When an estuary or coastal environment becomes over-enriched with nutrients excessive growths of algae can occur (eutrophication). These include growths of ‘opportunistic’ macroalgae such as the red seaweed Gracilaria chilensis, and blooms of potential harmful phytoplankton (microscopic algae that drift in water currents), which can include species that release biotoxins.
Usage guide: Toggle between tabs to see different nutrient monitoring summaries. Click and drag the year slider on each map (if available) to see change over time, and hover over map data to see specific values. The chart below the map displays each sites' data temporally, hovering over lines will also show specific values and highlight that site on the map.
Opportunistic macroalgal blooms are a primary consequence of estuary eutrophication (nutrient enrichment). Macroalgal blooms can deprive seagrass beds of light, causing their decline, while decaying macroalgae can accumulate subtidally and on shorelines causing oxygen depletion and associated nuisance odours in the sediments beneath. The main problem species in New Zealand are the red seaweed Gracilaria chilensis and the bright green Ulva. In Porirua Harbour over recent years, there has also been an increased prevalence of the filamentous green mat-forming species Chaetomorpha ligustica.
See Stevens & Forrest 2020 for technical methods, data tables, and further information