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Algal communities act as sensitive indicators of past and present climate effects on northern lakes, but their responses can vary considerably between ecosystems. Functional trait-based approaches may help us better understand the nature of the diverse biotic responses and their underlying ecosystem changes. We explored patterns in diatom (Bacillariophyceae) growth forms and species composition during the Neoglacial in two shallow lakes typical of subarctic regions, including a dark-colored woodland lake and a clear tundra lake. Sediment carbon and nitrogen elemental and isotope biogeochemistry and spectral indices were used to track broadscale changes in lake productivity, the inflow of organic carbon from land, and benthic substratum over the past three millennia. The biogeochemical indices tracked declines in land-lake connectivity as well as lake-water and sediment organic enrichment above and below the subarctic treeline driven by Neoglacial cooling. This broadscale environmental transition was intercepted by periods of elevated primary production associated with transient Neoglacial warm anomalies and, in particular, the twentieth century warming. Although the Neoglacial development of the lakes showed conspicuous similarities, diatom functional and taxonomic responses were not uniform between the lakes pointing to intrinsic differences in the development of benthic habitats and underwater-light regimes. Many of the observed biotic shifts aligned with expectations based on earlier research linking diatom functional traits to changing light and organic levels but the results also point to further research needs, particularly to better differentiate the individual and interactive effects of substratum and light. Despite distinct anthropogenic imprints in the biogeochemical record, the scale of human impact on the lakes’ biota has not, as yet, been profound, but the changes are nonetheless clear when compared to the previous three millennia of natural lake development.

In ice-covered polar lakes, a narrow ice-free moat opens up in spring or early summer, and then persists at the edge of the lake until complete ice loss or refreezing. In this study, we analyzed the horizontal gradients in Ward Hunt Lake, located in the Canadian High Arctic, and addressed the hypothesis that the transition from its nearshore open-water moat to offshore ice-covered waters is marked by discontinuous shifts in limnological properties. Consistent with this hypothesis, we observed an abrupt increase in below-ice concentrations of chlorophyll a beyond the ice margin, along with a sharp decrease in temperature and light availability and pronounced changes in benthic algal pigments and fatty acids. There were higher concentrations of rotifers and lower concentrations of viruses at the ice-free sampling sites, and contrasts in zooplankton fatty acid profiles that implied a greater importance of benthic phototrophs in their inshore diet. The observed patterns underscore the structuring role of ice cover in polar lakes. These ecosystems do not conform to the traditional definitions of littoral versus pelagic zones but instead may have distinct moat, ice-margin, and ice-covered zones. This zonation is likely to weaken with ongoing climate change.

We compared temporal changes in the concentration of photoprotective compounds (PCs) in zooplankton of two adjacent (600 m apart) tropical high mountain lakes, El Sol and La Luna. The lakes have the same geological origin, age and drainage basin. However, they differ in underwater light and UV penetration and in the presence of Oncorhynchus mykiss, only found in El Sol. Whereas Daphnia ambigua from the clear La Luna had carotenoids and melanin, in El Sol, the same species lacked pigmentation. The copepod Leptodiaptomus cuauhtemoci was only found in El Sol and relied on accumulation of MAAs and carotenoids. The maximum concentration of PCs was found over the period with highest incident ultraviolet radiation (UVR). Our data suggest that tropical species of zooplankton respond to UVR by accumulating PCs that are too different in relation to exposure to UVR. However, we cannot discard the possibility that the presence of fish in Lake El Sol influences also their phenotypical and behavioral responses. Overall, zooplankton exhibited an ample phenotypic plasticity in the type and concentrations of PCs in response to the high and variable doses of UVR prevailing in low-latitude lakes, similar to the zooplankton of their high-latitude counterparts.

