peer reviewed | The Mediterranean seagrass species Posidonia oceanica forms extensive meadows that provide numerous ecological and economic services. Among the human activities threatening these meadows, boat anchoring causes severe degradation resulting in meadow fragmentation, exposure of the dead matte, and sediment disruption. In this study, we assessed the natural recolonisation dynamics of P. oceanica in anchoring-degraded sites focusing on both shallow and deep sites. Over two years, photogrammetry was employed to monitor recolonisation dynamics with a focus on patchs' edges expansion and storm-fragments accumulation. Our results show distinct recolonisation patterns between shallow and deep sites, with shallow patches displaying more variable dynamics of erosion and recolonisation, while deep patches showed slower but more consistent recovery. Additionally, the abundance of storm-fragments, primarily in shallow areas, suggests potential for enhanced recovery through natural trapping structures. Despite recent regulations reducing anchoring pressures, recolonisation rates remain insufficient to counteract the extent of degradation in a reasonable timespan. These findings underline the importance of designing tailored restoration strategies based on site-specific recolonisation potential: high-density transplantation with durable anchoring structures in shallow areas to withstand hydrodynamic forces, and more cost-effective solutions like iron staples in deeper areas. Additionally, the study supports the use of trapping substrates to retain storm-fragments in shallow sites to boost natural recolonisation. This approach is crucial for enhancing seagrass meadow resilience, especially within a context of climate change and increasing pressures on coastal ecosystems.

The effects of dike construction on the geomorphology and sedimentary processes of tidal flats were investigated using high-precision topographic profiling, short cores, and unmanned aviation vehicle (UAV)-assisted photogrammetry to understand their adverse consequences on the benthic ecosystem. Tidal flats at the south of Shinsi Island near one of the two sluice gates of the Saemangeum dike, display prominent morphologic features known as shelly sand ridges or cheniers (sensu Otvos, 2000) that have migrated landward about 5 m in a year. The tidal flats were dominated by erosion from winter to spring and by deposition during the remainder of the year except for the periods of heavy precipitation when tidal drainage channels became larger and deeper by headward erosion. With overall coarser-grained surface sediments, the presence of actively migrating wave-built cheniers are in stark contrast to muddy tidal flats with a monotonous morphology before the completion of the Saemangeum dike in 2006. Southeasterly waves reflected from the dike during winter to spring when north to northwesterly winds prevail account for the wave-induced onshore sediment transport and rapid morphologic changes in the tidal flats despite their location protected from offshore waves. The diversity and biomass of major macrofauna species tend to increase during rapid erosion and decrease during rapid deposition, highlighting the anthropogenic effect of dike-induced physical disturbance on the benthic ecosystem in the otherwise sheltered tidal flats.

The clean-up effort that is occurring across the region affected by the 2011 Fukushima Daiichi Nuclear Power Plant accident is unprecedented in its magnitude as well as the financial cost that will eventually result. A major component of this remediation is the stripping of large volumes of material from the land surface, depositing this into large waste storage bags before placing these 1 cubic meter bags into specially constructed stores across Fukushima Prefecture.In this work, using an unmanned aerial vehicle to perform radiological surveys of a site, the time-resolved distribution of contamination during the construction of one of these waste storage sites was assessed. The results indicated that radioactive material was progressively leaching from the store into the surrounding environment. A subsequent survey of the site conducted eight months later revealed that in response to this survey and remedial actions, the contamination issue once existing on this site had been successfully resolved. Such results highlight the potential of low-altitude unmanned aerial systems to easily and rapidly assess site-wide changes over time – providing highly-visual results; therefore, permitting for prompt remedial actions to be undertaken as required.Use of UAV radiation mapping and airborne photogrammetry to produce a time-resolved assessment of remediation efforts within a Fukushima temporary storage facility.

Unmanned aerial vehicles can collect high-resolution and real-time photos while emitting fewer greenhouse gases than ordinary airplanes and therefore are considered economic and environmentally friendly platforms. However, quantitative analyses of the sustainability of using unmanned aerial vehicles for aerial photography based on their performance and technical constraints compared to that of airplanes are lacking. The purpose of this study is to analyze the economically and environmentally appropriate monitoring coverage of unmanned aerial vehicle photogrammetry according to wing type (such as fixed-wing and rotary-wing types) and desired image resolution (such as 5 cm/pix and 20 cm/pix for the ground sample distance). To determine the sustainable monitoring coverage, the total photogrammetry costs must include the social cost to reduce the emitted greenhouse gases during operation, resulting in a feedback relation. As a result, the sustainable monitoring coverage of fixed-wing unmanned aerial vehicles should be less than 27.50 km² when the resolution is 5 cm/pix and 30.64 km² when the resolution is 20 cm/pix. Rotary-wing unmanned aerial vehicles are sustainable when their monitoring coverage is less than 23.98 km² at a resolution of 5 cm/pix and 26.75 km² at a resolution of 20 cm/pix. These results provide information on the number of unmanned aerial vehicles and the standing unmanned aerial vehicle deployment plans required to monitor the survey area.

