Sea Bottom Type Research Articles

Spatial distribution of the demersal chondrichthyan community from the western Mediterranean trawl bycatch

IntroductionChondrichthyans (sharks, batoids and chimaeras) play key roles in the regulation of marine food webs dynamics. However, more than half of the assessed species in the Mediterranean are threatened, primarily by fishing pressure and compounded by habitat degradation and climate change. Nevertheless, there is an important knowledge gap in identifying the underlying drivers of their community structure and spatial distribution.Methods and ResultsWe provide insights into the current bycatch rates of chondrichthyans in the western Mediterranean commercial bottom trawling fishery by accurately depicting the unaltered practices of the local fleet. A total of 17 species were recorded in the studied fishing grounds (ranging from 50 to 800 m deep), including 7 sharks, 9 batoids, and 1 chimaera, although the total catch was dominated by few species. Furthermore, we tested the effect of environmental and fishing-related factors on multiple community descriptors by using analysis of community structure (multidimensional scaling and analysis of similitude) and generalized linear mixed models to further understand the drivers of the chondrichthyan community distribution and structure. This study revealed the importance of combining environmental and anthropogenic drivers to further understand the spatial distribution patterns of chondrichthyan communities. Our results indicate that depth was the main driver of the community structure, with deeper areas within the fishing grounds hosting a higher diversity. Sea bottom temperature and substrate type also influenced the distribution of the community, with substrate effects changing depending on the intensity of fishing pressure. In all cases, density, biomass, and diversity of chondrichthyans were negatively impacted by increasing fishing effort. DiscussionUnderstanding the drivers of the structure and distribution of the chondrichthyan community is crucial to understand the potential impacts that increased fishing pressure, habitat loss and global change may entail. The ongoing challenges that the Mediterranean chondrichthyans and their ecosystems are facing highlights the need for continued monitoring and improved chondrichthyan-focused fisheries management.

Discriminant analysis of environmental data based on zero inflated spatial auto-beta models

In this paper, a supervised classification problem of classifying feature observation into one of two populations is considered. Classical supervised classification in this work is expanded for non-Gaussian spatial data specified by zero inflated auto-beta models. A classification rule based on the Bayes discriminant function (BDF) that uses conditional probability density functions in the expression is proposed. This rule is applied to real data set for identifying sea bottom type by using Black carrageen concentration data over the southeastern Baltic Sea. Different feature observation models are chosen and classification results are compared using a hold-out error rate measure.

Surface wave disturbance during internal wave propagation over various types of sea bottoms

In this study, we used a numerical model to simulate the propagation of internal waves (IWs) over various topographies, such as those with a flat bottom or bottom with a triangular trench or a ridge, and investigate the development, propagation, and dissipation mechanisms of IWs. Detailed evolution of IWs and vortices and their effects on the disturbance of the ocean surface were studied. The numerical results show that strong mixing and water exchange occur during IW propagation, resulting in severe convergence and dispersion, which lead to strong free surface flow and create noticeable free surface waves. The shapes of free surface waves and IWs have opposing orientations. In addition, there exists a close relationship between IWs and ocean surface waves, which may assist researchers in retrieving the amplitude of IWs by observing the behavior of free surface waves. The resonant interaction of IWs and surface waves was analyzed as IWs passed various types of sea bottom. The results indicate that IWs and surface waves move in the same phase, and the spatial variation of the waves shows that both wave types have the same wavelength.

Degradation of Crude Oil and PAHs in Iron–Manganese Concretions and Sediment from the Northern Baltic Sea

ABSTRACTThe ability of different sea bottom types to recover from oil contamination under oxic and anoxic conditions is poorly known in the brackish Baltic Sea. We carried out microcosm experiments to examine the capacity of iron–manganese concretions and sediment to remove petroleum compounds at 10°C. The biological degradation potential of polycyclic aromatic hydrocarbons (PAHs) was indicated by the 1000-fold increase in the copy numbers of PAH-degradation genes resulting in 2.2 × 106 gene copies g−1 DW. In the experiments 35−81% of the crude oil and 96% of PAHs disappeared through abiotic and biotic pathways, and there was little difference between the concretions and sediment. Bacterial community analysis revealed that the bacterial sequences obtained from the oil-treated concretions were affiliated to groups typical for concretions and metal-rich environments, whereas oil-treated sediment sequences were similar to those originating from sediments and oil-contaminated environments. The high frequency of concretion clones affiliated with specific taxonomic groups of α-, β-, γ-, and δ-proteobacteria may indicate the existence of new clades of bacteria within the Rhizobiales and Rhodospirillales of the α-proteobacteria, Burkholderiales—incertae sedis of the β-proteobacteria, Chromatiales of the γ-proteobacteria and the Syntrophobacteriales of the δ-proteobacteria. Our study suggests that concretions and bottom sediment maintain rich, distinct bacterial communities under oil exposure that have the potential to remove petroleum compounds in oxic and anoxic conditions.

