Species Of Gracilaria Research Articles

Taxonomic Challenges and Distribution of Gracilarioid Algae (Gracilariales, Rhodophyta) in Tanzania

This paper reviews the taxonomical literature of the gracilarioid algae from Tanzania, and provides information about their ecology and distribution based on an intensive regime of local collection. Its aim was to provide names, even if on a preliminary basis, for local gracilarioid taxa. Our revision shows that species misidentification is widespread and that some species are in need of further critical taxonomic study. Nine species of Gracilaria are reported in the region, including one unidentified Gracilaria or Gracilariopsis . Keywords : Gracilaria , Gracilariales, taxonomy, distribution,Tanzania West Indian Ocean Journal of Marine Science Vol. 3 (2) 2004: pp. 143-150

Development of an eco-friendly agar extraction technique from the red seaweed Gracilaria lemaneiformis

The red seaweed, Gracilaria lemaneiformis growing as an aquaculture bioremediator along the coasts of Liaodong Peninsula, China, was investigated for the agar production. An eco-friendly method called agar photobleaching extraction process was developed for the benefit of workers’ health and safety of the environment. The native agar (NA), alkali-modified agar (AA), chemical-bleached agar (CA) and photobleached agar (PA), which were extracted using different processes, were evaluated for their physical and chemical properties. The PA showed most desirable performances in terms of gel strength, gelling temperature, sulfate content and 3,6-anhydro- l-galactose content. Among the different processed agars, PA gel strength was 1913 g/cm 2, the highest among the different processed agars, which increased 8.6% on the basis of the AA. Further we applied this new technique to extract agars from Gracilaria asiatica, and similar results were obtained with that of G. lemaneiformis. This indicates that the agar photobleaching extraction process is a feasible method for Gracilaria species and has a potential application. During the whole agar photobleaching extraction process the pigment content of G. lemaneiformis declined gradually and the TOC concentration in photobleaching solution increased along with the increase in the irradiation time. The mechanism of agar photobleaching could be elucidated by the photolysis theory.

Effect of irradiation on the protein profile, protein content, and quality of agar from Gracilaria asiatica Zhang et Xia (Rhodophyta)

There are about 15 species of Gracilaria reported in Vietnam. Of these, Gracilaria asiatica Zhang et Xia is being cultivated on a large scale in Northern Vietnam, which has a subtropical climate. During the rainy season, from May to October, the growth of G. asiatica is drastically reduced or even ceases due to very low salinity and high temperature. Therefore, it is important to improve the tolerance of G. asiatica to a wide range of salinity and temperatures. This paper presents the results of research on strain improvement of G. asiatica using irradiation and selection media. Three irradiation doses of 20, 60, and 100 krad were tested against the control (with no irradiation). Afterward, the seaweed biomass was cultivated on a selected medium, ESS-1, containing NaCl in concentrations of 23‰ (C1) and 0‰ (C2). The results showed that a higher survival rate of G. asiatica was observed with the 20- and 60-krad doses. The protein content and composition of selected seaweeds were analyzed and compared with the control. SDS-PAGE showed no remarkable difference in the protein composition between the control and irradiated samples. However, the 67-kDa protein band of seaweed treated with 20 and 60 krad, then grown on ESS-1 medium with 23% NaCl, had a higher density than other samples. This protein was reported to play an important role in G. asiatica, by enhancing its tolerance to variable salinity and temperature. Although the organic and inorganic content of all samples remained almost the same, the content and quality of agar extracted from irradiated seaweeds were higher than those of the controls. Due to the high amount of 3.6 anhydro-α-L-galactose combined with low amounts of sulfate found in irradiated seaweeds, the freezing and melting points of extracted agar were lower. Eventually, this resulted in higher condensation and better quality of agar, such as in its gel-forming ability. The quality of fluid agar extracted from selected seaweeds improved as shown in the remarkable decrease in Ca2+, Mg2+, and total Fe ion content, thus lowering its melting point compared with the control.

