Rising sea temperatures
Oceans are highly vulnerable to the impacts of rising temperatures. They absorb much of the additional energy in the earth’s atmosphere trapped by increasing greenhouse gases.
As ocean water warms, its volume expands, resulting in sea-level rise. Increased ocean and air temperatures can also melt polar ice that adds to rising sea levels.
Projections suggest that sea-surface temperatures in New Zealand will increase 0.8C-2.5C by the end of this century.
This increase in temperature means the ocean's crucial role in removing carbon dioxide from our atmosphere is reduced, while the increased absorption of carbon dioxide makes our oceans more acidic.
Rising temperatures affect water bodies and their inhabitants across our districts. Warmer water can have impacts on aquatic life by reducing the amount of dissolved oxygen available in the water, as well as increasing the frequency of algal blooms. Algal blooms affect mahinga kai as well as recreational fishing and swimming.
We’re lucky that so far, the world’s oceans have taken up a lot of the carbon dioxide we’ve produced. But this comes at a cost – our oceans are becoming more acidic, which affects marine life, making it harder for kaimoana to build their shells or skeletons.
Around our coasts, sea level rise is a key concern for our coastal communities. Average sea levels around Aotearoa have already risen by around 20 cm since 1900, and depending on the rate of ice melt in Greenland and Antarctica, sea levels could rise by a metre by the end of the century.
Changes in sea temperatures can significantly impact our marine life, including precious taonga species. Marine life may need to change location to seek their preferred temperatures, or may not be able to survive at all, leading to extinction. Warmer water may bring invasive species and diseases to our ocean and shores. However, new species migrating to our oceans may also result in new fishing opportunities.
A warmer sea-surface temperature can affect the abundance of phytoplankton, which are microscopic organisms that play a crucial part in ocean ecosystems. The effect of this may be less in our region compared to the subtropical waters in northern parts of New Zealand.
Increased acidity can have a real impact on our aquaculture industry, of which more than 60 per cent is mussels. Shellfish are particularly vulnerable to increased ocean acidity, especially as they form their shells in their early and juvenile life stages.
Pāua, cockles, kuku, and kina are taonga species with hard shells that are valued for recreational and cultural reasons. All are vulnerable to increased ocean acidity.
Increasing storm frequency and intensity can all impact the growth cycle of kuku (green-lipped mussels).
Māori marine knowledge and practices are passed from one generation to the next, based on observations over centuries.
These long histories in kaitiakitanga can help us recognise the impacts of long-term environmental changes, although climate change may mean that some traditional Māori tohu or marine indicators can no longer be used in the same way.
For example, traditionally when pōhutukawa bloomed, it was time to harvest kina. Today, the reproductive period of kina occurs at a different time due to changes in sea temperatures. Kaitiakitanga and traditional management methods and commercial practices are changing because of the different environmental conditions.