SECTION 2 COMPARISONS OF IMPACTED AND PRISTINE REEFS

This section discusses the initial work that was completed early in the season comparing an impacted reef with a pristine site and determining the causes of the impact (2.2). Follow on work examining the diversity of coral species and the structural heterogeneity of the reef and how these affected fish abundance and diversity is described in section 2.3.

Introduction

The reef surrounding the Bajo village of Sampela in the Wakatobi Marine National Park is of great economic importance to the village, yet previous research had shown that this important resource was extensively impacted. The reef is slowly degrading and has a large amount of bare ground and dead coral cover. This is of huge significance as the reef is currently acting as a protective barrier to Sampela. If the coral reef continues to degrade through this decreased rate of calcification the effects on Sampela will be disastrous. It will be detrimental to the community, both economically as the main source of income is through local fisherman, and as a coastal protection barrier.

Brain Coral ; Photo Adam Powell

• Assess the diversity of the Scleractinia present on the Sampela wall and to compare this diversity with a non-impacted reef system.
• Assess the effects of sedimentation on the coral community structure.
• Assess the rate of sedimentation on the Sampela wall as compared to a non-impacted reef system and to determine the dynamics of this sediment.
• Produce a habitat map of the sublittoral environment surrounding Sampela and to determine the abundance and species diversity of seagrasses.
• To measure the erosion rates of sediment surrounding Sampela and to correlate these rates with the density of seagrass.
• To determine the characteristics of the material being deposited on the Sampela reef community and to determine the source of these sediments.

These objectives include research into the causative factors of the degradation , how these factors are impacting the reef system and the extent of the impact. In order to make an accurate assessment on the impact the entire system needed to be examined which includes the seagrass beds surrounding Sampela as these are interactive with the reef system.

Methods

To accurately examine the impact the pristine reef system of Kaledupa was used as a control site for use as a comparison.

Quadrats of 5 x 2m² were laid on the reef at depths of 5m and 10m at both Sampela and Kaledupa, 5 at each depth at each site (total area survey = 200 m²). These were attached to dead coral rubble or rocks so as not to cause further impact to the reef. Over a period of three weeks teams of divers surveyed the quadrats, initiated by identification of all the Scleractinian corals present down to species level. Once identified the growth form, diameter, circumference of each colony, and the number of colonies of each species was recorded.

To assess the rates of sedimentation, sediment traps were placed randomly within the reef at both sites. These were made using two mineral water bottles, one cut in half and attached to the other bottle acting as a funnel. The concept being to trap sediment that settles, and prevent it from washing back out by the narrow neck. These traps were left in the reef for five days then collected by snapping the funnel off the top and placing a bottle cap on to keep the sediment in. Once the sediment settled in the bottle the samples were then frozen and analysis for CHN, particle size, and organic matter will be completed. This will give an indication of the dynamics and origin of the sediment and will represent the amount of sediment that is settling on the reef.

These were carried out along 250m transect lines from varying bearings around Sampela. At intervals of 50m three quadrats were placed and within these the percentage cover of each seagrass species was recorded, three blade lengths of the dominant seagrass species were recorded and any other organisms that were present.

Ten, three sided, bamboo baskets were covered with rice sacks and attached to the reef slope with wooden stakes. These will collect any rubble and debris falling from the reef, and indicate the erosion rates in the two sites. These will be measured after six, and twelve weeks and then again after eight months, with the content being identified and measured.

Two species that are known to be abundant in both Kaledupa and Sampela, Diploastrea heliopora and Favia speciosa have been marked and their colony size measured. After eight months they will be measured again to give growth rates of both sites.

Preliminary Results

There was a significant difference between the diversity of Scleractinian corals at Sampela and Kaledupa (a mean of 2.4 and 3.1 for Sampela and Kaledupa respectively). There was no significant difference between the 5 and 10 m quadrats within a site. The number of species of Scleractinian corals also differed significantly between sites (ranging from 15 – 20 and 33 and 35 for Sampela and Kaledupa respectively). There was a significant difference between the 5 m and 10 m quadrats at Sampela but not at Kaledupa. The number of coral colonies recorded in 10 m² quadrats were approximately 3 times higher at Kaledupa compared to Sampela and were significantly higher in 5 compared to 10 m quadrats.

The structure of the coral community also differed between sites with corals depending on a more heterotrophic rather than an autotrophic life style dominating at Sampela. Cluster analyses and Polar Coordinate Analyses will be used to examine the differences in community structure.

The Scleractinian coral community of Sampela was dominated by encrusting corals with a limited diversity of other growth forms. This was in direct contrast to Kaledupa where all growth forms were well represented. There was no difference with depth.

There was no significant difference between the diameters of the coral colonies recorded from both sites or depths although the number of colonies were significantly different.

Observational studies of sedimentation rates suggests that sedimentation is approximately 3 – 4 x higher in Sampela (by volume) compared to Kaledupa but further analyses is required to quantify this difference. Basic observations of the sediment types suggests that the sediment being deposited on the Sampela reef consists of fine sub-littoral sands similar in composition to the sediment surrounding Sampela village. In contrast the material collected from Kaledupa was much coarser consisting of coraline material and algal spores. Further analyses using CHN ratio techniques are required to type source the depositing sediments.

