Morphostructural Characterization of the Heterogeneous Rhodolith Bed at the Marine Protected Area “Capo Carbonara” (Italy) and Hydrodynamics

Mediterranean rhodolith beds are priority marine benthic habitats for the European Community, because of their relevance as biodiversity hotspots and their role in the carbonate budget. Presently, Mediterranean rhodolith beds typically occur within the range of 30–75 m of water depth, generally located around islands and capes, on flat or gently sloping areas. In the framework of a collaboration between the University of Milano-Bicocca and the Marine Protected Area “Capo Carbonara” (Sardinia, Italy), video explorations and sampling collections in three selected sites revealed the occurrence of a well developed and heterogeneous rhodolith bed. This bed covers an area >41 km2 around the cape, with live coverage ranging between 6.50 and 55.25%. Rhodoliths showed interesting morphostructural differences. They are small compact pralines at the Serpentara Island, associated with gravelly sand, or bigger boxwork at the Santa Caterina shoal associated with sand, whereas branches are reported mostly in the Is Piscadeddus shoal, associated with muddy sand. Both in the Santa Caterina shoal and the Serpentara Island, rhodoliths generally show a spheroidal shape, associated with a mean value of currents of 4.3 and 7.3 cm/s, respectively, up to a maximum of 17.7 cm/s at Serpentara, whereas in the Is Piscadeddus shoal rhodolith shape is variable and current velocity is significantly lower. The different hydrodynamic regime, with a constant current directed SW, which deviates around the cape towards E, is responsible for such morphostructural heterogeneity, with the site of the Serpentara Island being the most exposed to a constant unidirectional and strong current. We can associate current velocity with specific rhodolith morphotypes. The morphostructural definition of the heterogeneity of rhodoliths across large beds must be considered for appropriate management policies.

Modeling the Habitat Distribution of Acanthopagrus schlegelii in the Coastal Waters of the Eastern Taiwan Strait Using MAXENT with Fishery and Remote Sensing Data

Black sea bream, Acanthopagrus schlegelii, is among the most commercially valuable species in the coastal fishery industry and marine ecosystems. Catch data comprising capture locations for the gillnet fisheries, remotely sensed environmental data (i.e., sea surface temperature, chlorophyll-a concentration, and current velocity), and topography (bathymetry) from 2015 to 2018 were used to construct a spatial habitat distribution of black sea bream. This species is concentrated in coastal waters (<3 nm) from December to April (spawning season). The maximum entropy (MaxEnt) method and corresponding habitat suitability index among seasons were used to clarify the species’ spatial distribution and identify the seasonal variations in habitat selection. The patterns corresponded closely to the changes in oceanographic conditions, and the species exhibited synchronous trends with the marine environment’s seasonal dynamics. Chlorophyll-a concentration and bathymetry substantially influenced (80.1–92.9%) black sea bream’s habitat selection. By applying the MaxEnt model, the optimal habitats were identified with four variables including depth and satellite-derived temperature, current velocity and chlorophyll-a concentration, which provides a foundation for the scientific assessment and management of black sea bream in coastal waters of the Eastern Taiwan Strait.

Three-Dimensional Numerical Modelling of Tidal Current in Balikpapan Bay Using Delft 3D

