Photosynthetic characteristics of the freshwater red alga Batrachospermum delicatulum (Skuja) Necchi & Entwisle

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Phenology of a dioecious population of Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in a stream from southeastern Brazil

The seasonal dynamics of a dioecious population of Batrachospermum delicatulum (Skuja) Necchi and Entwisle was evaluated biweekly during the growth period of the macroscopic gametophyte, from late autumn (May) to early spring (October) in a third-order stream from the northeast region of Sao Paulo State, southeastern Brazil (20°43'S, 49°13'W). The population fluctuated throughout the study period in terms of percentage cover, frequency and chlorophyll content. Percent cover and frequency showed a clear pattern with the lowest values at the initial and final stages of the growth period and the highest in July-August (winter). Gametophyte growth was associated with high illumination and low temperature, which agrees with most observations on Batrachospermales in stream environments. Relatively wide variations in reproductive characteristics were observed during the growth period, which were not correlated with percentage cover, frequency and chlorophyll content. The phenologic pattern observed in this population was characterized by a synchronic development of female/male plant ratio with the number of spermatangia per plant resulting in. (i) a higher proportion of fertilized (carposporophytic) plants associated with more male plants; (ii) higher fertilization rates during the periods with higher production of spermatangia per plant; and (iii) higher production of spermatangia per plant when the population had more male plants. These characteristics were largely associated with water temperature and ion content. In terms of reproductive success, the population studied can be regarded as highly efficient, considering the relatively low proportion of male to female plants and high fertilization rates. These data are consistent with a hypothesis to explain high fertilization rates in dioecious species in lotic habitats consisting of outcrossing among adjacent plants with intermingled male and female branches within an algal cluster. Efficient reproductive strategies have been reported in dioecious, monoecious and even mixed populations of B. delicatulum and can be interpreted as adaptations to successfully colonize streams with different characteristics.

Reproductive ecology of the freshwater red alga Batrachospermum delicatulum (Batrachospermales, Rhodophyta) in three tropical streams

Batrachospermum delicatulum specimens from three stream segments were analyzed from a tropical region in south-eastern Brazil (20°18′- 20°49′S, 49°13′-49°46′W). Physical and chemical parameters and the spatial placement of thalli were investigated along with the reproductive characteristics of the gametophytic phase. Sequence data of the cox 2-3 spacer region was also utilized to evaluate genetic variation in individuals within and among stream segments. Gametophyte occurred under relatively diverse environmental conditions, whereas thalli abundance was weakly or not correlated to environmental variables within the stream segments. All specimens examined were dioecious. The ratio of male/female plants was relatively low (0.5 to 1.3) and male plants tended to occur as clumps (two or three plants together). High reproductive success was observed, as indicated by the occurrence of 100% fertilized (carposporophytic) female plants. This is similar to previous reports for this and other dioecious species, which is remarkable considering the relatively low proportion of male/female plants. Results support the two hypotheses to explain the high reproductive success in dioecious species. The occurrence of male plants in clumps was evidence for a strict spatial relationship (i.e. male plants located in upstream position of female plants in order to release spermatia, which would be carried by eddies through female plants). In contrast, the occurrence of male and female plants adjacent to each other allowed outcrossing among neighboring plants with intermingled male and female branches, which seemed more applicable to some situations (low turbulence habitats). The cox 2-3 spacer region from the 18 individuals sequenced was 376 bp and the DNA sequence was identical with no base pair substitutions. Likewise, a previous study of another Batrachospermum species showed that the same haplotypes were present in all stream segments from the same drainage basin, even though the stream segments were a considerable distance apart. Short distance dispersal either by small birds or waterway connectivity might explain these findings.

Respostas de curto período das características fotossintéticas da alga vermelha Batrachospermum delicatulum a temperatura e irradiância

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Spatial and temporal distribution of tropical phytoplankton species and biomass in the Gulf of Carpenteria, Australia

The biomass and species composition of tropical phytoplankton in Albatross Bay, Gulf of Carpentaria, northern Australia, were examined monthly for 6 yr (1986 to 1992). Chlorophyll a (chl a) concentrations were highest (2 to 5.7 mu g l(-1)) in the wet season at inshore sites, usually coinciding with low salinities (30 to 33 ppt) and high temperatures (29 to 32 degrees C). At the offshore sites chi a concentrations were lower (0.2 to 2 mu g l(-1)) and did not vary seasonally. Nitrate and phosphate concentrations were generally low (0 to 3.68 mu M and 0.09 to 3 mu M for nitrate and phosphate respectively), whereas silicate was present in concentrations in the range 0.19 to 13 mu M. The phytoplankton community was dominated by diatoms, particularly at the inshore sites, as determined by a combination of microscopic and high-performance liquid chromatography (HPLC) pigment analyses. At the offshore sites the proportion of green flagellates increased. The cyanobacterium genus Trichodesmium and the diatom genera Chaetoceros, Rhizosolenia, Bacteriastrum and Thalassionema dominated the phytoplankton caught in 37 mu m mesh nets; however, in contrast to many other coastal areas studied worldwide there was no distinct species succession of the diatoms and only Trichodesmium showed seasonal changes in abundance. This reflects a stable phytoplankton community in waters without pulses of physical and chemical disturbances. These results are discussed in the context of the commercial prawn fishery in the Gulf of Carpentaria and the possible effect of phytoplankton on prawn larval growth and survival.

