There is a widely accepted paradigm that mangroves and other coastal habitats provide a safe and productive environment for juvenile fish. Otherwise known as nurseries, these habitats are believed to be important for many commercially important species during their early life stages (Laegdsgaard and Johnson 1995). Most of our knowledge of nurseries has resulted from studies conducted in tropical coastal systems, and these results are often applied to temperate systems such as those we have here in SA. Payne & Gillanders (2009) set out to find out if the proximity to mangroves influenced fish assemblages in coastal mudflats. Their study is one of the few studies in temperate mangroves, and uses consistent sampling equipment across all sites. They found that fish assemblages did not differ significantly with distance from mangroves, however this changed when looking at specific species of fish. For example, yellowfin whiting and yellow-eyed mullet were both considered “mangrove residents” as they were more abundant in mangrove habitats. Although fish assemblages did not differ with distance from mangroves, there was some variation between the three different mangroves locations (Fig.1).
Figure 1. No difference was detected between assemblages of fish in mudflats at varying distances from mangroves. However, significant differences were seen in fish assemblages between the different mangrove sites.
The primary driver behind variation between locations is the subject of my own research, as we would expect to see similar distributions of species between sites which are relatively close together along the Yorke Peninsula. I have been surveying mangrove sites around SA and taking measurements of a number of parameters in order to establish a general condition index for each site. These parameters include canopy density, tree size, root size and soil characteristics. The aim is to identify whether the driver of variation in fish assemblages is due to mangrove condition, size, structure or soil properties such as pH or salinity. We hope to be able to promote the conservation and protection of mangrove habitats, by demonstrating condition as a driver in their ability to provide nursery habitat to commercially important fish.
Laegdsgaard, P, Johnson, CR (1995) Mangrove habitats as nurseries: unique assemblages of juvenile fish in subtropical mangroves in eastern Australia. Marine Ecology Progress Series 126, 67-81.
Payne, NL, Gillanders, BM (2009) Assemblages of fish along a mangrove-mudflat gradient in temperate Australia. Marine and Freshwater Research 60, 1-13.