Year

2012

Degree Name

Master of Science - Research

Department

School of Biology

Abstract

Currambene Creek sanctuary zone is located within Jervis Bay Marine Park, New South Wales (NSW). In NSW, sanctuary zones are established with the aim of conserving biodiversity and maintaining ecological processes. While these aims are well defined by the Marine Parks Act 1997, no study yet has been undertaken to establish whether sanctuary zones do maintain ecological processes. Ecological processes that include benthic metabolism and nutrient cycling, control fundamental sediment–water interactions. The aim of this study was to investigate the affect sanctuary zone protection, compared to an experimental disturbance, had on the benthic metabolism and nutrients in a tidal mudflat to provide benchmarks to guide the management of NSW estuaries and sanctuary zones.

Benthic flux measurements of oxygen (O2), ammonium (NH4+), nitrite and nitrate (NOx), dissolved inorganic nitrogen (DIN) and phosphorous (PO43-) were estimated using the sediment core incubation technique. Two sites were exposed to three different experimental disturbances subjected to both dark and light conditions. The three disturbances were control (undisturbed), trample (trampled sediment) and trample bait-pumping (trampled sediment and bait-pumping of the common ghost shrimp, Biffarius arenosus). These disturbances are typical human activities that would take place on an intertidal mudflat. Additionally, chlorophyll α was also examined.

Benthic metabolism displayed autotrophic characteristics as gross primary production (GPP) exceeded respiration. Benthic community respiration (BCR) was significantly different among treatments with both trample and trample pump disturbances influencing respiration. The presence or absence of macrofauna such as B. arenosus and other taxa was shown to partly cause the differences found in BCR. The presence of macrofauna in samples from the control treatment consumed more O2, while in the disturbed treatments there was a reduced number of macrofauna, therefore accounting for the reduced consumption of O2.

In general, nutrient fluxes did not typically display diel variations, with the sediments being a net sink for all nutrients. Dark and light differences were attributed to the dominating photosynthetic activities of benthic microalgae (BMA). Once again, the presence or absence of macrofauna influenced the difference between NH4+ in the disturbed and undisturbed treatments. The metabolic excretion of NH4+ from the macrofauna had the biggest measurable influence on uptake in the disturbed treatments. However, BMA dominated the sediments and had a significant influence over all nutrients.

Benthic metabolism and nutrient fluxes in Currambene Creek were dominated by BMA and the experimental disturbances had a limited affect because of their activities. Nutrient budgets showed that the sediment could not meet the demands of the BMA mostly because the BMA sequestered nutrients from the water column. While the experimental disturbances had a significant influence on macrofaunal abundance (data from a parallel study), that consequently had an influence on respiration and some nutrients, it was difficult to determine whether ecological processes were maintained in the MPA.

This study demonstrated that trampling and bait pumping impact upon the Currambene Creek sanctuary zone benthic metabolism, nutrient cycling, respiration rates and some nutrients. Whereas, production and other nutrients (e.g. DIN) were not affected by the disturbances. A dramatic change to these ecological processes would have seen the disturbances subsequently change the net autotrophic characteristics of the sediments into net heterotrophic sediment, however this did not happen.

Changes in benthic metabolism and nutrient cycling due to the experimental disturbances suggest that in the Currambene Creek sanctuary zone BMA influence ecological processes more than benthic macrofauna. However, the macrofauna still had a significant influence of respiration and NH4+. The nutrient fluxes of Currambene Creek provide essential nutrient benchmarks for the management of NSW estuaries from which future changes or disturbances can be assessed.

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