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