Light is a fundamental resource for phytoplankton. To utilize the available light, most phytoplankton species possess pigments in taxon‐specific combinations and quantities, which in turn result in a specific use of certain wavelengths. This optimizes the light use efficiency, allows for a complementary use of light, and may be an additional driver for community structure. While the effects of light intensity on phytoplankton biomass production and community composition have been intensively studied, here we focused on the effects of specific light spectrum quality (thus light color) on a natural phytoplankton community. In a controlled mesocosm experiment we reduced the supplied wavelength range to its blue, green, or red part of the light spectrum and compared the responses of each treatment to a full spectrum control over 28 d. Highest community growth rates were observed under blue, lowest under red light. Light absorption by the communities showed adaptation toward the supplied wavelength range. Community composition was significantly affected by light quality treatments, driven by Bacillariophyta and Chlorophyta, whereas pigment composition was not. Furthermore, lower species richness but higher evenness occurred when communities were exposed to red light compared to the full spectrum. We expected the response of phytoplankton communities to changes in the light spectrum to be driven by a combination of species sorting and pigment acclimation; however, the effect of species sorting turned out to be stronger. Our study showed that, even if species might acclimate, changes in the available light spectrum affect primary production and phytoplankton community composition.

The ocean has many underwater light niches, but the selection pressure for chromatic acclimaters (generalists) compared to blue or green-specialists is not well understood. Here, we tested the hypo...

The use of non-physical barriers, particularly based on acoustic and luminous stimuli has been historically used to influence the behavior of fish, mainly for fishing purposes. Nowadays, behavioral barriers and guidance systems have been developed, not only to deter movements of fish, but also to promote behavioral responses with the objective of native fish protection, in particular the potamodromous species, reducing their mortality in the hydraulic structures of dams and guiding them towards transposition systems or to replacement habitats in regularized water bodies. This review details the use of acoustic and luminous systems and their evolution in recent years (Scopus 2012–2019) for the development of selective behavioral barriers for fish. We found that recent technologies try to identify new acoustic and luminous sensory ranges. Ambient sound, sound of predators or luminous spectral bands with different wavelengths have been used to selectively stimulate target and non-target species, in order to improve the effectiveness of repulsive/attractive systems for fish. Guidelines for future research in the area are also present. This work is supported by National Funds by FCT—Portuguese Foundation for Science and Technology, under the project UIDB/04033/2020. info:eu-repo/semantics/publishedVersion

Recent studies have indicated changes in the light climate of the North Sea. An overall reduction of water clarity over the twentieth century could be observed in measurements, and more recent analysis suggests that these trends continue. Inorganic sediment is often named one of the driving factors in these changes and it has been shown to locally increase. With 20 years\' worth of satellite-derived sediment data, we were able to conduct basin wide investigations of the temporal dynamics of the biogeochemical state of the North Sea. To identify the impact of inter-annual and seasonal changes in sediment, we fed from two different remote sensing sources (GlobColour & IFREMER) into a 3D coupled hydrodynamic and biological model. The light scheme in the Carbon Silicon Nitrogen Ecosystem model (CoSiNE) was modified to account for sediment specific attenuation. We performed a total of five numerical experiments for the period of 2000–2017. The main two experiments were conducted using monthly averaged data. Additionally, as controls, one experiment with annually averaged and one with a 20 years average of sediment, as well as a fifth one without sediment were performed. Our model showed a clear relation between changes in sediment and water clarity. Phytoplankton biomass was reduced only in areas with high nutrient availability.

In order to receive high quality photo and video images with underwater vision systems an important factor is to choose an appropriate artificial light source. We propose calculation to estimate light source parameters to perform underwater surveillance in real time with underwater towed camera. We provide underwater light source parameters to guarantee high performance of underwater camera. We present images received during research vessel «Academic Mstislav Keldysh» expedition and analyze their quality.

