This paper was prepared for the Department of Botany at NUIG as part of my undergraduate work. Please feel free to cite it in your work, please include the website name.
Algae as Indicators of Climate Change John Paul Tiernan
Seaweeds and climate change have a special, perhaps symbiotic relationship in that each can have a particular influence upon the other. For example, seaweeds may exert an influence on climate change in the form of providing a sink for CO2 thus offsetting the build-up of greenhouse gases, whereas climate change may exert an influence on seaweed by altering the geographic boundaries of some seaweeds due to increased warming of oceanic waters. The processes can also be interchangeable with one process affecting the other, which then subsequently has an affect on the first. One of the most valuable aspects of this relationship is the ability of algae to be used as indicators of climate change. This has shown to be and will no doubt continue to be of paramount importance in understanding and gaining information on climate change about which, more is undoubtedly needed.
First it is necessary to gain an understanding and definition of climate change, its causes and projected future paths. The U.N. Framework Convention on Climate Change defines it as “a change of climate which is attributed directly or indirectly to human activity that alters the composition of the global atmosphere and which is in addition to natural climate variability observed over comparable time periods” (http://www.unfccc.int <http://www.unfccc.int>).
It is believed that anthropogenic causes of climate change are mainly the greenhouse effect, not to be confused with the decrease in stratospheric ozone which is a completely separate process and not as destructive or influential as greenhouse gas build-up in the long term. On a very simple level, this is the trapping of the sun’s energy by gases such as CO2, NO2, which have accumulated in the atmosphere. This results in the warming of the earth and subsequent influences on climate. However it is important to note that climate change is not just a modern phenomenon as it has been occurring naturally throughout the earth’s history and indeed there is much debate over whether anthropogenic actions are causing modern climate change.
This essay will approach the subject in a two fold manner: First I will seek to explore why algae would be used as indicators of climate change. Second, I will look at how algae (both micro and macro) have been used as indicators of climate change by looking at specific research that has been done. I will look at how algae have been used to indicate both past and present climate changes.
On a very fundamental level the type of environment that algae inhabit (i.e. aquatic) will always be a good place to start when assessing climate as aquatic ecosystems will always react to changes in climate, be it increasing ocean temperatures or run off from glacial melt. They also inhabit an important position at the bottom of food webs in the aquatic environment (Mc Cormick et al 1994). Any changes in these environments will first present themselves in algae. On a short timescale, algae respond rapidly to any environmental changes (Mc Cormick et al 1994) and also can have very strict limitation boundaries i.e. coldwater kelps and summer isotherms. In these cases in the northern hemisphere, northern boundaries are set by low lethal winter temperatures and southern boundaries are set by high lethal temperatures or by winter temperatures too high for a crucial stage in the life history to survive (Breemen, 1990). On longer timescales, assemblages of algae can be extremely useful for documenting any changes or disturbances in biological conditions. (Mc Cormick et al, 1994)
The use of freshwater algae as an indicator of climate change is extremely well evaluated in a review by Smol and Cuming, (2000); “Tracking long term changes in climate using algal indicators in lake sediments”. They reviewed a large amount of research that has been published on paleoclimatic data from algal fossils in lake sediments. They focused mainly on siliceous algal microfossils (diatom valves and crysophyte cysts and scales). They identified key environments where algal lake fossils can be used to glean important data about past climates.
High arctic regions are identified as important as they are areas which are especially sensitive to global warming and can have repercussions for other areas should any changes take place (i.e. melting ice).
Arctic treelines, (i.e. the northern limits of coniferous forests) can be used to infer data about climate. Therefore the dissolved organic carbon in algae in lakes near these tree lines can be useful in determining their density, positions and patterns of growth.
Arid regions can be sensitive to climatic processes which may affect precipitation and evaporation. This would affect salinity in lakes which can be determined by algal fossils in lakes in these regions.
They concluded by suggesting that a global network of paleoclimnological studies on algal lake fossils would be extremely valuable in understanding climate change as lakes are present on all continents and can be used in a variety of ways to gain accurate data about past climatic events. Thus, it is clear why fresh water algae would be used as indicators of climate change.
Beardall and Raven (2004) looked at the potential effects global climate change has on micro-algal photosynthesis, growth and ecology. They looked specifically at the effects of enhanced CO2 levels, elevated UV-B radiation and temperatures on the eco-phsyiology of micro algae.
With respect to elevated CO2 levels, they found differences in responses by different species of micro-algae to concentrations of CO2. They decided that any atmospheric CO2 level changes will likely result in changes to competition and to species’ community compositions.
Increased UV-B radiation was shown to have a range of consequences for micro-algae; however some organisms have developed UV screening compounds such as mycopsorine-like amino acids. Some algae have also developed mechanisms to repair photo-damage caused by UV radiation.
Increased temperatures consequences were found to be similar to increased CO2 effects in that some species will see increased metabolic activity and growth whereas some will be above their temperature tolerance which will lead to changes in competition and species and community competition again.
