FIRST DATA ON THE BENTHIC ASSEMBLAGES OF HARMFUL MICROALGAL SPECIES IN THE GULF OF TARANTO (NORTHERN IONIAN SEA)

Abstract The benthic assemblages of harmful microalgal species have been detected for the first time in the Gulf of Taranto (Northern Ionian Sea).The most abundant species was Ostreopsis cfr. ovata, which€was present in all the samples collected. The microalgal association was mostly composed of Ostreopsis cfr. ovata, Coolia monotis, Amphidinium carterae and Coscinodiscus sp., and showed features typical of both the Mediterranean and tropical assemblages. Keywords: Algae, Toxic Blooms, Ionian Sea, Phytobenthos1 11 Introduction The biogeographical spreading of benthic dinoflagellates constitutes a major issue since the majority of them are capable of producing toxins [1], and raises questions about their origin and possible dispersal mechanisms [2, 3]. Among these dinoflagellates, the most known species Ostreopsis have today exceeded the biogeographical boundaries once considered for them (tropical and sub-tropical areas) and their presence in the Mediterranean Sea is actually well-documented [4]. In the tropical regions Ostreopsis genera are usually found in association with Gambierdiscus, Prorocentrum and Amphidinium species [5]. In the Mediterranean Sea, the assemblages of Ostreopsis with Coolia monotis, Prorocentrum lima and Coscinodiscus sp. [6, 7] have been detected. The aim of this study is to describe for the first time the benthic assemblages of harmful micro-algal species in the Gulf of Taranto (Northern Ionian Sea).€€ Material and mehods In August 2008 samples of sediment were collected from three stations, located along the coastline of the Northern Ionian Sea (Mediterranean Sea) (1 = Mar Piccolo of Taranto; 2 = Mar Grande of Taranto; 3 = Lido Bruno) (Fig. 1). Samples of sediment (50–150 gr wet weight) were collected from depths between 0.5 and 1.5 m, placed in plastic bottles with filtered seawater and kept in the dark. In laboratory, sediment samples were vigorously shaken; the material was then passed through 250 and 100 mm mesh sieves to remove large particles, and was finally fixed with lugol’s solution. The sediment was dried and then weighed. The fixed material was settled in 2–10 ml chambers for the appropriate time according to Utermohl’s sedimentation method [8]. Samples were examined and counted with an inverted microscope. The epiphytic abundance was expressed as cells gr dry weight of sediment (dws). € Fig. 1. Map of the Gulf of Taranto with sampling stations. Results and discussion The microalgal assemblages of sediments was dominated by dinoflagellates, the most of them potentially toxic (Table 1). Ostreopsis cfr. ovata, which was present in all the examined samples, reached the highest concentration at the stn. 3. The harmful dinoflagellates Coolia monotis, Prorocentrum lima and Amphidinium carterae were also abundant. Among diatoms, the genera Coscinodiscus and Nitzschia were important components of the assemblage. The benthic microalgal association detected in the Gulf of Taranto (Ostreopsis cfr. ovata, Coolia monotis, Prorocentrum lima and Coscinodiscus sp.) was