Balikpapan is one of the main port cities with residential areas, industry, trade, and vital objects scattered from north to south along the coast of Balikpapan Bay. This dense activity increases traffic in Balikpapan Bay. Thus, the hydrodynamic conditions in these waters are essential to be reviewed. The purpose of this research is to simulate hydrodynamics in Balikpapan Bay. The simulation results of the hydrodynamic model for sea-level elevation values are close to the conditions in the field, as indicated by the correlation coefficient 0.98, skill 0.99, and RMSE 0.15 m. The ocean current velocity verification includes the average correlation for x-direction and y-direction, up to 0.93, RMSE 0.05 m, and the percentage error of 6.7%. The significant current velocity is at low tide during spring tide with an average of 0.1 m/s and a maximum speed of 1.62 m/s. Temporally, the observation point at the mouth of Balikpapan Bay has the most significant Bed Shear Stress magnitude with an average of 0.05 N/m2. Spatially, the highest Bed Shear Stress magnitude is at the time of spring tide when it recedes towards the tide with an average Bed Shear Stress in the bay of 0.16 N/m2. The most dominant tidal components are M2 and S2, with a contribution value of 65.3%. The phase propagation from mouth to upstream of Balikpapan Bay for the M2 component in Balikpapan Bay is 10.5° (22.77 minutes) and 5.5° (11 minutes) for the S2 component.

The existence of epiphyte on thallus Eucheuma denticulatum (Rhodophyceae) in varying depths cultivated with vertical net method

The existence of macroepiphyte is one of the issues seaweed farmers often face. This research aims to explore the existence of macroepiphyte attached to seaweed Eucheuma denticulatum at varying depths using vertical net method. Research found that the highest and the lowest velocity of macroepiphyte on day -10 in the depth of 50 cm and 200 cm is 248,4 and 121,28 ind/m2/day. On day-20, in the depth of 100 cm and 200 cm is 333,54 and 270,01 ind/m2/day. The most dominating macroepiphyte in the attachment velocity is C. Crasa. Physical and chemical parameter showed around 29o-30oC. Current velocity 0,050-0,067 m/sec. Brightness 92%. Salinity 30-33‰. Nitrate 0,237-0,0416 mg/L. Phosphate 0,0015-0,0036 mg/L. Dissolved oxygen 5,7-6,2 mg/L. The obtained optimum environmental parameter and the type of the macroepiphyte attachment did not show any significant negative effect to the growth of E. denticulatum.

Co-existence of Epiphytes on Eucheuma Denticulatum (Rhodophyceae) in Varying Depths Cultivated with Verti Net Method

The existence of macroepiphytes is one of the issues seaweed farmers often face. This research aimed to explore the co-existence of macroepiphytes with seaweed Eucheuma denticulatum at varying depths using verti net method. Results showed that the highest and the lowest density of macroepiphyte were obtained on day -10 in the depth of 50 cm and 200 cm at 248,4 and 121,28 ind/m2/day, respectively. On day-20, in the depth of 100 cm and 200 cm the densities were 333,54 and 270,01 ind/m2/day, respectively. The most dominant macroepiphyte y is Chatomorpha crasa. Physical and chemical parameters showed a temperature of 29°-30°C, current velocity of 0,050-0,067 m/sec, brightness 92%, salinity 30-33‰, nitrate 0,237-0,0416 mg/L, phosphate 0,0015-0,0036 mg/L and dissolved oxygen 5,7-6,2 mg/L. The obtained optimum environmental parameters and the type of the macroepiphytes did not show any significant negative effect on the growth of E. denticulatum.

Forecasting Current Velocity and Profile in a Strait Water using Warped Gaussian Process

Ocean current forecast is vital for developing tidal energy and construction of offshore structures in the strait waters. This paper developed a short-term ocean current forecasting approach using the warped Gaussian process (WGP), which consists of the measured data preprocessing, kernel function selection, and data forecasting using WGP. A preprocessing using the wavelet thresholding method was proposed to enhance the quality of the measured raw data. The theory of WGP and the commonly used kernel functions were briefly introduced. The sliding time window and one-step ahead strategies were employed to increase the accuracy of predictions. Observations collected during an ocean current measurement campaign executed in a strait water on the coast of the East China Sea were used as an example dataset. The current velocity and profile were forecasted and validated using the example dataset as an illustration of the framework of the developed approach. The effects of window length, kernel function, and time interval on the WGP forecasting efficiency and precision were investigated. The forecasting performance of the developed WGP model was discussed by comparing it with the standard GP model. The current profile with a 95% confidence interval was also predicted by the developed WGP model at a certain point. The validation shows that the developed model is efficient in the short-term ocean current forecast.

