Coralligène formations in the eastern Mediterranean Sea: Morphology, distribution, mapping and relation to fisheries in the southern Aegean Sea (Greece) based on high-resolution acoustics

Coralline algae are one of the most important constructors of biogenic habitats. In the Mediterranean Sea, the dominant coralline algae species form crusts comprising formations known as coralligène, considered as very important fishing grounds by fishermen. Due to the destructive effect of fishing gear activities over coralligène, these formations were recently protected from the use of active benthic gears by the EU 1967/2006 Mediterranean fisheries management Regulation. However, the lack of maps and information on their distribution makes the effective application of these measures impossible. The present publication contributes to the mapping of coralligène in the southern Aegean Sea (eastern Mediterranean), and to the study of coralline algae formation morphology, distribution, development conditions and relation to fisheries using a combination of single-beam echo sounder, sidescan sonar, sub-bottom profiler recordings and biological and sedimentological ground-truthing techniques. The coralligène formations were recognized as two distinct acoustic signatures of localized backscatter facies distinguishable from other hard substrate reflectors at depths ranging from 55.9 to 114.0 m, but mainly between 70 and 90 m. Two types of formations were identified: minute reefs 0.5-2.5 m in height and superficial layer formations no more than 0.2 m thick over the substrate. The seismic profiles revealed a cavernous internal structure of the minute reefs and recorded their development on both hard and soft substrates. The distribution of formations was contagious, creating aggregations. The finding of superficial layer formations and coralline shreds around minute coralligène reefs indicated that the former could be an intermediate development type between isolated small coralline pebbles, rhodoliths, and minute reefs. Regarding the development conditions, sidescan sonar imagery indicated that the optimal conditions for the establishment and development of coralligène formations are medium intensity currents. Concerning human activity over coralligène, trawl traces were recorded near but not over minute reefs and both near and crossing superficial layer type aggregations, while a submarine cable was also recorded among minute reefs. The mapping of coralligène aggregation areas is essential for the application of the EU Regulation and the protection of this important marine habitat.     

Rapid fluctuations in flow and water-column properties in Asan Bay, Guam: implications for selective resilience of coral reefs in warming seas

Hydrodynamics and water-column properties were investigated off west-central Guam from July 2007 through January 2008. Rapid fluctuations, on time scales of 10s of min, in currents, temperature, salinity, and acoustic backscatter were observed to occur on sub-diurnal frequencies along more than 2 km of the fore reef but not at the reef crest. During periods characterized by higher sea-surface temperatures (SSTs), weaker wind forcing, smaller ocean surface waves, and greater thermal stratification, rapid decreases in temperature and concurrent rapid increases in salinity and acoustic backscatter coincided with onshore-directed near-bed currents and offshore-directed near-surface currents. During the study, these cool-water events, on average, lasted 2.3 h and decreased the water temperature 0.57 °C, increased the salinity 0.25 PSU, and were two orders of magnitude more prevalent during the summer season than the winter. During the summer season when the average satellite-derived SST anomaly was +0.63 °C, these cooling events, on average, lowered the temperature 1.14 °C along the fore reef but only 0.11 °C along the reef crest. The rapid shifts appear to be the result of internal tidal bores pumping cooler, more saline, higher-backscatter oceanic water from depths >50 m over cross-shore distances of 100 s of m into the warmer, less saline waters at depths of 20 m and shallower. Such internal bores appear to have the potential to buffer shallow coral reefs from predicted increases in SSTs by bringing cool, offshore water to shallow coral environments. These cooling internal bores may also provide additional benefits to offset stress such as supplying food to thermally stressed corals, reducing stress due to ultraviolet radiation and/or low salinity, and delivering coral larvae from deeper reefs not impacted by surface thermal stress. Thus, the presence of internal bores might be an important factor locally in the resilience of select coral reefs facing increased thermal stress.     

