Cycles of coral reef ‘turn-on’, rapid growth and ‘turn-off’ over the past 8,500 years: a context for understanding modern ecological states and trajectories.

This is the author's post-print version of an article published in Global Change Biology, Vol. 17, pp. 76 - 86. Copyright © Wiley-Blackwell 2011. The definitive version is available at www3.interscience.wiley.comHuman activities threaten reef ecosystems globally, forcing ecological change at rates and scales regarded as unprecedented in the Holocene. These changes are so profound that a cessation of reef accretion (reef ‘turn-off’) and net erosion of reef structures is argued by many as the ultimate and imminent trajectory. Here, we use a regional scale reef growth dataset, based on 76 core records (constrained by 211 radiometric dates) from 22 reefs along and across the inner-shelf of the Great Barrier Reef, Australia, to examine the timing of different phases of reef initiation (‘turn-on’), growth and ‘turn-off’ during the Holocene. This dataset delineates two temporally discrete episodes of reef-building over the last 8500 years: the first associated with the Holocene transgression-early highstand period [∼8.5–5.5 k calibrated years bp (cal ybp)]; the second since ∼2.3 k cal ybp. During both periods, reefs accreted rapidly to sea level before entering late evolutionary states – states naturally characterized by reduced coral cover and low accretion potential – and a clear hiatus occurs between these reef-building episodes for which no records of reef initiation exist. These transitions mimic those projected under current environmental disturbance regimes, but have been driven entirely by natural forcing factors. Our results demonstrate that, even through the late Holocene, reef health and growth has fluctuated through cycles independent of anthropogenic forcing. Consequently, degraded reef states cannot de facto be considered to automatically reflect increased anthropogenic stress. Indeed, in many cases degraded or nonaccreting reef communities may reflect past reef growth histories (as dictated by reef growth–sea level interactions) as much as contemporary environmental change. Recognizing when changes in reef condition reflect these natural ‘turn-on’– growth –‘turn-off’ cycles and how they interact with on-going human disturbance is critical for effective coral reef management and for understanding future reef ecological trajectories

Transitions in coral reef accretion rates linked to intrinsic ecological shifts on turbid-zone nearshore reefs

Nearshore coral communities within turbid settings are typically perceived to have limited reef-building capacity. However, several recent studies have reported reef growth over millennial time scales within such environments and have hypothesized that depth-variable community assemblages may act as equally important controls on reef growth as they do in clear-water settings. Here, we explicitly test this idea using a newly compiled chronostratigraphic record (31 cores, 142 radiometric dates) from seven proximal (but discrete) nearshore coral reefs located along the central Great Barrier Reef (Australia). Uniquely, these reefs span distinct stages of geomorphological maturity, as reflected in their elevations below sea level. Integrated age-depth and ecological data sets indicate that contemporary coral assemblage shifts, associated with changing light availability and wave exposure as reefs shallowed, coincided with transitions in accretion rates at equivalent core depths. Reef initiation followed a regional ∼1 m drop in sea level (1200–800 calibrated yr B.P.) which would have lowered the photic floor and exposed new substrate for coral recruitment by winnowing away fine seafloor sediments. We propose that a two-way feedback mechanism exists where past growth history influences current reef morphology and ecology, ultimately driving future reef accumulation and morphological change. These findings provide the first empirical evidence that nearshore reef growth trajectories are intrinsically driven by changes in coral community structure as reefs move toward sea level, a finding of direct significance for predicting the impacts of extrinsically driven ecological change (e.g., coral-algal phase shifts) on reef growth potential within the wider coastal zone on the Great Barrier Reef

eReefs modelling suggests Trichodesmium may be a major nitrogen source in the Great Barrier Reef

Trichodesmium can fix nitrogen that is later released into the water column. This process may be a major source of ‘new’ nitrogen in the Great Barrier Reef (GBR), but to date this contribution is poorly resolved. We have estimated the seasonal, spatial and annual contributions of Trichodesmium to the annual nitrogen budget of the GBR using the eReefs marine models. Models were run for the interval December 2010 to November 2012. During this period La Niña conditions produced record rainfalls and widespread flooding of GBR catchments. Model outputs suggest nitrogen fixation by Trichodesmium in the GBR (which covers about 348,000 km2) contributes approximately 0.5 MT/yr, exceeding the total average annual riverine nitrogen loads (0.05–0.08 MT/yr). Nitrogen fixation loads are exceeded by riverine loads only if the comparison is restricted to inshore waters and during the wet season. The river pollution is likely to have impacts in freshwater wetlands, mangroves, seagrasses and in-shore coral reefs; while Trichodesmium blooms are likely to be less intense but more widespread and affect offshore coral reefs and other oceanic ecosystems. Phosphorus and iron are suggested to be potential drivers of Trichodesmium growth and nitrogen fixation. This result is provisional but reinforces the need for more detailed assessment and reliable quantification of the annual nitrogen contribution from nitrogen fixation in the GBR and other coastal waters. Such advances will improve understandings of the role of terrestrial nitrogen loads in the GBR and of terrestrial phosphorus and iron loads which can modulate Trichodesmium abundance. These findings will help to broaden the focus of water quality management programmes and support management to improve GBR water quality

