Hawaiian Coral Research Articles

Ocean warming drives decline in coral metabolism while acidification highlights species-specific responses

ABSTRACTOcean warming and acidification can have negative implications on coral reefs. This mechanistic study aims to evaluate the proximal causes of the observed negative response of Hawaiian corals to climate change scenarios. Net calcification (Gnet), gross photosynthesis, and dark respiration were measured in three species of Hawaiian corals across a range of temperature and acidification regimes using endpoint incubations. Calcification rates showed a curvilinear response with temperature, with the highest calcification rates observed at 26°C. Coral response to ocean acidification (OA) was species dependent and highly variable. OA enhanced calcification rates by 45% in the perforate coral, Montipora capitata, but had no short-term effect on the calcification or photosynthetic rates of imperforate corals, Pocillopora damicornis or Leptastrea purpurea. Further investigations revealed M. capitata to effectively dissipate protons (H+) while increasing uptake of bicarbonate (), therefore maintaining high rates of Gnet under acute OA stress. This study demonstrates the first experimental evidence of the ability of a coral species to take advantage of increased dissolved inorganic carbon and overcome an increasing proton gradient in the boundary layer under OA conditions. These observed differences in coral metabolism may underlie the species-specific responses to climate change.

Photosynthesis by marine algae produces sound, contributing to the daytime soundscape on coral reefs.

We have observed that marine macroalgae produce sound during photosynthesis. The resultant soundscapes correlate with benthic macroalgal cover across shallow Hawaiian coral reefs during the day, despite the presence of other biological noise. Likely ubiquitous but previously overlooked, this source of ambient biological noise in the coastal ocean is driven by local supersaturation of oxygen near the surface of macroalgal filaments, and the resultant formation and release of oxygen-containing bubbles into the water column. During release, relaxation of the bubble to a spherical shape creates a monopole sound source that ‘rings’ at the Minnaert frequency. Many such bubbles create a large, distributed sound source over the sea floor. Reef soundscapes contain vast quantities of biological information, making passive acoustic ecosystem evaluation a tantalizing prospect if the sources are known. Our observations introduce the possibility of a general, volumetrically integrative, noninvasive, rapid and remote technique for evaluating algal abundance and rates of primary productivity in littoral aquatic communities. Increased algal cover is one of the strongest indicators for coral reef ecosystem stress. Visually determining variations in algal abundance is a time-consuming and expensive process. This technique could therefore provide a valuable tool for ecosystem management but also for industrial monitoring of primary production, such as in algae-based biofuel synthesis.

Modeled larval connectivity of a multi-species reef fish and invertebrate assemblage off the coast of Moloka'i, Hawai'i.

We use a novel individual-based model (IBM) to simulate larval dispersal around the island of Moloka‘i in the Hawaiian Archipelago. Our model uses ocean current output from the Massachusetts Institute of Technology general circulation model (MITgcm) as well as biological data on four invertebrate and seven fish species of management relevance to produce connectivity maps among sites around the island of Moloka‘i. These 11 species span the range of life history characteristics of Hawaiian coral reef species and show different spatial and temporal patterns of connectivity as a result. As expected, the longer the pelagic larval duration (PLD), the greater the proportion of larvae that disperse longer distances, but regardless of PLD (3–270 d) most successful dispersal occurs either over short distances within an island (<30 km) or to adjacent islands (50–125 km). Again, regardless of PLD, around the island of Moloka‘i, connectivity tends to be greatest among sites along the same coastline and exchange between northward, southward, eastward and westward-facing shores is limited. Using a graph-theoretic approach to visualize the data, we highlight that the eastern side of the island tends to show the greatest out-degree and betweenness centrality, which indicate important larval sources and connectivity pathways for the rest of the island. The marine protected area surrounding Kalaupapa National Historical Park emerges as a potential source for between-island larval connections, and the west coast of the Park is one of the few regions on Moloka‘i that acts as a net larval source across all species. Using this IBM and visualization approach reveals patterns of exchange between habitat regions and highlights critical larval sources and multi-generational pathways to indicate priority areas for marine resource managers.

Evidence of acclimatization or adaptation in Hawaiian corals to higher ocean temperatures.

