It is produced on the land but ultimately ends up in the waters of coastal regions. There are various types of pollution originating from different sources as a result of activities on the land, for example, Sedimentation resulting from shore development, runoff from urban storm waters, agriculture, and forestry ( Figure 1 ). The sediment loads produce a pressure and cover that may result in the smothering of corals thereby damaging the soft tissues and ultimately leading to the death of corals (Erftemeijer et al., 2012; Yeemin et al., 2013; Lamb et al., 2018). The primary stress for the recovery and existence of the coral species and their habitats is sedimentation. The deposited sediments onto the coral reefs result in the smothering of corals interfering with the food intake, growth, and reproduction potential. Pollution of nutrients damages the coral reefs. Nitrogen and phosphorus from fertilizer use in agriculture and residential use, animal wastes, and sewage unloads such as septic systems and plants for treatment of wastewater are adversely impacting the corals which are habituated to low levels of nutrients. Enhancement of the nutrients results in an imbalance in the nutrient exchange between the corals and the zooxanthellae, it also promotes the growth of the phytoplankton that hinders the penetration of light through the coral reefs and the most damaging aspect among all is the stimulation and expansion in the growth of seaweeds that may outgrow very quickly smothering the corals and ultimately replacing the corals which usually have a slow growth rate, in typical tropical ocean environments with low concentrations of nutrients. These alterations result in an imbalance that adversely affects the coral reef ecosystems. Microbe growth is also promoted in an environment rich in nutrients such as fungi and bacteria that may infect corals.

Corals are affected badly by toxic substances such as organic chemicals, metals, industrial toxic discharges, agriculture and urban runoff, sunscreens, landfills, and mining activities. The growth, physiological pathways and reproduction of corals are adversely affected by the pesticides. Symbiotic algae are in particular affected by herbicides. The interaction of these algae with corals is damaged resulting in bleaching. Organic chemicals like dioxin, oxybenzone PCBs (polychlorobiphenyls), and metals including lead and mercury are also supposed to impact the feeding, growth rate, defense reactions, and reproduction of corals. There is also a direct hazardous impact of trash like fishing gear, and plastic debris on coral reefs and various benthic communities through killing or damage to benthic organisms and stony corals, entanglement, and introduction of potential pathogens and parasites (Chiappone et al., 2005; Dameron et al., 2007; Abu-Hilal and Al-Najjar, 2009; Gilardi et al., 2010; Niaounakis, 2017; Sheehan et al., 2021; Lamb et al., 2018). Therefore, the land-generated pollution of plastics, enrichments of nutrients, and contaminations of chemicals degrade the water quality thus resulting in blooms of algae, dysfunction of ecosystems, and diseases in corals.

Coral decline also results by the disease outbreak caused by abiotic or biotic factors or both (Woodley et al., 2008). Significant alterations occur as a result of destructive diseases in the growth, and reproduction of corals which eventually modify the structure of the community, the abundance of organisms related to reef as well as the diversity of various species ( Table 1 ) (Mulya et al., 2023). Furthermore, diseases caused by biotic factors including viruses, bacteria, protozoa, and fungi produce bands or lesions due to tissue loss on colonies of corals and ultimately impact the ecosystems of the reef as a whole (Sokolow et al., 2009). Increased temperature also impacts the factors controlling the virulence of coral-related microbes that disrupt photosynthesis and result in the disintegration of algae having symbiotic relationships (Ben-Haim et al., 2003; Rosenberg and Falkovitz, 2004) leading to the bleaching of corals. Biotic factors present in insufficient treated sewages, stormwater, and livestock pens runoff are adversely affecting the corals. Though very rare but parasites and bacteria present in the fecal contaminations produce disease in the corals specifically if there are stress conditions from other environmental factors. Diseases of corals may occur in even healthy ecosystems but the intensity and frequency of outbreaks are exacerbated in the presence of pathogens-borne pollution ( Figure 1 ).

Harvesting of corals for trades of aquariums, curios, and jewelry leads to the extensive hunting of the specified species, biodiversity reduction, and reef habitat devastation. Coral reefs are destroyed at many locations when brightly colored reef fishes and coral heads are harvested for jewelry and aquarium trade. Untrained and careless divers stomp the delicate corals whereas various techniques used for fishing cause destruction. Heavy explosives or dynamites are used in blast fishing to startle fish out of the stashing places which kills a lot of organisms indiscriminately and also produce stress and cracks in corals to a level where zooxanthellae are expelled destroying large zones of reefs ( Figure 1 ). Dumping or spraying of cyanide, in cyanide fishing, on coral reefs for capturing and stunning the live fish also damages polyps besides degrading the habitat of reefs. More than 15 countries are impacted by cyanide fishing and approximately 40 countries are reported to be influenced by blast fishing activities; (Hoegh-Guldberg et al., 2007).

