Impacts of Marine Bioinvasions
Biological invasions are considered to be a major threat to biodiversity. While many species are dwindling due to overfishing and habitat destruction, others invade new regions using anthropogenic vectors. These changes are rooted in human activities more than a millennium old, but have accelerated dramatically in the past few decades due to new technology and increased connectivity among regions. Also, apart from range extension of native species due to climate change, increasing temperatures at medium and high latitudes have the potential to facilitate the establishment of species invading from warmer waters, thus affecting community structure and potentially function. The invasion of non-native species has increased exponentially in the past 200 years, and does not show signs of slowing down or leveling off. In the Mediterranean, one of the most invaded regions in the world, a new invader is being discovered every week. But what are the ecological consequences of these invasions to both community structure and ecosystem functions. This is not a trivial question, and it is one that has been seldom experimentally-tested on the Israeli coast.
The Mediterranean is unique in its rates of invasions mainly because it has a unique vector, the Suez Canal, which created a new direct link to the Red Sea (and the Indian Ocean). This invasion was named Lessepsian migration after the name of the Canal’s engineer, Ferdinand Lesseps.
Many claims have been made about the impact of Lessepsian invaders on Mediterranean biodiversity (as well as human wellbeing), but very rarely this impact was experimentally tested. We normally think of the impact as negative, such as in the case of the invasive siganids fish that devour all fleshy macroalgae on Levant reefs leaving only bare rock or turf. However, theoretically, as the southeastern Mediterranean coast starts losing local species due to climate change, more adapted warm-loving Lessepsians might replace them as well as some of the natives’ functions – and that could then be considered a positive impact. In our lab, we are trying to study the population dynamics of some major invaders as well as to test their impacts on both biodiversity and ecosystem functions.
We have so far tested the impact on biodiversity by one dominant invertebrate and one algae and are now testing invaders’ impacts on ecosystem functions at the community level.
One of the most dominant invasive species is the Indopacific mussel, Brachidontes pharaonis. It was one of the first invaders to the Mediterranean, but was rare for the first 120 years. It became abundant on many vermetid reefs sometimes in the 1980s creating large beds in many but not all sites. For several years, we have been following its recruitment dynamics in several sites using artificial settlement collectors (tuffies) and we also compared community structure and biodiversity in invaded and uninvaded (macroalgae dominated) plots on the vermetid reefs.
Galaxaura rugosa is a branching, calcareous tropical macroalgae that has become abundant in the shallow subtidal creating large patches in some areas on the northern Mediterranean coast of Israel. In many cases it is abundant in areas that are now dominated mostly by low-lying turf; areas which we assume were once dominated by branching brown algae that are now being overgrazed by the siganid fish invaders. It is possible that this new branching algae is replacing some of the functions lost by the overgrazing of native brown algae, for example, as ecosystem engineers. We have compared the epibenthic communities on the invader and on several native species to see if the abundance and diversity are compatible or does the invader represent a new habitat as a host. We are now testing also how a community dominated by the invader is functioning (focusing on carbon cycling) compared to turf-dominated and native-dominated reef communities using novel in-situ incubation chambers.