Coral Assemblages Research Articles

Genomic insights into hybridization of reef corals

Hybridization plays a fundamental role in speciation and diversification of plants and animals. Hybridization among highly diverse assemblages of reef corals is well known and widely reported, but the ecological and evolutionary consequences of hybridization among reef corals are only just beginning to become apparent. In this perspective, I introduce introgression and polyploidy in the hybridization (reticulate evolution) of reef corals and then discuss the roles of hybridization in the evolution of Acropora with recent genomic evidence. Finally, I discuss how advances of genomics will facilitate the study of hybridization in reef corals. Together, understanding the genomic basis of reef coral hybridization provides new insights into coral resilience, as well as coral reef biodiversity and conservation.

Testing Industrial-Scale Coral Restoration Techniques: Harvesting and Culturing Wild Coral-Spawn Slicks

Accelerating the recovery of marine coastal ecosystems is a global challenge that has been attempted on many systems around the world. Restoration efforts have shown varying levels of success at localized-scales, but developing techniques for large-scale application are still in their nascent stage for many systems. For seagrass meadows and marsh plants, large-scale successes have been realized by distributing seeds from moving boats or planes, respectively. Similarly for coral reefs, the harvesting, culturing and releasing of wild coral-spawn slicks to targeted reefs is anticipated to achieve cost-efficient, large-scale restoration of coral communities with low-impact technology. Yet, operational protocols for full-scale application still require development by practitioners. In this study we conducted a field trial to evaluate the actual feasibility of harvesting wild coral-spawn slicks for large-scale restoration activities, incorporating technologies used in oil spill remediation, dredging operations, and land-based aquaculture. Testing the potential for scalability to commercial vessels, our trial focused on concentrating and collecting wild coral-spawn slicks for culturing until settlement competency using an experimental 50,000 L aquaculture facility built on a tugboat. Five objectives were set and all were achieved successfully, with only one requiring further optimization. Overall, this restoration approach allows for long-distance translocation of genetically diverse coral assemblages, and may be combined with other larval conditioning techniques that are being developed to increase the resistance to stress and survival of coral recruits. Most importantly, it is fully scalable to produce billions of coral larvae for delivery to target reefs, with negligible impact to source populations.

Extreme spatial heterogeneity in carbonate accretion potential on a Caribbean fringing reef linked to local human disturbance gradients.

The capacity of coral reefs to maintain their structurally complex frameworks and to retain the potential for vertical accretion is vitally important to the persistence of their ecological functioning and the ecosystem services they sustain. However, datasets to support detailed along‐coast assessments of framework production rates and accretion potential do not presently exist. Here, we estimate, based on gross bioaccretion and bioerosion measures, the carbonate budgets and resultant estimated accretion rates (EAR) of the shallow reef zone of leeward Bonaire – between 5 and 12 m depth – at unique fine spatial resolution along this coast (115 sites). Whilst the fringing reef of Bonaire is often reported to be in a better ecological condition than most sites throughout the wider Caribbean region, our data show that the carbonate budgets of the reefs and derived EAR varied considerably across this ~58 km long fringing reef complex. Some areas, in particular the marine reserves, were indeed still dominated by structurally complex coral communities with high net carbonate production (>10 kg CaCO3 m−2 year−1), high live coral cover and complex structural topography. The majority of the studied sites, however, were defined by relatively low budget states (<2 kg CaCO3 m−2 year−1) or were in a state of net erosion. These data highlight the marked spatial heterogeneity that can occur in budget states, and thus in reef accretion potential, even between quite closely spaced areas of individual reef complexes. This heterogeneity is linked strongly to the degree of localized land‐based impacts along the coast, and resultant differences in the abundance of reef framework building coral species. The major impact of this variability is that those sections of reef defined by low‐accretion rates will have limited capacity to maintain their structural integrity and to keep pace with current projections of climate change induced sea‐level rise (SLR), thus posing a threat to reef functioning and biodiversity, potentially leading to trophic cascades. Since many Caribbean reefs are more severely degraded than those found around Bonaire, it is to be expected that the findings presented here are rather the rule than the exception, but the study also highlights the need for similar high spatial resolution (along‐coast) assessments of budget states and accretion rates to meaningfully explore increasing coastal risk at the country level. The findings also more generally underline the significance of reducing local anthropogenic disturbance and restoring framework building coral assemblages. Appropriately focussed local preservation efforts may aid in averting future large‐scale above reef water depth increases on Caribbean coral reefs and will limit the social and economic implications associated with the loss of reef goods and services.

