Farewell Spit and the adjacent intertidal flats (10 000 ha) have been designated as a wetland of international importance under the Ramsar Convention, especially because of the numbers of shorebirds present. Monitoring of shorebird numbers has revealed a reduction of about 75% in numbers of red knots (Calidris canutus) between 1961 and 2001, whereas other species have remained stable or increased. The reason(s) for this are unknown, but may relate to changes in food supply and/or availability; however, information on the macrozoobenthos of the tidal flats is limited. This project aimed to collect baseline information on the distribution and abundance of intertidal macro-benthic organisms, with particular reference to prey species for shorebirds.
The tidal flats were surveyed over a spring tide period in March 2003 using a regular 500 x 1000 m grid. A total of 192 sampling stations was visited on the tidal flats. Information was also obtained on eelgrass (Zostera) occurrence and sediment characteristics. Supplementary samples were taken at eight sites along the exposed ocean beach.
The tidal flats are composed predominantly of medium-sized sand (0.18–0.50 mm). Coarser sediments (over 0.5 mm) are mostly found on the southern and western edge of the central flats. Zostera is widespread, occurring across a 15 km stretch of the central flats, particularly in the mid- to lower-level flats, but surface area coverage varies considerably.
A total of 12 839 specimens of 91 taxa was recorded. Six taxa dominated the samples numerically, accounting for almost 70% of individuals recorded: the cockle (Austrovenus stutchburyi) spionid polychaetes, pipi (Paphies australis), amphipods, a barnacle (Eliminius modestus), and isopods. Most taxa were quite widely distributed and there was evidence of an increase in species diversity with increasing Zostera cover. There is some evidence that numbers of shorebirds at high tide roosts may be related to the amount of potential prey present in adjacent intertidal areas.
Sampling was done at a time when shorebird numbers are at an annual maximum, and thus prey stocks may have been depleted. There is a need to assess seasonal changes in prey availability. This survey has laid the groundwork for the development of a long-term monitoring programme, which is needed to meet requirements under the Ramsar Convention, especially in the face of increasing environmental pressures in adjacent areas.