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Light and photosynthesis in aquatic ecosystems
\"Beginning systematically with the fundamentals, the fully-updated third edition of this popular graduate textbook provides an understanding of all the essential elements of marine optics. It explains the key role of light as a major factor in determining the operation and biological composition of aquatic ecosystems, and its scope ranges from the physics of light transmission within water, through the biochemistry and physiology of aquatic photosynthesis, to the ecological relationships that depend on the underwater light climate. This book also provides a valuable introduction to the remote sensing of the ocean from space, which is now recognized to be of great environmental significance due to its direct relevance to global warming. An important resource for graduate courses on marine optics, aquatic photosynthesis, or ocean remote sensing; and for aquatic scientists, both oceanographers and limnologists\"-- Provided by publisher.
Book
Responses of phytoplankton community dynamics to reduced underwater light in spring
Air pollution and lake eutrophication have led to a reduction in incident total radiation and water transparency in many lakes, resulting in a decrease in available underwater light. This reduction in available light depends significantly on the dynamics of spring phytoplankton communities. However, the process and mechanisms behind these effects are not yet well understood. In this study, we conducted a field mesocosm experiment to observe the responses of the phytoplankton community to varying levels of light intensity (100%, 85%, and 65% photosynthetically active radiation, PAR). Our study revealed that reducing PAR resulted in an earlier peak of cyanobacterial biomass in spring, while the biomass of chlorophytes and bacillariophytes declined with decreasing light intensity. The weakening of light intensity promoted the recovery of photosynthetic activity in cyanobacteria but reduced the photosynthetic activity in chlorophytes and bacillariophytes. Additionally, the decrease in light intensity reduced the diversity of phytoplankton communities, accelerating the rate of species turnover. However, the rate of species turnover slowed down as the dominance of cyanobacteria was established in the later stages of the experiment. Therefore, the weakening of light intensity is beneficial to the early establishment of the dominance of cyanobacteria in the phytoplankton community structure, accelerating the succession process of phytoplankton community. These findings contribute to the exploration of the effects of reduced light intensity on the establishment of cyanobacterial dominance in spring, providing valuable insights for the management of lake ecosystems.
Journal Article
Spectral Irradiance Distribution in Underwater Light Field Generated by an LED Light Source
Yang, P.; Wu, Z.; Chen, Y.; Guo, Y.; Zhang, P., and Song, H., 2020. Spectral irradiance distribution in underwater light field generated by an LED light source. In: Yang, Y.; Mi, C.; Zhao, L., and Lam, S. (eds.), Global Topics and New Trends in Coastal Research: Port, Coastal and Ocean Engineering. Journal of Coastal Research, Special Issue No. 103, pp. 453–457. Coconut Creek (Florida), ISSN 0749-0208. Artificial underwater illumination has a wide range of applications in coastal zone research, marine engineering, marine resource exploration and development, and marine ecological environment monitoring. In this article, the distribution of spectral irradiance has been discussed for an underwater light field generated by an underwater LED light source. Theoretical representations of the spectral irradiance have been derived according to physical principles and underwater spectral irradiance measurement have been accrued out along the optical axis of the light source and in the vertical plane perpendicular to the optical axis. Experimental results show that the spectral irradiance along the optical axis of the light source decays with respect to the distance, following the law of square attenuation and exponential attenuation. The irradiance in the vertical plane approximately matches the Gaussian distribution.
Journal Article
Effect of a Coccolithophore Bloom on the Underwater Light Field and the Albedo of the Water Column
The goal of this work is to study the influence of coccolithophore blooms on the underwater light field and albedo of the water column. A coccolithophore is a single-celled alga with spherical cells surrounded by disk-shaped calcite plates (coccolites), which produce strong light scattering. Because of that, we can observe coccolithophore blooms on satellite ocean color images. We calculated the angular underwater radiance distributions and their integral parameters by the exact numerical method with the input parameters, corresponding to real conditions observed in the Barents Sea and Black Sea. Using the results of the exact calculations, we estimated, for various situations, the accuracy of the approximating formulas applied to the assessment of the water radiance reflectance and the diffuse attenuation coefficients and we make recommendations for their application. As a finding of practical importance, we can note the estimate of the accuracy of the widely used Gordon’s formula for the diffuse attenuation coefficient; this formula results in large errors under strong coccolithophore blooms. We also mention the interesting and important results concerning the features of the asymptotic regime under such conditions.
Journal Article
Photosynthesis in the Marine Environment
\"Marine photosynthesis provides for at least half of the primary production worldwide...\" Photosynthesis in the Marine Environment constitutes a comprehensive explanation of photosynthetic processes as related to the special environment in which marine plants live. The first part of the book introduces the different photosynthesising organisms of the various marine habitats: the phytoplankton (both cyanobacteria and eukaryotes) in open waters, and macroalgae, marine angiosperms and photosymbiont-containing invertebrates in those benthic environments where there is enough light for photosynthesis to support growth, and describes how these organisms evolved. The special properties of seawater for sustaining primary production are then considered, and the two main differences between terrestrial and marine environments in supporting photosynthesis and plant growth are examined, namely irradiance and inorganic carbon. The second part of the book outlines the general mechanisms of photosynthesis, and then points towards the differences in light-capturing and carbon acquisition between terrestrial and marine plants. This is followed by discussing the need for a CO2 concentrating mechanism in most of the latter, and a description of how such mechanisms function in different marine plants. Part three deals with the various ways in which photosynthesis can be measured for marine plants, with an emphasis on novel in situ measurements, including discussions of the extent to which such measurements can serve as a proxy for plant growth and productivity. The final chapters of the book are devoted to ecological aspects of marine plant photosynthesis and growth, including predictions for the future.
