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Herbivory is widely accepted as a vital function on coral reefs. To date, the majority of studies examining herbivory in coral reef environments have focused on the roles of fishes and/or urchins, with relatively few studies considering the potential role of macroherbivores in reef processes. Here, we introduce evidence that highlights the potential role of marine turtles as herbivores on coral reefs. While conducting experimental habitat manipulations to assess the roles of herbivorous reef fishes we observed green turtles (Chelonia mydas) and hawksbill turtles (Eretmochelys imbricata) showing responses that were remarkably similar to those of herbivorous fishes. Reducing the sediment load of the epilithic algal matrix on a coral reef resulted in a forty-fold increase in grazing by green turtles. Hawksbill turtles were also observed to browse transplanted thalli of the macroalga Sargassum swartzii in a coral reef environment. These responses not only show strong parallels to herbivorous reef fishes, but also highlight that marine turtles actively, and intentionally, remove algae from coral reefs. When considering the size and potential historical abundance of marine turtles we suggest that these potentially valuable herbivores may have been lost from many coral reefs before their true importance was understood.

On September 29, 2009 at 17:48 UTC, an Mw = 8.1 earthquake in the Tonga Trench generated a tsunami that caused heavy damage across Samoa, American Samoa, and Tonga. One of the worst hits was the volcanic island of Tutuila in American Samoa. Tutuila has a typical tropical island bathymetry setting influenced by coral reefs, and so the event provided an opportunity to evaluate the relationship between tsunami dynamics and the bathymetry in that typical island environment. Previous work has come to differing conclusions regarding how coral reefs affect tsunami dynamics through their influence on bathymetry and dissipation. This study presents numerical simulations of this event with a focus on two main issues: first, how roughness variations affect tsunami run-up and whether different values of Manning’s roughness parameter, n, improve the simulated run-up compared to observations; and second, how depth variations in the shelf bathymetry with coral reefs control run-up and inundation on the island coastlines they shield. We find that no single value of n provides a uniformly good match to all observations; and we find substantial bay-to-bay variations in the impact of varying n. The results suggest that there are aspects of tsunami wave dissipation which are not captured by a simplified drag formulation used in shallow-water waves model. The study also suggests that the primary impact of removing the near-shore bathymetry in coral reef environment is to reduce run-up, from which we conclude that, at least in this setting, the impact of the near-shore bathymetry is to increase run-up and inundation.

The instrumental observations of dust storm (DS) in China and in most countries of the world have only a history of 50–60 years, and the DS variability beyond this timescale cannot be understood properly. Here, we show that the DS frequency can be reconstructed using the coral reef environment records as a proxy. Based on the high-resolution sea surface temperature (SST) records previously reconstructed by Liu et al. (2008) and Sun et al. (2004), we reconstructed the variations of DS frequency and strong wind frequency in China from 1908 to 1959, using the 5-year moving average of the longitudinal SST gradient (GX-H,SST,5m) in the northern South China Sea (SCS) as an indicator. The calibration equation shows that GX-H,SST,5m explains 66% of the variation in the 5-year average of the DS frequency (FDS,5m) and 86% of the variation in the 5-year moving average of strong wind (FSW,5m) in China, respectively. A comparison between the reconstructed long series (1908–1990) and the observed short series (1960–1990) FDS,5m indicates that the mean, maximum, and minimum of the latter series is 10.8, 20.9, and 36.1% smaller than that of the former, demonstrating that the DS frequency strongly depends on timescales; the statistical characteristics over short timescales are quite different from those over long timescales.

