Degradation Of Coral Reef Habitats Research Articles

The effect of coral reef degradation on the trophic structure of reef fishes from Bahía Culebra, North Pacific coast of Costa Rica

Fishes play numerous key ecological roles that are critical for maintaining the structure and function of coral reefs. Natural and anthropogenic disturbances can produce structural changes in coral reef habitats, which consequently may affect the trophic structure and dynamics of reef fish assemblages. Therefore, changes in the coral cover of coral reefs, caused by disturbance events can impact the abundance of reef fishes. This study determined the effect of habitat degradation on the trophic structure of coral reef fishes from Bahia Culebra, a bay located in the north Pacific of Costa Rica. We examined whether spatial and temporal changes in live coral cover (LCC) and substrate type between two periods (1995–1996 and 2014–2016) influenced the trophic structure of coral reef fishes. While planktivorous fishes maintained similar abundances between periods, omnivorous fishes (mainly facultative corallivores) were less abundant in sites with low LCC. There was a decline in abundance of mesopredators (e.g. sharks, groupers, snappers), probably because of both shelter loss and overfishing. Macroalgae feeders, herbivores-detritivores and invertivores showed high abundance in disturbed coral reefs, which could be related to predator decline or to increased algal resource abundance. Despite high abundance of herbivorous fishes, high macroalgae coverage persisted during the 2014–2016 period. The results from this study suggest that degradation of coral reef habitats from Bahia Culebra have affected the trophic structure of reef fish assemblages, and potentially the functioning of this coastal ecosystem.

Bommies away! Logistics and early effects of repositioning 400 tonnes of displaced coral colonies following cyclone impacts on the Great Barrier Reef

SummaryFor over 40 years, management of the Great Barrier Reef Marine Park (GBRMP) in Australia has focused on limiting human‐use impacts to facilitate natural resilience and recovery. Compounding acute disturbances and chronic stressors have resulted in degradation of coral reef habitats in many areas of the Marine Park. Given current trends and predictions of escalating climate‐driven disturbances, it is increasingly evident that effective management of the GBRMP requires adaptive and novel approaches to protect and restore coral reef health. Here, we provide an overview of the logistical requirements and early‐stage ecological benefits of repositioning 400 tonnes of moderately sized (1–3 m diameter) Porites spp. coral colonies (bommies) that were displaced by cyclone‐generated swells that impacted reefs in the Whitsunday Islands during March 2017. An ecological survey conducted 16 months after the bommie repositioning revealed that several genera of hard coral had settled onto the bommies and that a range of reef fish species were associating with the restored habitat. Early findings suggest that the repositioning of the displaced bommies has assisted in restoring reef habitat structure and settlement habitat for juvenile corals, while improving natural aesthetics, vessel access and tourist experiences at Manta Ray Bay.

Changes in the population and community structure of corals during recent disturbances (February 2016-October 2017) on Maldivian coral reefs

Climate change is the greatest threat to coral reef ecosystems. In particular, increasing ocean temperatures are causing severe and widespread coral bleaching, contributing to extensive coral loss and degradation of coral reef habitats globally. Effects of coral bleaching are not however, equally apportioned among different corals, leading to shifts in population and community structure. This study explored variation in bleaching susceptibility and mortality associated with the 2016 severe mass bleaching in the Central Maldives Archipelago. Five dominant coral taxa (tabular Acropora, Acropora humilis, Acropora muricata, Pocillopora and massive Porites) were surveyed in February 2016 and October 2017 to test for changes in abundance and size structure. Substantial taxonomic differences in rates of mortality were observed; the most severely affected taxa, Acropora, were virtually extirpated during the course of this study, whereas some other taxa (most notably, massive Porites) were relatively unaffected. However, even the least affected corals exhibited marked changes in population structure. In February 2016 (prior to recent mass-bleaching), size-frequency distributions of all coral taxa were dominated by larger size classes with over-centralized, peaked distributions (negatively skewed with positive kurtosis) reflecting a mature population structure. In October 2017, after the bleaching, coral populations were dominated by smaller and medium size classes, reflecting high levels of mortality and injury among larger coral colonies. Pronounced changes in coral populations and communities in the Maldives, caused by coral bleaching and other disturbances (outbreaks of crown-of-thorns starfish and sedimentation), will constrain recovery capacity, further compounding upon recent coral loss.

Historical and contemporary determinants of global phylogenetic structure in tropical reef fish faunas

Identifying the main determinants of tropical marine biodiversity is essential for devising appropriate conservation measures mitigating the ongoing degradation of coral reef habitats. Based on a gridded distribution database and phylogenetic information, we compared the phylogenetic structure of assemblages for three tropical reef fish families (Labridae: wrasses, Pomacentridae: damselfishes and Chaetodontidae: butterflyfishes) using the net relatedness (NRI) and nearest taxon (NTI) indices. We then related these indices to contemporary and historical environmental conditions of coral reefs using spatial regression analyses. Higher levels of phylogenetic clustering were found for fish assemblages in the Indo‐Australian Archipelago (IAA), and more particularly when considering the NTI index. The phylogenetic structure of the Pomacentridae, and to a lower extent of the Chaeotodontidae and Labridae, was primarily associated with the location of refugia during the Quaternary period. Phylogenetic clustering in the IAA may partly result from vicariance events associated with coral reef fragmentation during the glacial periods of the Quaternary. Variation in the patterns among fish families further suggest that dispersal abilities may have interacted with past habitat availability in shaping the phylogenetic structure of tropical reef fish assemblages.

