Annual Biology Conference (ABC) 2016, University of Canterbury, New Zealand
Alfonso Siciliano, Mads S. Thomsen, David R. Schiel
Seagrasses are marine plants that take up nutrients, stabilize sediments, increase habitat complexity and thereby also increase biodiversity of sedimentary coastal ecosystems. Seagrasses also facilitate seaweeds that can become entangled around seagrass leaves and stems. However, relatively little is known about interactions between entangled seaweeds and seagrass, their effects on seagrass-associated invertebrates and if their interactions are modified by abiotic conditions, like nutrient and sedimentation levels. We aimed to test the hypotheses that (i) seaweeds have negative effects on seagrass (competing for limited resources) but positive effect on invertebrate biodiversity (by increasing habitat-complexity), across seasons in the Avon-Heathcote estuary, (ii) that similar processes occur in other estuaries, and (iii) that the magnitude of effects increases with increasing levels of inorganic nutrients and sediments. To test the first two hypotheses, we collected cores from the Avon-Heathcote estuary and from six other estuaries. To test the third hypothesis, we manipulated nutrient and sedimentation levels in two field-experiments. Preliminary data analysis supports our hypotheses: seaweeds had negative impact on seagrass but positive effects on the abundance of many invertebrates. We also found that enhanced sediments, but not nutrients, had strong negative impact on seagrass with cascading negative impacts on the invertebrate community.