Measuring fish length and assessing behaviour in a high‐biodiversity reach of the Upper Yangtze River using an acoustic camera and echo sounder

In the past decade improved acoustic hard‐ and software have enabled estimations of abundance and distribution patterns of aquatic organism, including non‐intrusive monitoring of fish migrations and behaviour. In this study, a high frequency acoustic camera (DIDSON‐LR, 1.2 MHz, 0.7 MHz) and a portable split‐beam scientific echo sounder (Simrad EY60, 200 kHz) collected acoustic data on 192 and 157 individuals within 24 hr (19–20 April 2011) in the Mituo reach of the Yangtze River, China. Mean fish length estimated from the acoustic camera data was 18.7 ± 5.6 cm, with an average swimming speed of 0.19 ± 0.13 m s^?1. The mean fish target strength (TS) produced by the echo sounder was ?43.8 ± 4.4 dB, which corresponded to 5.7–119.9 cm fish length when converted by three different TS‐length equations. Average swimming speed was 0.11 ± 0.06 m s^?1 from the echo sounder. Compared with the actual fish catch by the three layers of drift gill net in the survey area, the target length indicated by DIDSON was more accurate than the EY60 results, which were highly affected by the choice of TS length equations. It was determined that the two devices used synchronously could estimate fish length effectively to investigate their behaviour and distribution.     

Closing the circle: is it feasible to rehabilitate reefs with sexually propagated corals?

Sexual propagation of corals specifically for reef rehabilitation remains largely experimental. In this study, we refined low technology culture and transplantation approaches and assessed the role of colony size and age, at time of transfer from nursery to reef, on subsequent survival. Larvae from Acropora millepora were reared from gametes and settled on engineered substrates, called coral plug-ins, that were designed to simplify transplantation to areas of degraded reef. Plug-ins, with laboratory spawned and settled coral recruits attached, were maintained in nurseries until they were at least 7 months old before being transplanted to replicate coral limestone outcrops within a marine protected area until they were 31 months old. Survival rates of transplanted corals that remained at the protected in situ nursery the longest were 3.9–5.6 times higher than corals transplanted to the reef earlier, demonstrating that an intermediate ocean nursery stage is critical in the sexual propagation of corals for reef rehabilitation. 3 years post-settlement, colonies were reproductively mature, making this one of few published studies to date to rear a broadcasting scleractinian from eggs to spawning adults. While our data show that it is technically feasible to transplant sexually propagated corals and rear them until maturity, producing a single 2.5-year-old coral on the reef cost at least US$60. ‘What if’ scenarios indicate that the cost per transplantable coral could be reduced by almost 80 %, nevertheless, it is likely that the high cost per coral using sexual propagation methods would constrain delivery of new corals to relatively small scales in many countries with coral reefs.     

Herbivorous fishes,ecosystem function and mobile links on coral reefs

Understanding large-scale movement of ecologically important taxa is key to both species and ecosystem management. Those species responsible for maintaining functional connectivity between habitats are often called mobile links and are regarded as essential elements of resilience. By providing connectivity, they support resilience across spatial scales. Most marine organisms, including fishes, have long-term, biogeographic-scale connectivity through larval movement. Although most reef species are highly site attached after larval settlement, some taxa may also be able to provide rapid, reef-scale connectivity as adults. On coral reefs, the identity of such taxa and the extent of their mobility are not yet known. We use acoustic telemetry to monitor the movements of Kyphosus vaigiensis, one of the few reef fishes that feeds on adult brown macroalgae. Unlike other benthic herbivorous fish species, it also exhibits large-scale (>2 km) movements. Individual K. vaigiensis cover, on average, a 2.5 km length of reef (11 km maximum) each day. These large-scale movements suggest that this species may act as a mobile link, providing functional connectivity, should the need arise, and helping to support functional processes across habitats and spatial scales. An analysis of published studies of home ranges in reef fishes found a consistent relationship between home range size and body length. K. vaigiensis is the sole herbivore to depart significantly from the expected home range–body size relationship, with home range sizes more comparable to exceptionally mobile large pelagic predators rather than other reef herbivores. While the large-scale movements of K. vaigiensis reveal its potential capacity to enhance resilience over large areas, it also emphasizes the potential limitations of small marine reserves to protect some herbivore populations.     

