Too hot to handle?

The ice is disappearing… Over this winter there was no walking on the sea around Helsinki, or in much of Finland for that matter.

In January the ice cover was dramatically lower than normal for the Baltic Sea. Normally the ice should extend from the northern parts of the Baltic down to the Gulf of Finland and the Gulf of Riga, however this year the ice was limited to just a small section of the Bothnian Bay.

Indeed this lack of ice is a tell-tale sign of a milder winter, both on land and in the sea.

Extent of ice coverage (jäätä) in the northern Baltic Sea under normal condition and those observed in January 2020. Number on ice indicate thickness. Source: Finnish Meteorological Institute

But was last winter an odd exception?

It appears not. The earth is experiencing a warming of the marine environment in general, but the Baltic Sea is warming far more severely than the average global ocean. The Baltic Sea temperature is now higher than that average temperature recorded between 1981-2010 (European Environmental Agency, 2019)

Decadal global and Baltic Sea averaged sea-surface temperature anomalies relative to a 1981-2010 baseline. Source: European environmental agency

However it is not solely the increase in temperature that is concerning for the marine environment. Shorter spells of prolonged warmer temperatures, called marine heatwaves, are also troubling.

Due to climate change the IPCC (2013) expects marine heatwaves to become more frequent, and those that we do experience to be far more intense. Already the marine environment has experienced a 54% increase in annual marine heatwave days (Oliver et al., 2018).

And Finland is no exception. Monitoring at the University of Helsinki’s Tvärminne Zoological Station points that last winter was just one long marine heatwave. Exceptionally warm conditions lasted an outstanding  142 days, and even included record breaking temperatures in February 2020 (@Tvärminne, 2020).

Water temperature over the winter of 2019/2020 recorded by temperature loggers in shallow areas near Tvärminne. Source: Tvärminne Zoological Station .

Are marine heatwaves really all that bad?

Prolonged high temperatures can induce heat stress in marine plants and seaweeds with disruptive consequences to the survival of these organisms.

This stress can reduce a marine plant or algae’s ability to persist within previously inhabited areas. Consequently heatwaves have the potential to cause local extinctions.

By 2200 three currently common seaweeds; bladder, serrated and knotted wrack; will have disappeared from any North-Atlantic shore south of 45 ° latitude due to marine heatwaves and the other effects of climate change (Jueterbock et al., 2013).

4 © OCEANA Juan Cuetos 70537

Serrated wrack, Urter island, Karmøy, Norway (Image source ©OCEANA)

How will marine heatwaves affect Baltic Sea ecosystems?

Recent research at GEOMAR Helmholtz Centre for Ocean Research sheds some light on this.

By using large, outdoor tanks called ‘mesocosms’, researchers tested how eelgrass and bladderwrack respond to heatwaves (Saha et al., 2019). Within these 1,500l tanks the eelgrass and bladderwrack were subjected to 9 day heatwaves.

EUO © OCEANA Carlos Minguell 20130706_Puck Bay_157

Eelgrass meadow, Puck Bay, Poland (Image source ©OCEANA)

So how did the plant and seaweed cope?

Well is seems that both eelgrass and bladderwrack are fairly resilient to heatwaves. The eelgrass did experience impaired growth, but also showed good signs for potential recovery. Bladderwrack, on the other hand, showed no impaired growth with the only significant effect being seen on the bacterial community living on the algae.

Therefore it seems that both eelgrass and bladderwrack will likely be able to endure short heatwaves similar to those of this experiment when experienced within the natural environment.

EUO © OCEANA Carlos Suárez 45888_2

Wrack, Västra Banken, Bothnian Sea, Sweden (Image source ©OCEANA)

However it is not all good news. The effects of long heatwaves will probably be fairly different. In a previous study subjecting eelgrass to a continuous 3 week heatwave far greater detrimental effects where observed (Winters et al., 2011).  

So a tolerance to short heatwaves does not necessarily equate to a tolerance to longer ones. Consequently the length of each heatwave will be critical to determining the effects on eelgrass and bladderwrack.

We will have to endure more and hotter marine heatwaves, as will the resident plants and animals of the Baltic Sea, yet at least eelgrass and bladderwrack seem somewhat prepared for the future.


