Gibson, K., & Marsden, I. D. (2016). Seagrass Zostera muelleri in the Avon-Heathcote Estuary/Ihutai: Summer 2015–2016. University of Canterbury. 

In March 2010 a new ocean outfall was commissioned to divert the discharge of treated wastewater from into the Avon-Heathcote Ihutai estuary to the ocean. However, the 2011 Christchurch earthquake broke many sewage pipelines, leading to untreated sewage flowing back into the estuary. This excess of nutrients triggered mass growth of algal sea lettuce which smothered valuable Zostera muelleri seagrass beds.

Written in 2015-16, the purpose of this summer research project was to map the health, location, and size of the Ihutai seagrass bed, providing some information on how seagrass habitats may have changed after the 2010-11 earthquakes. Overall, they found that the main seagrass bed in Te Ihutai had grown by 0.23km2 since 2003, that seagrass was mainly found on the eastern side with sea lettuce, and that sediment around the seagrass beds was regularly anoxic. They also found a new seagrass recruitment area within McCormack’s Bay and that seagrass transplantation was possible in Northern areas of the estuary. This report aimed to build on similar previous research, but a large data gap between 2004 and 2015 made this difficult. The report therefore recommended that annual seagrass surveys in the estuary be conducted, and that alternative mapping and transplant techniques be explored.