The influence of sea level and cyclones on Holocene reef flat development: Middle Island,central Great Barrier Reef

The geomorphology and chronostratigraphy of the reef flat (including microatoll ages and elevations) were investigated to better understand the long-term development of the reef at Middle Island, inshore central Great Barrier Reef. Eleven cores across the fringing reef captured reef initiation, framework accretion and matrix sediments, allowing a comprehensive appreciation of reef development. Precise uranium–thorium ages obtained from coral skeletons revealed that the reef initiated ~7873 ± 17 years before present (yBP), and most of the reef was emplaced in the following 1000 yr. Average rates of vertical reef accretion ranged between 3.5 and 7.6 mm yr^?1. Reef framework was dominated by branching corals (Acropora and Montipora). An age hiatus of ~5000 yr between 6439 ± 19 and 1617 ± 10 yBP was observed in the core data and attributed to stripping of the reef structure by intense cyclones during the mid- to late-Holocene. Large shingle ridges deposited onshore and basset edges preserved on the reef flat document the influence of cyclones at Middle Island and represent potential sinks for much of the stripped material. Stripping of the upper reef structure around the outer margin of the reef flat by cyclones created accommodation space for a thin (<1.2 m) veneer of reef growth after 1617 ± 10 yBP that grew over the eroded mid-Holocene reef structure. Although limited fetch and open-water exposure might suggest the reef flat at Middle Island is quite protected, our results show that high-energy waves presumably generated by cyclones have significantly influenced both Holocene reef growth and contemporary reef flat geomorphology.     

Length measurement accuracy of adaptive resolution imaging sonar and a predictive model to assess adult Atlantic salmon (Salmo salar) into two size categories with long-range data in a river

Imaging sonars are used around the world for fish population monitoring. The accuracy of the length measurements has been reported in multiple studies for relatively short (<15 m) ranges and high image resolution. However, imaging sonars are often used at longer ranges (i.e., >15 m) where the images produced from sonar returns become less detailed. The accuracy of the length measurements from the Adaptive Resolution Imaging Sonar (ARIS) was tested by releasing n = 69 known-sized adult Atlantic salmon (Salmo salar) directly into the sonar field at ranges between 15 and 29 m, and measuring their echoes manually by four users and semi-automatically using a computer workflow in Echoview software. Overall, the length measurements were very variable: compared to true (fork) lengths, the mean of differences varied between −9.9 cm and 7.8 cm in the human-generated datasets, and between −42.8 cm and −20 cm in the computer-generated dataset. In addition, the length measurements in different datasets were only in poor or moderate agreement with each other (intraclass correlation <0.61). Contrary to our expectations, the distance from the transducer or the subjectively assessed echo quality did not have an effect on the measurement accuracy in most of the datasets and when it did, the effect was not systematic between the datasets. Therefore, a size class and length prediction model was implemented in a Bayesian framework to group salmon into two size categories: One-Sea-Winter (<63 cm) and Multi-Sea-Winter (≥63 cm) groups. The model correctly predicted the size category in 83% of the fish in the computer-generated dataset and ranged from 68% to 74% in the human-generated datasets. We conclude that fish length measurements derived from long-range imaging sonar data should be used with caution, but post-processing can improve the usefulness of the data for specific purposes, such as adult Atlantic salmon population monitoring.     

Sediment resuspension and transport patterns on a fringing reef flat,Molokai, Hawaii

Corals are known to flourish in various turbid environments around the world. The quantitative distinction between clear and turbid water in coral habitats is not well defined nor are the amount of sediment in suspension and rates of sedimentation used to evaluate the condition of reef environments well established. This study of sediment resuspension, transport, and resulting deposition on a fringing reef flat off Molokai, Hawaii, uses a year of time-series data from a small, instrumented tripod. It shows the importance of trade winds and ocean wave heights in controlling the movement of sediment. Sediment is typically resuspended daily and the dominant controls on the magnitude of events (10–25 mg/l) are the trade-wind-generated waves and currents and tidal elevation on the reef flat. The net flux of sediment on this reef is primarily along the reef flat in the direction of the prevailing trade winds (to the west), with a secondary direction of slightly offshore, towards a zone of low coral abundance.These results have application to reef studies and reef management in other areas in several ways. First, the observed resuspension and turbidity results from fine-grained terrigenous sediment that appears to be trapped and recycled on the reef flat. Thus corals are subjected to light attenuation by the same particles repeatedly, however small the amount. Secondly, the measurements show high temporal variability (from daily to seasonal scales) of sediment resuspension, indicating that single measurements are inadequate to accurately describe conditions on a reef flat.Communicated by: P.K. Swart     

