23.010, P = 0.0001) between 1999 and 2000, thus showing an increase in coral mortality from 1998 – 2000. There was a significant increase (F = 4.307, P = 0.030) in the mean total fish biomass in all seven sites over the latter three years. Estimated mean total fish biomass was 63.73, 446.92 and 647.33 metric tons per square kilometer (MT/sq km) for 1998, 1999 and 2000 (Figure 3), respectively. This dramatic increase in fish stocks represents more than 900% rise since 1998. It was the presence of large schools of pelagic fish species that accounted significant increase (F = 4.246, P = 0.031) while demersal fish species showed no significant changes over time (Figure 3). Although mean density of total fish species decreased by 10% from 1999 to 2000, the value for year 2000 was 36% higher than that recorded for 1998. Pelagic species, Caesonids, significantly increased in mean density from 1998 to 2000 (F = 5.091, P = 0.018) while Carangids displayed increasing trends. Some commercially important demersal fish families such as Lethrinids and Serranids showed an increase in both mean density and biomass over the study period, however, these were not statistically significant.

      For the purpose of comparing the relationship of benthic cover and fish biomass, the mean total fish biomass for three transect sites used in the survey of benthic communities were calculated. The estimated mean total fish biomass was 56.98, 128.92 and 302.09 MT/sq km for 1998, 1999 and 2000, respectively. This increase was not statistically significant (F = 4.470, P = 0.065), nevertheless, this still represented a 530% increase in total fish biomass.

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Discussion

Coral Reef Benthic Communities

       The decline in coral reef cover was attributed to the bleaching event caused by the El Niņo phenomenon in 1998. Compared to other countries, the bleaching in the Philippines was relatively fair. The bleaching in the country was described by Wilkinson et al (1998) as moderate and patchy on some reefs in large areas, with a mix of coral recovery and approximately 20-50% mortality. Other countries recorded as high as a 95% mortality rate (Wilkinson et al, 1998). The bleaching all over the world was most pronounced in shallow water (less than 15 meters deep) and particularly affected staghorn and plate Acropora and other fast growing species (Wilkinson et al, 1998). Dead but intact Acropora forests were observed in Site 1 and 5. This observation could be the after effect of the bleaching event when algae colonizes over corals unable to recover after being bleached and an explanation for the significant increase in algal assemblage (AA) between 1998 and 1999. There was no significant change in live coral cover from year to year, nevertheless, there was a recorded 24.9% decline from 1997 to 1999. The recorded 3.3% increase in live coral cover from 1999 to 2000 could indicate the absence of both natural and anthropogenic stresses within the year and could indicate signs of recovery.

        The coral mortality index was highest in year 2000. However, the low coral mortality index in 1999 could be an underestimated value; the significant increase in algae in 1999 could have covered areas of dead coral which the observer was unable to distinguish , thus some accounted for algae and not dead coral with algae (DCA). 

Fish Visual Census

Fish Density and Biomass

       The mean total density of fish in the seven sites decreased from 1999 to 2000, mainly due to the decrease in damselfish density. In 1999, 58% of the average fish density was made up of damselfishes, this lessened to 49% in year 2000. It was noted in year 2000 that fish density was not comprised mainly of the smaller reef fishes such as anthiases and damselfishes compared to the past years. It was observed that there were greater aggregations of larger fish species, such as more encounters with pelagic species. Total fish density in 2000 was still higher than in 1998. In support of this data, according to the Tubbataha report of Sulu Fund and the Coastal Resource Management Program (CRMP), average fish density has increased by 26% since 1996 (White et al, 2000).

      Compared to the past years, there were larger commercially valuable fishes in 2000. This explains the large increase in fish biomass. Important food fish and pelagic species which accounted for the significant increase were present in greater numbers in the recent year compared to 1999. In year 2000, pelagic species made up 77% of the total biomass (501.57 MT/sq km). In 1998 and 1999, pelagic species made 16% (12.55 MT/sq km) and 58% (275.01 MT/sq km) of the total biomass, respectively. Unlike demersal species, pelagics are not permanent residents of a reef. Instead, they only visit seaward reef dropoffs or enter deep lagoons and are adapted to life in the open ocean (Lieske and Myers, 1996).