Natural and anthropogenic disturbances are leading to changes in the nature of many habitats globally, and the magnitude and frequency of these perturbations are predicted to increase under climate change. Globally coral reefs are one of the most vulnerable ecosystems to climate change. Fishes often show relatively rapid declines in abundance when corals become stressed and die, but the processes responsible are largely unknown. This study explored the mechanism by which coral bleaching may influence the levels and selective nature of mortality on a juvenile damselfish, Pomacentrus amboinensis, which associates with hard coral. Recently settled fish had a low propensity to migrate small distances (40 cm) between habitat patches, even when densities were elevated to their natural maximum. Intraspecific interactions and space use differ among three habitats: live hard coral, bleached coral and dead algal-covered coral. Large fish pushed smaller fish further from the shelter of bleached and dead coral thereby exposing smaller fish to higher mortality than experienced on healthy coral. Small recruits suffered higher mortality than large recruits on bleached and dead coral. Mortality was not size selective on live coral. Survival was 3 times as high on live coral as on either bleached or dead coral. Subtle behavioural interactions between fish and their habitats influence the fundamental link between life history stages, the distribution of phenotypic traits in the local population and potentially the evolution of life history strategies.

Shallow water coral reefs are the most diverse marine ecosystems, but there is an immense gap in knowledge when it comes to understanding the diversity of the vast majority of marine biota in these ecosystems. This is especially true when it comes to understudied small and cryptic coral reef taxa in understudied ecosystems, such as mesophotic coral reef ecosystems (MCEs). MCEs were reported in Japan almost fifty years ago, although only in recent years has there been an increase in research concerning the diversity of these reefs. In this study we describe the first stoloniferous octocoral from MCEs, Hadaka nudidomus gen. nov. et sp. nov., from Iriomote and Okinawa Islands in the southern Ryukyus Islands. The species is zooxanthellate; both specimens host Cladocopium LaJeunesse & H.J.Jeong, 2018 (formerly Symbiodinium ‘Clade C’) and were collected from depths of ~33 to 40 m. Additionally, H. nudidomus gen. nov. et sp. nov. is both sclerite-free and lacks free pinnules, and both of these characteristics are typically diagnostic for octocorals. The discovery and morphology of H. nudidomus gen. nov. et sp. nov. indicate that we still know very little about stoloniferous octocoral diversity in MCEs, their genetic relationships with shallower reef species, and octocoral–symbiont associations. Continued research on these subjects will improve our understanding of octocoral diversity in both shallow and deeper reefs.

The scarcity of the isopod material of the fossil sites from the \"Pesciara di Bolca\" (Verona Province, Northern Italy) did not leave much room up to now for conclusions concerning the systematic relationship of this fauna. In this study, we reinvestigate fossils of the cymothoidan Palaega acuticauda Secretan, 1975 and the sphaeromatidean Heterosphaeroma veronensis Secretan, 1975. We argue that both species do not differ substantially in dorsal morphology from recent genera, and we place them among more likely congeners: Cirolana acuticauda n. comb., and Dynamenella veronensis n. comb. A detailed redescription of both species is made on the basis of additional material that came from Pesciara di Bolca and Monte Postale marine fish and terrestrial plant bearing layers. Two environmental scenarios are discussed: one in which the palaeoenvironment is thought to be mainly lacustrine, another in which discoveries of more fossil sphaeromatideans and other cymothoidans in Italy suggest seawater affinities, coral reef environments, or estuarine conditions.

This contribution will expose and discuss the environmental impacts of tourism on the coral reef environment through the analysis of case studies of Indian Ocean and Caribbean Island Developing States. The objective is to demonstrate that the situation of islands and archipelagos is complex and diverse as numerous factors influence both the nature and extent of tourism environmental impacts and as tourism development produces contradictory impacts on the coastal environment. As a consequence, diagnosis must be moderate and gross generalization avoided. The first part of this paper will expose the major physical constraints that such countries have to face in order to achieve economic growth, as the reduction of these constraints largely determines the adverse environmental impacts of coastal development. Secondly, we will present the most common negative impacts of tourism-related projects and tourism activities on the coral reef environment. Then, we will demonstrate that tourism development has often played a major role in the setting up of coastal planning and environment preservation in various ways. Finally, we will sum up the main drivers of tourism environmental impacts.