Sources:

@Tvärminne, 2020. Tvärminne Zoological Station. Date accessed: 28/5/20. https://www.facebook.com/Tvarminne/posts/2426296717472671

European Environmental Agency, 2019. Decadal average sea surface temperature anomaly in different European seas. Date accessed: 29/5/20. https://www.eea.europa.eu/legal/copyright

IPCC, 2013: Climate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 1535 pp, doi:10.1017/CBO9781107415324.

Jueterbock, A., Tyberghein, L., Verbruggen, H., Coyer, J.A., Olsen, J.L. and Hoarau, G., 2013. Climate change impact on seaweed meadow distribution in the North Atlantic rocky intertidal. Ecology and evolution3(5), pp.1356-1373.

Saha, M., Barboza, F.R., Somerfield, P.J., Al‐Janabi, B., Beck, M., Brakel, J., Ito, M., Pansch, C., Nascimento‐Schulze, J.C., Jakobsson Thor, S. and Weinberger, F., 2020. Response of foundation macrophytes to near‐natural simulated marine heatwaves. Global Change Biology26(2), pp.417-430.

Winters, G., Nelle, P., Fricke, B., Rauch, G. and Reusch, T.B., 2011. Effects of a simulated heat wave on photophysiology and gene expression of high-and low-latitude populations of Zostera marina. Marine Ecology Progress Series435, pp.83-95.

The demise of Baltic Sea wrack?

Another post about climate change, but this time closer to home. Climate change has been identified as one of the largest contributors to environmental change within the Baltic Sea. It is predicted that Baltic waters will heat by some 2–4°C and become up to 50% fresher by the end of the twenty-first century (Meier 2015).

Coastlines of the Southern Baltic Sea

Coastline of the Southern Baltic Sea

But how will Baltic wracks fair under these new conditions?

Unfortunately the future doesn’t look good for bladderwrack. Research by Antti Takolander and colleges at the University of Helsinki indicated that warming waters and increased freshness pose real threats to bladderwrack. The once abundant brown seaweed may struggle to cope with these new environmental conditions and consequently be lost from much of the Baltic Sea.

Bladder wrack peeking up above the water 4

Bladderwrack – Brofjorden, Sweden

Climate change looks bad for bladderwrack, but is that the case for all wracks of the Baltic Sea?

It seems that the future may not be as bleak for all the Baltic Sea wracks after all. Narrow wrack, having evolved within the Baltic Sea from bladderwrack, can be found nowhere else in the world. As a unique seaweed to the Baltic you might expect that the dramatically changing conditions predicted pose an even greater threat to this sister of bladderwrack. Yet a study by Luca Rugiu and colleges at the University of Turku indicates that this is in fact not the case. By subjecting narrow wrack to higher temperatures and fresher conditions replicating predicted future conditions they assumed that narrow wrack would fair as poorly as bladderwrack; however their results were surprising. Though the predicted future conditions did lead to higher mortality, those individuals that did survive were larger and grew faster.

Bladderwrack (Fucus vesiculosus) and Narrow wrack (Fucus radicans) living side by side – SW Gulf of Bothnia (northern Baltic Sea) [From Pereyra et al., 2009; CC BY 2.0]

Does this mean that narrow wrack may benefit from climate change?

In short: Yes. Those narrow wrack individuals that can withstand the predicted future conditions will benefit from the increased growth and gain a competitive advantage over those that cannot. Since where each wrack can be found is largely affected by competition between the species the future looks even worse for bladderwrack. Both wracks frequently grow side by side and if narrow wrack profit and bladderwrack lose out from future climate conditions bladderwrack may be lost from these areas and instead replaced with narrow wrack.

The future looks bleak for bladderwrack; we may end up losing vast swathes of bladderwrack forest in the Baltic. Though there is the small silver-lining that narrow wrack appears somewhat tolerant to climate change. So the future may not be all bad. We won’t see the disappearance of all the wracks from the Baltic Sea; though we will see a very different Baltic then we see today.


Sources:

Meier HEM (2015) The BACC II Author Team, Second Assessment of Climate Change for the Baltic Sea Basin, Regional Climate Studies, DOI 10.1007/978-3-319-16006-1_13

Takolander, A., Leskinen, E. and Cabeza, M., 2017. Synergistic effects of extreme temperature and low salinity on foundational macroalga Fucus vesiculosus in the northern Baltic Sea. Journal of Experimental Marine Biology and Ecology495, pp.110-118.

