Why your kelp-based products could be bad news for biodiversity

The kelp forests of the oceans are a habitat for a wide range of marine species, rivaling even the great tropical forests for sheer richness of biodiversity, according to scientists from the KELPER project, which studies these marine algae ecosystems.

The kelp species, or marine algae, that make up these seaweed strands anchored to rocks on the seafloor are typically Macrocystis pyrifera, or giant kelp, and Lessonia trabeculata, known locally as huiro palo. The largest natural reserves of these algae are found off the coast of Chile and southern Argentina, according to the United Nations Food and Agriculture Organization (FAO). Chile is the main beneficiary of this abundance, with an important industry dedicated to kelp harvesting, primarily L. trabeculata, making the country the world’s largest producer of macroalgae.

Algae contain a carbohydrate called alginate that’s used as a thickener in a large number of products in the food industry, such as desserts, ice creams, dairy products, sauces and condiments. It’s also used in the textiles and pharmaceuticals industries, including in the production of creams and toothpaste.

Until 2005, these long strands of kelp were collected on the beach by fisher-gatherers when, after a swell, the waves pulled them up from the seafloor and deposited them on the shore. Since then, increasing demand for alginate — a market estimated at $1 billion a year, according to a KELPER Project report — has driven the industry to start harvesting the kelp directly from the source in the sea, in a practice known locally as barreteo. According to the most recent figures published by the Chilean National Fisheries Service (Sernapesca), 40,261 tons of L. trabeculata were cut from the seafloor this way in 2018.

Amid the boom, however, marine algae remain relatively understudied, and scientists are drawing attention to this information gap, warning that harvesting the kelp in large volumes could have significant ecological impacts.

For the KELPER Project, the overarching question is: Can seaweed be extracted in a way that doesn’t impact ecosystems negatively? Having begun in Chile, the project is looking to expand north into Peru with the aim of studying the connectivity of kelp ecosystems across the Humboldt Current that hugs the coast of both countries.

In the lab and at sea

Unlike many other marine species whose reproduction occurs in the water column and whose fertilized eggs and larvae are thus swept along by the current, with kelp the fertilization takes place at the bottom of the sea, between the rocks where these marine algae take root. That means the potential for small new algae to disperse more widely is low, and therefore so is the possibility of new colonies being established.

The larger the kelp forest, the greater its reproductive capacity, says Alejandro Pérez Matus, assistant professor at the Department of Ecology at the Catholic University of Chile and the main researcher with the KELPER Project. This is why one of the project’s main goals is to identify the source or parent colonies that have the ability to provide new specimens.

To achieve this, the researchers are carrying out genetic tests to determine how closely related different kelp populations are and how far they’re located from one another. The idea is “to find out which populations we can extract and which we cannot extract,” says Alex Gamarra, another member of the project and a researcher at the Marine Institute of Peru (IMARPE).

A second key aim is to evaluate the resilience of kelp forests and their capacity to bounce back from being harvested.

“We are trying to find out how long it takes for a forest to recover after extraction events,” Pérez Matus says. To do this, the researchers are also studying which ecological agents speed up and slow down kelp recovery, for example the presence of herbivorous fish that feed on the plants.

The researchers are carrying out several experiments simultaneously. One of them consists of fertilizing algae in a laboratory at different temperatures to evaluate the impacts of climate change. Another is to set up cages around patches of kelp to keep out all fish. Similar caged plots allow some fish in while excluding sea urchins and herbivorous invertebrates that eat the kelp.

“The goal is to see which agent inhibits the recovery of these ecosystems,” Pérez Matus says. This will give the researchers the necessary data to “propose measures with gatherers to determine where, when and how to extract these algae.”

Experiments have already taken place in various locations between the north of Chile and the country’s central region, with an aim to extend them to Peru. This work should have begun in March 2020, but the COVID-19 crisis has put this stage of the project on hold indefinitely.

A threat to biodiversity

What scientists have observed is that a given patch of kelp forest takes about four years to recover after being harvested. That’s considered slow for a habitat-forming species. Approximately 110 species live exclusively at the base of these algae, several of which are of commercial interest, such as the Chilean abalone (Concholepas concholepas) and the red urchin (Loxechinus albus).

“There is evidence that commercial species decrease in the absence of algae, which has an impact on fishing,” Pérez Matus says.

He adds there are already places in Chile where the negative impacts of barreteo are apparent, but the extent of the problem has not yet been quantified. “The algae have not been able to recover after their extraction,” he says.

The alginate industry isn’t as advanced in Peru as in Chile; it wasn’t until 2001 that large populations of kelp were observed and people began exploiting the resource, Gamarra says. This late start has allowed conservationists to stay ahead of the industry — for now.

“Seeing what was happening in Chile, where a lot of huiro palo was being removed, we banned the extraction of this species,” Gamarra says.

Harvesting of kelp in Peru still occurs the traditional way: on beaches, where fishers gather up the strands washed ashore by the tide. However, “if somebody wants to extract a meadow, IMARPE does a population assessment,” Gamarra says. “We use vessels, divers, a crew on board who do a survey of the algae to see how much there is and whether part of it can be extracted.”

He adds that requests for barreteo-type harvesting have grown more frequent. Small-scale fishers in particular are taking up kelp harvesting to complement their catches of mahi-mahi (Coryphaena hippurus) or Humboldt squid (Dosidicus gigas). This is especially the case when their catch numbers decline or they need more income, such as during Christmas or the beginning of the school year.

“We are seeing a tendency toward algae extraction,” Gamarra says, which is why “it is important to improve our capacity to respond to this demand from small-scale fishing.”

The KELPER researchers say they hope to begin their experiments in Peru this year, once it’s deemed safe enough to carry out field studies. For now, they’re working on other tasks that will permit them to ramp up their studies quickly. The goal is to figure out how to sustainably manage this increasingly exploited resource to protect not only the kelp forests themselves but also the rich marine diversity that depends on them.