Ocean temperatures have been accelerating at an alarming rate mainly due to anthropogenic fossil fuel emissions. This has led to an increase in the severity and duration of coral bleaching events. Predicted projections for the state of reefs do not take into account the rates of adaptation or acclimatization of corals as these have not as yet been fully documented. To determine any possible changes in thermal tolerances, manipulative experiments were conducted to precisely replicate the initial, pivotal research defining threshold temperatures of corals nearly five decades ago. Statistically higher calcification rates, survivorship, and lower mortality were observed in Montipora capitata, Pocillopora damicornis, and Lobactis scutaria in the present study at 31 °C compared to the original 1970 findings. First whole colony mortality was also observed to occur sooner in 1970 than in 2017 in M. capitata (3 d vs. 15 d respectively), L. scutaria (3 d vs. 17 d), and in P. damicornis (3 d vs. 13 d). Additionally, bleaching occurred sooner in 1970 compared to the 2017 experiment across species. Irradiance was an important factor during the recovery period for mortality but did not significantly alter calcification. Mortality was decreased by 17% with a 50% reduction in irradiance during the recovery period. These findings provide the first evidence of coral acclimatization or adaptation to increasing ocean temperatures for corals collected from the same location and using close replication of the experiment conducted nearly 50 years earlier. An important factor in this increased resistance to elevated temperature may be related to removal of the discharge of treated sewage into Kāne‘ohe Bay and resulting decrease in nitrification and eutrophication. However, this level of increased temperature tolerance may not be occurring rapidly enough to escape the projected increased intensity of bleaching events, as evidenced by the recent 2014 and 2015 high coral mortality in Hawai‘i (34%) and in the tropics worldwide.

Spatial distribution of sewage pollution on a Hawaiian coral reef

While sewage pollution is contributing to the global decline of coral reefs, its offshore extent and direct reef impacts from water column mixing and benthic seeps are poorly documented. We addressed this knowledge gap on a Hawaiian coral reef using sewage indicator and benthic cover measurements, macroalgal bioassays, and a pollution scoring tool. Fecal indicator bacteria (FIB) and nutrient concentrations were spatially variable in surface and benthic waters, with shoreline values being highest. Shoreline macroalgae δ15N and %N indicated high nitrogen loads containing sewage, while offshore surface and benthic values suggested lower nitrogen loads from environmental sources. Coral cover was negatively correlated with FIB, macroalgal δ15N, and nutrient concentrations. Benthic salinity and temperature measurements detected daily tidal groundwater pulses which may explain these associations. While pollution scores revealed that sewage was largely concentrated along the shoreline, results showed some reached the reef and may be contributing to its declining condition.

A simple molecular technique for distinguishing species reveals frequent misidentification of Hawaiian corals in the genus Pocillopora.

Species within the scleractinian genus Pocillopora Lamarck 1816 exhibit extreme phenotypic plasticity, making identification based on morphology difficult. However, the mitochondrial open reading frame (mtORF) marker provides a useful genetic tool for identification of most species in this genus, with a notable exception of P. eydouxi and P. meandrina. Based on recent genomic work, we present a quick and simple, gel-based restriction fragment length polymorphism (RFLP) method for the identification of all six Pocillopora species occurring in Hawai‘i by amplifying either the mtORF region, a newly discovered histone region, or both, and then using the restriction enzymes targeting diagnostic sequences we unambiguously identify each species. Using this approach, we documented frequent misidentification of Pocillopora species based on colony morphology. We found that P. acuta colonies are frequently mistakenly identified as P. damicornis in Kāne‘ohe Bay, O‘ahu. We also found that P. meandrina likely has a northern range limit in the Northwest Hawaiian Islands, above which P. ligulata was regularly mistaken for P. meandrina.

Influence of salinity and sedimentation on Vibrio infection of the Hawaiian coral Montipora capitata.