Molecular Cloning and Characterization of a Novel β-Agarase, AgaB, from Marine Pseudoalteromonas sp. CY24

Agarases are generally classified into glycoside hydrolase families 16, 50, and 86 and are found to degrade agarose to frequently generate neoagarobiose, neoagarotetraose, or neoagarohexaose as the main products. In this study we have cloned a novel endo-type beta-agarase gene, agaB, from marine Pseudoalteromonas sp. CY24. The novel agarase encoded by agaB gene has no significant sequence similarity with any known proteins including all glycoside hydrolases. It degrades agarose to generate neoagarooctaose and neoagarodecaose as the main end products. Based on the analyses of enzymatic kinetics and degradation patterns of different oligosaccharides, the agarase AgaB appears to have a large substrate binding cleft that accommodates 12 sugar units, with 8 sugar units toward the reducing end spanning subsites +1 to +8 and 4 sugar units toward the non-reducing end spanning subsites -4 to -1, and enzymatic cleavage taking place between subsites -1 and +1. In addition, 1H NMR analysis shows that this enzyme hydrolyzes the glycosidic bond with inversion of anomeric configuration, in contrast to other known agarases that are retaining. Altogether, AgaB is structurally and functionally different from other known agarases and appears to represent a new family of glycoside hydrolase.

Using gigartinine to track the distribution of an alien species of Gracilaria in New Zealand

The presence of gigartinine has been used previously as a taxonomic marker for the positive identification in Manukau Harbour (west coast, Auckland) of Gracilaria sp., which has apparently been introduced to New Zealand waters and is easily confused morphologically with the native species, G. chilensis. Thirty two estuarine/harbour populations of Gracilaria in New Zealand were screened for the presence of gigartinine to further test the utility of gigartinine as a reliable species marker. DNA fingerprinting was used to confirm the identity of a subset of the specimens surveyed. Using genetic rather than chemical characterisation, it was discovered that Gracilaria sp. is also present in Orakei Basin (east coast, Auckland). Although a sample from the wild did not have the anticipated gigartinine content, tank cultivation of thalli from this population in an artificially elevated nitrogen environment allowed the plant to accumulate nitrogen as gigartinine. This confirmed the unusual ability of this species of Gracilaria to store nitrogen in this form, unlike the widespread, morphologically similar, G. chilensis.

Long interspersed elements in three species of Gracilaria (Gracilariaceae, Rhodophyta)

In order to find out whether long interspersed elements (LINEs) existed in macro-algae genomes or not, we tested the LINE homologues in representative families (species): Gracilaria (G. eucheumoides Harv., G. tenuistipitata Chang et Xia, and G. textorii (Sur) De-Toni), Laminaria (L. longissima Miyabe and L. japonica Aresch.), and Ulva (U. lactuca L. and U. pertusa Kjellm.) during 2004 to 2005. Polymerase Chain Reaction (PCR) was carried out with degenerate oligonucleotide primers designed from LINEs of rice homologues and Cin4 of maize. Cloning and nucleotide sequencing of the PCR products revealed that 4 clones that derived from 3 species of Gracilaria have LINE homologues. The nucleotide sequences of the 4 LINE homologues diverged greatly, but the amino acid sequences deduced from them were relatively conserved. The endonuclease regions of the LINE homologues greatly diverged from that of other plants, but they had closer phylogenetic relationship to Zepp elements in Chlorella sp., which indicated that sequence divergence by vertical transmission has been a major influence on the evolution of algal LINEs.

Observations on Flattened Species of Gracilaria (Gracilariaceae, Rhodophyta) from Taiwan

Four flattened Gracilaria species have been reported from Taiwan: G. spinulosa, G. vieillardii, G. textorii and G. punctata, identified based on branching pattern, the presence or absence of spines, and characters that often vary seasonally. Gracilaria spinulosa was originally described from the type locality, Tainan. Species with toothed margins are usually referred to G. “vieillardii”; those with smooth margins to G. “textorii”, and those with smooth margins and dark spots scattered over the blade to G. “punctata”. Molecular analyses show that specimens with marginal teeth cluster in three different groups: a G. “vieillardii” clade, a G. spinulosa clade, and a clade sister to G. spinulosa. An undescribed species comprises the third clade, which is distinguished by its relatively large gonimoblast cells and weakly developed tubular nutritive cells. The three clades can be separated by the character of the tubular nutritive cells, the size of gonimoblast cells and certain vegetative features. Plants with entire margins form a single clade characterized by cystocarps with basal tubular nutritive cells and their absence in the cystocarp cavity. They are nested in the Hydropuntia complex and are referred to as Gracilaria “punctata” here. The records of G. textorii and G. punctata from Taiwan require reinvestigation in comparison with the Japanese species.

