Fish fauna characterization after the onset of a turbid condition in a clear vegetated shallow lake

Recent anthropogenic increases in algal turbidity in aquatic habitats have been suggested to affect the ability of fish to assess predation risk. We investigated the response of feeding three‐spined sticklebacks (Gasterosteus aculeatus) exposed to a sudden appearance of an avian predator (the silhouette of common tern, Sterna hirundo), under clear and turbid water conditions. As stickleback use social cues to aid in predator avoidance, we also tested whether turbidity affected social information use by manipulating group size. We found that in turbid water, a smaller proportion of fish would escape from the feeding area, that the distance escaped was shorter and that a smaller proportion of fish fled into shelter. Larger group size was associated with longer escape distance and greater shelter use. However, there was no effect of group size on the proportion of fish that escaped the arena. The effect of group size was similar for turbid and clear water. Our finding that the fish showed a weaker antipredator response suggests that turbidity impedes their risk assessment capability. However, the sticklebacks were still able to benefit of the social facilitation provided by being in a group. This suggests that algal turbidity has detrimental effects on the ability of sticklebacks to assess predation risk from avian predators in shallow water. An implication is that in shallow water fish may be more vulnerable to avian predation under turbid conditions.

Small and shallow lakes make up most of the lake-covered area in the world, and immature Chironomidae generally constitute the dominant group among invertebrates in these systems, exhibiting a wide distribution and tolerance to various levels of water quality. The changes in trophic features associated with the dominance of different major primary producers (macrophyte and phytoplankton) are reflected in the functioning of these ecosystems and likely in their phytophilous Chironomidae species richness and abundance. These were thus studied in a Brazilian shallow lake over a 11-year period characterized by both clear and turbid water conditions in relation to water quality and dominant macrophytes. The results revealed differences in Chironomidae composition but not in richness associated with clear and turbid waters. The Goeldichironomus genera predominated during all years and for different macrophyte types (freefloating, floating leaf, and submerged). We attribute the variability of Chironomidae assemblages to changes in macrophyte dominance and water trophic status, such as the concentration of nutrients and chlorophyll-a, during the 11-year period. Submerged macrophytes were associated with clear waters and harbored the highest diversity, which emphasized the importance of these environmental conditions for preserving the biodiversity of Chironomidae in shallow lakes.

Human-induced eutrophication, resulting in increased algal growth and water turbidity, is an alarming problem in aquatic systems. Many studies have focused on the effects of algal turbidity on mate choice and sexual selection in fish, but little emphasis has been given to the ways it can constrain mating success. Here we experimentally investigated the effects of algal turbidity on maximum male mating success and parental care in the sand goby, Pomatoschistus minutus, a fish with a resource-defence mating system and male parental care. For this purpose, we introduced to 1 nest-holding male 5 random-sized ripe females in either clear or in turbid water. After spawning, we observed how many mates and eggs the male received and followed his parental behaviour and egg survival for 6 days under turbid or clear water conditions. When spawning took place in clear water, the number of eggs the male received into his nest increased with the total weight of five females in his tank. However, when spawning took place in turbid water, there was no relationship between female size and the number of eggs laid, although the number of females that spawned was the same as in clear water. The results indicate that females adjust the number of eggs they lay according to water turbidity. This could explain previous findings that mating success is more evenly distributed among males in turbid than clear water conditions.Significance statementThe first responses of animals to human-induced changes in the environment are behavioural. Subtle changes in the behaviour of individuals can have profound consequences for populations and communities. Human-induced eutrophication, leading to algal blooms and water turbidity, is a major environmental problem in aquatic systems worldwide. Our results on the sand goby suggest a new mechanism by which water turbidity may affect fish mating systems and weaken sexual selection. When spawning takes place in clear water, the number of eggs accumulated in a males’ nest is an increasing function of the fecundity of the females. However, when spawning in turbid water, this positive relationship between female size and egg numbers disappears. We believe this is because females do not perceive the competition from other females in turbid water and therefore invest less in present reproduction.

