Revision of the genus Dasya ( Ceramiales , Rhodophyta ) in Galicia ( NW Spain ) and the addition of a new alien species Dasya sessilis Yamada for the European Atlantic coasts

A revision of the genus Dasya in northwestern Iberian Peninsula is presented. Three species (Dasya hutchinsiae, D. ocellata and D. sessilis) are confirmed whilst other three (Dasya corymbifera, D. punicea and D. rigidula) are excluded from the Galician seaweeds flora. The alien species Dasya sessilis Yamada is a new record for the European Atlantic coasts. The study of the herbarium material reveals that D. sessilis was misidentified with other Dasyaceae species and that it has been collected on the Galician coasts for more than 16 years. Morphological and anatomical features of D. sessilis as well as its distribution and chronological data on the Galician coasts are provided. A comparison of the Iberian specimens with the Mediterranean and Asian plants is also included. Dasya sessilis was found growing on a wide range of substrata, from the lower intertidal to subtidal at moderate wave-exposed and sheltered areas. It is abundant in harbours and aquaculture areas together with other alien species such as Heterosiphonia japonica and Undaria pinnatifida. The comparative study between D. sessilis and similar European and Iberian Dasyaceae species is undertaken to prevent further misidentifications. Dasya sessilis is the largest Dasya species, with broader main axes (1-2 mm wide vs 200500 μm in D. ocellata and 500-600 μm in D. hutchinsiae); pseudolaterals of D. sessilis are 3-5 times pseudodichotomously branched compared to 5-8 times in D. hutchinsiae and 4-5 times in D. ocellata; pseudolateral tips are broader in D. sessilis than in D. ocellata, but smaller than pseudolateral apices of D. hutchinsiae; tetrasporangial stichidium of Dasya sessilis has 6-7 periaxial cells (and 6-7 tetrasporangia) per fertile whorl vs. 4-5 in the rest of the native species; and tetrasporangial stichidia of D. sessilis are longer and cystocarps broader than those in D. hutchinsiae. The alien Dasyaceae species Heterosiphonia japonica, similar in size to Dasya sessilis, differs from it in main axes branching (alternate or distichous in H. japonica vs. spiral in D. sessilis), the number of periaxial cells in the vegetative axes (4 in H. japonica vs. 5 in D. sessilis), and color (pinkish red vs. deep red). Other distinctive characters are the tips of main axes (70-90 μm wide in H. japonica vs. 100-130 μm in Resumen Se presenta una revisión del género Dasya en el noroeste de la Península Ibérica que confirma la presencia de tres especies (Dasya hutchinsiae, D. ocellata y D. sessilis) y excluye la de otras tres (Dasya corymbifera, D. punicea y D. rigidula) de la flora bentónica marina gallega. La especie alóctona Dasya sessilis Yamada es nueva para el Atlántico europeo. El estudio de material de herbario revela que D. sessilis ha sido confundida con otras especies de Dasyaceae y que ha sido recolectada en la costa gallega desde hace más de 16 años. Se presentan las características morfológicas y anatómicas de D. sessilis así como su rango de distribución y la cronología de introducción en la costa gallega. Asimismo se lleva a cabo la comparación del material gallego de D. sessilis con especímenes mediterráneos y asiáticos. Dasya sessilis aparece sobre una gran variedad de sustratos, desde el intermareal inferior a infralitoral, en costas semiexpuestas a protegidas. Es además abundante en zonas portuarias y de cultivos marinos, donde aparece junto con otras especies introducidas tales como Heterosiphonia japonica y Undaria pinnatifida. Con el objetivo de facilitar futuras identificaciones se realiza un estudio comparado de D. sessilis y otras especies similares de Dasyaceae presentes en el Atlántico Ibérico y Europa. Dasya sessilis es la especie de Dasya más grande, con ejes principales anchos (12 mm frente a 200-500 μm en D. ocellata y 500-600 μm en D. hutchinsiae); pseudolaterales que se ramifican pseudodicotómicamente cada 3-5 veces frente a 5-8 veces en D. hutchinsiae y 45 veces en D. ocellata, y con ápices más anchos que en D. ocellata pero más estrechos que en D. hutchinsiae; estiquidios de los tetrasporocistes con 6-7 células periaxiales (y 6-7 tetrasporocistes) por segmento fértil frente a 4-5 en el resto de especies de Dasya europeas y son más largos y los cistocarpos más anchos que los de D. hutchinsiae. Otra Dasyaceae alóctona, Heterosiphonia japonica, también alcanza un gran tamaño, pero difiere de Dasya sessilis en la ramificación de ejes principales (alterna o dística en H. japonica, helicoidal en D. sessilis), el número de células periaxiales de los ejes vegetativos (4 en H. japonica, 5 en D. sessilis) y el color (rosado rojo frente a rojo oscuro). Otros caracteres de identificación de ambas especies son el ancho de los