Taxonomy and phylogeny of flattened species of Gracilaria (Gracilariceae, Rhodophyta) from Korea based on morphology and protein-coding plastid rbcL and psbA sequences

M.-S. Kim, E.C. Yang and S.M. Boo. 2006. Taxonomy and phylogeny of flattened species of Gracilaria (Gracilariceae, Rhodophyta) from Korea based on morphology and protein-coding plastid rbcL and psbA sequences. Phycologia 45: 520–528. DOI: 10.2216/05-38.1Despite extensive studies on cylindrical Gracilaria species, the taxonomy and phylogeny of the flattened species of the genus has received little attention. We studied the morphology and molecular phylogeny of three flattened species of Gracilaria, hitherto reported from Korea. Gracilaria textorii is characterized by having a wider blade relative to other species, margins entire or proliferous, coriaceous thallus texture, one to three large cells in the medulla, and shallow male conceptacles. Gracilaria cuneifolia is membranous in texture, and has shallow spermatangial conceptacles (approximately 10 µm in depth). We generated psbA and rbcL sequences from 32 specimens of G. textorii, G. cuneifolia and its putative relatives in Korea and surrounding waters. Twenty-three specimens of G. textorii from Korea, including two from Japan, were almost identical in both rbcL and psbA regions, except for some specimens that were different by one to four nucleotides. Three specimens of G. cuneifolia were identical in both rbcL and psbA. However, we found no evidence for the occurrence of G. incurvata in Korea. In all analyses of rbcL, psbA, and rbcL + psbA data sets, G. textorii was determined to be a unique species, with G. incurvata from Japan as a sister species. Gracilaria cuneifolia is more closely related to the G. tikvahiae group from the Atlantic than G. textorii and G. incurvata.

Different patterns of carotenoid composition and photosynthesis acclimation in two tropical red algae

To be able to survive, marine macroalgae in shallow coastal waters need mechanisms for short-term acclimation to fast changes in their environment. Of major importance are mechanisms that regulate the efficiency of photosynthesis by protecting PS II from photo-oxidative damage. Carotenoids, xanthophyll cycles and non-photochemical quenching (NPQ) are central constituents of such protection mechanisms. Red algae as a group do not have a universal carotenoid composition. We screened ten red algal species and selected two species, originating from similar ecological conditions but with different carotenoid compositions, for use in irradiance-acclimation experiments. We selected the tropical intertidal species Gracilaria domingensis and Kappaphycus alvarezii with antheraxanthin and lutein as major xanthophylls, respectively. Simultaneous in vivo fluorescence and O2 evolution experiments were performed at different irradiance levels, which allowed a direct comparison of overall photosynthetic performance with NPQ. Interconversions of xanthophylls (violaxanthin, zeaxanthin, β-cryptoxanthin and one unidentified carotenoid) did occur in G. domingensis, but not in response to sudden exposure to light. Thus, NPQ was not correlated with any xanthophyll cycle during short-term acclimation to light. G. domingensis had five times higher weight-specific photosynthetic rates than K. alvarezii, which can be explained by the thicker thallus of K. alvarezii. Chlorophyll-specific gross photosynthetic rates were higher in K. alvarezii, but net rates were the same for both species. G. domingensis showed an immediate strong onset of NPQ upon exposure to irradiance, followed by downregulation to the NPQ level required. In K. alvarezii NPQ increased slowly until the required NPQ level was reached. At high irradiance G. domingensis downregulated photosynthesis while K. alvarezii continued to produce O2 even at 2,000 μmol photons m−2 s−1 without NPQ increase. The strategy of K. alvarezii may provide short-term gains but with the risk of oxidative damage. The fast onset of NPQ in G. domingensis even at subsaturating irradiance as well as downregulation of photosynthesis when NPQ is saturated might provide this species with a competitive advantage under conditions of changing irradiance in the field.

Distribution and Identification of an Invasive Gracilaria Species that is Hampering Commercial Fishing Operations in Southeastern North Carolina, USA

A newly abundant Gracilaria species in the sounds of southeastern North Carolina has become a problem for commercial fishing and industries drawing water from the lower Cape Fear River. DNA sequence analyses have shown that this species is Gracilaria vermiculophylla, a taxon originally described from East Asia. Surveys for G. vermiculophylla have shown that it has a discontinuous distribution in the sounds of southeastern North Carolina, and suggest that it is spreading. Gracilaria vermiculophylla meets 6 of the 10 criteria used to help identify invasive species in that it has only recently appeared in southeastern North Carolina; is associated with human mechanisms of dispersal; has a restricted distribution; has disjunct populations in isolated oceans; no means of active dispersal, and an exotic evolutionary origin. The species may also meet two additional criteria as its local range is believed to be expanding, and it is filling a previously unoccupied seasonal niche. These factors taken together strongly suggest that G. vermiculophylla is an invasive species in southeastern North Carolina.

