The effects of salinity and water temperature on growth and survival of Chaetomorpha sp., one of the green tidal filamentous algae, were investigated. Field surveys revealed that this alga was abundant throughout the year in stagnant coastal waters of central Thailand. Chaetomorpha sp. was found in salinities of 3.4-90.0 and water temperatures of 20.1-40.9°C. Chaetomorpha sp. biomass fluctuated between 9.2 and 162 kg dry weight in a saline swamp, without significant differences among seasons. The highest mean specific growth rate of approximately, 60 % day -1 was observed in laboratory experimental trials at salinities of 20-30 at 30°C. Salinity and water temperature significantly affected growth of this alga independently and interactively. Based on these results, Chaetomorpha sp. can easily grow, survive and monopolize in stagnant waters where the salinity and temperature greatly fluctuate because of their euryhaline and eurythermal nature as well as their high growth rate.

The increase in global demand for fishery products has led to a fivefold increase in aquaculture production since 1990. Commercial feed is the highest production cost in intensive aquaculture, and residual commercial feed leads to eutrophication; hence it is important to find a low-cost alternative that has less environmental impact. We investigate the use of the filamentous green algae, Chaetomorpha sp., as a raw feed for giant tiger prawns. The giant tiger prawn, Penaeus monodon was grown in monoculture, and in co-culture with Chaetomorpha sp. to investigate the potential benefits of co-culturing. Five 20-day-old giant tiger prawn juveniles were released in 70-L monoculture and co-culture tanks, and the specific growth rate (SGR) and feed conversion ratio (FCR) were measured after 10 weeks. The final mean body weight of co-cultured prawns was approximately 50 % heavier than that of monocultured prawns. The SGR in co-culture tanks was 4.79 ± 0.08 % day -1 , which was higher than that in monoculture tanks (4.14 ± 0.27 % day -1 ). The FCR was 38.9 % lower in co-culture than in monoculture tanks. The protein content of Chaetomorpha sp. obtained from proximate analysis was almost the same or a little lower than other filamentous green seaweeds; however, the Chaetomorpha sp. has higher fiber and gross energy. These results show that Chaetomorpha sp. has potential for reducing feed costs in prawn intensive aquaculture through co-culturing.

Knowledge of the planktonic species that appear in mangrove estuaries in tropical areas is still poor. We believe that case report data on the appearance of species is important for clarifying the ecosystem of the mangrove estuary. We report in this paper on the occurrence of blooms and discuss the factors that influence blooming, based on an observed bloom consisting of two dinoflagellates in the mangrove estuary of Samut Songkhram, Thailand, in December 2012. From fluorescence microscopic observation of the armors of the dinoflagellates after calcofluor white staining, we identified these dinoflagellates as Ceratium furca and Diplopsalis lenticula. In addition, from the annual data on air temperature and precipitation for that year, it was found that the bloom occurred in early dry season. Additionally, diatoms that inhibit the growth of dinoflagellates were observed at low densities. These results suggested that the two dinoflagellates, C. furca and D. lenticula, grew during disappearance of diatoms.

The unique beauty of spherical aggregation forming algae has attracted much attention from both the scientific and lay communities. Several aegagropilous seaweeds have been identified to date, including the plants of genus Cladophora and Chaetomorpha. However, this phenomenon remains poorly understood. In July 2013, a mass occurrence of spherical Cladophora aggregations was observed in a salt field reservoir in Central Thailand. The aims of the present study were to describe the habitat of the spherical aggregations and confirm the species. We performed a field survey, internal and external morphological observations, pyrenoid ultrastructure observations, and molecular sequence analysis. Floating spherical Cladophora aggregations (1–8 cm in diameter) were observed in an area ~560 m2, on the downwind side of the reservoir where there was water movement. Individual filaments in the aggregations were entangled in each other; consequently, branches growing in different directions were observed within a clump. We suggest that water movement and morphological characteristics promote the formation of spherical aggregations in this species. The molecular sequencing results revealed that the study species was highly homologous to both C. socialis and C. coelothrix. However, the diameter of the apical cells in the study species was less than that of C. coelothrix. The pyrenoid ultrastructure was more consistent with that of C. socialis. We conclude that the study species is C. socialis. This first record of spherical aggregations in this species advances our understanding of these formations. However, further detailed physical measurements are required to fully elucidate the mechanism behind these spherical formations.

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