Halimeda tuna is a type of green seaweed that is found in the ocean. It’s a calcareous seaweed, meaning it has a hard, calcium-rich structure.
This seaweed is found in the Atlantic Ocean, the Indo-Pacific region, and the Mediterranean Sea.
The name “tuna” comes from the Taíno language and means “cactus,” because the seaweed looks like a cactus.
What Does Halimeda tuna Look Like?
Thallus Structure
Halimeda tuna has a unique structure called a thallus. The thallus is made up of a single cell that forms a tube with many cell nuclei.
Inside the cell wall, there is the cytoplasm, which is a fluid that allows the cell contents to move around.
Segments and Utricles
The tube of the thallus has flat, disc-like segments connected by flexible joints. On the surface of these segments, there are swollen areas called utricles.
The utricles create a flat, table-like surface called a “cellular pavement.”
Calcium Carbonate and Aragonite
In between the utricles, there are gaps where the fluid inside the cell is saturated with calcium carbonate.
This fluid forms crystalline needles of a mineral called aragonite. The aragonite gives the seaweed a hard, stiff structure and makes it unpalatable to fish.
Where Does Halimeda tuna Grow?
Halimeda tuna grows in tropical and subtropical regions of the world. It’s found in the Indo-Pacific area, the Mediterranean Sea, and the western Atlantic Ocean.
The seaweed grows on rocky reefs, from the shallow subtidal zone down to depths of about 230 feet (70 meters).
Habitats in The Mediterranean Sea
In the Mediterranean Sea, Halimeda tuna is found in two different types of habitats.
In the central Mediterranean, it lives in shallow, warm lagoons and sheltered places.
In the northwest Mediterranean, it grows in deeper water (18 meters or 60 feet) on rocky habitats.
Habitats in The Florida Keys
In the Florida Keys, Halimeda tuna is the dominant green algae in shallow back reef locations and deeper, less well-lit reef slope habitats.
What Is the Ecology of Halimeda tuna?
Epiphytes
The thallus of Halimeda tuna is often covered by other plants called epiphytes.
These plants grow on the seaweed and are most abundant during the summer.
New Growth
Sometimes, the segments of the seaweed get damaged by storms.
However, new growth occurs when the temperature rises, and there is more sunlight and dissolved nutrients in the water.
Deepwater Habitats
In deepwater habitats in the Mediterranean, Halimeda tuna is the dominant species. It often grows with an encrusting red algae called Mesophyllum lichenoides.
In these habitats, the seaweed grows on vertical walls, under overhangs, and in places where there is not much sunlight.
Adaptations to Dim Light
Halimeda tuna is adapted to grow in dim light because it contains two accessory photosynthetic pigments, siphonein, and siphonaxanthin, along with chlorophyll a and chlorophyll b.
These pigments help the seaweed to absorb light and carry out photosynthesis.
How Does Halimeda tuna Reproduce?
In Florida, Halimeda tuna reproduces both sexually and asexually.
Sexual reproduction happens when up to 5% of the thalli (plural of thallus) develop special structures called gametangia.
Asexual reproduction occurs through fragmentation or the growth of vegetative stolons.
What Are the Human Uses of Halimeda tuna?
Halimeda tuna is edible and can be eaten with oil, vinegar, and salt. It has been described as having a pleasant taste.
You can check out what this plant looks like over here.
Halimeda tuna Characteristics
| Required Lighting: | Low High |
| Maximum Size: | 5 in (12.7 cm) |
Scientific Classification
| Kingdom: | Plantae |
| Order: | Bryopsidales |
| Family: | Halimedaceae |
| Genus: | Halimeda |
| Scientific Name: | Halimeda tuna |
| Also Known As: | Cactus Algae |
| Conservation Status: | Unknown |