Rugiu, L., Manninen, I., Rothäusler, E. and Jormalainen, V., 2018. Tolerance to climate change of the clonally reproducing endemic Baltic seaweed, Fucus radicans: is phenotypic plasticity enough?. Journal of phycology54(6), pp.888-898.

Free-living Bladderwrack – Why should we care?

To answer this question it helps to look at the bigger picture: Why should we care about the natural environment at all? Though the reasons are many, one of the most obvious is that their functioning directly affects our society. This idea is the basis for the ecosystem services concept.

Ecosystems Services – What are they and why do we need them?

Ecosystem services are the benefits provided by the natural environment to society. They are the foundation of human well-being. These services are numerous and highly varied depending on the ecosystem. In forests and woodlands the production of wood as a raw material for the use in manufacturing is one such service. On a smaller scale, individual species can also provide important services, such as bees acting as pollinators for agricultural plants. These services are invaluable to human existence, and often come with no accompanying monetary cost. Being freely available, many are undervalued and consequently protection for the environments that provide them is frequently limited.

Though ecosystem services are often taken for granted, they are hugely important. Imagine if the continued use of pesticides, most famously neonicatoids, led to the extinction of numerous bee species. Many fruit and seed producing crops would be left unpollinated, leading to crop failure and the consequential food shortages within shops and supermarkets. Hence the ecosystem services we take for granted can have monumental effects on society and our quality of life. It therefore seems necessary to provide protections for these environments so that they can continue to provide the services we rely on.

So now we know what Ecosystem Services are – How does this relate to bladderwrack?

As an underwater environment that many people rarely, if ever, see bladderwrack forests are a hugely underrated environment in terms of their value and the ecosystem services they provide. However bladderwrack forests can be considered similar to giant kelp forests, which are some of the most productive habitats on earth.

Bladderwrack forests are highly productive environments storing large quantities of carbon. Because some of this carbon is sequestered bladderwrack can be considered to provide a service in reducing CO2 within the atmosphere and thus help our society with mitigating climate change.

This is not the only services these underwater forests provide. As an ecosystem engineer; a creature that modifies its environment; bladderwrack also provides the additional benefits of food and shelter for a myriad of different plants and animals, all of which themselves contribute to the ecosystem services provided by this habitat. Notably bladderwrack plays an important part in food production by providing nursery and feeding habitat for juvenile fish of commercial importance including cod, pike and perch. By supporting populations of these important fish species they also provide valuable recreational services including recreational fishing, boating and SCUBA diving.

Plaice resting next to an attached bladderwrack stand

An entirely different service that bladderwrack provides influences people’s health by reducing their contact with harmful environments. Within the Baltic Sea, the enrichment of water bodies with excessive nutrients has led to widespread eutrophication and resulting nuisance blooms of cyanobacteria. These blooms can be detrimental for human health and are monitored by the Finnish Environmental Institute SYKE. Importantly though, bladderwrack forests can act as filters against high nutrient inputs from terrestrial sources, providing a service in reducing excessive load of nutrients and consequently benefiting human health and well-being.

These are just a few of the ecosystem services this fascinating habitat provides, though there are numerous others that have not been listed here. We can therefore conclude that both bladderwrack and the associated community of plants and animals are important for the Baltic Sea ecosystem and many of the services we require.

What about free-living bladderwrack and the associated animal community?

Since free-living bladderwrack fulfils a similar ecological niche to the attached form, albeit generally on soft bottoms rather than rocky substrates, we surmise that it provides similar ecosystem services as well. Both forms support a similar animal community living around and on the seaweed, but the free-living form also supports an additional community living within the sediment below the algal mats. It is likely that this community will provide additional services that benefit us, however what these services are is difficult to tell unless we have a greater understanding of the associated animal communities of the free-living form. Hence this is where our study comes in. In one of our projects we are interested in identifying the animals on and below the surface of the sediment, and how these communities vary from those of bare, soft bottoms. To find out how important these creatures are to our society we will delve below the surface of this barely studied habitat.

Free-living bladderwrack forest

The curious case of free-living Fucus: what is it and where does it come from?