Biopolymers from the Mauritian Marine Environment

AbstractTo the best of our knowledge, the extraction of biopolymers from algae and seaweeds still remains untapped. Prior studies in this area have been limited to a taxonomic survey of algae and seaweeds found around our coastal regions. In this paper, we report on the extraction of biopolymers from Hypnea, Eucheuma and Gracilaria species collected around the coastal regions of Mauritius. Various extraction conditions were used and their effects on yield and structure of the corresponding biopolymers were investigated. The extracted polysaccharides were characterized by a combination of IR, NMR, SEC, viscometry and elemental analyses. These revealed that polysaccharide extracted from Gracilaria is a highly methylated agar and Hypnea/Eucheuma contain κ‐carrageenan.

MOLECULAR SYSTEMATICS OF THE GRACILARIACEAE (GRACILARIALES, RHODOPHYTA) WITH EMPHASIS ON SOUTHERN AFRICA1

Southern Africa has economically exploited populations of terete gracilarioids on the cool temperate west coast and numerous species of endemic and Indo‐Pacific tropical Gracilariaceae on the south and east coasts. Gross morphological characters have been the main means of identification, and incorrect applications have led to a number of misidentifications. In this study, small subunit rDNA and RUBISCO spacer sequences were used to determine phylogenetic relationships. Whereas rDNA sequences successfully differentiate major groups within the family as well as species belonging to the Gracilariopsis and the Curdiea/Melanthalia clade, RUBISCO spacer sequencing was required to distinguish between species of Gracilaria. The southern African gracilarioid complex (stringy, terete, elongate members of the Gracilariaceae) was resolved into three species: Gracilaria gracilis, Gracilariopsis longissima, and Gracilariopsis funicularis. South African Gracilaria protea was shown to be conspecific with tropical Indian Ocean G. corticata. Apart from G. gracilis and G. corticata, South African Gracilaria species were differentiated into a temperate‐tropical terete grouping and a temperate‐tropical flattened grouping.

Morphological and taxonomic studies of Gracilaria and Gracilariopsis species (Gracilariales, Rhodophyta) from South Africa

Southern Africa has an extremely rich and diverse seaweed flora with a wide variety of marine habitats. Increased commercial interest in these seaweed resources has been the stimulus for biodiversity studies. The Gracilariaceae (Rhodophyta) has emerged as one of the families that possess economic potential as a source of agar and as a potential feed for abalone. A lack of knowledge concerning the taxonomic status of many members of this family is a concern. Gross morphological characters have been the main means of identification and incorrect applications have led to a number of misidentifications. Consequently, a comprehensive reappraisal and revision of these species was carried out. The species count for the South African Gracilariaceae is now two Gracilariopsis species, and nine Gracilaria species. Gracilaria crassa has been reduced to a synonym of G. canaliculata. It is believed that G. foliifera was erroneously identified and specimens in South Africa referred to as G. millardetii and G. protea are assigned to G. corticata. South African Gracilariopsis, previously referred to as Gs. lemaneiformis, is confirmed to be conspecific with European Gs. longissima. This species occurs along the west and south coasts of South Africa, co-existing in a few habitats with G. gracilis. The taxonomic identity of G. vieillardii specimens from South Africa and the differentiation of G. canaliculata and G. salicornia has been confirmed based on morphology. Three species of Gracilaria (G. aculeata, G. beckeri and G. capensis) are endemic or near endemic to the South African coast, and a fourth species, G. denticulata is localised in southeast Africa.

Effect of water motion on the cultivation of the economic seaweed Gracilaria parvispora (Rhodophyta) on Molokai, Hawaii

