Hypereutrophic Grand Lake St Marys (GLSM) is a large (52 km2), shallow (mean depth ~ 1.5 m) reservoir in an agricultural watershed of western Ohio (USA). GLSM suffers from extensive cyanobacterial harmful algal blooms (cHABs) that persist much of the year, resulting in total microcystin concentrations that are often above safe contact levels. Over two summers (2020 and 2021), two phosphorus (P) binding agents (alum and lanthanum/bentonite clay Phoslock, respectively), in conjunction with a P-binding algaecide (SeClear) in 2021, were applied to a 3.24-ha enclosure to mitigate cHAB activity and create a ‘safe’ recreational space for the public. We evaluated these applications by comparing total phosphorus (TP), total microcystin, total chlorophyll, and phycocyanin concentrations within the enclosure and the adjacent lake. Some evidence for short-term reductions in TP, microcystin, chlorophyll, and phycocyanin concentrations were observed following each P binding treatment, but all parameters rapidly returned to or exceeded pre-application levels within 2–3 weeks after treatment. These results suggest that in-lake chemical treatments to mitigate cHABs are unlikely to provide long-lasting benefits in these semi-enclosed areas of large, shallow, hypereutrophic systems, and resources may be better applied toward reducing external nutrient loads (P and nitrogen) from the watershed.

The aquaculture industry requires good water quality for its successful operation but produces wastes that can cause environmental deterioration and pose high risks to the sector. Adequate waste treatment and recycling are necessary to make aquaculture a sustainable and profitable industry and contribute to the circular economy. Polluted water sources, excess feeding, overstocking, use of antibiotics/chemicals and harmful algal blooms are major causes of water quality deterioration and low production in aquaculture systems. Discharges of untreated wastes would have serious impacts on the receiving water bodies, and eventually on the aquaculture industry itself. Possible solutions include technological innovations in environmentally friendly production systems, use of efficient processes in water quality management and improved legislation and governance. Environmentally feasible aquaculture production technologies such as recycling aquaculture system, integrated multi-trophic aquaculture and aquaponics including features of waste recycling are viable options in aquaculture schemes. Best aquaculture practices integrating advanced water quality treatment processes and technologies, supported by automation and sensors, modeling and artificial intelligence-internet of things are necessary for a sustainable aquaculture environment, production and stable value chain. In general, low-cost technologies for aquaculture waste treatment and environmental impact reduction through good governance are crucial for achieving sustainability in the aquaculture industry and natural environmental management.

The frequency and intensity of harmful algal bloom (HAB) events have been increasing in many places around the world. Heterosigma akashiwo is a marine raphidophyte species known to cause HABs in many places across tropical and temperate climates. Studies of temperate strains have identified that H. akashiwo blooms are driven by mass activation of cysts which, for this species, can only form at <15°C temperatures. Although these temperatures do not occur in the tropics, there have been no comparative studies for tropical H. akashiwo. This study aimed to investigate whether tropical H. akashiwo can form cysts under warm temperatures, therefore having different responses from temperate strains. Results showed that tropical H. akashiwo were similar with temperate strains and could only form round cyst-like structures at 5°C but not 25°C. We also observed novel response of a decline and recovery in cell densities at 25°C. The decline was interrupted when the cultures were diluted, implying a tendency for H. akashiwo to rapidly spread and accumulate within surrounding waters, thereby facilitating blooms. This behaviour presents unique bloom concerns. Close monitoring of H. akashiwo distribution patterns is needed for better assessment of the bloom threat posed within tropical waters.

Harmful algal blooms caused by raphidophyte species of the genus Chattonella (i.e. Chattonella antiqua, Chattonella marina and Chattonella ovata) have been documented in temperate coastal regions around the world. To understand the effects of physicochemical factors on bloom development of Chattonella spp., we investigated the variations of vegetative and resting cells (i.e. cysts) of Chattonella spp. and environmental variables in two coastal environments, Uranouchi Inlet (extremely closed) and Nomi Inlet (semi-closed), with contrasting enclosed natures. Although the vegetative cells and cysts of Chattonella spp. were distributed in both coastal regions, the densities were remarkably higher in Uranouchi Inlet than in Nomi Inlet. The mud content in the sediments of Uranouchi Inlet was also higher than that in the sediments of Nomi Inlet, meaning that fine particles such as cysts are likely to accumulate in the former region. Because of the extremely closed nature of Uranouchi Inlet, warm oceanic waters of the Kuroshio Current penetrate the inlet only infrequently. These results suggest that the closed nature of coastal regions is an important factor influencing either water exchange or the resultant accumulation of Chattonella cells in coastal environments.

Two benefit-transfer approaches are used to estimate welfare losses from closure of Lake Erie beaches. We identify conditions for which the function transfer, which is more time-consuming and data-intensive, is worth the effort relative to a simple value transfer. The function transfer was essential for estimating beach demand (trips) and demand elasticity (change in trips); when evaluating individual beach closures with known trip demand, the two methods yielded similar results. Results produced by the two transfer methods deviated (up to 106 percent) when multiple beaches were closed simultaneously because value transfer did not account for the loss of beach substitutes.

Microalgal blooms are a natural part of the seasonal cycle of photosynthetic organisms in marine ecosystems. They are key components of the structure and dynamics of the oceans and thus sustain the benefits that humans obtain from these aquatic environments. However, some microalgal blooms can cause harm to humans and other organisms. These harmful algal blooms (HABs) have direct impacts on human health and negative influences on human wellbeing, mainly through their consequences to coastal ecosystem services (fisheries, tourism and recreation) and other marine organisms and environments. HABs are natural phenomena, but these events can be favoured by anthropogenic pressures in coastal areas. Global warming and associated changes in the oceans could affect HAB occurrences and toxicity as well, although forecasting the possible trends is still speculative and requires intensive multidisciplinary research. At the beginning of the 21st century, with expanding human populations, particularly in coastal and developing countries, mitigating HABs impacts on human health and wellbeing is becoming a more pressing public health need. The available tools to address this global challenge include maintaining intensive, multidisciplinary and collaborative scientific research, and strengthening the coordination with stakeholders, policymakers and the general public. Here we provide an overview of different aspects of the HABs phenomena, an important element of the intrinsic links between oceans and human health and wellbeing.

This paper deals with the economic impact of the invasion of a scallop fishery by an exotic shellfish that was accidentally imported some decades ago. The invasive alien species, a slipper-limpet, Crepidula fornicata, is a space competitor for local scallops, and its spread threatens the sustainability of the ongoing scallop restocking program. Facing this invasion, the local fisheries committee has initiated a containment project intending to make the restocking program consistent with the exotic species presence in the fishery. The issue is complicated by the occurrence of occasional toxic micro-algae blooms affecting the scallop fishery. The paper presents a model dealing with the economic impact of the invasive process, and a methodology for cost-benefit analysis of invasion management. According to numerical simulation, the invasion is a serious threat to the economic viability of the restocking program, and invasion management would help maintaining the long term sustainability of the fishery. Sensitivity tests highlight the importance of long term equilibrium scallop catches on the program result, depending on scallop farming technical performance and ecosystem disturbance.