Color pattern complexity in dwarf minke whales (Balaenoptera acutorostrata) of the northern Great Barrier Reef of Australia

Complex color patterning is a characteristic feature of dwarf minke whales (DMWs; Balaenoptera acutorostrata) which has been used to photographically identify (photo-ID) individuals and to research an aggregation on Australia's Great Barrier Reef (GBR). DMW color patterns have been described and applied in various studies, but a detailed and systematic analysis of their complexity is yet to be performed. Here, we applied a novel categorization tool to assess the variation, asymmetry, and association of several DMW color pattern elements, subelements, and their character states. Proportions, hierarchical clustering, and multiple correspondence analysis revealed a high level of asymmetric color pattern variation, with white markings dominant and associated on the right of the body. Our results will improve the citizen science driven photo-ID of this little-known cetacean as labor-intensive manual methods transition to more efficient automated approaches. Such advancement will be challenging, yet beneficial for broader research into the poorly understood areas of DMW life history, evolution, genetics, social structure, and feeding. This could also potentially allow investigation into the functional significance of their color patterns

Multi-scale records of reef development and condition provide context for contemporary changes on inshore reefs

Comparisons between historical and contemporary photographs of coral reef flats from the inshore Great Barrier Reef (GBR) have been cited by various authors and agencies as evidence of reef degradation since European settlement and have been presented as proof of widespread reef decline. The diminished condition is inferred from reduced live coral cover and structural diversity depicted in the contemporary photographs. Anthropogenic causes for this deterioration are most often proposed, usually because it is argued to have coincided with modifications to coastal catchments by European settlers. However, changes in reef condition inferred from photographic comparisons have rarely been verified against quantitative assessments of reef geomorphic state or current reef status. Photographs taken in the late 1800s of the reef flat at Stone Island, located in Edgecumbe Bay in the inshore central GBR, have been compared by others with more recent images to interpret significant reductions in coral cover and diversity over the past 120 or so years. We examined the internal structure of fringing reefs at two locations on Stone Island by collecting 14 percussion cores across the reef flats. Sedimentological analyses coupled with uranium-thorium dating allowed for the reconstruction of reef development over the past ~ 7000 years. Both reefs at Stone Island initiated prior to 7000 calendar years before present (yBP, where present is 1950 AD) and both reef flats were almost entirely emplaced by 4000 yBP. Surveys of the benthic ecology of reefs at Stone Island and at Middle Island, also in Edgecumbe Bay, indicate that coral cover and diversity across reef flats and slopes was patchy and varied spatially within each location and throughout the region. Live coral cover on the Middle Island reef flat reached an average (± 1σ standard deviation) of 63.1 ± 20.2%. This was much higher than the live coral cover on Stone Island reef flats, where only a few small living coral colonies were recorded. We evaluate the use of photographic records from Stone Island to depict regional changes in reef condition by comparing the trends in reef condition determined from photographic records with underlying reef geomorphic state reconstructed from reef cores. We conclude that inferred changes in reef condition at Stone Island are localised and should not be used as evidence of widespread regional decline on the GBR

Fine-suspended sediment and water budgets for a large, seasonally dry tropical catchment: Burdekin River catchment, Queensland, Australia

The Burdekin River catchment (~130,400 km2) is a seasonally dry tropical catchment located in north-east Queensland, Australia. It is the single largest source of suspended sediment to the Great Barrier Reef (GBR). Fine sediments are a threat to ecosystems on the GBR where they contribute to elevated turbidity (reduced light), sedimentation stress, and potential impacts from the associated nutrients. Suspended sediment data collected over a 5 year period were used to construct a catchment-wide sediment source and transport budget. The Bowen River tributary was identified as the major source of end-of-river suspended sediment export, yielding an average of 530 t km−2 yr−1 during the study period. Sediment trapping within a large reservoir (1.86 million ML) and the preferential transport of clays and fine silts downstream of the structure were also examined. The data reveal that the highest clay and fine silt loads—which are of most interest to environmental managers of the GBR—are not always sourced from areas that yield the largest total suspended sediment load (i.e., all size fractions). Our results demonstrate the importance of incorporating particle size into catchment sediment budget studies undertaken to inform management decisions to reduce downstream turbidity and sedimentation. Our data on sediment source, reservoir influence, and subcatchment and catchment yields will improve understandings of sediment dynamics in other tropical catchments, particularly those located in seasonally wet-dry tropical savannah/semiarid climates. The influence of climatic variability (e.g., drought/wetter periods) on annual sediment loads within large seasonally dry tropical catchments is also demonstrated by our data

Comprehensive investigation of congenital anomalies in cerebral palsy: Protocol for a European-Australian population-based data linkage study (The Comprehensive CA-CP Study)