The Scleractinian coral community of Sampela has been severely impacted by depositing sediments which has resulted in decreased species and topographic diversity and the density of coral colonies. The impact is sedimentation which can lead to the suffocation of corals, whilst also decreasing light penetration resulting in decreased growth and calcification rates. Kaledupa is not impacted by depositing sediments and hence has a much greater species diversity and coral abundance. The similar sizes of coral colonies analysed from both sites are a result of quite different limiting factors. Rather than being light limited the coral community of Kaledupa is limited by space which is clearly demonstrated by examining the number of colonies per 10 m² quadrats.

It appears obvious from basic observations that the reef of Sampela is eroding and from the results obtained from this study, that the coral community is limited by sedimentation. We therefore anticipate that there is a net loss of material from Sampela, which if not checked, could result in the loss of this protective barrier which would be to the detriment of the sublittoral sand flats and hence Sampela village. This impact or the possible erosion of sand flats may be elevated in 1 of 2 ways: 1) by decreasing the level of sedimentation e.g. establish greater seagrass coverage which entrap otherwise mobile sediments; 2) by creating an artificial barrier using the existing reef as a foundation. It may be possible to use fossilised coral rubble to produce this barrier. Further work will be carried out at Essex and at the field site in the future to determine the exact source of the sediment, the possibility of seagrass establishment and the production of a budget which would enable us to accurately predict the future of the reef.

Reports and Papers

Five different dissertations on aspects of the above projects will be produced by March 2001 by Essex University students.  The data from this study is being incorporated into the following paper:  Smith, D. J., Crabbe, J. and Budianto, A. (in prep) The physical and biological characteristics of  a light-limited and non-light-limited reef system within the Wakatobi Marine National Park (SE Sulawesi, Indonesia). Coral Reefs.

Introduction

The purpose of this project is to compare benthic diversity on an impacted site with a non-impacted, or pristine site. The pristine site at Kaledupa was chosen as it appears to have no obvious anthropogenic or sedimentation damage. In contrast the site at Sampela is heavily affected by sedimentation with an apparent reduction in benthic and fish diversity. Comparison of the two sites was carried out through benthic line intercept transects and quadrat surveys, and observations of fish diversity and abundance along the same transects. It appears that the difference between the two sites are due mainly to sedimentation, therefore sedimentation data was also collected.

Apocora Chromis Coral ; Photo Adam Powell

Sedimentation is assumed to be the main limiting factor in the growth and diversity of corals at Sampela. This was investigated by placing sediment traps to enable comparison of amounts and composition of sediment at the two sites, and by measuring the orientation of the hard corals which may indicate that corals at a site heavily affected by sedimentation prefer an orientation towards vertical to discourage sedimentation. It is hypothesised that lowered benthic diversity associated with high sedimentation levels will be correlated with lower fish diversity and abundance.

Methods

Sediment data collected by use of sediment traps which are collected and replaced every 5 days for a 10 day period. These traps were placed at the reef crest (3-5 metres) and on the reef slope (10 metres). This is to ensure that sediment levels are higher at Sampela than Kaledupa and to enable chemical analysis of the sediment to determine its origin.

Benthic composition was assessed through use of 20 metre line intercept transects which were placed on the reef crest (3-5 metres) and on the reef slope (10 metres). Any change in benthic cover was noted under general headings with hard corals being identified to genera and growth forms recorded. The height above the substrate of the coral was recorded at each 0.5m along the transects. Quadrats were used to estimate the percentage cover of hard and soft corals, rock, rubble or sand. The height, width and circumference of hard corals and general orientation of the hard coral (degrees from horizontal) in the quadrats was also recorded. The size of the quadrats used varied from 5 X 2m quadrats at Sampela where the coral communities are widely scattered and 2 X 2 m quadrats at the Kaledupa site which had a high percentage coral cover.

Fish surveys conducted along the same transects as the benthic surveys. These surveys involved counting in five metre sections, numbers and species of fish which came within 2.5 metres either side of the transect over a period of three minutes (see section 3.2 for more detailed description of the methodology)

Preliminary Results

Benthic diversity is not as different between the two sites as might have been expected, the main difference in benthic composition being in the number of colonies found, with a far higher number of colonies being found on the pristine site at Kaledupa. Another surprising result is the relative lack of difference in the sizes of colonies found at the two sites. This may be due to the presence of a limiting factor at Kaledupa which had not been considered. This factor may well be the lack of space for expansion due to high competition. At Sampela the limiting factor is assumed to be sedimentation.

Again a surprising result with fish diversity with comparable results between the two sites, with the major difference being in abundance, with far higher numbers of fish found at Kaledupa. There were common species found on both sites but many were different suggesting different trophic guilds may be present.

Reports

Dissertations entitled The Differences in Benthic Diversity and the Biodiversity and Abundance of Fish between an Impacted and Pristine Reef in the Wakatobi Marine National Park was produced in March 2001 by Holly Adams from the University of Birmingham, David Martin from the University of Wales, Bangor, Katherine Moir from the University of Oxford and Chris Shelbourne from the University of Portsmouth.  Copies of the dissertations from Holly Adams and David Martin are available at the Hoga field centre and from the Op Wall UK offices.

Dissertations entitled The Effect of Substrate Heterogeneity on the Diversity and Abundance of Fish was produced by Grace Wong from the University of Reading in May 2001.  A similar dissertation was also prepared by Laura Freedman from the University of Birmingham.