A dense Ecklonia radiata (Laminariales) kelp forest extending at least 35 km has been found between 45 and 60 m depth range within the mesophotic zone inside the iSimangaliso marine-protected area (MPA) at the iSimangaliso Wetland park World Heritage Site on the east coast of South Africa. This is the first visual confirmation of the occurrence of E. radiata beds in subtropical South Africa, in an area situated between the tropical and subtropical bioregions, in an area that spans the Natal and Delagoa bioregions of the south-western Indian Ocean, more than 350 km north of its previously documented South African range. The kelp was found to be present across the length of the MPA, but dense beds were present only in the southern Natal bioregion, with sparse occurrences observed elsewhere on soft-coral and sponge-dominated reefs in the upper mesophotic zone. The footage was collected in November 2020, May 2021 and November 2022 during remotely operated vehicle and drop camera surveys of the mesophotic zone inside the MPA. This discovery adds to the body of knowledge on the global distribution of Laminariales populations in deep tropical and subtropical settings and the diversity of habitats within South Africa's largest coastal MPA.

Underwater vehicles are rich systems with attractive and challenging properties such as nonlinearities, external disturbances, and underactuated dynamics. These make the design of an advanced and robust controller quite a challenging task. This paper focuses on designing a model-free high-order sliding mode controller in a six-degree-of-freedom trajectory tracking task. The purpose of the control is accurate trajectory tracking and considerably reducing the chattering phenomenon in situations where the remotely operated vehicle (ROV) works in the presence of external disturbances, measurement errors, and actuator dynamics and nonlinearity, which is not seen in previous research. To demonstrate the stability of the closed-loop system, the Lyapunov theory is employed to ensure the asymptotic stability of tracking errors. A linear Kalman filter for estimating measurement errors is proposed to be used to correct positioning system outputs (speed, position, and attitude). In a hardware-in-the-loop test, the proposed controller for the ROV is tested in a real-time application, considering external disturbances, measurement errors, and actual thrusters. In addition, comparing the outcomes with the performance of the PID controller and the supper twisting controller shows the superiority of the proposed controller. Due to the existence of the measurement noise, spectrum analysis is also performed.

This paper focuses on depth trajectory tracking control for a Remotely Operated Vehicle (ROV) with dead-zone nonlinearity and saturation nonlinearity of thruster; an adaptive sliding mode control method based on neural network is proposed. Through the analysis of dead-zone nonlinearity and saturation nonlinearity of thruster, the depth trajectory tracking control system model of a ROV which uses thruster control signals as system input has been established. According to the principle of sliding mode control, an adaptive sliding mode depth trajectory tracking controller is built by using three-layer feed-forward neural network for online identification of unknown items. The selection method and update laws of the control parameters are also given. The uniform ultimate boundedness of trajectory tracking error is analysed by Lyapunov theorem. Finally, the effectiveness of the proposed method is illustrated by simulations.

Underwater position data is a key requirement for the navigation and control of unmanned underwater vehicles. The proposed navigation scheme can be used in any vessel or boat for any shallow water vehicle. This paper presents the position estimation algorithm developed for shallow water Remotely Operated Vehicles (ROVs) using attitude data and Doppler Velocity Log data with the initial position from the Global Positioning System (GPS). The navigational sensors are identified using the in-house developed simulation tool in MATLAB, based on the requirement of a position accuracy of less than 5%. The navigation system is built using the identified sensors, Kalman filter and navigation algorithm, developed in LabVIEW software. The developed system is tested and validated for position estimation, with an emulator consisting of a GPS-aided fibre optic gyro-based inertial navigation system as a reference, and it is found that the developed navigation system has a position error of less than 5%.

Understanding the role played by sunken vessels in Mediterranean marine ecosystems is acquiring increasing importance. The aim of this research was to study the fish communities associated with four shipwrecks, by means of underwater visual censuses performed by a remotely operated vehicle, and to test the differences in composition of fish assemblages between these shipwrecks and the adjacent soft bottoms, considered as control sites. Multivariate analysis on the total fish assemblage showed significant differences between wrecks and controls. Results also showed higher levels of species richness and abundance near all wrecks than at a short distance from them on soft bottoms, thus indicating that these sunken vessels, thanks to their higher habitat complexity, act as artificial reefs, attracting aggregations of fish species and leading to a greater diversification of the local fish assemblage. Nevertheless, shipwrecks, which are an ideal target for recreational fishermen, could contribute to the over-exploitation of some high-value fish species, such as Mycteroperca rubra, Dentex dentex and Diplodus spp., attracted by the artificial hard substrate of the vessel-reefs. The recent European directives suggest an urgent need for a better understanding of the crucial role played by these potential sources of pollutants on marine environments and ecosystems. An ecosystem approach to study and monitor these pollutant sources is, therefore, mandatory for appropriate remediation and/or mitigation of the potential negative effects on a productive and healthy ocean.

