Scientific research topics 1997

1.) GROWTH OF HERMATYPIC CORALS I: SELECTION OF COLONIES AND BASELINE MEASUREMENTS
Julia Prochazka, Eva Grünberger, Annemarie Kramer

ABSTRACT
This contribution describes the first step in measuring the annual growth of reef-building corals in the Gulf of Aqaba. This project was initiated in November ´97 and the first results on coral growth are expected in November ´98.
We measured branching and massive corals of the species Acropora sp., Stylophora pistillata, Stylophora sp., Pocillopora damicornis, Astreopora myriophthalma, Favia pallida, Favia sp., Leptoseris sp. and the Hydrocorallia Millepora dichotoma.
In order to detect potentially different growth-patterns, the corals were selected from a range of depths between 3 to 21 m. The highest and widest extension of each coral was measured. Additional single branches were marked with cable-binders and measured. Photographs were taken of each coral and sketches of the parts were measured drawn. In order to relocate the corals in the following years, bearings and exact locations were recorded in divemaps.

2.) INVESTIGATIONS ON THE MIGRATION OF TECTUS DENTATUS
Roland Zöggeler, Bettina Riedel

ABSTRACT
26 specimens of Tectus dentatus were measured and marked. Weights varied between 93 g and 339g. The migrations of the snails were observed and recorded from 04.11.1997 to 08.11.1997. The distances moved erery day were short (less than 2 m/day), except on the 7th of November 1997. On this day there was rough sea and most individuals moved from the exposed front side to the more protected sides of the jetty. Furthermore one specimen moved across sand bottom to a stone 9 m away from the jetty. Most of the marked specimens could be found again on at least one of the following days.

3.) THE DISTRIBUTION OF DIADEMA SETOSUM AND OTHER ABUNDANT ECHINODERMS
Helmut Koller, Andreas Traxler

ABSTRACT
Diadema setosum is a nocturnal sea urchin which is one of the most common species in the coral reefs of the Red Sea. Its most preferred habitats during the day are semi-shaded niches at the basis of coral rocks in a depth between 0,5 and 6m. Below this level it becomes less frequent. These niches are used as resting places, which are left at dusk. It then moves around, but not more than a few meters away from its resting place, and grazes over the reef-surface. Apart from this, some individuals also enter the adjacent sandy bottoms, where they feed on the detritus in the upper layer of the substrate. These individuals, which remain on sandy surfaces, form conspicuous aggregations during the day. This behaviour reduces exposure to predators. D. setosum is very competitive. It was concluded from the investigations by the Univ. of vienna in November 1995, that this species excludes the occurrence of other sea urchins to a large extent, but only in areas where D. setosum is most abundant. For example the reef flat in the uppermost zone is settled by other species; first of all by Echinometra mathaei, which dominates this habitat, typified by high-energy wave and current action, probably because of its small size and stronger attachment to the substrate.
It was the aim of this investigation to determine the most important factors regulating the distributionpatterns of D. setosum in the coral reef. Furthermore the occurrence of other echinoderm species was recorded.

4.) INTER- AND INTRASPECIFIC AGGRESSION OF DASCYLLUS TRIMACULATUS
Pamela Zolda, Daniela Knosp, Georg Scattolin, Michael Kuba

Abstract
The aim of the Red Sea field study, which was conducted in November 1997 at Aqaba (Jordan) was to do research on aggressive behavior in the poamcentrid fish Dascyllus trimaculatus (Rüppell, 1828). Dascyllus trimaculatus feeds mainly on zooplankton amd lives in an association of many females with many males in open water a few meters above the ground. During the mating season the adult males separate from the school, cahnge color, descend to rocky ground and seek out certain territories which they defend against intruders. This has the advantage that the males can be identified clearly and their aggressive behavior can be studied at close range and individually for every single fish. This study consisted of recording the frequency of attacks on intruding fish over a certain time period and the identification of the attacked species. At an average depth of 18 meters, several territories of D. trimaculatus were observed in 13 intervals of 10 minutes. The different species of attacked fish are indicated in table 1. All territorial males showed evident aggressive behavior. No obvious difference between intra- and interspecific aggression could be detected. For the most part fish of other pomacentrid genera were subject to attacks. Intrudion into the territory of D. trimaculatus was the most common reason for an attack. The size of the intruder was apparently unimportant to the territorial D. trimaculatus. Larger fish such as parrotfish were also attacked. Boxfishes like Ostracion cyanurus were not attacked as fiercely as Thalassoma lunare from teh family Labridae, which feeds mainly on fish eggs and therefore posed an immediate threat to D. trimaculatus.

