Habitat use of Sulfur damsel Pomacentrus sulfureus Klunzinger, 1871 in Masbat Bay (Gulf of Aqaba, Red Sea).
Alexander Kools - November 2012 - Universität Hamburg
The general habitat as well as specific substrate compositions and structures were checked for their influence on the spatial distribution and the probability of occurrence of Pomacentrus sulfureus. The study was conducted in Masbat Bay, Egypt, at south Sinai's shoreline of the Gulf of Aqaba. Masbat Bay was divided into 77 squares for data acquisition whereby in a period of five weeks 63 squares were surveyed. Using snorkeling techniques, the substrate composition was recorded in quantity and quality after the line intercept transect method and the fishes were counted using the visual fish census method. Furthermore, the environmental parameters time of the day, tides, water temperature, water depth, distance to the shore, distance to the reef edge, visibility and wave height were recorded to consider their potential influence on the spatial distribution of P. sulfureus.
Descriptive statistics show that the distribution and abundance of P. sulfureus is almost completely limited to the reef edges, where, compared to the other parts of the bay the main part of live coral cover is distributed. Multivariate statistics on the basis of logistic regression habitat suitability models present a strong dependence of the probability of occurrence of P. sulfureus only on live coral cover, whereby all other substrate categories and environmental parameters had to be excluded from the model. Additional models developed under considerations of the results obtained from the first model, revealed relations between the more detailed topographical and structural complex substrate category "branching like corals" (included in live coral cover) and the probability of occurrence of P. sulfureus. Finally, a third model showed an enhancing influence of branching Acropora colonies, a very detailed substrate category which could be suggested as the determining variable of the microhabitat of P. sulfureus in the bay.
Analysis of Reef Check data from the Red Sea
Sebastian Niklas Petschko - August 2012 - GeoBioCenter LMU München
Monitoring programs and surveys are very important tools in marine sciences, most involving
census of organisms and measurements of substrate. The Dahab Reef Monitoring
programm is an extended and locally adapted version of the standardised Reef Check programm.
Analysis of such data is statistically complex, with many unkown or uncertain
variables, noises, natural and anthropogenic uctuations, bias and instantaneous variations.
The study tries to asses the health state of coral reefs in Dahab at a dive site
resolution and correlate the development with the fast urbanisation of the region, using
General Estimating Equation (GEE). Here limitations of the resolution, the magnitude of
overshing and the fragility of selected dive sites is shown. It has been achieved to show
signicant trends in the abundance of indicatororganisms on a dive site scale, compared
to the regional approach of previous works. The abundance of food is either very
low or decreasing alarmingly at all sites and my study indicates unsustainable shery as a
reason. The dive site resolution analysis for the substrate and coral cover was not possible
due to the amount of data and the collection method. The main restriction of this study
is the amount of available data and the partially unkown variables leading to variance
of organism occurence. This study comes to conclusions, which hopefully help to further
improve the Dahab Reef Monitoring and shows the power and weaknesses of analysing it
with statistics. My study anticipates the danger and the extent of our lacking knowledge
about marine ecosystems.
Diversität von Indikatorfischtaxa im
gezeigt anhand ausgewählter Tauchplätze
der Korallenriffe um Dahab, Ägypten
Christoph Gassner, Bachelor-Arbeit, März 2011, Paris-Lodron-Universität Salzburg
This thesis is based on the data gathered in the Dahab Reef Monitoring & Reef Conservation
Project 2010 (DRM). The DRM was organized by the Red Sea Environmental Centre (RSEC)
from the 30th July 2010 to the 16th September 2010 in Dahab, Egypt. The aim of the project
is to record and gain data both about the influences and effects of the massive (dive) touristic
boom and natural impacts (e.g. storms, coral bleaching) in Dahab and its surrounding
underwater environment, and analyze possible reasons.