Size distribution and swimming activity of the sea scallop, Placopecten magellanicus, were measured in situ from high-definition video recordings collected by a remotely operated vehicle on a fished scallop bed on German Bank, Gulf of Maine in August 2010. Scallop densities ranged from 0.004 to 3.89 m−2 and shell height (SH) ranged from 16.3 to 193.8 mm. The size distribution was bimodal, with high abundance from 20 to 40 mm SH indicating a recent recruitment event in the area. The low abundance of scallops >100 mm SH was likely due to the active fishery in this area. Of 535 observed swims, 200 were characterized for swim distance, time, velocity and distance travelled per adduction. The size of scallops observed to swim ranged from 18.9 to 99.9 mm SH. Both swim time and swim distance increased linearly with SH, and quadratic relationships were observed between velocity and SH, and between distance travelled per adduction and SH. Swimming velocities peaked at ~ 50 cm s−1 for scallops between 60 and 80 mm, and maximum velocity was 103.2 cm s−1observed for an individual of 64.0 mm SH. Our study provided a unique opportunity to investigate size distribution and associated swimming activity of scallops in their natural habitat, rather than in a simulated study in the laboratory, and at depths not reachable by SCUBA diving.

The longfin gunnel, Pholis clemensi, was previously reported to range as far south as Point Arena California in the Pacific Ocean. New observations are documented south to Point Lobos with geo-referenced photographs from remotely operated vehicles extending the known range to 304.5 km.

Recent exploration of the New England and Corner Seamounts revealed four new species of Chrysogorgia, described here using a combination of molecular and morphological data. These four species are characterized by a sinistral spiral, a character that, with one known exception, has only been reported for Pacific species. In addition, two species have a sclerite composition typical of the Pacific (‘squamosae typicae’). This faunal connection between the Atlantic and the Pacific is confirmed by analysis of the mitochondrial msh1 gene. The exceptional preservation of specimens collected with remotely operated vehicles allows us to discuss the effect of growth on some morphological characters.

The response of a deep-water megafaunal assemblage to sedimentation disturbance from hydrocarbon drilling was investigated using remotely operated vehicle video off the Atlantic coast of Venezuela. This was the first assessment of megafauna in bathyal waters in this region. A two-way analysis of variance (ANOVA) design was used to assess patterns in density and assemblage structure both temporally, before and after the drilling event, and spatially, at different distances from the disturbance. High levels of sedimentation occurred within a radius of 20 to 50 m from the drilling site. Megafaunal densities were reduced with high levels of disturbance (from 0.60 m−2 to 0.17 m−2 <20 m from the drilling site). The responses of motile and sessile fauna were different. Sessile fauna were most common (77% total) and reflected trends for total density. Motile megafaunal density was generally higher after drilling (up to double the pre-drill density). Species richness was reduced by disturbance and proximity to the disturbance. Multivariate ANOVA revealed significant differences in assemblage composition with distance and before and after drilling but no interaction. This was most likely a result of variable species-specific responses to disturbance. Megafaunal densities were generally much higher than reported densities from comparable depths in the Gulf of Mexico or from deeper locations in the Caribbean Sea. The responses to sedimentation disturbance were generally less obvious than observed elsewhere and may result from the fauna being adapted to the naturally high levels of sedimentation deriving from the Orinoco River.

Here we report direct underwater observations of the pom pom anemone Liponema multicornis at sites in the western Gulf of Maine. The paucity of records from historic collections as well as recent studies suggest this species is widespread but numerically rare across the region. We found this species hosts high numbers of the commensal amphipod Stenothoe brevicornis amongst the tentacles. In addition, pandalid shrimp were observed using the anemone for shelter by occupying space around the distal edges of the tentacles and as a food source by feeding on bits of mucous. Krill were also observed feeding on amphipods occurring amongst the tentacles. A long history of using bottom contact fishing gear in the region may have reduced abundance, thereby reducing the functional role of L. multicornis as a source for refuge and prey of several crustacean species.

Four individuals of the large scyphozoan jellyfish Stygiomedusa gigantea were observed in the northern Gulf of Mexico over 2005–2009 by industrial remotely operated vehicles as part of the SERPENT Project. One of these observations included the symbiotic bythitid fish Thalassobathia pelagica. Prior to these observations, neither S. gigantea nor T. pelagica had been observed in, or collected from the Gulf of Mexico. In order to summarize the available information on S. gigantea, we located 110 observations obtained over 110 years (1899–2009) representing 118 individual specimens of this species from around the world. The resulting dataset confirms that this species is cosmopolitan occurring with records from all oceans except the Arctic. While the depth-range of the four Gulf of Mexico specimens was bathypelagic, there appears to be a pattern of S. gigantea occurring in mesopelagic and epipelagic depth-zones at high latitudes, particularly in the Southern Ocean and mesopelagic and bathypelagic depths at mid- and low-latitudes. This pattern may be related to the meridional vertical distribution of temperature or perhaps avoidance of light levels that could degrade porphyrin pigments. There was no evidence that this species migrates vertically. Two of the individuals in the Gulf of Mexico appeared to be actively clinging to subsea structures and we speculate that this is a consequence of its normal mode of feeding, which may entail using its large oral lobes to hold on to, and trap prey.