*4.3. Corals*

Despite a significant increase in algal cover between surveys, total coral cover was similar in 2000 and 2018. *Porites compressa* sustained a high percent cover over 18 years at the fringing reef despite decreasing in percent cover by 22.9% in 14 years (1999–2012) across the Hawaiian Islands, with significant declines on the island of O'ahu [10]. *Porites compressa* is known to be sensitive to increased temperatures, which can cause bleaching and decreased calcification rates for the species [44]. Despite temperature increases over the 18 years, *P. compressa* has maintained its dominance as the most prevalent coral species at Malauka'a fringing reef, supporting its ability to acclimatize and persist in warming waters [24].

The *Montipora capitata* percent cover remained at a similar level between surveys despite increasing in percent cover by 56.8% in 14 years (1999–2012) across the Hawaiian Islands [10]. However, this study extended transects only to the end of the continuous reef pavement and many *M. capitata* colonies were located inshore of the reef (personal observation, K.A.B., July 2018). *Montipora capitata* colonies in Kane'ohe Bay have shown resilience through the ability to acclimatize ¯ /adapt to temperature increases (2.6 ◦C) over the past 47 years [13]. The continued presence of *M. capitata* at Malauka'a fringing reef despite temperature increases supports the findings of [13] through indicating resilience in lab experimentation and field long-term monitoring.

Percent cover of *Pocillopora damicornis* decreased significantly between the 18 years. The species is known to be highly sensitive to decreased salinity levels [15]. Increased freshwater input onto the southern portion of the surveyed reef may have impacted the abundance of *P. damicornis*. Following biocultural restoration of the Paepae o He'eia, water exchange between the fishpond and the adjacent reef increased, with an additional 14,418 m<sup>3</sup> of pond water being flushed out onto the reef during each ebb tidal cycle [27].

In 2000, *P. lobata* was a common reef-building coral at the study site. However, *P. lobata* was not observed in the 2018 survey. *Porites lobata* was described as 'common to Kane'ohe Bay' in ¯ 1999 [45]; however, more recently it was estimated to have 0–1% cover along Kane'ohe's fringing ¯ reefs [46,47]. Previous work suggests that *P. lobata* and *P. compressa* are di fferent morphotypes of the same species and/or hybridize frequently [48]. Therefore, the disappearance of *P. lobata* may mean one morphospecies was selected over the other. Due to similarities between *P. lobata* and *P. compressa* as well as the possibility of hybridizations, there may be potential misidentifications in the 2000 survey.

Similar to *P. lobata, P. meandrina* was also estimated to have 0–1% cover along fringing reefs in Kane'ohe Bay, supporting its absence in the 2018 survey [ ¯ 46,47]. *Pocillopora meandrina* has been similarly decreasing in percent cover across the Hawaiian Islands, with a 36.1% decrease from 1999–2012 [10]. Following the 2015 bleaching event, 98% of *P. meandrina* colonies on the west side of the island of Hawai'i were partially or fully bleached, demonstrating they are one of the more susceptible species to thermal stress [49]. They were similarly listed as the least resistant species to thermal stress at Kahe Point, Oahu [50]. The species vulnerability to increased temperatures may explain its disappearance in the 2018 survey.

*Lobactis* (formely *Fungia*) *scutaria* was recorded during the 2000 survey but not observed in the 2018 survey. Low densities of *L. scutaria* are expected at the site, as the species is abundantly found on patch reefs in Kane'ohe Bay, not fringing reefs [ ¯ 51]. Future studies of the area should employ a survey method such as the 'quadrat method', which avoids sampling from a small number of points to ensure rare and very rare species are included [28].

*Leptastrea purpurea* was the only new species seen in the 2018 survey. This encrusting species is tolerant to elevated temperatures and has been seen in areas where other coral species have succumbed to thermal stress [50]. The hardy species has been declared one of the 'long-term winners' as *L. purpurea* increase in abundance during thermal stress events [52,53]. *Leptastrea purpurea* has a relatively low metabolic rate, a characteristic known to help corals tolerate high temperatures [54]. Increasing temperatures may have allowed *L. purpurea* to settle in an area it had not before been present in, as it now holds a competitive advantage over other species which are less tolerant to thermal stress [53].