For that purpose several indicator groups (fish, invertebrates, substrate and coral damage)
representing the coral reef health have been selected and monitored through underwater
surveys (belt transects of 100 m x 5 m). 12 different dive sites with various dive frequencies
have been surveyed, all surveys have been carried out in three depths (5 m, 10 m, 15 m). The
gained underwater survey data has been evaluated, as well as the overview pictures of the reef
(taken vertically above the transect line to give information about the current coral cover and
the coral diversity). The results will provide data for the global Reef Check Database, and are furthermore intended to serve as an instrument for ecological conservation management
programs of the South Sinai coastal environment (e.g. dive site management).
This bachelor thesis compares the fish diversity between three different survey sites (Blue
Hole, Gabr el Bint und Islands South) and three different water depths by means of the
Shannon-Wiener-Index (SWI),. Summarizing the results of the SWI comparing, it was
observed that all three sites generally show a relative high fish diversity (SWI between 0.6
and 0.8. However, the values of the SWI of Islands South 5 m and Blue Hole 5 m are
significantly lower than the other sites (0.3 and 0.55). This may be caused by the recent
storms and a Crown-of-Thorns-Starfish (Acanthaster planci) plague at the Islands South
(destroying many corals and so habitats and nourishment of fish), and at the Blue Hole
because of a high diver impact due to the high number of divers and snorklers at 5 m depth,
disturbing the fish community.
Characterisation of surgeonfish Ctenochaetus striatus defecation sites suggests possible functions of this behaviour
Ana Rodriguez Perez - Bachelor Thesis - August 2011 - University of Tübingen
The characteristics of spots used by Ctenochaetus striatus for defecation were compared to "toilets" of three different habitats. Moreover, long time monitoring of some of the defecation sites was performed in order to find out if the "toilets" were used constantly over the surveyed period of time. The study revealed that all toilets were to some extent sheltered, which was the most relevant characteristic. Moreover, when sand was available, it was preferably chosen as substrate type as it was stated before. There was also a tendency for the less sheltered defecation sites being oriented towards the open sea. Finally, the surveyed "toilets" were continuously used over the monitored period of five weeks as defecation patches. Altogether, these findings reveal two main functions resulting from the defecation behaviour of this species. Firstly, C. striatus is not only, as mentioned in previous studies, directly responsible for sediment transport off-reef by feeding on the upper reef crest and defecating in deeper areas, but also indirectly through defecation in sites which are less sheltered towards the open sea; therefore, sediment drift through hydrodynamic agents is likely to occur in this direction. Secondly, another main function seems to be the transport of sediment from areas of high hydrodynamic exposure to sheltered patches. Taken together with the findings of the long time monitoring, namely that the defecation sites were used over at least five weeks, this behaviour could enhance the microbial growth on faecal sediment, as abrasion is a limiting factor for the expansion of microbes. These microorganisms could process nutrients of C. striatus faeces not accessible for other organisms and provide a direct trophic link between the microbes and organisms that ingest them. Hence, through this defecation behaviour, the internal nutrient flow within the reef ecosystem could be supported. However, this novel hypothesis needs to be verified.
A potential mutualism between the reef sweeper
Ctenochaetus striatus and the territorial grazer Acanthurus sohal (Acanthuridae)
Anouk-Isabell Neuhaus - Bachelor Thesis - July 2011 - University of Tübingen
Sedimentation is detrimental for coral health and sediment removal thus vital for the
resilience of reefs. The surgeonfish Ctenochaetus striatus removes sediment and
accumulates it due to its characteristic defecation behaviour. Individuals of this species
use certain spots (ʻtoiletsʼ) for repeated defecation events over a longer period of
time. Thereby it facilitates a directed sediment transport. Another surgeonfish, the
herbivore Acanthurus sohal, might benefit from this effective and lasting removal as it
might promote algal growth. A mutualistic relationship may arise from these circumstances.
Indeed I found out that A. sohal tolerates the presence of C. striatus in its territory although this large surgeonfish aggressively defends its territory against other
species. It could not be confirmed that sediment removal enhances algal growth.
In conclusion, a mutualistic relationship between the two surgeonfishes can be considered
possible but the advantage for A. sohal could not be ultimately identified in
this study and should be the subject of subsequent studies.