With the ongoing loss of coral cover and the associated flattening of reef architecture, understanding the links between coral habitat and reef fishes is of critical importance. Here, we investigate whether considering coral traits and functional diversity provides new insights into the relationship between structural complexity and reef fish communities, and whether coral traits and community composition can predict structural complexity. Across 157 sites in Seychelles, Maldives, the Chagos Archipelago, and Australia’s Great Barrier Reef, we find that structural complexity and reef zone are the strongest and most consistent predictors of reef fish abundance, biomass, species richness, and trophic structure. However, coral traits, diversity, and life histories provided additional predictive power for models of reef fish assemblages, and were key drivers of structural complexity. Our findings highlight that reef complexity relies on living corals—with different traits and life histories—continuing to build carbonate skeletons, and that these nuanced relationships between coral assemblages and habitat complexity can affect the structure of reef fish assemblages. Seascape-level estimates of structural complexity are rapid and cost effective with important implications for the structure and function of fish assemblages, and should be incorporated into monitoring programs.

Difficulties in scaling up theoretical and experimental results have raised controversy over the consequences of biodiversity loss for the functioning of natural ecosystems. Using a global survey of reef fish assemblages, we show that in contrast to previous theoretical and experimental studies, ecosystem functioning (as measured by standing biomass) scales in a non-saturating manner with biodiversity (as measured by species and functional richness) in this ecosystem. Our field study also shows a significant and negative interaction between human population density and biodiversity on ecosystem functioning (i.e., for the same human density there were larger reductions in standing biomass at more diverse reefs). Human effects were found to be related to fishing, coastal development, and land use stressors, and currently affect over 75% of the world's coral reefs. Our results indicate that the consequences of biodiversity loss in coral reefs have been considerably underestimated based on existing knowledge and that reef fish assemblages, particularly the most diverse, are greatly vulnerable to the expansion and intensity of anthropogenic stressors in coastal areas.

A manipulative experiment in which a reef is alkalinized in situ shows that calcification rates are likely to be lower already than they were in pre-industrial times because of acidification. Ocean acidification effects on coral Ocean acidification is one of several factors projected to threaten coral reef ecosystems, but disentangling its effects from other factors such as temperature is difficult. These authors used a manipulative experiment in which sodium hydroxide was added to seawater flowing over a natural coral reef community in situ . When ocean chemistry was restored closer to pre-industrial conditions, net community calcification increased. This suggests calcification rates are already lower than they were in pre-industrial times because of acidification. Deliberate alkalinization has been proposed as a geoengineering technique to offset ocean acidification, and this work suggests that the method could be effective, but only on a small scale — in protected bays or lagoons, for example. Approximately one-quarter of the anthropogenic carbon dioxide released into the atmosphere each year is absorbed by the global oceans, causing measurable declines in surface ocean pH, carbonate ion concentration ([CO 3 2− ]), and saturation state of carbonate minerals ( Ω ) 1 . This process, referred to as ocean acidification, represents a major threat to marine ecosystems, in particular marine calcifiers such as oysters, crabs, and corals. Laboratory and field studies 2 , 3 have shown that calcification rates of many organisms decrease with declining pH, [CO 3 2− ], and Ω . Coral reefs are widely regarded as one of the most vulnerable marine ecosystems to ocean acidification, in part because the very architecture of the ecosystem is reliant on carbonate-secreting organisms 4 . Acidification-induced reductions in calcification are projected to shift coral reefs from a state of net accretion to one of net dissolution this century 5 . While retrospective studies show large-scale declines in coral, and community, calcification over recent decades 6 , 7 , 8 , 9 , 10 , 11 , 12 , determining the contribution of ocean acidification to these changes is difficult, if not impossible, owing to the confounding effects of other environmental factors such as temperature. Here we quantify the net calcification response of a coral reef flat to alkalinity enrichment, and show that, when ocean chemistry is restored closer to pre-industrial conditions, net community calcification increases. In providing results from the first seawater chemistry manipulation experiment of a natural coral reef community, we provide evidence that net community calcification is depressed compared with values expected for pre-industrial conditions, indicating that ocean acidification may already be impairing coral reef growth.