Cod, salmon and eels and other native cold water fish might eventually become a rarity in Irish waters—and not necessarily because of overfishing, pollution or habitat destruction. Long-term changes in the temperature and salt content of our regional seas, brought about by climate change, may force species such as these into deeper, colder waters and replace them with warm water species such as sea bass and boarfish.
As an island off the Atlantic coast of Western Europe, Ireland is an ideal laboratory from which to study the effects of climate change on the oceans, which in turn are the largest drivers of weather patterns on the planet. Almost 70% of the earth is covered by the sea, which acts not only as a transporter of solar heat from the equator to the poles, but also as the world’s largest natural processor of atmospheric carbon dioxide. Understanding the interactions between the oceans and the atmosphere is one of the greatest challenges facing climate scientists—not least of which is the difficulty in telling which changes occur naturally and which might be due to global warming.
These challenges were identified as part of Sea Change-A National Strategy for Marine Research, Technology and Innovation 2006-2013 under which a special Marine Climate Change (MCC) Programme of research was set up in 2007 under the national Strategy for Science, Technology and Innovation and funded with €2.2 million. Its strategy for measuring, understanding and predicting subtle changes in complex natural marine systems into the future was to start by establishing what historic records of climate-related phenomena already existed from the past. From there it will develop sophisticated computer models that can explain what happened in years gone by and then, once those historic records are fully understood, it will use those models to look forward and predict the future.
“We set about working in three teams,” explained Dr Glenn Nolan of the Marine Institute, who is heading up the MCC Programme, “one here at the Marine Institute, looking primarily at oceanographic and marine fisheries data, one at NUI Galway looking at the phenomenon of ocean acidification due to rising atmospheric carbon dioxide levels, and one at NUI Maynooth examining the Burrishoole Catchment information and the effects of climate change on migratory fish. The first year or so was spent researching relevant historic records. These included: over fifty years of continuous data from the Burrishoole River Catchment system at Newport in County Mayo, which would give us an idea of what might be happening to anadromous fish such as salmon, sea trout and eels; catch records of the annual groundfish survey carried out by the Marine Institute, which would show us how commercial marine fish stocks were being effected; seawater temperature recordings from the Malin Head observatory in Donegal dating back to 1958; and samples taken by the continuous plankton recorder network all over Europe.”
As well as looking back into the past, the three MCC teams also looked to cutting-edge technology to measure what is going on in the present. Data from the network of floating weather buoys around the coast, readings from underwater “gliders” and observations made from space by satellites are all being analysed at the Marine Institute’s headquarters at Oranmore to make sense of what has been going on in our seas over the last fifty years, what is happening today and, using a new supercomputer system, to produce forecasts of what might reasonably be expected to happen in the future. Even now, some worrying trends in the data are starting to emerge, which confirms anecdotal information that the seas around Ireland are warming up.
Oceanographers have long known that seawater surface temperature in the Atlantic Ocean rises and falls naturally over a cycle of between 50 – 58 years according to a phenomenon called the Atlantic Multidecadal Oscillation (AMO). At present the Atlantic is in its warm phase, which is expected to further increase the temperature of the ocean’s surface around Ireland for the next fifteen to thirty years. On top of this naturally occurring increase however, records of sea surface temperature kept at the Malin Head observatory in Donegal since 1958 demonstrate that the present warm cycle is half a degree warmer than the last one. Furthermore, the Malin Head data shows an increasing rate of warming since the 1990s, with the warmest years on record occurring since 1995. This is consistent with datasets from other sources that show a gradually upward trend in Irish sea surface temperatures averaging
0.3 o C over the 1850-2006 period.
But the worrying thing is that the sharpest rates of increase have been since the late 1990s, with the warmest years on record being 2006, 2005 and 2003. This suggests that even though the AMO will reduce seawater temperatures as the warm phase abates in around the year 2020, the increases could be even greater when it rises again, fifty years on. Clearly, the seas around Ireland are getting warmer beyond the limits of natural fluctuations, and that trend is continuing upwards.
