The Stressors Impacting The Coral Reef Ecosystem

The coral reef population is dwindling. 19% of the coral reef population is permanently lost, and 60% of the population is in danger of human interaction dangerously affecting the coral reef. A large part of managing a conservation plan is the balance between local between local habitats and certain demands on Reef resources. Marine spatial planning, which is based off of the ability to organize ocean space for human uses and as well as users in the marine environment, is being proposed as a suitable alternative to the current non-spatial strategy. This management strategy may be suitable in areas with excessive urbanization such as mega cities where the resources are used by a large number of stakeholders. However there still is the unknown of how far a large urban area’s influence can reach and what local and regional stressors it will have on the environment. Of today´s 28 megacities cities with more than 10 million people, where many megacities are located on the coast, the most prevalent dangers to a coral reef are human caused such as water pollution, depletion of fishery resources, seafood contamination, loss of habitat, coastal littering, an excessive richness of nutrients, and increased sedimentation rates. Local anthropogenic stressors can disrupt reef communities and become the principal drivers in shaping benthic community composition. The stressors can lead to an ecosystem that functions in a way that is not well understood. In coral reef conservation, understanding the intricate processes that help a coral reef community function properly while suffering from multiple stressors and contend with large coastal development is vital in helping the ecosystem survive.

Most Scleractinia coral species live in association with dinoflagellates in the genus Symbiodinium, also known as Zooxanthellae. This mutualistic symbiosis is responsible for the growth and formation of coral reefs through the transfer of photosynthetic products from Symbiodinium to coral tissues. The algae will provide its coral host the energy that the coral needs to rapidly decompose of calcium carbonate and as needed for other metabolic processes. This relationship between the host and its symbiote is crucial for the corals ability to survive and defend against other stressors. Numerous studies have reported that the growth and the resources of coral reefs depend on a great number of environmental variables, such as temperature, irradiance, sedimentation, salinity, pH, and nutrients. These factors have an influence over physiological processes and the overall coral survival. During prolonged periods of abnormally high sea temperatures, the coral and algae symbiosis can be disrupted, and corals can appear bleached as the concentration of symbiotic algae in their tissue is reduced. When a coral is bleached it has removed it algae symbiote, which gives the coral its color, and appears white. While a bleached coral is not dead, it does become more susceptible to disease. Constant thermal increases generate mass bleaching events and can result in coral mortality over regional and global scales.

Health of Reef

There have been several regression models that show similar rates of bleaching and growth O. patagonica. Studies have shown that O. patagonica growth rates were similar in clear water environments such as the Marine Protected Area (MPA) of the Spanish Tabarca Island as well as turbid environments such as the Alicante Harbor of Spain. Light attenuation, or reduction in the amplitude of light, seems to increase coral bleaching mainly during summer due to the inability of the symbiotes to photosynthesize and provide the coral with sufficient defense. In a turbid environment if organic matter is relatively healthy it can account for the attenuation of light making it easier for corals to heal faster during severe bleaching event. The impact of temperature changes coral growth along with coral bleaching rates has been reported before. However, for the temperature to rise to the optimal temperature range certain factors have to be in place for Coral growth to be inhibited. It is because o. Patagonia is size dependent with the growth rate in larger colonies being smaller than other species that coral size is not a good factor to calculate whether the species can establish itself successfully. Previous Studies have shown that the growth rate of O. patagonica is mainly temperature dependent with the lowest threshold being 13 degrees Celsius during the colder months and the upper threshold being 28 degrees Celsius during the warmer months or during an El Nino event. The temperature fluctuation of the Mediterranean Sea for other corals is too much but because of o. patagonica temperature threshold it is well adapted. This study constructed a regression model where the criteria of bleached O. patagonica had four environmental variables: percentage of mud, percentage of organic matter, chlorine concentration in the seawater, and shade effect. The growth rate regression model was different for each environment.

The two environments were separately analyzed as to not confuse the data. The Harbor experienced a 58. 8 % bleaching rate; while the MPA showed a 64. 4 % bleaching rate both due to light attenuation and high sea temperature. The results showed a clear correlation between bleaching and high-temperature seawater in both sites. An important fact to note was that it was more of a long exposure to high temperatures as opposed to a maximum temperature when discussing the results. Light attenuation could act such as local stress that depresses the thermal tolerance of this species and increases the coral bleaching under thermal stress. A recent study provided evidence that heat stress that was at 32 °C or above along with light attenuation act on the zooxanthellae via different mechanisms during bleaching. When looking at the Harbor versus the MPA, the Harbor reefs were able to recover more quickly than the reefs in the MPA and this may have been caused by a higher food availability making it easier for those reefs to recover O. patagonica has a broad tolerance to seawater temperature, irradiance and trophic water conditions, in addition to its ability to thrive through bleaching events, which could be contributing to the spread of this species along the Mediterranean coasts. Bleaching events seems to be a complex process where several environmental parameters are a determinant; therefore, further studies of this species are needed to reveal possible adaptive modifications (either the symbiotics zooxanthellae, coral host or both) among populations inhabiting different environmental conditions and across the Mediterranean Sea.

