University of Bremen: Algae mats as a haven for many animals in the Mediterranean

Almost all marine ecosystems worldwide are threatened by anthropogenic climate change. The warming of the oceans caused by climate change, often in combination with overfishing and over-fertilization, lead to the transformation of these ecosystems. Changes in seafloor communities can be observed worldwide: Invertebrates such as corals or plants such as seagrass, which form habitats, are often replaced by algae.

These changes are often accompanied by a loss of characteristic ecosystem functions such as structural complexity and biodiversity, i.e. the diversity of living beings. In the Mediterranean, classic habitats with high biodiversity, such as seagrass meadows or horn coral forests on rocky subsoil, are currently overgrown by red algae mats in many locations. However, little is known about these changes and their consequences.

Scientists of an international research project led by the Department of Marine Ecology of the University of Bremen in partnership with the Institute of Marine Biology on the island of Giglio, Tuscany, Italy, have investigated the species composition and diversity within the red algal mats at several locations around Giglio and with compared to neighboring seagrass meadows.

Understand emerging ecosystems

“Our knowledge of these red algal mats, which seem to be becoming more common, is severely limited. Research projects that shed light on this are therefore necessary in order to be able to understand these new ecosystems,” explains Professor Christian Wild, head of the Department of ‘Marine Ecology’ at the University of Bremen. His research associate Dr. Yusuf C. El-Khaled is first author of the study, which was recently published in the journal Communications Biology .

A total of six bachelor theses by students at the University of Bremen who examined these red algae mats and whose results are synoptically summarized in this article have achieved exciting results. All six bachelor students are also co-authors of the publication. “We have shown that the typical picture of species-poor, algal-dominated ecosystems does not correspond to reality in this case. On the contrary, these red algae mats are full of small invertebrates such as starfish, mussels, tube worms, bryozoans, and sea squirts. Both the number of species and the number of individuals significantly exceed that of the neighboring seagrass beds,” says El-Khaled. “All common indices that are typically used to compare biodiversity have shown:

Assumption: red algae have a key function

“We suspect that these long-lived red algal mats could play a key role, since seagrass meadows and horn coral forests are not only – but also – threatened in the Mediterranean and their distribution is declining,” explains Professor Wild. “So these red algal mats could act as a refuge habitat for invertebrates in difficult times. Should conservation measures for seagrass beds and horn coral forests be successful and current declines halted or reversed, recolonization could occur from the red algal mats – where many animals no longer found elsewhere have found refuge.”