Jim T. Luong-Van

Seasonal variation in the chemical composition of tropical Australian marine macroalgae

The proximate chemical composition (ash, soluble carbohydrate, lipid and protein) was determined in 30 common species of tropical Australian marine macroalgae from Darwin Harbour (12∘26′S, 130∘51′E), in summer (hot and wet) and winter (cool and dry). There was a wide diversity of species in both seasons (19 species in summer and 20 species in winter). In most species, the major component was soluble carbohydrate (chlorophytes range 2.5–25.8% dry weight (dw), phaeophytes range 8.4–22.2% dw, rhodophytes range 18.7–39.2% dw) with significantly higher (p < 0.05) percentages only in winter season rhodophytes. Highest percentages of protein were found in rhodophytes collected in the summer (range 4.8–12.8% dw), with significantly lower percentages (p < 0.05) during winter. All species had lipid contents within the range 1.3–7.8% dw, with highest percentages in summer phaeophytes, but no significant differences between species or season. Most species had moderate to high ash contents (24.2–89.7% dw), with the highest percentages during summer. Compared with summer samples, macroalgae collected in winter had higher energy value and slightly lower percentages of inorganic matter. The variation of algal groups and chemical composition may influence the availability of the food source for the majority of herbivores, which in turn is likely to effect their ecology and community structure.

Phylogenetic study of Gymnodinium dorsalisulcum comb. nov. from tropical Australian coastal waters (Dinophyceae)

A new species of the dinoflagellate genus Gymnodinium Stein, previously considered a member of Katodinium Fott, is characterized from two marine benthic habitats in tropical northern Australia. Gymnodinium dorsalisulcum comb. nov. was found to be very abundant at times, and in culture produced large quantities of mucus. We analyzed two regions of ribosomal DNA from this species (partial large subunit and complete small subunit sequences), using Bayesian analysis and phylogenetic models appropriate to alignments of ribosomal RNA genes. We compared it to eight species of the ‘true’Gymnodinium clade and to other dinoflagellates. The results show that it is a member of the Gymnodinium clade, and is closely related to Gymnodinium impudicum and G. chlorophorum. Katodinium was originally defined as having cells with an epitheca that is much larger than the hypotheca. However, this character is clearly inadequate, and the genus requires a re‐investigation to determine the apomorphies of the type species.

Assessment and monitoring of nutrient loading in the sediments of tidal creeks receiving shrimp farm effluent in Quang Ninh, Vietnam

Coastal shrimp farming may lead to the contamination of sediments of surrounding estuarine and marine ecosystems as shrimp farm effluent often contains high levels of pollutants including a range of organic compounds (from uneaten feed, shrimp feces, and living and dead organisms) which can accumulate in the sediments of receiving waterways. The assessment and monitoring of sediment quality in tidal creeks receiving shrimp farm effluent can support environmental protection and decision making for sustainable development in coastal areas since sediment quality often shows essential information on long-term aquatic ecosystem health. Within this context, this paper investigates nutrient loadings in the sediments of tidal creeks receiving shrimp farm effluent in Quang Ninh, Vietnam, which now have a high concentration of intensive and semi-intensive shrimp farms. Sediment samples taken from inside creek sections directly receiving effluent from concentrated shrimp farms (IEC), from main creeks adjacent to points of effluent discharge outside concentrated shrimp farms (OEC), and few kilometers away from shrimp farms (ASF) as reference sites were collected and analyzed before and after shrimp crops to investigate spatial and temporal variation. The results showed that there were statistically significant differences in the concentrations of total nitrogen, total phosphorus, and total organic carbon among IEC, OEC, and ASF sites while the seasonal variation being limited over study times. A sediment nutrient index (SNI) computed from coefficient scores of the factor analysis efficiently summarizes sediment nutrient loads, which are high, albeit quite variable, in canals directly receiving effluents from farms but then decline sharply with distance from shrimp farms. The visualization and monitoring of sediment quality data including SNI on maps can strongly support managers to manage eutrophication at concentrated shrimp farming areas, contributing to sustainable development and management at coastal zones.

Immobilized Tetraselmis sp. for ease of TEM processing and for ultrastructure research

We report an experimental procedure that results in the immobilization of the motile Tetraselmis in an alginate bead, thereby providing clonal populations for ultrastructure research and greatly facilitating transmission electron microscope (TEM) studies. The Prasinophyte Tetraselmis CS317, which is a potential candidate species for aquaculture, was used in our study. The cells were immobilized in Ca-alginate beads and allowed to grow within the beads for 2 weeks. Each cell in the bead divided repeatedly, resulting in a dense clonal population which could be easily distinguished under a compound microscope. Portions of the Tetraselmis-alginate beads containing the clonal populations were then used for TEM processing for a fine structure study without the need for centrifugation. The normal TEM processing of microalgae by repeated centrifugations during processing or a centrifugation-agar embedding mixture is very time consuming and unreliable due to the nature of the agar and, in the case of the motile Tetraselmis, the force of centrifugation required to sediment the cells. Our results revealed that the alginate did not interfere with the fixation, embedding and sectioning, and the cells appeared to possess all of the structural characteristics of Tetraselmis cells, including the flagella apparatus. We conclude that immobilized Tetraselmis in alginate provides a simple experimental system for ultrastructural research.