Introduction
Dasya sessilis Yamada (Dasyaceae, Ceramiales) is an introduced Asian species which has been previously reported from the European coast only in the Mediterranean Sea (Verlaque, 2002).It is present in the sheltered and shallow waters of the Thau Lagoon (France), where it was usually misidentified with other native European species of Dasya, like D. hutchinsiae Harvey.Similar confusions were already pointed out by Yamada (1928), who indicated misidentifications between D. sessilis and D. punicea (Zanardini) Meneghini ex Zanardini on the Japanese coasts.Here we report the discovery of this taxon for the Iberian Peninsula.Although its distribution is likely to be broader in the NE Atlantic, where it could be more common than expected in mariculture and harbour areas, so far it has been only detected in Galicia.As occurs with French materials, the Galician populations of D. sessilis were also confounded with other Dasya species, and a study of the herbarium material reveals a high number of wrong identifications of Dasyaceae species for more than 16 years.In this study we present a morphological and anatomical description of Dasya sessilis, its known distribution and chronological sequence of appearance in the Iberian Peninsula.Moreover, we present the comparative study between D. sessilis and similar Iberian Dasyaceae species to prevent further misidentifications.According to Bárbara & al. (2005), five Dasya species are reported for the benthic marine flora of Galicia: D. corymbifera J. Agardh, D. hutchinsiae Harvey in Hooker, D. ocellata (Grateloup) Harvey, D. punicea and D. rigidula (Kützing) Ardissone.Another alien Dasyaceae species common along the Atlantic Iberian Peninsula coasts is Heterosiphonia japonica Yendo which was formerly reported as Dasysiphonia sp.(Bárbara & al., 2003).Both alien species are similar in morphology and frequently occur together in the same habitats, like aquaculture and harbour areas.
Tetrasporangial stichidia (350)400-900(950) µm long, (100)110-130(150) µm wide, with 6-7 periaxial cells, elongate, ovoid to cylindrical and pointing to monosiphonous tips, sessile or borne on 1-2-celled stalks on monosiphonous branches bases, rarely terminal in middle and upper parts of the plant.Cylin-    (Yamada, 1928;Verlaque, 2002), the Iberian material matches with the Asian and the Mediterranean ones despite some quantitative differences concerning reproductive structures such as the diameter of the cystocarps and the length of spermatangial branches and tetrasporangial stichidia (Table 1).As in the Mediterranean plants, the Atlantic tetrasporophytic plants were found almost all year round.However, sexual plants were found from March to October whereas the Mediterranean plants developed spermatangial branches and cystocarps from July to November.We also observed that the Atlantic plants reached their largest size in February and November.
According to Verlaque (2002), Dasya sessilis is restricted in the Mediterranean Sea to rocky and hard substrata, between the water surface and 6-8 meters depth, on shallow and sheltered waters of the Thau Lagoon.Contrary to the Mediterranean plants, the Galician ones occur both sheltered and moderate waveexposed areas, from lower intertidal to subtidal (to 16 meters depth) growing on a wide range of substrata (bedrock, mud and sand gravel, epizoic on Mytilus and Balanus as well as epiphytic on maërl beds).It is partic-ularly abundant in harbours and aquaculture areas like the extensive mussel cultures which are widely distributed along the middle and central parts of the Rías (Figs. 4a,b,5), where it usually coexists with other alien species such as Heterosiphonia japonica and Undaria pinnatifida (Harvey) Suringar.

