The structural complexity of coral reefs plays a major role in the biodiversity, productivity, and overall functionality of reef ecosystems. Conventional metrics with 2-dimensional properties are inadequate for characterization of reef structural complexity. A 3-dimensional (3D) approach can better quantify topography, rugosity and other structural characteristics that play an important role in the ecology of coral reef communities. Structure-from-Motion (SfM) is an emerging low-cost photogrammetric method for high-resolution 3D topographic reconstruction. This study utilized SfM 3D reconstruction software tools to create textured mesh models of a reef at French Frigate Shoals, an atoll in the Northwestern Hawaiian Islands. The reconstructed orthophoto and digital elevation model were then integrated with geospatial software in order to quantify metrics pertaining to 3D complexity. The resulting data provided high-resolution physical properties of coral colonies that were then combined with live cover to accurately characterize the reef as a living structure. The 3D reconstruction of reef structure and complexity can be integrated with other physiological and ecological parameters in future research to develop reliable ecosystem models and improve capacity to monitor changes in the health and function of coral reef ecosystems.

Corals at the lower limits of mesophotic habitats are likely to have unique photosynthetic adaptations that allow them to persist and dominate in these extreme low light ecosystems. We examined the host–symbiont relationships from the dominant coral genus Leptoseris in mesophotic environments from Hawai'i collected by submersibles across a depth gradient of 65–125 m. Coral and Symbiodinium genotypes were compared with three distinct molecular markers including coral (COX1–1-rRNA intron) and Symbiodinium (COI) mitochondrial markers and nuclear ITS2. The phylogenetic reconstruction clearly resolved five Leptoseris species, including one species (Leptoseris hawaiiensis) exclusively found in deeper habitats (115–125 m). The Symbiodinium mitochondrial marker resolved three unambiguous haplotypes in clade C, which were found at significantly different frequencies between host species and depths, with one haplotype exclusively found at the lower mesophotic extremes (95–125 m). These patterns of host–symbiont depth specialization indicate that there are limits to connectivity between upper and lower mesophotic zones, suggesting that niche specialization plays a critical role in host–symbiont evolution at mesophotic extremes.

Despite widespread climate-driven reductions of coral cover on tropical reefs, little attention has been paid to the possibility that changes in the geographic distribution of coral recruitment could facilitate beneficial responses to the changing climate through latitudinal range shifts. To address this possibility, we compiled a global database of normalized densities of coral recruits on settlement tiles (corals m −2) deployed from 1974 to 2012, and used the data therein to test for latitudinal range shifts in the distribution of coral recruits. In total, 92 studies provided 1253 records of coral recruitment, with 77% origi nating from settlement tiles immersed for 3−24 mo, herein defined as long-immersion tiles (LITs); the limited temporal and geographic coverage of data from short-immersion tiles (SITs; deployed for < 3 mo) made them less suitable for the present purpose. The results from LITs show de clines in coral recruitment, on a global scale (i.e. 82% from 1974 to 2012) and throughout the tropics (85% reduction at < 20°latitude), and in creases in the sub-tropics (78% increase at > 20°latitude). These trends indicate that a global decline in coral recruitment has occurred since 1974, and the persistent reduction in the densities of recruits in equatorial latitudes, coupled with increased densities in subtropical latitudes, suggests that coral recruitment may be shifting poleward.

Reef-building corals inhabiting the mesophotic zone (30−150 m) not only survive but thrive in light-limiting environments. Similar to shallow corals, mesophotic corals also exhibit coral fluorescence. Because fluorescent proteins (FPs) absorb high-energy light and emit lowerenergy light, FPs could play an important role in mesophotic coral physiology and ecology. For 4 species of the Hawaiian mesophotic reef-building coral Leptoseris (65−125 m), we investigated the abundance of fluorescent morphs, types of FPs, fluorescence emission phenotypes, and the physiological relationship between coral fluorescence and endosymbiotic Symbiodinium (dinoflagellate; Dinophyta). Cyan/green coral fluorescence emission was widespread in mesophotic Leptoseris spp.; more than 70% of corals fluoresced, yet fluorescent and nonfluorescent corals cooccurred at all depths investigated. Coral fluorescence was attributed to 2 proteins, a cyan fluorescent protein (CFP, λ ex = 424 nm, λ em = 490 nm) and a green fluorescent protein (GFP, λ ex = 478 nm, λ em = 502 nm). The type of FP in Leptoseris colonies was correlated with depth; CFP was dominant in corals from shallower depths (65−85 m), GFP was dominant in corals from deeper depths (96−125 m), and CFP and GFP were present in corals from middle depths (86−95 m). Coral FP emission was primarily localized in the coenosarc and/or the oral disc. Symbiodinium from corals with and without fluorescence emission had similar genotypes, abundances, photosynthetic pigments, photosynthetic efficiencies, photosynthetic rates, and chlorophyll excitation spectra. As such, it is unlikely that these FPs play a significant role in enhancing symbiont photosynthesis. The high abundance of fluorescent morphs (> 70%) dominating this energetically limited environment may suggest that FPs play an integral and conserved physiological role in corals.

The persistence of reef building corals is threatened by human-induced environmental change. Maintaining coral reefs into the future requires not only the survival of adults, but also the influx of recruits to promote genetic diversity and retain cover following adult mortality. Few studies examine the linkages among multiple life stages of corals, despite a growing knowledge of carryover effects in other systems. We provide a novel test of coral parental preconditioning to ocean acidification (OA) to better understand impacts on the processes of offspring recruitment and growth. Coral planulation was tracked for three months following adult exposure to high pCO2 and offspring from the second month were reciprocally exposed to ambient and high pCO2. Offspring of parents exposed to high pCO2 had greater settlement and survivorship immediately following release, retained survivorship benefits during one and six months of continued exposure, and further displayed growth benefits to at least one month post release. Enhanced performance of offspring from parents exposed to high conditions was maintained despite the survivorship in both treatments declining in continued exposure to OA. Preconditioning of the adults while they brood their larvae may provide a form of hormetic conditioning, or environmental priming that elicits stimulatory effects. Defining mechanisms of positive carryover effects, or positive trans-generational plasticity, is critical to better understanding ecological and evolutionary dynamics of corals under regimes of increasing environmental disturbance. Considering parental and environmental legacies in ecological and evolutionary projections may better account for coral reef response to the chronic stress regimes characteristic of climate change.