Kelp Forests Return to Peru’s Coastline

Young kelp forests have re-emerged along part of Peru’s coastline after scientists replanted giant seaweed in areas where it had almost disappeared.

Fish that had vanished from nearby waters are already returning to the regenerating habitat, offering an early sign that the damaged marine ecosystem is reviving.

Kelp patches return

On the rocky seabed off El Carbón beach in Pucusana, young Macrocystis pyrifera kelp is once again growing from ground that had become mostly barren.

Paul Baltazar Guerrero of the Scientific University of the South (UCSUR) monitored the returning plants, recording how newly installed kelp can attach itself and persist at the recovering location.

In around a year, approximately 200 seedlings planted throughout the site developed into tall fronds – kelp’s long, leaf-like blades – while nearby shoals of anchovy and silverside began to return.

Storms and currents can nevertheless dislodge immature kelp, meaning that every new patch is an initial stage in restoring a broader underwater forest.

Jars used as nurseries

Around 100 seedlings were transported in filtered seawater inside 0.95-litre jars, travelling from the laboratory to the dive boat.

At the Marine Culture Research Laboratory (LICMA), technicians sterilised the water and added nitrate and phosphorus to safeguard the seedlings.

Following a 3.5-hour journey in a cooler, divers secured the seedlings to local rocks and placed them at a depth of about 6 metres.

Even a 25-minute journey by boat can shake the cargo, while LICMA teams later take plants away for measurement.

Holdfasts support tiny life

For giant kelp, the holdfast – a tangled base that clings to rock – provides shelter for small animals.

The twisting branches within this base catch fragments of algae and sand, creating hiding places for worms, crabs and snails.

While carrying out fieldwork in Pucusana, researchers collected 11 of these bases and identified 40 animals to species level.

As kelp patches expand, this concealed community can recover quickly because many young fish feed on these creatures first.

Fish require kelp cover

Along this coastline, fish commonly shelter among kelp during their most vulnerable early weeks, before they are able to escape predators.

Dense fronds reduce water movement and provide shade, and the holdfast community offers juveniles small, manageable food.

Silversides, a small fish that is popular in Peru, deposit their eggs among kelp, so barren seabeds result in fewer young fish.

As kelp cover declines, fish lose safe locations for spawning and local catches may fall even when boats continue fishing.

Currents undo progress

Morning dives at El Carbón, a rocky fishing ground near Pucusana on Peru’s central coast, can quickly become difficult, with storms capable of pulling out seedlings before they take hold.

Powerful currents and moving sand may break fronds, while monitoring activities occasionally remove plants for laboratory inspection.

Cloudy water and cross-currents complicated planting, and divers sometimes needed to swim against the flow simply to get around.

Previous El Niño heatwaves reduced local kelp forests, and warmer oceans may make sustained recovery more difficult.

Kelp stores ocean carbon

Growing kelp absorbs carbon dioxide from seawater and converts it into fresh tissue.

When fronds detach and fall, some of their carbon reaches the seabed as blue carbon, meaning carbon stored in ocean sediments.

At UCSUR, technicians monitored kelp biomass and began calculating carbon capture from growth in the newly established patch.

Measuring carbon remains complex because currents may carry kelp out to sea, and researchers still disagree over how much ultimately sinks permanently.

Fishing is linked to kelp

For Pucusana’s small-boat fishers, each additional kelp patch may provide more fish within reach during a single trip.

Greater structure on the seabed creates extra prey and shelter, potentially improving survival for the following generation.

“Seaweed provides refuge for other species, helps with oxygen production and carbon recycling, and also assimilates pollutants such as nitrogen and phosphorus,” explained Baltazar.

Without local rules governing harvesting and anchoring, small restored sites may vanish, returning fishers to their original situation.

Seaweed as a food source

Seaweed is also served as food, with cooks near the LICMA laboratory incorporating it into stews, sauces and salads.

A 2025 review associated some kelp with high concentrations of carotene, a pigment that the body converts into vitamin A.

“We should encourage children to eat more of it every day so their immune systems improve,” said Erika Oscata, a server at Cevichería San Andrés.

However, high iodine concentrations can create difficulties for some people, so dietary guidance requires careful testing and labelling.

Economic value of kelp

In addition to food, brown seaweeds are collected for alginate, a gel-forming fibre used to thicken food and medicines.

A 2022 review reported that commercial kelp may contain up to 40% alginate by dry weight.

When calcium is present, alginate chains cross-link to create gels, a property used in dressings, capsules and sauces.

Should extraction expand without restrictions, harvesters could remove habitat more rapidly than it can regrow, harming both income and ecology.

Rebuilding kelp forests

The new kelp patches near Lima may be small, yet the animals inhabiting their holdfasts indicate that food webs are beginning again.

Moving from scattered patches to a stable kelp forest will need consistent ocean conditions, long-term monitoring and effective local management.