Diversity of dermal denticle structure in sharks: Skin surface roughness and three‐dimensional morphology

Shark skin is covered with numerous placoid scales or dermal denticles. While previous research has used scanning electron microscopy and histology to demonstrate that denticles vary both around the body of a shark and among species, no previous study has quantified three‐dimensional (3D) denticle structure and surface roughness to provide a quantitative analysis of skin surface texture. We quantified differences in denticle shape and size on the skin of three individual smooth dogfish sharks (Mustelus canis) using micro‐CT scanning, gel‐based surface profilometry, and histology. On each smooth dogfish, we imaged between 8 and 20 distinct areas on the body and fins, and obtained further comparative skin surface data from leopard, Atlantic sharpnose, shortfin mako, spiny dogfish, gulper, angel, and white sharks. We generated 3D images of individual denticles and measured denticle volume, surface area, and crown angle from the micro‐CT scans. Surface profilometry was used to quantify metrology variables such as roughness, skew, kurtosis, and the height and spacing of surface features. These measurements confirmed that denticles on different body areas of smooth dogfish varied widely in size, shape, and spacing. Denticles near the snout are smooth, paver‐like, and large relative to denticles on the body. Body denticles on smooth dogfish generally have between one and three distinct ridges, a diamond‐like surface shape, and a dorsoventral gradient in spacing and roughness. Ridges were spaced on average 56 µm apart, and had a mean height of 6.5 µm, comparable to denticles from shortfin mako sharks, and with narrower spacing and lower heights than other species measured. We observed considerable variation in denticle structure among regions on the pectoral, dorsal, and caudal fins, including a leading‐to‐trailing edge gradient in roughness for each region. Surface roughness in smooth dogfish varied around the body from 3 to 42 microns.     

Age structure of massive Porites lutea corals at Luhuitou fringing reef (northern South China Sea) indicates recovery following severe anthropogenic disturbance

Luhuitou fringing reef at Hainan Island (northern South China Sea) has experienced severe anthropogenic disturbance, with live coral cover declining by > 80 % since the 1960 s. To assess the size structure of Porites lutea, we measured the sizes of 1,857 colonies from the reef flat (0 m) and slope (2–4 m depth). Both populations were positively skewed and leptokurtic in shape, indicating a high abundance of smaller colonies (averaging 21.4 ± 2.3 cm on the flat and 31.9 ± 2.8 cm on the slope). Age structure of populations was determined through growth rates extracted from X-rays of P. lutea cores. The majority of colonies (> 95 %) were < 50 yr old, with 55 % of P. lutea on the reef flat having recruited following the establishment of a marine reserve in 1990. The abundance of younger colonies indicates significant recovery of P. lutea following the removal of chronic anthropogenic disturbance.     