A.3. Comparison of
The re-examination of Atlantic collections showed that hitherto D. sessilis has been misidentified with other Dasya species, and also that only three species of the genus grow in northwestern Iberian Peninsula: Dasya hutchinsiae, D. ocellata, and D. sessilis.The taxonomic features to distinguish between these species, as well as their habitat in Galicia are given in the Table 2. Dasya sessilis is the largest Dasya species, with main axes 1-2 mm wide vs. 200-500 µm in D. ocellata (Fig. 6c) and 500-600 µm in D. hutchinsiae (Figs.6e, f The ecology of all the Atlantic Dasya species is similar; all of them are epilithic, epizoic and epiphytic from lower intertidal to subtidal, although Dasya ses-silis is more abundant at subtidal level (to 16 m depth).In similar habitats grow the introduced species Heterosiphonia japonica (to 18 m depth), and both alien species frequently occur together in aquaculture and harbours areas.Heterosiphonia japonica is also a large plant, reaching 30 cm in height (Figs. 6m,n), and therefore misidentifications are likely to occur in such areas.The main characters to separate both species are the main axes branching (spiral in D. sessilis but alternate or distichous in H. japonica), and the number of periaxial cells in vegetative axes, 5 in D. sessilis but 4 in H. japonica (Tab.2).Other characters include the width of the main axes near the apex (100-130 µm in D. sessilis, 70-90 µm in H. japonica); color (deep red in D. sessilis, pinkish red H. japonica); shape of pseudolaterals, usually narrower at the base and broader at tips in D. sessilis.Further features exclusive of H. japonica are the presence of adventitious polysiphonous branches as well as axes less corticated than in D. sessilis (Figs.6k, l).

B. Excluded species of Dasya from the Galician seaweeds flora
Dasya punicea was reported as a new record for Galicia from Ría the Arousa and Ría de Vigo by Veiga & al. (1998) and, subsequently, from Ría de A Coruña by Peña & Bárbara (2002).Afterwards Bárbara & al. (2004, fig. 4) described the spermatangial stichidia of D. punicea for the first time.However, the revision of these specimens and the rest of the Galician material of D. punicea revealed that they correspond to D. sessilis, and therefore D. punicea is excluded from the Galician seaweeds flora.

Conclusions
From our study of the genus Dasya in northwestern Iberian Peninsula, we confirm the presence in the area of three species, Dasya hutchinsiae, D. ocellata, and D. sessilis, instead of the five formerly reported.The Galician material previously attributed to D. punicea is D. sessilis, whilst the herbarium material of D. rigidula and D. corymbifera are in fact D. hutchinsiae.
An important diagnostic feature to distinguish D. sessilis from native European Dasya species is the number of periaxial cells in each tetrasporangial stichidium (D. sessilis has 6-7 periaxial cells instead of 5).The alien Dasyaceae species Heterosiphonia japonica was also considered due to similarities with D. sessilis in vegetative morphology and ecology; it can be distinguished from D. sessilis by the alternate to distichous arrangement of its vegetative axes, which have 4 periaxial cells, its pinkish-red color, and wider pseudolaterals to the base.
Dasya sessilis collected in Galicia is a new record for the Atlantic European coasts.The Galician specimens match with descriptions of previous studies (Yamada, 1928;Verlaque, 2002), although there are some quantitative differences in reproductive structures such as the diameter of cystocarp and the length of spermatangial branch and tetrasporangial stichidium.In Galicia, D. sessilis grows on a wide range of substrata including maërl beds, from the lower intertidal to subtidal (-16 m depth) at moderate waveexposed and sheltered areas.The species is specially abundant in harbours and aquaculture areas located in the middle and central parts of the Rías, together with other alien species such as Undaria pinnatifida and Heterosiphonia japonica.In the northwest of the Iberian Peninsula Dasya sessilis was formerly collected from different Rías since 1989, although these records were misidentified as Dasya hutchinsiae, D. ocellata and D. punicea.Nowadays, D. sessilis is widely distributed along the Galician coast, although its distribution is surely wider along the NE Atlantic, where the species should be specially looked for in mariculture and harbour areas.-1984, 14-VI-1984, 12-VII-1984, 26-I-1990, 20-III-1992