Rehabilitation of Dead Coral Rocks in the Gulf of Aqaba, Red Sea; Coral Engineering Protocol
Fuad A Al-Horani1,2* and Chris Langdon2
1School of Basic and Marine Sciences, The University of Jordan, Aqaba, Jordan
2Rosenstiel School of Marine and Atmospheric Science, University of Miami, Miami, USA
Submission: May 20, 2024; Published: July 10, 2024
*Correspondence author: Fuad A Al-Horani, School of Basic and Marine Sciences, The University of Jordan, Aqaba, Jordan
How to cite this article: Fuad A Al-Horani* and Chris Langdon. Rehabilitation of Dead Coral Rocks in the Gulf of Aqaba, Red Sea; Coral Engineering Protocol. Oceanogr Fish Open Access J. 2024; 17(4): 555967. DOI: 10.19080/OFOAJ.2024.17.555967
Abstract
Coral deterioration is often linked with coastal pollution and other anthropogenic impacts. In many cases, the impacts can be severe and may lead to death of corals and eventual loss of coral reef ecosystems. The Gulf of Aqaba is seen by many scientists as a coral refuge for the rest of the world, and therefore it is important to conserve its coral reef habitats. Because of this, each individual coral can be very important for the survival of the whole ecosystem. This study aims to develop an effective, easy to apply and relatively cheap method to rehabilitate dead coral rocks to bring them back into function within the ecosystem. To do this, small and medium sized coral fragments were cultured on ceramic tiles in a raceway before being transplanted to the sea. The survival rates, growth rates and coral fusion were observed over a period of two years. The results obtained have shown high survival and growth rates, where all cultured fragments were able to fuse and form bigger colonies. The tiles with the fused corals were then fixed to the dead skeletons of corals in the sea. Preliminary results from the field over a short period of observation showed a hundred percent survival rates of the transplanted corals, which suggests high success rates. The method used seems to be effective in rehabilitating the dead coral rocks, although long term observations are required to determine the length of time needed for the surfaces of the coral rocks to be fully covered with living tissue. The method is simple and cost effective and is recommended to be applied in any impacted coral ecosystem in the world. Though, in areas where extreme environmental conditions are prevailing, a careful field evaluation might be needed to assess the applicability of this method.
Keywords: Coral; Rehabilitation; Coral rocks; Conservation; Gulf of Aqaba; Red Sea; Coral engineering
Introduction
Coral reefs are one of the planet’s most important marine ecosystems due to their productivity, complexity and species richness [1]. These ecosystems represent important sources of food and drugs, nursery habitats for commercial fish species and tourism assets in coastal areas [2-5].
The Red Sea has globally significant and highly diverse coral reefs [6]. The Gulf of Aqaba (GoA), which extend to the north east from the Red Sea represents the only marine access to Jordan, while all sea-related activities are concentrated in the relatively short coastline [7,8]. Fringing coral reefs are dominating the bottom habitat along the coastal region, which makes them particularly vulnerable to impacts from overlapping human activities [9]. Current pressures that have already been observed in the region include industrial wastes, solid waste and ship- based discharges, impacts resulting from corallivores and coral diseases as well as marine dredging and sedimentation from port constructions in adjacent coastal habitats [10,11]. This continuous and uncontrolled anthropogenic coastal development and possible influence may threaten the existence of coral reefs in the GoA [9]. Specifically, the increased presence of marine pollutants constitutes a major threat to marine ecosystems through accumulation of pollutants inside marine organism tissues [12].
Natural recovery of the deteriorated coral reefs is a very long process that can be complicated by many environmental factors. It takes many years for some of the impacted coral reef constituents to get back to its original status, while the main framework constituents, stony corals, may need several decades for complete recovery [2]. This is because corals grow at very slow rates, which may not exceed 1 cm per year such as the case in massive corals (Figure 1). Furthermore, natural recovery process might be impeded by factors like invertebrate herbivores, overgrowth by algae and pollution [13-16]. When algae are established in the site, it will prevent coral recruitment, which makes it difficult to revert back to a coral dominated community [17,18]. In such cases, restoration activities are needed. Restoration is the process of assisting the recovery of an ecosystem that has been degraded and is critical for habitats where natural recovery is hindered [19]. Activities like establishing coral nurseries (the gardening concept) and artificial reefs were adopted in the Gulf of Aqaba [8,20-22]. Ecological engineering was also adopted in some cases [23,24].
This study aims at applying the coral engineering concept on dead and aged individual coral colonies to restore the living tissue layer within a relatively short period of time.
Methods
Coral Samples
Coral samples representing Pachyseris sp., Porites sp., Coscinaraea monile, Pavona sp., Acropora sp., Galaxea fascicularis, Blastomussa sp., and two species from the genus Favia were collected from areas destined for possible sea reclamation process and/or from shallow reef slopes (<10 m) at the Marine Science Station (MSS) Aqaba. The Mother colonies were kept at the coral wet laboratory in a flow-through seawater raceway fed with seawater directly from the sea with ambient sea conditions. Natural light was used in the wet laboratory raceway. There were no special treatments or feeding for the coral samples in the raceway. The only difference made between the raceway conditions and the field was the cleanup of grazers and any intruding species that may harm the corals in the raceway.
