A Review: Modern Coral Characterization Studies in Malaysia

Coral reefs are highly diverse and productive ecosystem in the ocean that provides various goods services to human and environment. Located within the renowned ‘Coral Triangle’ region, Malaysia is one the thriving countries in Southeast Asia that possess rich marine resources and coral reefs. Like other coral reef around the world, coral reefs in Malaysia are exposed to multiple threat that jeopardize their well-being. Those relying on these ecosystems may face severe consequences if they are lost. In recent decades, research on characterizing modern coral reefs has increased in Malaysia, including identifying key species and their distribution, understanding the factors that control coral growth and assessing the impacts of environmental stressors on reef health. This study is aimed to provide an overview of the current state of knowledge of modern coral characterization studies conducted in Malaysia. It presents the distribution maps of these coral reef studies conducted throughout Malaysia and discusses the techniques employed to characterize them. Most of the studies was conducted in South China Sea, particularly in East Coast of Peninsular Malaysia with Tioman Island, Pahang being identified as having the greatest number of studies. And, visual assessment have the higher frequency of use in characterizing Malaysia coral reef. Going forward, future studies in Malaysia should continue to explore others Malaysia reef, and techniques for characterizing coral reefs, while also conduct more studies in locations with limited research. These studies could have served as foundation resource for future conservation efforts in the face of ongoing threat and challenges.


Introduction
Coral reef is the most diverse ecosystem in the ocean and are acknowledged for their remarkable biological diversity and productivity (Hoegh-Guldberg, 1999), providing various goods services.They have a higher structural complexity that provides variety niches and habitats for vast marine organisms to thrive in (Sale et al., 2014) including fish, crustaceans and other invertebrates making them biodiversity hotspot.In addition, coral reef also supports human well-being in the form of fisheries and tourism for important food sources and livelihood, coastline protection against coastal hazard by acting as natural breakwaters, and cultural service for local communities (Costanza et al., 2014;Harris et al., 2018;Spalding et al., 2017).A coral reef is a potential carbon storage for carbon sequestration.This carbon is locked up in the skeleton of corals that build the reef structure.Through the precipitation of calcium carbonate, they recycle CO2, forming their framework and accompanying inter-reefal deposits (Heap et al., 2009).Due to this reason, coral reefs are thought to function as natural carbon sinks.Given all that, coral reefs are a key ecosystem in the marine environment.
Despite of their importance, coral reefs around the world are exposed to large numbers of local and global anthropogenic stressors over the last few decades (Bellwood et al., 2004;Eddy et al., 2021;Hughes et al., 2010), which has raised concern about their declination.The stressors that contribute to reef decline include coral bleaching, ocean acidification, coral diseases, overfishing, coastal development and nutrient enrichment (Eakin et al., 2010;O. Hoegh-Guldberg et al., 2007;Weil and Rogers, 2011;Zaneveld et al., 2016;Vega Thurber et al., 2014).The stressors are significant and multifaceted.According to the report by Global Coral Reef Monitoring Network, approximately 75% of the world's coral reefs are estimated to experience the threat level because of natural and anthropogenic disturbance by 2050 (Burke et al., 2011).If no action is taken, coral reefs are at risk of being lost.The loss of these ecosystems can have severe consequences for the communities that rely on them.Therefore, it is important to enhance the conservation efforts and effective management strategies for coral reefs, in order to ensure the continued provision of their ecosystem.
Malaysia, one of the prosperous countries in Southeast Asia, is a home to coral reefs and marine resources as it lies within the renowned 'Coral Triangle', where its coral reefs extend to Indonesia, Philippines, Papua New Guinea, Solomon Islands, and Timor-Leste (White et al., 2014).Advantages due to these facts are boosting Malaysia's tourism and economic growth, by promoting Malaysia as an outstanding tourism destination.Geography of Malaysia is unique with two distinct regions: West Malaysia (Peninsular Malaysia and East Malaysia (Sabah and Sarawak).Both regions are blessed with extensive coral reefs that cover vast area along the east coast in both regions has been documented and recorded in a wide range of coral species.Evident to that, 398 species were found in Peninsular Malaysia and 248 species were found on the west coast of Sabah (Huang et al., 2015).Importantly, coral reefs are widespread in Malaysia, with the most of the are being concentrated in the South China Sea, which is recognized as a significant hotspot of marine biodiversity.
Over the past few decades, research on characterizing modern coral reefs in Malaysia has seen to increase, including identifying key species and distribution patterns, underlying factors that control coral growth, and assessing the impacts of environmental stressors on reef health.This interest can be attributed primarily due to the growing concern for the conservation and preservation of coral reef ecosystem.In the quest to characterize the modern coral reefs in Malaysia, researcher have utilized advanced technologies and interdisciplinary approaches.These findings have helped to shed light on the resilience and vulnerability of coral reefs to environmental stressors.As such, the increased research efforts on modern coral reefs in Malaysia have not only helped in advancing our understanding of these ecosystems, but also in guiding conservation and management practices for their sustainability.This research aims to provide an overview of the current state of knowledge of modern coral characterization studies conducted in Malaysia, highlighting the key findings, research gaps, and opportunities for future research.By doing so, this study will contribute as a foundation resource for future studies and enable the research to obtain a wealth of information on coral studies, facilitating their efforts to build upon previous research.Given the critical roles that coral reefs play in supporting marine biodiversity and human well-being, it is essential that we continue to build upon our knowledge of these complex ecosystem.