Environmental cofactors alter host-pathogen interactions and influence disease dynamics by impairing host resistance and/or increasing pathogen virulence. Terrestrial runoff is recognized as a major threat to coral reef health. However, the direct links between runoff and coral disease are not clear. Montipora white syndrome (MWS) is a coral disease that occurs in the Hawaiian archipelago, can be caused by various bacterial pathogens, including Vibrio species, and is linked to conditions associated with heavy rainfall and runoff. The objective of this study was to determine whether a short-term hyposalinity stress (20 ppt for 24 h) or sedimentation stress (1000 g m-2 d-1) would influence bacterial infection of the coral Montipora capitata. Hyposalinity increased M. capitata susceptibility to infection by 2 MWS pathogens, Vibrio coralliilyticus strain OCN008 and Vibrio owensii strain OCN002. Specifically, hyposalinity allowed OCN008 to infect at lower doses (106 CFU ml-1 compared with 108 CFU ml-1) and reduced the amount of time before onset of OCN002 infection at high doses (108 CFU ml-1). In contrast, short-term sedimentation stress did not affect M. capitata infection by either of these 2 pathogens. Although several studies have found a correlation between runoff and increased coral disease prevalence in field studies, this is the first study to show that one aspect of runoff (reduced salinity) enhances bacterial infection of coral using manipulative experiments.

Intra-colony disease progression induces fragmentation of coral fluorescent pigments

As disease spreads through living coral, it can induce changes in the distribution of coral’s naturally fluorescent pigments, making fluorescence a potentially powerful non-invasive intrinsic marker of coral disease. Here, we show the usefulness of live-imaging laser scanning confocal microscopy to investigate coral health state. We demonstrate that the Hawaiian coral Montipora capitata consistently emits cyan and red fluorescence across a depth gradient in reef habitats, but the micro-scale spatial distribution of those pigments differ between healthy coral and coral affected by a tissue loss disease. Naturally diseased and laboratory infected coral systematically exhibited fragmented fluorescent pigments adjacent to the disease front as indicated by several measures of landscape structure (e.g., number of patches) relative to healthy coral. Histology results supported these findings. Pigment fragmentation indicates a disruption in coral tissue that likely impedes translocation of energy within a colony. The area of fragmented fluorescent pigments in diseased coral extended 3.03 mm ± 1.80 mm adjacent to the disease front, indicating pathogenesis was highly localized rather than systemic. Our study demonstrates that coral fluorescence can be used as a proxy for coral health state, and, such patterns may help refine hypotheses about modes of pathogenesis.

New evidence of Hawaiian coral reef drowning in response to meltwater pulse-1A

Fossil coral reefs are valuable recorders of glacio-eustatic sea-level changes, as they provide key temporal information on deglacial meltwater pulses (MWPs). The timing, rate, magnitude, and meltwater source of these sea-level episodes remain controversial, despite their importance for understanding ocean-ice sheet dynamics during periods of abrupt climatic change. This study revisits the west coast of the Big Island of Hawaii to investigate the timing of the −150 m H1d terrace drowning off Kawaihae in response to MWP-1A. We present eight new calibrated 14C-AMS ages, which constrain the timing of terrace drowning to at or after 14.75 + 0.33/-0.42 kyr BP, coeval with the age of reef drowning at Kealakekua Bay (U-Th age 14.72 ± 0.10 kyr BP), 70 kms south along the west coast. Integrating the chronology with high-resolution bathymetry and backscatter data, detailed sedimentological analysis, and paleoenvironmental interpretation, we conclude the H1d terrace drowned at the same time along the west coast of Hawaii in response to MWP-1A. The timing of H1d reef drowning is within the reported uncertainty of the timing of MWP-1A interpreted from the IODP Expedition 310 Tahitian reef record.

Follow that fish: Uncovering the hidden blue economy in coral reef fisheries.