A cage culture system was previously developed for the red alga Gracilaria parvispora Abbott on Molokai, HI; however, yields have shown marked variation, even among cages with identical stocking rates and fertilization treatments. Water motion, which can be affected by location and arrangement of the cages in the grow-out area, was hypothesized to be a factor contributing to the variation in yield. To examine this, the growth rates of thalli and the development of sporelings in relation to water motion were determined in replicated trials both in tanks and in small-scale field experiments. Generally, water motion had a substantial effect on both thallus growth rate and spore development. In the tank cultures of thalli, water velocities ranged up to 13.7 cm s −1, and relative growth rates (RGRs) ranged from 2.8% to 8.9% day −1. In the lagoon, water velocities ranged between 3.6 and 11.6 cm s −1. Relative growth rates of the thalli in the lagoon trials were 0.02–10.3% day −1. Sporeling density, a measure of spore development, was also significantly affected by water motion. In the tank trials, water motion ranged from near 0 to 6.50 cm s −1, and sporeling densities ranged from 1.4 cm −2 at lower water motion levels to 11.6 sporelings cm −2 at higher levels. Similar results were obtained in lagoon trials, with sporeling densities ranging from 0.2 to 6.7 cm −2. However, sporeling length was not significantly correlated with water motion. In previous trials, we have been able to achieve high sporeling densities, but elongation of sporelings has been inhibited. In the present trials, we were able to break the apparent sporeling dormancy by incubating the sporelings in tanks enriched in nutrients supplied by fish cultures. Consideration of the effects of water motion is important in designing culture systems for species of Gracilaria and other marine algae. The results also suggest that nutrients play a key role in regulating the early development of G. parvispora sporelings.

Agars from three species of Gracilaria (Rhodophyta) from Yucatán Peninsula

Gracilaria cervicornis, Gracilaria blodgettii and Gracilaria crassissima growing along the coasts of Yucatán were investigated for their agar content. The effect of different concentrations of NaOH in the alkali treatment was evaluated. The three species of Gracilaria produced agars, both native and alkali treated, with different properties confirming the heterogeneity of the agar polymers in this genera. G. cervicornis produces agar polymers with an occurrence of methoxylation and sulphation at the C-6 of the β- d-galactose residues, and with an extra methylation due to the presence of the 4- O-methyl-α- l-galactose residue. The presences of these residues is responsible for the extremely poor gelling ability of its agarocolloids, whose commercial value seems to be quite low. Agar extracts from G. blodgettii showed the typical pattern of unsubstituted agar with a very low degree of methylation on both galactose residues. The discrepancy found between sulphate content and NMR data of agar from this species requires a more detailed structural investigation. G. crassissima produces a good quality agar after sulphate precursor sequences have been removed by alkaline treatment, and it may be considered for exploitation as a source of commercial grade agar. Alkali treatment was effective both in removing alkali-labile sulphate and increasing the gel strength in G. crassissima but not in G. cervicornis and G. blodgettii.

Occurrence of Conjugated Polyenoic Fatty Acids in Seaweeds from the Indian Ocean

Three species of red marine macro algae (Rhodophyta) from the Indian Ocean were analysed for the occurrence of conjugated polyenes. The composition of different lipid classes in these seaweeds along with their fatty acid composition has also been reported. Analysis of lipid classes of these seaweeds revealed that both Acanthophora spicifera (Ceramiales, Rhodophyta) and two species of Gracilaria, viz. G. edulis and G. folifera (Gracilariales, Rhodophyta) were rich in glycolipids followed by neutral- and phospholipids. The fatty acid composition of these seaweeds revealed C16:0 as the predominant fatty acid in all three species. However, A. spicifera had significantly higher amounts of eicosapentaenoic acid (EPA) and arachidonic acid (AA) as compared to negligible amount of these fatty acids in both species of Gracilaria. The red seaweed Acanthophora spicifera contained conjugated eicosapentaenoic acid (CEPA) and conjugated arachidonic acid (CAA) in all lipid classes except glycolipids.

Ecology of the Invasive Red Alga Gracilaria salicornia (Rhodophyta) on O'ahu, Hawai'i

The red alga Gracilaria salicornia (C. Agardh) E. Y. Dawson was introduced intentionally to two reefs on O'ahu, Hawai'i, in the 1970s for experimental aquaculture for the agar industry. Some 30 yr later, this species has spread from the initial sites of introduction and is now competing with native marine flora and fauna. The goals of this study were to quantify various aspects of G. salicornia ecology in Hawai'i in an effort to develop control or eradication tools. Experimental plots were established to determine cover and biomass of G. salicornia per square meter and to determine the amount of time and person hours needed to remove G. salicornia from these plots. Substantial amounts of G. salicornia become dislodged from the reef during large wave events and periodically become deposited onto the beach in front of the Waikiki Aquarium. Algal beach wash biomass was quantified and positive relationships were established between swell height and the amount of algae that washed up onto the beach in this location. We then quantified the ability of G. salicornia vegetative fragments to regrow after desiccation to determine if algal biomass stranded on shore survives the tidal cycle until being washed back out on the reef at high tide. Gracilaria salicornia was remarkably resistant to temperature, salinity, and chemical treatments examined as possible in situ control options. Herbivore preference tests showed that a native Gracilaria species is consumed far more frequently than the alien congener. Finally, large-scale community volunteer efforts were organized to remove drifting G. salicornia fragments from the reef area in front of the Waikiki Aquarium. Over 20,000 kg of alien algal fragments were removed from this location in five 4-hr cleanup events. However, based on G. salicornia growth rates, ability to fragment, physical tolerance, and low herbivory, it is clear that a large-scale dedicated effort will be needed to control this invasive species on Waikiki's reefs.

