Analysis of Reef Check data from the Red Sea

Sebastian Niklas Petschko - August 2012 - GeoBioCenter LMU Munich

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.

 

Niklas Petschko

Sebastian Niklas Petschko

Dahab Reef Monitoring

 
 

Diversität von Indikatorfischtaxa im räumlichen Vergleich gezeigt anhand ausgewählter Tauchplätze der Korallenriffe um Dahab, Ägypten

Christoph Gassner, Bachelor-Arbeit, March 2011, Paris-Lodron-University 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.

 

Lukas

Christoph Gassner

Dahab Reef Monitoring

 

 

 

 

 
 

Herbivory effects on benthic algal composition and growth on a coral reef flat in the Egyptian Red Sea - Christian Jessen, Christian Wild

MEPS prepress abstract  -  doi: 10.3354/meps10157

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 coast lines 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 four months, this study investigated the impact of herbivory as 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 months. Although herbivorous fish occurred in much lower abundance (0.6 ± 0.1 individuals m-2; means ± SE) compared to sea urchins (3.4 ± 0.2 individuals 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 important top-down factor controlling both benthic algal biomass and composition at the study location. Results also indicate potential of rapid benthic community change at the study site if herbivory is impeded. 

 

coral erosion

coral erosion

 
 

Short outline of our Coral Project:

Coral Diversity and Distribution Project
Different sites of the reef provide diverse environmental factors and require different adaptations of coral species (Loya 1972). One goal is to characterise chosen reefs and provide an overview of coral species, their abundance, density and distribution in different zones at the fringing reefs in the region of El Quseir. This project focuses on the species, the morphology and the size (and age) of coral colonies and tries to correlate these characteristics with their locations. Furthermore, the density of species in different locations is of major interest.

Monitoring of Abundance and Coral Health:
Monitoring of the corals concerning their abundance in various zones, bleaching and disease or other damage and algal overgrowth is a long term activity, which will provide information on possible seasonal changes in the reef or changes due to other (climatic or anthropogenic) impacts.

Coral Sexual Reproduction Project:
Study on the sexual reproduction biology of the corals will be conducted. A study recording the spawning events is planed, as up to now these data is rare for the Red Sea (Shlesinger et al. 1998, Hanafy et al. 2010).
Precisely synchronized spawning allows the stationary animals to mix genetically and to disperse offspring over great distances. It is important that synchronic spawning events are recorded and a schedule for these events is developed in order to facilitate effective management. In particular, human disturbances should be prohibited during spawning seasons, ensuring that the seasonal reproduction and reef replenishment is not disturbed.

Coral Recruitment Project:
Recruitment is the measure of the number of young individuals entering the adult population and it is an essential factor in cases of damage or decrease of the reef due to climatic or anthropogenic disturbances. The study of the natural rates of coral recruitment helps to better understand the potential of repopulation in the reef. Documentation of recruitment in the reef is important for estimating the recovery rate of a reef (Hughes et al. 1999, Loch et al. 2004).
Long term study will be conducted in order to collect data on the recruitment patterns in the Red Sea throughout the year. Quantitative analysis and species specific analysis of young coral recruits are possible here (Babock et al. 2003).

Defined environmental abiotic parameters will be seasonally recorded accompanying the data of the above sketched studies to allow a correlation of such abiotic data sets with the observed results.

Collected data is valuable in terms of biological interest. Furthermore, the collected data will provide a foundation for the design of protective and recovery measures that will enable reef preservations for appropriate and long-term future use.

 

 

Acropora

Acropora

Fluor

Acropora

Acropora

 
 

Biodiversity and Biogeography of Red Sea Scleractinians

Generally most scleractinian species show a certain variation, environmental and regional, which made the identification quite difficult. Veron (2000) ascribes to this fact the certainty with which a local taxonomist is able to identify a particular coral species decreases gradually with distance from the region he works. The difficulty of assessing the extent of hybridisation between coral species and the influence of a possible reticulate evolution (hypothesis) are further obstacles to coral identification. The references regarding distribution and species number for the Red Sea in the literature (Sheppard & Sheppard 1991, Wallace 1999, Veron 2000) differ to some extent, especially in the genus Acropora. Wallace (1999) gives 43 species compared to 52 of Veron (2000). Veron (2000) excludes 5 of the species given by Wallace (1999) from the Red Sea and in addition assesses 6 more as uncertain. In return he gives species unidentified by Wallace (1999) Acropora anthocercis). In addition, 15 species are stated as uncertain for the Red Sea by Veron (2000).

  Coral bleaching

coral erosion
 
 

Extreme low tide caused coral death at South Sinai’s coast (March 2007)

Tidal events belong to the most predictable natural fluctuations in coral reef habitats. They determine intertidal zonation patterns and limit the vertical growth of corals, but are rarely reported to cause mass mortality among corals. Corals are reported to tolerate a certain time of aerial exposure while enhancing mucus production to prevent desiccation. However, the combination of extreme low tides and high solar irradiances has the potential to cause widespread damage among corals. A report from the Great Barrier Reef reveals 40-75% of corals on reef flats were either bleached or suffered partial mortality from such an event. We observed a similar phenomenon on reef flats in Dahab at the end of March this year and assume an additional factor has contributed to the coral mortality during this event. Within four days (March 19-22), absolute calm conditions coincided with extreme low tides and high solar irradiances. Moderate to strong wind speed would produce waves, surf and spray which may prevent corals from drying out and decrease the effect of strong insolation. We observed the coral mortality on reef flats of various sites in Dahab. Most likely this natural disturbance affected the whole coastline of the Gulf of Aqaba. Many of the smaller coral colonies were killed completely whereas most of the larger ones only suffered partial mortality. It seems that coral tissues disintegrated and formed shreds hanging from the coral before getting washed away. First, the wall of coral skeleton became visible while tissue was still left inside. Understandably, the upper portions of colonies affected were more heavily damaged. Coral bleaching, in the sense of corals having ejected their symbiotic algae while retaining their elsewhere intact tissue, was not observed. Partly affected colonies certainly are able to recover to a certain extent but have to struggle against algae quickly taking possession of any part of stripped skeleton. After one week all the affected colonies were tinted in shining dirty yellowish-green hues covering the white witnesses of this event. We estimate the natural damage to coral colonies on the reef flat to be in the order of 25-75%. The first survey we did after the event revealed a mortality of 50 % at a known reef site south of Dahab.

