Seagrass Extent Research Articles

The influence of seagrass type on the distribution and abundance of postlarval and juvenile tiger prawns ( Penaeus esculentus and P. semisulcatus) in the western Gulf of Carpentaria, Australia

Postlarval and juvenile tiger prawns ( Penaeus esculentus and P. semisulcatus) were sampled by beam trawls in different seagrass communities of the western Gulf of Carpentaria to test the influence of seagrass characteristics on their distribution and abundance. Two sampling regimes were carried out: fortnightly sampling over a 3 month period during the time of peak recruitment to investigate the importance of different seagrass types to tiger prawns; and at one time to investigate the wider geographic patterns of distribution and abundance of tiger prawns. The results from both studies showed that the pattern of distribution and abundance of 1–1.9 mm carapace length (CL) postlarvae differed from those for the 2–2.9 mm CL postlarvae and juvenile tiger prawns (≥3 mm CL). The 1–1.9 mm CL size class consists of individuals that are about to settle and those that have recently settled: this size class was more widely distributed than the larger postlarvae and juveniles and was sometimes found on substrates where no seagrass was present. Larger tiger prawns were found in higher numbers on seagrass beds where the tall, broad-leaved seagrass Enhalus acoroides was the dominant species. Although seagrass biomass was not a consistent linear predictor of juvenile tiger prawn numbers, mean catches of both the 2–2.9 mm CL postlarvae and juvenile P. esculentus were highest when the biomass of seagrass exceeded 100 g m −2. However, these high biomass seagrass beds contribute only 6% to the total extent of seagrasses in the shallow waters (<2.5 m deep) of the Gulf of Carpentaria. Although the numbers of juvenile tiger prawns were lower in the low-biomass seagrass beds, because of their extent, these seagrass beds are the main nurseries for sustaining the production of the valuable Northern Prawn Fishery in Australia.

Pattern and process in southern Western Australian seagrasses

Posidonia and other seagrass genera cover vast areas along the coast of temperate Western Australia, where it seems that disturbance and recolonisation are the dynamic forces which govern the pattern of seagrass beds. Some species of Posidonia may take 60–100 years to cover cleared substratum while species of other genera may come and go within a year. Three case studies of spatially widely separated seagrass beds are given. They illustrate that depth, weather and location make great differences to the extent and diversity of seagrasses. Comments on reproductive ability and observations on seedling growth and vegetative propagation are given with emphasis on the “ Posidonia ostenfeldii” complex.