Grimsditsch et al Pemba Resilience Survey 2009 low res
Grimsditsch et al Pemba Resilience Survey 2009 low res.pdf Grimsditsch et al Pemba Resilience Survey 2009 low res.pdf
Major Findings on the site that is not allowing recruits to grow. Two sites stand out as having very low recruitment (pg 27); Msuka Bay and Fundo Lagoon, probably due to their geographical positioning. Msuka Bay is to the north of the island, not connected to the dominant currents in the area, and in a high wave energy, Sargassumdominated area where it is difficult for coral recruits to settle. Fundo Lagoon is in a sheltered bay area, and although there is tidal exchange of water, it appears that coral larvae do not successfully reach or settle there. However, although recruitment may be higher in degraded sites, recruit survivorship is much lower. The number of corals bigger than 2.5 centimetres decreases dramatically in sites such as Paradise or Simba. This trend continues with larger size classes, as fewer and fewer corals reach bigger sizes at these sites. In fact, only in Misali is there a full range of coral size classes with high cover of medium size (21-40 cm) and larger (>80 cm) corals characteristic of healthy reef ecosystems (pg 25-26). Therefore it is clear that local stresses in currently degraded sites are preventing coral recruits from reaching large sizes. If threats are identified and mitigated, it would be possible for currently degraded sites to recover as coral recruits survive and grow. One plausible explanation could be increasing populations of crown-of-thorns starfish. At Paradise the high incidence of crown-of-thorns predation scars on corals (5% of colonies predated) indicates that these corallivores are a major cause of recruit mortality (pg 28). A crown-of-thorns outbreak was also observed at Fundo Inner, with over 50 individuals sighted. It is unknown what the trigger for population outbreaks is. Removal of starfish predators through over-fishing, improved survival of larvae due to land-based nutrient inputs and increasing sea-surface temperature have all been postulated as potential triggers. Crown-of-thorns starfish outbreaks have recently become a regular occurrence on Pemba’s reefs, and are a major cause of coral mortality on the island. It is important to identify and understand the triggers for crown-of-thorns starfish population outbreaks in order to mitigate this threat. Left: Crown-of-thorns outbreak at Fundo Inner. Three individual starfish are eating one Echinopora coral colony. Over 50 individuals were seen at this site with subsequent high mortality. © Jerker Tamelander, IUCN. Right: Typical scene from Paradise. An Acropora recruit on a framework of dead coral, completely predated by crown-ofthorns starfish. © Jerker Tamelander, IUCN. 11
Major Findings Algae communities Msuka Bay had the highest macro-algal cover (35%) due to dominance by the brown macro-algae Sargassum (pg 19). However, this is probably the natural state for this site, as it is more exposed to wind and wave energy from the northwest and these are conditions typically associated with Sargassum dominance. Msuka Bay also had the highest incidence of algal attack on corals, with 9% of hard corals being attacked, killed and overgrown by macro-algae. All other sites had macro-algal cover lower than 15%. Dictyota (brown algae), Cyanophyta (blue-green bacteria), Sargassum (brown algae) and Jania (red algae) were the most common macro-algae found (pg 19). Overall, macro-algae are not yet dominating Pemba’s western reefs, meaning that a complete phase shift to an algal reef has not yet occurred and with careful management this could be avoided. Msuka Bay- Astreopora coral being overgrown by Sargassum algae. © Jerker Tamelander, IUCN. Fish populations Fish data show that Pemba is being extremely overfished. During surveys, herbivorous fish were classified into different functional groups depending on their feeding modes and preferred diet. Each functional group plays a different role in coral-algal dynamics and thus a unique implication for coral reef resilience. Large excavators such as Bolbometopon spp. Chlorurus spp. >35 cm in Length are major agents of bioerosion on reefs, taking larger bites of the dead substratum as they feed and expose hard surface for coral recruitment. Small excavators and scrapers (parrotfish) are important for preventing the establishment of macro-algae, removing algal turf and preparing the substrate for colonization by coral recruits. Grazers (surgeonfish, 12