Vector Current Measurement Using Doppler Scatterometry with Optimally Selected Observation Azimuths

The Doppler scatterometer is a new style of remote sensing tool that can provide current measurements over a wide swath for rapid global coverage. The existing current estimation method for Doppler scatterometry uses the maximum likelihood method to jointly derive the wind and current fields but shows high computational complexity. Moreover, the current radial speeds measured along two arbitrary observation azimuths are used to derive the vector current according to the parallelogram rule, which is not applicable for the case where two observation azimuths are not perpendicular. In this paper, a vector current velocity inversion method using an optimally selected observation azimuth combination—as well as a general current velocity calculation method—is proposed for Doppler scatterometry. Firstly, current radial speeds along several different observation azimuths are estimated using an interferometric phase difference matching method with low computational complexity. Then, two current radial components of each point are arbitrarily selected to estimate a preliminary current direction using the proposed vector current velocity derivation method. Finally, two observation azimuths that have the smallest intersection angles with the preliminarily estimated current direction are selected for vector current velocity determination. With the Ocean Surface Current Analyses Real-time (OSCAR) data as current input, vector current estimation experiments were conducted based on simulation analysis using an instrument conceptual design model for a pencil-beam scatterometer. The results show that the standard deviation of the estimated current velocity magnitude is 0.06 m/s. Compared with the reported results obtained by the existing method, the inversion accuracy of velocity magnitude is improved by 67%.

Velocity Estimation of Ocean Surface Currents in along-Track InSAR System Based on Conditional Generative Adversarial Networks

Velocity estimation of ocean surface currents is of great significance in the fields of the fishery, shipping, sewage discharge, and military affairs. Over the last decade, along-track interferometric synthetic aperture radar (along-track InSAR) has been demonstrated to be one of the important instruments for large-area and high-resolution ocean surface current velocity estimation. The calculation method of the traditional ocean surface current velocity, as influenced by the large-scale wave orbital velocity and the Bragg wave phase velocity, cannot easily separate the current velocity, characterized by large error and low efficiency. In this paper, a novel velocity estimation method of ocean surface currents is proposed based on Conditional Generative Adversarial Networks (CGANs). The main processing steps are as follows: firstly, the known ocean surface current field diagrams and their corresponding interferometric phase diagrams are constructed as the training dataset; secondly, the estimation model of the ocean surface current field is constructed based on the pix2pix algorithm and trained by the training dataset; finally, the interferometric phase diagrams in the test dataset are input into the trained model. In the simulation experiment, processing results of the proposed method are compared with those of traditional ocean surface current velocity estimation methods, which demonstrate the efficiency and effectiveness of the novel method.

Surface currents modeling based on tidal cycles and monsoon in tropical estuary, Indonesia

The modeling uses a software-based numerical model DHI MIKE user interface developed by The Danish Hydraulic Institute (DHI) Water and Environment, Denmark. Simulation of current uses a 2-dimensional model (averaging to depth) with a finite element approach. Modeling of currents was conducted to know current dynamics by tidal cycle and seasonal variation (west and east monsoon). The models were validated using correlation coefficient value (r) by comparing direct measurement and model output. The r-value for current velocity during west monsoon was 0.653 and east monsoon was 0.697 and for current direct during west monsoon was 0.887 and the east monsoon was 0.857. While the r-value for the tide was 0.858. All these r values showed a strong correlation and these indicated the models were valid. The result of the simulation of the current models showed that the surface currents were strongly influenced by the tidal cycles. The currents direct flowed to the south at flood tide and to the eastern at ebb tide. The maximum current velocity during the west monsoon was 0.50 m/sec and during the east monsoon was 0.40 m/sec. The averages of currents direct were more dominant eastward of Jeneberang estuary.