Status of Coral Reef in Malaysia
For several years, coral reefs in Malaysia have been subjected to monitoring, with their health being evaluated based on coral health criteria (Chou et al., 1994), shown in Table 1.One of the earliest coral assessments which covered 193 reef sites in Malaysia reported that 52.8% of the reefs were rated as being in 'good' condition (Chou et al., 1995).As compared to the latest Annual Survey Report 2021 (Reef Check Malaysia, 2021), the average condition of Malaysian reefs is 'fair' with live coral is 40.13%.Importantly, this remark is the first occasion of the improvement since 2015, attributed to the reduction of tourist and tourism activity due to movement restriction during a COVID-19 pandemic.In the last two decades, data on coral conditions showed inconsistent patterns, with many reefs evaluated were in 'fair' than 'good' condition (Waheed et al., 2015;Safuan et al., 2016;Shahbudin et al., 2017;Safuan et al., 2018).However, despite the improvement in the overall condition of Malaysia reefs, there is still cause for concern as it is below the 'good' and 'excellent' rates and many reefs are still confronting different types of threats that put their well-being in jeopardy.
Multiple threats have been identified as having an impact on coral reefs in Malaysia (UNEP, 2011;Praveena et al., 2012), with the nature and severity of these threats vary depending on the location.Among these threats, sedimentation stand out as a significant factor in the deterioration of coral health in Peninsular Malaysia, particularly on the west coast Malaysia (Khodzori et al., 2019;Toda et al., 2007).The lasting effects of sedimentation on this region have caused the reef to have a less coral cover and diversity compared to the east coast of Peninsular Malaysia (Khodzori et al., 2019;Toda et al., 2007).Sedimentation occurs due to human activities such as land reclamation, degrading, and construction of coastal or coastal infrastructure.This can lead to increased turbidity, smothering of corals, and reduced light penetration, which can have a negative impact on their health.
Coral reefs in the east coast of Peninsular Malaysia face threat from both disease and predation (UNEP, 2011;Praveena et al., 2012).There have been records of more than 20 diseases affecting coral reefs around the world (Jaafar et al., 2023), with some of these diseases also recorded in Malaysia include black band disease (BBD), brown band disease, yellow band disease (YBD) and white syndrome (Miller et al., 2015;Akmal and Shahbudin, 2020).For example, the most prevalent disease observed in Tioman Island Marine Park, Malaysia was yellow band disease/YBD (Akmal and Shahbudin, 2020).These diseases are caused by various factors, Table 1.Coral Reef Health Criteria (Chou et al., 1994) Percentage of live coral cover Rating 0-25 Poor 26-50 Fair 51-75 Good 76-100 Excellent including bacterial infections, environmental stress, and water pollution.Meanwhile, predation by various organisms such as the Crown-of-thorns, snails, and some fish species also threatens Malaysian coral reefs.Crown-of-thorns, in particular, have been known to cause tissue loss and skeleton abrasion.Therefore, efforts have been taken to remove this eating predator (Chak et al., 2018).It is evident that coral reefs in Malaysia are susceptible to various diseases and predation.
In east Malaysia, coral reefs have been severely impacted by destructive fishing practices and overfishing, which are identified as the main reasons of reef degradation in the region.For example, coral reefs in Sabah have been ruined by destructive fishing practices, such as blasts and cyanide (UNEP, 2011;Praveena et al., 2012).These damages are attributed to inadequate enforcement and overreliance on coastal fisheries.As result, Sabah experienced a loss of more than 80% of its original coral cover (Yasin et al., 1998).Destructive fishing practices can cause physical damage to the reefs and result in coral mortality.Overfishing, on the other hand, can lead to the depletion of fish population and smothering coral reefs, which disrupt the ecological balance of the reef system.
Coral reefs in Malaysia are not excluded from experiencing coral bleaching.Severe and widespread coral bleaching on Malaysian reefs was not observed prior to 2010, including during the 1997/98 global event when coral bleaching was mild and localized (Wilkinson, 1998;Kushairi, 1998).Bleaching events are associated with high and fluctuating seawater temperatures, which have been linked to climate change.When coral is exposed to warmer water, causing them to expel their dinoflagellate endosymbionts, commonly known as zooxanthellae which essential for the growth of stony corals and coral reef ecosystems (LaJeunesse et al., 2018).As a result of this process, corals may take on a pale, white, or luminescent appearance, leading to the phenomenon known as coral bleaching.As consequence, coral bleaching results in coral mortality and a reduction in the overall health of the reefs.As these stressors become more severe, coral bleaching events are likely to become more frequent and intense, further straining the already fragile system.
Coral status provides information about the health and resilience of the coral reef ecosystems for understanding and addressing the threats facing them.Threats to coral reefs have been a topic of discussion among marine and coral biologist in Malaysia (Praveena et al., 2012), as these ecosystems face numerous challenges.However, despite ongoing research and monitoring efforts, the full extent of damage to Malaysia's coral reefs remains relatively unknown.Nevertheless, coral reefs in Malaysia, like those in many other parts of the world, are under significant stress and require urgent attention and action to ensure their survival.