Rapid decline of a relatively high latitude coral assemblage at Weizhou Island, northern South China Sea

“Refuge theory” suggests that global warming would be beneficial to corals in high latitude waters. In theory, then, the Weizhou Island reef (21°00′–21°10′N, 109°00′–109°15′E), which is located in a relatively high latitude area in the northern South China Sea, is a refuge for corals under global warming. Yet, the corals here have degenerated significantly. We investigated the ecological status of the Weizhou Island reef in 2015 and recorded 11 families, 22 genera, and 41 coral species. The mean living coral cover has decreased from ~ 42% in 1984 to ~ 10% in 2015 and there are many dead Acropora in the study area, especially at the reef flat. Coral assemblage structure has undergone degradation with the dominant group shifting from high complexity branching, foliaceous and massive colonies to a simpler group of massive morphologies. The only sign indicating the corals here benefiting from global warming is the occurrence of a large amount of juvenile Porites lutea (31.91% of the total population), which represents the recovery potential of the Weizhou Island reefs. Further analysis concludes that the main reason for the rapid degeneration is escalating anthropogenic impact, such as seawater pollution, unsustainable tourism activities, ongoing overfishing, all of which degrade the local ecological environment. It seems that intensive anthropogenic activities have weakened the “refuge” function significantly. Decreasing living coral cover as well as degraded assemblage structure all suggest that Weizhou Island offers limited potential as refuge habitat for corals in the context of global warming and intensive human activities.

Differential consumption of scleractinian and non-scleractinian coral larvae by planktivorous damselfishes

Planktivorous fishes are known to consume coral larvae due to their high nutritional value that can benefit both the individual and their progeny. However, how the consumption of coral larvae varies among coral and fish taxa, between day and night and with the density of coral larvae is not well understood. Here, we used a series of laboratory feeding assays to determine how the consumption of coral larvae by five planktivorous damselfish species (Abudefduf sexfasciatus, Amblyglyphidodon curacao, Dascyllus trimaculatus, D. reticulatus, and Chromis viridis) differed (1) between larvae of the broadcast-spawning scleractinian coral Acropora tenuis and the brooding non-scleractinian coral Heliopora coerulea when offered at a constant density (100 larvae/50 L), (2) between day and night (A. tenuis only), and (3) among larval densities (A. tenuis: 5–500 larvae/50 L; H. coerulea: 5–250 larvae/50 L). When coral larvae were offered at 100 larvae/50 L, all five fish species examined consumed A. tenuis (78–97 larvae h−1) at a greater rate than H. coerulea (23–57 larvae h−1), with these differences likely related to the behavior and/or pigmentation of the larvae. Consumption also varied among the fishes examined, though the differences were small when compared to differences between coral species. Consumption of A. tenuis was twofold higher at day than night likely reflecting the diurnally active feeding behavior of the fishes examined. When the density of coral larvae offered to the fishes was varied, three of five species exhibited a type II functional response (decelerating intake rate) for A. tenuis, while four out of five damselfish species exhibited a type III (sigmoidal intake rate) or type I (linear intake rate) for H. coerulea. This study demonstrates that predation by fishes contributes significantly to coral larvae mortality and that differences in consumption rates among coral species may affect the composition of coral recruits and ultimately coral assemblages.