Effects of Ctenochaetus striatus' Defecation Behaviour on Coral Reefs' Endobenthic
Agnes Förster - Bachelor Thesis - July 2011 - University of Tübingen
The Striped Bristletooth surgeonfish (Ctenochaetus striatus) stands out due to his special defecation
behaviour. Fish of this species defecate away from their feeding grounds at individually belonging
toilets, which are mostly located on sand (Krone et al. 2008) and in sheltered positions (Goatley and
Bellwood 2010). Since the constant defecation at distinct spots comes along with an input of organic
matter and nutrients (Krone et al. 2010), the following two assumptions were made: (1) The density
of meiofaunal organisms in sediments below toilets is higher than in the surrounding area and (2) the
composition of meiofaunal taxa differs between sediments below toilets and sediments below nontoilets.
In total, 26 sediment samples with a volume of 15 ml each were taken from 13 toilets and 13
other sand spots. The meiofauna was extracted, counted and identified, and then samples from
toilets and non-toilets were compared. To exclude influences of other factors on the results, grain
size of the samples was analyzed and exposure to hydrodynamic action, water depth and tides were
recorded. A significant higher density of meiofaunal organisms in toilets compared to non-toilets
could be proven. Furthermore, a significant change in the meiofaunal composition, which mainly
based on a shift in proportions of foraminiferans and copepods was found. Hence, a new aspect of
the defecation behaviour of C. striatus was revealed. Thereby this study contributes to the
understanding of the Striped Bristletooth's ecological role.
Defecation behaviour of Ctenochaetus striatus as a strategy to avoid parasites
Sabrina Hug - Bachelor Thesis - December 2011 - University of Tübingen
The Striped Bristletooth surgeonfish (Ctenochaetus striatus) has a specific defecation behaviour, since individuals of this species defecates on specific spots, away from their feeding grounds. These ‗toilets' are mainly located on sand (Krone, et al., 2008) and mean additional distances to swim, when they forage in their feeding grounds and swim away to a defecation spot. A possible explanation for this defecation behaviour could be a strategy to avoid a re-uptake of endoparasites (J. Choat, 1991), which may be contained in the faeces of C. striatus. For that reason 26 samples of faecal pellets were collected and examined for endoparasites. However, no endoparasites could be found in any of the excrements, neither in the egg, larvae, oocyst stage nor in the adult stage. Moreover, the excrements were examined for organisms, which are transported in the faeces. A wide range of meiofaunal organisms were found. Hence, the densities of meiofaunal organisms (1) between the faeces and adjacent sand samples and (2) between faecal samples of two different locations were compared. A significant higher density of meiofaunal organisms in the Canyon reef to the reef of Mashraba could be proven. However, there was no significant difference of the densities of meiofaunal organisms between faecal pellets and sand samples. Nevertheless, the excrements of C. striatus have a positive effect on the density of the endobenthic meiofauna living in the sediment of its toilets' (Förster, 2011). Therefore, the Striped Bristletooth has another important role for the coral reef ecosystem due to the input of organic and inorganic material.
Habitat Preferences of Fish Assemblages in Masbat Bay, Dahab (Red Sea, Egypt)
Johanna Sophie Zimmerhackel - Bachelor Thesis - August 2010 - University of Hamburg, Section Ichthyology
Possible effects of habitat characteristics on fish assemblages were investigated in the Masbat
Bay in South Sinai, Egypt using snorkelling techniques. Therefore, the Masbat Bay was
divided into squares containing transects for data acquisition and in a time period of six weeks
a total number of 40 transects was examined. The visual census method by ENGLISH et al.
(1994) was used to estimate the number of all fishes inside these transects. A total of 114
different species belonging to 37 families was counted. The quality and quantity of substrate
was measured using the line intercept method (LIT) by ENGLISH et al. (1994) and ten
environmental parameters, namely the time of day, water depth, wave height, distance from
the shore, distance from the end of the reef, water temperature, current direction and intensity,
tide and visibility were recorded. The high correlation found by regression of substrate
diversity and fish diversity indicated that habitats in which the substrate was more structurally
or topographically complex were favoured by the majority of observed fish species.
