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Subtidal surveys 1 Halania Island


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YEMEN PAM / CZM PROJECT SUBTIDAL SURVEYS – Pilot area 1

Subtidal surveys

1) Halania Island

Survey date: 17 May 2005

GPS: 13° 59.244' N, 48° 19.039' E

Surveyor: Yasser XX, Adnan XX, Aref Hamoud, Michael Eisinger

The permanent monitoring station at Halania Island was installed at depths between 8 and 10 m. The site is characterized by a highly structured underwater landscape composed of big colonies of the stony coral Porites lobata (Fig. 1a, 1b). The coral community was affected by the 1998 bleaching event which resulted in a patchy distribution of dead coral heads and a significant amount of coral rubble. Nevertheless, average living coral cover is still very high (47%).


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Fig. 1. Coral community at Halania Island. A and B. Porites lobata is the dominant stony coral species. C. Branching corals of the genera Acropora and Pocillopora. D. Pavona cactus patch.

Dominant stony coral species is Porites lobata with a portion of 53.8% of the total scleractinian cover (Fig. 3), followed by Pocillopora damicornis, two Montipora species, Pavona cactus and a bushy Acropora species. All these species tend to form large monospecific patches in between the large Porites lobata heads (e.g. Fig. 1D). In total, 23 scleractinian coral species were documented within the line intercept transects. The actual coral biodiversity, however, should be significantly higher.



Fig. 2. Distribution of major benthic taxa and substrate categories at Halania Island. The presented values are means of five 20 m long line intercept transects.

Despite a high amount of available unoccupied hard substrate (29% “rock”), recruitment rates are comparably low. This matter of fact makes this coral community very susceptible to any sort of anthropogenic stress.


Fig. 3. Percentage cover of documented stony coral species (proportionate values of the total coral cover shown in Fig. 1). The presented values are means of five 20 m long line intercept transects.

2) Sikkha Island (south)

Survey date: 19 May 2005

GPS: 13° 55.809' N, 48° 23.140' E

Surveyor: Yasser XX, Adnan XX, Aref Hamoud, Michael Eisinger

The chosen permanent monitoring site at Sikkha Island is located in depths between 8 and 12 m. The coral community is dominated by large colonies of Porites lobata which reach diameters and heights of up to 5 m. In contrast to the Porites formations at Halania Island or Ghaddarayan Seghir, these giant colonies are often solitary and separated by sand and rubble patches. Due to erosion most of the Porites lobata colonies are “mushroom”-shaped with dead colony bases (Fig. 4A and B). These dead areas are often colonized by other stony corals such as foliose Montipora species or Stylophora pistillata (Fig. 4C). Unfortunately, this exceptional high-relief community badly suffered from the 1998 bleaching event: large areas had died and were colonized by the very competitive corallimorpharian Rhodactis cf. rhodostoma. Fig. 4D shows a section of a P. lobata colony which has been gradually overgrown by the very aggressive corallimorpharian. Consequently, recovery is significantly impeded by the presence of R. rhodostoma.


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Fig. 4. Aspect of the coral community within the chosen monitoring site. A. Highly eroded Porites lobata colony; only the “head” is alive. B. Typical “mushroom”-shaped P. lobata colonies. C. A foliose Montipora species growing at the bases of P. lobata colonies D. and E. Overgrowth of dead colony sections by the corallimorpharian Rhodactis cf. rhodostoma.

Fig. 5. Distribution of major benthic taxa and substrate categories at Sikkha Island south. The presented values are means of five 20 m long line intercept transects.

33.3% of the hard substrate was covered by the corallimorpharian R. rhodostoma, whereas living hard coral cover was comparably low (20.5%). Worth mentioning is the occurrence of a foliose to plate-forming Millepora species which is very common around Sikkha Island but rare elsewhere in the area.



Fig. 6. Percentage cover of documented stony coral species (proportionate values of the total coral cover shown in Fig. 1). The presented values are means of five 20 m long line intercept transects.

Species diversity of scleractinian corals was very low: only 6 species were documented with Stylophora pistillata being dominant (45%), followed by Porites lobata (37%). Pocillopora damicornis and branching Acropora species were rare.




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Fig. 7. Aspect of the coral community in depths between 3 and 7 m. A. and B. Transition between the “high-relief” community and the “low-relief” community with massive Porites lobata colonies, large Stylophora pistillata and foliose Montipora sp. colonies and soft coral colonies. C. and D. Low-relief coral community with monospecific Millepora sp. stands (C) and mixed patches of Millepora sp. and foliose Montipora sp.

Another community type was documented in shallower depth between 3 and 7 m (outside the monitoring site, see Fig. 7). The structural complexity here is much lower: smaller Porites lobata colonies are mixed with Stylophora pistillata, Montipora sp., Millepora sp.and soft coral colonies in deeper areas, whereas in shallow depths the same Millepora and Montipora species occur in large monospecific stands and patches (Fig. 7D). Living coral cover in this “low-relief” community was very high suggesting that this community is better adapted to seasonal high and sporadic very high temperatures (“bleaching events”) than the deeper “high-relief” community.

It will be of particular interest to follow up the further development and potential recovery of the deeper community within the limits of the fixed monitoring site.

3) Ghaddarayan Seghir

Survey date: 20 May 2005

GPS: 14° 00.368' N, 48° 23.243' E

Surveyor: Yasser XX, Adnan XX, Aref Hamoud, Michael Eisinger



The monitoring site is located in the north-eastern part of the Island Ghaddarayan Seghir. Benthic communities around this island have the tendency to form large monospecific stands with very high stony coral cover. The chosen coral patch has a stony coral cover of 66 % which represents one of the highest values documented in the area. With 71.5 % Porites lobata is by far the dominating coral species In the shallower zones the Porites colonies form a sort of “reef crest” (Fig. 8A, right side) whereas between 3 and 6 m colonies partially form extensive “carpets” (Fig. 8A, foreground). Species diversity is very low: only 9 different stony coral species were found within the transects (Fig. 10).


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Fig. 8. Subtidal monitoring site at Ghaddarayan Seghir. A. Aspect of the Porites lobata community in the center of the coral patch with reef-crest-like formations in the shallower zones (right side) and carpet-like formations between 4 and 6m (in the foreground). B. At the edges of the coral patch Pocillpora damicornis represents the second most abundant species (right side).

Fig. 9. Distribution of major benthic taxa and substrate categories at Ghaddarayan Seghir (northeast). The presented values are means of five 20 m long line intercept transects.


Fig. 10. Percentage cover of documented stony coral species (proportionate values of the total coral cover shown in Fig. 9). The presented values are means of five 20 m long line intercept transects.
To the west of the monitoring site massive monospecific coral formations of Pocillopora damicornis extending from 2 to 10 m were documented. Fig. 11 shows such a formation with living coral cover of almost 100%. A neighboring patch, however, exhibited very high mortalities of up to 90%. The reason for this microscalic phenomenon is unclear but could be a result of varying genotypes with different susceptibilities to high temperatures.



Fig. 11. Monospecific Pocillopora damicornis formations (“banks”) in the vicinity of the monitoring site.





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