Suspended particles washed into the marine reserve during storms increase sedimentation and reduce visibility
Image: Kirsten Rodgers | Creative Commons
The water quality of the reserve is rated 'good to excellent' by Auckland Council.
Storms can release sediment from the catchment into the marine reserve and resuspend settled sediment, causing a short-term drop in water quality. These events may not be captured in regular monitoring and the cumulative effect of sedimentation from storms is not known.
No consistent change in water quality has been recorded in the last 20 years. No change is expected in the near future.
Auckland Council has been monitoring the water at Goat Island monthly since 1993 for a standard range of parameters including salinity, pH, turbidity, suspended sediment, nitrate and enterococci bacteria.
This site has a history of excellent water quality so it is no longer included in the council’s weekly summer Safeswim monitoring programme.
Ostreopsis algal bloom
Algal blooms occasionally affect the marine reserve during long periods of calm, warm weather. These blooms coat seaweeds, sea urchins and other organisms on shallow reefs with a slimy rusty-brown film, caused by a dinoflagellate called Ostreopsis siamensis.
The blooms can be fatal to sea urchins, whose spines bend over and then fall off. It is not known if the ostreopsis toxin transfers to fish that eat the sea urchins. People are advised not to touch the brown film.
Ostreopsis is a tropical species that was not seen in New Zealand before 1998. Its range is increasing into northern New Zealand and other temperate areas around the world as ocean temperatures rise.
- Marine water quality annual report is published by Auckland Council each year.
- Spatio-temporal patterns in coastal turbidity – Long-term trends and drivers of variation across an estuarine-open coast gradient. Seers and Shears, 2015.
- Blooms of benthic dinoflagellates of the genus Ostreopsis; An increasing and ecologically important phenomenon on temperate reefs in New Zealand and worldwide. Shears and Ross, 2009.