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Floating algae: Transportation for marine invertebrates

Atualizado: 18 de mar. de 2020

A study in the Chilean Patagonia...

During college, I did a summer internship in Chile with a professor of marine ecology. A month before the trip I met up the professor at a meeting in Brazil, where we discussed my project. The project would be concentrated on studying “floating algae.” What? Yeah, he wanted me to get on a boat and hunt for algae that were floating in the middle of the ocean, in order to analyze the accompanying fauna. Hmmm…OK, and?

The professor explained that these algae were detached because of strong marine currents, storms, and winds, and they were now drifting on the surface, a term called rafting. Along with the algae, some fauna would likely be attached, sheltered in between the leaves. Most of these companion fauna are marine invertebrates with no larval phase. Without a planktonic larval phase, many invertebrates have a limited distance they can move on their own. By hitching a ride on these floating algae, the algae become a mechanism for dispersion and connectivity for many marine species!

Macrocystis pyrifera floating. By Ivan Hinojosa.

Photo: Schematic of benthic and floating algae and the most common animals found in both states. By Ivan Hinojosa.

This professor and his team had previously reported the presence of native species in different regions of the country, but the majority of those animals lacked a larval phase. It didn’t make sense how these animals could be so widely dispersed in different areas. This could only be explained by a “loading” of these species to new regions. It was then discovered that the floating algae were the means of transportation for these marine communities. The algae is like a bus, but instead of picking up and dropping off around a city, the algae can float for hundreds of miles in the ocean. Interesting, no?

And it was! Since my internship only lasted three months, I wasn't able to participate in the collection of my samples (the cool part), because the identification of fauna would take too long after returning. However, the professor did take me on an expedition for another project! Imagine a paradise, with big waves, lots of sun, but very cold weather. Three of us were floating in a small boat, GPS in one hand, binoculars in the other, paper and pencil at the ready to take notes. We couldn't take our attention from the sea, always searching for the algae rafts. Oh, and man was I seasick! But in those moments, you just contract your stomach and remember your love for science, and everything will work out.

Left: Me and the boat in Punta Choros before the expedition; Right: People collecting a raft of floating macroalgae with a sieve so animals cannot escape. Pics: Ivan Hinojosa

My project aimed to compare the fauna accompanying floating algae with that of algae that have not yet detached, which we call benthic. Benthic algae are fixed to the bottom or to some substrate, like a stone, for example. The benthic algae were collected through scuba diving. The specific algae I studied were Macrocystis pyrifera, which form giant kelp forests in the Pacific Ocean.

On the left are fronds of a benthic algae, the famous marine kelp. To the right is a close-up image of Macrocystis pyrifera, with its leaves and aerocysts. Second photo by Ivan Hinojosa

In the lab, the algae were washed in strainers to size fractionate and retain the animals that we wanted to identify. After that, the algae were weighed and measured. We identified the animals with magnifying glasses.

So, onto the results! The benthic algae had abundant companion fauna, which were different from the floating algae. Some groups like sea urchins and some crustaceans (called decapods) were only found on the benthic algae, likely because they were unable to hold onto the non-fixed algae while it drifted.

Graph of the occurrence of different taxa within each kind of algae; floating and benthic. By Izadora Mattiello and Ivan Hinojosa.

Another interesting finding was that despite the lower number of species, floating algae mostly supported species with direct development (those without a larval phase). This further reinforces our initial hypothesis that floating algae contribute to species dispersal. A well-known case on the Chilean coast is the bivalve mollusk Gaimardia trapesina.

Unfortunately, almost everything has a downside. In this case, it is garbage loading! With all of the human-produced plastic waste that has been thrown into the ocean, the algae end up carrying litter in addition to animals. During my analysis, I got tired of throwing plastic away; there were bottle lids, pieces of rope, etc. that ended up entangled in the algae. It is very clear how much we have abused this ecosystem.

Do you like rubbish in your car, the subway, or on an airplane? The next time you are at the beach, try to remember how tiny marine animals are transported, and grant them the same respect you expect for yourself.

To the next!

by Ivan Hinojosa.

Know more at: Lab BEDIM

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