Background information about the coastal areas of Christchurch.
There are a number of coastal areas within Christchurch City Council’s jurisdiction, including harbours, ports and estuaries; in particular, Akaroa and LytteltonHarbours, and the Avon Heathcote Estuary/Ihutai.
The Avon Heathcote Estuary/Ihutai is the largest semi-enclosed shallow estuary in Canterbury (Bond et al, 2005) and is largely intertidal, with large intertidal banks that are muddy at the river mouths and gradually change to sand towards the outlet (Estcourt, 1967). These mudflats and sand flats are home to numerous fauna including crabs, mud snails, cockles, pipis and small marine worms (Bolton-Ritchie, 2013a). The estuary also supports 5-6% of the South Island pied oystercatcher population (Bond et al, 2005; Owen, 1992) and is home to 16 fish species, with the most numerous typically yellow-eyed mullet, common smelt and sand flounder (Woods et al, 2014). Adult inanga (a whitebait species) also utilise the estuary as a migration route to the river mouths where they spawn amongst tidally-inundated grasses (Taylor & McMurtie, 2004). Salt marsh areas are present around the margins of the estuary and contain a variety of species including raupo, oioi and sea rush (Estcourt, 1967; Jupp et al, 2007; Owen, 1992).
Lyttelton Harbour includes expansive tidal mudflats, sandy beaches in sheltered bays, intertidal rock platforms and rock-walled harbour heads. The extensive areas of intertidal mudflats that occupy the western end of the harbour are recognised as an Area of Significant Natural Value (ASNV; Environment Canterbury, 2005). These saltmarshes and tidal flats support a range of wading bird and waterfowl species, such as the bar-tailed godwit, South Island pied oystercatcher and pied stilt (Environment Canterbury, 2012; Lyttelton Port Company, 2014). The upper reaches of the harbour are also recognised as important habitats for fish species such as sole, red cod and flounder (Sneddon, 2014), and contain significant beds of cockles (Hart et al, 2008). The area surrounding RipapaIsland is also an ASCV. Within LytteltonHarbour is the Port of Lyttelton; one of New Zealand’s busiest shipping ports.
The shoreline of Akaroa Harbour grades from gently sloping mudflats in the upper harbour, to increasing steep rocky shores, to rugged shores and vertical cliffs at the head of the harbour (Bolton-Ritchie, 2013b; Fenwick 2004). The upper harbour has large intertidal flats that are home to Zostera sp. beds which are an important part of the intertidal community, as they provide habitat and a source of food for a range of animals such as gastropods and crustaceans (Bolton-Ritchie, 2005). The intertidal flats also contain populations of cockles which are an important food source for wading birds, flounders and predatory molluscs, as well as a for human consumption (Bolton-Ritchie, 2005). There are several ASNV within Akaroa harbour; these are the tidal flats of the upper harbour, the area surrounding OnaweIsland, and the area at the mouth of the harbour from Nikau Palm Gully to Akaroa (Environment Canterbury, 2005). The latter also forms the Akaroa Marine Reserve. Akaroa harbour is ranked as nationally important (Department of Conservation, 1990) on the grounds that is an important habitat for both the Nationally endangered Hector’s dolphin (Baker et al, 2010) and the nationally vulnerable yellow-eyed penguin (Robertson et al, 2013), as well as being part of the Banks Peninsula Marine Mammal Sanctuary (Bolton-Ritchie, 2013b).
There are other coastal areas within Christchurch City and Banks Peninsula that also provide particularly good habitat for flora and fauna. Important roosting grounds for many wading birds are provided by the Southshore Sand Spit. A number of the birds here and on the Avon-Heathcote Estuary are international migrants from the Arctic, including the eastern bar-tailed godwit. The sea cliffs from Sumner to Godley Head also provide nesting sites for spotted shag colonies, and support a hardy collection of native and exotic grasses, herbs and small shrubs. The isolated bays and coves at the base of Godley Head are home to white flippered penguins. To help protect the penguin colonies at Godley Head a predator fence has been erected. Control of pests is generally ongoing in this environment.