Predicting Temperature, Salinity and More

Predicting Temperature, Salinity and More Parker McCready is LiveOcean lead researcher and Professor of Oceanography at the University of Washington

A new computer model is giving aquaculture a lifeline as it seeks to adapt to ever-changing undersea conditions, reports Bonnie Waycott.

In the Pacific Northwest (Oregon, Washington and British Columbia) a range of marine species including salmon, crabs, oysters and clams, have been thriving in stable marine conditions. But over the years, climate change has had substantial impacts in the area, changing biodiversity and promoting toxic algal blooms. Industries such as aquaculture and commercial fishing have also been affected.

Ultimately for fishermen and fish farmers, knowing about conditions underwater in advance is key. Now, a group of scientists at the University of Washington (UW) has developed a new computer model that predicts complex undersea interactions and conditions underwater. LiveOcean simulates water properties and ocean currents in the coastal waters of the Pacific Northwest. It currently covers various important coastal estuaries such as Willapa Bay and the large fjord-estuary system known as the Salish Sea, which contains Puget Sound and the Strait of Georgia. Each day, it creates realistic three-day forecasts for the region like a weather forecast model. These are then made available online to the public and other researchers.

"The programme started about five years ago when Washington State decided to respond to the issue of ocean acidification," said Parker McCready, LiveOcean lead researcher and Professor of Oceanography at the University of Washington.

"The Washington Ocean Acidification Center at the University of Washington was then established to coordinate a number of research projects, including the creation of short-term forecasts of ocean acidification."

LiveOcean focuses on the local shellfish industry and two managed species in particular - oysters and razor clams. Pacific oyster farming is one of the biggest industries in the coastal and inland estuaries that are covered by the LiveOcean model, and scientists have found that larval oysters cannot survive in water that is too corrosive for them to generate their shells.

The razor clam is another key species and an important, recreational, commercial and subsistence fishery in areas covered by LiveOcean. Although they feed on all phytoplankton in the surf zone, they sometimes eat the diatom Pseudo-nitzschia, which forms a neurotoxin called Domoic Acid. This is poisonous to anyone who eats the clams. Today, LiveOcean is part of a system used by shellfish managers in Washington and Oregon to ensure safe razor clam harvests and high water quality for oyster farming.

"With the oysters, we've found that levels of aragonite are particularly low in the local waters they grow in, but aragonite is necessary because it's the form of calcite that larval oysters use to make their shells," said Parker. "So LiveOcean forecasts aragonite levels, as well as other measures of water quality and microplankton. For the razor clams, Live Ocean predicts when water from known Pseudo-nitzschia growth areas offshore might reach nearby beaches."

Running daily on a UW supercomputer, LiveOcean also generates three-day forecasts of sea level, currents, temperature and salinity, and simulates biology and chemistry including nitrate, phytoplankton, organic particles and dissolved oxygen. By taking in information about the state of the ocean, atmosphere and rivers on any given day, it uses the law of physics to predict how underwater conditions are likely to change. Data on currents, temperature and salinity on the seaward edges of the LiveOcean domain come from a global ocean forecast model called the Hybrid Coordinate Ocean Model or HYCOM, which is run by the US Navy, while data on atmosphere, including winds, sunlight and clouds, is generated from a regional forecast model. Other information such as river flow data comes from observations and short-term forecasts made by US and Canadian agencies.Parker and his team also conduct regular tests to see how the model is working.

For aquaculture, understanding how climate change is linked to threats to water quality and fish health is essential to predicting where and when certain areas might be damaging to species and farms. LiveOcean also uses particle tracking codes to simulate the spread of invasive species such as the European Green Crab, and could help industries like shellfish farming gain a deeper understanding of the potential impacts of changing undersea conditions on their work, allowing them to adapt farming schedules before more permanent solutions can be established.
Daily forecast movies can also be viewed on the LiveOcean website, but in order to make the forecast fields more relevant to the decisions made by people such as fish farmers, Parker and his team are engaging in conversations with users, in particular shellfish growers, to learn more about what metrics they would like to see.

"There is a growing cohort of daily forecast models in coastal areas around the world," said Parker. "LiveOcean is designed to do the best possible job at predicting the coastal ocean. It's also designed to easily allow further refinement: nested sub-models of specific estuaries where finer spatial resolution is required."

Feedback has been enthusiastic and positive. At a recent shellfish growers' conference where LiveOcean was presented, audience members praised the computer programme but requested that the information be made available in simpler forms and more directly relevant to shellfish growers. One way of achieving this would be to make maps of both seasonal patterns and daily forecasts for where it is "good or bad" to set out oyster seed based on a range of parameters such as salinity or aragonite saturation state.

Parker McCready and his team are working to combine LiveOcean with satellite-based observations to better predict harmful algal blooms on the outer Washington-Oregon coast. This is currently being done in partnership with the University of Strathclyde in Scotland. Hopes are high that it can be adapted to help predict harmful algal blooms that are a major concern for Scotland's salmon aquaculture.

A different ocean model system has been developed independently for the Scottish coast and sea lochs where salmon aquaculture is concentrated (the Scottish Shelf Model). Parker and his team hope that strategies for merging transport maps and water properties from ocean models, as well as maps of plankton abundance from satellites, will be portable.

"The model is always evolving and improving, based on new information sources, comparisons with data and increasing computer power," said Parker.

"In the next year we will also be adding high resolution sub-models of several areas such as Willapa Bay and South Puget Sound, both important shellfish aquaculture areas. LiveOcean is designed to forecast the carbon chemistry that shapes ocean acidification, and will be useful for testing future scenarios where atmospheric carbon dioxide increases. It could be run to test other scenarios if needed. There is always room for improvement, however, and top of the list right now is to do more comparisons with data concerning carbon chemistry and to better define uncertainty metrics in our forecasts."

"Having said that, however, the model has many possible uses," he continued. "Our goal is to make it relevant to as many groups as possible, not only shellfish farmers but also fishermen or beachgoers."

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