Studies on the seasonal cycle of sea surface temperatures, salinities and phytoplankton in Puttalam Lagoon, Dutch Bay and Portugal Bay along the west coast of Ceylon.

The monthly average temperatures at Puttalam Lagoon, Dutch Bay, Portugal Bay towards Kovilmunai and Portugal Bay towards Pallugaturai showed a distinct annual cycle. The peak was in April and values gradually fell till September. There was a further gradual fall in temperature from October to January. The highest temperatures in all four stations were in April. The highest salinities in all the stations were from May to October i.e., during the south-west monsoon. The salinities at Dutch Bay and Portugal Bay were high in March and April corresponding to the highest temperatures reached during these months. Two maxima have been observed in phytoplankton production. A primary maximum in May-June and a secondary maximum in October. The primary and secondary maxima are due to the influx of nutrient laden waters from the rivers Kal Aru and Pomparippu Aru. The phytoplankton producing blooms were Rhizosolenia alata. Rhizosolenia imbricata, Chaetoceros lascinosus, Chaetoceros pervianus, Ch,aetoceros diversus, Coscinodiscus gigas, Thallasionema nitzschioides, Thalassiosira subtilis, Thallassiothrix frauenfeldii, Asterionella japonica, Sceletonema costatum, Bacteriastrum varians and Biddulphia sinensis. Sudden outbursts of a single species were common. These diatoms were species of Chaetoceros and Rhizosolenia, and Thallassiothrix frauenfeldii. Wide fluctuations have been observed in the distribution of phytoplankton but no definite conclusions can be drawn as the period of observation was only one year.

Distribution of Rhodophyta in streams from São Paulo State, southeastern Brazil

Distribution of Rhodophyta was investigated in 172 stream segments, which were sampled from May to October in 1992-1993 and 1996-1997 in six natural regions (parts of biomes or geological areas) of São Paulo State, southeastern Brazil. Red algae occurred in 60.5 % of stream segments sampled, a high frequency in comparison with other major surveys in the world (18-65 %). 17 species of freshwater red algae were found, of which the most widespread was Batrachospermum delicatulum occurring in 17 sites of five regions. The proportion of morphological types was as follows: gelatinous filaments (62.5 %), free filaments (19 %), tufts (12.5 %) and crusts (6 %); all but free filaments can be considered as having mechanisms to tolerate stress provoked by current velocity. No significant difference was found between the frequency distributions of variables measured for all streams and for those with red algae. Rhodophyta occurred under the following conditions (means): temperature (19.0 degrees C), current velocity (48 cm s(-1)), specific conductance (74 mu S cm(-1)), turbidity (8 NTU), oxygen (67.3 %) and pH (6.9 +/- 0.7). on the basis of species composition among the regions, the following patterns were evident: 1) the number of red algal species per region ranged from 1 to 10; 2) the highest proportion of sites with red algae (65-73 %) was found in hard water regions and in Atlantic rainforest, whereas the lowest (50 %) was found in tropical rainforest; 3) more than half of the species were exclusive from a single region, whereas the higher proportion of exclusive species was in the subtropical rainforest (50 %). No combination of stream variables was clearly associated with the occurrence of red algae for the regions as a whole. Species composition for streams and rivers of São Paulo State revealed higher similarities with other tropical regions and had few species in common with freshwater red algal floras of other continents.

Distribution of stream macroalgae in three tropical drainage basins of southeastern Brazil

Three drainage basins belonging to different drainage systems, but in close proximity, were evaluated to compare the distribution of macroalgal communities in the northwest region of São Paulo State, southeastern Brazil. Monthly samplings were carried out from September 1992 through September 1993 in three sites along the main river of each basin. 10 m length cross segments were evaluated for species per cent cover and richness, on both the population and community levels. Selected stream variables were measured: specific conductance, temperature, turbidity, mean cross-sectional area of the reach, current velocity, pH, and oxygen saturation (%). Principal Coordinate Analysis (PCO), chi-square good-of-fitness, and Pearson Product-Moment correlation coefficient were applied to evaluate the distribution of the macroalgal species. The survey resulted in 36 taxa of macroalgae, of which Cyanophyta was the dominant group (17 taxa or 41.7% of the total), followed by Chlorophyta (15 taxa or 41.7%), Rhodophyta (3 taxa or 8.3%) and Chrysophyta (1 taxon or 2.8%). Stigeoclonium helveticum, 'Chantransia' stage of Batrachospermum spp., and B. delicatulum were the most widespread and frequent macroalgae throughout the basins. The analyses showed that conductance and current velocity were the factors most closely related to the distribution of the macroalgal species. Positive correlation between richness and percent cover was determined, which reinforces the patchiness of stream macroalgal distribution.