Dinoflagellate cysts and Chattonella resting stages from recent sediments of the southeast coast of Iran

Many harmful microalgae, including dinoflagellates and raphidophytes, produce long-lived, resistant, resting stages called resting cysts. Mapping the presence and abundance of these stages in coastal sediments combined with germination studies can provide valuable information on the distribution of potentially harmful species in an area. The resting cyst flora of equatorial and tropical regions of the world is poorly known, particularly in coastal waters. This thesis examines the dinoflagellate resting cyst flora in coastal marine sediments collected along the southern coast of Iran. The aim of the study was twofold. Firstly, to determine whether potentially harmful dinoflagellates or raphidophytes are present in the area. Secondly, to document the species diversity of dinoflagellate resting cysts in a little studied tropical region.Nine sediment samples were collected at three locations (i.e. the Bahoo-kalat estuary, Pasabandar coast and Chabahar Bay) along the southeast coast of Iran. Dinoflagellate cyst species abundance and diversity was examined by light and scanning electron microscopy, and the resting cyst identity and affinity confirmed by cyst germination, where possible. Established cultures were further characterised by PCR amplification and DNA sequencing of the large subunit ribosomal RNA gene (LSU-rDNA) and internal transcribed spacer (rDNA-ITS) regions.Over forty ( 40) distinct cysts morphotypes were identified in the samples examined. The most common groups identified were: Scrippsiella species (79%), Protoperidinium species (10%) and, at three sites (Pasabandar) an unusual angular, trapeziform resting cyst was common (7% ). Potentially harmful species were also found in some sites; for example, the paralytic shellfish poisoning (PSP) causative species, Alexandrium tamarense, yessotoxin producing species Lingulodinium polyedrum.Cyst incubation and germination studies established over 30 dinoflagellate cultures that were further characterised by detailed morphological (LM and SEM) and molecular approaches. The unusual trapeziform resting cysts were successfully germinated and identified as a previously undescribed dinoflagellate. Morphological studies of the resting cysts showed a microreticulate paratabulation, with the pattern reflecting amphiesmal patterning of the motile cell, including the cingulum and sulcus. Using cultures established from cyst germination the phylogenetic affinities ofthe species was examined by comparison of partial LSU-rDNA sequences with a range of other Gymnodinioids. The resulting analyses indicated a clear relationship to the other three known microreticulate cyst-forming Gymnodinoid species, Gymnodinium catenatum, G. nolleri and G. microreticulatum. Identical resting cysts were also successfully produced in nutrient depleted laboratory cultures, and the pattern of successful crosses indicated a homothallic mating system for this species. This dinoflagellate is described as a new species G. trapeziforme Attaran-Fariman & Bolch sp. nov.The majority of the remaining cultures established from single cyst incubations were found to be allied with the Calciodinelloidean genera Scrippsiella, Calciognellum, Calciodinellum. Of these cultures, four distinct morphotypes were identified and subjected to DNA sequencing ofthe rDNA-ITS regions. Three morphotypes were allied with Scrippsiella trochoidea var. aciculifera, Scrippsiella sp., and Scrippsiella trochoidea respectively. The fourth morphotype, possessing a small second anterior intercalary plate, was allied with but distinct from the similarly tabulated Scrippsiella precaria and S. ramonii. Morphological examination shows that its overall size and shape is similar to S. precaria, but with a more equatorially placed cingulum, an antapically placed nucleus and a larger, rounded 2nd anterior intercalary plate similar to S. ramonii. This species is described here as Scrippsiella irregularis AttaranFariman & Bolch sp. nov.Mixed sediment incubations from site 6 (Pasabandar coast) also commonly released a raphidophyte belonging to the genus Chattonella Biecheler. Uni-algal cultures established from incubations were examined and determined to be allied with Chattonella subsalsa Biecheler. Analysis ofthe LSU-rDNA and rDNA-ITS regions sequences compared to other known Chattonella species showed that this species is related to C. subsalsa, but is genetically distinct, and may represent a new species.