Marine life impact on the reef

Mortality rates correlating with mass bleaching events were first described in 1987, with the frequency and intensity of bleaching increasing ever since. The Caribbean, mortality associated with mass bleaching events was first described in 1987, and the frequency and intensity of bleaching events has increased, while defining the parameters of an ecosystem such as structural community and competition of coral and algae, the ability of coral to benefit from the addition of super symbiotes is a major variable. If greenhouse gases can be reduced it will have a strong effect on the response of corals that have been implanted with this super symbiote. While testing under low carbon emissions, two of the three symbiotes types were able to maintain coral cover even when the super symbiote was placed on damaged coral within 60 years. The third symbiote was only able to maintain cover under standard carbon emissions and can only be established on damage coral within 25 years. The coral cover was between 30% and 40% with a low carbon emission scenario however it depended on the coral type and the super symbiote. Under the low carbon emissions scenario, the super symbiote only needed to become dominant for two of the coral species remain coral cover for a short while. The Super symbiote needed to be dominant for all four coral species to survive for a longer period of time because it has a higher number of bleaching events. The benefit of the super symbiote at this time is uncertain with the cost of the health of the coral being unknown, however the potential of the adaptation has been tested and quantified. When changing the gas emissions from low to normal, it proved to be a larger challenge. Under the new normal gas emissions scenario, there was only one symbiote the contribute a net benefit to the reef. To ensure the reefs survival, the super symbiote would have to be established within 10 years, 2. 5 times faster than the low emissions scenario. The model predicts that all four coral species would need to be dominated by the super-symbiote. Even when three of the four coral species had been found to be capable of switching to a different symbiote during bleaching, some species appear to be more likely to switch than others. This led to a high proportion of the colonies that switched to revert to the original symbiote type within two years of the bleaching event. Therefore, the likelihood of all coral species becoming infected and then retaining the super-symbiote is lower than that of only two species, as needed for the low emissions scenario. If some species are unable to cohabitate with more thermally tolerant symbiotes, then it may have been placed at a greater evolutionary disadvantage if greenhouse gases continue to appear.

Ecological Stressors

The Gulf of Mannar (GoM) is located along the southeast coast of India. It is one of the four major coral reef areas in the country with 117 corals species. The reefs in GoM are formed mainly around the 21 uninhabited islands situated between Rameswaram and Tuticorin. The study, the 21 islands have been placed under three groups: Tuticorin group, Keelakarai group and Mandapam group. Temperature range in GoM is comparatively higher as it has been reported to be between 26°C and 33. 5°C. During annual bleaching periods, temperature level crosses 30C when corals begin to bleach, and recover within three months (April–June) when the level comes down to less than 30C. Thus, the corals in GoM are exposed to a comparatively higher temperature level and are acclimatized to the same. In the Malvan coast of Maharashtra in the Arabian Sea, temperature threshold of 29. 8C caused coral bleaching and subsequent mortality in December 2015. Massive corals such as Porites, Favia and Favites were found to be resistant to bleaching, and these slow-growing species escaped death. The coast of GoM is densely populated and the traditional fisherfolk numbering over 100,000 mainly depend on the reef-associated fishery resources for their livelihood. Though GoM was once considered a biological paradise, decades of exploitation have caused the destruction of reef areas in an unprecedented manner. Coral mining coupled with destructive fishing practices has caused severe damages. Inshore trawling, shore seine operation and pollution are the major factors. In GoM, coral recovery after the 2010 mortality was noticeable by significant increase in the live coral cover; a predominant additional contribution to this increase was by coral recruits (0–10 cm) and young adult colonies (11– 40 cm), as they were relatively unaffected by bleaching.