We propose an underwater image enhancement algorithm for improving underwater robot visibility. Images captured in underwater environments are typically degraded by the effects of absorption, scattering, and noise. Degraded images impede underwater robot task performance (e.g., inspection, detection, and visual simultaneous localization and mapping). In this study, we improve the underwater light model by considering floating particle noise and non-uniform illumination from artificial light sources. Specifically, a systematic underwater enhancement method that includes a floating particle removal algorithm and an image-dehazing algorithm is proposed. Our method is effective for underwater image enhancement applications in real-world scenarios. We compare and evaluate our proposed method with state-of-the-art methods, with an underwater evaluation and a feature-matching performance. The experimental results show that our method yields comparable (and even better) results than state-of-the-art methods.

In the Arctic, rising seawater temperatures and increasing underwater light caused by reductions in sea ice cover are expected to change the structure of arctic marine communities. Substantial, som ...

The studied section of the river Buriganga besets with urban catchment contained higher values of pH, alkalinity, CO2, conductivity, TDS, SRP, SRS and NO3-N concentration compared to its counterpart, namely a section of the river Gomti having rural catchment characteristics. The mean values for a period of six months for the river Buriganga were 8.34, 1.48 meq/l, 8.49 mg/l, 686 μS/cm, 155.17 mg/l, 493 μg/l, 36.07 mg/l and 810.28 μg/l for pH, alkalinity, CO2, conductivity, TDS, SRP, SRS and NO3-N, respectively. While the same for the river Gomti was 7.86, 1.18 meq/l, 5.42 mg/l, 284.44 μS/cm, 79.91 mg/l, 188.37 μg/l, 26.41 mg/l and 203.99 μg/l, respectively for pH, alkalinity, CO2, conductivity, TDS, SRP, SRS and NO3-N. In the river Gomti, the concentration of DO was better (7.87 mg/l) compared to that of river Buriganga (5.53 mg/l). Because of a hilly origin of the river Gomti and availability of sediments in its water, the underwater light climate was poor compared to the river Buriganga. The Secchi depth recorded for Gomti and Buriganga were 0.26 and 0.54 m, respectively. Both the rivers were found diatom dominant in terms of population but the species prevailed were different. Fragillaria virescens Ralfs was the dominant diatom of the river Buriganga. Its density ranged from 6.5-11.09×105 ind/l which was the highest compared to the population of all other groups of potamoplankton. In Gomti another diatom namely, F. pinnata Ehrenberg was dominant and the density of which ranged from 8.45 - 12.65 × 105 ind/l. Community structure of the potamoplankton revealed 30 species from the river Buriganga and 22 species from Gomti. The study reveals that relatively higher concentration of nutrients prevails in the water of the river course having urban catchment characters compared to the rural ones. Dhaka Univ. J. Biol. Sci. 27(2): 191-200, 2018 (July)

The underwater light climate has important effects on primary producers. The aim of this research was to evaluate its variability in a turbid river-floodplain system. Photosynthetically active radiation (PAR) was measured in the Middle Paraná River during different hydrological phases to (a) analyse the photosynthetically active radiation attenuation coefficient (k) and euphotic depth (Zeu) as well as their associations with optically active components and (b) develop and evaluate indices and regression models based on Secchi disc (SD) measurements to estimate k and Zeu. Values of k were higher in the fluvial system than in the floodplain and during low-water stage than high-water stage. Particulate components controlled the light climate variability. Chromophoric dissolved organic matter and chlorophyll-a had significant effects during floods. The estimation of k and Zeu was sensitive to temporal but not to spatial variations. The highest prediction accuracy was observed when using specific non-linear regressions for each hydrological phase, especially for Zeu estimation (low stage: k = 1.76 × SD−0.80, Zeu = 2.62 × 1/SD−0.80; high stage: k = 2.04 × SD−0.53, Zeu = 2.26 × 1/SD−0.53). The indices k × SD and Zeu/SD were significantly different from those proposed for clear water environments. It is concluded that temporal variations should be considered when estimating k and Zeu in turbid river-floodplain systems because of the temporal heterogeneity in optically active components. Considering that ecological implication of the light climate depends on Zeu:depth ratio, we propose to estimate Zeu instead of k. Finally, indices proposed for clear water environments are not recommended to be applied to turbid environments. Fil: Mayora, Gisela Paola. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina Fil: Devercelli, Melina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Santa Fe. Instituto Nacional de Limnología. Universidad Nacional del Litoral. Instituto Nacional de Limnología; Argentina

