24.09.2024 – The transparent sail

Today there were Bottlenose dolphins (Tursiops truncatus) and Blainville’s beaked whales (Mesoplodon densirostris) on all tours. On the evening tour, there were several animal sailors on the blue ocean.

The By-the- sea- sailer (Velella velella) is a fascinating, colony-forming marine organism. It belongs to the class of hydrozoans, a subgroup of cnidarians, and is therefore closely related to jellyfish and corals. The By-the- sea- sailer lives in the surface waters of the oceans and often floats on the water in large aggregations. The By-the- sea- sailer has a transparent, oval ‘sail’ that sits vertically on its flat, blue body. It allows the jellyfish to drift with the wind. The orientation of the sail is crucial: depending on the angle, they sail in different directions, which helps them to spread out over the sea surface. Although the By-the- sea- sailer looks like a jellyfish, it actually consists of a colony of many small, specialised polyps. Each of these polyps has a specific function, such as catching food or reproducing. The By-the- sea- sailer feeds on tiny plankton organisms, which it catches with its tentacles.

One of our guests wanted to know whether the By-the- sea- sailer is dangerous to humans? Although it has stinging capsules, it is not. Unlike other stinging jellyfish such as the Portuguese man o’ war, its stinging cells are too weak to penetrate human skin. Occasionally, masses of By-the- sea- sailers are washed up on beaches, which is an impressive but deadly phenomenon for the animals. In nature, the By-the- sea- sailer plays an important role in the marine food web. They are eaten by fish, birds and sea turtles. Their life in the open seas and their adaptation to wind currents make them a fascinating example of the diversity and adaptability of marine life.

By Fatima Kutzschbach

Sightings of the day

Ribeira Brava

09:30 Bottlenose dolphins, Blainville’s beaked whales

13:30 Bottlenose dolphins, Blainville’s beaked whales

Stenella

09:30 Bottlenose dolphins, Blainville’s beaked whales

14:00 Bottlenose dolphins, Blainville’s beaked whales

17:00 Bottlenose dolphins, Blainville’s beaked whales, By-the-sea-sailers