Mesophotic depths as refuge areas for fishery-targeted species on coral reefs

Coral reefs are subjected to unprecedented levels of disturbance with population growth and climate change combining to reduce standing coral cover and stocks of reef fishes. Most of the damage is concentrated in shallow waters (<30 m deep) where humans can comfortably operate and where physical disturbances are most disruptive to marine organisms. Yet coral reefs can extend to depths exceeding 100 m, potentially offering refuge from the threats facing shallower reefs. We deployed baited remote underwater stereo-video systems (stereo-BRUVs) at depths of 10–90 m around the southern Mariana Islands to investigate whether fish species targeted by fishing in the shallows may be accruing benefits from being at depth. We show that biomass, abundance and species richness of fishery-targeted species increased from shallow reef areas to a depth of 60 m, whereas at greater depths, a lack of live coral habitat corresponded to lower numbers of fish. The majority of targeted species were found to have distributions that ranged from shallow depths (10 m) to depths of at least 70 m, emphasising that habitat, not depth, is the limiting factor in their vertical distribution. While the gradient of abundance and biomass versus depth was steepest for predatory species, the first species usually targeted by fishing, we also found that fishery-targeted herbivores prevailed in similar biomass and species richness to 60 m. Compared to shallow marine protected areas, there was clearly greater biomass of fishery-targeted species accrued in mesophotic depths. Particularly some species typically harvested by depth-limited fishing methods (e.g., spearfishing), such as the endangered humphead wrasse Cheilinus undulatus, were found in greater abundance on deeper reefs. We conclude that mesophotic depths provide essential fish habitat and refuge for fishery-targeted species, representing crucial zones for fishery management and research into the resilience of disturbed coral reef ecosystems.     

Ground-level spectroscopy analyses and classification of coral reefs using a hyperspectral camera

With the general aim of classification and mapping of coral reefs, remote sensing has traditionally been more difficult to implement in comparison with terrestrial equivalents. Images used for the marine environment suffer from environmental limitation (water absorption, scattering, and glint); sensor-related limitations (spectral and spatial resolution); and habitat limitation (substrate spectral similarity). Presented here is an advanced approach for ground-level surveying of a coral reef using a hyperspectral camera (400–1,000 nm) that is able to address all of these limitations. Used from the surface, the image includes a white reference plate that offers a solution for correcting the water column effect. The imaging system produces millimeter size pixels and 80 relevant bands. The data collected have the advantages of both a field point spectrometer (hyperspectral resolution) and a digital camera (spatial resolution). Finally, the availability of pure pixel imagery significantly improves the potential for substrate recognition in comparison with traditionally used remote sensing mixed pixels. In this study, an image of a coral reef table in the Gulf of Aqaba, Red Sea, was classified, demonstrating the benefits of this technology for the first time. Preprocessing includes testing of two normalization approaches, three spectral resolutions, and two spectral ranges. Trained classification was performed using support vector machine that was manually trained and tested against a digital image that provided empirical verification. For the classification of 5 core classes, the best results were achieved using a combination of a 450–660 nm spectral range, 5 nm wide bands, and the employment of red-band normalization. Overall classification accuracy was improved from 86 % for the original image to 99 % for the normalized image. Spectral resolution and spectral ranges seemed to have a limited effect on the classification accuracy. The proposed methodology and the use of automatic classification procedures can be successfully applied for reef survey and monitoring and even upscaled for a large survey.     

