On-board Diary: East of Ibiza: La Llosa de Santa Eulalia and Llado del Sur

Author: Ricardo Aguilar
Date: September 9, 2006



Today is the start of the final part of this year’s expedition. We’re going to be taking samples from the sea beds around the Balearic Islands using divers, a robot submarine and dredging to classify the different biological communities in the area. During the first few days we’ll be diving between Ibiza and Formentera, and later on we’ll be heading for to Majorca and Minorca.

There have been a few changes to the crew and the team, so initially we’re going to take it slowly until all of us are coordinating well and have a good working dynamic. Off the east of Ibiza we’re going to be studying some shallow rocky sea beds in search of places with photophile algae.

The water temperature here is very high, in addition to which the thermocline goes very deep. The temperatures do not go below 25 ºC until the bottom, which here is 25 metres. The fish species found here are typically Mediterranean, including damselfish (Chromis chromis), ornate wrasse (Thalassoma pavo), rainbow wrasse (Coris julis), painted combers (Serranus scriba), combers (Serranus cabrilla), etc., and in the more pelagic areas big shoals of young fish are attacked by groups of yellowmouth barracuda (Sphyraena viridensis) and bonitos (Sarda sarda), but the sea bed is thickly covered by an invasive red algae (Lophocladia lallemandii) which means the native algae of this region are barely visible, such as Dictyota dichotoma and Padina pavonica: the red algae is a real plague. There is also a small meadow of Posidonia oceanica which has accumulated quite a lot of mucilage.

The overall impression is worrying. On the one hand, most of the algae is discoloured and seems to be being affected by the high water temperatures. On the other, the huge spread of this invasive alga definitely represents a threat to the area’s ecosystem.