Studies on coral reef characterization in Malaysia
Studies of modern coral reef characterization have been carried out in various locations across west and east Malaysia, with researchers exploring areas such as Strait of Malacca, South China Sea, Sulu Sea and Celeb Sea. Figure 1 present the distribution map of these studies conducted throughout Malaysia.It is evident from the map that a significant portion of these studies were conducted in South China Sea region.South China Sea is a significant location for coral reef studies as it has some of the most diverse and abundant coral reefs in the world.Thus, it is not surprising that this area is of particular interest in coral reef studies and most of the modern coral characterization studies have been conducted in this area.Some studies have been conducted in the Strait of Malacca, which is a narrow waterway that runs between the Malay Peninsular and the Indonesia island of Sumatra.The Strait of Malacca is an important shipping route and experience significant human activity, which can have negative impacts on the health of the coral reefs in the area.
From the graph in Figure 2, it is evident that the majority of the coral reef studies were conducted in the East Coast of Peninsular Malaysia, particularly around the South China Sea.23 studies covered area of East Coast of Peninsular Malaysia, while 12 studies focused on the West Coast of Peninsular Malaysia.Additionally, 13 studies delved into the coral ecosystem of West Malaysia.This may indicate that east coast of Peninsular Malaysia is more accessible to conduct coral reef research.The presence of numerous study sites in this area may also indicate the availability of suitable coral reef habitats, research infrastructure, and logistical support for scientists and researchers.The accessibility of the east coast may be attributed to factors such as proximity to research institutions, established research stations, and favorable sea conditions for fieldwork.However, it is important to note that the concentration of studies in this region does not diminish the significance of other coastal areas in Malaysia, as they may hold valuable and understudied coral reef ecosystems.Locations having the highest number of studies, Payar Island with five studies, and Redang Island and Bidong Island with both four studies.These islands are located on the East Cost of Peninsular Malaysia and are known for their high coral diversity and abundance.In West Malaysia, such studies have been conducted in the islands of Tunku Abdul Rahman Marine Park, Tun Mustapha Park, and Tun Sakaran Marine Park.However, it is worth noting that coral characterization studies have not been conducted in all areas of Malaysia, indicating still many islands yet to be explored.These islands may have important coral ecosystems that are currently under threat from anthropogenic activities.Ergo, it is essential to conduct further research, particularly in regions where studies have been limited, to better understand the coral conditions in that region.
Some studies have looked at the spatial distribution of different coral species and their associations with other organisms, which can provide important insight into the ecological functioning of coral reefs to better understand how they respond to changes in water quality and environment conditions.From these studies, a wide range of topics have been explored, including, not limited to, health evaluation, chemical composition, and mapping to better understand the current state of coral reefs in Malaysia.These studies demonstrate the importance of continued research into coral characterization in order to support effective conservation and management efforts.

