Proceedings of the Second Mediterranean Symposium on Marine

PROCEEDINGS OF THE SECOND MEDITERRANEAN SYMPOSIUM ON MARINE VEGETATION (ATHENS, 12-13 DECEMBER 2003)
244
PRELIMINARY RESULTS OF THE EPIBIOTIC FLORA
ON EUNICELLA SINGULARIS (GORGONACEA) COLONIES
FROM THE NORTH AEGEAN SEA
George SKOUFAS 1 & Anastasia TSIRIKA 2
1 Technological Educational Institute <strong>of</strong> Thessaloniki, Department <strong>of</strong> Fisheries Technology and Aquacultures, N. Miltiadi 1, GR- 623
00, Nea Moudania, Greece
2 Aristotle University <strong>of</strong> Thessaloniki, Department <strong>of</strong> Biology, Institute <strong>of</strong> Botany, GR- 541 24, Thessaloniki, GREECE
ABSTRACT
The gorgonian branches denudation is described as necrosis. Gorgonian necrosis
phenomena have been observed in tropical seas, as well as in <strong>the</strong> <strong>Mediterranean</strong> Sea.
The denuded gorgonian branches <strong>of</strong>fer an important hard substrate for <strong>the</strong> installation <strong>of</strong>
a very rich epibiotic fauna and flora. However, gorgonian epibionts change
hydrodynamical properties <strong>of</strong> <strong>the</strong> axis and water currents can uproot <strong>the</strong> colonies.
Although <strong>the</strong> existence <strong>of</strong> epibiotic algae on denuded gorgonian branches has been
recorded in <strong>the</strong> <strong>Mediterranean</strong> Sea, almost no data on <strong>the</strong> identity <strong>of</strong> those macroalgae
species have been given. The aim <strong>of</strong> <strong>the</strong> present study is to report <strong>the</strong> dominant
macroalgae species installed on <strong>the</strong> colonies <strong>of</strong> a Eunicella singularis gorgonian
population that presented a mass mortality phenomenon in Arethoussa (Kavala bay,
North Aegean Sea). The examined Eunicella singularis population expanded at a depth
range between 5 and 15 meters. In situ observations at 350 gorgonian colonies showed
that 342 (97.7%) colonies were affected by partial or total necrosis. Total necrosis and
coverage <strong>of</strong> <strong>the</strong> denuded branches by epibiotic algae exhibited 287 (82%) colonies. In
addition, 55 (15.7%) colonies presented partial mortality and exhibited both denuded
and not denuded branches. Only 8 colonies from <strong>the</strong> investigated gorgonian population
exhibited no mortality spots. Seasonal samples <strong>of</strong> approximately 15 colonies were
collected with SCUBA-diving during 1997. The investigation <strong>of</strong> <strong>the</strong> epibiotic algae
exhibited significant seasonal variations <strong>of</strong> <strong>the</strong> algae wet weight and algae coverage. The
maximum <strong>of</strong> <strong>the</strong> algae wet weight was observed in spring and <strong>the</strong> maximum <strong>of</strong> <strong>the</strong> algae
coverage during <strong>the</strong> summer. Fur<strong>the</strong>rmore, it was observed that <strong>the</strong> algae surface was
remarkably bigger than <strong>the</strong> surface <strong>of</strong> <strong>the</strong> denuded gorgonian branches. The above algae
features displayed a significant spearman correlation to <strong>the</strong> biometric parameters <strong>of</strong> <strong>the</strong>
denuded branches. The dominant macroalgae species installed on <strong>the</strong> denuded
branches were <strong>the</strong> red algae Womersleyella setacea, Botryocladia botryoides, Fauchea
repens and <strong>the</strong> brown algae Sphacelaria plumula, Dictyopteris polypodioides, Dictyota
dichotoma, Halopteris filicina, Stypocaulon scoparium and Zanardinia typus. The red
alga Falkenbergia rufolanosa (tetrasporophyte <strong>of</strong> Asparagopsis armata) was found as
an epiphyte on Womersleyella setacea in all <strong>the</strong> seasons being remarkably abundant in
winter. Ano<strong>the</strong>r red alga, growing as an epiphyte and being recorded for <strong>the</strong> first time at
Greek coasts in <strong>the</strong> present study, was Trailliella intricata (tetrasporophyte <strong>of</strong>
Bonnemaisonia hamifera). This filamentous species was present throughout <strong>the</strong> year,
forming dense tufts (up to 15 mm in diameter), on <strong>the</strong> brown alga Dictyopteris
polypodioides.