179 research outputs found
sj-docx-1-hol-10.1177_09596836221114291 – Supplemental material for The mid-Holocene sea-level change in the Arabian Gulf
No full textSupplemental material, sj-docx-1-hol-10.1177_09596836221114291 for The mid-Holocene sea-level change in the Arabian Gulf by Barbara Mauz, Zhixiong Shen, Mohammad Alsuwaidi, Daniele Mellini, Giorgio Spada and Sam J Purkis in The Holocene</p
sj-xlsx-2-hol-10.1177_09596836221114291 – Supplemental material for The mid-Holocene sea-level change in the Arabian Gulf
No full textSupplemental material, sj-xlsx-2-hol-10.1177_09596836221114291 for The mid-Holocene sea-level change in the Arabian Gulf by Barbara Mauz, Zhixiong Shen, Mohammad Alsuwaidi, Daniele Mellini, Giorgio Spada and Sam J Purkis in The Holocene</p
Morphometric parameters of the Squid Mounds (SQM), Namibian coral mound province
No full textQuantitative morphometric analyses were carried out for each mound following the workflows presented by Purkis et al. (2007) The coral mound base was defined following the methodological approach of Correa et al. (2012) using the dip angle map, generated from the digital elevation model (DEM), to extract closed polygons that follow the 3°-contour line. This 3°-cutoff has been qualitatively validated with a comparison between the DEM and the dip angle (Fig. 2). Small-scaled polygons within mound perimeters and resulting from bathymetric artifacts were filtered out. Manual editing was applied to split simple merged mound structures (e.g. twin-peak mounds) based on higher cut-off slope values (4-5°). Furthermore, polygons describing the mound footprint have been corrected to remove unrealistic shapes especially common for the CBM. The DEM was subsequently re-gridded to generate hypothetical bathymetric maps without mounds, for which the vertical relief beneath each removed mound was interpolated from the mound perimeters. The newly interpolated surfaces were then subtracted from the original DEMs to evaluate the volume and heights of the coral mounds. Only features with a footprint area greater than 900 squared meters (corresponding to a two-dimensional array of 3 × 3 DEM grid cells) and with a height of >2 m above the surrounding seafloor (4 × 0.5 m of vertical precision) were considered as coral mounds and quantitatively analyzed
Morphometric parameters of the Coral Belt Mounds (CBM), Namibian coral mound province
No full textQuantitative morphometric analyses were carried out for each mound following the workflows presented by Purkis et al. (2007) The coral mound base was defined following the methodological approach of Correa et al. (2012) using the dip angle map, generated from the digital elevation model (DEM), to extract closed polygons that follow the 3°-contour line. This 3°-cutoff has been qualitatively validated with a comparison between the DEM and the dip angle. Small-scaled polygons within mound perimeters and resulting from bathymetry artefacts were filtered out. Manual editing was applied to split simple merged mound structures (e.g. twin-peak mounds) based on higher cut-off slope values (4-5°). Furthermore, polygons describing the mound footprint have been corrected to remove unrealistic shapes especially common for the CBM. The DEM was subsequently re-gridded to generate hypothetical bathymetric maps without mounds, for which the vertical relief beneath each removed mound was interpolated from the mound perimeters. The newly interpolated surfaces were then subtracted from the original DEMs to evaluate the volume and heights of the coral mounds. Only features with a footprint area greater than 900 suared meters (corresponding to a two-dimensional array of 3 × 3 DEM grid cells) and with a height of >2 m above the surrounding seafloor (4 × 0.5 m of vertical precision) were considered as coral mounds and quantitatively analyzed
Dynamics of Gulf Coral Communities: Observations and Models from the World’s Hottest Coral Sea
No full text[Chapter Abstract] Coral reefs are adapted to a relatively narrow band of environmental optima and the harsh Gulf environment tests the physiological and ecological limits of reef corals. The environmental variability (minimal and maximal annual temperatures, salinity extremes, etc.; Chap. 2; Sheppard et al. 1992, 2010) are outside the range of typical tropical reefs. Regular summer temperatures are several degrees above the bleaching and mortality thresholds of some regions in the Great Barrier Reef and the Caribbean (Baker et al. 2008; Chap. 6). Yet, corals thrive in the Gulf. However, they have recently been exposed to severe temperature anomalies at a recurrence faster than in any other coral reef region (Riegl 2002, 2003; Sheppard and Loughland 2002; Riegl and Purkis 2009; Sheppard et al. 2010) and it appears that hot-anomalies are increasing in severity and frequency (Nasrallah et al. 2004). Thus, corals in the Gulf already exist in a thermal environment that is equal to, or even worse than, what is predicted (IPCC 2007) as occurring throughout the tropical oceans by 2099 and recognized as likely causing problems for coral reef persistence. Clearly, important lessons can be learned from Gulf corals about environmental extremes that corals can survive and, given the high frequency of disturbances, maybe even lessons in adaptability. Since the world is getting warmer and extremes are becoming more pronounced, the study of such extreme reef systems gains increased relevance.https://nsuworks.nova.edu/occ_facbooks/1128/thumbnail.jp
Remote Sensing Tropical Coral Reefs: The View from Above
