Improved fish and crustacean passage in tidal creeks following floodgate remediation.
Boys CA, Kroon FJ, Glasby TM and Wilkinson K (2012) Improved fish and crustacean passage in tidal creeks following floodgate remediation. Journal of Applied Ecology, 49: 223–233.
[available online: http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2664.2011.02101.x/abstract]
SummaryDispersal is a critical ecological process in which individuals move within and between populations, as well as colonising new habitat. Habitat fragmentation, in combination with habitat loss, detrimentally affects dispersal success with associated impacts on biodiversity. Within New South Wales (NSW) alone, there are over one thousand floodgates which fragment important coastal habitats and have had negative impacts on fish and crustacean assemblages. Importantly, 99% of all these floodgates are considered modifiable to enhance connectivity. When such works occur, however, they are rarely accompanied by rigorous monitoring of fish and crustacean responses.
In collaboration with managers and land holders, tidal flushing and connectivity was restored through opening of floodgates at three tidal creeks in the Macleay and Clarence Rivers in northern NSW. Changes in fish and crustacean assemblages were evaluated by regular sampling over a two-year period. Changes in assemblages in managed creeks were compared to those in reference creeks (i.e., without floodgates) and control creeks (with closed floodgates).
Following floodgate opening, managed creeks showed an immediate shift in assemblage composition to closely resemble those in reference creeks, which was sustained for the duration of the study in at least two out of the three creeks. This change was driven primarily by an increase in the number of estuarine-marine species (including commercially important fish and prawn species) and was clearly a result of floodgate opening, as similar shifts were not observed in (un-gated) reference and (gated) control creeks in either estuary.
Our study demonstrates that restoration of connectivity in tidal creeks through regular and frequent opening of floodgates leads to strong, rapid and sustained recolonisation of habitats. Hence, implementation of management solutions associated with improving connectivity, particularly those that consider differences in the dispersal capabilities of animal, will significantly benefit coastal aquatic biodiversity and fisheries production. Our study strengthens the case for robust experimental design of restoration studies to ensure that ecological objectives are being achieved and success (or otherwise) is quantified.