Patterns of recruitment and microhabitat associations for three predatory coral reef fishes on the southern Great Barrier Reef, Australia

This study examined recruitment patterns and microhabitat associations for three carnivorous fishes, Plectropomus maculatus, Lutjanus carponotatus and Epinephelus quoyanus, at the Keppel Islands, southern Great Barrier Reef, Australia. Habitat selectivity was highest for recruits that were found mostly with corymbose Acropora, predominantly on patches of live coral located over loose substrates (sand). Adults were more commonly associated with tabular Acropora. The proportion of P. maculatus (72 %) found with live corals was higher than for L. carponotatus (68 %) and E. quoyanus (44 %). Densities of recruits were highly variable among locations, but this was only partly related to availability of preferred microhabitats. Our findings demonstrate that at least some carnivorous reef fishes, especially during early life-history stages, strongly associate with live corals. Such species will be highly sensitive to increasing degradation of coral reef habitats.

Rarity and extinction risk in coral reef angelfishes on isolated islands: interrelationships among abundance, geographic range size and specialisation

Determining the species most vulnerable to increasing degradation of coral reef habitats requires identification of the ecological traits that increase extinction risk. In the terrestrial environment, endemic species often face a high risk of extinction because of an association among three traits that threaten species persistence: small geographic range size, low abundance and ecological specialisation. To test whether these traits are associated in coral reef fishes, this study compared abundance and specialisation in endemic and widespread angelfishes at the remote Christmas and Cocos Islands in the Indian Ocean. The interrelationships among traits conferring high extinction risk in terrestrial communities did not apply to these fishes. Endemic angelfishes were 50–80 times more abundant than widespread species at these islands. Furthermore, there was no relationship between abundance and ecological specialisation. Endemic species were not more specialised than widespread congeners and endemics used similar resources to many widespread species. Three widespread species exhibited low abundance and some degree of specialisation, which may expose them to a greater risk of local extinction. For endemic species, high abundance and lack of specialisation on susceptible habitats may compensate for the global extinction risk posed by having extremely small geographic ranges. However, recent extinctions of small range reef fishes confirm that endemics are not immune to the increasing severity of large-scale disturbances that can affect species throughout their geographic range.

Isolation and characterization of 29 microsatellite loci for studies of population connectivity in the butterflyfishes Chaetodon trifascialis and Chaetodon lunulatus

The highly specialised coral feeding butterflyfish Chaetodon trifascialis is increasingly threatened by the global degradation of coral reef habitats. To reveal the population genetic structure of C. trifascialis across its Indo-Pacific range, primers for thirteen independent microsatellite loci were developed. Observed heterozygosities ranged from 0.174 to 1 and expected heterozygosities ranged from 0.043 to 0.920 in 20 individuals from one Northern Great Barrier Reef location. Primers for 16 independent loci were also developed for the related butterflyfish Chaetodon lunlulatus to enable comparative studies of population genetic structure. These loci had observed heterozygosities ranging from 0.476 to 0.952 and expected heterozygosities ranging from 0.484 to 0.933. Good amplification success and levels of polymorphism were obtained when cross-testing the loci between the two species. These loci will therefore be useful to examine population genetic structure in C. trifascialis and C. lunulatus and possibly other related butterflyfish species.

Coral community dynamics at multiple scales

Our understanding of ecosystem dynamics is directly linked to the scale at which we make our ecological observations. The ecological dynamics of Pleistocene coral communities varies with spatial and temporal scale of study. Reef coral communities studied over small spatial and temporal scales show ecological chaos where disturbance prevents ecological equilibrium, and those studied at the largest biogeographic scales show large differences due to history, chance, dispersion, and regional-scale processes. However, communities that are located within tens of kilometers of one another appear to show a large degree of order, probably due to underlying principles of niche similarity. Similarly, temporal studies conducted over large temporal scales show persistence in coral community structure through tens of thousands of years. The history of Caribbean reef coral communities shows that this persistence has been recently interrupted by massive degradation of coral reef habitats. Whether such habitat reduction and change in species composition are unprecedented and due to the acceleration of human consumption and pollution, or whether they represent a short-term fluctuation in an otherwise predictable community structure, is one of the most important questions facing reef managers today. Investigations of coral community structure at different spatial scales illuminate the dependence of ecological dynamics on spatial scale, and at different temporal scales show that present trends are not predicted from history but may well be related to human-induced environmental modification.

Restoration of Coral Reefs in Pacific Costa Rica

Abstract: Loss and degradation of coral reef habitats are increasing in the eastern Pacific. Intense, frequent natural and human‐induced disturbances have devastated most reefs in this region during the last decade. Slow recovery combined with intense bioerosion has led to extensive destruction of the reef frameworks. At some reefs along the Pacific coast of Costa Rica, 100% mortality of the dominant coral (Pocillopora spp.) occurred in shallow water. Surviving individuals for some pocilloporid species are extremely small, and reef recovery by sexual or asexual means has been lowered A restoration experiment was conducted in two different shallow habitats inside a marine biological reserve. Coral fragments (n = 110) imported from nearby reefs were transplanted onto dead reef frameworks, and after three years, survivorship was 79%–83%. Furthermore, fragmentation caused a 41%–115% increase in new colonies. These results suggest that coral transplantation for reef management and restoration is a feasible tool in the eastern Pacific region.