On-board Diary: Ausias March. More carnivorous sponges and the importance of rhodoliths.

Author: Silvia García
Date: August 5, 2010



This is the second of the seamounts in the Balearic Islands that we are going to take samples of. In previous campaigns, we have documented its peak, which rises up to 90 m from the surface from a 400 m deep bottom. Finding a carnivorous sponge species again, as occurred in the 2007 expedition, was one of our man goals. As it rises to a relatively shallow depth, it still receives enough light for some species of algae to survive. Some of them thus form a type of habitat called maërl or rhodoliths that we found in vast expanses.

 

These are a type of corallinaceous red algae, that is, they segregate calcium carbonate which gives them a mineral appearance. They may seem to us like red rocks, almost round, full of little inlets and outlets. This creates a small-scale three-dimensional environment in which a great number of species make use of them to settle and find shelter. This characteristic has conferred these algae the category of protected habitat in the Mediterranean, and aggressive fishing techniques such as trawling or deep-sea longline fishing have been banned there where it is present. The red algae species that comprise it are included on numerous national and international lists of protected species. The problem we have come across to enforce protection is that there is still no comprehensive mapping of the distribution of this type of habitat in Spanish waters and the entire Mediterranean. Therefore, it is very difficult to apply the prevailing regulations.

 

And to finish up, underscore the finding of not one, but three specimens of Asbestopluma hypogea, a small carnivorous sponge that traps small invertebrates via filaments that serve as hooks. Their presence in this area, at this depth and on this type of seabed, has enormously expanded and modified the available information on the distribution and preferences of types of this species’ habitat.