       However, the presence of pelagics in great numbers, being carnivorous, could indicate the abundance of food resources in the area. Demersal fishes (biomass) on the other hand, decreased by only 5% from 1999 to 2000, but recorded an increase of 45% from 1998 to 1999. This could be explained by the 123% increase in Acanthurid density, which are herbivores. Although not statistically significant, this increase could be explained by the significant increase in algae between 1998 to 1999. Despite of the increase in total live coral cover from 1997 to 1999, the mean total fish biomass in the three permanent transect sites (N1, N3, and S5) from 1998 to 2000 was also increasing although not statistically significant.

       The significant increase in total fish biomass and increasing trends in density of some commercially important fishes in the seven sites are promising in terms of Tubbataha’s recovery. These increases could suggest the decline in fishing pressure due to the increased enforcement in the protection of the Park. It is believed that the increased patrols in Tubbataha have curtailed fishing inside the Park. According to Salm et al (2000), predatory fishes such as groupers, emperors, jacks, and snappers are the first fishes to disappear from heavily fished areas. Conversely, their presence in increasing numbers supports the grounds that the decrease in fishing pressure could be one of the main reasons why fish biomass has increased substantially.

      The resulting increase in biomass that could indicate the decrease in fishing pressure over the years is starting to pay conservation dividends. Anecdotal evidence from Cagayancillo (nearest municipality to Tubbataha), fishermen seem to bear out that there has been some kind of spillover effect. The spillover effect is the adult (post-settlement) movements from reserve to fished areas (Russ and Alcala, 1996). The fishermen have observed large fish species coming back into their fishing grounds and a number of them attributed this to the protection of Tubbataha.

      Due to the prevailing currents in the Sulu Sea, fish larvae may not be retained in Tubbataha reefs until recruitment size, but may be carried by water currents to other reefs (Dolar and Alcala, 1993). Therefore, Tubbataha could also serve as a source of fish larvae and other larval recruits (Alcala, 1993).

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Recommendations

       The surveys were conducted on the reef crest and some on the upper reef wall, which only gives a fraction overview of the reef. To serve as baseline data to monitor change over time, the comprehensiveness of the data collected is essential for understanding the reef ecosystem. The data collected so far do not give the full view of Tubbataha Reef. The reef crest of an atoll is strongly influenced by wind and waves (Castro and Huber, 1997), therefore, more exposed to stresses compared to the reef slopes and walls. Bleaching and mortality were also more pronounced in water with less than 15 meters depth (Wilkinson et al, 1998). Tubbataha is known for its steep slopes and walls and these were not surveyed due to time constraints. Therefore, more transect surveys at different depths to show different habitats should be done to give a fuller view of the status of the Tubbataha Reef. The outer reef slope and reef walls could display more resiliency being relatively free from environmental stresses and minimally affected by bleaching, thus displaying a different status than that of the reef crest.

Conclusion

       The monitoring of Tubbataha’s complex marine ecosystem found increases in fish populations and decrease in live coral cover due to bleaching. This outcome is promising for the ecosystem’s conservation and is rewarding for conservation organizations working to save this natural World Heritage Site. Tubbataha’s remoteness and relative resiliency to stresses compared to other reefs in the country sets its reputation for being the last marine frontier of the Philippines. Other studies that explore this reef’s importance and connectivity to other reefs should be done to further expand knowledge to implement the appropriate management of the Park.


Presented by : Mr. Manuel N. Mejia
Kabang Kalikasan ng Pilipinas / WWF – Philippines
At   the Symposium on Wetland Management
World Wetlands Day 2001 (02 February)
Visitors’ Center, Ninoy Aquino Nature Center
Quezon City, Philippines
For more information about the study:
Kabang Kalikasan ng Pilipinas
23 Maalindog Street, UP Village
Diliman, Quezon City 1101, Philippines
          T (63)(2) 433-3220 to 2    F (63)(2) 426-3927
          e-mail:
[email protected]

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