Multivariate analyses were performed to explain the variation of fish assemblages in relation
to the measured variables using the Canonical Correspondence Analysis (CCA) by TER
BRAAK (1987). A large part of the variability of reef fish assemblages was explained by
distance from shore and substrate diversity. Upon further examination, the differences in fish
assemblages of a number of habitat types that were found in Masbat Bay were shown to be
mostly influenced by the substrate types: branching corals, sand, algae and rubble.
The results of this study may gather extensive information about the diversity and abundance
of fish assemblages in Masbat Bay, and should thereby provide knowledge as an applicable
tool for the nature conservation management of the Masbat Bay area.
Fish Fauna Diversity in Relation to Habitat Structure at
an Isolated Fringing Reef at Masbat Bay, Dahab, South
Katharina Fietz - Bachelor Thesis - September 2009 - University of Hamburg,
Diversity of a fish assemblage was determined and compared to substrate structure, to the
amount of coral damage, as well as to defined environmental variables on an isolated fringing
reef off the coast of Egypt. A total of 95 different species belonging to 35 families were
counted in the reef adjacent to the tourist resort town Dahab. Labridae and Pomacentridae
dominated fish assemblages in terms of species diversity while Pomacentridae were most
abundant with 1262 counted individuals out of a total of 4165.
Abiotic cover was the most frequented in substrate analysis followed by life coral cover and
algae cover. The reef divided into three main zones: the coral area in the centre showed
highest live coral cover dominated by Acropora spp. and highest fish abundance. The area
closest to shore showed high algae cover and high abiotic cover and was dominated by
Porites, while a high abiotic cover and low coral cover defined the outer edge of the reef area.
Variation in total number of fishes between transects, variation in reef fish diversity, as well
as distribution of the most abundant fish species and significant changes of abiotic cover
between transects further clarified this differentiation of the reef.
Multivariate analyses showed that substrate structure influenced fish assemblages strongest of
all investigated environmental variables. Water depth, distance from shore, and distance from
the beginning of the reef also revealed a good correlation to fish assemblages. Analysis of
coral damage correlation to fishes suggested little influence of damaged coral colonies on
variation in fish assemblages. Results of coral damage data analyses, however, can only
limitedly be interpreted due to a lack of relative amounts of damage in the reef. Diurnal
changes in fish assemblage composition were not detected.
Time for sex change! 3D-reconstruction of the copulatory system of the 'aphallic'
Hedylopsis ballantinei (Gastropoda, Acochlidia)
Kohnert P, Neusser TP,, Jörger KM & Schrödl M - Bavarian State Collection of Zoology - Published in Thalassas, 27(2):113-119
Within hedylopsacean acochlidians an
evolutionary trait from a simple unarmed copulatory
system towards complex hypodermal injection
systems was recognized. This culminates in a
large, trap-like spiny rapto-penis of several limnic
Acochlidiidae having a sperm injection stylet plus
an additional injection system with an accessory
gland. The only exception was the mesopsammic
hedylopsacean species Hedylopsis ballantinei Sommerfeldt & Schrödl, 2005, since it was assumed
to be aphallic. Specimens with mature autosperm
and oogonia in the hermaphroditic gonad showed no
trace of any male copulatory organs. Sperm transfer
via spermatophores was thus suggested, as known
to occur in the generally aphallic microhedylaceans.
The present study re-examines several series of
semithin sections used for the original description.
Additionally, one specimen of H. ballantinei wasnewly collected near the type locality in the Red Sea.
