A new remote sensing method for high-resolution quantification of submersion regimes in wave exposed shores (original) (raw)
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Brazilian Journal of Oceanography, 2007
This paper introduces a method for temporal studies of steep rocky intertidal communities. It combines the use of digital image technology with field methodology, so that a wide area of the community can be sampled in a short time. Two current nondestructive percent cover estimation methods (visual estimation and point intersection) were compared in terms of cost, operational advantages and data quality, with a proposed method for a sucessional study . The proposed method used sequential photos to sample multiple fixed vertical transects over time. Reproduction of the mid-intertidal transect over time was possible by overlaying temporal transects in an image editing program. This method was similar to the point intersection quadrat method used to estimate percent cover. Benefits included reduced time on field work, economic advantages and other advantages of using digital photography, such as recording. Temporal photography of transects provided measurements of recruitment, mortalit...
PLoS ONE, 2012
Observing spatial and temporal variations of marine biodiversity from non-destructive techniques is central for understanding ecosystem resilience, and for monitoring and assessing conservation strategies, e.g. Marine Protected Areas. Observations are generally obtained through Underwater Visual Censuses (UVC) conducted by divers. The problems inherent to the presence of divers have been discussed in several papers. Video techniques are increasingly used for observing underwater macrofauna and habitat. Most video techniques that do not need the presence of a diver use baited remote systems. In this paper, we present an original video technique which relies on a remote unbaited rotating remote system including a high definition camera. The system is set on the sea floor to record images. These are then analysed at the office to quantify biotic and abiotic sea bottom cover, and to identify and count fish species and other species like marine turtles. The technique was extensively tested in a highly diversified coral reef ecosystem in the South Lagoon of New Caledonia, based on a protocol covering both protected and unprotected areas in major lagoon habitats. The technique enabled to detect and identify a large number of species, and in particular fished species, which were not disturbed by the system. Habitat could easily be investigated through the images. A large number of observations could be carried out per day at sea. This study showed the strong potential of this non obtrusive technique for observing both macrofauna and habitat. It offers a unique spatial coverage and can be implemented at sea at a reasonable cost by non-expert staff. As such, this technique is particularly interesting for investigating and monitoring coastal biodiversity in the light of current conservation challenges and increasing monitoring needs.
Predicting wave exposure in the rocky intertidal zone: Do bigger waves always lead to larger forces
Hydrodynamic forces from breaking waves are among the most important sources of mortality in the rocky intertidal zone. Information about the forces imposed by breaking waves is therefore critical if we are to interpret the mechanical design and physiological performance of wave-swept organisms in an ecologically and evolutionarily relevant context. Wave theory and engineering experiments predict that the process of wave breaking sets a limit on the maximum force to which organisms can be subjected. Unfortunately, the magnitude of this limit has not been determined on rocky shores. To this end, at a moderately exposed shore in central California, we measured the maximum hydrodynamic forces imposed on organism-sized benthic objects and related these forces to nearshore significant wave heights. At 146 of 221 microsites, there was a significant and substantial positive correlation between force and wave height, and at 130 of these microsites, force increased nonlinearly toward a statistically defined limit. The magnitude of this limit varied among sites, from 19 to 730 newtons (N). At 37 other sites, there was no significant correlation between surf zone force and wave height, indicating that increased wave height did not translate into increased force at these sites either. At only 16 sites did force increase in proportion to wave height without an apparent upper bound. These results suggest that for most microsites there is indeed a limiting wave height beyond which force is independent of wave height. The magnitude of the limit varies substantially among microsites, and an index of local topography was found to predict little of this variation. Thus, caution must be exercised in any attempt to relate observed variations in ocean ''waviness'' to the corresponding rates of microsite disturbance in intertidal communities.
Underwater Visual Census of Deeper Vertical Rocky Reefs
Turkish Journal of Fisheries and Aquatic Sciences, 2020
Diver-based underwater visual census (UVC), particularly transect-based survey, is a widely used method for the study of tropical and temperate fish assemblages. However, due to logistical constraints associated with conventional SCUBA diving, deeper habitats, such as vertical rocky reefs, are rarely studied and poorly known. This paper describes the Deep Vertical Transect (DVT) method as a safe and effective method for assessing fish in waters up to 50 m of depth. It is based on sampling of vertical transects browsing within it (S-type transect) by divers using Full HD video cameras. The diving profile includes the use of deep decompression stops and Nitrox 50 as a decompression gas. Hence, the study yields information on fish assemblages associated with deeper vertical coralligenous reefs. The results of 51 recorded species, yielded 41 considered as reef-associated and 10 as occasional. This suggests that underwater steep coralligenous reefs are marine biodiversity hotspots. They may be considered to represent a distinctive marine subecosystem, possessing its own food chain, with the depth, in relation to temperature, as the most important factor responsible for the diversity of fish assemblages within this habitat.