Author: Christian Alter

Supplementary note:

We wish to underline that the observed decimation of coral cover has been caused entirely by natural processes. The observed phenomenon may not be distributed equally among reef flat zones due to natural variations in geomorphology and, thus , various degrees of exposure. The observed event and its assessment described in this article is restricted to relatively shallow reef zones. However, the observed decimation may not be very obvious and only recognized by trained persons.
Coral mortality, caused by the same low tide event, was also observed by Dr. Moshira Hassan during an excursion with biology students from the American University of Cairo to Marsa Ghozlani (Ras Mohammed National Park) in early April this year (see photos).
Similar events have been described earlier by the scientific community e.g. for the Red Sea (Fishelson, 1973) and the Great Barrier Reef Anthony & Kerswell, 2007)).

Anthony, K. R. N. & A. P. Kerswell (2007) Coral mortality following extreme low tides and high solar radiation. Springer, Marine Biology, Vol. 151: 1623-1631.
Fishelson, L. (1973) Ecological and Biological Phenomena Influencing Coral-Species Composition on the Reef Tables at Eilat (Gulf of Aqaba, Red Sea). Marine Biology 19: 183—196.

 

 

 

 

 

 

 

first dayAerially exposed coral colony (Pocillopora verrucosa) on the first day

second dayAffected colony (Platygyra daedalea) on the second day. Bare skeletal parts are clearly visible on the upper part.

after three daysAlmost entirely killed colony (Pocillopora verrucosa) after three days

After 2 weeksAfter two weeks, a layer of algae covers the recently killed corals

After 1 weekAfter two weeks, the affected colonies are covered with green algae

 
 

 

Banquet for corals: Nocturnal feeding with planktic wing snails on the menu

Author: MSc (biologist) Christian Alter
Red Sea Environmental Centre, Dahab

Who has ever observed stony corals getting in a sort of "hunting fever"? The role of corals as an important predator in the reef is mostly unknown. Food acquisition at night remains mostly obscured to divers and the naked eye of the beholder due to the microscopic size of the coral’s prey and the photophobic/light-sensitive response of the polyps to disturbance from the divers torch. Quite commonly known is the mutualistic symbiosis between reef-building corals and single-cell algae (zooxanthellae) thriving in the tissues of the polyps. These algae are responsible for the coloration of the coral and supply carbohydrates (organic carbon compounds) to the corals in exchange for nitrogen and phosphorus. Also, the zooxanthellae facilitate limestone precipitation of the coral by removing CO2 from the polyps’ tissues. Most corals are virtually inactive during daytime displaying retracted polyps. However they have an army of unicellular algae working for them all sunlit daytime long and performing photosynthesis, though inconspicuously. This is the general appearance of stony corals divers and snorkelers are well familiar with. Some observant divers may yet have studied corals during their active feeding phase at night: A lawn of polyps moving their heavily armed tentacles with the water, each of them furnished with myriads of stinging cells. Thus, at night the corals have little in common with their appearance during daytime and pose a deadly threat for plankton organisms such as crustacean, mollusc or fish larvae. Indeed all these potential prey organisms run into danger to be pierced and narcotized or stuck at a touch with the hostile tentacles. The tentacles transfer the captured food directly into the “stomach” (gastric cavity), where it is decomposed except for the indigestible parts (skeletons, shells) and where nutrients are taken up (resorbed) by the “stomach wall”. After the meal, the polyps egest the indigestible remains through the mouth opening. In this fashion, innumerable populations of corals are filtering tons of plankton out of the water night by night, while we are basically unaware of it. On the next morning, usually nothing is left over to provide evidence of the precedent nocturnal feast.
In one instance however a different situation was encountered: In a particular morning in spring we saw a lot of coral colonies seemingly covered with “needles”, resembling a hedgehog. What had happened? An unusual nocturnal banquet of the coral community appeared to be responsible for the traces still visible on the next day. The event had obviously been triggered by a mass occurrence of tiny wing snails from the plankton, pteropods in scientific terminology. This group of snails comprises species with various forms of shells or without any shell and with a foot reshaped to some sort of wings. What we observed was that the majority of polyps still had the elongate shells stuck in their mouths with the thicker end of the shells inside. Perhaps the polyps did not have completed their meals yet or they encountered some problems in finally ridding themselves of the bulky snail remainders accounting for over 1 cm in length. Most of the observed coral colonies riddled with “needles” were representatives of the honeycomb and brain corals, respectively (family Faviidae) which mostly exhibit larger polyps with larger mouth apertures. So just in case you happen to observe a coral during your dive looking like a hedgehog, you will know what it is all about …

 

koralle A smooth brain coral (Platygyra lamellina) covered with shells of wing snails

koralleShells stacking in the openings of a rough brain coral (Platygyra daedalea)

koralleHoneycomb coral (Echinopora gemmacea) with “needles”