INTRODUCTION:Cerebral palsy (CP), an umbrella term for non-progressive conditions of cerebral origin resulting in motor impairments, is collectively the most common cause of physical disability in childhood. Cerebral and/or non-cerebral congenital anomalies are present in 15%-40% of children with CP. In order to identify effective prevention strategies for this substantial proportion of CP, a comprehensive understanding of the epidemiology of these congenital anomalies is required. International collaboration is needed, as previous attempts have fallen short due to a lack of power, since the anomalies are individually rare and CP comprises many clinical descriptions. The aim of this study is to generate new knowledge about the aetiologies of CP through a focused investigation into the role of congenital anomalies. METHODS AND ANALYSIS:This collaborative, population-based data linkage study includes nine geographic regions (six in Europe, three in Australia) served by both congenital anomaly and CP registers. Register data for children with CP (both with and without congenital anomalies) and children with specific congenital anomalies (without CP) born between 1991 and 2009 will be linked and de-identified within each region. The resulting linked data sets will be quality assured, recoded, harmonised and then pooled into one data set. Analysis of the combined data set will include: frequencies/proportions of congenital anomalies and outcomes (type of CP, severity, impairments); descriptive analyses comparing timing of congenital anomaly development and brain injury/abnormality responsible for CP; ORs to calculate the odds of CP following a specific congenital anomaly; and identification of anomalies on causal pathways to CP. ETHICS AND DISSEMINATION:Ethics approval for this collaborative study, The Comprehensive CA-CP Study, has been obtained from the Cerebral Palsy Alliance Human Research Ethics Committee (EC00402). Study findings will be disseminated at conferences and published in peer-reviewed journals, and recommendations will be made regarding the collection and classification of congenital anomaly data by CP registers.Shona Goldsmith, Guiomar Garcia Jalon, Nadia Badawi, Eve Blair, Ester Garne, Catherine Gibson ... et al

Global declines in coral reef calcium carbonate production under ocean acidification and warming

Ocean warming and acidification threaten the future growth of coral reefs. This is because the calcifying coral reef taxa that construct the calcium carbonate frameworks and cement the reef together are highly sensitive to ocean warming and acidification. However, the global-scale effects of ocean warming and acidification on rates of coral reef net carbonate production remain poorly constrained despite a wealth of studies assessing their effects on the calcification of individual organisms. Here, we present global estimates of projected future changes in coral reef net carbonate production under ocean warming and acidification. We apply a meta-analysis of responses of coral reef taxa calcification and bioerosion rates to predicted changes in coral cover driven by climate change to estimate the net carbonate production rates of 183 reefs worldwide by 2050 and 2100. We forecast mean global reef net carbonate production under representative concentration pathways (RCP) 2.6, 4.5, and 8.5 will decline by 76, 149, and 156%, respectively, by 2100. While 63% of reefs are projected to continue to accrete by 2100 under RCP2.6, 94% will be eroding by 2050 under RCP8.5, and no reefs will continue to accrete at rates matching projected sea level rise under RCP4.5 or 8.5 by 2100. Projected reduced coral cover due to bleaching events predominately drives these declines rather than the direct physiological impacts of ocean warming and acidification on calcification or bioerosion. Presently degraded reefs were also more sensitive in our analysis. These findings highlight the low likelihood that the world’s coral reefs will maintain their functional roles without near-term stabilization of atmospheric CO2 emissions

Supporting beginner teacher identity development: external mentors and the third space

This paper reports findings from a study of support provided by non-school-based mentors of secondary science teachers in England. It focuses on the identity development of beginning teachers of physics, some of the recipients of the mentoring. Drawing on the analysis of interview and case study data, and utilising third space theory, the authors show how external mentors (experienced, subject specialist teachers who were not based in the same schools as the teachers they were supporting) facilitated opportunities for mentees to negotiate and shape their professional identities, and made valuable contributions to three distinct and important aspects of beginning teachers’ identity development. The paper argues that non-judgemental support from external mentors enhances beginner teachers’ professional learning and identity development through the creation of a discursive ‘third’ space in which mentees are able to openly discuss professional learning and development needs, discuss alternatives to performative norms and take risks in classrooms. Opportunities for beginner teachers to engage in such activities are often restricted in and by the current climate of schooling and teacher education within England

Loss of coral reef growth capacity to track future increases in sea level

Water-depths above coral reefs is predicted to increase due to global sea-level rise (SLR). As ecological degradation inhibits the vertical accretion of coral reefs, it is likely that coastal wave exposure will increase but there currently exists a lack of data in projections concerning local rates of reef growth and local SLR. In this study we have aggregated ecological data of more than 200 tropical western Atlantic and Indian Ocean reefs and calculated their vertical growth which we have then compared with recent and projected rates of SLR across different Representative Concentration Pathway (RCP) scenarios. While many reefs currently show vertical growth that would be sufficient to keep-up with recent historic SLR, future projections under scenario RCP4.5 reveal that without substantial ecological recovery many reefs will not have the capacity to track SLR. Under RCP8.5, we predict that mean water depth will increase by over half a metre by 2100 across the majority of reefs. We found that coral cover strongly predicted whether a reef could track SLR, but that the majority of reefs had coral cover significantly lower than that required to prevent reef submergence. To limit reef submergence, and thus the impacts of waves and storms on adjacent coasts, climate mitigation and local impacts that reduce coral cover (e.g., local pollution and physical damage through development land reclamation) will be necessary