Rapid increase in coral cover on an isolated coral reef, the Ashmore Reef National Nature Reserve, north-western Australia

Against a background of coral reef ecosystem decline, understanding the propensity for coral communities to recover after acute disturbances is fundamental to forecasting and maintaining resilience. It may be expected that offshore reef ecosystems are less affected by anthropogenic disturbances compared with reefs closer to population centres, but that recovery may be slower on isolated reefs following disturbances. To test the hypothesis that community recovery is slow in isolated locations, we measured changes in coral cover and relative abundance of coral genera over a 4 year period (200509) at Ashmore Reef, north Western Australia, following severe bleaching. The percent cover of hard coral tripled, from 10.2% (±1.46 s.e.) in 2005 to 29.4% (±1.83 s.e.) in 2009 in all habitats (exposed and lagoonal) and depth zones (25 and 810m), and the percent cover of soft corals doubled, from 4.5% (+0.63 s.e.) in 2005 to 8.3% (+1.4 s.e.) in 2009. Significant shifts in the taxonomic composition of hard corals were detected. Our results imply that coral recovery in isolated locations can occur rapidly after an initial delay in recruitment, presumably through the interacting effects of self-recruitment and reduced exposure to additive impacts such as coastal pollution

Bikini Atoll coral biodiversity resilience five decades after nuclear testing

Five decades after a series of nuclear tests began, we provide evidence that 70% of the Bikini Atoll zooxanthellate coral assemblage is resilient to large-scale anthropogenic disturbance. Species composition in 2002 was assessed and compared to that seen prior to nuclear testing. A total of 183 scleractinian coral species was recorded, compared to 126 species recorded in the previous study (excluding synonomies, 148 including synonomies). We found that 42 coral species may be locally extinct at Bikini. Fourteen of these losses may be pseudo-losses due to inconsistent taxonomy between the two studies or insufficient sampling in the second study, however 28 species appear to represent genuine losses. Of these losses, 16 species are obligate lagoonal specialists and 12 have wider habitat compatibility. Twelve species are recorded from Bikini for the first time. We suggest the highly diverse Rongelap Atoll to the east of Bikini may have contributed larval propagules to facilitate the partial resilience of coral biodiversity in the absence of additional anthropogenic threats

Taxonomy and phylogenetic relationships of the coral genera Australomussa and Parascolymia (Scleractinia, Lobophylliidae)

Novel micromorphological characters in combination with molecular studies have led to an extensive revision of the taxonomy and systematics of scleractinian corals. In the present work, we investigate the macro- and micromorphology and the phylogenetic position of the genera Australomussa and Parascolymia, two monotypic genera ascribed to the family Lobophylliidae. The molecular phylogeny of both genera was addressed using three markers, the partial mitochondrial COI gene and the nuclear histone H3 and the ribosomal ITS region. Based on molecular data, Australomussa and Parascolymia belong to the Lobophylliidae and they cluster together with the genera Lobophyllia and Symphyllia within the same clade. While A. rowleyensis and P. vitiensis are closely related based on the three gene regions examined, their macro and micromorphology suggest that these species are distinct, differing in several characters, such as continuity and thickness of the costosepta, the number of septa, septal tooth height, spacing, and shape, and the distribution and shape of granules. Thus, we revise the taxonomic status of the genus Australomussa as a junior synonym of Parascolymia

Diminishing potential for tropical reefs to function as coral diversity strongholds under climate change conditions

First published: 29 August 2021Aim: Forecasting the influence of climate change on coral biodiversity and reef functioning is important for informing policy decisions. Dominance shifts, tropicalization and local extinctions are common responses of climate change, but uncertainty surrounds the reliability of predicted coral community transformations. Here, we use species distribution models (SDMs) to assess changes in suitable coral habitat and associated patterns in biodiversity across Western Australia (WA) under present-day and future climate scenarios (RCP 2.6 and RCP 8.5). Location: Coral reef systems and communities in WA. Methods: We developed SDMs with model prediction uncertainty analyses, using specimen-based occurrence records of 188 hermatypic scleractinian coral species and seven variables to estimate present-day and future changes to coral species distribution and biodiversity patterns in WA under climate change conditions. Results: We found that suitable habitat is predicted to increase across all regions in WA under RCP (2050)(2.6), RCP (2050)(8.5) and RCP (2100)(2.6)scenarios with all tropical and subtropical regions remaining coral biodiversity strongholds. Under the extreme RCP (2100)(8.5) scenario, however, a clear tropicalization trend could be observed with coral species expanding their range to mid-high latitude regions, while a substantial drop in coral species richness was predicted at low latitude tropical coral reefs, such as the inshore Kimberley and offshore NW reefs. Despite the predicted expansion south, we identified a net decline in coral biodiversity across the WA coastline. Main conclusions: Results from the models predicted higher net coral biodiversity loss at low latitude tropical regions compared with net gains at mid-high latitude regions under RCP (2100)(8.5). These results are likely to be representative of latitudinal trends across the Southern Hemisphere and highlight that increases in habitat suitability at higher latitudes may not lead to equivalent biodiversity benefits. Urgent action is needed to limit climate change to prevent spatial erosion of tropical coral communities, extinction events and loss of tropical ecosystem services.Arne A. S. Adam, Rodrigo A. Garcia, Ronen Galaiduk, Sean Tomlinson, Ben Radford, Luke Thomas, Zoe T. Richard

