First record of the red alga Asparagopsis taxiformis ( Delile ) Trevisan de Saint-Léon in Greece

The red alga Asparagopsis taxiformis, a seaweed that is possibly introduced in the Mediterranean Sea, is recorded for the first time in Greece. Although no invasive behaviour was observed at any studied site, its spread seems to have been progressive during the last couple of years. However, the origin of the population on the Greek coasts remains uncertain.

Today, the genus Asparagopsis is represented in the Mediterranean Sea by two species, A. armata and A. taxiformis. A. taxiformis is a typical tropical to warm temperate species which was first found in the Mediterranean Sea near Alexandria (Egypt) by Delile (1813); its distribution seems to be confined in the eastern basin (Sala and Boudouresque 1997).However, it has been recently dispersed towards the western basin, having been found along Italian coasts as well as in the Balearic Islands around the end of 1990s (Ballesteros andRodriguez-Prieto 1996, Barone et al. 2003).Similar sudden westwards dispersion has been observed for other alien marine macroalgae, such as Caulerpa racemosa var.cylindracea (Piazzi et al. 2005).In the Gulf of Naples (Italy) A. taxiformis exhibits an invasive pattern (Flagella et al. 2003) and it is generally considered to be an invasive species in the western Mediterranean basin (Verlaque et al. 2005).
The origin of A. taxiformis in the Mediterranean Sea is debatable.Some authors believe that it could be a possible introduced species from the Indo-Pacific via shipping or spreading via the Suez Canal (Boudouresque and Verlaque 2002), while others consider it to be a possible Tethyan relict (Cormaci et al. 2004) or a prelessepsian immigrant introduced into the Mediterranean Sea via waterways built during Pharaonic and/or Roman Times (Por 1978).The latter hypothesis seems to be the more probable for the eastern Mediterranean records (Boudouresque 2005), while recent findings in the western basin probably correspond to recent introductions from the Indo-Pacific via shipping.The most likely scenario is that several strains of A. taxiformis co-occur in the Mediterranean Sea and that at least one of them is definitely introduced (Andreakis et al. 2004).
In Greece A. taxiformis (gametophytic stage) was first found in Rhodes Island (Southeastern Aegean -Figure 1) in January 2006 (Tsiamis et al. 2007 -misidentified as A. armata).The single specimen was observed on rocky substrate at 0.5 m depth on the far northern coast of Rhodes Island, inside the port marine area.
Later, A. taxiformis was collected in the inner part of Saronikos Gulf (South Aegean -Figure 1) in March 2006, during the national monitoring of pollution originating from the urban area of Athens and from the port of Piraeus (HCMR 2007 -misidentified as A. armata).The taxon was collected on rocky substrata at depths of 0,5m at the northeastern coast of Aegina Island (near Aegina's port), where it formed a relatively small population.
Few months later, in September 2006, a few specimens were found again in the inner part of Saronikos Gulf (HCMR 2007 -misidentified as A. armata).They were observed on rocky substrata at 1 m depth on the eastern coast of Salamina Island (Kaki Vigla bay).Since then, A. taxiformis has been present off Aegina Island and in Kaki Vigla Bay in Saronikos Gulf, exhibiting relatively low abundances.Finally, a cast ashore specimen of A. taxiformis was found on the southern coast of Salamina Island (Peristeria bay) in March 2007.
It is widely known that taxonomic differentiation of the two Asparagopsis species is problematic (Ni Chualáin et al. 2004), especially when it comes to the tetrasporophytic 'Falkenbergia' stages.Since most records of A. armata in Greek coasts (which date back to 1972, Koussouris et al. 1973) are based only on 'Falkenbergia' stages, some of them could correspond to A. taxiformis.However, among the records of A. armata on Rhodes Island and in Saronikos Gulf (Koussouris et al. 1973, Diapoulis et al. 1986, Salomidi et al. 2003 for Rhodes Island;Panayotidis andChryssovergis 1998, Panayotidis andMontesanto 2001 for Saronikos Gulf), only one of them refers to the gametophytic stage (Salomidi et al. 2003 -Rhodes Island).Therefore, in our opinion, the presence of A. taxiformis can only be considered as recent in the above mentioned localities, especially when it comes to the gametophytic stage.
In conclusion, the spread of A. taxiformis seems to have been progressive during the last couple of years along the coast of Saronikos Gulf.With regard to native algae, it apparently does not show competitive behavior since its abundance has remained relatively low until now.Its recently recorded presence on Greek coasts could be attributed to recent introduction either from the southeastern populations of the Mediterranean Sea (maybe due to climatic changes) or from the Indo-Pacific via shipping.We conclude that A. taxiformis in Greek coasts should be considered as of questionable status regarding its origin and more detailed study of this species is necessary