Review of coral reef ecosystem remote sensing

Coral reef communities face unprecedented pressures at local, regional and global scales as a consequence of climate change and anthropogenic disturbance. Remote sensing, from satellites or aircraft, is possibly the only means to measure the effects of such stresses at appropriately large spatial scales. In the past 30 years, remote sensing of coral reefs has made rapid progress. However, the current technology is still not mature enough to monitor complicated coral reef ecosystems. Compared with foreign research in this field, our work lags far behind. There are still deficiencies in many aspects, such as basic data collection, theoretical research and platform construction. In our nation, it is even unclear how coral reefs disperse and where they may be unhealthy. In this paper, general characteristics of coral reef ecosystems and spectral features of different reef benthos have been summarized, based initially on a review of relevant literature in recent years. Based on the spectral separability of different reef types or benthos, remote sensing can be used to monitor two aspects of coral reefs: (1) Measurement of the ecological properties of reefs. (2) Health assessment of the coral reef ecosystem. In the first part, optical remote sensing methods are widely used to map reef geomorphology and habitats or biotopes. The investigation of geomorphologic zonation has proven to be one of the most successful applications, as different geomorphologic zones are associated with characteristic benthic community structures and occur at spatial scales of tens to hundreds of meters, they are amenable to remote detection by moderate to high resolution sensors. With more and more attention on the ecological problems of coral reefs, a number of studies have used high resolution sensors to map reef communities. The number of classes distinguishable depends on many factors, including the platforms, resolution (spectral, spatial and temporal resolution) and environmental conditions (water depth, water clarity, surface roughness, etc.). Compared with deep water color remote sensing, or terrestrial remote sensing, three techniques for the measurement of reef ecological properties are examined in this paper: (1) Coral reef classification system using remote sensing. (2) Techniques of sea surface correction and water column correction. (3) Techniques of coral reef information extraction from images. In terms of the complexity of coral reef ecosystems, the current techniques still need further improvement or optimization. In the health assessment of coral reef ecosystems, there are two ways to carry out the monitoring using remote sensing: (1) Monitoring the pigment or symbiotic zooxanthellae contents in corals. (2) Measuring the environmental properties of reefs. The first way is theoretically feasible, but difficult to achieve in practice. Currently, most reef health assessments are carried out by measuring environmental parameters, including sea surface temperature, solar radiation, ultraviolet radiation, water color, wind speed and direction, rainfall, ocean acidification, sea level, etc., of which sea surface temperature has been routinely measured by NOAA to monitor coral bleaching. In addition to the contents above, this article puts forward five main prospects for development in the future: (1) Establishment of a coral reef classification system using remote sensing. (2) Satellite launch for monitoring coral reefs. (3) Theoretical and methodological development. (4) Establishment of a spectral database for different reef benthos. (5) Integrated application of multi-source remote sensing data. It is hoped that the information provided here will be a reference for subsequent similar studies.     

An autocorrelation model of bat sonar

Their sonar system allows echolocating bats to navigate with high skill through a complex, three- dimensional environment at high speed and low light. The auditory analysis of the echoes of their ultrasonic sounds requires a detailed comparison of the emission and echoes. Here an auditory model of bat sonar is introduced and evaluated against a set of psychophysical phantom-target, echo-acoustic experiments. The model consists of a relatively detailed simulation of auditory peripheral processing in the bat, Phyllostomus discolor, followed by a functional module consisting of a strobed, normalised, autocorrelation in each frequency channel. The model output is accumulated in a sonar image buffer. The model evaluation is based on the comparison of the image-buffer contents generated in individually simulated psychophysical trials. The model provides reasonably good predictions for both temporal and spectral behavioural sonar processing in terms of sonar delay-, roughness, and phase sensitivity and in terms of sensitivity to the temporal separations in two-front targets and the classification of spectrally divergent phantom targets.     

The influence of multiple factors upon reef fish abundance and species richness in a tropical coral complex

The present study was conducted on Tamandaré reefs, northeast Brazil and aimed to analyse the importance of different factors (e.g. tourism activity, fishing activity, coral abundance and algal abundance) on reef fish abundance and species richness. Two distinct reef areas (A ver o mar and Caieiras) with different levels of influence were studied. A total of 8239 reef fish individuals were registered, including 59 species. Site 1 (A ver o mar) presented higher reef fish abundance and richness, with dominance of roving herbivores (29.9 %) and mobile invertebrate feeders (28.7 %). In contrast, at Site 2 (Caieiras) territorial herbivores (40.9 %) predominated, followed by mobile invertebrate feeders (24.6 %). Concerning the benthic community, at Site 1 macroalgae were recorded as the main category (49.3 %); however, Site 2 was dominated by calcareous algae (36.0 %). The most important variable explaining more than 90 % of variance on reef fish abundance and species richness was macroalgae abundance, followed by fishing activity. Phase shifts on coral reefs are evident, resulting in the replacement of coral by macroalgae and greatly influencing reef fish communities. In this context, it is important to understand the burden of the factors that affect reef fish communities and, therefore, influence the extinction vulnerability of coral reef fishes.     

