Estuarine mangrove forests are an important ecosystem that fulfils a variety of ecological roles, including nurseries and feeding grounds for many marine and freshwater species. However there has been little research aimed to describe what benthic invertebrate reside within the forest, and hence little understanding of the food availability for juvenile fish. As mangrove forests feature anoxic sediments, it is likely that dissolved oxygen (DO) concentration could be a limiting factors for most benthic organism, especially in areas influenced by macro-tides, where the forest is only inundated for a limited period of time each day. The present study investigated the density and species composition of the benthic fauna of Rhizophora stylosa forests across multiple macro-tidal estuaries in north Queensland, Australia. Additionally we investigated the DO fluctuations inside the investigated mangrove forests during multiple tidal cycles. The benthic fauna was collected using a corer at three distances (outside the forest, at 10 and 40 meters inside), while the DO was collected by mean of YSI ProOdo loggers that collected readings at 5 minutes intervals. A Random Forest approach was used to create a predicting model and determine the most influential variables in affecting DO fluctuations and related DO to invertebrate assemblages.
Results/Conclusions
The forests investigated are species-poor and lacked a number of taxonomic groups (e.g. Peracarida crustaceans) of particular importance for fish diets, which were present outside the forest. This contrast indicate a strong habitat specificity in prey availability and benthic community assemblages. The invertebrate distribution and composition would seems to correlate with the observed fluctuations in DO. During tidal connection DO was influenced by a variety of factors that were often interlinked to one another, including: root density, forest elevation, tidal phase, and height. However as the tide ebbed the remnant water inside the forest quickly become strongly hypoxic (< 10% saturation), suggesting that only the most adapted organisms to low DO are capable to inhabit the macro-tidal forests investigated. These findings are particularly important if we consider that in the last few decades there has been a net increase in human induced hypoxia in coastal waters around the globe and this could have detrimental effects on how fish utilize mangrove forests and the surrounding estuarine habitats.