Light environment drives the shallow‐to‐mesophotic coral community transition

AbstractLight quality is a crucial physical factor driving coral distribution along depth gradients. Currently, a 30 m depth limit, based on SCUBA regulations, separates shallow and deep mesophotic coral ecosystems (MCEs). This definition, however, fails to explicitly accommodate environmental variation. Here, we posit a novel definition for a regional or reef‐to‐reef outlook of MCEs based on the light vs. coral community–structure relationship. A combination of physical and ecological methods enabled us to clarify the ambiguity in relation to the mesophotic definition. To characterize coral community structure with respect to the light environment, we conducted wide‐scale spatial studies at five sites along shallow and MCEs of the Gulf of Eilat/Aqaba (0–100 m depth). Surveys were conducted by technical‐diving and drop‐cameras, in addition to one year of light spectral measurements. We quantify two distinct coral assemblages: shallow (&lt;40 m) and MCEs (40–100 m), exhibiting markedly different relationships with light. The depth ranges and morphology of 47 coral genera were better explained by light than depth, mainly, due to photosynthetically active radiation (PAR) and ultraviolet radiation (UVR) (1% at 76 and 36 m, respectively). Branching coral species were found mainly at shallower depths, that is, down to 36 m. Among the abundant upper‐mesophotic specialist corals, Leptoseris glabra, Euphyllia paradivisa, and Alveopora spp. were found strictly between 40 and 80 m depth. The only lower‐mesophotic specialist, Leptoseris fragilis, was found deeper than 80 m. We suggest that shallow coral genera are light‐limited below a level of 1.25% surface PAR and that the optimal PAR for mesophotic communities is at 7.5%. This study contributes to moving MCE ecology from a descriptive phase into identifying key ecological and physiological processes structuring MCE coral communities. Moreover, it may serve as a model enabling the description of a coral zonation worldwide on the basis of light quality data.

Refugia under threat - mass bleaching of coral assemblages in high-latitude eastern Australia

Refugia under threat - mass bleaching of coral assemblages in high-latitude eastern Australia

Refugia under threat - mass bleaching of coral assemblages in high-latitude eastern Australia

Refugia under threat - mass bleaching of coral assemblages in high-latitude eastern Australia

Refugia under threat - mass bleaching of coral assemblages in high-latitude eastern Australia

Refugia under threat - mass bleaching of coral assemblages in high-latitude eastern Australia

Refugia under threat: Mass bleaching of coral assemblages in high-latitude eastern Australia.

Environmental anomalies that trigger adverse physiological responses and mortality are occurring with increasing frequency due to climate change. At species' range peripheries, environmental anomalies are particularly concerning because species often exist at their environmental tolerance limits and may not be able to migrate to escape unfavourable conditions. Here, we investigated the bleaching response and mortality of 14 coral genera across high-latitude eastern Australia during a global heat stress event in 2016. We evaluated whether the severity of assemblage-scale and genus-level bleaching responses was associated with cumulative heat stress and/or local environmental history, including long-term mean temperatures during the hottest month of each year (SSTLTMAX ), and annual fluctuations in water temperature (SSTVAR ) and solar irradiance (PARZVAR ). The most severely-bleached genera included species that were either endemic to the region (Pocillopora aliciae) or rare in the tropics (e.g. Porites heronensis). Pocillopora spp., in particular, showed high rates of immediate mortality. Bleaching severity of Pocillopora was high where SSTLTMAX was low or PARZVAR was high, whereas bleaching severity of Porites was directly associated with cumulative heat stress. While many tropical Acropora species are extremely vulnerable to bleaching, the Acropora species common at high latitudes, such as A. glauca and A. solitaryensis, showed little incidence of bleaching and immediate mortality. Two other regionally-abundant genera, Goniastrea and Turbinaria, were also largely unaffected by the thermal anomaly. The severity of assemblage-scale bleaching responses was poorly explained by the environmental parameters we examined. Instead, the severity of assemblage-scale bleaching was associated with local differences in species abundance and taxon-specific bleaching responses. The marked taxonomic disparity in bleaching severity, coupled with high mortality of high-latitude endemics, point to climate-driven simplification of assemblage structures and progressive homogenisation of reef functions at these high-latitude locations.

