Dr Maria Schreider

© CSIRO 2015. Saltmarsh-dwelling grapsid crabs release free-swimming larvae (i.e. zoeae) into ebbing tides during spring-tide cycles that inundate saltmarshes, where initial inundation is a cue for larval release on subsequent inundations. In a saltmarsh environment, crab zoeae are the main food for fish (including the glassfish, Ambassis jacksoniensis), which 'fast' at other times. This saltmarsh-feeding model was tested by obtaining glassfish from near saltmarshes in a reasonably unmodified tributary of a large temperate estuary on flood and ebb tides during the night in two spring-tide events in austral autumn of 2009. Glassfish fed only on ebbing tides, with stomachs being similarly full on both spring-tide events. Thalassinid larvae (including Trypaea australiensis) dominated the dietary volumes, especially on the night before saltmarsh inundation, presumably being released during inundation of intertidal mud and sand habitats. Although glassfish progressively 'switched' to feeding on greater volumes of crab zoeae (presumably released after inundation of a saltmarsh) over both spring-tide cycles, such zoeal contributions never exceeded those of thalassinid larvae. The above differences highlight that, although ebb tides trigger feeding by glassfish, this ambassid focuses on different prey in a reasonably unmodified environment. The ability of glassfish to switch prey, and thus accommodate environmental differences, helps explain their high abundance in estuaries of this region.

© 2015 Elsevier Ltd. The shift from seagrass to macroalgae, particularly the "boom and bust" cycle of the ephemeral Chlorophyta in estuarine environments has occurred worldwide, most likely as a result of anthropogenic nutrient loading. Contrary to popular view, these algal blooms are not harmful to humans, although they are perceived as unsightly and negatively affect aquatic leisure activities. Macroalgal blooms mostly occur in spring and summer when rainfall prior to and during this time is low and temperatures are high. Water quality data have been collected before and during an algal bloom at Avoca lagoon on the Central Coast of NSW, Australia, to identify changes in water quality associated with a bloom. Water dissolved oxygen declined significantly whereas turbidity and available phosphate increased significantly during the bloom. The changes could be detected only using intensive spatial and temporal replication. Identifying water quality changes during a bloom is a crucial first step for understanding the conditions under which extensive growth of algae occur and has important implications for prediction and management of the blooms in coastal lagoons.