It is externally identical with but smaller than the original specimens. The specimen was embedded
into Spurr's resin and serially cut into semithin
histological sections. Reproductive systems were
compared in detail and that of a specimen in the
male phase was 3-dimensionally reconstructed
using AMIRA software. The copulatory organs
comprise the posterior-leading vas deferens passing
into a voluminous tubular prostate, a presumable
paraprostate and a bipartite penis with a large apical,
hollow penial stylet and with a cuticular, solid thorn
on top of the basal swelling. As already known
for H. spiculifera (Kowalevsky, 1901), its European
sister species, H. ballantinei thus is a sequential
hermaphrodite with sex change. The male phase
precedes the female one, in which male copulatory
organs completely disappear. Sperm transfer is likely
by hypodermal injection. Hedylopsis ballantinei in
the male phase has an external sperm groove, while
specimens in the female phase possess a ciliary field;
the latter may have a function related to building or
placing the egg mass. Hedylopsis ballantinei now
fits well with evolutionary traits observed within
other hedylopsacean acochlidians known in detail.
Herbivory effects on benthic algal composition and growth on a coral reef flat in the Egyptian Red Sea
Published: MEPS 476:9-21 (2013)
Christian Jessen*, Christian Wild
Coral Reef Ecology Group (CORE), Leibniz Center for Tropical Marine Ecology (ZMT) and University of Bremen, Fahrenheitstr. 6, 28359 Bremen, Germany
ABSTRACT: One of the major threats facing coral reefs is intense benthic algal growth that can result in overgrowth and mass mortality of corals if not controlled by herbivore grazing. Unlike the well-studied coastlines of the Caribbean, there is currently a lack of knowledge regarding the effects of herbivory on benthic communities in the Red Sea. This is particularly relevant today as the local impacts in the Red Sea are increasing due to growing population and tourism. Over 4 mo, this study investigated the impact of herbivory as a potential key factor controlling algal growth on a reef flat in the Egyptian northern Red Sea. The main experiment consisted of in situ deployment of exclosure cages in combination with quantification of sea urchins and herbivorous fish. When all herbivores were excluded, our findings showed a significant 17-fold increase of algal dry mass within 4 mo. Although herbivorous fish occurred in much lower abundance (0.6 ± 0.1 ind. m-2; mean ± SE) compared to sea urchins (3.4 ± 0.2 ind. m-2), they were 5-fold more efficient in reducing algal dry mass and 22-fold more efficient in reducing autotrophic production of nitrogen. A significant shift from benthic turf to macroalgae (mostly Padina sp. and Hydroclathrus clathrathus) was observed when grazers were excluded. These algae may serve as early warning indicators for overfishing. Findings suggest that herbivorous fish act as an important top-down factor controlling both benthic algal biomass and composition at the study location. Results also indicate the potential of rapid benthic community change at the study site if herbivory is impeded.
KEY WORDS: Herbivory · Benthic algae · Cage experiment · Reef flat · Red Sea · Sea urchin · Herbivorous fish
Einfluss der Herbivorie auf das Algenwachstum auf dem Riffdach im Roten Meer,
Christian Jessen, Diplomarbeit, Mai 2010, Zoologischen Institut der Freien Universität Berlin
Eine der größten Bedrohungen für Korallenriffe heutzutage ist die starke Konkurrenz von
Algen, die, wenn wenig oder gar nicht kontrolliert, die Korallen überwachsen können und
damit abtöten. Eine intakte und ausgeglichene Herbivorie verhindert den Konkurrenzvorteil
der Algen und sorgt damit für den Erhalt und die Widerstandsfähigkeit von
Korallenriffen. Um die Schlüsselfaktoren für die Kontrolle des Algenwachstums auf dem Riffdach zu
identifizieren, wurde von Oktober 2009 bis Februar 2010 der Einfluss von Herbivoren auf
das Vorkommen und Wachstum der Algen auf dem Riffdach des Korallenriffs Shaab Tina
bei El Quseir (Ägypten, Rotes Meer) untersucht. Während bereits zahlreiche vergleichbare
Untersuchungen an anderen Korallenriffen wie etwa in der Karibik, Hawaii oder am Great
Barrier Reef durchgeführt wurden, ist der Wissensstand für das Rote Meer noch sehr gering,
insbesondere in Bezug auf Untersuchungen des Riffdachs, das aufgrund seiner
leichten Zugänglichkeit von Land oft stark befischt wird.
