Inter-estuary variation and intertidal zonation of free-living nematode communities in tropical mangrove systems

Abstract

Variation in population densities and community structure of free-living marine nematodes within 5 tropical mangrove systems in northeastern Australia were examined. Nematode densities In surface (0 to 5 cm) mangrove sediments were generally low (F = 150 ind 10cm-~) and ranged from 3 to 987 ind 1 0 c m ~ Highest densities (c = 1266 ind 10cm-~) occurred in winter in a seagrass flat near the Lockhart River estuary. Densities were not significantly different among estuaries, but dlffered seasonally (summer > winter) and with intertidal position (low > mid > high). Species diversity (H') was low to moderate (F = 2.43; range: 2.02 to 2.91) and number of species per site was low (F = 23; range: 11 to 53 species). Numerical classification, detrended correspondence analysis and nodal analysis suggested that nematode fauna1 groups differed in specles composition among intertidal zones and estuaries. Of the 205 species identified, only 3 were found in all 5 estuaries: the deposit feeders Terschellingia longicaudata and Anoplostoma viviparum, and the predator Trissonchulus oceanus. Combining all stations, deposit feeders were the dominant trophic group (c = 50 %) with nearly equal relative abundances of epistrate-feeders (c = 28 %) and omnivore/predators (2 = 22 90). Population densities and species diversity of nematodes in these tropical estuaries are low compared to nematode assemblages in other littoral habitats suggesting that nematode communities in tropical Australian mangroves are subjected to greater stress (e.g. soluble tannins, monsoonal rains) than their counterparts in other intertidal habitats.