Sea Bottom Classification by Means of Bathymetric LIDAR Data

Light Detection and Ranging (LIDAR) provides high horizontal and vertical resolution of spatial data located in point cloud images, and is increasingly being used in a number of applications and disciplines, which have concentrated on the exploit and manipulation of the data using mainly its three dimensional nature. Bathymetric LIDAR systems and data are mainly focused to map depths in shallow and clear waters with a high degree of accuracy. Additionally, the backscattering produced by the different materials distributed over the bottom surface causes that the returned intensity signal contains important information about the reflection properties of these materials. Processing conveniently these values using a Simplified Radiative Transfer Model, allows the identification of different sea bottom types. This paper presents an original method for the classification of sea bottom by means of information processing extracted from the images generated through LIDAR data. The results are validated using a vector database containing benthic information derived by marine surveys.

Remote Sensing of shallow sea floor for digital earth environment

Understanding the sea floor biodiversity requires spatial information that can be acquired from remote sensing satellite data. Species volume, spatial patterns and species coverage are some of the information that can be derived. Current approaches for mapping sea bottom type have evolved from field observation, visual interpretation from aerial photography, mapping from remote sensing satellite data along with field survey and hydrograhic chart. Remote sensing offers most versatile technique to map sea bottom type up to a certain scale. This paper reviews the technical characteristics of signal and light interference within marine features, space and remote sensing satellite. In addition, related image processing techniques that are applicable to remote sensing satellite data for sea bottom type digital mapping is also presented. The sea bottom type can be differentiated by classification method using appropriate spectral bands of satellite data. In order to verify the existence of particular sea bottom type, field observations need to be carried out with proper technique and equipment.

中層・底層定置網の箱網用海亀脱出装置に対する海亀の行動

中層・底層定置網の箱網用海亀脱出装置に対する海亀の行動

Geo-spatial multi-criteria analysis for wave energy conversion system deployment

The growing requirements for renewable energy production lead to the development of a new series of systems, including wave energy conversion systems. Due to their sensitivity and the impact of the aggressive marine environment, the selection of the most adequate location for these systems is a major and very important task. Several factors, such as technological limitations, environmental conditions, administrative and logistic conditions, have to be taken into account in order to support the decision for best location. This paper describes a geo-spatial multi-criteria analysis methodology, based on geographic information systems technology, for identification of the best location to deploy a wave energy farm. This methodology is not conversion system dependent and therefore can be easily customized for different systems and implementation conditions. Selection factors can include, for example, ocean depth, sea bottom type, existing underwater cables, marine protected areas, ports location, shoreline, power grid location, military exercise areas, climatology of wave significant height, period and power. A case study demonstrating this methodology is presented, for an area offshore the Portuguese southwest coast. The system output allows a clear differential identification of the best spots for implementing a wave energy farm. It is not just a simple Boolean result showing valid and invalid locations, but a layer with a valued suitability for farm deployment.

Fish assemblage of the marine protected area of Cinque Terre (NW Mediterranean Sea): First characterization and assessment by visual census

The main objective of this study is to improve the knowledge of the coastal fish assemblage of ‘Cinque Terre’ Italian national Marine Protected Area (Ligurian Sea), focusing on the characterization of the fish fauna in the core zone A (no entry–no take). The study relates to the main sea-bottom types and bathymetric ranges, and evaluates the effect of the protection on fish abundance and size composition in this 5-yr-old MPA. Field activities were carried out in 2003 by means of visual census techniques. In the A zone, fish-assemblage composition are strictly related to depth and sea-bottom type. Recorded data did not permit detection of a clear reserve effect on fish fauna, probably due to the recent institution of the MPA. Several significant differences were detected only considering the size-class composition of target species.

