Congdon, N., & Marsden, I. (2004, April). Seagrass Zostera novazelandica in the Avon-Heathcote Estuary. University of Canterbury.

This report was prepared in 2004 as part of a summer scholarship programme provided by the Avon-Heathcote Ihutai Estuary Trust and Hagley Ferrymead Community Board. Its main purpose was to determine the distribution and health of the seagrass species, Zostera novazelandica, in the Ihutai estuary. It measured the distribution and history of the seagrass beds, and the characteristics of the patches, including size, biomass, and density. This type of research was important because Zostera novazelandica is the only endemic seagrass species in Aotearoa New Zealand. Seagrasses play a vital role in stabilising estuary sediment, yet face many natural and anthropogenic threats.

Overall, the researchers found there were many fluctuations in Zostera novazelandica abundance and location between 1951 and 2002, with the highest value of 1 km2 occurring in 1975. In the summer of 2003-2004, the total seagrass area was estimated as 0.29 km2 (~4% of the total estuary area). Notably, seagrass was recorded in only 10% of the quadrats sampled, and although the plants appeared healthy, they had no reproductive structures. This combination of factors led the researchers to conclude that although the seagrass population and biomass in Te Ihutai was within the range given for other seagrass beds worldwide, the patches were unstable and there was an urgent need for regular monitoring.