Maclaren, S., & Marsden, I. (2005, February). The ecology of the Avon-Heathcote estuary: Macrobenthic survey, Summer 2004-2005. University of Canterbury.

Prepared in 2005 for the Avon-Heathcote Estuary Ihutai Trust, at the time of publishing, this research report was the most comprehensive quantitative survey of estuarine biota in the Ihutai estuary undertaken for 30 years. Its objectives were to assess the current distribution and density of all benthic macro-organisms within the Ihutai estuary and to compare this data with previous studies. It recorded all intertidal macrobiota to a depth of 5cm along 9 transects covering the Ihutai estuary, sampling a total of 74 sites. It also calculated and mapped the distribution and area of seagrass (Zostera novazealandica) beds in the Ihutai estuary. Additional environmental measurements included temperature, salinity, sediment type, and the anoxic layer.

Overall, 41 different taxa were identified in the Ihutai estuary: 35 invertebrates, 2 macroalgae, and one flowering plant. Invertebrate distribution and density was similar to previous studies, however, there were decreases in total seagrass bed areas and Amphibola crenata densities. Seagrass populations had also moved significantly North since the previous year’s survey.

To monitor future changes, the report suggested the development of an ongoing monitoring scheme for benthic organisms across the whole estuary which focused on benthic indicator species of ecological change, used permanent quadrats, and included additional transect lines across McCormacks Bay.