Diversity and Abundance of Scleractinian Corals in the East Coast of Peninsular Malaysia: A Case Study of Redang and Tioman Islands

The species lists of scleractinian hard corals in Peninsular Malaysia have not been updated for 15 years. The present study aimed to determine the diversity and abundance patterns of scleractinian hard corals at twenty eight fringing reef sites along the coast of Redang and Tioman Islands. Visual photograph analyses of the coral video transect method revealed a total of 128 species from 47 genera in Redang and 239 species from 55 genera in Tioman. Following recent taxonomy of scleractinian corals, coral surveys and past studies revealed a total of 166 species from 53 genera in Redang and 350 species from 67 genera in Tioman. Current data at both islands presented a total of 358 species from 69 genera and 15 families of scleractinian corals with an additional 8 new species records for the east coast of Peninsular Malaysia. Acropora, Montipora and Porites were the most dominant genera and were found distributed within the coral assemblages. The reefs around both islands can be categorized under “good” coral conditions with the live corals cover from 40.9% to 73.5%. Overall findings indicated that the less affected reef zones by coastal development and human activities at both islands have established good coral conditions and coral genera diversity.

Molecular species delimitation of reef-building coral genera, Porites and Turbinaria (Anthozoa: Scleractinia), from the intertidal fringing reefs of Gulf of Kutch, India reveals unrecognized diversity

Knowledge of extant biodiversity with accurate species boundaries is one of the crucial prerequisites for guiding conservation priorities in the face of global climate change. DNA taxonomy promises to provide a rapid and reliable tool for species delimitation of morphologically challenging taxa, such as reef-building corals. Despite harbouring diverse coral assemblages, molecular studies of hard corals occurring in the seas around India are lacking. The Gulf of Kutch (GoK), located in the north-western part of India, is one such region. Information on coral species inhabiting this unique ecosystem is limited to morphology, which is often highly variable and phenotypically plastic, obscuring species boundaries. Here, we present the first exploration of molecular divergence of hard corals of the GoK in order to identify evolutionarily distinct lineages. Nuclear ribosomal ITS and mitochondrial COI markers were sequenced for samples of dominant genera, Porites and Turbinaria for phylogenetic comparisons with available data from other ecosystems of the world. Five molecular species delimitation methods were applied to the datasets and their performance was evaluated. Our analyses clearly suggest the occurrence of unique genotypes of both these genera in the GoK, unequivocally discerned by all the five methods as well as microskeletal features. This first integrative assessment provides implications for the phylogeny of these genera and identifies previously unrecognized scleractinian species hidden in the GoK ecoregion.

Spatial variability in benthic assemblage composition in shallow and upper mesophotic coral ecosystems in the Philippines

Mesophotic coral ecosystems (MCEs) have received increasing attention in recent years in recognition of their unique biodiversity and also their potential importance as refuges from disturbance events. However, knowledge of the composition of MCEs and how they vary in space is lacking in many regions, particularly the Coral Triangle biodiversity hotspot. Here, we compared the benthic components and coral genera composition between shallow-water reefs (SWRs, 8–13 m depth) and upper MCEs (30–40 m) in four locations in the Philippines that are exposed to differing environmental conditions. Coral cover, abundance, and generic diversity were lower in MCEs than SWRs at three of the four locations. Benthic composition and coral generic composition also varied significantly among locations for both shallow and deep sites. Differences in benthic composition among sites was due primarily to variation in hard corals, macroalgae, sand and silt, while variation in coral assemblage was due to differences in abundance of encrusting Porites, branching Acropora, branching Seriatopora. Our results showed that the composition of MCE communities varied significantly from adjacent shallow reefs, but also among MCEs in differing geographic locations. Furthermore, our results suggest disturbances affecting shallow-water reefs, particularly sedimentation, also negatively impact MCEs, and that depth therefore provides no potential refuge from these disturbances. We recommend that conservation of MCEs consider spatial variability in community composition among sites, and urge further research to better understand the spatial variation in the composition of MCE communities in the Philippines.

Social-environmental drivers inform strategic management of coral reefs in the Anthropocene.

Without drastic efforts to reduce carbon emissions and mitigate globalized stressors, tropical coral reefs are in jeopardy. Strategic conservation and management requires identification of the environmental and socioeconomic factors driving the persistence of scleractinian coral assemblages-the foundation species of coral reef ecosystems. Here, we compiled coral abundance data from 2,584 Indo-Pacific reefs to evaluate the influence of 21 climate, social and environmental drivers on the ecology of reef coral assemblages. Higher abundances of framework-building corals were typically associated with: weaker thermal disturbances and longer intervals for potential recovery; slower human population growth; reduced access by human settlements and markets; and less nearby agriculture. We therefore propose a framework of three management strategies (protect, recover or transform) by considering: (1) if reefs were above or below a proposed threshold of >10% cover of the coral taxa important for structural complexity and carbonate production; and (2) reef exposure to severe thermal stress during the 2014-2017 global coral bleaching event. Our findings can guide urgent management efforts for coral reefs, by identifying key threats across multiple scales and strategic policy priorities that might sustain a network of functioning reefs in the Indo-Pacific to avoid ecosystem collapse.