Despite their importance for human well-being, nearshore fisheries are often data poor, undervalued, and underappreciated in policy and development programs. We assess the value chain for nearshore Hawaiian coral reef fisheries, mapping post-catch distribution and disposition, and quantifying associated monetary, food security, and cultural values. We estimate that the total annual value of the nearshore fishery in Hawaiʻi is $10.3-$16.4 million, composed of non-commercial ($7.2-$12.9 million) and commercial ($2.97 million licensed + $148,500-$445,500 unlicensed) catch. Hawaii’s nearshore fisheries provide >7 million meals annually, with most (>5 million) from the non-commercial sector. Over a third (36%) of meals were planktivores, 26% piscivores, 21% primary consumers, and 18% secondary consumers. Only 62% of licensed commercial catch is accounted for in purchase reports, leaving 38% of landings unreported in sales. Value chains are complex, with major buyers for the commercial fishery including grocery stores (66%), retailers (19%), wholesalers (14%), and restaurants (<1%), who also trade and sell amongst themselves. The bulk of total nearshore catch (72–74%) follows a short value chain, with non-commercial fishers keeping catch for household consumption or community sharing. A small amount (~37,000kg) of reef fish—the equivalent of 1.8% of local catch—is imported annually into Hawaiʻi, 23,000kg of which arrives as passenger luggage on commercial flights from Micronesia. Evidence of exports to the US mainland exists, but is unquantifiable given existing data. Hawaiian nearshore fisheries support fundamental cultural values including subsistence, activity, traditional knowledge, and social cohesion. These small-scale coral reef fisheries provide large-scale benefits to the economy, food security, and cultural practices of Hawaiʻi, underscoring the need for sustainable management. This research highlights the value of information on the value chain for small-scale production systems, making the hidden economy of these fisheries visible and illuminating a range of conservation interventions applicable to Hawaiʻi and beyond.

A budget of algal production and consumption by herbivorous fish in an herbivore fisheries management area, Maui, Hawaii

AbstractThe relative rates of carbon fixed by primary producers vs. consumption by primary consumers shape the community of organisms in ecosystems. On coral reefs, it is important to understand the demography of algae, given known competitive dynamics with reef‐building corals. Numerous studies have shown that fleshy algal abundance is enhanced in the absence of top‐down control by herbivores on coral reefs. However, fewer studies have quantified and compared rates of production by the benthic fleshy algal community and consumption by herbivores. Here, we estimate a budget for fleshy algal growth and herbivorous fish consumption on a Hawaiian coral reef based upon integration of field‐measured and taxonomically specific variables. Data were collected at Kahekili Herbivore Fisheries Management Area, Maui, established in 2009, in which taking of herbivorous fish and urchins is prohibited. Daily algal production was determined by quantifying benthic community composition, standing stock of algal biomass, and growth rates of common algal components. Consumption was determined using distributions of biomass and size classes of herbivorous fish species, consumption rates of herbivores on different algal species, and herbivore bite sizes. Our results show that throughout the first five years of herbivore protection, algal production consistently exceeded the grazing capacity of the herbivorous fish assemblage, but by a diminishing margin since 2010 (consumption 20.8% of production) to the end of the study in 2014 (consumption 67.0% of production). Further, larger size classes of herbivorous fishes in the scraper/excavator herbivore guild contributed more to consumption in later years, which could have additional feedbacks that promote reef‐building taxa. Projecting the budget using data from a neighboring decades‐long protected herbivorous fish assemblage indicated that the production and consumption budget for Kahekili could become balanced in future with continued management.

Divergent evolutionary histories of DNA markers in a Hawaiian population of the coral Montipora capitata.

We investigated intra- and inter-colony sequence variation in a population of the dominant Hawaiian coral Montipora capitata by analyzing marker gene and genomic data. Ribosomal ITS1 regions showed evidence of a reticulate history among the colonies, suggesting incomplete rDNA repeat homogenization. Analysis of the mitochondrial genome identified a major (M. capitata) and a minor (M. flabellata) haplotype in single polyp-derived sperm bundle DNA with some colonies containing 2–3 different mtDNA haplotypes. In contrast, Pax-C and newly identified single-copy nuclear genes showed either no sequence differences or minor variations in SNP frequencies segregating among the colonies. Our data suggest past mitochondrial introgression in M. capitata, whereas nuclear single-copy loci show limited variation, highlighting the divergent evolutionary histories of these coral DNA markers.

Coral reef soundscapes may not be detectable far from the reef.

