Harmful algae: Identification, isolation, and culturing techniques
The professional practice took place in the "Marine Botany" department of the Polytechnic University of Marche and focuses on the identification, isolation, and cultivation techniques of the microflora of the Adriatic Sea. In particular, the study of toxic species and their influence on the trophic network are essential components of marine botanical research. In collaboration with the Experimental Zooprophylactic Institute of Umbria and Marche, an experimental project is being carried out to study the impact of different concentrations of the toxic dinoflagellate Ostreopsis ovata, native to the Adriatic Sea, on commercial sea bass. Besides the cultivating activities of Ostreopsis ovata and the control species Skeletonema marinoi, several microscopic techniques are applied to identify the diatom and dinoflagellate species which were collected in field trips.
Diatoms and Dinoflagellates in the Adriatic Sea
Diatoms constitute the algae group with the highest abundance in aquatic environments and exist in benthic and pelagic ecosystems. While some species form colonies other stay unicellular. The exoskeleton (frustule) of hydrated silica (SiO2 + nH2O) is compiled by two overlapping halves, the Epitheca and Hypotheca.
Diatoms are autotrophic and are commonly divided into two orders based on symmetry and shape: the round Centrales and the elongated Pennales. The microalgae reproduced themselves by vegetative and sexual reproduction. After mitosis, a smaller valve is reconstructed so that one cell with the same size as the previous generation and one cell characterized by a smaller size is formed. The asexual reproduction continuous until a minimum size is reached and the individuals initiate a sexual reproduction form cells obtaining the largest size Battarbee et al., 2002).
Biodiversity of Diatoms in the Adriatic Sea
Centrales
Skeletonema spp. are centric diatoms forming colonies, which possess a wide range of tolerance of salinity and temperature. Therefore, species of this genus are worldwide distributed, especially in coastal systems. Due to their high abundance, Skeletonema marinoi is used as control species to investigate the effect of toxic algae on the trophic web (Godhe et al., 2006).
Thalassisiora ssp. are distributed in marine as well as in freshwater ecosystems and represent a model organism to study diatoms’ physiology and genome sequence due to their small 34 Mb genome. The species can possess various shapes from cylindrical to discoid or spherical. The cells can stand alone or form colonies through chitin filaments, which connect individual cells (Armbrust et al., 2004).
Chaetoceros spp. represents the largest genus of planktonic diatoms. Due to their high tolerance to temperature, salinity, light incidence, and nutrients, they occur cosmopolitical and can form persistent blooms. Due to their high abundance, they represent an important food source in the water column and contribute a significant part to the oxygen production of the phytoplankton (Johansen et al., 1990).
Pennales
Pleurosigma spp. constitute a large planktonic group of diatoms that are worldwide detected. Especially in bays, inlets, and ports, a high abundance of Pleurosigma species is observed. The body of the diatoms possesses a symmetric biraphid shape, which pulsates and initiates a gliding movement and circular rotation (Sterrenburg et al., 2000).
Nitzschia spp. are widespread marine diatoms in Arctic and Antarctic waters, while some species, such as Nitzschia longissima, also occur in warmer waters. Several species can produce neurotoxin, which is responsible for Amnesic Shellfish Poisoning (ASP) (Kaczmarska et al., 2007).
Licmophora spp. are marine benthic species, which epiphytes on marine shores and are considered members of fouling communities. Additionally, they occur on natural coral reef systems and benthic filamentous algae. The diatoms are characterized by a high tolerance of temperature from 5°C to 20°C in marine ecosystems. The species distinguished a funnel-shaped and living alone or in colonies. Two visible chloroplasts characterized Licmophora abbreviate while Licmophora flabellate possesses a higher amount of chloroplasts (Macatugal et al., 2019).
Biodiversity of Dinoflagellates in the Adriatic Sea
Dinoflagellates represent the second largest group of phytoplankton after diatoms and occur predominantly as unicellular organisms, although in rare cases they can form colonies. The group shows great diversity in shape and size but is mainly characterized by two different flagella, the transverse and longitudinal flagella, which originate from the central cell side.
The planktonic protists have various functions in marine ecosystems. They provide the basis for higher trophic levels in the food web and play a significant role as endosymbionts of marine animals (e.g. corals). Other heterotrophic and mixotrophic dinoflagellates cause top-down control of smaller microbes, while autotrophic species contribute to oxygen production. For rapid growth and population expansion, dinoflagellates reproduce vegetatively until sexual reproduction is initiated due to nutrient, temperature, or light reduction in late summer and autumn (Hasle et al., 1996).
autotrophic dinoflagellates
Ostreopsis spp. represents a widespread genus, which occurs in benthic, epiphytic, and planktonic conditions and can form toxic blooms. The endemic species O. ovata constitute the smallest species and possess a tear-shaped form, which contains golden chloroplasts (Faimali et al., 2012 David et al., 2013). Ostreopsis ovata is used to investigate the effect of palytoxin on sea bass.
Amphidinium spp. is an autotrophic toxic alga, which lives epiphytically in coastal waters worldwide. A. massartii possesses a round shape and a single plastid and can produce polyketide (Echigoya et al., 2005 Cyronak and Tomas, 2006) .
mixo- and heterotrophic dinoflagellates
Ceratium spp. is a mixotrophic cosmopolitan genus. C. furca possesses a straight body with a short right and a long left posterior horn. This species causes ret tides due to eutrophication in coastal ecosystems. The non-toxic species C. tricornutum possesses equal U-shaped (Da Burns and Mitchell 1980, Baek et al. 2009).
Protoperidinium spp. represents a cosmopolitan heterotrophic genus that feeds on diatoms via extracellular digestion and follows coastal diatom blooms. Species are characterized by varying shapes, such as the leaf shape of P. micas, and lack chloroplasts due to their nutritional mode. Some species also produce the neurotoxin azaspiracid Jeong et al., 2004).
About me
I am an IMBRSea student pursuing a scientific career in ecological research. Microalgae are not only essential for oxygen production, but they also constitute the basis of the marine food web. Therefore, expanding knowledge about phytoplankton is an important goal of biological research.
