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Type: Thesis
Title: An intertidal monitoring program for Mobil, Port Stanvac (Sth. Australia):anthropogenic versus natural disturbance
Author: Leanne M., Piller
Issue Date: 1998
School/Discipline: School of Animal and Veterinary Sciences
Abstract: A problem associated with operation of Mobil's Port Stanvac Oil Refinery, situated in Gulf St Vincent (GSV), South Australia, is the accidental release of oil into the marine environment. If this occurs, the adjacent rocky coastline is likely to be impacted. A challenge in this situation is to partition the variation associated with an oil spill from that arising naturally or from other human induced disturbances (such as recreational pressure). This thesis focuses on the development and implementation of a monitoring program for Mobil, Port Stanvac. The thesis includes a number of phases. Initially a pilot study and a literature review were completed; the latter to outline pertinent characteristics of GSV, review the impacts of oil and identify appropriate monitoring designs and biomonitoring techniques. A preliminary study focused on temporal and spatial patterns in the intertidal assemblage in GSV. This was followed by computer modelling of the fate of oil spilt from the Port Stanvac refinery and an investigation of the effectiveness of Bembicium nanum as a bioindicator animal. It was likely that trampling could be a confounding influence at study sites and the impact of this perturbation was experimentally investigated. Finally, the outcomes of these phases were used as a basis for designing and initiating an ongoing monitoring program. Pilot Study The mid-eulittoral section of a number of sites within GSV were sub-divided into two 'zones' ('upper' and 'lower') and sampled for dominant intertidal biota. These were identified and counted and those physical parameters likely to influence distribution and abundance were concurrently measured. Various census methods were also trialed. The pilot study identified nine sites for further monitoring and indicated the most efficient sampling methods to be used for the remainder of the study. Literature Review and Selection of a Monitoring Design The literature review established that although confounding factors (e.g. dredging, storm water outfalls, the Christies Beach wastewater outfall and recreational shore use) were operating in GSV their impact on the selected study sites was likely to be minimal. A "Beyond-BACI" monitoring design (see Underwood 19921 ) using a population level focus and an appropriate bioindicator was used during preliminary monitoring so that if a perturbation intervened its effect could be assessed statistically. The spatial scale ofrelevance to a 'moderate' operational oil spill was at the level of the 'reef (or equivalent region on the rocky shore) and the temporal scales of interest were weeks (designated 'Times') and seasons (designated 'Periods'). The two errors (a. and p) which can arise during a statistical analysis were considered equally undesirable and were set a priori to 0.05. Preliminary Study Selected sites were monitored for 15 months (commencing in February/March 1995) using sampling protocols identified as optimal in the pilot study. Owing to a paucity of intertidal macroflora the study concentrated on the spatial and temporal patterns of the intertidal animal assemblage, an approach which was necessary as no a priori indicator species had been identified. Preliminary sampling highlighted enormous spatial and temporal variability in the intertidal assemblage. This variability obscured identifiable seasonal trends apart from increased variability in winter and spring. Despite differences in assemblage structure most sites were dominated by the small gastropod B. nanum. Two disturbances intervened during the preliminary study; northward sand drift, which resulted in severe decimation of assemblages at one site, and a ruptured refinery effluent pipe. A "Beyond-BACI" assessment of the effects of these perturbations on the abundance of B. nanum detected a significant effect at the longest temporal scale of 'Before-After' in the case of the sand pe1turbation only. However, th6 analytical !Juwer iu ut:iect impacts at rh,e temporai scales of 'Times' and 'Periods' was lower than desired due to the early intervention of the two perturbations and confounding effects caused by storm mobilisation of substrata at a number of 'control' sites. B. nanum - a useful Bioindicator The abundance of B. nanum and its usefulness in investigating the 'unplanned' perturbations during the preliminary study suggested it may be a useful bioindicator for the monitoring program. Its sensitivity to fresh Arabian light crude oil and Mobil petroleum was therefore assessed experimentally. No mortality resulted when B. nanum individuals were exposed to small doses of either type of oil for a short time. However, significant behavioural changes (including loss of adherence) were noted and this could potentially manifest as a population level response to oiling. Therefore, B. nanum was recommended as the bioindicator of choice for inclusion in the monitoring program. Modelling of Oil Transport To optimise site choice for the monitoring program likely oil spill grounding sites needed to be predicted. This was done using the 'FLOWM' Model of Dr. J. Bye (Flinders University) to produce computer simulations of oil transport under various tidal and seasonal conditions. The model parameters were validated and refined on the basis of an oil spill at the refinery in September 1996. Seasonal simulations revealed some trends but considerable variation in the location and extent of oiling depending on the timing of oil release and prevalent wind, wave and tidal conditions. Therefore, the maximum possible number (and spread) of study sites for inclusion in ongoing monitoring was advocated. Confounding Factors Trampling was identified as the primary disturbance associated with recreational shore use. To quantify this a number of trampling experiments were conducted targeting gastropods in the 'bare' substrata characteristic of the majority of the GSV sites. These animals were not sensitive to trampling at low intensities, implying that the trampling levels associated with monitoring were not likely to significantly impact on assemblages at study sites. However, under heavy 'weekend' and moderate 'school-holiday' trampling regimes reduced abundances of small B. nanum were seen. Ongoing Monitoring The results from the previous phases led to recommendations for an ongoing monitoring program using a "Beyond-BACI" design and incorporating two temporal scales of sampling in the ' upper' zone at eight 'stable' sites in GSV. The abundance of B. nanum in each of four size classes was the biological variable of interest and it is recommended that this is assessed in conjunction with substrata composition and the degree of oiling prevalent at selected study sites. The oil induced effect size to be detected by the monitoring program is a 50% greater change in the abundance of B. nanum (excluding very small settlers) than occurs (on average) in the set of 'control' sites. One sampling run was completed prior to the project being handed over to Mobil.
Advisor: Butler, Alan
Sheldon, Fran
Baudinette, Russ
Dissertation Note: Thesis (M.Sc.) -- University of Adelaide, Dept. of Zoology, 1998
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