Desmarestia viridis

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Desmarestia viridis is a type of brown seaweed, also called stringy acid kelp. It belongs to the group of brown algae known as Ochrophyta and is famous for being very acidic.

What makes it unique
- It releases sulfuric acid when damaged, which can harm or kill the kelp itself and nearby plants. Its internal acidity can be extremely high (a vacuolar pH around 1).
- Despite its danger to neighbors, it is a normal part of many coastal ecosystems.

Appearance and size
- Desmarestia viridis can grow up to about 1.2 meters (roughly 4 feet) tall.
- It attaches to rocks with a disk-shaped holdfast, has a cylindrical central stem, and fronds that branch in a bushy pattern.
- It looks brown because the pigment fucoxanthin dominates its color, masking other pigments.

Where it lives
- This kelp favors colder, shallow waters around the world and can be found in both subtidal and intertidal zones.
- It prefers hard rock substrates and can tolerate both protected and exposed sites.
- It is most common in places like Ireland, Great Britain, and the Isle of Man, and it is found in many oceans except the Indian Ocean.

Reproduction
- Desmarestia viridis reproduces both asexually and sexually, like many brown algae.
- The life cycle has two stages: it first releases flagellated spores, which fertilize and settle to form new plants. The mature plants then release spores again, continuing the cycle.

Role in the ecosystem
- It is a primary producer, using photosynthesis to make food.
- Like other brown algae, it uses chlorophyll but relies mainly on fucoxanthin to capture light for photosynthesis.

Interactions with sea urchins
- Studies in Norway looked at how this kelp affects the green sea urchin, Strongylocentrotus droebachiensis.
- They found that urchin densities were much lower in areas with high amounts of Desmarestia viridis.
- In the lab, sea urchins exposed to acidic water (similar to the kelp’s sulfuric acid) tended to move away, while neutral water slowed their movement.
- The presence of Desmarestia viridis can thus influence where urchins feed and how they behave.