- Page 1 and 2: Coral Reef Resilience Assessment of
- Page 3 and 4: Coral Reef Resilience Assessment of
- Page 6 and 7: Executive Summary 1 Executive Summa
- Page 8 and 9: Executive Summary 2. Tackle the ove
- Page 10 and 11: The Study coral colony and coral co
- Page 12 and 13: The Study Table 2.1. Sites surveyed
- Page 14 and 15: The Study 7. Resilience indicators
- Page 18 and 19: Major Findings rabbitfish, angelfis
- Page 20 and 21: Major Findings 2. Tackle the overfi
- Page 22 and 23: Detailed Results 4 Detailed Results
- Page 24 and 25: Detailed Results % coral colonies 1
- Page 26 and 27: Detailed Results 4.2 Coral communit
- Page 28 and 29: Detailed Results 4.3 Coral populati
- Page 30 and 31: Detailed Results Moderate Faviid Su
- Page 32 and 33: Detailed Results 4.4 Crown-of-thorn
- Page 34 and 35: Detailed Results Density 250m2 200
- Page 36 and 37: Detailed Results 4.6 Resilience ind
- Page 38 and 39: Detailed Results Influence of resil
- Page 40 and 41: Detailed Results Fundo Lagoon Msuka
- Page 42: INTERNATIONAL UNION FOR CONSERVATIO
Major Findings<br />
Algae communities<br />
Msuka Bay had the highest macro-<strong>al</strong>g<strong>al</strong> cover (35%) due to dominance by the brown macro-<strong>al</strong>gae Sargassum<br />
(pg 19). However, this is probably the natur<strong>al</strong> state for this site, as it is more exposed to wind and wave<br />
energy from the northwest and these are conditions typic<strong>al</strong>ly associated with Sargassum dominance. Msuka<br />
Bay <strong>al</strong>so had the highest incidence of <strong>al</strong>g<strong>al</strong> attack on cor<strong>al</strong>s, with 9% of hard cor<strong>al</strong>s being attacked, killed and<br />
overgrown by macro-<strong>al</strong>gae. All other sites had macro-<strong>al</strong>g<strong>al</strong> cover <strong>low</strong>er than 15%. Dictyota (brown <strong>al</strong>gae),<br />
Cyanophyta (blue-green bacteria), Sargassum (brown <strong>al</strong>gae) and Jania (red <strong>al</strong>gae) were the most common<br />
macro-<strong>al</strong>gae found (pg 19). Over<strong>al</strong>l, macro-<strong>al</strong>gae are not y<strong>et</strong> dominating <strong>Pemba</strong>’s western reefs, meaning that<br />
a compl<strong>et</strong>e phase shift to an <strong>al</strong>g<strong>al</strong> reef has not y<strong>et</strong> occurred and with careful management this could be<br />
avoided.<br />
Msuka Bay- Astreopora cor<strong>al</strong> being overgrown by Sargassum <strong>al</strong>gae. © Jerker Tamelander, IUCN.<br />
Fish populations<br />
Fish data show that <strong>Pemba</strong> is being extremely overfished. During surveys, herbivorous fish were classified<br />
into different function<strong>al</strong> groups depending on their feeding modes and preferred di<strong>et</strong>. Each function<strong>al</strong> group<br />
plays a different role in cor<strong>al</strong>-<strong>al</strong>g<strong>al</strong> dynamics and thus a unique implication for cor<strong>al</strong> reef <strong>res</strong>ilience. Large<br />
excavators such as Bolbom<strong>et</strong>opon spp. Chlorurus spp. >35 cm in Length are major agents of bioerosion on<br />
reefs, taking larger bites of the dead substratum as they feed and expose hard surface for cor<strong>al</strong> recruitment.<br />
Sm<strong>al</strong>l excavators and scrapers (parrotfish) are important for preventing the establishment of macro-<strong>al</strong>gae,<br />
removing <strong>al</strong>g<strong>al</strong> turf and preparing the substrate for colonization by cor<strong>al</strong> recruits. Grazers (surgeonfish,<br />
12
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