Hermatypic Coral Growth Banding as Environmental Recorder

Study of incremental banding in coral skeletons was initiated by Ma and later extended by Wells and others. More recently, discrete annual banding in the skeletons of certain hermatypic corals has been described. Here we present an analysis of annual band width measurements from Bermuda corals which relates, through regression techniques, coral band time series to air temperature and air pressure variations. Our results indicate that coral bands record important aspects of their environment and therefore become useful where reconstruction of palaeoclimatic variables is of interest. Specifically the coral time series may be used as a palaeotemperature indicator or, when coupled with relatively well established palaeotemperatures, for palaeobarometric pressure determinations. Derived series of otherwise unobtainable palaeovariables are important not only for work on coral physiology, but also for construction and testing of climatic models; in this later instance information on palaeopressure is particularly desirable

The potential for coral reef establishment through free-living stabilization

Corals thrive in a variety of environments, from low wave and tidal energy lagoons, to high energy tidal reef flats, but remain dependent upon suitable substrate. Herein we reviewed the phenomenon of free-living corals (coralliths), examined whether they have the capacity to create their own stable habitat in otherwise uninhabitable, poor substrate environments through 'free-living stabilization', and explore their potential ecological role on coral reefs. This stabilization could be achieved by coral settlement and survival on mobile substrate, with subsequent growth into free-living coralliths until a critical mass is reached that prevents further movement. This allows for secondary reef colonization by other coral species. To preliminarily test this hypothesis we provide evidence that the potential to support secondary coral colonisation increases with corallith size. Due to the limited diversity of corallith species observed here and in the literature, and the lack of physiological differences exhibited by coralliths here to static controls, it seems likely that only a small selection of coral species have the ability to form coralliths, and the potential to create their own stable habitat

Sensitivity of Calcification to Thermal Stress Varies among Genera of Massive Reef-Building Corals

Reductions in calcification in reef-building corals occur when thermal conditions are suboptimal, but it is unclear how they vary between genera in response to the same thermal stress event. Using densitometry techniques, we investigate reductions in the calcification rate of massive Porites spp. from the Great Barrier Reef (GBR), and P. astreoides, Montastraea faveolata, and M. franksi from the Mesoamerican Barrier Reef (MBR), and correlate them to thermal stress associated with ocean warming. Results show that Porites spp. are more sensitive to increasing temperature than Montastraea, with calcification rates decreasing by 0.40 g cm−2 year−1 in Porites spp. and 0.12 g cm−2 year−1 in Montastraea spp. for each 1°C increase. Under similar warming trends, the predicted calcification rates at 2100 are close to zero in Porites spp. and reduced by 40% in Montastraea spp. However, these predictions do not account for ocean acidification. Although yearly mean aragonite saturation (Ωar) at MBR sites has recently decreased, only P. astreoides at Chinchorro showed a reduction in calcification. In corals at the other sites calcification did not change, indicating there was no widespread effect of Ωar changes on coral calcification rate in the MBR. Even in the absence of ocean acidification, differential reductions in calcification between Porites spp. and Montastraea spp. associated with warming might be expected to have significant ecological repercussions. For instance, Porites spp. invest increased calcification in extension, and under warming scenarios it may reduce their ability to compete for space. As a consequence, shifts in taxonomic composition would be expected in Indo-Pacific reefs with uncertain repercussions for biodiversity. By contrast, Montastraea spp. use their increased calcification resources to construct denser skeletons. Reductions in calcification would therefore make them more susceptible to both physical and biological breakdown, seriously affecting ecosystem function in Atlantic reefs

Differential Impact of Monsoon and Large Amplitude Internal Waves on Coral Reef Development in the Andaman Sea

The Andaman Sea and other macrotidal semi-enclosed tropical seas feature large amplitude internal waves (LAIW). Although LAIW induce strong fluctuations i.e. of temperature, pH, and nutrients, their influence on reef development is so far unknown. A better-known source of disturbance is the monsoon affecting corals due to turbulent mixing and sedimentation. Because in the Andaman Sea both, LAIW and monsoon, act from the same westerly direction their relative contribution to reef development is difficult to discern. Here, we explore the framework development in a number of offshore island locations subjected to differential LAIW- and SW-monsoon impact to address this open question. Cumulative negative temperature anomalies – a proxy for LAIW impact – explained a higher percentage of the variability in coral reef framework height, than sedimentation rates which resulted mainly from the monsoon. Temperature anomalies and sediment grain size provided the best correlation with framework height suggesting that so far neglected subsurface processes (LAIW) play a significant role in shaping coral reefs

Mangrove-forest evolution in a sediment-rich estuarine system: opportunists or agents of geomorphic change?

The majority of the world's mangrove forests occur on mostly mineral sediments of fluvial origin. Two perspectives exist on the biogeomorphic development of these forests, i.e. that mangroves are opportunistic, with forest development primarily driven by physical processes, or alternatively that biophysical feedbacks strongly influence sedimentation and resulting geomorphology. On the Firth of Thames coast, New Zealand, we evaluate these two possible scenarios for sediment accumulation and forest development using high-resolution sedimentary records and a detailed chronology of mangrove-forest (Avicennia marina) development since the 1950s. Cores were collected along a shore-normal transect of known elevation relative to mean sea level (MSL). Activities for lead-210 (Pb-210), caesium-137 (Cs-137) and beryllium-7 (Be-7), and sediment properties were analysed, with Pb-210 sediment accumulation rates (SARs), compensated for deep subsidence (similar to 8 mm yr(-1)) used as a proxy for elevation gain. At least four phases of forest development since the 1950s are recognized. An old-growth forest developed by the late-1970s with more recent seaward forest expansion thereafter. Excess 210Pb profiles from the old-growth forest exhibit relatively low SARs near the top (7-12 mm yr(-1)) and bottom (10-22 mm yr(-1)) of cores, separated by an interval of higher SARs (33-100 mm yr(-1)). A general trend of increasing SAR over time characterizes the recent forest. Biogeomorphic evolution of the system is more complex than simple mudflat accretion/progradation and mangrove-forest expansion. Surface-elevation gain in the old-growth forest displays an asymptotic trajectory, with a secondary depocentre developing on the seaward mudflat from the mid-1970s. Two-to ten-fold increases in 210Pb SARs are unambiguously large and occurred years to decades before seedling recruitment, demonstrating that mangroves do not measurably enhance sedimentation over annual to decadal timescales. This suggests that mangrove-forest development is largely dependent on physical processes, with forests occupying mudflats once they reach a suitable elevation in the intertidal. Copyright (C) 2015 John Wiley & Sons, Ltd