A repulsive effect, that some induced primary stimuli, like sound and light, is known to be provoked in fish behavior. In the present study, two strobe light frequencies, 350 flashes/minute and 600 flashes/minute, were tested in laboratorial conditions, using three native freshwater fish species of northern Portugal: Brown trout (Salmo trutta), Northern straight-mouth nase (Pseudochondrostoma duriense) and Iberian barbel (Luciobarbus bocagei). The results showed a differential repulsive behavior of the fish species to light stimulus, and particularly to a frequency of 600 flashes/minute. S. trutta presented the most repulsive behavior, whereas the L. bocagei showed less repulsion to the light stimulus. No relevant differences were found between pre-test and post-assessments, confirming a rapid recovery of natural fish behavior after the deterrent effect. The results highlighted the potential of behavioral barriers, particularly in salmonid streams, based on strobe light stimulus. The project n 13737: Original Solutions—ENI and CITAB-UTAD was funded project: ANI/QREN/FEDER. European Investment Funds by FEDER/COMPETE/POCI—Operational Competitiveness and Internationalization Programme, under Project POCI-01-0145- FEDER-006958 and National Funds by FCT— Portuguese Foundation for Science and Technology, under the project UID/AGR/04033/2013. Acknowledgments: The present study was technically supported by Instituto da Conservação da Natureza e Florestas (ICNF—Departamento Norte), namely the facilities at the fish farm “Posto Aquicola de Castrelos”, for the execution of the experimental design. info:eu-repo/semantics/publishedVersion

Light determines macrophyte distribution, community composition and biomass in shallow lakes. Therefore, it is vital to determine the critical underwater light climate thresholds for macrophyte degradation and recovery. In this study, we first proposed a novel index, defined as the ratio of euphotic depth (Zeu) to water depth (WD), as a measure of the underwater light supply for macrophytes. The underwater light environment in Lake Taihu (a large, shallow, eutrophic lake) was then characterized based on this index (Zeu/WD) using field measurements collected from 2006 to 2013 (8 years × 4 seasons × 32 sites). The distribution of the macrophyte presence frequency (MPF, the number of investigations that identified macrophytes divided by the total number of investigations) was greater than 0.70 in Xukou Bay and East Lake Taihu over the 32 investigations, followed by the other sites distributed in East Lake Taihu. The proportion of macrophyte coverage increased with the increase in Zeu/WD. A significant relationship was observed between Zeu/WD and MPF for the 19 sites with macrophytes (r2 = 0.48, p

The eyes of apex predators, such as the shark, have fascinated comparative visual neuroscientists for hundreds of years with respect to how they perceive the dark depths of their ocean realm or the visual scene in search of prey. As the earliest representatives of the first stage in the evolution of jawed vertebrates, sharks have an important role to play in our understanding of the evolution of the vertebrate eye, including that of humans. This comprehensive review covers the structure and function of all the major ocular components in sharks and how they are adapted to a range of underwater light environments. A comparative approach is used to identify: species-specific diversity in the perception of clear optical images; photoreception for various visual behaviours; the trade-off between image resolution and sensitivity; and visual processing under a range of levels of illumination. The application of this knowledge is also discussed with respect to the conservation of this important group of cartilaginous fishes.

Underwater images present blur and color cast, caused by light absorption and scattering in water medium. To restore underwater images through image formation model (IFM), the scene depth map is very important for the estimation of the transmission map and background light intensity. In this paper, we propose a rapid and effective scene depth estimation model based on underwater light attenuation prior (ULAP) for underwater images and train the model coefficients with learning-based supervised linear regression. With the correct depth map, the background light (BL) and transmission maps (TMs) for R-G-B light are easily estimated to recover the true scene radiance under the water. In order to evaluate the superiority of underwater image restoration using our estimated depth map, three assessment metrics demonstrate that our proposed method can enhance perceptual effect with less running time, compared to four state-of-the-art image restoration methods.

