During one of Dr. Patrick Gagnon’s very first scientific dives in Newfoundland and Labrador, he came across a strange sight that inspired an entirely new line of research.
The professor of ocean sciences was exploring the waters off the coast of Portugal Cove-St. Philip’s when he found red stone-like structures blanketing the sea floor at depths of 10-25 metres.
“I had seen similar nodules during my 2,000-plus dives in Eastern Canada, but never this big, and certainly not in such high densities,” said Dr. Gagnon.
“They covered nearly every centimetre of the sea floor as far as the eye could see. I got very excited, as I knew I had just come across a world of mystery.”
When he got back to the lab and started looking at the literature, Dr. Gagnon discovered they were rhodoliths — unattached red algae that deposit calcium carbonate inside their cell walls to form hard structures that resemble coral.
“The more I read about rhodoliths from other seas around the world, the more I realized little was known of their biology and ecology,” he said.
“The first published sightings in the Northwestern Atlantic was in the 1960s, but since then nobody had questioned how important they might be to other marine organisms or how sensitive they are to variation in the physical and chemical environment.”
According to Dr. Gagnon, one interesting aspect of rhodoliths is their high structural complexity.
He says the surface of rhodoliths in Newfoundland and Labrador is highly corrugated, with tens to hundreds of holes that run towards the centre, depending on the shape and size of the rhodolith. These holes provide habitat to a number of organisms, mainly juvenile invertebrates.
“It suggests that rhodolith beds are nursery areas for ecologically and economically important species.”
World’s largest examples
His lab’s discovery of a major bed in Portugal Cove-St. Philip’s and another in Holyrood presented an opportunity to write a paper providing the first integrated, quantitative analysis of rhodolith morphology, biogenic potential and organization as beds in the sub-Arctic Northwestern Atlantic. The paper, published in 2012, highlighted the different characteristics of the two beds.
“The Holyrood rhodoliths are unusually big — if you look at the literature, they are probably the biggest ever quantified in the world — while the St. Philip’s rhodoliths are much smaller but more abundant,” said Dr. Gagnon.
The size of the rhodoliths at Holyrood is especially impressive considering the speed at which they grow. Dr. Gagnon’s lab recently demonstrated rhodoliths grow just a few hundred microns per year under the best conditions, which is very slow growth.
“We think the massive Holyrood rhodoliths are probably a few hundred years old and it’s amazing to think about them being on the sea bed that long without being buried by sediment, so we are also looking into how ocean sedimentation affects rhodoliths and the beds they form.”
A significant part of Dr. Gagnon’s current research aims to clarify the role of rhodolith beds in the general functioning of ocean biological systems and how likely they are to respond to ongoing changes in ocean conditions.
He says rhodoliths are marine calcifiers, meaning they rely on carbonate ions in the ocean to construct their hard matrix.
Ocean acidification has the potential to significantly reduce the abundance of such building blocks, which could have pervasive effects on rhodolith growth, survival, and abundance.
Dr. Gagnon believes researchers need to know more about the factors that affect their growth, reproduction, and ability to cope with ongoing changes in the ocean chemistry.
“Understanding the resistance and resilience of rhodolith beds to anthropogenic disturbances is key to developing conservation strategies,” said Dr. Gagnon. “It may well be these beds are vulnerable to human activities, but we just don’t know at this point.”
Dr. Gagnon thinks his lab’s research is essential to elevate the functional importance of rhodoliths in this province and help protect them as needed, particularly since they seem to act as ecosystem engineers — meaning they create, modify and maintain habitats by modulating the availability of resources to other species.
So far, his lab has found more than 100 different animal species living inside or on the surface of rhodoliths in this province.
And they are still finding them.
“Brittle stars, chitons, worms, and bivalves are among the dominant species found in rhodoliths, but there is also a whole suite of less charismatic, yet ecologically important organisms,” he said.
“We even find fish eggs in the centre of those larger, hollow rhodoliths.”
Dr. Gagnon obtained additional Natural Sciences and Engineering Research Council funding in 2013 to study the distribution and structure of rhodolith beds along the coast of Labrador with colleagues at University of Toronto and the Smithsonian Institution.
“Preliminary research yielded very promising results, showing clearly that rhodolith beds are a dominant feature of marine systems in this province, and should be given more attention,” he said.
Now Dr. Gagnon is working towards establishing an international group of collaborators to address questions of global importance about the ecology of rhodolith beds.
Most research so far has focused on determining the presence or absence of rhodolith beds along coastlines, but he says his work needs to go beyond that.
“Beds differ around the world and there is substantial geographical variation in the red algal species that form rhodoliths,” he said. “This gives rise to rhodoliths of various shapes, forms, and density.
“The species that recruit within rhodoliths are not the same either and changes in ocean conditions also vary geographically, so it is therefore unlikely that rhodolith beds around the world will change in the same way, at the same pace.”
Their main mandate and challenge as an international group is to come up with a set of procedures and protocols that will allow researchers around the world to study rhodolith beds in a consistent fashion to generate comparable metrics and standard databases.
“This common framework will allow us to determine global trends in rhodolith bed productivity and stability and how these ecological systems might change over the next few decades.”