El Niño-associated catastrophic coral mortality at Jarvis Island, central Equatorial Pacific

The 2014–2017 Global Coral Bleaching Event is the longest, most widespread, and impactful on record. Rapid ecological assessment surveys by NOAA’s Pacific Reef Assessment and Monitoring Program reported widespread coral mortality at Jarvis Island in the aftermath of the 2015–2016 super-El Nino warming event; hard coral cover declined from 18.7% in April 2015 (pre-bleaching) to 0.4% in May 2016 (post-bleaching), representing a catastrophic > 98% decline. Between 2015 and 2016, corals at Jarvis experienced maximum heat stress of 22.25 °C-weeks exceeding the bleaching threshold (28.72 °C) for 66 consecutive weeks. Mass coral bleaching was observed in November 2015, which resulted in mass mortality across all coral taxa, depths, and island sectors. The bleaching event altered the benthic community composition including the coral assemblage. In the 2 yrs post-bleaching, the benthic community has transitioned from a short-lived increase of encrusting macroalgae to a more recent near-recovery of crustose coralline algae. Coral cover had not recovered by 2017 and could be potentially delayed by fast-growing turf algae. Within the coral community, the pre-bleaching dominant genus Montipora exhibited extreme mortality and only a handful of colonies of this taxon were enumerated in the 2016 surveys and none in 2017. Some coral taxa have persisted in low densities, including the ESA-threatened Acropora retusa and colonies of encrusting Pavona, Psammocora, and the free living Fungia. As the frequency and intensity of these high-temperature events is projected to increase in coming years, it is essential to track how remote ecosystems normally undisturbed by human influence, such as Jarvis, respond to a climate change.

Reef fish larvae visually discriminate coral diversity during settlement

To survive the pelagic stage, reef fish larvae need to find a settlement habitat and determine its suitability using a combination of environmental cues. Previous studies have shown that fish larvae are attracted by different components of their settlement habitat, such as conspecifics, algae, coral rubble, or living corals. However, it is not known whether larval fish use coral diversity as a settlement cue. Here, we tested the ability of presettlement reef fish larvae to discriminate coral diversity in laboratory experiments. We constructed coral assemblages of equal surface area, but with different coral species richness using live coral colonies of five species [Acropora cervicornis (Lamarck, 1816), Dichocoenia stokesii Milne-Edwards and Haime, 1848, Montastrea cavernosa (Linnaeus, 1767), Siderastrea siderea (Ellis and Solander, 1786), and Stephanocoenia intersepta (Lamarck, 1836)] and recorded the settlement choice of individual reef fish larvae. We found that reef fish larvae seem to prefer to settle on assemblages with higher coral diversity, regardless of the species used. We then used a two-choice tank to test the potential of reef fish larvae to visually perceive different coral species diversity and found that higher diversity attracts more settlement stage reef fish larvae, potentially changing the distribution of settlers at local scales. If preference for higher coral diversity stems from attraction to olfactory or other long-range cues—in addition to visual preference—coral diversity may play a role in connectivity among fish populations. This mechanism may further explain why degraded coral reefs do not maintain abundant fish populations.

Late Pleistocene reef fauna from the Red Sea coast, Northwest Saudi Arabia

ABSTRACT The Late Pleistocene reef unit of the last interglacial marine isotope stage 5e stretches all over most of the coastal cliffs and wadi cuts and interrupted only in wadi entrances along the Red Sea coast, northwest Saudi Arabia. It studied and sampled from 12 localities between Duba and Sharma for micro-and macrofossils record. Twenty-four foraminifera, 67 coral, 79 gastropod and 63 bivalve species were identified. The identified assemblages, particularly scleractinians indicated a deepening upward pattern for the studied late Pleistocene reef unit, starting with a coral assemblage of coral rock zone at the base, above a conglomeratic bed, followed by reef crest facies, and grades into the upper reef slope assemblages. The recorded taxa mostly have the Indo-Pacific affinity, and few elements have Atlantic-Mediterranean and cosmopolitan realm.

