Review thesis: Proteomic changes in Scleractinian corals in response to environmental changes: A review for novel biomarker (title subject to change depending on FYP conclusion) Chapter 3: Cellular...

Running Head: SCLERACTINIAN CORALS                        1
SCLERACTINIAN CORALS                                16
SCLERACTINIAN CORALS
Table of Contents
Question 1    3
Physiological process and Homeostasis in coral reefs    6
Question 2    8
Question 3    9
Question 4,5,6    9
References    12
Question 1
    Coral reefs forms a major part of the diverse marine ecosystem and it is home to several marine species such as crabs, crustaceans, mollusks, cnidarians, tunicates, echinoderms, worms, fish and sponges. The shallow coral reefs occupies less than 0.1% of total ocean’s area and yet they are known to accommodate 25% of the marine species.Warming up of global system is a bad news for the coral reefs that live close to upper limits of thermal temperatures in the tropical oceans. Due to their closer proximity to surfaces, during average seasonal summers there is a breakdown of symbiotic relationship between corals and algae. According to Lough, Anderson, Hughes (2019), the coral acts as a host and depends upon the algae (Symbiodinium) for the photosynthetic products which allows for the corals to calcify quickly resulting in the build up of calcium carbonate skull that forms backbone of the reef ecosystems. Due to loss of algae, coral tissue becomes white resulting in “Coral Bleaching” and once thermal stress gets removed corals starts dying.According to Sully et al. (2019), coral bleaching results in coral mortality as well as morbidity which cause losses to their cover as well as leads to significant changes in the coral community.
     There are several triggers associated with coral bleaching such as elevated water temperatures, bacterial infections, oxygen concentrations high/low, herbicides, ocean acidification etc. According to Ghoora et al. (2020), release of heavy metals especially petrochemical hydrocarbons, in the marine water bodies pose threat to the ecosystem since heavy metals in large concentration leads to toxicity as well as is known to reduce photosynthetic processes in marine organisms which are essential for their survival. According to Carlson, Foo and Asner (2019), approximately 25% of coral reefs globally are at a risk of degradation on account of heavy use of pollutants in agricultural industry. Few intensive agricultural practices are known to cause soil erosion transmitting certain organic as well as inorganic pollutants in the vulnerable reefs.
    The Red Sea is known to have a rich scleractinian coral reef ecosystem framework along its coastal line. According to Fine et al. (2019), oil spills has been a major issue since oil tankers transports a large quantity of crude oils closer to the surface of coral reef resulting in environmental pollution. It has been studied that there is a rapid decline in coral reefs since they’re vulnerable to UV irradiation alongwith environmental pollutants like oil spillage. Toxic chemicals belonging to aromatic hydrocarbons family, such as PAH (Polycyclic aromatic hydrocarbons) and MAH (Monocyclic Aromatic hydrocarbons) both are known to be significant components of oils that are spilled in the seas and are toxic to the pelagic and benthic species of marine ecological system. The subsurface aquatic life is also damaged by another mode of petroleum pollutants where lipid membranes gets accumulated with dissolved aromatics resulting in homeostasis and cell disintegration. Oxidative stress and DNA damage are some other harmful effects caused due to the oil spillage. As stated by Nordborg et al. (2020), high levels of UV radiation exposure on shallow reefs results in phototoxicity which is caused due to oil spillage through the process of photosensitisation.
    Anthropogenic eutrophication is known to deplete dissolved oxygen levels in the oceans. According to Gao et al. (2019), another major factor affecting coral reefs is the anthropogenic releases of excessive phosphorus and nitrogen containing compounds in the seawaters. As indicated by Adam et al. (2021), these nutrients rich anthropogenic inputs are quite dangerous since it can lead to persistent growth of harmful and useless algae that depletes the oxygen from the subsurfaces disrupting fisheries as well as reduces the water clarity. It is also known to negatively impact the coral growth by dramatically altering its physical structure and normal functions. Due to global warming there is an increase in the green-house gases which results in ocean acidification. The atmospheric CO2 gets absorbed into the ocean causing an alteration like decrease in pH value which results in reduced calcification rates amongst the coral reef building microorganisms associated with it. This overall process is described as ocean acidification and is very harmful to the coral reefs.
    Hypoxia is low levels of oxygen present in seawaters and it is known to cause a major threat to marine ecology especially the coral reefs which is on a rapid decline.According to Johnson, Rodriguez, Altieri (2019), due to persistent lowconcentrations of oxygen in the shallow coral reef there was high mortality observed amongst the benthic invertebrates below a depth of 3-4 metres. According to Belrauch and Blewett (2019), it is known to alter metabolic rate in coral reef however studies have been going on to determine how the coral reefs are affected by hypoxic anoxic environments.
    Corals are known to be infected by the pathogenic bacteria and virusesproduced by plastic pollutants and is known to cause black-band and yellow-band diseases in them. According to Wolfsohn et al. (2020),this results in atrophy in their structural changes and causes necrosis of underlying tissues resulting in fragmented body wall. Commonly found bacteria is Rickettsiales-like organisms (RLO), alongwith diversified microbial communities as well as certain viruses which are known to cause white plaguelike infections.AccordingtoJacquemotet al. (2018), Vibrio coralliilyticus a bacterial pathogen has been known to cause wide number of infections in the corals thus leading to coral bleaching and death.
    The corals are also studied for the effects of turbidity on them which is caused by dredging activities which increases the concentrations of SSCs (Suspended sediment concentrations). According to Jones et al. (2020), a number of physiological responses like bleaching in corals, changes in morphologies as well as changes in lipid levels were observed in corals within high turbidity conditions (low light). According to Roik et al. (2018), high salinity can alter the osmotic balance as well as physiological conditions of corals. However, salinity effects on thermotolerance of coral reefs is anecdotal.
Physiological process and Homeostasis in coral reefs
    The marine ecological system is a storehouse of biodiversity and contains 25% of the marine species taking shelter under coral reefs. The environmental stress factors such as pollutants, heavy metals, ultraviolet radiations, turbidity, pH, salinity, nutrient enrichment, thermal stress, pathogens are all known to cause a negative impact on the coral reefs.
    According to Williams et al. (2021), stony corals Scleractinia exchange metabolites with Symbiodiniaceae which is an algal photosymbiont and forms the foundation of coral reef ecosystems. Normally 90-95% of energetic requirements of host (coral) is provided by the algal cells in the form of lipids, proteins, carbohydrates and oxygen. In return the algae uses nitrogen and inorganic compounds from the coral reef to initiate cell metabolism in algae. This symbiotic relationship between corals and algae is significantly harmed by environmental stress caused by climatic changes such as an increase in temperature thereby resulting in coral bleaching. It...