Semi-Automated Object-Based Classification of Coral Reef Habitat Using Discrete Choice Models

As for terrestrial remote sensing, pixel-based classifiers have traditionally been used to map coral reef habitats. For pixel-based classifiers, habitat assignment is based on the spectral or textural properties of each individual pixel in the scene. More recently, however, object-based classifications, those based on information from a set of contiguous pixels with similar properties, have found favor with the reef mapping community and are starting to be extensively deployed. Object-based classifiers have an advantage over pixel-based in that they are less compromised by the inevitable inhomogeneity in per-pixel spectral response caused, primarily, by variations in water depth. One aspect of the object-based classification workflow is the assignment of each image object to a habitat class on the basis of its spectral, textural, or geometric properties. While a skilled image interpreter can achieve this task accurately through manual editing, full or partial automation is desirable for large-scale reef mapping projects of the magnitude which are useful for marine spatial planning. To this end, this paper trials the use of multinomial logistic discrete choice models to classify coral reef habitats identified through object-based segmentation of satellite imagery. Our results suggest that these models can attain assignment accuracies of about 85%, while also reducing the time needed to produce the map, as compared to manual methods. Limitations of this approach include misclassification of image objects at the interface between some habitat types due to the soft gradation in nature between habitats, the robustness of the segmentation algorithm used, and the selection of a strong training dataset. Finally, due to the probabilistic nature of multinomial logistic models, the analyst can estimate a map of uncertainty associated with the habitat classifications. Quantifying uncertainty is important to the end-user when developing marine spatial planning scenarios and populating spatial models from reef habitat maps

Reticulate Reef Patterns - Antecedent Karst Versus Self-Organization

Reticulate ridges of reefs and sediment in Holocene lagoons are usually interpreted as an inheritance of antecedent karst topography. Satellite imagery served as a template for integrating plan-view geometry with published data from coring, drilling and seismic surveys to test the antecedent-karst hypothesis. The link between karst morphology and overlying reef patterns can be demonstrated convincingly for a rather limited number of examples, particularly those on a substrate of tower karst with high relief. On very young limestones, doline karst with reticulate patterns develops very slowly because of the high porosity. Moreover, karst control can be ruled out for the significant number of reticulate reefs that are founded on terrigenous sediment or on demonstrably flat pre-Holocene rock surfaces. One likely cause of reticulate patterns is biotic self-organization that has been shown to generate reticulate and labyrinthic patterns of mussel beds on tidal flats and tree cover of arid ecosystems. Another pathway to reticulate reefs may be the colonization of reticulate hydrodynamic bedforms by reef builders. Thus, reticulate patterns of Holocene reef-sediment ridges are highly ambiguous indicators of antecedent karst

Coral Population Dynamics Across Consecutive Mass Mortality Events

Annual 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

Methods to Preserve Coral Reef Futures

This is a short comment to article: Pandolfi, J.M., S.R. Connolly, D.J. Marshall, and A.L. Cohen. 2011. Projecting Coral Reef Futures Under Global Warming and Ocean Acidification. Science. 333 (6041): 418-422

Markov Models for Linking Environments and Facies in Space and Time (Recent Arabian Gulf, Miocene Paratethys)

If, as comparative sedimentology maintains, knowledge of the Recent can sometimes be helpful to explain the past (and vice-versa), common quantitative denominators might exist between Recent and fossil systems. It may also be possible to describe dynamics and find linkages between space and time with a unique set of quantitative tools. To explore such conceptual links, spatial facies patterns mapped using satellite imagery were compared with temporal patterns in analogous ancient outcropping facies using Markov chains and graphs. Landsat and Ikonos satellite imagery was used to map benthic facies in a nearshore carbonate ramp (Ras Hasyan) and offshore platform system (Murrawah, Al Gharbi) in the Recent Arabian Gulf (United Arab Emirates), and results were compared to the Fenk quarry outcrop in Burgenland, Austria, a carbonate ramp of the Miocene (Badenian) Paratethys. Facies adjacencies (i.e. Moore neighbourhood of colour-coded image pixels of satellite image or outcrop map) were expressed by transition probability matrices which showed that horizontal (spatial) facies sequences and vertical (temporal) outcrop sequences had the Markov property (knowledge of t-th state defines likelihoods of t+1st state) and that equivalent facies were comparable in frequency. We expressed the transition probability matrices as weighted digraphs and calculated fixed probability vectors which encapsulate information on both the spatial and temporal components (size of and time spent in each facies). Models of temporal functioning were obtained by modifying matrices (digraphs) of spatial adjacency to matrices (digraphs) of temporal adjacency by using the same vertices (facies) but adjusting transitions without changing paths. With this combined spatio-temporal model, we investigated changes in facies composition in falling and rising sea-level scenarios by adjusting transition likelihoods preferentially into shallower (falling sea-level) or deeper (rising sea-level) facies. Our model can also be used as a numerical analogue to a Ginsburg-type autocyclic model. The fixed probability vector was used as a proxy for final facies distribution. Using Markov chains it is possible to use vertical outcrop data to evaluate the relative contribution of each facies in any time-slice which can aid, for example, in estimation of reservoir sizes and to gain insight into temporal functioning as derived from spatial pattern

The Emerging Role of LiDAR Remote Sensing in Coastal Research and Resource Management Full Access

