Seagrass macrobenthic biodiversity does not vary in conformity with a leaky-lagoonal confinement gradient

Coastal lagoon ecology often changes on progression from the open, well-flushed mouth region to the depositional zone furthest from the open sea. This is generally considered consequent on increasing 'confinement' and associated features, rather than on the often co-occurringly decreasing salinity. The 12 km Rainbow Channel connecting part of Moreton Bay, a microtidal leaky lagoon, to the adjacent Pacific provides a gradient of increasing confinement without any significant salinity change, i.e. a tenfold increase in water residence time for a salinity decrease of <1. Macrobenthic faunal assemblages characterising intertidal Zostera seagrass at strategic points along its length were compared to test whether their nature changed in conformity with confinement models. Results suggest that it does not; faunal abundance, species richness, evenness and composition remaining effectively unchanged along the gradient. Seagrass systems may constitute a special case because they decouple renewal times of the overlying water and local organic enrichment/decomposition; as may leaky lagoons because of their high tidal velocities.

Automated summary

Coastal lagoon ecology changes on progression from the open to the depositional zone, mainly due to increasing confinement rather than decreasing salinity. The Rainbow Channel in Moreton Bay provides a gradient of increasing confinement without significant salinity change. The faunal assemblages in intertidal Zostera seagrass along the channel did not change significantly.