Minimising the risk of harm to aquaculture and human health from advective harmful algal blooms through early warning

Phytoplankton are free-floating plants found in marine and freshwaters that, through their photosynthetic growth, form the base of the aquatic food chain. A small subset of the phytoplankton may be harmful to human health or to human use of the ecosystem. The species that cause harm are now widely referred to as 'Harmful Algae' with the term 'Harmful Algal Bloom' (HAB) commonly being used to describe their occurrence and effects.

Some HABs can be harmful to humans through their production of biotoxins that are concentrated in the flesh of filter feeding shellfish, leading to a health risk if the shellfish are consumed by humans. Other HABs can kill farmed fish. HAB events of either type can have serious financial consequences for aquaculture.

Early warning of HAB events provides a mechanism to protect human health and minimise business risk for aquaculture.

Many important HABs develop offshore. Two of the most important in the UK and worldwide are the genus Dinophysis sp. that causes diarrhetic shellfish poisoning, and the species Karenia mikimotoi that can kill farmed fish. These organisms are transported to coastal aquaculture sites by oceanic currents. For K. mikimotoi we can use satellite remote sensing to identify their offshore blooms, for Dinophysis we know the locations and times of the year that are most high risk.

In this project we shall use a combination of satellite remote sensing, in situ measurement (using free floating and moored scientific instruments that measure the properties of the water column) and mathematical modelling of oceanic currents and HABs to get a better understanding of where these harmful blooms develop and under what conditions they will be transported to the coast and subsequently into the fjords where aqaculture is located.

Our results will be used to improve risk assessment bulletins that are produced weekly for use by aquaculture practitioners. The new knowledge gained in this project will allow us, for the first time, to interpret modelled ocean current forecasts to provide forecasts of the likelihood of these currents carrying advective HABs to the coast. The work will also allow us to determine if on reaching the coast, water exchange will allow blooms to enter the sheltered fjords within which aquaculture is practiced. This will allow industry to better plan their husbandry and harvesting to minimise HAB risk to business and health.

HABs are a threat to aquaculture globally. Filter feeding shellfish vector HAB toxins to human consumers, with icthyotoxic genera impacting finfish aquaculture. Many HABs develop offshore and are advectively transported to coastal aquaculture locations. Early warning of such blooms would minimise the risk of harm to human health and aquaculture business operation.

In UK waters the most prevalent shellfish toxin producing phytoplankton genera is the Dinophysis (that causes diarrhetic shellfish poisoning) and the organism of greatest threat to finfish farming is Karenia mikimotoi.

While not all HAB organisms can be detected by satellite remote sensing, K. mikimotoi is suitable for this approach. We shall therefore use existing data sets to further develop an optical classifier for K. mikimotoi discrimination.

We shall undertake offshore drifter deployments (drogued to two depths) and near shore mooring based CTDs. Data generated will allow us to evaluate how different current and tidal conditions are likely to transport water and associated HABs to coastal and fjordic aquaculture sites and in particular to evaluate factors such as dispersion and the influence of the water depth at which the HAB is present.

We will use the data to ground truth a new FVCOM based unstructured grid model of these waters. Such models are too computationally demanding to run in real time forecast mode, and hence we will run a range of "what if" scenarios to produce a "knowledge base" of the role of currents in HAB transport in the region. HAB transport into fjords will be assessed using the ACExR model.

Project synthesis will use operational oceanography products in the form of Mercator model forecasts of ocean currents for the week ahead, interpreted on the basis of the scientific advances detailed above, to evaluate the HAB likelihood at aquaculture sites in each forthcoming week. These forecasts will be included in weekly HAB bulletins issued to the aquaculture industry.

The project's primary aim is to enhance the reliability of bulletins of harmful algal bloom (HAB) risk that are issued weekly to the finfish and shellfish aquaculture industries.

HABs impact aquaculture in a number of ways:

1) Some HAB genera impact human health through their production of natural biotoxins that are accumulated within filter feeding shellfish. Human consumption of these shellfish can be harmful to health.

2) Other organisms can cause the mortality of farmed fish, either through very high abundance/biomass or the production of toxins.

3) Both of the above events can have a significant economic impact on aquaculture through the loss of product, or in the case of shellfish poisoning, the potential for lost sales through negative public perception.

A rage of mitigation measures to protect health and the economics of the aquaculture industry can be undertaken given sufficient early warning of bloom events. These include moving fish cages or reducing stocking density, early or delayed harvest of shellfish and/or increased end product testing.

HABs are temporally and spatially variable and early warning is therefore not straightforward. Currently UK shellfish consumers are protected by regulatory monitoring of HAB cell abundance and shellfish flesh toxin concentrations. However, as evidenced by the 2013 UK diarrhetic shellfish poisoning event, that generated extensive human illness, increases in advective HAB cell abundance may occur too rapidly to be captured by this weekly monitoring.

Hence, to provide enhanced protection UK shellfish and finfish aquaculture practitioners have commissioned weekly risk assessment bulletins.

This project will provide a step change in the level of information within these bulletins.

Currently bulletins are effectively a summary of present conditions, from which forecasts are made based on expected trends. The project will move the bulletins to the realm of true forecasts that use remote sensing, improved scientific understanding and state of the art modelling of oceanographic currents to determine the likely location and timing of advective HAB events that may negatively impact aquaculture.

The project will be centered on the Shetland Isles that has the highest concentration of UK aquaculture activity. However, the techniques developed will be easily utilized elsewhere in the UK and abroad in the many locations that suffer from advective HABs.

Direct knowledge exchange to the aquaculture industry will be achieved through the weekly issuing of the enhanced bulletins in the latter part of the project. However, we recognize that it is important that industry have confidence in the science behind our predictions and that the bulletins are easily interpretable and are in a format that is suitable for industry use. Hence, we will work closely with an industry based advisory group on an ongoing basis throughout the project to ensure two way knowledge exchange that enhances the final product.