Die Datenaufnahme bestand aus 2 Schwerpunkten. Zum einen wurde mithilfe von Käfig-
Aussschluss-Experimenten der Zustand eines überfischten Riffdachs simuliert, sodass der
Einfluss von reduzierter Herbivorie auf das Algenwachstum untersucht werden konnte.
Zum anderen wurde ein detaillierter Fisch- und Seeigelzensus durchgeführt, um die
Hauptherbivoren zu identifizieren und um Aussagen über den Zustand des Riffs machen zu
können. Ergänzend wurden mehrere abiotische Faktoren, wie Temperatur, Salzgehalt,
Wasserbewegung und Sedimentationsmenge sowie die stabile Isotopensignatur und der
Kohlenstoff- und Stickstoffgehalt der Algen untersucht, die ebenfalls einen Einfluss auf
das Algenwachstum haben und bei der Erklärung der Ursachen eine Hilfe darstellen sollen.
Die Ergebnisse der Käfigexperimente zeigten eine signifikante Zunahme der Algenbedeckung
an den Orten, an denen die Herbivoren ausgesperrt wurden im Gegensatz zu
Kontrollstellen zu denen sie freien Zugang hatten. Daher konnte mit der Studie gezeigt
werden, dass herbivore Riffdachbewohner eine entscheidende Rolle in der Kontrolle des
Algenwachstums haben und damit in der Aufrechterhaltung der Biodiversität. Auf dem
untersuchten Riffdach waren die Algenfresser nicht nur in einer ausreichenden Dichte vorhanden,
sondern es gab sowohl benthische (Seeigel) und pelagische (Fische) Vertreter, die
bei der Kontrolle der Algen ergänzend wirken können. Die Ergebnisse zeigen, dass das Riffdach von Shaab Tina nicht unmittelbar gefährdet ist, jedoch wurden aufgrund von
Untersuchungen der Zusammensetzung der Riffdachbewohner einige Anzeichen aufgedeckt,
die eine fortgeschrittene Überfischung erkennen lassen.
Die Untersuchungen zeigen allerdings auch, dass innerhalb weniger Wochen ein schneller
Anstieg in der Algenbedeckung erfolgen konnte, wenn keine oder eine nur unzureichende
Dichte an herbivoren Fischen vorhanden war.
Die Ergebnisse der vorliegenden Studie deuten daher die Notwendigkeit eines nachhaltigen
Riffmanagements im Untersuchungsgebiet an. Dies erscheint insbesondere sinnvoll vor
dem Hintergrund der zuletzt stark zugenommenen Belastung der Küstenregionen durch
intensive touristische Erschließung.
The Behaviour of Dugong dugon and the Influence of Tourism on
the Dugong in Abu Dabab in Marsa Alam, a Popular Dive Site in
Maya Bode, Field report on BSc Study, University of Goettingen
Sightings of Dugongs in Egyptian waters have become extremely rare (Gohar 1957). Marsa
Abu Dabab is a popular dive site in the south of Egypt. The seagrass meadow in the bay,
consisting of Halodule uninervis and Halophila stipulacea, is periodically frequented by one
Dugong. In this study the behaviour of this Dugong (Dugong dugon (Müller, 1776)) was
analysed and the influence of the divers and snorkelers on the Dugong was determined.
In March 2009 underwater observations were made. The hours spent in the bay per day
averaged 6,4 (± 2,6) h. The mean dive time was 296 (± 61) s at a mean maximum dive depth
of 7,3 (± 1,6) m. The forage time averaged 473 (± 66) s. 96,9% of the dives were feeding
dives. During 84% of the feeding dives the Dugong fed on Halodule uninervis. The Dugong
took a mean of 3,4 (± 1) breaths between the dives. The time spent in water deeper than 1,5
m averaged 78,8% of one hour, 21,2% of the hour were spent less than 1,5 m at the surface.