After acclimation to raceway conditions, the mother colonies were fragmented into small pieces (1-5 cm in diameter) using a chisel and hammer for the branching species, while a rock saw (Type; Marmo Macchine Mark, Company; Italian Stone Technology, Italy) was used to fragment the massive coral species. Mini-fragments (less than 1 cm in diameter) and single polyps were made using wire cutter to cut small pieces from the mother colonies. The fragments were left in plastic trays for a week time to recover and get rid of the mucus. Any fragment that showed weakness or signs of tissue necrosis were excluded. The study was comprised of two phases, the first phase was conducted in the wet laboratory unit of the coral laboratory, while the second phase was conducted in the sea as a continuation of the work done in the lab. In the first phase (i.e. ex situ experiments), the coral fragments produced were glued on ceramic tiles and/or dead coral colonies using underwater epoxy as described by Al- Horani [8]. Pictures were taken for the cultured corals with time and the image analysis was done by using AmScope software to measure growth rates.
The dead coral colonies (rocks) were collected from damaged coral reef areas and were kept in the lab until use. In the sea, coral rocks that were found in sea were used as a target coral head for phase two of the project. Corals grown in the lab were prepared for field plantation by making holes in their ceramic tiles using a drill and were then affixed to dead coral colonies (coral rocks) using screws. Then, routine observation for the planted corals was done by SCUBA divers.
Results
Growth rates of the corals were expressed as changes in surface area per unit time. The rates varied from one species to another (Table 1). Depending on the coral shape and fragment size, the results obtained have shown that branching and leafy corals achieved higher growth rates per unit time, while massive corals grew at slower rates. Smaller coral fragments grew faster than larger fragments for all species. For example, a direct comparison between relatively small and big fragments obtained from the same mother colony for the coral Porites sp. (average sizes of 0.4 and 0.71 cm2, respectively) revealed that smaller coral fragments achieved an average monthly growth rate of 0.51 cm2 compared with 0.38 cm2 for the bigger coral fragments. The percent increase relative to the original size was about 130% per month for the small fragments compared with about 53% per month for the bigger fragments (Table 1). The survival rates were close to 100% for all cultured corals for all coral genera that were cultured (Figures 2 & 3). The coral fragments could fuse with each other within a period of 14-28 months after fragmentation depending on the type of coral. For example, a distance of about 2.5 cm between fragments was covered with coral tissue within 19 months for the coral Porites sp. (Figures 2E & 2F), while Acropora sp. needed only 5 months to cover a distance of about 1.5 cm between fragments (Figures 3C & 3D).
In phase two of the study, the corals that were cultured in the lab were transplanted to coral rocks, where they were affixed to the surface of dead coral colonies (Figure 4). The coral rocks were selected randomly, which means that any dead coral colony was targeted without respect to the type of the dead coral. This part of the study is still at its early stages and therefore no measurements were conducted. At this stage of the study, the survival rate is the most important as it represents the transfer from the laboratory conditions to the field conditions. All planted corals showed 100% survival, though it is hard to notice any growth within the relatively short period that has passed since their transplantation.
Discussion
When the interactions of the coral with ecosystem components is weakened or lost, the coral may become unable to cope with the requirements of the ecosystem and will die after sometime of resistance. The weakness of the coral can be caused by either physical-chemical stresses or by biological factors, such as diseases and coralivorous organisms. After death, the remaining of the coral skeleton will be used by boring organisms and may be occupied by other opportunistic reef organisms, which might lead to community shifting. In some cases, the coral skeleton may be tens or hundreds of years old, which represents huge loss for the ecosystem as this represents the framework of the reef structure. When corals are lost from the ecosystem, the food chains will be affected. The loss of the reef ecosystem can be much more, when the death of corals become massive as they can lose their roles as food and oxygen suppliers to the reef community. There might be a community shifting towards becoming algae dominated communities instead of coral dominated ones. The main goal of this study was focused on developing cost-effective techniques that can bring those coral rocks back into function in the coral reef ecosystem after they lose their living tissues.
The rates observed for the coral deterioration and bleaching episodes have accelerated dramatically over the past few decades [25]. Some factors were directly linked to climate change and natural disasters, while others were linked to anthropogenic reasons. In many cases, direct interventions were described to conserve the natural habitats and maintain the functions of the coral reef ecosystems [25,26]. This is because the traditional management activities and natural recovery processes are not sufficient to confront the accelerated reef damages events [21,27,28]. Therefore, the development and use of active restoration techniques for the rehabilitation of the damaged reefs became very popular in past few decades [24,27]. This study has made use of the accumulated knowledge in restoration techniques to establish a method for the recovery of the dead coral colonies. The method described here is cost effective and relatively fast and easy to apply. In this method, the corals were cultured in raceways in a wet lab before being used for rehabilitation of the dead coral colonies in the sea. Several coral types with a variety of colony sizes were cultured on ceramic tiles for up to two years in the lab.