The physical structure and function of the reef ecosystem are being jeopardized by the extensive loss of corals and their associated alterations of coral reef habitats (Hughes et al., 2003). In a few cases, corals are replaced by fleshy macroalgae (Seaweeds) as the predominant community thereby resulting in hurdles on the reclamation and replenishment capacity of corals assembly (Hughes et al., 2007, 2010). As an alternate, various sessile biota like soft corals, sponges, and ascidians flourish after the serious damage of hard corals (Scleractinian) (Norström et al., 2009; Tebbett and Bellwood, 2019). This shifting is further supported by variations in the ecological processes that may enhance the existence of non-coral biota and further restrict corals’ recruitment, survival, and growth (Hughes et al., 2010). Among all these non-coral biota, Algal turf is the widely distributed species. An algal turf ubiquitous growth found in most of the low-lying coral reef ecosystems exhibits a pertinacious changed state (Jouffray et al., 2015; Smith et al., 2016; Bellwood et al., 2018) strengthened by hazardous impacts of sediments captured in the turfs on the disposition of the coral juveniles (Ricardo et al., 2017; Speare et al., 2019). This settlement is further substantiated by the extensive fishing or the assemblage of terrestrial sediments that primarily change the function and behavior of the grazing fishes in the reefs (Goatley et al., 2016; Tebbett et al., 2017).

Deep water trawling is another destructive fishing method in which the fishing net is dragged along the bottom of the sea besides the muro-ami netting technique where coral reefs are stomped with heavy bags for startlement of fishes out of the hides. Among the serious effects are those in connection with the application of fishing gears which, even when lost or abandoned, continue to work uncontrolled and passively and contribute to the phenomenon called “ghost fishing”. (Al-Masroori et al., 2009; Gilardi et al., 2010; Gilman, 2015; Uhlmann and Broadhurst, 2015) whereas the abandoned equipment is known as “derelict fishing gear” (Morishige and McElwee, 2012; Edyvane and Penny, 2017), or “ghost nets” (Baeta et al., 2009; Butler et al., 2013; Wilcox et al., 2015), “fishery debris” (Ryan et al., 2009). The lost fishing gear is often called marine litter or debris (Gall and Thompson, 2015; Kühn et al., 2015; de Carvalho-Souza et al., 2018; Naranjo-Elizondo and Cortés, 2018) and is believed to be a vital contributor to sea plastic destroying corals and various sea animals (Lamb et al., 2018). In the Great Pacific Garbage Patch, almost 46% is the ghost nets (Lebreton et al., 2018). Marine life is endangered by the discarded gear and can kill or trap indiscriminately ocean animals, including those that belong to the endangered species or which are economically important. This hazard is quite prevalent in higher animals and hence the study of the impact of fishing gear and different ocean debris on vertebrates is given prime importance (Wilcox et al., 2013; Thiel et al., 2018). Food web structure can be altered by extensive fishing and may result in cascading impacts like a decline in the grazing fish number that is responsible for the cleaning of corals from overgrowth of algae.

During the recent past, climatic change has evolved as a viable threat endangering the coral reefs. Elevating sea temperatures are believed to be the cause of mass bleaching of corals during the last decade and this ocean warming may accelerate the severity and frequency of bleaching of corals in the decades to come (Donner et al., 2005). Prolonged or severe bleaching may kill colonies of corals or expose them to various other threats including diseases caused by biotic agents. It is a source of deliberation among the scientific community regarding the potential of corals and their symbionts to adjust to the changing climatic conditions as well as the chemistry of the ocean (Baker, 2004). The changing climate poses a precarious threat to the survival and functioning of coral reef ecosystems across the globe. Emissions of greenhouse gases are the predominant constituent during the present climatic change across the world (Cheng et al., 2019). The ocean is a big sink for the absorption of carbon dioxide, enhancing ocean acidification (Cornwall et al., 2021). Bleaching of corals and extensive damage to the ecosystem of coral reefs has become quite common resulting from the thermal strain due to the increased temperature of the ocean (Büscher et al., 2017). Shortage of nutrition required for the sustenance of the ecosystems of coral reefs and disturbance in the dispersal of larvae are both attributed to modified currents, upsurge, and/or vertical mixing due to changing winds and currents ( Table 2 ) (Goreau, 2003). Cyclones and storms are the “agents of mortality” in the coral reef ecosystems and it may have a direct effect on the local distribution and structure of coral reef assemblages, predominantly by large waves produced by them (Dietzel et al., 2021). Declined salinity resulting from increased run-off to adjacent shore reefs and heavy rainfall during storms, or cyclones results in blooming algal growth besides other damaging outcomes (Baird et al., 2021; Kjerfve, 2021). The rising sea levels, resulting due to the expansion by increased temperature and the ice melting on land, exhibited variated trends in different parts of the world during the last century, showing an average approx. 20 cm rise (Tay et al., 2022).

