*3.2. Potential for Recovery of Maldivian Reefs*

Maldivian coral reefs experienced severe bleaching in 1998 [43,44] and again in 2016 [12], and between these dates also endured a series of mild bleaching events in 2003, 2005, 2007, and 2010 [45–47]. During this recovery period, Maldivian reefs faced other disturbances, such as a tsunami in 2004 [48] and outbreaks of crown-of-thorns starfish (*Acanthaster planci*), both of which contributed to further coral mortality and influenced

recovery capacity in the impacted localized areas [49]. Following the 1998 bleaching event, which resulted in mass mortality (90%) of hard corals [50] and a near total disappearance of tabular coral [51], Maldivian reefs underwent a recovery trajectory that spanned the next 18 years. Initial mortality of acroporids (up to 90% [51]) led to a shift in assemblage composition of coral cover, from *Acropora*-dominated to *Porites*-dominated, for the first eight-plus years of recovery [43,49,52,53]. By 2014, 15 years post bleaching, reefs in the region resembled pre-1998 bleaching assemblages, however, with an absence of species that had yet to recover [46,49]. After the 1998 bleaching event the constructional capacity (i.e., bioconstruction potential, carbonate deposition, and reef accretion) of Maldivian reefs was severely affected, with two to three years required for renewed carbonate deposition and 14–16 years required before accretion rates were high enough to ensure constratal (low-relief) growth [54].

Recovery of Maldivian reefs post 1998 bleaching event was slower than rates reported in the neighbouring Chagos Archipelago [49,55,56], which lacks local human threats and recovered in 10 years [9]. Slower recovery was likely related to the increased level of human pressures that Maldivian reefs experience (e.g., overexploitation of resources, pollution, and coastal development) that influence the success of coral reef recovery, overall coral reef health, and resilience (e.g., [57,58]). Environmental degradation associated with humaninduced pressures have increased in the Maldives, particularly related to local population growth, coastal development, land reclamation works, and tourism [59–62]. Whereas local populations reached 344,023 in 2014, increases in the numbers of tourists grew by 400% between 1997 and 2019, reaching 1.5 million visitors in 2019 [35].

Following the 2016 bleaching event, coral mortality was greater at coral reefs exposed to increased human pressures (e.g., North and South Malé [35]). For example, reefs in proximity to land reclamation projects experienced four-fold increases in sedimentation loads and exhibited significant reductions in live coral cover post bleaching event in comparison to reefs not impacted by both land reclamation activities and bleaching [62]. Land reclamation and associated dredging (Figure 5a) and dumping activities contribute to increased suspended sediments and deposited sediment loads (i.e., sedimentation). Increased suspended sediments reduce light levels required by corals to photosynthesize [63–65], but even low levels of sediment or other particulate deposition reduces suitable reef substrate for coral recruitment [66,67]. Bleached corals are less capable of removing sediments from their tissue surface [68], resulting in prolonged smothering and increased energy expenditure to clear sediments [69,70]. Recent investigations into cumulative impacts of increased suspended sediments and bleaching events indicate that these impacts can be synergistic when suspended sediments are at high concentrations, resulting in greater mortality than would be observed with either individual event [71].

**Figure 5.** Maldivian coral reefs are exposed to local disturbances such as coastal development and land reclamation projects (**a**) and crown-of-thorns starfish that prey on corals (**b**). These additional pressures and thermal stress events may contribute to cumulative pressures on coral reef health and influence reef resilience and recovery.

Although land reclamation activities were not taking place near the coral reef sites surveyed in the present study, two crown-of-thorns starfish (Figure 5b) were observed at Hurasdhoo, which exhibited the highest coral mortality. Coral mortality caused by bleaching can be compounded and/or exacerbated by crown-of-thorns starfish, which favor branching corals as prey [34], and likely contributed to the higher reported mortality at this reef site.

The 2016 bleaching event resulted in lower coral mortality than the 1998 event and initial recovery has been faster [54]. By May 2017 hard coral cover had increased to a mean of approximately 30% (at eight reef sites surveyed across the atolls of Ari Felidhoo, Gaafu Alifu (Suvadiva), North Malé, South Malé, Rasdhoo, and Thoddoo), however, *Acropora* spp. had yet to show evidence of recovery at that time [54]. Current research shows that recovery trajectories are following different trends post 1998 and post 2016 bleaching events [54]. These differences are not surprising given that local human pressures have increased while pre-bleaching coral assemblage and reef health differed. Though faster recovery rates are positive for these reefs, the projected increases in both the frequency and intensity of bleaching events, lengthy recovery timeframes, and local disturbances suggest that Maldivian reefs may not have time to recover before the next severe bleaching event [35,54]. It is therefore critical that policies and management actions are created and implemented that focus on reducing local and regional stressors. Effective management initiatives will be crucial in facilitating the future resilience of both Maldivian reefs and the livelihoods of those that depend on them.
