Monitoring Giant Kelp
The temperate waters around Wellington sustain highly diverse and productive marine ecosystems. Large brown kelp species dominate the rocky reefs along the coastlines and provide shelter, habitat and food and act as natural shore protection. Giant kelp (Macrocystis pyrifera) is particularly visible with fronds reaching up from the seafloor and floating along on the surface (it can grow a staggering 60 cm a day under ideal conditions!).
Giant kelp is less likely to occur in areas where water temperatures exceed 18-19°C and the inner bays of Wellington harbour have already been noted as the very limit of growth. We were very interest to see how summer water temperatures effect the growth and abundance of giant kelp at Kau Bay, one of the common dive sites in Wellington harbour. To account for summer and winter season we snorkelled around the giant kelp bed in May/June and Nov/Dec and used a GPS device to plot the surface area. We also used temperature monitoring data from the regional council at the site to get an indication of a warm summer (red arrow, water temperature exceeds 18-19°C frequently) or cooler summer (blue arrow, water temperature mainly below 18-19°C).
Seaweed forests face a range of threats beside increasing water temperatures – sedimentation, sand inundation, coastal development and pollution (including impact by weed killers). Overgrazing by exploding numbers of kina due to the lack of natural kina predators through overfishing can turn thriving seaweed forests into barren rock within a couple of years.
Read more about the project and the amazing seaweed functions in our marine ecosystem: Monitoring Giant Kelp (June 2016 – June 2019, pdf)