Scientific research topics 2001

1.) ASSESSMENT OF CORAL REEF DAMAGE IN AQABA, JORDAN (2001)
Natascha Miljkowic, Nicole Schreyer, Julia Zekely

ABSTRACT
During the field research trip to Aqaba from 31 October to 14 November 2001, we observed the health status of the reef according to modified RRAP- guidelines. Eight line transects á 9 m length were laid parallel to the coastline in various depths (5 to 21 m). Along the line transects, 102 hard coral colonies were identified and measured, the percentage of soft corals, algae and sponges near the observed hard corals or growing on the hard coral surface, as well as the percentage of recently and long dead coral surface was estimated by SCUBA diving. Moreover the number of sea urchins (e.g. Diadema setosum) half a meter on both sides of the line was counted. By re-visiting coral colonies marked in earlier years, the progress of coral death due to diseases such as tissue bleaching (TB) or others were documented. The living coral surface is lowest at the first and second, most shallow, transects as well as at the deepest transect. The high number of snorkelers and divers visiting the RDC each year play a role, but other threats like water pollution caused by industrial complexes along the coast also affect the health of corals.

2.) REEF FISH SURVEY FOCUSED ON POMACENTRID FISH DISTRIBUTION IN THE GULF OF AQABA (NORTHERN RED SEA)
Alexander Kotrschal, Astrid B. Taumberger, Fritz Monika, Tanja Nikowitz

ABSTRACT
The main topic of this survey was the distribution of reef fishes, in particular of pomacentrid species, and their correlation with selected correlating factors such as depth and substrate structure. Three different visual fish census techniques were applied: stationary fish census, belt transects the and random swim technique . The comparison of the data obtained by these methods yielded arguments in favor or against their applicability for different questions. Based on the data from five transects, 11 pomacentrid species were characterized as to their frequency and distribution. Moreover, a list of all observed species (183) was compiled. It showed, that the eleven pomacentrid species we concentrated on were occurring highly correlated with certain substrate structures and depths.

3.) PATCH REEFS IN SEAGRASS MEADOWS - COMMUNITY STRUCTURE AND SHAPING FACTORS
Christina Marchesani, Gabriel Singer, Katharina Zoufal

ABSTRACT
24 small patch reefs of different sizes and at various depths were examined over a period of 10 days in Aqaba, Jordan. Biodiversity, degree of isolation, size and depth were recorded and analysed. A dominance of distinct fish species was observed, so that typical communities of small patch reefs were defined. However, community structure also seems to be highly variable and dependent on abiotic features of the reef. Community structure and biodiversity were found above all to be positively correlated to the size of the patch reef and negatively correlated to the degree of isolation. The dominant species were juveniles of Dascyllus trimaculatus, juveniles and adults of Dascyllus marginatus, juveniles of Pomacentrus trichourus and Epinephelus fasciatus. Besides the main tendencies for single different positive correlations species where found. Thus, for the presence of D. trimaculatus the depth was an important criterion, D. marginatus preferred a higher degree of isolation and the presence of P. trichourus was positively correlated with patch reef height. Comparison with the closest main reef revealed that many in the patch reefs encountered species had different size- and age structure, which is also expressed in different behaviour patterns. We hypothesize that small patch reefs in seagrass meadows have an important function in the lifecycle of certain species, due to less interspecific concurrence and predator abundance, by acting as "cradles" for juvenile fish.

4.) DISTRIBUTION OF SEA CUCUMBERS
Claudia Wurth, Verena Schmelz, Iris Rubin

ABSTRACT
Abundance distribution, movement activity, body dimensions and defecation of 5 holothurian species from a fringing reef were investigated in November 2001 in the Gulf of Aqaba, Jor-dan. 121 individuals comprising 5 species were recorded in a total sample space of 2400m² between depths of 1.7m and 23m. Synapta maculata, dominating in the seagrass meadow, was the most abundant species (0.075ind.m-2), followed by Holothuria fuscogilva (0.026ind.m-²), which was exclusively found among the coral outcrops on sandy bottom. The strategy of avoiding high light intensities by covering the body with plant material and sedi-ment grains could explain the high abundance of H. atra and H. cf. edulis in the shallowest parts of the sea.

H. cf. edulis moved on average 3.6m.d-1, whereas H. fuscogilva (2.3m.d-1) and H. atra (0.6m.d-1) travelled smaller distances. The lower radius of action may reflect disturbance (strong wave action, snorkelers, divers), low sedimentary organic matter and numerous barri-ers in some habitats. There was a positive correlation between body length and total wet weight for H. fuscogilva. The derived formula allows the calculation of the biomass alterna-tive to weighing all individuals.

Assuming that the amount of egested sediments is directly proportional to the consumption of sediments enriched with organic matter, H. fuscogilva and H. atra showed the highest defeca-tion and therefore the highest sediment uptake. H. cf. edulis, which occurred frequently in the seagrass meadow, injested only one sixth of the sediments consumed by the two other species but the organic carbon content of the faeces was highest. This implies that the higher level of organic matter in the sediment of the seagrass habitat is reflected in a lower assimilation effi-ciency. The concentrations of organic carbon were approximately three to six times higher in the faeces than in adjacent sediments, which would support results of previous studies that holothurians are capable of chemical selection of nutrient-rich sediment grains.