5.) COMPARISON OF JUVENILE AND ADULT CLEANER WRASSE
Ruth Byrne, Janja Ceh, Angelika Sorgo, Anna Wressnig

ABSTRACT
The aim of our research was to compare adult and juvenile Labroides dimidiatus (cleaner wrasse) in terms of different home ranges and "cleaning customers".
This project was carried out using the SCUBA-method, whereby individual cleaning stations were marked and measured. A total of 35 ten-minute protocols were taken and recorded on underwater writing tablets.
The juvenile cleaning fish are primarily located in small protected sites. The cleaning stations of the juveniles are on average 5.1 m apart. As the juveniles rarely leave their cleaning stations, they are mostly visited by small host fish that fit into their stations. To attract host fish they show a dancing behaviour.
On the other hand, the habitat of adult L. dimidiatus is more exposed and is thus visited by bigger fish. The average distance between cleaning stations of adults measured 5.6 m. They also leave their cleaning stations more often to follow their host fish and to search for new ones. Dancing behaviour by adults was only rarely observed. This might be attributed to the fact that the stations are already established and actively sought by cleaning customers.
In the case of both adults and juveniles, Anthias sp. is the most common customer (juveniles 53.2 %, adults 39.8 % of all customers). In addition there is a distinct size difference between the customers of adults and juveniles. For example, the second and third most frequent customers of the juveniles are Pomacentrus sp. (11.7 %) and Chromis dimidiata (9,9 %). In contrast, Parupeneus forskali (16.8 %) is the second most abundant customer of adults. In addition they also accept divers as hosts (6.6 %), which indicates that they are rather unspecific in selecting their customers.

6.) FEEDING BEHAVIOUR OF REEF FISH
René Hexel, Andrea Nussbaumer, Sonja Reder, Christina Berger

ABSTRACT
In coral reef environments a surprisingly large number of animals can be found that feed on coral and algae. In this work the feeding habits of four different species of reef fishes and their impact on the abundance of live and dead corals was studied and compared. After two days of observation the fishes, which were most frequently seen to feed on live and dead corals were identified: Chaetodon austriacus (Chaetodontidae, butterfly fishes), Chaetodon paucifasciatus (Chaetodontidae), Sufflamen albicaudatus (Balistidae, trigger fishes), and Scarus sp. (Scaridae, parrot fishes). Surveys of feeding habits showed that Chaetodon austriacus is strictly coralivor and Chaetodon paucifasciatus is mainly coralivor, while the other two species are mainly herbivor, feeding on algae (and perhaps small invertebrates living amongst corals), which they scrap from dead corals and/or sand. With their strong jaw and tooth-plates parrot and trigger fish are well adapted to scraping growths from hard substrate, even breaking off whole branches of dead corals. This feeding habit in conjunction with the frequent defecation of coral sand makes Scarus sp. and Sufflamen albicaudatus an important producer of sediment in the coral reef. In contrast to that indirect impact on the living corals, Chaetodontidae feed specifically on living coral. Their mouth is well adapted to eat living polyps off a coral colony without picking up limestone. Thus, they have a direct impact on the living coral they dwell upon. Chaetodontidae change colonies much more frequent, eating only two to three times in one place (on average) before moving on. This feeding habit could be understood as a preservation strategy for their food resources. Furthermore, a colony of Porites porites (Poritidae) was examined, which showed marks of bites from Scarus sp. On an area of 20x20 cm an average of 32 scars with an average size of 108 square millimeters each was found, giving a total destruction of approximately 8.1 % of the coral surface. These affected Porites porites were only found in a depth down to three meters in absence of territorial Pomacentridae (damselfishes). This supports the theory that the growth rate of corals is higher in the presence of aggressive territorial fish, which defend their territory.