# Variable Responses to a Marine Heat Wave in Five Fringing Reefs of Southern Taiwan
## 1 Introduction  
Earth has fully entered the \"Anthropocene,\" an era in which no ecosystem has been spared from the wide reach of civilization [1]. Coral reefs in particular have been severely degraded due overfishing, pollution, and climate change (especially the associated ocean warming [2]), and marine heatwaves will only become more common and extreme in years to come [3]. Coincidingly, mass coral bleaching events, whereby the coral-dinoflagellate (family Symbiodiniaceae) endosymbiosis breaks down, are predicted to increase in frequency and magnitude, with widespread coral loss expected to have immense impacts on marine ecosystem function and services [4]. This poses a substantial risk to the myriad marine organisms that depend on these ecosystems, as well as the livelihoods of those individuals that rely on coral reefs for stustemance and income (e.g., fisheries & tourism). High temperature-induced bleaching events have been well documented since the early 1980s, with global scale events occurring in 1998, 2010, 2014-2017, and 2020 [5]. The frequency and intensity of bleaching events are rapidly approaching unsustainable levels since, in the absence of acclimatization or adaptation, there is no longer sufficient recovery time between events [6]. Some corals can shift to heterotrophy in their bleached states [7], but this tends to be a short-term survival strategy at best; unless thermotolerant dinoflagellate endosymbionts are rapidly re-uptaken, bleached corals will perish [8]. The abiotic milieu of coral reef habitats (e.g., temperature, light, pH, flow, etc.) can change dramatically over short-term time-scales (e.g., the tidal cycle [9]) and differ markedly across small spatial gradients (\(\sim\)cm-m [10]); this extensive variation can modulate bleaching frequency and severity [11]. For example, corals of highly variable temperature environments have been shown to be \"stress-hardened\" to better combat future increases in temperature [12; 13; 14; 15]. The type of reef, whether it be natural or \"artificially modulated,\" defined herein as a habitat either shaped directly by human activities (e.g., a seawall) or one whose structural and/or abiotic environment has been fundamentally altered by human activities at the local scale (beyond the global climate change-induced changes experienced by all reefs), could also have implications for the response of the resident corals to temperature increases, especially since their community structures and thermal histories may fundamentally differ from those of natural reefs [16; 17; 18; 19]. Fringing coral reefs are well-developed along the coast of Southern Taiwan's Hengchun Peninsula, and reefs within Taiwan's southernmost embayment, Nanwan Bay, frequently experience cold-water intrusions driven by internal wave-induced upwelling and mesoscale eddies [20]. One reef within Nanwan Bay, the \"Outlet\" (OL), is episodically immersed in the warm-water effluent from a nearby nuclear power plant; this thermally charged wastewater, in combination with an El Nino-Southern Oscillation (ENSO) event, caused the first documented bleaching events at OL in 1987 and 1988 [21]. Specifically, bleaching occurred at around four \"degree-heating weeks\" (DHWs) according to the National Oceanic and Atmospheric Administration's (NOAA) Coral Reef Watch (CRW). Since then, region-wide coral bleaching events have occurred in 1998, 2007, 2016, 2017, and 2020 (with minor ones in 2010 & 2014 [20]). The UN Environment Programme [22] predicts that bleaching will become an annual phenomenon in Southern Taiwan by 2037. Coral abundance in Nanwan Bay has fluctuated over time as a result of these bleaching events [23], as well as annual typhoons that occur in the boreal summer [24]. The spatial heterogeneity in coral abundance and recovery [25] suggests that reef resilience could vary over small (m-km) spatial scales (_sensu_[26]). Nanwan Bay could consequently be an ideal region for understanding climate change impacts on coral reefs [27].