This paper introduces an auto-tuning range-gated imaging system in turbid medium. The automated gated imaging system is able to auto-tune the best image quality by using the MTF evaluation technique. For a typical gated system, the gated images are recorded into video format in increasing gate opening time, each frame of the video recorded is basically to “slice” the targets at different distance from camera (based on time of light). Each frame would only able to show the targets within the specifically “sliced” target distance, which limits the capability of gated imaging system. Thus, it is necessary to develop auto-tuning system that will overcome the limitation in turbid water condition. In this paper, all enhanced target images within the field of view (FOV) are fused into one 3D image, and this will increase the efficiency of the study and works under turbid medium condition. Works had been done in selecting a quantitative image quality index for automated tuning system so that images with better quality can be detected accurately in turbid conditions. The non-reference measuring index-Modulation Transfer Function (MTF) can perform better in analyzing images under turbid condition thus is selected for this application. Experiment results show that the mid-band spatial frequencies from 21 to 61 demonstrate the degradation of image quality due to the turbid water backscattering noises. Thus, we propose to use MTF in the auto-tuning system to select best quality target from multiple images that scan thru the various gate timing. Subsequently, image fusion is performed to fuse multiple gate opening time images into a 3D extended targets turbid condition.

The proportion of rainbow trout (Oncorhynchus mykiss) concealing themselves in simulated interstitial spaces was examined in the presence of surface ice, in turbid water, and in clear water. Tests were conducted in enclosures in a small Idaho stream with structures that provided five rectangular spaces varying in width and height, one circular space, and one triangular space. Space use was assessed each morning by trapping test fish inside the structures. Significantly more fish concealed themselves under clear water conditions than under either surface ice or turbid water conditions. Spaces narrower than the width of a test fish with extended pectoral fins and spaces taller than the height of a test fish with dorsal fin extended were used less than would be expected if space use was random. The frequency with which two or more fish occurred together in the same space was similar to that expected if fish occurred together at random. Fish rarely returned to the same space on consecutive nights.

Aiming at developing underwater battery recharging system, the author developed a docking system using stereo-vision-based visual servoing and a 3D marker. The 3D marker consists of red, green, blue spheres that do not emit the light which is named as a passive marker. Real-time relative pose (position and orientation) estimation was implemented utilizing the 3D model-based matching method and real-time multi-step genetic algorithm (RM-GA). Given the situation that the docking aims for battery recharging in the deep-sea bottom, the pitch-dark and turbid environment should be considered as an inevitable condition for battery recharging. In our previous works, the docking experiments were conducted in the actual sea, having verified the effectiveness of the proposed system using the passive 3D marker in the daytime environment with turbid water condition. Since lighting passive 3D marker by light from the vehicle in turbid water environment results in a situation that the images taken by video cameras set on the vehicle were looked wholly white, some new idea seems to be required. To overcome this difficulty, the newly lighting 3D marker (active 3D maker) has LEDs inside was introduced in the previous work. The main objective of this study is to check the feasibility area of the proposed system for the docking application, comparison of recognition performance using the active and passive 3D marker that was conducted in the simulated pool with the turbid water is focused. And then, the experiment using the active 3D marker in the actual sea has been performed. The experimental results have confirmed that the new active 3D marker with no-lighting from the vehicle could be recognizable in dark and turbid environment than the passive 3D marker with the lighting from the vehicle.

Fitoperifiton de un lago somero y su relación con los estados de biequilibrio

Turbidity, caused by suspended particles in the water column, induces light scattering and shifts in the wavelengths of light. These changes may impair the ability of fish to use physical cues and hence may modify social interactions. We experimentally investigated the social interactions of guppies, Poecilia reticulata, in clear and turbid water. Fish were significantly less active, formed smaller shoals and were found to be more often alone in turbid than in clear water. A Markov chain analysis revealed significant differences in the social dynamics when comparing clear and turbid water conditions. The probability of leaving a particular nearest neighbour and the probability of choosing some neighbour after swimming around alone differed between the treatments. Our results indicate that turbidity has a number of different effects on the social interactions of the guppy, and we discuss their potential costs and benefits and wider implications.