Spatial variation of reef fishes and the relative influence of biotic and abiotic habitat traits

Patterns of distribution of reef fishes were examined across three spatial scales and related to habitat traits along 25 km of the northern Portuguese coast. Response variables included the multivariate assemblage structure, the total number of taxa and individuals, and the abundance of single groups categorized according to their preference for the benthic, proximo-benthic or pelagic environment, feeding and reproductive behaviour. Habitat traits included topographic elements (small and large ‘drops’ like cracks and crevices) and the extent of dominant morpho-functional types of macroalgae (kelp, large foliose, small erect, turf-forming filamentous, and encrusting). All fish responses were characterized by the largest variance at the smallest scale (among transects tens m apart), followed by that among reefs (hundreds m to 1 km apart) and almost null variance among sites (some km apart). Small and large ‘drops’ of the substratum explained, respectively, considerable variation of assemblage structure and the total abundance of individuals, while the extent of bare rock influenced the richness of taxa and that of benthic fishes, fishes feeding on sessile invertebrates and fishes laying benthic eggs or having nesting behaviour. Combinations of abiotic and biotic structural attributes of reefs influenced proximo-benthic fishes, the predators of mobile animals and fishes releasing pelagic eggs. The here reported associations between patterns of distribution of reef fishes and habitat traits have implications for the design of future protection schemes suitable to guarantee the conservation of reef fish communities and of the processes responsible for their variation. Within the SLOSS (single-large vs. several-small) debate in the design of marine reserves, for example, effective protection to the studied reef fishes would be provided by a set of small reserves, rather than a single large which might be appropriate for fishes having wider home ranges.     

Changes in the surface roughness of snow from millimetre to metre scales

The roughness of snow influences the movement of air across the snow surface and resulting transfers of energy. Here we focus on the roughness of the snowpack surface to determine its range of variability for different snow conditions (e.g., time since last snowfall), across spatial scales that ranged from 0.01 cm (card) to more than 1000 cm (transect) or more than 5-orders of magnitude, and due to the deposition of aeolian constituents. Digital photogrammetry of snow surfaces was used to compute two roughness metrics at two mountain sites in north-central Colorado. These metrics are the random roughness (RR) that disregards the spatial structure and the fractal dimension (D) computed from variogram analysis.At the crystal scale, D is between 1.67 (card) and 1.60 (board), which increases to 1.77 between 0.1 and 1.0 cm. At longer scales, D is 1.53 (board) to 1.56 (transect). There was no significant change in surface roughness during the accumulation season, with RR values at about 0.002. During the melt season the surface roughness doubled, with the RR values increasing from about 0.002 to 0.004. Snow was more rough parallel to the wind when dunes were present, and roughness varied spatially. The average RR value computed for the white snow surface of 0.014 is substantially greater than the value computed for the red dust surface of 0.0032. Due to undulations of smaller amplitude and as a result of the dust itself, the red dust surface is more random (D is 2.62 versus 2.23 for the white snow). Our results show that there is consistency in roughness over different scales, yet large scale processes (e.g., wind and radiation activity) influence the magnitude of roughness metrics much more than small scale processes (e.g., crystal form and metamorphism).     

Effect of decomposing post-fire coarse woody debris on soil fertility and nutrient availability in a Mediterranean ecosystem

Post-fire coarse woody debris can represent a valuable nutrient reservoir for a regenerating ecosystem, helping to prevent soil fertility losses after a wildfire. However, there is scarce information on its effect on soil nutrient cycling and availability. We established three study sites along an altitudinal gradient in a burnt pine forest (SE Spain). At each site we determined: (1) decomposition rates and nutrient dynamics in charred logs left on the ground, 2 and 4 years after the fire, and (2) available nutrients in the soil and in the microbial fraction below charred logs and in bare soil areas. Despite the relatively slow decay rates in this Mediterranean climate (ca. 10 % of dry weight lost after 4 years), N and P were progressively released by logs, accounting for ca. 40 and 65 % of the initial content respectively after 4 years. This implies that the total aboveground biomass of the burnt forest released around 20 kg ha^?1 of N and 2 kg ha^?1 of P during this period. The presence of post fire coarse woody debris consistently increased soil organic matter by around 18 %, total C and N by 42 and 26 %, respectively, dissolved organic C and N by 47 %, available inorganic P by 68 %, and microbial biomass and nitrogen by some 36 and 48 %, respectively. By contrast, soil bulk density decreased by ca. 18 % under logs compared to bare areas. Thus, the fire-killed wood was useful in the recovery of soil fertility and nutrient availability. Leaving the post-fire woody debris on site can enhance the biogeochemical sustainability, microbiological processes and soil ecological functioning. The detrimental effect of post-fire salvage logging on soil fertility should be therefore considered when making management decisions.     