In addition, the amount of salt in the sea (the salinity) around Ireland is also showing an upward trend. These warmer and saltier conditions, which are becoming increasingly like the Mediterranean rather than the Atlantic, are having a gradual but profound change on the marine animals and plants that live there. Sample records from the Continuous Plankton Recorder (CPR) survey carried out over the years shows that microscopic plant species (called Phytoplankton) that used to only bloom during the spring and summer, now appear to have an extended growth season.
Further up the food chain there is some evidence that species of microscopic carnivores called zooplankton have extended their range northwards associated with warm water currents that can extend further north in some years, depending on the balance of water current regimes in the North Atlantic. This change in turn is reflected in the abundance of large carnivorous fish which rely on these zooplankton as food in their own early stages of life. Records from the Marine Institute’s annual ground fish stock survey of commercial species over the years show a gradual decline in coldwater species such as cod, with an increasing abundance of warmer water species such as lesser spotted dogfish, poor cod and even boarfish. Seawater temperature and the availability of zooplankton may also be driving the large changes in population size of salmon, sea trout and eel observed by analysing records of the Burrishoole Catchment in Mayo. Such “anadromous” fish species, which also spend part of their lives in freshwater, will also be effected by any variations in river flow, water levels or freshwater food abundance brought about by climate change, which makes them doubly vulnerable.
"If we can identify and understand the complex web of climate change on species such as salmon and eel, and in particular the impacts of climate change at the catchment, river and stream scale, vital to their very survival, we will have uncovered a crucial piece in the jigsaw puzzle,” says Dr Rowan Fealy of the Maynooth Group. “The Burrishoole catchment provides a unique opportunity in which we can study such phenomena and hopefully enable us to project both the direction and magnitude of future changes, so that adequate adaptation strategies can be developed to minimise or even manage the impacts of climate change on these species."
While changes in commercial fish species are inconvenient for the fishing industry, they can at least be adapted to over time as boats move from fishing one set of species to another. What is much more worrying on a global scale is the theory that increased atmospheric carbon dioxide could increase the acidity of the oceans. Carbon dioxide, when dissolved in water, produced carbonic acid. Seawater, which contains hundreds of chemicals acting together in a chemical “ecosystem” to create an ongoing balance between acidity and alkalinity, is buffered to withstand a certain amount of this gas. Indeed, the tiny plants living in the ocean rely on carbon dioxide and sunlight to produce life giving oxygen.
Theoretically, if the ocean’s continue to absorb carbon dioxide at rates described for the past century the elevated acidity of the seawater might affect the plankton communities that live there and reduce their productivity.
As Dr Colin O’Dowd of NUI Galway explains, “There are two components to the CO2 study: the first is to quantify the flux of carbon dioxide between the atmosphere and the ocean and its impact on carbon dioxide concentrations in the sea; the second component is to quantify the impact of carbon dioxide concentrations in seawater on the carbonate chemistry system, total alkalinity and ultimately ocean acidification.”
The flux study involves continuous measurements of carbon dioxide flux both at NUI Galway’s Mace Head Research Station on the west coast, supported by a Marine Institute marine chemistry buoy moored a couple of kilometres offshore, and on board the research vessel RV Celtic Explorer. “This programme is initially enabling capacity within Ireland to conduct such studies and will provide a basis for longer-term assessment of changes in the carbonate system and the level of ocean acidification ultimately required to predict risk to marine ecosystems,” says Dr. O’Dowd.
While the picture painted so far may seem gloomy, it has to be remembered that the differences in ocean temperature so far recorded are extremely small. It must also be pointed out that a rise in ocean temperature could also bring with it opportunities as well as threats. Rising water temperatures could bring with them more southerly fish species such as sea bass, red mullet and John Dory, while a longer tourist season and increased visitor numbers to Ireland could lead to increased employment in the tourism industry.
It is also worth pointing out that the sea offers a major source of renewable energy that creates no carbon dioxide emissions whatsoever. Quarter scale prototype devices capable of generating electricity from the motion of ocean waves are already being tested at the Marine Institute’s wave energy test site off Spiddal, in County Galway in collaboration with Sustainable Energy Ireland. Plans to test larger scale devices are also well advanced.
In any event, the more we know about the complex systems of the ocean through research, technology and innovation, the more chance we have to predict change, to take mitigating actions to reduce negative effects and to investigate sustainable alternatives. It really is all about knowledge.
Sea bass and chips anyone?
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