Toxic marine microalgae and noxious blooms in the Mediterranean Sea: A contribution to the Global HAB Status Report

• Published in: Harmful algae Vol. 102; p. 101843
• Main Authors: Zingone, Adriana, Escalera, Laura, Aligizaki, Katerina, Fernández-Tejedor, Margarita, Ismael, Amany, Montresor, Marina, Mozetič, Patricija, Taş, Seyfettin, Totti, Cecilia
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.02.2021
• Subjects: Adriatic Sea; aerosols; Alexandrium minutum; algal blooms; aquaculture; Azadinium; benthic organisms; biomass; Black Sea; ciguatera; coastal water; coasts; Dinophysis; domoic acid; fish kills; Gambierdiscus; HABs; human health; information systems; Marmara Sea; Mediterranean Sea; Microalgae; monitoring; mucilages; OBIS; poisoning; poisonous algae; risk; river deltas; shellfish; shellfish poisoning; summer; tourism; Toxicity; toxins; water quality; Marmara Sea; Adriatic Sea; Black Sea; Mediterranean Sea; OBIS; Microalgae; HABs; Toxicity; Mediterranean Sea
• ISSN: 1568-9883; 1878-1470; 1878-1470
• DOI: 10.1016/j.hal.2020.101843

•The Mediterranean Sea harbors more than 80 toxin-producing species, with a few cases of DSP and PSP and about 300 toxic events in 31 years, with an impact mainly on aquaculture.•The number of toxic species detected in the area has remarkably increased since the 1980s, but with no clear trend in toxin-related harmful events.•Large amounts of palytoxin-like toxins produced by Ostreopsis accumulate along rocky shores in summer since the 1990s, with sporadic problems caused by direct contact or aerosol.•Non-toxic events such as seawater discolorations and mucilages show wide fluctuations over the years with no clear trends, but represent the main risk in the MS for their possible impact on tourism and recreational activities. We review the spatial distribution of toxic marine microalgal species and the impacts of all types of harmful algal events (Harmful Algal Blooms, HABs) in the Mediterranean Sea (MS), including the Black Sea, the Sea of Marmara, coastal lagoons and transitional waters, based on two databases compiled in the Ocean Biogeographic Information System (OBIS). Eighty-four potentially toxic species have been detected in the MS (2,350 records), of which 16 described from these waters between 1860 and 2014 and a few suspected to have been introduced. More than half of these species (46) produce toxins that may affect human health, the remainders ichthyotoxic substances (29) or other types of toxins (9). Nevertheless, toxicity-related events are not frequent in the MS (308 records in 31 years), and mainly consist of impacts on aquaculture, caused by the dinoflagellates Dinophysis and Alexandrium, along with a few actual shellfish poisoning cases. Pseudo-nitzschia blooms are widespread, but domoic acid in shellfish rarely exceeds regulatory levels. Fish kills are probably less sporadic than reported, representing a problem at a few places along the southern MS coasts and in the Ebro River Delta. Since the last decade of the 20th century, blooms of the benthic dinoflagellates Ostreopsis cf. ovata have regularly occurred all along rocky shores of the MS, at times with human health problems caused by toxic aerosol. New records of Gambierdiscus and Fukuyoa, until now reported for the westernmost and easternmost MS coasts, raise concerns about the risk of ciguatera, a syndrome so far known only for subtropical and tropical areas. Recent discoveries are the dinoflagellates Vulcanodinium rugosum, responsible for the presence of pinnatoxins in French lagoons’ shellfish, and the azaspiracid-producers Azadinium spp. Mucilages and discolorations have a major impact on tourism in summer. Reports of toxic species and HABs have apparently increased in the MS over the last half century, which is likely related to the increased awareness and monitoring operations rather than to an actual increase of these phenomena. Indeed, while the case of Ostreopsis appears as a sudden upsurge rather than a trend, no actual increase of toxic or noxious events has so far emerged in intensively studied areas, such as the French and Spanish coasts or the Adriatic Sea. Moreover, some cases of decrease are reported, e.g., for Alexandrium minutum blooms disappearing from the Harbour of Alexandria. Overall, main HAB risks derive from cases of massive development of microalgal biomass and consequent impacts of reduced coastal water quality on tourism, which represents the largest part of the marine economy along the MS coasts.