The crucial physiological reef processes are jeopardized and intensified as a result of potential sedimentary processes activated by the increasing ocean levels like feeding, photosynthesis, and replenishment eventually inducing serious hazards to the coral reefs and their ecosystems like mangrove forests and seagrass meadows (Field et al., 2011; Woodroffe and Webster, 2014). This hazard along with the enhanced CO2 (carbon dioxide) release, adversely impacts the important ecosystems. In the absence of efficient strategies at the local level and without collaborative efforts to reduce CO2 emissions, these hazardous impacts are further intensified leading to the devastation of the ecological balance and biodiversity of the marine environment, which is unprecedented (Godoy and Lacerda, 2015).

Unplanned coastal development is not only a serious threat to coral reefs; it also leads to long-term socioeconomic loss. With the worldwide coastal population expected to double by 2050, coral reefs will be facing increased pressure from unmanaged development along the coasts. Building near the coast may smother corals through pollutants and sedimentation. According to Erftemeijer et al. (2012) and Cunning et al. (2019), recent studies have shown compelling evidence that dredging operations and port activities pose a serious threat to corals due to exacerbated sedimentation. This has resulted in mass coral mortality that ranges from thousands to millions of coral colonies. According to a recent finding from the Lakshadweep islands (Ravindran et al., 2014), even little coastal development may have a major negative impact on coral mortality, habitat degradation, and vulnerability. Furthermore, unless environmental sustainability policies are truly enforced, the ecological cost of these coastal development projects may significantly outweigh the economic value realized (Hussain et al., 2016).

Shifting the residents from the damaged islands or shoring up the shorelines of the ocean against elevating levels of the sea also results in additional impacts on the economies of the world (Wilkinson and Buddemeier, 1994). An economic “Rationalist” analysis revealed that it is better to surrender the cultures of islands rather than face the very high costs of managing the CO2 output across the globe (Adams, 1993). For example, Melanesian Indigenous tribes have a different perspective on coral reefs than do scientists because they usually see them through a spiritual lens and have a personal relationship to the ecology. The sea has enormous spiritual significance in Indigenous Melanesian culture. According to legend, “place spirits” reside on reefs and take the form of particular animals like rays, sharks, and dolphins. Sea burials, which are revered rituals that may result in the closure of entire reef areas to the public, are also frequent in coral reef zones (Foale, 2008). Shallow islands of coral will be abandoned with a mere 0.5 m rise of sea levels or even less due to the contamination of waters in the ground and erosion of coastal lines.

Several reports revealed awareness of the significant damages to the reefs as a result of fishing and mining by employing destructive techniques besides those that are directly related to these activities in the reef islands (Perera et al., 2002). Nevertheless, the damaging impacts of these techniques are impacting other populations like tourists fellow fishermen, etc. Hence, increasing awareness among the broader group of people is a must to help support the enforcement of legal and protective measures. For coral reefs to survive, awareness-building regarding restoration is essential. Educating the public through workshops and social media campaigns, including communities in volunteer programs and citizen science initiatives, pushing for legislative reforms that save coral reefs, and motivating people via artistic expression and storytelling are all examples of successful tactics (Hesley et al., 2017). It seems especially vital to enhance the awareness and will of the people involved in political circles.

Indirect or passive strategies like launching Marine Protected Areas must target the decline of pressures on the coral reef islands supporting these to recover naturally. Natural recovery with no human involvement (Passive recovery) seems to be progressively insufficient (Ortiz-Lozano et al., 2018) as the bleaching of corals and their mortality incidences are getting more and more serious and frequent, thereby increasing the local anthropogenic stressors effects like pollution and extensive fishing (Hughes et al., 2018). Although MPAs protect about 18.7% of the world’s 527,072 km2 of coral reefs, less than 0.01% of them are low-risk, no-take MPAs that do not allow poaching (Mora et al., 2006). MPAs (Marine Protected Areas) are categorized as the most efficient techniques to recover coral reefs and their associated ocean systems (McLeod et al., 2009), nevertheless, these do not inevitably furnish safety against thermal impacts (Graham et al., 2007). Hence, proper investigation is necessary to help select the reef islands prone to destruction due to increasing temperatures (Obura et al., 2017; McClanahan et al., 2005).