eBook
Importance of underwater light field in selecting phytoplankton morphology in a eutrophic reservoir
This study attempted to reveal the effect of solar radiation fluctuation on the dynamics of phytoplankton communities expressed as cell morphology in eutrophic water bodies where the impacts of nutrients could be considered as small. Two morphological descriptors were proposed, cellular projected area (
φ
p
) and flattening index (
f
), which were able to he cellular light-harvesting potential and energy requirement, respectively. A model was established to describe the effects of natural light availability on selecting phytoplankton assemblages with underwater field and mixing process in the water column considered. Based on the data collected from the eutrophic Yanghe Reservoir, the model was derived as
V
=
37.92
λ
φ
p
(
R
2
=
0.673
,
P
<
0.01
)
,
where
V
is bio-volume,
λ
is a function of solar elevation angle (θ) and mixing/euphotic depth ratio (
z
mix
/
z
eu
) in water, and
φ
p
.
Post-analysis of the model results revealed that species with large
φ
p
and
f
in general have advantages in spring and winter when underwater light availability is low; by contrast, those with small
φ
p
and
f
have advantages in summer. Larger
φ
p
and
f
mean that the cells could harvest more light energy and consumed less, allowing them to be selected under low light availability; and vice versa. We thus concluded that the underwater light field probably the most important factor in selecting phytoplankton morphology in eutrophic water bodies.
Journal Article
Design of an Underwater Optical Communication System Based on RT-DETRv2
Underwater wireless optical communication (UWOC) is a key technology in ocean resource development, and its link stability is often limited by the difficulty of optical alignment in complex underwater environments. In response to this difficulty, this study has focused on improving the Real-Time Detection Transformer v2 (RT-DETRv2) model. We have improved the underwater light source detection model by collaboratively designing a lightweight backbone network and deformable convolution, constructing a cross-stage local attention mechanism to reduce the number of network parameters, and introducing geometrically adaptive convolution kernels that dynamically adjust the distribution of sampling points, enhance the representation of spot-deformation features, and improve positioning accuracy under optical interference. To verify the effectiveness of the model, we have constructed an underwater light-emitting diode (LED) light-spot detection dataset containing 11,390 images was constructed, covering a transmission distance of 15–40 m, a ±45° deflection angle, and three different light-intensity conditions (noon, evening, and late night). Experiments show that the improved model achieves an average precision at an intersection-over-union threshold of 0.50 (AP50) value of 97.4% on the test set, which is 12.7% higher than the benchmark model. The UWOC system built based on the improved model achieves zero-bit-error-rate communication within a distance of 30 m after assisted alignment (an initial lateral offset angle of 0°–60°), and the bit-error rate remains stable in the 10−7–10−6 range at a distance of 40 m, which is three orders of magnitude lower than the traditional Remotely Operated Vehicle (ROV) underwater optical communication system (a bit-error rate of 10−6–10−3), verifying the strong adaptability of the improved model to complex underwater environments.
Journal Article
How functional traits of submerged macrophytes response to underwater light quality?
Eutrophication of water bodies causes the disappearance of submerged macrophytes and frequent blooms of phytoplankton, which leads to changes in the underwater light environment in the aspect of light intensity and light quality. However, compared with underwater light intensity, only few studies have been concentrated in the effect of light quality on submerged macrophytes. The effect of light quality on plants is heterogeneous, and there are two absorption peaks in red and blue wavelengths. Thus, we carried out a mesocosm experiment to study the effects of a series of red and blue light ratios (red/blue light ratio = 1/8, 1/4, 1/1, 4/1, and 8/1) on two submerged macrophyte species,
Hydrilla verticillata
and
Vallisneria natans
. We hypothesized that functional traits (growth strategy, morphological, photosynthetic, and nutritional traits) of submerged macrophytes will be modified by different red/blue light ratios. With the increase of red/blue light ratio, plant height of the two submerged macrophytes decreased, while tillers number increased. We could not completely verify our hypothesis, but we found species-specific differences. The leaf area of
H. verticillata
under 8/1 red/blue light ratio was significantly higher than that under 1/8 red/blue light ratio, whereas the leaf area of
V. natans
under 4/1 red/blue light ratio was lower than that under 1/8 red/blue light ratio. Our results are helpful to understand the disappearance mechanism of submerged macrophytes in eutrophic lakes and devise more appropriate measures for the recovery of submerged macrophytes.
Journal Article
Contrastive Feature Disentanglement via Physical Priors for Underwater Image Enhancement
Underwater image enhancement (UIE) serves as a fundamental preprocessing step in ocean remote sensing applications, encompassing marine life detection, archaeological surveying, and subsea resource exploration. However, UIE encounters substantial technical challenges due to the intricate physics of underwater light propagation and the inherent homogeneity of aquatic environments. Images captured underwater are significantly degraded through wavelength-dependent absorption and scattering processes, resulting in color distortion, contrast degradation, and illumination irregularities. To address these challenges, we propose a contrastive feature disentanglement network (CFD-Net) that systematically addresses underwater image degradation. Our framework employs a multi-stream decomposition architecture with three specialized decoders to disentangle the latent feature space into components associated with degradation and those representing high-quality features. We incorporate hierarchical contrastive learning mechanisms to establish clear relationships between standard and degraded feature spaces, emphasizing intra-layer similarity and inter-layer exclusivity. Through the synergistic utilization of internal feature consistency and cross-component distinctiveness, our framework achieves robust feature extraction without explicit supervision. Compared to existing methods, our approach achieves a 12% higher UIQM score on the EUVP dataset and outperforms other state-of-the-art techniques on various evaluation metrics such as UCIQE, MUSIQ, and NIQE, both quantitatively and qualitatively.
Journal Article