Avis scientifique sur les proliférations d'algues nuisibles dans les écosystèmes marins du Canada : état actuel, effets et conséquences, et lacunes dans les connaissances

Abstract

Harmful algae (HA) are phytoplankton, and to a lesser extent sympagic algae species, with the potential to cause harm to organisms, food webs, ecosystems and human health via the production of phycotoxins, mechanical action, or hypoxia. As such, harmful algal events (HAEs) have emerged as an important stressor for marine ecosystems. HA species, phycotoxins, and HAEs in Canada’s three oceans were reviewed based on Canadian published and unpublished reports. A 30-year time series of 593 Canadian records (1987 to 2017) from the Harmful Algal Event Database (HAEDAT) was analyzed for the Atlantic and Pacific coasts that showed recurring HAEs have been widespread. No HAEDAT records exist for the Arctic. To date, 70 harmful algal species (including 45 in the Arctic), known to have caused, or to have been associated with, HAEs on the coasts of Canada or elsewhere, have been reported in Canadian waters. A conceptual bow tie model was developed as a framework to link causes to outcomes of HAEs. It incorporates three natural drivers and five emerging anthropogenic pressures that influence the occurrence of HAEs in Canadian marine waters and was applied to identify national and regional knowledge gaps that might limit Fisheries and Oceans Canada’s (DFO) ability to manage consequences of HA, especially those linked to DFO’s mandate. Nationally, overarching knowledge gaps include limited HA monitoring, and limited understanding of the effects of specific emerging anthropogenic pressures that drive changes in HA species, phycotoxins, and bloom development and toxicity. These knowledge gaps prevent the development of effective predictive HAE models, which hinders our forecasting/hindcasting capability and hampers development of mitigation and prevention strategies. Information regarding the role of climate change, including extreme events and ocean acidification, on HAEs was identified as a key knowledge gap in Canada. Fundamental knowledge gaps exist in the Arctic Region, where there is a lack of basic information on the presence of HA and phycotoxins, and their impacts on species and ecosystems. Understanding the effects (including sublethal and cumulative) of HA and phycotoxins on the growth, physiology, reproduction and behaviour of marine biota is essential to evaluate impacts on food webs, ecosystems and human health, and consequences to species-at-risk, marine mammals, aquaculture, fishery and fish population health, ecosystem health, and food safety and security. Monitoring of phytoplankton and phycotoxins should be continued and expanded by developing novel methods, and using new and existing capacity and partnerships. This is especially important for areas where information is lacking, particularly the Arctic.