Scales of spatial and temporal variation of small bodied nekton within intermittently closed/open lakes and lagoons (ICOLLs) in south-eastern Australia

Abstract

Intermittently open/closed lakes and lagoons (ICOLLs) are common in temperate regions of the southern hemisphere and are also found in parts Europe and North America. They are important nursery grounds for a variety of fish and crustacean species, and while they are regularly studied for a variety of purposes, dedicated analysis aimed at identifying levels of spatial and temporal variance, particularly for abundant smaller nekton are lacking. A hierarchical study was undertaken using cast nets, spanning four estuaries at multiple nested spatial and temporal scales to determine at which levels greater variation occurs. The four most common species including Glassfish (Ambassis jacksoniensis), Small-mouth Hardyhead (Atherinosoma microstoma), Eastern King Prawn (Penaeus plebejus) and Glass Shrimp (Macrobrachium intermedium) were considered separately. A consistent pattern emerged where high levels of spatial variance occurred among individual samples, while the least was generally observed among sites nested within estuaries. A similar pattern occurred when the nekton community was considered as a whole. However levels of residual variation were reduced by pooling individual casts into fewer replicates from each site, resulting most notably in an increase in the variation attributed to the Estuary scale. This produced a good balance in capturing both the small scale variation and broader patterns among estuaries. Temporal levels of variation were lower than the spatial observations for all four common species, as well as the community as a whole. However, greater variation was observed among seasons compared to months nested within seasons. These findings should provide guidance for future studies in ICOLLs where an efficient sampling program would focus on increased replicate samples within a site rather than sampling a large number of sites within a system and focus on seasonal variation.