Coringa-Herald National Nature Reserve Marine Survey 2007

This report combines the results of two surveys of coral, macroinvertebrate and fish communities in the Coringa-Herald National Nature Reserve (CHNNR or the Reserve). The first survey, conducted by JCU in May 2007, surveyed the Herald Cays (NE and SW Herald). The C&R Consulting survey in October 2007 focused on South East Magdelaine Cay (SE Magdelaine), Chilcott Islet (Chilcott) and South West Coringa Islet (Coringa). Ecological communities were found to be in a similar condition to those described in previous surveys, with very little recovery of hard coral cover.\ud \ud Reefs in the CHNNR support approximately 7.3% hard coral cover and a relatively species poor fish community. Coral cover, already historically low, has been slow to recover from disturbances in the last two decades, probably due largely to the small size of the reefs, as well as isolation and exposure. SE Magdelaine supported the highest coral cover, coral and reef fish diversity and the highest general abundance of surveyed reef species, while SW Herald had the largest populations of some large reef fish families. The presence of Pacific Ocean corals lends support to the suggestion that Coral Sea reefs provide stepping-stones for the dispersal of species between the Great Barrier Reef and Pacific Ocean reefs.\ud \ud Corals of the genus Acropora were expected to be diverse and abundant on the clearwater CHNNR reefs, but very few live or dead colonies were encountered during the survey. Acropora species are the most vulnerable to disturbance and are also early colonisers of disturbed sites. Along with the small size and sexual immaturity of other hard coral, soft coral and sponge colonies, the low cover of Acropora is typical of reefs in the early phase of recovery.\ud \ud Algal turf, coralline algae and Halimeda spp. were the predominant benthic taxa in the CHNNR. Algal turf is an important food source for a range of marine invertebrates and herbivorous fish, and was dominant primarily in sheltered back reef habitats, corresponding with the greatest density of large herbivorous fish. Coralline algae, often indicative of heavy grazing, was abundant on the reef front, and the low abundance of grazing herbivores in these habitats suggests that the high coralline algae cover is another historical feature of the reefs.\ud \ud Densities of holothurians and tridacnid clams were similar to those found in other surveys of isolated, oceanic reefs. Some holothurians of high commercial value were more abundant in the CHNNR, suggesting successful protection from exploitation. Gastropods valuable for the ornamental shell industry were found in high densities in some areas of the Reserve, indicating that it may be important to include these species in future surveys.\ud \ud Key fish species were found in low densities, potentially as a result of the low microhabitat complexity, resulting in lower food and habitat availability. Apex predators such as serranids and sharks, along with large keystone invertebrate feeders and herbivores, are economically valuable and globally vulnerable to overexploitation, highlighting the need for their protection and the careful monitoring and safeguarding of their habitat.\ud \ud By nature of their isolation, oceanic reefs such as those in the CHNNR harbour unique communities. They also have few sources of propagules, and tend to recover slowly from disturbance. Many key species occur in low numbers, making them highly vulnerable to local extinction. Recommendations arising from these surveys focus on the continued protection and effective monitoring of the Reserve. The protection of the hard coral community and of key fish and invertebrate species are crucial to the safeguarding of the resilience of these reefs in the light of expected climate change.\u

The state of Western Australia’s coral reefs

Western Australia’s coral reefs have largely escaped the chronic pressures affecting other reefs around the world, but are regularly affected by seasonal storms and cyclones, and increasingly by heat stress and coral bleaching. Reef systems north of 18°S have been impacted by heat stress and coral bleaching during strong El Niño phases and those further south during strong La Niña phases. Cumulative heat stress and the extent of bleaching throughout the northern reefs in 2016 were higher than at any other time on record. To assess the changing regime of disturbance to reef systems across Western Australia (WA), we linked their site-specific exposure to damaging waves and heat stress since 1990 with mean changes in coral cover. Since 2010, there has been a noticeable increase in heat stress and coral bleaching across WA. Over half the reef systems have been severely impacted by coral bleaching since 2010, which was further compounded by cyclones at some reefs. For most (75%) reef systems with long-term data (5–26 yrs), mean coral cover is currently at (or near) the lowest on record and a full recovery is unlikely if disturbances continue to intensify with climate change. However, some reefs have not yet experienced severe bleaching and their coral cover has remained relatively stable or increased in recent years. Additionally, within all reef systems the condition of communities and their exposure to disturbances varied spatially. Identifying the communities least susceptible to future disturbances and linking them through networks of protected areas, based on patterns of larval connectivity, are important research and management priorities in coming years while the causes of climate change are addressed