We make a comparison of the mesopelagic sound scattering layers (SLs) in two contrasting optical environments; the clear Red Sea and in murkier coastal waters of Norway (Masfjorden). The depth distributions of the SL in Masfjorden are shallower and narrower than those of the Red Sea. This difference in depth distribution is consistent with the hypothesis that the organisms of the SL distribute according to similar light comfort zones (LCZ) in the two environments. Our study suggest that surface and underwater light measurements ranging more than 10 orders of magnitude is required to assess the controlling effects of light on SL structure and dynamics. publishedVersion

Marine optical parameters required for ocean color satellite applications must be measured with high accuracy and errors within the permissible limits. These stringent requirements demand careful measurements of optical parameters. Though the free-fall radiometer is found to be a better option for measuring underwater light parameters as it avoids the effects of ship shadow and is easy to operate, the measurements demand profiling the radiometer vertical in water with minimum tilt. Here we present the results of our observations on the tilts of the radiometer from the measurements in the Arabian Sea. Since there is hardly any study carried-out on the tilt of the profiling radiometer, the result of this study will help in the better design of such marine instruments. The tilt of the radiometer near the surface of the water is attributed to the mode of deployment and environment parameters, while the tilt at depth of the water is influenced by the density variations of the water. Here we also demonstrate a ...

Cyanobacteria and algae are problematic in California rice fields that are typically shallow and have high nutrient levels, providing ideal growing conditions. Nostoc spongiaeforme is a problem because extensive floating mats dislodge rice seedlings or smother them when the mats accumulate in windward areas. There is little published information on growth requirements for N. spongiaeforme. We grew N. spongiaeforme in BG-11 medium at 24 combinations of light (22, 87, 162, and 400 µM m−2 s−1) and temperatures (10°C, 15°C, 20°C, 25°C, 30°C, and 35°C). Results were summarized as a quadratic equation relating light and temperature to growth and indicate that optimal growth occurred at 26°C and 227 µM m−2 s−1 of light. Thus, N. spongiaeforme grows well at water temperatures and light levels similar to those measured in rice fields during the critical 30 days following initial flooding of the field.

Based on the data obtained, in reality not a few fishermen find it difficult to catch fish. In addition, the lack of their catch is the main impact of the above problems. If this happens continuously then the number of traditional fishermen will decline so that the need for a concept and tools that can help in increasing the catch one of them is the application of technology LACUBA. The purpose of this research is to apply LACUBA technology (Lampu Kecup under water) which can help the income of fisherman community and to know the fisherman's response to LACUBA technology (Water dye underwater lamp) specially on coastal community Cilelang, Kab. Barru. Implementation of this activity is in the village of Cilellang Kab. Barru in May 2018. This research instrument uses LACUBA (Dye underwater light) which is the result of a series of some electronic components such as Aki (Accu), Dimmer Series and Inverter Circuits. From the calculation of the results of the analysis of fishermen's income data in the village of Cilellang, Kab. Barru before and after the use of LACUBA (Submersible underwater lights) changes significantly. From the data obtained shows that before the use of LACUBA Technology, Fishermen Society only get the catch of an average of 21.88 Kg / day. Meanwhile, after the use of LACUBA technology, the average of the acquisition increased to 43.78 kg / day. Based on the results of this study it can be concluded that there is a significant influence on the use of technology LACUBA (Water dye underwater light) to the fishing results in the village of Cilelang Kab. Barru

(2008). Wave-induced variability of the underwater light climate in the littoral zone. SIL Proceedings, 1922-2010: Vol. 30, No. 4, pp. 627-632.