Author:Judi E Hewitt , C Lundquist, N Hancock, J Halliday, L Chiaroni
Source:Auckland Regional Council
In October 2000, a State of the Environment monitoring programme was developed for the Central Waitemata Harbour, with a design matching those carried out in Mahurangi and Manukau Harbours. The focus of the programme was to monitor the ecological status and trends of change in macrobenthic communities in the Central Waitemata. Five intertidal soft-sediment sites and twenty taxa were selected for monitoring. This report presents the results from monitoring between October 2000 –
Each site is representative of a distinct habitat within the harbour and physical and biological conditions such as sediment grain-size, organic content, chlorophyll a content and wind-wave exposure generally differ. These differences have been maintained over time, although changes in sediment characteristics have been noted at 2 of the sites. At the Hobsonville site, the mud and fine sand content has decreased by ~ 37%. At the Henderson Creek site, sediment has become firmer, probably reflecting increased fine sand content (~30% increase).
Even with only 3.5 years worth of data, seasonal cycles of abundance in a number of taxa have been observed. This is helpful for future interpretations of the data as predictable seasonal cycles in abundance aid in detection of long-term trends. Of the five sites, the site near the Whau River has the fewest taxa exhibiting seasonal cycles in abundance, while the site in Shoal Bay has the most. Similar to Manukau, there are some taxa at all sites which exhibit low, consistent abundances over time.
Apparent trends in abundance over time have been detected for a few taxa from each site. However, experience from the Manukau monitoring programme suggests that many of these may prove to be part of longer-term cycles in abundance, especially for Boccardia and Macomona.
Data for many taxa show similar patterns of abundance over time to those monitored in Manukau and Mahurangi. This bodes well for the integration of the three monitoring programmes and suggests that comparing abundance patterns in Mahurangi, Manukau and Central Waitemata will help us determine whether apparent changes are natural cycles or may be responses to anthropogenic disturbances.
The ability of the monitoring programme to detect a number of cyclic patterns after only 3.5 yrs, similar to the Manukau monitoring programme, demonstrates the utility of sampling at 2 monthly intervals, rather than at 3 monthly as in Mahurangi. Continuing the monitoring for another 2 years will allow us a greater ability to determine whether the increases and decreases observed at some sites are part of long-term changes.
Auckland Regional Council technical publication, TP233