IC35_NZ

Understanding the dispersal characteristics of benthic marine invertebrates is of importance to estimating population connectivity in large meso-tidal estuaries. Many of these systems are generally considered to be well mixed and well flushed and therefore thought to be open to the coast. However, this does not consider the influence of complex morphological features, including position of estuarine islands, sand banks and constricted sub-estuary entrances. It is hypothesised that complex morphology contributes to residual circulation patterns within these systems, thus contributing to complex larval dispersal pathways, increasing within estuary larval retention. To investigate this hypothesis, analysis of water column larval counts for three landward to seaward transects has be undertaken to investigate the community composition and abundances between the upper, mid and lower areas of the southern Tauranga Harbour (New Zealand). Results of this indicate that the larval communities differ both in abundance and composition between the upper and lower harbour, and that the morphology near Omokoroa Point contributes to the larval transport pathways. A calibrated hydrodynamic model was coupled to a larval tracking algorithm to confirm the patterns indicated by the field results, and to investigate if retention is also influenced. Model results showed that areas that are influenced by morphological controls are always retentive, whereas other location may also be retentive dependant on the timing and direction of initial transport.

Bivalves have several cultural and recreational befits and provide numerous ecosystem services, and therefore are the focus of this research. In Tauranga Harbour Austrovenus stutchbuyri (cockle) and Paphies australis (pipi) are key Kai moana (seafood) species, and represent an intertidal and a subtidal bivalve species respectively. The previously applied model will be further developed to include larval behaviours to investigate the between population connectivity in Tauranga Harbour. Comparisons will be made between the known populations and between the two species. Model results will be analysed using dispersal kernels, providing probability distributions of connectivity between bivalve populations. Bivalve population connectivity results from the Tauranga Harbour will be compared to Macoma balthica and Cerastroderma edule populations in the Jade Bay (Germany) to highlight the influence of long term anthropogenic change on bivalve species. Like Tauranga Harbour, the Jade Bay has been developed to allow shipping and other harbour developments including a training wall. The Jade Bay is a large macro-tidal estuary, providing the opportunity for additional comparisons to the meso-tidal Tauranga estuary.