While finding clearly that climate change will have effects for micro-algae, they concluded by saying that any overall consequences will be a reflection of complex interactions between climate change and other environmental factors, not just climate change alone. Thus, it can be inferred how three of the main symptoms of climate change are indicated in micro-algae.
I will now look at specific cases where algae have been used as indicators of climate change to illustrate in more detail how algae are used in this way.
As I have previously mentioned when discussing the review of algal indicators in lake sediments by Smol and Cuming (2000), dinocysts have been used extensively to investigate past climates. One example of this is work carried out by Blake et al (2001) on sea surface conditions in northernmost Baffin Bay during the Holocene. They used dinocyst assemblages to estimate sea surface temperature, salinity and sea ice cover.
They employed various methods to yield information from the dinocyst assemblages: Dinocysts were identified to species level. Sea surface conditions were reconstructed using a reference data base of present assemblages and relevant associated conditions from the North Atlantic. These were compared with the sampled assemblages. Radiocarbon dating was used to date the stratigraphy and provide a chronological framework which was used for such information as various abundances at various times. They found using reconstructions of sea surface conditions by dinocyst assemblages, marked post glacial changes in the sea surface conditions such as sea surface temperature increased at about 9000 bp. to similar levels to present. Sea surface temperatures were higher than present at 6.400 bp. (Blake et al, 2001)
The dinocyst record indicated climate change by supporting the idea of a thermal optimum in the early to mid Holocene.
Mudie et al (2002) studied polynological records of red-tide producing species in Canada. The term red tide denotes occurrences or blooms of harmful algae resulting from local or regional accumulations of a single phytoplankton species which have a negative effect on the environment (Anderson, 1994).
Records from North America show an increase in harmful algal blooms in the last 50 years. What is interesting is that this was on both the Pacific and Atlantic sides which suggests global forces such as warming are responsible (Mudie et al, 2002).
They examined dinoflaggelate cysts from varved marine sediments relating to the Holocene era at a high resolution (10 – 25 years).
Their results showed that Pacific and Atlantic red tide occurrences share a similar succession of high production blooms in the late Glacial to early Holocene period. The only common characteristics of this period were a warmer sea surface temperature in summer. They believe that this is a strong implication of the importance of global warming in relation to historical increases in red-tide frequencies.
Danin et al (1980) studied the use of algae in an entirely different way of paleoclimnological interpretation. They looked at the paleoclimatic significance of limestone and dolomite weathering by blue-green algae (and lichens). The study was carried out between the Judean Mountains and the Dead Sea. This ranges from a Mediterranean zone (550mm rainfall) to a desert zone (100mm rainfall). In the 100mm isohyet, the blue green algae carve pits 10 – 30mm deep in the rock, whereas in the 300mm isohyet, they carve pits 0.1 – 0.5 mm deep. Fossils of deep pits characteristic of the desert zone were recorded in the 550mm Mediterranean zone. This is evidence of a different climate being at one stage present here. This is an interesting and unusual way in which blue green algae can be used as indicators of climate change.
As well as looking at research on historical data, it is of use to look at present data which shows associations between algae and climate changes. An example of this is a study carried out in New Zealand by Rhodes et al (1993) which looked at algal blooms and climate anomalies.
A phytoplankton bloom occurred off the north east coast of New Zealand from August to December, 1992. The duration of the bloom was compared with data from the nearby Leigh Marine Laboratory which has been maintaining marine data such as sea surface temperature since 1967.
They found that the commencement of the bloom coincided with the lowest sea surface temperature in 26 years in that area. Temperatures were below average in the preceding 21 months and became more extreme over the period. A marked increase in solar radiation occurred 2 weeks prior to the start of the bloom. The low sea surface temperature was not just a local event as satellite images show reduced temperatures over much of the south west pacific for that time. A 4 year steady decline in water temperatures previous to this correlates to the Southern Oscillation Index. Lesser onshore winds and wave surges were also recorded. This correlates to the El-Nino phase of the Southern Oscillation Index.
They concluded that the idea of a widespread climatic factor forcing these blooms is supported by a total set of biological patterns. (Rhodes et al, 1993)
While data also suggests these events are linked to the El-Nino conditions of the Southern Oscillation Index, it is still significant that the algal bloom was indicative of conditions associated with climate anomalies.
Severe bleaching in red algae off Ireland’s west coast was suggested as an indication of climate change in work carried out by Loughnane and Stengel at National University of Ireland, Galway. Red algae may be useful indicators of climate change as pigment concentrations reflect irradiance conditions. Specimens of 5 morphologically diverse species were collected from two areas in Galway Bay, one of which where exceptional bleaching of Corralina officinalis had been recorded. Photosynthetic pigment concentrations were then determined from each sample.
