Our latest paper has just appeared in Science Advances. In it, we present widespread evidence that aquatic consumers use terrestrial resources depending on the features of surrounding catchments. It is really nice to see this out as it caps the food web workshop we organised in Cambridge more than two years ago and includes data we collected during our summer 2014 field campaign. There’s a nice write up of the work put out by our friends at the Cary Institute.
The work emerged out of our forest fuel fish growth story, which hinted that there can be a lot of variation in the extent to which lake food webs use terrestrially derived material, depending on the features of the surrounding catchments. With funding from a NERC collaborative grant, our new paper managed to assemble the largest dataset to date of the isotopic composition of zooplankton and their associated food webs from across 147 lakes spanning the boreal to subtropics. Our aim was to address the use of terrestrial resource in lake food webs once and for all.
Algae and land plants differ in their assimilation of heavy versus light forms of atoms such as carbon, allowing the ratios between these two forms to be used as dietary tracers. Using these isotopic signatures, we discovered that half of all the zooplankton samples we amassed were comprised of at least 42% terrestrially derived material, but this was underpinned by large variation ranging from 11 to 83%. Using some awfully complex stats, we go on to show that terrestrial support of zooplankton was generally greatest in lakes with long shorelines and surrounded by dense vegetation and rich soils. This work now explains the large variation in terrestrial resource use by aquatic food webs and delivers a major advance towards resolving the ‘controversy’ around this process.
This week, I was lucky enough to go to Lausanne, a small Swiss city on Lac Léman, to attend the MELiSSA Workshop. What is MELiSSA? As an ecologist, it is unlikely that you are acquainted with this European Space Agency (ESA) project, which stands for Micro-Ecological Life Support System Alternative. It was created in 1989 (read more on how it began here) and brings together European and Canadian partners from 13 different countries in an attempt to fulfill human needs in outer space via the development of life in closed systems. The main ideas include: recycling waste and carbon dioxide aboard spacecraft by using bacteria; and producing food, water, and oxygen in a regenerative way to keep costs low. Put in their words, it aims “at a total conversion of the organic wastes and CO2 to oxygen, water and food”.
It has been a busy summer for our NERC-funded project RELATED (that stands for Restoring Ecosystems by Linking Aquatic and Terrestrial Ecological Dynamics). The project aims to test experimentally whether the productivity of aquatic food webs increases with the quantity and quality of terrestrial organic matter deposited in nearshore delta habitats. It builds on our previous work that showed forests fuel the growth of juvenile fish by subsidizing the base of the aquatic food web. RELATED will also feature much more work on unlocking the microbial ‘black box’ at the base of the food web as well as better understanding how greenhouse gas emissions might change with surrounding vegetation. Inland waters are major sources of atmospheric carbon and predicting their responses to future change is of major interest (some great recent work here, here, and here).
New experiment behind the beautiful Living with Lakes Centre
We’ve now just finished launching the experimental platform behind RELATED. Over the last 8 weeks, we’ve had a team of 8+ working tirelessly to submerge artificial lake sediments in 3 lakes. This has involved collecting, mulching, and sifting organic and inorganic materials, mixing these at an industrial scale, and outfitting nearly 300 mesocosms with the appropriate sampling gear. By replicating our experiment in 3 different lakes, we’ll be able to study terrestrial-aquatic linkages along gradients in eutrophication and climate change – the main drivers of change in the world’s inland waters. We’ve also had excellent student help from Laurentian University’s School of Architecture work to design and build a network of sampling platforms that will allow us to work without disturbing our sediments.
Artificial sediments with increasing organics from left to right.
Here’s the main team celebrating the deployment of the experiment in Ramsey Lake:
Our latest paper in the Proceedings of the Royal Society on the “jellification” of temperate lakes has gotten an impressive amount of on-line attention. At the time of writing this blog, Altmetric scores it as the 22nd highest ranking paper ever published in the journal. You can read summaries from the Washington Post, New York Times, Daily Mail, CBC, CBC Radio, and Yahoo, among others. I’ve also done four separate interviews this week with BBC radio stations (BBC Radio 5, BBC Wales, BBC Cambridgeshire). You can catch the latest, with the BBC World Service from the 26th of Nov, below:
The main finding of the paper is that a small planktonic animal named Holopedium glacialis has been dramatically increasing in two very different lake regions of Canada as the keystone grazer in these lakes, the water flea (Daphnia spp.), has been disappearing. Our results show that this is mainly driven by declines in lake water [Ca]. Daphnia need large amounts of Ca to build their body shell, while Holopedium surround themselves in a gelatinous polysaccharide “bubble”:
An individual Holopedium with the jelly capsule clearly visible. (Photo: Ian Gardiner / E-Fauna BC)
This jelly also protects Holopedium from predators. By contrast, Daphnia are increasingly susceptible to predators at low [Ca] because their ability to induce evolved defences is also impaired. Our analyses show how vanishing Daphnia have now left more algae uneaten for their competitors to exploit, allowing them to multiply in number. Many media reports have picked up on this as Holopedium liking ‘pollution’, with low [Ca] somehow being the result of this. But it is more in fact a legacy of pollution. While we have curbed industrial emissions and reduced acid rain, the historical depletion of base cations from the thin soils of the boreal shield, have left behind much lower [Ca] than present prior to industrial activity. Ca concentrations have consequently been falling across much of North America and Europe.