Biological sounds produced on coral reefs may provide settlement cues to marine larvae. Sound fields are composed of pressure and particle motion, which is the back and forth movement of acoustic particles. Particle motion (i.e., not pressure) is the relevant acoustic stimulus for many, if not most, marine animals. However, there have been no field measurements of reef particle motion. To address this deficiency, both pressure and particle motion were recorded at a range of distances from one Hawaiian coral reef at dawn and mid-morning on three separate days. Sound pressure attenuated with distance from the reef at dawn. Similar trends were apparent for particle velocity but with considerable variability. In general, average sound levels were low and perhaps too faint to be used as an orientation cue except very close to the reef. However, individual transient sounds that exceeded the mean values, sometimes by up to an order of magnitude, might be detectable far from the reef, depending on the hearing abilities of the larva. If sound is not being used as a long-range cue, it might still be useful for habitat selection or other biological activities within a reef.

Coral reefs at a tipping point

Researchers divided Hawaiian coral reefs into regimes based on the marine life present, human impacts, and other characteristics. (Top) A degraded reef in Waimanalo on Oahu, classified as regime 1 (high macroalgae, low fish). (Bottom) A reef near Kona that represents regime 5 (highest coral cover but low predator biomass). Images courtesy of (Top) Joseph Lecky (photographer) and (Bottom) Brian Neilson (Hawaii Department of Land and Natural Resources, Honolulu).

Relative sensitivity of five Hawaiian coral species to high temperature under high-pCO2 conditions

Coral reef ecosystems are presently undergoing decline due to anthropogenic climate change. The chief detrimental factors are increased temperature and increased pCO2. The purpose of this study was to evaluate the effect of these two stressors operating independently and in unison on the biological response of common Hawaiian reef corals. Manipulative experiments were performed using five species (Porites compressa, Pocillopora damicornis, Fungia scutaria, Montipora capitata, and Leptastrea purpurea) in a continuous-flow mesocosm system under natural sunlight conditions. Corals were grown together as a community under treatments of high temperature (2 °C above normal maximum summer temperature), high pCO2 (twice present-day conditions), and with both factors acting in unison. Control corals were grown under present-day pCO2 and at normal summer temperatures. Leptastrea purpurea proved to be an extremely hardy coral. No change in calcification or mortality occurred under treatments of high temperature, high pCO2, or combined high temperature–high pCO2. The remaining four species showed reduced calcification in the high-temperature treatment. Two species (L. purpurea and M. capitata) showed no response to increased pCO2. Also, high pCO2 ameliorated the negative effect of high temperature on the calcification rates of P. damicornis. Mortality was driven primarily by high temperature, with a negative synergistic effect in P. compressa only in the high-pCO2–high-temperature treatment. Results support the observation that biological response to temperature and pCO2 elevation is highly species-specific, so generalizations based on response of a single species might not apply to a diverse and complex coral reef community.

Length-based assessment of coral reef fish populations in the main and northwestern Hawaiian islands.

The coral reef fish community of Hawaii is composed of hundreds of species, supports a multimillion dollar fishing and tourism industry, and is of great cultural importance to the local population. However, a major stock assessment of Hawaiian coral reef fish populations has not yet been conducted. Here we used the robust indicator variable “average length in the exploited phase of the population ()”, estimated from size composition data from commercial fisheries trip reports and fishery-independent diver surveys, to evaluate exploitation rates for 19 Hawaiian reef fishes. By and large, the average lengths obtained from diver surveys agreed well with those from commercial data. We used the estimated exploitation rates coupled with life history parameters synthesized from the literature to parameterize a numerical population model and generate stock sustainability metrics such as spawning potential ratios (SPR). We found good agreement between predicted average lengths in an unfished population (from our population model) and those observed from diver surveys in the largely unexploited Northwestern Hawaiian Islands. Of 19 exploited reef fish species assessed in the main Hawaiian Islands, 9 had SPRs close to or below the 30% overfishing threshold. In general, longer-lived species such as surgeonfishes, the redlip parrotfish (Scarus rubroviolaceus), and the gray snapper (Aprion virescens) had the lowest SPRs, while short-lived species such as goatfishes and jacks, as well as two invasive species (Lutjanus kasmira and Cephalopholis argus), had SPRs above the 30% threshold.