They found that chlorophyll-a concentrations declined in C. officinalis and Lithothamnia in the summer with no recovery recorded. Phycobiloprotein concentrations in Chondrus crispus declined in June / July in the areas of the shore where it was subjected to increased irradiance. Species which are high light adapted had increased photosynthetic pigment concentrations which they believed may suggest a photo-damage avoidance strategy to counteract increased irradiances. They suggested further studies into the recent bleaching of C. officinalis as it may be an indication of increased U.V. radiation. (Loughnane & Stengel, unpublished data, 2005)
This study is another example of how present data may show an association between algal processes and climate change.
A brown algae was seen to be a possible indicator of climate change in a study on long term patterns of rocky bottom macrobenthic community structure in an Arctic fjord in relation to climate variability by Beuchel et al (2002). They investigated temporal variations in community structures from 1980 to 2003. The study was done in relation to the North Atlantic Oscillation Index (NAOI). The NAOI influences temperature and current regimes in the North Atlantic and is a measure of the mean deviation from the average atmospheric sea level pressure (Tunberg & Nelson, 1998). Their most significant finding was a large increase in the cover of brown algae carpets on the benthos. This was mainly Desmarestia spp. and occurred in years of low NAOI. The brown algae were seen to increase dramatically. This co-incides precisely with a shift in NAOI from a positive to a negative. This could be attributed to increased nutrient supply to the benthos during low NOAI.
This large scale appearance of brown algae represented a major congruence between the NAOI as a large scale climate driver and benthic species diversity. (Beuchel et al, 2006).
To gain a perspective on how algae are responding to and may respond to or act as indicators of climate change in the British Isles in the future, I will look at a report to Scottish Natural Heritage from the Marine Biological Association of the United Kingdom by Hiscock et al (2001) This report dealt with the impact of climate change on subtidal and intertidal benthic species, including several algae, in Scotland.
Algal species they looked at in detail included Fucus distichus distichus and Lithothamnion glaciale (maerl). Fucus distichus distichus has a distribution north of the 13˚ isotherm in Britain, so it could be assumed that should the summer sea temperature rise by 1˚ – 2˚ c, F. distchus would become extinct in Britain as the 13˚ isotherm moved north. However laboratory tests have indicated that this may not be the case as day length may be a critical factor in receptacle formation. Therefore any climate induced changes in distribution remain uncertain. Lithothamnian glaciale has a southern limit at Lundy in Scotland and Galway in Ireland. For a significant change to take place however, temperatures would have to rise by 2˚c or more.
Other species were looked at briefly. High shore species such as: Porphyra spp. and Enteromorpha spp. may be affected by increased storminess (which may be attributed to global warming) as their zones of habitation are increased landward.
Species which occur in rockpools such as Cystoseira tamariscifolia may have their limits extended northwards as air temperatures would have a greater effect.
The coldwater kelp, Alaria esculenta would not be expected to decrease in abundance in Scotland, but it is possible in SW England and Wales. Ascophyllum nodosum, which has southern limits in northern France, is seen to be under stress in southern Britain. (Hiscock et al, 2001).
Perhaps more than any other environment, the marine environment is the one most closely tied to climate changes, both in its regulation of climate and the effects climate have on it. The most subtle climate changes manifest themselves on areas such as sea surface temperature which then can have a large bearing on local and global weather. Evidence currently available suggests that inshore sea temperatures will continue to show variations of 2˚ above or below average, but with a trend toward higher temperatures. (Hiscock et al, 2004).
We have seen the ways in which algae, due to their sensitivity to the environments they occupy, can react to even the most subtle changes to these environments. Therefore they are especially good indicators of any change, short term or long term in the climate.
The wide range of ecosystems that algae inhabit including what we have looked at: dinoflaggelates in alpine lakes and polar icecaps; micro algae and macro algae in temperate oceans; blue-green algae in the desert, makes for a comprehensive worldwide source of information on the planet’s climate.
We have seen how algae may be used to tell us about past climates. Climate change has been occurring since the earth’s inception and understanding the patterns and effects of past climate changes is vital to the understanding of present and future changes.
This encompassed a wide range of uses: red tide blooms and correlations with sea surface temperature in the Pacific and Atlantic oceans, comparing blue-green algal fossils to their characteristic climates in Israel and using dinocyst assemblages to reconstruct past climates in the Arctic.
We have also seen how present climatic anomalies are being indicated in algae. This can reflect the relatively immediate way in which algae react to climate shifts, from a matter of weeks when comparing phytoplankton blooms to sea surface temperature in New Zealand to a matter of years when comparing macrobenthic communities to the NAOI index in Norway. Although the most common way in which climate influences algae is through warming, we have seen how UV radiation is thought to be affecting red algae in the west of Ireland.
It is most likely that the phenomena of climate change will continue and probably increase in importance as the most topical issue in the world of science in the near future. There is an endless thirst for information on the subject. Therefore it is reasonable to assume that algae will continue to play an ever increasing role as indicators of climate change.
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