Coral Characterizing Techniques
The coral characterization technique refers to a set of methods and technologies used to study and analyse the characteristic of coral reefs for understanding the structure, composition, health, and resilience of coral reef ecosystems.This paper will discuss these techniques, which include both qualitative and quantitative approaches ranging from visual assessment, remote sensing, and geochemical analysis.The advantages and limitations of these techniques will be highlighted, which can aid in selecting the most appropriate method respected to the research objective.Figure 3 provides a summary of techniques used in coral characterization study in Malaysia, showing their respective frequencies of use.
Within 45 published papers reviewed, it was found that visual assessment (underwater) has the higher frequency of use, accounting the most used technique in characterizing Malaysia coral reef with 27 studies employed this method (Figure 3).While 10 studies utilized remote sensing technique and 8 studies employed geochemical analysis.Graph in Figure 4 further support these findings, showing the prevalence of visual assessment as the most frequently employed technique in the three regions mentioned.This preference for visual assessment can be attributed to the aim of many coral studies in Malaysian is to aim to assess coral health and diversity, which is accomplished through visual assessment.However, the use of other two techniques is also important in understanding Malaysia coral reef.underwater observation of coral reefs' condition by snorkelling or diving using techniques such as in situ quadrats, line transect, and manta tows (Miller and Müller, 1999), as well as coral video transect (CVT).

Visual Assessment (Underwater)
Add to these techniques is comprised with digital photography and computer image analysis.Visual assessment is often used for health status evaluation, which may include documenting parameters such as coral cover, growth forms, species diversity, and the occurrence of diseases and bleaching.
Organization like Reef Check Malaysia have carried out previous assessment to determine the coral cover in Malaysia.The Line Intercept Transect (LIT) and Point Intercept Transect (PIT) have been the main methods used in these studies (Praveena et al., 2012;Toda et al., 2007).These methods start by laying a measuring tape along the reef, followed by the process of counting or identifying the coral species that intercept the tape.However, these methods have limitation and are prone to observer bias, which may affect the accuracy of the results.To address this limitation, a study conducted by Safuan et al. (2015) compared the efficiency of the CVT and LIT methods in assessing coral cover and species diversity.The CVT method allows for later analysis of the video footage, using Coral Point Count with Excel extension (CPCe), a tool proposed by Kohler and Gill (2006), which eliminates observer bias and provides more detailed information on the coral communities.Furthermore, this method consumes a short amount of time in the field, but it is time-consuming during the counting of coral reef components in the laboratory.12 studies have employed the CVT method for visual assessment (Table 2).Many researchers employed CVT method to evaluate and determine reef condition, the generic diversity and abundance patterns, community structure, and disease prevalence (Safuan et al., 2016;Khodzori et al., 2019;Akmal and Shahbudin, 2020).