The effects of growth anomaly on susceptibility of Montipora capitata to turf algal overgrowth

One of the most prominent coral diseases in Hawai‘i is growth anomaly (GA) of the skeleton. GA reduces key biological functions of Montipora capitata, but the effect of this disease on the ecological competitiveness of the coral has not been investigated. This study evaluated the effect of the GA on the susceptibility of an endemic Hawaiian coral M. capitata to algal overgrowth at Wai‘ōpae, Hawai‘i. Field surveys and photo analyses were conducted to collect epizootiological data. A relationship was found between GA severity and turf algal growth at the colony level; however, this relationship was weaker than expected. Despite the fact that GA lesions can provide areas of protuberant exposed coral skeleton, turf algal overgrowth was no more prevalent on GA-affected colonies than on unaffected colonies. As algal overgrowth is ephemeral compared to the progression of GA, we suggest that filamentous algae takes advantage of ideal environmental conditions regardless of the availability of new surfaces to invade presented by GA lesions.

UTILIZING UNDERWATER THREE-DIMENSIONAL MODELING TO ENHANCE ECOLOGICAL AND BIOLOGICAL STUDIES OF CORAL REEFS

Abstract. The structural complexity of coral reefs profoundly affects the biodiversity, productivity, and overall functionality of reef ecosystems. Conventional survey techniques utilize 2-dimensional metrics that are inadequate for accurately capturing and quantifying the intricate structural complexity of scleractinian corals. A 3-dimensional (3D) approach improves the capacity to accurately measure architectural complexity, topography, rugosity, volume, and other structural characteristics that play a significant role in habitat facilitation and ecosystem processes. This study utilized Structure-from-Motion (SfM) photogrammetry techniques to create 3D mesh models for several Hawaiian corals that represent distinct morphological phenotypes. The orthophotos and digital elevation models generated from the SfM process were imported into geospatial analysis software in order to quantify several metrics pertaining to 3D complexity that are known to affect ecosystem biodiversity and productivity. The 3D structural properties of the reconstructed coral colonies were statistically analyzed to determine if the each species represents a unique morpho-functional group. The SfM reconstruction techniques described in this paper can be utilized for an array of research purposes to improve our understanding of how changes in coral composition affect habitat structure and ecological processes in coral reef ecosystems.

Spawning event of Pherecardia striata followed by washed up individuals in Hawaii

Pherecardia striata (Kinberg 1857) is a polychaete worm of the family Amphinomidae. Amphinomids are known as ‘fireworms’ due to the discomfort and itching sensation if touched. P. striata is an active predator that can swallow pieces of fish and live prey such as small crabs, shelled gastropods, and other worms and even be hand fed in aquaria (Glasby and Bailey-Brock 2001). This is a large species reaching up to 20 cm in length in Hawaii and distributed throughout the IndoPacific (Bailey-Brock 1987). In Hawaiian shallow coral reefs, this species is known to spawn on a summer night, an event most likely triggered by a full moon. The spawning event was photographed on the night of July 25, 2005 in Coconut Island, Kaneohe Bay (Darlyne Murawski pers. comm.) and featured in Holland (2007) in a special issue of National Geographic. On the morning of August 17, 2014, dozens of individuals of Pherecardia striata were found dead at Kahanamoku Beach, 21.281602, -157.838943 (Fig. 1). Nearly ten years before, on August 6, 2004, about 200 individuals were found in a nearby beach (Ala Moana Beach , 21.288693, -157.847722) as reported in a local newspaper (Fujimori 2004). Although spawning events for this species are known to occur annually, heavy rains may have caused the massive deaths of individuals reported in 2004 and 2014. Predictions on spawning events of marine worms are very exact for the palolo worm (Palola viridis Gray in Stair, 1847) that spawns at the third quarter of the moon in October or November. This event is highly celebrated as the worms are eaten raw in the South Pacific. The three spawning events recorded for Pherecardia striata are documented herein for the third quarter of the moon of July or August and can be further investigated and celebrated by night divers and tourists.

Complete Genome Sequence of Pseudoalteromonas sp. Strain OCN003, Isolated from Kāne'ohe Bay, O'ahu, Hawaii.

Pseudoalteromonas sp. strain OCN003 is a marine gammaproteobacterium that was isolated from a diseased colony of the common Hawaiian reef coral, Montipora capitata, found on a reef surrounding Moku o Lo’e in Kāne’ohe Bay, Hawaii. Here, we report the complete genome of Pseudoalteromonas sp. strain OCN003.