Spectral library of macroalgae and benthic substrates in Estonian coastal waters

Benthic algal cover and trends in its changes are indicators of water state in coastal areas. Mapping benthic algal cover with conventional methods (diving) provides great accuracy and high resolution yet is very expensive and is limited by the time and manpower necessary to monitor large bodies of water and long stretches of coastline. Mapping of benthic macroalgal cover by remote sensing requires knowledge about optical signatures of different bottom types. We measured reflectance spectra of red, green, and brown macroalgae, seagrass, sand, pebble, and wet and dry decaying mats of macroalgae and higher plants. Comparing optical properties of the Baltic Sea macro- algae with results of other studies from different parts of the world allows us to conclude that reflectances of three large groups (red, green, and brown algae) are relatively consistent in shape. Most of the variability within the groups occurs in reflectance values. The within-species variability in reflectance values of the brown alga Fucus vesiculosus and the red alga Furcellaria lumbricalis is as great as the variability in reflectance values within brown and red algae groups, correspondingly. This suggests that the feasibility of mapping the benthic macroalgal cover in the coastal waters of the Baltic Sea by remote sensing on species level is highly unlikely. The collected spectral library of the Baltic Sea bottom types allows us to interpret remote sensing data using supervised classifi- cation methods, such as Spectral Angle Mapper, which require availability of reflectance spectra of different bottom types. The spectral library together with a bio-optical model allows estimating the suitability of different remote sensing sensors for mapping Baltic Sea bottom types. Thus, collecting the spectral library is an important step in mapping shallow water bottom types by remote sensing.

Complex reflection phase gradient as an inversion parameter for the prediction of shallow water propagation and the characterization of sea-bottoms.

In this paper a quantity is proposed, referred to as the complex reflection phase gradient, whose use in a matched field inversion procedure allows for the rapid extraction of first order geo-acoustic information about the sea-bottom. It is based on the observation that at low grazing angles the reflection phase and bottom loss for a wide range of sea-bottom types commonly exhibits an approximate linear relationship to the vertical component of the acoustic wave number at the seabed. The real part of this quantity specifies the rate at which the reflection phase varies with vertical acoustic wave number while the imaginary part quantifies the rate of change of bottom loss. Despite being defined with just two real parameters it is shown that it provides an accurate prediction of the sound field for a wide range of bottom types. In addition, its measurement permits an estimate to be made for the input impedance to the seabed in the zero grazing angle limit and, in the case of a homogeneous elastic half-space of known density, the compressional and shear wave speed. The main advantage of the two-parameter seabottom representation is that each parameter is readily inverted from comparatively few acoustic pressure measurements. The usefulness of the technique is illustrated by the results from computer simulated acoustic pressure measurements made at just eleven sensors in a simple shallow water channel, and results from a 10 cm deep laboratory channel at frequencies between 10 kHz and 75 kHz.

Markov Random Field and Fuzzy Logic Modeling in Sonar Imagery: Application to the Classification of Underwater Floor

This paper proposes an original method for the classification of seafloors from high resolution sidescan sonar images. We aim at classifying the sonar images into five kinds of regions: sand, pebbles, rocks, ripples, and dunes. The proposed method adopts a pattern recognition approach based on the extraction and the analysis of the cast shadows exhibited by each seabottom type. This method consists of three stages of processing. First, the original image is segmented into two kinds of regions: shadow (corresponding to a lack of acoustic reverberation behind each “object” lying on the seabed) and seabottom reverberation. Second, based on the extracted shadows, shape parameter vectors are computed on subimages and classified with a fuzzy classifier. This preliminary classification is finally refined thanks to a Markov random field model which allows to incorporate spatial homogeneity properties one would expect for the final classification map. Experiments on a variety of real high-resolution sonar images are reported.

Dependence of aerosol fluxes and their residence times on different types of sea bottoms

Dependence of aerosol fluxes and their residence times on different types of sea bottoms

千葉県南部沿岸のアワビ稚貝場の地形並びに流況

The authors studied these factors of sea bottom type and its current which seemed to make nursery ground. In the bottom types, it was discovered that the frequency of rock undulations in the abalone habitat were 0.60 to 0.81 per meter, and the relation between surf course and rock lines was almost 90 degrees. The depth of abalone habitats was less than 7 meters mainly. And the bottom consists of rock or mixed with sandy zone. As regards the current factor, the current speed of 0.07 to 0.48 meter per second in Kawaguchi and Otohama nursery ground of abalone, was verified. Especially, we got slow current on the nursery ground which were 0.02 to 0.21 meter per second except one station. We anticipated the existence of some eddy zones by the figure of residual current, and eddy zones were made behind the nursery habitat.

Application of multiple echoes energy measurements for evaluation of sea bottom type : Orlowski, Andrzej, 1984. Oceanologia, Warsz., 19:61–78

Application of multiple echoes energy measurements for evaluation of sea bottom type : Orlowski, Andrzej, 1984. Oceanologia, Warsz., 19:61–78