Coral cover did not significantly change over the past 18 years, although temperatures increased by 0.8 ◦C and two bleaching events (2014 and 2015) occurred during that time frame. While the fringing reef has shown resilience, it is unclear whether or not acclimatization and resistance to climate change has impacted its success. Previous work [13] has found all three species (i.e., *M. capitata, L. scutaria, P. damicornis*) of Hawaiian corals tested within Kane'ohe Bay have higher survivorship at 31 ¯ ◦C today than they did in 1970, suggesting that these corals can adapt to higher temperatures. As the corals in this study were from similar locations as those used by References [13] and [24], it is possible the resilience seen on the reef can be attributed in part to adaptation or acclimatization. The persistence of the coral cover at this site occurred while other sites within Kane'ohe Bay decreased in coral cover. ¯ From 2012–2016, Hawaii Coral Reef Assessment & Monitoring Program (CRAMP) reef sites at He'eia and Moku o Lo'e decreased by 19.7% and 42.2%, respectively [11].

However, while the total coral cover remained relatively stable over the past 18 years, the species composition has changed. The decrease in the total number of coral species present in the survey (6 in 2000, 4 in 2018) represents an overall loss in biodiversity. Additionally, two (or one if *P. lobata* is considered to be the same species as *P. compressa*) species of coral were lost in the 18 years while one non-reef building coral (*L. purpurea*) was added. This change suggests a temperature-driven shift in species composition over the 18 years. While the total coral cover remains high, the loss of locally uncommon species has negative impacts as rarer species often support more vulnerable and unique ecosystem functions [55].

Despite a shift in coral species composition, total coral cover percent remained unchanged over the 18 years and populations of the two dominant species of coral remained at comparable levels. Despite evidence of Hawaiian coral adaptation to increased temperatures, this adaptation might not occur fast enough to tolerate projected increasingly frequent bleaching events [13]. While the Malauka'a fringing reef has shown resilience over the past 18 years, the amount of warming and the rate of temperature increase will determine the fate of these reefs.

**Author Contributions:** Conceptualization, K.A.B. and K.D.B.; methodology, K.A.B. and K.D.B.; software, K.A.B. and K.D.B.; validation, K.A.B. and K.D.B.; formal analysis, K.A.B.; investigation, K.A.B.; resources, K.D.B.; data curation, K.A.B. and K.D.B.; writing—original draft preparation, K.A.B.; writing—review and editing, K.D.B.; visualization, K.A.B. and K.D.B.; supervision, K.D.B.

**Funding:** K.A.B acknowledges NMBU's Noragric field stipend for travel support to conduct research and NMBU's Publishing Fund for supporting the article processing charges. K.D.B. also acknowledges NSF#OA14-16889 for salary support during the writing and publication process.

**Acknowledgments:** The authors would like to thank Ku'ulei Rodgers for field advice and Ian Bryceson for his feedback on early drafts. Thanks to Annette Breckwoldt for providing data from the original 2000 survey. Thanks to Snorre Sundsbø and Elildo AR Carvalho Jr for assistance in statistical analyses. Thanks to Ashley McGowan, Colleen Brown, Robert Barnhill and members of the Coral Reef Ecology Lab for field and logistical support. Water temperature data was provided in part by PacIOOS (http://www.pacioos.org), which is a part of the U.S. Integrated Ocean Observing System (IOOS ®), funded in part by National Oceanic and Atmospheric Administration (NOAA) Award ##NA16NOS0120024. We also thank three anonymous reviewers. We appreciate the time that each has invested to provide the review, and these comments have helped us improve the manuscript significantly.

**Conflicts of Interest:** The authors declare no conflict of interest.