Resolving the depth zonation paradox in reef-building corals.

Changes in abundance across a natural environmental gradient provide important insights into a species' realized ecological niche. In reef-building corals, a species' niche is often defined using its depth range. However, most reef-building coral species occur over a broad depth range, a fact that is incompatible with the strong zonation found in coral assemblages across depth. We resolve this paradox by modeling the abundance distributions of 110 coral species across a 45m depth gradient to show that most are in fact depth specialists and reveal that depth range alone is incapable of capturing a species' depth use. We then highlight the significance of our results by demonstrating how depth range greatly overestimates the potential number of species with a refuge at depth from global warming. Our findings illustrate both the limitations of the simple metric of depth range and the ecological insights that can be gained by moving beyond it.

High coral reef connectivity across the Indian Ocean is revealed 6\u20137\xa0Ma ago by a turbid-water scleractinian assemblage from Tanzania (Eastern Africa)

The present centre of coral diversity in the Western Indian Ocean is defined by the northern Mozambique Channel with an extension northward to Mafia Island in Tanzania (Eastern Africa). The geological and evolutionary history of this hotspot of marine biodiversity remains so far completely obscure, because Cenozoic fossil reef communities of this area are not well known. This study presents a new fossil scleractinian fauna from the Mikindani Formation in southern Tanzania. It comprises 16 symbiotic coral taxa of which nine could be identified to the species and five to the genus level. Coral habitat consisted of low-relief biostromes that developed in shallow water at the front of the Rovuma Delta under conditions of variable sediment input. The biostromes are dated to be Messinian based on associated calcareous nannoplankton and planktic foraminifers. The studied coral assemblage shows close affinities with the Recent Western Indian Ocean biogeographic province and Central Indo-West Pacific biogeographic region as well as with the Miocene of Indonesia. Faunistic relations with the Oligocene-early Miocene of Somalia and Iran do not exist. The patterns of species distribution document a major palaeobiogeographic change in the Indian Ocean that correlates with the onset of the Miocene Indian Ocean Equatorial Jet during the middle Miocene. The clear Indonesian affinity of the Messinian coral fauna from southern Tanzania implies that this westerly oceanic surface current provided high biogeographic connectivity across the Indian Ocean during the late Miocene. Today, the coastal waters of Indonesia are located in the Coral Triangle. Diversification of this global epicentre of marine biodiversity started in the early Miocene and it was established already during the middle Miocene. Our results indicate that the East African hotspot of coral biodiversity originated as an offshoot of the Coral Triangle in the middle to late Miocene.

Response of Corals Acropora pharaonis and Porites lutea to Changes in pH and Temperature in the Gulf

Coral reefs are harboring a large part of the marine biodiversity and are important ecosystems for the equilibrium of the oceans. As a consequence of anthropogenic CO2 emission, a drop in pH and an increase in seawater temperature is observed in the Gulf coastal waters that potentially threaten coral assemblages. An experimental study was conducted on two species of corals to assess the effect of ocean warming and ocean acidification on the net calcification rate. Two pH conditions 8.2 and 7.5 and three temperatures, 22.5, 27.5 and 32.5 °C, were considered. Net calcification rates were measured using 45Ca radiotracer. Both temperature and pH had a significant effect on net calcification rates following a similar pattern for both species. The highest calcification rate was observed at low temperature and high pH. Increased temperature and decreased pH led to a decrease in net calcification rates. An interactive effect was observed as the effect of pH decreased with increasing temperature. However, the two species of coral were able to calcify in all the tested combination of temperature and pH suggesting that they are adapted to short term changes in temperature and pH. Ability to calcify even at a high temperature of 32.5 °C that is identical to the summertime Gulf seawater temperature under both the ambient and low pH condition with no mortalities, raises a question: are these corals adapted to high seawater temperatures and low pH? More in-depth assessments will be required to confirm if this is an adaptation to higher temperatures in Persian Gulf corals.