The number of snorkelers per day averaged 178. During 88,1% of the encounters with
tourists, the tourists approached the Dugong within less than 3 m. During 40% of the
underwater observations the Dugong swam out of the bay and during 30% the Dugong
moved into deeper regions as a reaction to the tourists within a radius of 10 m. A short-term
influence of the tourist on behavioural patterns as dive times, forage times, distances
between foraging lots and number of breaths between dives could not be ascertained. But a
long-term influence on the Dugong cannot be excluded.
Cryptobenthic Fish of the El Quadim Bay,
El Quseir, Egypt
Andreas Scharl, Bakkalaureats-Arbeit, Fachbereich Organismische Biologie, Universität Salzburg
This study establishes a preliminary species list of cryptobenthic fishes: Apogonidae (four species), Blennidae (eight species), Gobiidae (thirteen species) and a Plesiopidae, on
Egypt's mainland Red Sea coast. Different methods of capturing and/or identifying these
fishes are evaluated, among them interference visual census and anaesthetisation by clove
oil as well as fish traps and a ground-net filled with coral rubble. Clove oil proved to be
most effective and a valuable tool when studying small and cryptic fishes. Additionally
the habitat preferences of the studied species have been listed revealing hard substrates
such as coral rubble, rock and live corals to be of greater importance to cryptobenthic
fish than sandy bottoms. A certain bias towards species living on the reef flat has to be
acknowledged as it was easy to catch fish hiding in pools and channels at low tide and the
time dedicated to capturing fish during research dives was limited.
Beziehung zwischen der
tsurnamali und Coelenteraten im Roten Meer
Gerlinde Aichinger - Masterarbeit - 2010 - Universität Salzburg
The mysid Idiomysis tsurnamali was found hovering over the jellyfish Cassiopeia
andromeda, the anemone Megalactis griffithsi and Cerianthus sp.. During the observations a
new species of the genus Idiomysis was found between the stings of the sea urchin Diadema
setosum. This new species, temporarily called Idiomysis sp. A, is going to be described. Some
of the collected specimens were observed under the scanning electron microscopy. The
correlation between the size of C. andromeda and the size of the mysid swarm could be
demonstrated, as well as the correlation between the size of the jellyfish and the distance the
swarm was hovering above its host as well as the distance the individuals of a mysid swarm
were keeping among themselves. Furthermore the behavior of the swarm during the approach
of a potential enemy and the return behavior after the dislocation of the swarm were observed.
Because of the swarm-behaviour during the night, it is assumed that the mysid I. tsurnamali
does not have any protection against the nematocysts of its host.
Aggressions- und Feinderkennungsverhalten von
Amphiprion bicinctus im Roten Meer
Magistra der Naturwissenschaften - Januar 2006 - Leopold-Franzens-Universität Innsbruck
In 1868 the symbiotic relationship between anemones and anemone fish was
described for the first time. Since then scientists investigated many different
fields concerning the symbiosis, the social organization of anemone fish, sexual
stunts and the immunity to the nematocysts of the host anemones. In the last
more than 170 years of investigation, research has led to a lot of contradictory
results. This thesis deals with the aggression behaviour of Amphiprion bicinctus
(the Red Sea Anemone fish) against predators and its reaction on enemy
A. bicinctus belongs to the Pomacentridae (Reef Perch) and is endemic in the
investigated area where it is at the same time the only species of anemone fish
found. Their natural distribution range includes the Red Sea and the Gulf of
Aden. Anemone fish are unique among Reef Perch because they live in lifelong
partnerships. Their small territory is probably the reason for this faithfulness.
The host anemone is in the centre of the territory in which the fish reproduce,
hide and search for food. All the species of anemone fish are obligate symbiosis-partners of sea
anemones. One benefit of the symbiosis to the fish is obvious: its major source
of protection is its anemone, which forms the core of its territory. The symbiosis
is commonly regarded as facultative for anemones. However, anemone fish
also provide protection against predatory fish to their hosts.