Effects of season on the yield and quality of agar from Gracilaria species (Gracilariaceae, Rhodophyta)

The effect of season on yield and physical properties of agars extracted from Gracia gracilis and G. bursa-pastoris were determined. The agar yield from G. gracilis was maximum during spring (30%) and minimum during autumn (19%). In G. bursa-pastoris, the agar yield was greatest in summer (36%) and lowest in winter (23%). Agar yield from G. bursa-pastoris was positively correlated with temperature ( r=0.94; P<0.01) and salinity ( r=0.97; P<0.01) and negatively with nitrogen content ( r=−0.93; P<0.01). Agar gel strengths fluctuated from 229 to 828 g cm −2 and 23 to 168 g cm −2 for G. gracilis and G. bursa-pastoris, respectively. The gelling temperature showed significant seasonal variation for both species. Chemical analysis of agar from the two seaweeds indicated variation in 3,6-anhydrogalactose and sulfate content ( P<0.01). Furthermore, there was an inverse correlation between the two chemical variables. In general, agar extracted from G. gracilis possessed better qualities than agar extracted from G. bursa-pastoris and can be considered a candidate for industrial use.

Agar from two coexisting species of Gracilaria (Gracilariaceae) from the Mexican Caribbean

Gracilaria cornea and G. crassissima are similar species that coexist at Bajo Pepito in the Mexican Caribbean. Differences in agar properties from both species were determined for two reproductive categories: carposporic and undetermined, the latter mainly composed of tetrasporophytes. Agar yield (AY), agar gel strength (GS), 3,6-anhydrogalactose content (AG) and sulfate content (S) of native and alkali-treated agar were determined for both reproductive categories. Significant differences in native and alkali-treated agar between the reproductive categories were recorded for AY, GS and S from G. cornea and G. crassissima, as well as for AG of native agar from the latter species. Our results, and previous studies, demonstrate that neither reproductive stage was predominant over the other(s) in terms of having greater or lower values of agar properties. The potential economic use of agar differences from plants of different reproductive stage remains very limited. Lower AY and GS were found for G. cornea from the Caribbean side of the Yucatan peninsula (this study), in comparison to agar values reported for the Gulf of Mexico side of the peninsula. Warmer and nutrient-poorer waters on the Caribbean side could cause those differences. No pattern for GS or S was found when these two and other tropical species of Gracilariaceae were compared to temperate species. When plants of both reproductive categories were pooled together for each Gracilaria species, significant differences were found in all agar properties. Interspecific and intraspecific differences between and within species of Gracilariaceae have also been found for phenological events. We suggest that the coexistence of G. cornea and G. crassissima requires different phenological responses by each species to the environment at Bajo Pepito, which in turn could be reflected in differences in the agar properties we measured, both at the interspecific and intraspecific levels.

Differentiation of Male Gametes in Gracilaria verrucosa (Rhodophyta, Gracilariales)

The development of male gametes (spermacia) in the red alga Gracilaria verrucosa has been studied using methods of transmission electron microscopy. Early spermatangia located along the wall of the conceptacle show an elongated shape in the thin sections. In the central part of the electron-dense cytoplasm of these cells there is a nucleus; numerous fibrous vesicles are arranged in the periphery. During the process of differentiation, the spermatangia become more rounded in shape and a large spermatangial vesicle is developed. The subsequent development of spermatium is accompanied by polarization of the spermatangium and the subsequent excretion of the spermatangial vesicle. The spermatia are oval cells containing a nucleus and fibrous vesicles. The process of differentiation of male gametes in G. verrucosa does not differ from that in five species of the genus Gracilaria, where it has already been studied. However, any conclusions about the degree of similarity between the spermatia in all the studied species can be made only after a detailed comparative analysis of the ultrastructural characteristics of these gametes.