No full textCarbonate precipitation has been a common life strategy for marine organisms for 3.7 billion years, as, therefore, has their construction of reefs. As favored by modern corals, reef-forming organisms have typically adopted a niche in warm, shallow, well-lit, tropical marine waters, where they are capable of building vast carbonate edifices. Because fossil reefs form water aquifers and hydrocarbon reservoirs, considerable effort has been dedicated to understanding their anatomy and morphology. Remote sensing has a particular role to play here. Interpretation of satellite images has done much to reveal the grand spatial and temporal tapestry of tropical reefs. Comparative sedimentology, whereby modern environments are contrasted with the rock record to improve interpretation, has been particularly transformed by observations made from orbit. Satellite mapping has also become a keystone technology to quantify the coral reef crisis—it can be deployed not only directly to quantify the distribution of coral communities, but also indirectly to establish a climatology for their physical environment. This article reviews the application of remote sensing to tropical coralgal reefs in order to communicate how this fast-growing technology might be central to addressing the coral reef crisis and to look ahead at future developments in the science.</jats:p
Human impact on atolls leads to coral loss and community homogenisation : a modeling study
No full textWe explore impacts on pristine atolls subjected to anthropogenic near-field (human habitation) and far-field (climate and environmental change) pressure. Using literature data of human impacts on reefs, we parameterize forecast models to evaluate trajectories in coral cover under impact scenarios that primarily act via recruitment and increased mortality of larger corals. From surveys across the Chagos, we investigate the regeneration dynamics of coral populations distant from human habitation after natural disturbances. Using a size-based mathematical model based on a time-series of coral community and population data from 1999–2006, we provide hind- and forecast data for coral population dynamics within lagoons and on ocean-facing reefs verified against monitoring from 1979–2009. Environmental data (currents, temperatures) were used for calibration. The coral community was simplified into growth typologies: branching and encrusting, arboresent and massive corals. Community patterns observed in the field were influenced by bleaching-related mortality, most notably in 1998. Survival had been highest in deep lagoonal settings, which suggests a refuge. Recruitment levels were higher in lagoons than on ocean-facing reefs. When adding stress by direct human pressure, climate and environmental change as increased disturbance frequency and modified recruitment and mortality levels (due to eutrophication, overfishing, pollution, heat, acidification, etc), models suggest steep declines in coral populations and loss of community diversification among habitats. We found it likely that degradation of lagoonal coral populations would impact regeneration potential of all coral populations, also on ocean-facing reefs, thus decreasing reef resilience on the entire atoll
The mid-Holocene sea-level change in the Arabian Gulf
No full textThe mid-Holocene sea-level highstand is a well-known phenomenon in sea-level science, yet the knowledge on the highstand’s spatial and temporal distribution remains incomplete. Here we study the southwest coast of the Arabian-Persian Gulf where a mid-Holocene sea-level highstand and subsequent sea-level fall may have occurred due to the Earth crustal response to meltwater load. Sea-level indicators were established using standard facies analysis and error calculations, then constrained through glacio-isostatic adjustment (GIA) modelling and though procedures based on Gaussian Process and exponential decay analysis. This work allowed to identify the highstand at 1.6 ± 0.4 m occurring 6.7–6.0 ka, in excellent agreement with GIA model results. The subsequent shoreline migration followed the geophysical constraint by prograding in line with the sea-level fall until around 3 ka. Then, the strength of the external control weakened and internal processes, in particular sediment binding through microbial activity, started controlling the geometry of the accommodation space
Coral Population Dynamics Across Consecutive Mass Mortality Events
No full textAnnual coral mortality events due to increased atmospheric heat may occur regularly from the middle of the century and are considered apocalyptic for coral reefs. In the Arabian/Persian Gulf, this situation has already occurred and population dynamics of four widespread corals (Acropora downingi, Porites harrisoni, Dipsastrea pallida, Cyphastrea micropthalma) were examined across the first-ever occurrence of four back-to-back mass mortality events (2009–2012). Mortality was driven by diseases in 2009, bleaching and subsequent diseases in 2010/2011/2012. 2009 reduced P. harrisoni cover and size, the other events increasingly reduced overall cover (2009: −10%; 2010: −20%; 2011: −20%; 2012: −15%) and affected all examined species. Regeneration was only observed after the first disturbance. P. harrisoni and A. downingi severely declined from 2010 due to bleaching and subsequent white syndromes, while D. pallida and P. daedalea declined from 2011 due to bleaching and black-band disease. C. microphthalma cover was not affected. In all species, most large corals were lost while fission due to partial tissue mortality bolstered small size classes. This general shrinkage led to a decrease of coral cover and a dramatic reduction of fecundity. Transition matrices for disturbed and undisturbed conditions were evaluated as Life Table Response Experiment and showed that C. microphthalma changed the least in size-class dynamics and fecundity, suggesting they were ‘winners’. In an ordered ‘degradation cascade’, impacts decreased from the most common to the least common species, leading to step-wise removal of previously dominant species. A potentially permanent shift from high- to low-coral cover with different coral community and size structure can be expected due to the demographic dynamics resultant from the disturbances. Similarities to degradation of other Caribbean and Pacific reefs are discussed. As comparable environmental conditions and mortality patterns must be expected worldwide, demographic collapse of many other coral populations may soon be widespread
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