Innumerable theories about how the anemone/fish-partnership works have been
elaborated. Behaviour and biochemistry, probably both, play roles to varying
degrees. In fish that live with many types of host behaviour is likely to be more
important to adaptation, whereas for host-specific fish biochemistry is probably
the more significant factor.
Facultatively symbiotic Pomacentridae of the genus Dascyllus may occupy
hosts instead of or along with true anemone fish. In some host anemones
shrimps and crabs live together with anemone fish. Juvenile Labridae (Wrasse),
Bleniidae (Blenny), Anthiidae (Fairy basslet) and Apogonidae (Cardinal fish)
sometimes seek refuge near the tentacles of the anemone. They are not
considered as true anemone fish, because the symbiotic relation is facultatively.
A. bicinctus lives in relatively large social units, often consisting of an adult pair
and a series of juvenile sub-adults. Size-related dominance hierarchy exists in
anemone fish. The larger female controls the production of other females by
aggressive dominance. Like in other species of marine fish with closed social
systems a subdominant individual can be induced to change sex by removal of
the dominant one. This phenomenon has been described as socially controlled
sex reversal. Sex change is relatively commonplace among fish, a remarkable
adaptation that helps prevent any lull in reproduction, but it typically involves a
female-to-male switch. The unusual male-to-female reversal in anemone fish is
known as protandrous hermaphroditism.
My field studies took place from July to September 2005 at the Red Sea
Environmental Centre in Dahab, in the Gulf of Aqaba. In total I did 80 dives with
more than 83 hours of underwater-observations. In the first half of my stay I
registered the exact sites of the anemone/fish-partnerships and the parameters
of the surrounding area to (e. g. depth, fish and anemone size, number of
anemone fish living in the anemones, etc.) to investigate their influence on the
behaviour of A. bicinctus.
After drawing up a behavioural catalogue I started my observations in twenty
minutes intervals at four different depths. In the second half of my studies I
carried our fake-experiments on A. bicinctus to see which contours evoke more
or less aggression to replenish my observation studies. I also prepared three
white-coloured replicas to see how big the influence of the natural colours on
the aggression behaviour is. It was obvious that the colour is an important
trigger of aggression behaviour. In the beginning of my field research I checked
the behavioural patterns of A. bicinctus and then I choose five particular
behaviours: spreading the dorsal fin and pectoral fins, presenting the broadside,
jerk swimming, whipping with the caudal fin and attack. I took notes how often
each of these behaviour patterns were carried out during one twenty minutes
interval and I also took notes against which other reef inhabitants the anemone
fish were aggressive. In the all together 1600 minutes of my observations I
attend 208 attacks of A. bicinctus against other reef inhabitants. There was an
obvious trend of aggression behaviour against Pomacentridae (Reef Perch),
Labridae (Wrasse) and Chaetodontidae (Butterfly fish). Those families are food
and territory rivals, egg and anemone predators. Serranidae (Grouper),
anemone fish predators, were in the fourth place.
A. bicinctus lives in association with five host anemones: E. quadricolor (Bulb
Tentacle Sea Anemone), H. magnifica (Magnificent Sea Anemone), H. crispa (Leathery Sea Anemone), H. aurora (Beaded Sea Anemone) and S. gigantea
(Gigantic Sea Anemone). The number of the anemones in the area has a big
influence on the social organization of anemone fish. In the investigated area,
the number of anemones was a restrictive factor for adult A. bicinctus.
The results showed, that the method of the observations also has an influence
on the behaviour of A. bicinctus. The fish showed more aggression behaviour
when I was snorkelling. They are probably less disturbed without the noise
coming from the diving equipment.
At different depths the composition of the species is varying. This means that at
different depths different enemies occur. The results showed, that the attacked
species vary, not the behaviour of A. bicinctus.
The size of the anemone fish has a big influence on the aggression behaviour.
Not only the number of attacks increases with it, but also the distance at which
enemies are attacked. No attacks from juvenile A. bicinctus were observed. The
frequency rises with the anemone size, as well as the distance at which passing
fish are attacked. A change of the frequency of attacks during the day could not
be proved. A. bicinctus showed before midday the most activity.