A late Quaternary lake record from the Qilian Mountains (NW China): evolution of the primary production and the water depth reconstructed from macrofossil, pollen, biomarker, and isotope data

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 227:233-239 (2002) - doi:10.3354/meps227233 RNA/DNA ratios of scleractinian corals suggest acclimatisation/adaptation in relation to light gradients and turbidity regimes E. H. Meesters1, G. Nieuwland1, G. C. A. Duineveld1, A. Kok1, R. P. M. Bak1,2,* 1Netherlands Institute for Sea Research (NIOZ), PO Box 59, 1970 AB Den Burg, Texel, The Netherlands 2Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, The Netherlands *Corresponding author. E-mail: rbak@nioz.nl ABSTRACT: RNA/DNA ratios are used in many organisms as an indicator of growth, biomass or metabolic functioning. We hypothesised that hermatypic corals, as they depend for growth largely on energy transferred from their algal symbionts, may show an effect in the RNA/DNA ratio with factors influencing irradiance. This was tested along 2 environmental gradients: in relation to depth (decreasing irradiance) and in relation to environmental degradation (increased turbidity). RNA/DNA ratios were determined by HPLC in coral samples collected over depth gradients in 3 islands off the coast of north-west Java, Indonesia. The reefs range from shallow reefs (depth <3 m) in very turbid water, which are close to eroded shores, to intermediate reefs (depth <6 m) further from the shore with less turbid water, to offshore clear water control reefs (depth <20 m). RNA/DNA ratio was shown to be negatively correlated with depth in all but the most turbid conditions, suggesting it is an expression of metabolic acclimatisation of the coral host-symbiont community with decreasing irradiance (i.e. photoadaptation). Comparing the RNA/DNA ratio in clear and turbid waters, the decrease with depth tended to be steeper over a shorter depth range under turbid conditions, analogous with the more rapid extinction of light in these conditions. The relationship between the RNA/DNA ratio and light was consistently higher under turbid conditions (p = 0.0037), indicating that RNA/DNA ratio had shifted to a higher level, possibly indicating a genetic adaptation in the metabolic functioning of corals in the turbid environment. The positive relation between light and RNA/DNA ratio would suggest the opposite, i.e. lower ratio under turbid conditions. The RNA/DNA ratio may provide a relatively reliable method to determine the metabolic functioning (health) of individual coral colonies. KEY WORDS: RNA/DNA ratios · Coral health · Environmental stress · Sediment · Turbidity · Photoadaptation · Growth · Bio-indicator Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 227. Online publication date: February 13, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.

We present an approach for optical sensing and detection in turbid water using multidimensional spatial-temporal domain integral imaging and dedicated signal processing algorithms. An optical signal is encoded using pseudorandom sequences, and an image sensor array is used to capture elemental image video sequences of light propagating through turbid water. Using the captured information, multidimensional image reconstruction followed by multi-dimensional correlation to detect the source signal is performed. We experimentally demonstrate scenarios in which turbidity causes conventional signal detection to fail, while our proposed multidimensional approach enables successful detection under the same turbidity conditions. Statistical analysis is provided to support the experimental results. To the best of our knowledge, this is the first report of using multidimensional integral imaging signal detection in turbid water conditions.

This paper presents experiments using a time of flight (ToF) camera modified to use 525 nm green laser illumination to capture amplitude and depth images of an underwater scene. Experiments in object imaging and ranging were conducted in both clear and turbid water. 3D imaging using flood illumination was successfully performed in clear water and in some turbid water conditions. Ranging using collimated laser beams was performed in turbid water. Several major error sources were observed, including low illumination levels, fixed pattern noise, and backscatter contribution to the phase measurement. To attempt to address these concerns, multiple lasers were used to improve illumination levels and spatial frequency domain filtering was performed to mitigate fixed pattern noise. Additionally, experiments with using multiple modulation frequencies suggested that there may be potential for discriminating backscatter from object reflection.