Fisheries Research, 2014
Underwater video techniques are increasingly used in marine ecology studies. Technological progress regarding video cameras, sensors (such as sounders), battery life and information storage make these techniques now accessible to a majority of users. However, diver-based underwater visual censuses, and catch and effort data, remain the most commonly used for observing coastal biodiversity and species. In this paper, we review the underwater video techniques that have been developed since the 1950s to investigate and/or monitor coastal biodiversity. Techniques such as remote underwater video, whether baited or not, diver-operated video and towed video are described, along with corresponding applications in the field. We then analyse the complementary of techniques, first from studies comparing video techniques with other observation techniques, whether video-based or not, and second by documenting their respective cost efficiencies. These findings are discussed with respect to current challenges in monitoring and investigating coastal biodiversity. Video should be more often considered and used, either in addition to or as an alternative to diver-based, fishing and acoustic techniques, as it may be particularly suited for monitoring coastal biodiversity in a variety of areas and on larger scales than hitherto and within an ecosystem-based approach to management and conservation. Highlights ► Underwater video is increasingly used in marine ecology. ► Video is less used than catch and underwater visual census. ► Video techniques comprise baited, unbaited, towed and diver-operated techniques. ► Video is a cost-efficient complement or alternative to other observation techniques.
Remote Sensing, 2020
The photogrammetric method is widely used in coastal areas and in submerged environments. Time-lapse images collected with unmanned aerial vehicles are used to reproduce the emerged areas, while images taken by divers are used to reproduce submerged ones. Conversely, 3D models of natural or human-made objects lying at the water level are severely affected by the difference in refractive index between air and seawater. For this reason, the matching of 3D models of emergent and submerged coasts has been very rarely tested and never used in Earth Sciences. The availability of a large number of time-lapse images, collected at the intertidal zone during previous snorkel surveys, encouraged us to test the merging of 3D models of emerged and submerged environments. Considering the rapid and effective nature of the aforementioned program of swim surveys, photogrammetric targets were not used during image acquisition. This forced us to test the matching of the independent models by recognizing prominent landforms along the waterline. Here we present the approach used to test the method, the instrumentation used for the field tests, and the setting of cameras fixed to a specially built aluminum support console and discuss both its advantages and its limits compared to UAVs. 3D models of sea cliffs were generated by applying structure-from-motion (SfM) photogrammetry. Horizontal time-lapse images, collected with action cameras while swimming parallel to the coastline at nearly constant velocity, were used for the tests. Subsequently, prominent coastal landforms were used to couple the independent models obtained from the emergent and submerged cliffs. The method was pilot tested in two coastal sites in the northeastern Adriatic (part of the Mediterranean basin). The first site was a 25 m sea wall of sandstone set within a small harbor, while the second site was a 150 m route below plunging limestone cliffs. The data show that inexpensive action cameras provide a sufficient resolution to support and integrate geomorphological field surveys along rocky coastlines.
Limnology and Oceanography, 2011
To distinguish the intertidal states of emergence, splash, surge, and submergence and record their relative durations, we deployed a water-level logger paired with a temperature logger in the mid-intertidal zone at each of 10 wave-exposed sites during the summer in the northeast Pacific. Relative durations of intertidal states were different among the different sites, even at sites close together. Splash was temporally variable, being recorded by the loggers on 50% or fewer days at most sites. Daily surge durations tended to be longer at sites in northern and central California compared with sites in Oregon and Washington. Return times to surge and submergence showed the opposite trend with longer return times in Oregon and Washington compared with California. We estimated the effect of interannual changes in tides on intertidal states by applying the logger data to tidal predictions and comparing duration and return time over the 18.6-yr tidal epoch. Over long time periods, compared with the logger deployments, daily durations of surge increased, return times to the surge state became more uniform, and return times to submergence lengthened.