Remote sensing
With remarkable technological advancements in recent years, remote sensing has become increasingly prevalent in coral studies.Remote sensing is a technology, tool, or technique that allows the collecting of data and information about an object, area, or phenomenon from a distance (in this context coral reef), without having to make direct physical contact but through data analysis obtained with a tool (Lillesand et al., 2015).This technique covers technologies from the hydroacoustic signal, satellite images, or drones for identifying, mapping, and assessing coral reef ecosystem health.Through remote sensing, high spatial resolution and frequency maps can be produced to depict the distribution and condition of coral reefs, allowing for a better estimation of the impact of climate change on reefs at regional scales (Foo and Asner, 2019).Therefore, the use of remote sensing in coral studies is expected to grow in the future as new and innovative technologies continue to emerge.In this review, the use of remote sensing includes six studies that use the hydroacoustic method, three studies that utilized satellite imagery, and one study that employed a drone (Table 2).
Initially introduced as an active sound (sonar) to evaluate fish biomass and spatial distribution, the hydroacoustic signal has now been expanded it's use in coral ecology and management (Abdullah et al., 2016), providee a whole new dimension in obtaining crucial coral reef baseline information.RoxAnn, a product of the Acoustic Ground Discriminating  The results show that the trace metals content vary between species, with some species having higher levels than others.System (AGDS) is a type of hydroacoustic sensing system that is used for seabed classification and mapping reef substrate (Lee, 2000;Mustajap et al., 2015;Lee and Lin, 2018;Yusop et al., 2021).Unlike traditional SCUBA diving, which can be timeconsuming and labor-intensive, the hydroacoustic sensing technique can cover larger areas in a shorter amount of time, making it a faster means of ground truthing (Bour, 1988).Moreover, it reduces the potential for human error that may result from subjective personal interpretation and observation during the survey (Yap, 2017).Even so, the technology may be affected by several environmental factors, such as water turbidity or seafloor topography, which can reduce the accuracy of the results.Importantly, hydroacoustics sensing can be used to study coral reef and their environment as it has the ability to map reef substrate type and coral growth forms (Lee, 2000).
The availability of satellite instruments for coral reef applications has grown over the last four decades.This growth began with the early Landsat and SPOT sensors (Smith et al., 1975;Bour, 1988) and has rapidly expanded in recent years with the introduction of high-resolution commercial satellites such as Ikonos, and Quickbird.For example, changes in coral reef communities have been detected using Ikonos satellite sensor imagery has been utilized for detecting changes in coral reef communities (Palandro et al., 2003), and tropical-marine benthic habitats have been identified and classified using QuickBird multispectral data (Mishra et al., 2006).Similarly, one of the studies in Malaysia has used ALOS satellite imagery to classify the coral reef and surrounding habitats based on their spectral characteristics thus capable of mapping the spatial distribution of this ecosystem (Mustapha et al., 2014).Satellites provide large-scale reconnaissance of coral reef health, yet, the spatial resolution may be relatively poor, especially when there is limited cloud cover (Teague et al., 2020).This limitation highlights the importance of using a variety of tools and techniques, including in situ observations, to complement satellite imagery in coral studies (Muslim et al., 2012).
The use of airborne technology such as drones has emerged as a viable option for obtaining detailed and rapid spatial data and information.A drone is categorized as UAV-based remote sensing.The use of UAV-based remote sensing has been found to be more effective in classifying coral habitat types over a finer spatial resolution compared to other highresolution commercial satellite image acquisitions such as WorldView-2, Ikonos, and Quickbird (Zaki et al., 2022).Furthermore, it has been proven the potential of drones as a low-cost and rapid survey tool on shallow-water coral reefs, producing multispectral and bathymetric data, provided that the environmental conditions are favorable, such as calm waters, low winds, and minimal sun glint (Casella et al., 2017).In this review, at least one study has used a drone in their coral study (Table 2).The study demonstrated the utilization of drone-based aerial photography is feasible for monitoring coral bleaching in Malaysia (Zuhairi et al., 2018), which is becoming increasingly common due to environmental stressors such as rising sea temperatures.This technology successfully identified bleaching point and provides results comparable to traditional in-water monitoring methods.Drones have proven to be advantageous in facilitating coral studies; however, they are limited by factors such as flight time, weather dependency, and workflow of data processing.Thus, nnumerous studies have been carried out to enhance the utilization of drones, aiming to maximize their potential for future application (Muslim et al., 2012;Muslim et al., 2019;Mohamad et al., 2022;Chong et al., 2022).