The results obtained have shown a 100% survival rates for most of the species used even after two years of culturing (Table 1). This is compared with survival rates of about 60% in the field [29]. It was suggested that a coral survival rate of more than 40% at 3–4 years post-transplantation would be a reasonable performance target for active coral restoration [30]. In the field, the survival rates of transplanted corals are affected by biological as well as environmental factors. It was suggested that fragment size is an important factor for determining the rates of survival, where smaller fragments showed a lowered survival rate [31]. For example, in a study carried out by Raymundo & Maypa [32], it was shown that fragment size of less than 0.5 cm had 0-2.5% survival rates, this rate has increased to 15% for medium sized fragments, while it reached about 45% for fragment sizes of 1-3cm. The biomass also affects coral survival, where lower biomass is linked with increased death of the coral [33]. Other factors include temperature and salinity fluctuations, Predators and grazers, overgrowth by algae, pollution and sedimentation [11,18,34-38]. Furthermore, the culture conditions provide an opportunity to enhance survival of a transplanted corals [32], though it was also claimed that growth and survival are better in the field than in the land-based tanks, which was suggested to be due to unrestricted water circulation in the field [34]. The 100% survival rates obtained in this study might indicate that the raceways provide perfect conditions for culturing corals.
Growth rates (expressed per unit area) varied among the different coral species and ranged between 0.2-4.81 cm2/month (Table 1). The percent growth rates ranged between 3%-129%. When the culturing conditions are fixed for all species, then growth rates might vary among the different species due to inherent reasons, the colony form, or the fragment size [34,39]. Although this is not an objective for this study, when different fragment sizes of the same coral (e.g. Porites sp.) was compared, it was found that small fragments (area = 0.4 cm2) achieved more than double growth rates (expressed as percent growth rate) in comparison with the bigger fragments (area = 0.7 cm2), with a monthly percent growth of 129% and 52% for the small and bigger fragments, respectively. Those results agree with previous findings by Page et al. [40] who found that smaller fragments had faster growth rates compared with the bigger fragments, while it contradicts with findings by Forsman et al. [41] who found the contrary. The contradictions among the different studies in the literature could be due to inherent factors of the corals used or to environmental conditions prevailing during the experiments. In either case, fragmentation of corals leads to growth enhancement [39]. It was also reported that coral transplantation lead to increased growth metrics [29]. Those reports together with the results obtained in this study indicate that this kind of technique allows for faster restoration process in the damaged reefs.
Almost all coral fragments, which were glued to the ceramic tiles were able to fuse with each other forming larger coral colonies (Figures 2 & 3). Such colony fusion is an important strategy for clonal organisms to increase access to shared resources, to compete for space, and to recover from disturbance [41]. Furthermore, fusion of the colonies may result in lowering the rates of mortality, which give better chances for the cultured corals to survive [32]. The colony fragmentation and fusion of the cultured fragments are key components of resilience to disturbance [41].
The last step in this study was to transplant the cultured corals from the raceways to the target dead coral rocks in the sea, where dead colonies were selected to fix the cultured corals on their dead skeleton (Figure 4). In this part, the tile with the grown corals on them were fixed using screws, which aid in reducing disturbance and is expected to enhance survival in the field. No further data were collected from the field, other than the survival rates, which were 100% for all transplanted corals. This is because the time passed so far (2 months) is not enough to collect data about their growth rates. Though, they will be subjected to continuous monitoring in future. This kind of strategy, which include culturing and fusion of coral fragments was suggested to enhance survival of transplanted populations since fusion will help them better resist field disturbances [32]. The cost effectiveness of the restoration processes is judged against the economic benefits of coral reefs [30]. Since the cost of the method described in this study is very low, in comparison with the normally used methods, it will likely be cost effective to conduct even in low-income countries [42-44].
From the above discussion, it was concluded that the culture technique used in raceways as a first step before transplanting to the field would be an important step for successful coral reefs restoration process, especially with the high survival rates and the successful fusion of the coral fragments, which aids in better survival rates in the field. The relatively low cost and the relative ease by which it can be applied, may suggest that this restoration method can be adopted in many areas around the world, especially in low-income countries. Finally, the field study needs more time to be evaluated, though a second study will be conducted to focus more on the restoration of dead coral colonies is being planned.
Acknowledgment
This study was conducted during the sabbatical leave of Al- Horani, F. from the University of Jordan, Aqaba. The study was funded by MERC-USAID (Grant No. TA-MOU-13-M33-001). The funding body had no roles in the design of the study and collection, analysis, interpretation of data, and in writing the manuscript. I am grateful to the Marine Science Station in Aqaba, Jordan for providing the laboratory facilities and equipment’s required for scientific analysis. Finally, I would like to thank M. Kteifan and I. Al-Zgoul for their assistance during the field and laboratory works and to Samantha K. Barnett for her role in native English editing and formatting of the final manuscript.
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