The estimation of the bathymetry and the detection of targets located on the seabed of shallow waters using remote sensing techniques is of great interest for many environmental applications in coastal areas such as benthic habitat mapping, monitoring of seabed aquatic plants and the subsequent management of littoral zones. For that purpose, knowledge of the optical effects induced by the neighborhood of a given seabed target and by the water column itself is required to better interpret the subsurface upward radiance measured by satellite or shipborne radiometers. In this paper, the various sources of photons that contribute to the subsurface upward radiance are analyzed. In particular, the adjacency effects caused by the neighborhood of a given seabed target are quantified for three water turbidity conditions, namely clear, moderately turbid and turbid waters. Firstly, an analytical expression of the subsurface radiance is proposed in order to make explicit the radiance terms corresponding to these effects. Secondly, a sensitivity study is performed using radiative transfer modeling to determine the influence of the seabed adjacency effects on the upward signal with respect to various parameters such as the bathymetry or the bottom brightness. The results show that the highest contributions of the adjacency effects induced by the neighborhood of a seabed target to the subsurface radiance could reach 26%, 18% and 9% for clear, moderately turbid and turbid water conditions respectively. Therefore, the detection of a seabed target could be significantly biased if the seabed adjacency effects are ignored in the analysis of remote sensing measurements. Our results could be further used to improve the performance of inverse algorithms dedicated to the retrieval of bottom composition, water optical properties and/or bathymetry.

Timms and Moss (1984) suggested that fertile shallow lakes may have alternative stable states, a clearwater state with dense vegetation and a turbid water state dominated by phytoplankton and with little submerged and floating-leaved vegetation. This phenomenon has also been observed and discussed by several other authors (e.g., Irvine et al., 1990; Jeppesen et al., 1990; van Donk et al., 1990; Blindow et al., 1993; Scheffer et al., 1993). According to the model of Scheifer (1989, 1990), the main controlling factor for the two alternative states is the turbidity of water regulating the vertical light penetration. When the nutrient level increases, phytoplankton growth is often stimulated, which in turn increases the turbidity. This leads to increased light attenuation and a reduction of the maximum growth depth of submerged vegetation. Increased nutrient concentrations will therefore reduce the bottom area covered by submerged vegetation until it is virtually absent. In shallow lakes with most bottom areas at similar depths, the change from high plant cover to plantless bottoms may be abrupt. Uncovered sediments in shallow lakes are much more vulnerable to resuspen-sion and more easily give rise to turbid water during periods of wind and wave action than in lakes with plant-covered sediments. Benthivorous fish may be favored under these circumstances and add to the turbidity by foraging on the sediment. A more-or-less stable turbid state may be the result.KeywordsShallow LakeSubmerged VegetationTurbid Water StateIsaac Newton TelescopeArmagh ObservatoryThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Shallow lakes in subtropical climate regions may have a clear water state with a predominance of submerged or floating macrophytes and a turbid water state with a predominance of phytoplankton. The relationship between microcrustaceans and these changes in alternative states is still incipient in the literature. And to better understand these relationships, the functional approach is an excellent tool. Thus, the present work seeks to test the hypothesis that changes in alternative stable states over time reflect the variability of composition and functional diversity of microcrustaceans. For this, samples of microcrustaceans collected in a subtropical shallow lake, which underwent alternate state changes in the period to 2000–2014, were used. Our results demonstrate a variation in composition and functional diversity among alternative states, thus supporting our hypothesis. In periods of clear water with a predominance of floating macrophytes, we found a greater functional diversity and richness of genera. This result may be associated with several factors such as greater habitat heterogeneity and lower predation pressure. The lowest values of functional diversity found in periods of turbid waters with predominance of phytoplankton and periods of clear waters with submerged macrophytes are related to the dominance of functional traits, such as scraper feeding type, herbivorous/omnivorous trophic group, littoral habitat and asexual reproduction. These traits are functional features of most Ostracoda genera, a taxonomic group abundant in these two alternative states. The predominance of this group may be related to the environmental characteristics of these periods, such as the high vegetation cover and the availability of niches unoccupied by more sensitive species, since most Ostracoda have high environmental tolerance. We conclude that the functional traits approach combined with taxonomic groups respond to temporal variations of alternative stable states and are important tools to detect environmental changes.