Airborne systems such as lightweight and highly portable unmanned aerial vehicles (UAVs) are becoming increasingly widespread in both academia and industry - with an ever-increasing range of applications, including (but not limited to), air quality sampling, wildlife monitoring and land-use mapping.In this work, high-resolution airborne photogrammetry obtained using a multi-rotor system operating at low survey altitudes, is combined with ground-based radiation mapping data acquired at an interim storage facility for wastes removed as part of the large-scale Fukushima clean-up program. The investigation aimed to assess the extent to which the remediation program at a specific site has contained the stored contaminants, as well as present a new methodology for rapidly surveying radiological sites globally. From the three-dimensional rendering of the site of interest, it was possible to not only generate a powerful graphic confirming the elevated radiological intensity existing at the location of the waste bags, but also to also illustrate the downslope movement of contamination due to species leakage from the large 1m³ storage bags. The entire survey took less than 1 h to perform, and was subsequently post-processed using graphical information software to obtain the renderings. The conclusions within this study not only highlight the usefulness of incorporating three-dimensional renderings within radiation mapping protocols, but also conclude that current methods of monitoring these storage facilities in the long term could be improved through the integration of UAVs within the standard protocol.

Natural ecological restoration is a cornerstone of modern conservation science and managers need more documented “success stories” to lead the way. In French mediterranean sea, we monitored Posidonia oceanica lower limit using acoustic telemetry and photogrammetry and investigated the descriptors driving its variations, at a national scale and over more than a decade. We showed significant effects of environmental descriptors (region, sea surface temperature and bottom temperature) but also of wastewater treatment plant (WWTP) effluents proxies (size of WWTP, time since conformity, and distance to the closest effluent) on the meadows lower limit progression. This work indicates a possible positive response of P. oceanica meadows to improvements in wastewater treatment and a negative effect of high temperatures. While more data is needed, the example of French wastewater policy should inspire stakeholders and coastal managers in their efforts to limit anthropogenic pressures on vulnerable ecosystems.

Sediments in algal turfs can modify a wide variety of key ecological processes on coral reefs. While some larger reef fishes can remove these turf-bound sediments, the role of small, yet abundant, cryptobenthic fishes is currently unclear. To address this knowledge gap, we explored the extent to which the blenny, Ecsenius stictus, can shape sediment dynamics on coral reefs by quantifying their sediment ingestion and space use. Per unit body mass, E. stictus process sediments at comparable rates to key parrotfish and surgeonfish species. However, in absolute terms, E. stictus has a negligible influence on net sediment dynamics, despite their abundance. Behavioural observations and 3D photogrammetry reveal that E. stictus preferentially feed and rest on elevated surfaces; potentially because of low sediment loads on these surfaces. Overall, E. stictus may be responding to sediment loads rather than manipulating them; it is a passenger rather than a driver in reef processes.

Marine activities may cause the degradation of coral reefs. The composition of benthic communities and seawater quality have been commonly used as the proxies to assess the impacts of marine activities. However, these proxies may not be able to detect the subtle differences within homogeneous environment. We used photogrammetry to quantify the subtle differences of structural complexity between heavily and lightly trafficked sites at Wanlitong, southern Taiwan. Our study demonstrated that the impacts of marine activities can be detected within tens of meters through quantifying structural complexity of coral reefs. Vector ruggedness measure (VRM) is a more suitable metric than conventional linear rugosity to detect such impacts. The correlations between structural complexity and coral cover have variances while comparing with previous studies. The results show that using photogrammetry to quantify the structure of coral reefs can provide a novel aspect to evaluate the subtle differences caused by marine activities.

Motorized vessels are a major source of anthropogenic noise and can have adverse effects on species relying on sound for communication and feeding. Monitoring noise levels received by endangered southern resident killer whales (SRKWs) requires knowing the number, distance, and speed of surrounding vessels, including small boats that do not have Automatic Identification Systems (AIS). A method for estimating their speed is required to predict received noise levels and compliance with vessel regulations. We compared theodolite and photogrammetry methods to estimate the number, distance, and speed of vessels in SRKW Salish Sea summertime critical habitat. By treating AIS as “truth”, we found photogrammetry-derived ranges and speeds were more variable than theodolite estimates. Error in photogrammetry-derived speeds increased with range. Overall, we found time saved in the field using photogrammetry was more than offset by long analysis time. Theodolite data were relatively easy to collect, and produced accurate and precise results.

The remote and uninhabited Northwestern Hawaiian Islands (NWHI) contain 70% of the shallow water coral reefs in the United States and are regularly exposed to derelict fishing nets. These nets snag on the shallow reefs, damaging or killing benthic communities. However, no data exist to quantify this impact. Here we use a novel application of photogrammetry, Structure-from-Motion (SfM), to calculate benthic cover from mosaic images at net-impact and control sites. Net-impact sites had significantly higher cover of bare substrate, sand, and crustose coralline algae and significantly lower coral and macroalgae cover compared to control sites. These differences were unrelated to net size and fouling. Our study demonstrates the utility of using SfM to efficiently quantify impacts of derelict fishing nets. Revisiting these sites will be essential to document how the reef recovers to further our understanding of the lasting impacts of derelict fishing nets on coral reef habitats.