However, in 2016, the recruits of fast-growing species also died in Mandapam and Keelakarai groups making recovery difficult. Due to lesser mortality and the consequent recovery in the Tuticorin group, corals are expected to recover in a couple of years if there is no further mortality due to bleaching and disease outbreaks. Also, corals from Tuticorin group of islands can supply larvae to the other groups, and a complete recovery is possible over the years if conducive environmental conditions prevail. The comparatively severe mortality in Mandapam group of islands could be attributed to the abundance of invasive organisms like coralline algae, turf algae and macroalgae, which invade the partially dead colonies and make recovery difficult. Current bleaching started in March 2016, which is earlier than normal, and persisted until June 2016. It is evident from the literature that corals can acclimatize to small-scale changes in the environment. However, they are unlikely to cope with increasing temperatures levels. Therefore, more thermal stress and mortality are expected in the future. The recovering ability of the reefs depends on many factors, including the kind of species involved, the environmental cues, predation, disease outbreaks and other stresses. The natural recovery process was also supplemented by coral rehabilitation for the increase of live coral cover in GoM. In the Tuticorin group of islands, coral recovery has been observed in several, large, affected colonies, but recovery was relatively slow in the Mandapam and Keelakarai groups. Coral rehabilitation with artificial structures using resistant native species is a well-proven option to enhance the recovery process in GoM. From earlier experience, the reefs in GoM are expected to show resilience in the coming days, if there is successful spawning and coral recruitment for increase of live coral cover, in which the coral colonies in the Tuticorin group of islands would play a major role.

Human Impact

The stress that is experienced by coral reefs that are near the shore is much different than reefs that lie in deeper water. These reefs have a proximity to human activity and therefore have an extra stressor to contend with. However, with the reefs being close to the shore there can also be a nutrient level increase from visitors feeding the marine life, and bird droppings being washed into the water. Tourism does have its flaws. When tourists want to experience the coral up close, the choice may be snorkeling and diving which may physically damage the coral. Even the platform that is placed for tourism can be a hindrance of coral reef with the anchoring chains for the platform, the snorkeling boundaries and the reef viewing stations that expose the coral due to the constantly changing tide. Since there are no published studies that survey the correlation between coral health, coral diseases, and tourism activity, a direct conclusion cannot be formed. However, a correlation can be drawn between reefs with permanent tourism platforms and adjacent reefs that do not have platforms and the prevalence of disease between the two reefs. The amount of coral diseases that appear on reefs with platforms for tourism purposes when compared with nearby reefs that lack a platform suggests that the activities have a major reduction of the reef’s ability to prevent disease. The known effects of tourism on coral reef is derived from a number of studies that deal with the changes in coral cover percentage after direct physical contact. Three studies considered coral damage due to snorkeling trails and permanent platforms with anchoring chains.

Since there was no major change in the coral cover percentage of all corals including the disease susceptible Acroporidae with or without platforms, it is probable that the difference in composition, species, and host density are very unlikely to have been the factor for the prevalence of diseases. A number of simulations correlate the increase in the bounty of corals that were marked with disease to the increase in host density meaning that the passing of pathogens is from contact via colony to colony. Increased susceptibility to infection from normally nonpathogenic local microbial communities, because of proximity to tourism platforms, could have played a role in the prevalence of coral diseases at these reefs. Thus, coral disease prevalence may represent a useful metric of human disturbance on coral reefs. A major challenge for managers of coral reefs is control of activities in heavily used areas that could severely damage corals, particularly branching species of Acropora. The availability of energy for allorecognition and cell-mediated immune responses declines during regeneration of damaged tissue in corals, sponges, and other invertebrates. Therefore, even if coral colonies survive breakage or damage from recreational activities, reductions in immunocompetence may increase their subsequent susceptibility to disease. Increased injury to corals near platforms may be contributing to increased disease prevalence and diversity. Injured colonies can become infected with black band disease after being transplanted downstream from diseased corals. Thus, dislodged black band mats, which comprise primarily cyanobacteria, may transmit the disease as they are transported by water currents and divers’ fins. Tourists themselves could serve as vectors of coral disease. It has been suggested that more than 5000 visitors per year damages reefs, each of the four tourism platform operators in this study reported over 40,000 visitors per year, although not all visitors enter the water. Boundaries limiting snorkeling activities are in place at all tourism platforms in our study, but much of the physical contact with corals is a result of uninformed or careless behavior. Managers can educate and compel visitors to reduce high-impact behavior (standing on and touching corals) and to engage in low-impact behavior.

Conclusion

Coral reefs are in danger and if not corrected effects are irreversible. Thus, meaning the loss of habitat for thousands of marine lives. Coral reefs are degrading at a steady rate. One of the main challenges of ecosystem and conservation management plans is to account for the connection between local habitats and the conflicting demands of different stakeholders on reef resources. If we lose coral reefs this can mean the loss of a myriad of marine life that we will lose the ability as well to research these organisms for bioprospecting. Pollution is the main anthropogenic stressor, with over 80% of variation in benthic community composition driven by sedimentation rate. The shift and decline in coral cover and composition has been extensively studied with a focus on large-scale gradients. Improved spatial management that accounts for both local and regional stressors is needed for effective marine conservation.