Jellyfish – Indicators of change?
Hi, I am Damien Haberlin, a PhD Researcher with the Centre for Marine and Renewable Energy (MaREI) based in University College Cork.
For many years’ jellyfish were a forgotten component of marine ecosystems, described in a rather derisory way as a “trophic dead end” and therefore not really worthy of consideration. This was quite the fall from grace, considering jellyfish had at one time, occupied the minds of some of history’s most influential naturalists. Charles Darwin, Thomas Huxley and Ernst Haeckel to name just a few were fascinated by these delicate creatures that might help them explain the mysteries of evolution and the radiation of different body forms.
In the last 30 years or so, there has been a renaissance of sorts in jellyfish ecology and we now know that they contribute significantly to marine ecosystems. Jellyfish can be voracious predators, consuming a variety of zooplankton including crustaceans, fish eggs and larvae and indeed other jellyfish. In this way, they compete directly with many fish species which rely on the same prey species as jellyfish. When conditions are favourable some species can bloom to enormous densities and come to dominate an ecosystem, significantly reducing the food available for other species. What exactly constitutes favourable conditions is not fully understood and undoubtedly varies from species to species, but jellyfish are well placed to thrive when ecosystems are pushed beyond tipping points. This is perfectly illustrated by events in the Black Sea during the 80s and 90s.
In the early 80s the Black Sea was a heavily populated and overfished body of water. It received catchment waters from a region of unregulated industry and intense agriculture within the former USSR territories, leading to eutrophication. All the bordering countries had competed over the highly prised sardine fishery with little attempt at cross border management of the resource, leading to vast reductions in fish numbers. At some point the ctenophore Mnemiopsis leidyi was accidentally introduced into the Black Sea and was able to thrive; feeding on crustaceans, fish eggs and larvae, the Mnemiopsis population exploded with catastrophic impacts on the fish and zooplankton abundance. Without a natural predator, Mnemiopsis dominated the region and spread into connected water bodies. Ironically, the introduction of another ctenophore Beroe ovata, which preys on other ctenophores, began to control Mnemiopsis abundance to some degree, allowing the ecosystem to partially return to the earlier regime.
The events in the Black Sea are complex and teasing them apart in hindsight is difficult, however, they highlight the ability of jellyfish to respond quickly to changes in an ecosystem. They also demonstrate that although the ecosystem changed rapidly, its resilience was probably eroded over a period of decades before being tipped over into a vastly different jellyfish dominated ecosystem.
The events in the Black Sea represent something of a worst case scenario and there is little evidence that it has been replicated elsewhere, least of all in the Celtic Sea. However, it does demonstrate that large scale ecosystems can be forced to change, whether that forcing comes from anthropogenic or natural sources. We can use our improving knowledge of jellyfish ecology to look at long-term datasets of jellyfish abundance in the Celtic Sea and try to spot changes in the ecosystem. Some species common in the Celtic Sea have multiple generations in a season and therefore they respond quickly to environmental changes, making them something of a sentinel species. In addition, we will use recent research cruises in the Celtic Sea to investigate the summer jellyfish abundance in the region. While this sampling only gives us a single snapshot in time, that snapshot extends over a large and complex water body with distinct water masses. Analysing the zooplankton community and abundance within these changing water masses can reveal important insights into changing zooplankton ecology.
What can dolphins and whales tell us?
My name is Dr Simon Berrow and I am Chief Science Officer with the IWDG [The Irish Whale and Dolphin Group (www.iwdg.ie)] and a Lecturer at GMIT [Galway-Mayo Institute of Technology].
How do we fit into the scope of the tipping points project you might ask. if you consider that the IWDG has been collecting cetacean (whales and dolphins) sightings and strandings data in Ireland since 1991 you can imagine the data base we currently hold is extremely important to explore long-term trends and identify conservation issues for cetaceans.
The Celtic Sea, where this project is focused, is an area especially rich in both species diversity and abundance of cetaceans. Since 1999 we have been studying the increasingly abundant fin and humpback whales that arrive seasonally to feed on herring and sprat. The IWDG believe top predators such as cetaceans can act as indicators to the health and robustness of the marine ecosystem. Changes in their distribution and abundance may indicate significant perturbations in the food chain that supports these whales, which could lead to a collapse or even identify a tipping point.
Thus, studies such as these which considered top predators and groups such as the IWDG who have collected large long-term datasets must work together to improve our understanding of marine systems and ensure they are healthy for both wildlife and coastal communities. Our involvement in this project is both to increase awareness and to provide databases which will be analysed by the project statisticians and modellers to identify if in fact cetaceans can be used as indicators of change.
Let me take you on a journey of discovery
As I begin to write we have not yet reached our final destination however, I will lead you along the path so far and if you stay in touch you will be rewarded, as I will be, to discover the outcomes of our voyage of discovery as seen through the eyes of the marine scientists involved in this challenging research project.
I guess it only makes sense to start at the beginning… with a hypothesis or an unanswered question by a curious scientist namely Deirdre [we shall talk to her a little later on in our blog!]. Deirdre wanted to know: “Can we use historic data to identify ‘Tipping Points’ in the Celtic Sea?”
Mmmhh should we not be looking towards the future? What can we learn from this data I hear you ask… don’t worry that is exactly the question of every research funding body out there – Why? And what are the benefits to us? Well interestingly we can learn a lot from historic data and in this case Deirdre had thought about this and coined the phrase “Learning from the Past to manage for the Future”.
In a world where we are witnessing the deterioration and depletion of the waters around us from various factors, for example new emergent pollutants such as microplastics [want to know more?] are being discovered at an alarming rate and are now considered ubiquitous in the marine and freshwater environment. I bet you are wondering how we are going to do it??Over the next number of blog entries I shall introduce you to our team of researchers and let each of them give you an insight into how they are contributing to answering the research question. Then we shall look at the research results that are coming out of the project to put it all into perspective…. and see have we identified those ‘little things’ that made the difference – the historic tipping points in the Celtic Sea Ecosystem…
Little things can make a big difference.
We see big changes in our environment after they’ve happened, but we never really notice the exact moment just before the change occurs. These thresholds can be defined as tipping points and they can be small factors which make a huge difference.
The study into different tipping points, especially climate change, has been widely researched but more studies need to be done into different tipping points of ecosystems, what are the causes that make these huge changes and at what point will an ecosystem be put over the edge. Studying these changes and learning about these issues is of vital importance for the survival of ecosystems.
Along with this blog we have created educational material to get people learning and talking about tipping points. We have made available a lecture which can be used as a resource to teach 3rd level students to get the future researchers of the world interested in the topic. The lecture can be used as is or used to supplement lectures own knowledge around the area. We have also made available an assignment question that can be used as a way for students to do their own learning and research around tipping points.
We hope you find the materials useful and that it will help to get people learning about finding the critical points that shape the environment around us.
Mt. Maunganui, Tauranga, New Zealand [Copyright Darragh Doyle]