Viable reclamation strategies like transplantation of corals and fragmentation at the micro level may enhance the recovery of reefs in the affected areas. Direct or active mediation like the transplantation of corals or reef artificial deployment targets reef rehabilitation by replacing the functional or structural features, at least, of the reef ecosystems that are lost or declined (Gomez et al., 2010). Direct transplantation of coral fragments from a donor reef to a recipient reef is the oldest and most popular technique of coral regeneration. The review database contains 94 descriptions of direct transplantation, which accounts for 20% of all records. Programs designed to save corals from planned construction projects that would otherwise destroy or disturb the colonies are the ones that use this technique the most. According to direct transplantation studies, transplanted corals had an average survival rate of 64% overall, with 20% having a survival rate of >90% (interactive database). Fast-growing corals have been the main focus of direct transplanting; branching coral morphologies have been used in over three-quarters of case studies (Young et al., 2012). Direct reef retrieval may be successful in the long term provided it also involves (a) Novel inventions like abetted recruitment and fertilization (Nakamura et al., 2011; dela Cruz et al., 2015); (b) conducts that increase the pace of adaptation or natural selection involving supported gene flow and orchestrated shifting (Aitken and Whitlock, 2013; Van Oppen et al., 2017) along with the feasible manifestation of abetted evolution and adaptation (Van Oppen et al., 2017); and (c) concentration of the preservation and increase in the diversity of various species and genetic variation in the populations of reef and orchestrated assembly of various species to fully augment the species consortia to its best (Zoccola et al., 2020).

Execution of these strategies will depend primarily on the direct reclamation in the areas where extensive fishing, pollution, and various human-triggered stressors onto the reefs are managed well. Direct restoration nonetheless aims at a very limited number of species and is also restricted to little spatial levels: even efforts at large scale stumble to reclaim a single hectare every year. The efficacy of the direct restoration hence is dependent on efforts to harvest population connectivity of corals to speed up the establishment of the thermal tolerant corals i.e. concentration reclamation on coral reefs where dispersal of larvae and their replenishment may trigger year-to-year dispersal and establishment over extended areas (Hock et al., 2017; Walsworth et al., 2019). In a few areas, restoration of structure is also required to improve the ecological reclamation of coastal lines (Beck et al., 2018) and the production of fishes (Rogers et al., 2018).

Execution of a comprehensive scheme encompassing land use management, management of water quality, and coastal safety ensures the health preservation of the coral reef ecosystem, however, approaches including traditional passive practices like enhancing the quality of water in catchments and the employment of marine no-take zones for the protection of coral reefs from immediate damaging acts have failed to a great extent in combating climate change affects (Suggett et al., 2023). The association of several regulatory bodies that supervise marine development with stakeholders in the private sector is pivotal to the fruitful ICZM implementation. The task demands unwavering government dedication to a coordinating system, like an interministerial commission or council comprising representation from all the private and public sectors. Besides, strategies ensuring appropriate execution are necessary, for instance, authoritative clarification, economic incentives, and accountable lead agencies such as retaining the funding for infrastructure till the project is implemented or completed. Consequently, efforts are made increasingly on active strategies of enhancing the coral reef persistence.

It is essential to decline the emissions of greenhouse gases and implement adaptive strategies to safeguard the coral reef ecosystems protecting these against hazards of climatic changes. Huge losses of the coral reefs and structure of reefs are anticipated if global warming increases by 1.5°C over the average pre-industrial temperatures (Hoegh-Guldberg et al., 2018), and the most efficient strategy to decrease the coral reefs decline would be an effective and quick alleviation of emissions of greenhouse gases (Hoegh-Guldberg et al., 2019). Besides alleviating greenhouse gas emissions, SRM (solar radiation modification) is another efficient means. Solar radiation modification comprises hypothetical approaches to divert sunlight to space like stratospheric aerosol injections which may act at a comprehensive scale, brightening the ocean cloud at the local scales. SRM is not condoned as it can’t decrease the acidification of the ocean and also it offers important risks and suspicions (Gattuso et al., 2018).