# A Survey on Unmanned Surface Vehicles for Disaster Robotics: Main Challenges and Directions
## 4 Use of USVs in Environmental Disasters with Contaminants
### Biological Hazards  
Although the microscopic planktonic algae are critical food for filter-feeding bivalve shellfish (e.g., oysters, mussels, scallops, clams), in some cases, the proliferation of plankton algae (so-called \"algal blooms\") can have an adverse effect to aquaculture, fisheries and tourism operations [142]. There are over 5000 algal species of documented phytoplankton species. However, about 50 of them can be harmful to the environment, due to the toxins they produce. Such toxins can harm and contaminate the water life and even kill a human [143]. Marine algal toxins are responsible for more than 60,000 intoxication incidents per year, with an overall mortality rate of 1.5% worldwide, and for die-offs of fish and shellfish and have been implicated in the mortality of marine mammals, birds, and other animals dependent on the marine food web [144]. The problem of Harmful Algal Bloom (HAB)is so severe that when it occurs in the United States or European Union, it results in sampled saxitoxin concentrations more than 80 \(\upmu\)g per 100 mg of molluscan tissue. Commercial and recreationalishers and growers are then precluded by law from harvesting and selling shellfish [143]. Due to the threat to freshwater ecosystems, the occurrence of massive development of noxious cyanobacteria (blue-green algae) is increasing. Such algae cause a variety of harmful impacts on the aquatic environment, since they produce toxic substances [145] and reduce the dissolved oxygen in water due to the decomposition of extensive amounts of organic material. To identify such toxins in HABs and avoid human exposure to hazardous conditions, researchers are considering USVs for performing HAB monitoring tasks. Table 4 presents the work that use USVs to conduct environmental monitoring for HAB identification, where \(NR\) means \"Not Reported\" to data not reported by the authors. [PERSON] et al. [146; 147] introduce the development of a new long-duration solar-powered USV known as the Ocean-Atmosphere Sensor Integration System (OASIS). The platform intends to function as a low-cost, long-duration, reusable, navigable, open maritime platform focusing on the collection of measurements at the ocean-atmosphere boundary layer. It is equipped with sensors for water measurements (e.g., temperature, salinity, depth, colored dissolved organic matter, chlorophyll, phycoerythrin, and rhodamine) and meteorological measurements (e.g., wind, barometric pressure, relative humidity, pressure, and temperature). One of the objectives of the OASIS is to contribute with the development of new systems and techniques for understanding and monitoring of HAB. [PERSON] et al. [148] suggested HAB characterization with a fleet of USVs. In that work, a Sensor Web-relevant system called the Telesupervised Adaptive Ocean Sensor Fleet (TAOSF) enables the in situ study of surface and sub-surface characteristics of HABs. The system is composed of OASIS USVs as well as the land-based control and communications infrastructure. The platform also provides a mast-mounted meteorological station enabling acquisition of atmospheric measurements including barometric pressure, air temperature, relative humidity, wind speed, and wind direction. Later [149], experiments were performed in the Chesapeake Bay area using OASIS platforms and autonomous kayak to test and validate sensors as well as assemble and to analyze HAB-related data. [PERSON] et al. [151] describe a Multilevel Autonomy Robot Telesupervision Architecture (MARTA) for multi-robot science exploration. The telesupervised architecture with a combination of unmanned systems involving the OASIS platform is used for the detection of HAB. Researchers designed a technique which uses an USV for monitoring and tracking harmful Dinoflagellate Cochlodinium polykrikoides, responsible for red tides that can kill fishes, damage coral reefs, and interfere with desalinization plants [159]. Besides the use of a USV, experiments are carried out using aerostat: an unmanned, lighter-than-air unpowered blimp on a tether.