Knowledge of coastal elevation is an essential requirement for resource management and scientific research. Recognizing the vast potential of lidar remote sensing in coastal studies, this Special Issue includes a collection of articles intended to represent the state-of-the-art for lidar investigations of nearshore submerged and emergent ecosystems, coastal morphodynamics, and hazards due to sea-level rise and severe storms. Some current applications for lidar remote sensing described in this Special Issue include bluegreen wavelength lidar used for submarine coastal benthic environments such as coral reef ecosystems, airborne lidar used for shoreline mapping and coastal change detection, and temporal waveform-resolving lidar used for vegetation mapping

Are Lionfish Set for a Mediterranean Invasion? Modelling Explains Why This is Unlikely to Occur

The Atlantic invasion of Indo-Pacific lionfish (Pterois volitans/P. miles) has been as swift as it has been disastrous. Lionfish are non-native to the Mediterranean, but an invasion is perhaps even more likely than for the Atlantic. First, as for the Atlantic, there are many major cities on the coast of the Mediterranean (where aquarium-keeping is a common practice and chances of accidental and deliberate releases are high), and second, lionfish are native to the Red Sea, to which the Mediterranean is connected via the Suez Canal. Furthermore, there have already been four records of lionfish in the Mediterranean and so the pretext for an invasion is already in place. Up until now, however, it has been difficult to gauge the likelihood of an infestation of lionfish in the Mediterranean as, unlike the Atlantic, this sea has not been examined in terms of its hydrodynamics, ocean climate, and bathymetry, all factors known to be relevant to assessing the possibility of invasion. Motivated by this knowledge-gap, this study used remote sensing and computer modeling to investigate the connectivity between areas along the Mediterranean coastline that fulfill the necessary physical criteria to serve as potential lionfish habitat. Model results from the Mediterranean were compared and contrasted to those from the Atlantic and eastern Pacific. The Atlantic was considered because the lionfish invasion there has been voracious. Meanwhile, the eastern Pacific is interesting as a site without native lionfish, but with plenty of opportunity for their introduction, but no invasion yet recorded. Results indicated that, unlike in the Atlantic, connectivity among potential lionfish habitats in the Mediterranean was low in the study and comparable to that in the eastern Pacific. Although oceanographic conditions in the Mediterranean were found unfavorable for wide dispersion of lionfish larvae, hotspots where numerous lionfish sightings would forewarn an impending invasion were identified. This paper can therefore serve as a guide to the most efficient monitoring of lionfish in the Mediterranean and to where removal efforts should be concentrated, should the species become established

A Coordinated and Sustained International Strategy is Required to Turn the Tide on the Atlantic Lionfish Invasion

Atlantic lionfish have caused measurable ecosystem damage in their invaded range. As a matter of urgency, strategies to suppress lionfish have therefore risen to the fore amongst the ocean management community. We use a biophysical model and ocean climate data to demonstrate how Atlantic lionfish larvae are dispersed by currents and how this dispersal, combined with their breeding strategy, negates effective control using methods traditionally executed on a local scale. This study quantitatively emphasizes the high level of larval connectivity that exists between the many nations whose waters now support established lionfish populations. For any given area, our results indicate that the key to suppressing the invasion is to simultaneously choke all upstream linkages that supply external larvae and renourish the local population. On the basis of a case study developed for the Carolinas, USA, an area of high lionfish abundance, the model suggests that such a strategy requires monthly culls that remove 20% of lionfish biomass in the Carolinas and all locations to which the Carolinas are linked hydrographically. Conversely, if culls target only those locales that deliver the majority (95%) of lionfish larvae to the Carolinas, and therefore ignore those locations which contribute the remaining 5% of lionfish larvae, the requisite cull rate exceeds 60% and suppresses lionfish abundance for only 5 yr. The latter finding exposes an intrinsic danger: sparse lionfish left uncontrolled may derail a concerted, yet not comprehensive, effort to control the invader. This study provides a modelling approach to quantitatively target and manage the lionfish population for nations whose waters are now plagued by invasive lionfish

Lionfish in the Eastern Pacific: A Cellular Automaton Approach to Assessing Invasion Risk

The lionfish invasion in the Atlantic and Caribbean has proceeded with vigor since their introduction in the 1980s or early 1990s. Lionfish affect recruitment of juvenile fish to reefs due to predation and are found in densities far surpassing that of their native Indo-Pacific. There is concern that the lionfish may become introduced and proliferate (through aquarium releases, transport on floating debris, or passage through the Panama Canal in ship ballast water) in the eastern tropical and north Pacific. This study presents the first known prediction of the potential for establishment of lionfish in the eastern Pacific Ocean. Through computational modeling, we compare and contrast the dynamics of random hypothetical introductions of lionfish into the eastern Pacific and Atlantic Oceans in order to highlight the different potentials for invasion in both basins. Connectivity between discrete regions (precincts) in both the Atlantic and eastern Pacific are examined and settlement densities are calculated to indicate possible locations of establishment of breeding lionfish populations. Our results suggest that lionfish, which are successful invaders in the Atlantic, may not be as successful in the eastern Pacific due to weak mesoscale connectivity which reduces the rapid spread of lionfish larvae

Diurnal, Land-Based Predation on Shore Crabs by Moray Eels in the Chagos Archipelago

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