Advances in assessing Sabellaria spinulosa reefs for ongoing monitoring

Standardized and repeatable data acquisition and analyses are required to enable the mapping and condition monitoring of reefs within Marine Protected Areas (MPAs). Changes in habitat condition must be reliably identified and reported to best support evidence‐based management. Biogenic reefs in temperate waters, that is, hard matter created by living organisms and raised above the seabed, provide food and shelter for many plant and animal species. This article explores the feasibility of habitat mapping, using remote sensing datasets, as well as metrics for repeatable and suitable assessment of areas of Sabellaria spinulosa for their status as biogenic reef. Data were gathered within the North Norfolk Sandbanks and Saturn Reef candidate Special Area of Conservation/Site of Community Importance in the southern North Sea. Six study areas were identified as potential locations of biogenic reef using previously acquired data, and these were targeted for further investigation using a combination of high resolution multibeam echosounder and sidescan sonar. Where potential S. spinulosa was identified from the acoustic data, a drop‐down camera system was employed for visual verification. Areas of known and potential S. spinulosa reef were mapped successfully at two of the six study areas, although future approaches should take careful consideration of the seabed morphology and predominant habitat backdrop to successfully interpret such data. Camera tows from S. spinulosa reef areas were broken up into 5‐s segments, with each segment scored for (a) average tube elevation; (b) average percentage cover; and (c) for the presence or absence of S. spinulosa. These metrics were utilized to create summary statistics, including a value of patchiness derived from presence/absence data, that is recommended for application as part of future monitoring programs. The application of this methodology could benefit wider assessments of similar threated or declining habitats such as intertidal Mytilus edulis beds on mixed and sandy sediments, Maerl beds, Modioulus modiolus beds, Ostrea edulis beds, and Zostera beds where patchiness may also be considered of environmental importance.     

“Choice” and destiny: the substrate composition and mechanical stability of settlement structures can mediate coral recruit fate in post-bleached reefs

Increasingly frequent and intense ocean warming events seriously test the buffer and recovery capacities of tropical coral reefs. Post-disturbance, available settlement structures on a reef (often dead coral skeletons) vary considerably in their mechanical stability and substrate composition, critically influencing coral recruit settlement choice and fate. In the wake of a coral mass mortality in the Lakshadweep archipelago, we examine (1) the relative availability of recruit settlement structures (from stable to unstable: reef platform, dead massive coral, consolidated rubble, dead corymbose coral, dead tabular coral, and unconsolidated rubble) in 12 recovering reefs across three atolls in the archipelago, (2) the substrate composition [crustose coralline algae (CCA), mixed turf, macroalgae] of these structural forms, and (3) whether the choice and fate of young coral are mediated by the substrate and stability of different structural forms. For this, we measured the abundance and distribution of recruit (<1 cm), juvenile (1–5 cm), and young adult (5–10) corals of 24 common coral genera. Four years after the mass mortality, reefs differed considerably in composition of settlement structures. The structures themselves varied significantly in substrate cover with dead tables largely covered in CCA [60 ± 6.05 % (SE)] and dead corymbose coral dominated by mixed turf (61.83 ± 3.8 %). The youngest visible recruits (<1 cm) clearly preferred CCA-rich structures such as dead massives and tables. However, older size classes were rarely found on unstable structures (strongly “avoiding” tables, Ivlev’s electivity index, E = ?0.5). Our results indicate that while substrate cover might mediate coral choice, the mechanical stability of settlement structures is critical in determining post-settlement coral survival. The composition and availability of settlement structures on a reef may serve as a characteristic signature of its recovery potential, aiding in assessments of reef resilience.