Geochemical analysis
Coral skeletons can provide a wealth of information about the environment in which they grew.By employing geochemical techniques, researchers can measure the concentration of trace elements in coral skeletons to obtain information about water quality, pollution levels, and other environmental stressors.An overview of some of the widely used analytical techniques, their advantages, and limitations for the estimation of trace element content has been provided (Hossain et al., 2021).The authors also have provided guidance on the selection of equipment and technique, including the preparation of various sample arrays.Some of these have been mentioned in this review such as Atomic Absorption Spectrometry (AAS), X-ray Fluorescence (XRF), Neuron Activation Analysis (NAA), Flame Atomic Absorption Spectrophotometry (FAAS), X-ray Diffraction (XRD), Scanning Electron Microscope with Energy Dispersive X-ray (SEM-EDX) and Inductively Couple Plasma Optical Emission Spectroscopy (ICP-OES).
The study carried out by (Mokhtar et al., 2001) can be considered one of the earliest studies in Malaysia to evaluate the concentration of trace elements in the coral.Using AAS and XRF, this study measured the level of Cd, Cr, Mn, Ni, Pb, and Zn in coral band.The levels detected were low, evident that the environment was clean.In another example, Lee et al. (2007) performed one of the early evaluations of trace metals in coral collected from Sabah.In this study, the concentration of Hg, Mg, Zn, and Cr in coral skeletons was measured through the use of FAAS.The results indicate that corals in Sabah, Borneo have accumulated high levels of some trace metals, possibly due to anthropogenic activities.Both studies shed light on the extent of trace metal contamination in coral reefs and the potential impact on the marine ecosystem.
The analysis of coral skeleton through geochemical methods presents several advantages such as help to reconstructing past environmental condition, identifying source of pollution and monitoring current environmental condition by tracking the trace element, for instance (Mazlin et al., 2001;Mokhtar et al., 2012;Amir and Mohamed, 2018).Even so, this analysis is a laborious process which time-consuming and required specialized equipment (Hossain et al., 2021).This makes it difficult to conduct large-scale studies and may limit the number of samples that can be analyzed.The collection of coral samples can also be challenging, especially in remote or protected areas.In addition, sampling can damage coral, so researchers must carefully balance the need for data with the need to protect coral reefs.Overall, geochemical analysis of

Comparison between visual assessment, remote sensing and geochemical analysis
The summary provided in Table 3 presents a comparison between the techniques of visual assessment, remote sensing, and geochemical analysis in characterizing coral reef.Each technique has its advantages and limitation in terms of their applicability, data quality, capability-time-effective and specialization requirements.By comparing and contrasting these techniques, researchers can better understand their respective strengths and weaknesses and make informed decisions about which method is most appropriate for their study objectives.
Overall, each of these modern techniques has its own strengths and limitations, and the choice of technique will depend on the research question being addressed, budget and the specific conditions of the study site.Combining multiple techniques may provide a more comprehensive understanding of coral health and condition.

Conclusion
In conclusion, this study has provided an overview of modern coral characterization studies in Malaysia, shed light on the numerous studies conducted in various locations across the country.Most of the studies was conducted in South China Sea, particularly in East Coast of Peninsular Malaysia with 23 studies, which Tioman Island, Pahang being identified as having the greatest number of studies.The techniques used in these studies have also been discussed, with the visual assessment have the higher frequency of used in characterizing Malaysia coral reef, being the most used method with 27 studies employed this method.While 10 studies utilized remote sensing technique and 8 studies employed geochemical analysis.Going forward, future studies in Malaysia should continue to explore others Malaysia reef, and techniques for characterizing coral reefs, while also conduct more studies in locations with limited research.This will help to provide a more complete picture of coral reef ecosystems in Malaysia, which is critical for effective management and conservation efforts.Scheme (FRGS) for this research, (Reference number = FRGS/1/2021/WAB02/UTP/02/1, Cost centre = 015MA0-146).The authors also want to thank you to Petroleum Geoscience Department, Universiti Teknologi PETRONAS with collaboration Universiti Malaysia Terengganu for support and participating in this research.

Figure 1 .
Figure 1.Geographical distribution of modern coral characterization studies across the state of Malaysia Figure 3. Frequency of use of coral characterization techniques

Figure 4
Figure 4 Frequency of use of coral characterization techniques based on the locations

Table 2 .
Summary of coral characterization studies in Malaysia

Table 3 .
Comparison of the techniques still considered an important approach for understanding the past, present, and future of coral reef ecosystems.