Estuaries in the Aparima
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Information to come on Jabobs River and Waimatuku estuaries.
Jacobs River Estuary Broad Scale Habitat Mapping 2017-18
Jacobs River Estuary is one of the key estuaries in Environment Southland's State of Environment Monitoring Programme. Part of this monitoring includes broad scale habitat mapping in the estuary on a 10 year cycle, in estuaries showing signs of concern focused monitoring of macroalgae and seagrass coverage is carried out annually, where possible. Seagrass is an important habitat in estuaries because it provides a nursery for fish species, habitat for macroinvertebrates, stabilises the estuary bottom and filters nutrients from the water column. Macroalgae, including Gracilaria Chilensis found in Jacobs River Estuary, is natural in New Zealand Estuaries. However in the presence of excess nutrients and mud macroalgae can become opportunistic and grow into thick mats across large areas which can displace seagrass habitat and reduce the sediment quality leading to areas known as "gross eutrophic zones". A "Gross Eutrophic Zone" is defined as an area that has low sediment oxygenation (<1cm aRPD), soft mud (>25% mud content) and the presence of high macroalgal cover (>50% cover), these areas are in poor condition and can no longer support most estuarine animals and shellfish.
The 2018 Jacobs River Estuary Broad Scale Habitat Mapping report summarises data collected since 2003 to 2018 (including the years 2003, 2007-2013, 2016 and 2018). Since 2003, dense seagrass cover decreased by 19%, however positively in between 2016 and 2018 there had been a small increase in seagrass on the Aparima River flats of the central basin an area previously smothered by mud and macroalgae (likely removed through a flood event). This observation has positive implications for management because it showed the estuary could potentially recover quickly if soft mud and nuisance macroalgal growth were reduced. The areas of the estuary experiencing poor conditions (no oxygen, excess macroalgal growth and soft mud), also known as gross eutrophic conditions, has increased from < 4% (<20ha) to 29% (144ha) from 2003 to 2018. This means that up to 29% of the estuary is currently in poor condition and estuarine animals and shellfish in these areas will struggle to survive. The estuary was assessed to be in poor condition showing significant symptoms of nutrient enrichment.