Bladderwrack (Fucus vesiculosus) is a brown algae commonly found within many parts of the Baltic Sea. It forms structurally complex habitats at depths of 0.5-7m, providing shelter and food for many marine invertebrates and fish. It is one of the major foundation species in the Baltic Sea coastal zone. Generally, bladderwrack is considered a rocky shore organism, being most notability found growing attached to rocks, boulders and pebbles. However, interestingly an unattached form can also be found.

A meadow of free-living bladderwrack, resulting in 100% coverage. Image taken in the Askö area (Sweden)

These unattached individuals form free-living populations, that can be quite extensive (10-100m2) occurring year after year at the same sites. They have been observed since the late 19th century (Kjellman, 1890) and are generally described as pieces torn from attached populations and deposited in sheltered locations, with no ecological significance. However with modern molecular techniques; including microsatellites and DNA barcoding; we aim to test this theory.

 

The origins of life?

Firstly we aim to test this long held idea that the free-living populations are solely supplied by the surrounding attached populations. To put it simply, do they rely on supplies of torn off pieces to start and replenish a population or are they fully or partially self-sustaining through their own means? This really is a question of ‘can they reproduce?’, and if so ‘how do they do it?’.

The processes involved in forming and maintaining free-living bladderwrack populations

We surmise that the founding members of any free-living population are supplied by pieces from attached populations, as has been suggested since their first documentation. However this is where the ideas diverge, rather than assuming any replenishment to the population are from supplies of material from the nearby attached population, we view that these free-living populations have some level of self-sustainability.

How do they do this? The current idea is through fragmentation, a method of asexual reproduction where new, smaller, genetically identical individuals are formed through breakage from the main individual. If you ever get your hands on a free-living bladderwrack individual, you will see how easily one individual becomes many with just the simplest of handling. Through splitting into many individuals that continue to grow and eventually break apart once more, soft bottoms can quickly become dominated by many genetically identical plants.

Two distinct morph types from different free-living populations around the Askö area (Sweden)

The level at which this asexual reproduction occurs will be defined by the amount of genetic variation within the population. If populations contain only a few genetically different individuals then we can assume that fragmentation plays a large role in maintaining these free-living populations. If we observe the reverse; many genetically different individuals; then it is likely that either attached populations are largely responsible for supplying these populations, or that the free-living plants can themselves reproduce sexually. The latter seems improbable, in part because few free-living individuals have been observed to form sexual structures known as receptacles.

 

Population connectivity?

Now that we have established the possible mechanisms for forming, maintaining and regenerating free-living populations, we can consider the dispersal of a normally immobile seaweed. It is frequently observed that broken off pieces from attached individuals can be transported by currents over great distances; and since reattachment is incredibly rare; either these free-floating pieces eventually sink becoming loose-lying pieces which eventually decay or they contribute material to free-living populations.

However the question is, are free-living individuals equally as mobile? Can free-living individuals migrate between patches, and do distances and other abiotic factors affect their dispersal?

We currently have little idea as to answering this question, but it seems likely that distance and geological features will be the major influences on the dispersal potential. By identifying the genetic variation; or the level of relatedness; between and among populations we will hope to answer this intriguing question.

 

Ecologically important?

Thirdly, we have little idea of the importance of free-living populations. What function and ecosystem services do they provide in the coastal zone? Through inhabiting soft bottoms, that are normally uninhabitable by the attached form of bladderwrack, they can provide a complex habitat that would normally not be found on this substrate type. Consequently this habitat can support a vast variety of plants and animals that would otherwise not be found in that location. Through environmental surveys and the monitoring of biological measurements we aim to identify the important functions and services that are provided by the free-living populations.

 

The importance of this study

Now comes the most important question: Why do we need to study these questions in the first place? As an integral part of the Baltic Sea ecosystem, free-living bladderwrack is considered an important biotope at risk of damage. As such they are listed on HELCOM Red List of biotopes and habitats as endangered (HELCOM, 2013). This means that policy makers and conservationists need to implement methods to best protect these populations. Without adequate knowledge, including the genetic diversity, of these populations successful management is doubtful. As such, if we wish to maintain the health of these populations and consequently that of the Baltic Sea, we need all the research we can collect.

 

References

HELCOM (2013) Red List of Baltic Sea underwater biotopes, habitats and biotope complexes. Baltic Sea Environmental Proceedings No. 138.

Kjellman FR (1890) Handbok i Skandinaviens hafsalgflora. I. Fucoidae., Stockholm