RECORDS OF THE WESTERN AUSTRALIAN MUSEUM 83 013–112 (2013) SUPPLEMENT Baseline survey of the terrestrial invertebrate fauna of Barrow Island Jonathan D. Majer1, Shae K. Callan1, Karl Edwards1,2, Nihara R. Gunawardene1 and Christopher K. Taylor1 1 Curtin Institute for Biodiversity and Climate, Curtin University, PO Box U1987, Perth, Western Australia 6845, Australia. Email: [email protected] 2 Chevron Australia Pty Ltd, 256 St Georges Terrace, Perth, Western Australia 6000, Australia. ABSTRACT – Barrow Island is Western Australia’s second largest offshore island and its flora and fauna have been able to evolve without major human disturbances. Chevron Australia Pty Ltd and its Joint Venture Participants made an application to construct a plant to liquefy natural gas on the island in 2001. One of the conditions under which approval was granted was the implementation of a rigorous biosecurity effort to ensure that no non-indigenous species (NIS) are introduced or allowed to establish on the island. To fulfil this condition it was first necessary to characterise what was already present on the island. A series of surveys have been performed using a purpose-designed sampling protocol in order to provide baseline data on the existing terrestrial invertebrates on Barrow Island. A total of 1,873 morphospecies were sampled but subsequent surveys and taxonomic developments have increased the count to 2,397. This compares with an estimated species richness of 2,481 terrestrial invertebrate species on the island. Composition of the fauna varied considerably between the wet and dry seasons and between years, even when samples were taken during the same month. Composition also varied with distance from the coast, which may be associated with soil type and vegetation association. Twenty five non-indigenous species and seven putative non-indigenous species have been found, all of which are believed to have been present prior to commencement of the Gorgon Gas Development project. KEYWORDS: species inventory, biodiversity survey, non-indigenous species, offshore island. INTRODUCTION causing undesirable environmental consequences (Government of Western Australia 2007). In other Barrow Island is Western Australia’s second words, if a non-indigenous species was to arrive on largest offshore island. Separated from the island, there should be at least an 80% certainty the mainland for 8,000 years, uninhabited by that it would be detected. indigenous people and un-colonised by Europeans, Barrow Island’s flora and fauna have been able Although this was a straightforward undertaking to evolve without major human disturbances. for plants and vertebrate animals because these Discovery of large gas deposits in the north-west components of the biota are well known on Barrow shelf prompted Chevron Australia Pty Ltd and its Island (Chevron Texaco Pty Ltd. 2005; Moro and Joint Venture Participants (see acknowledgements) Macauley 2010a, b and c), lack of data made this a to make an application to construct a plant to problematic task for the invertebrates. There had liquefy natural gas on the island in 2001. A number been a few taxon-specific surveys performed in the of conditions accompanied final approval of the 1970s through to the 1990s (Solem 1997—land snails; Gorgon Project. Included amongst these was the Perry 1972—termites; Smithers and Butler 1985— need to implement a rigorous biosecurity effort to dragonflies; Smithers 1984a—psocopterans; Smithers ensure that no non-indigenous species (NIS) are and Butler 1983—butterflies; Smithers 1984 b, 1988— introduced or allowed to establish on the island. neuropterans) but most of these were not exhaustive, Furthermore, the conditions required the design having been carried out during short, single visits and implementation of a detection program with a to the island. Recognising this deficiency, Chevron detection power of 0.8, or an appropriate alternative contracted entomologists at Curtin University power, for detecting NIS at an early enough stage to carry out a baseline survey of the terrestrial that eradication could be attempted without invertebrate fauna of Barrow Island (BWI). 14 J.D. MAJER, S. K. CALLAN, K. EDWARDS, N. R. GUNAWARDENE AND C. K. TAYLOR FIGURE 1 Monthly total rainfall and mean monthly minimum and maximum temperatures for the period covering the Pilot Study (green arrows), the Gas Plant survey (red arrows) and the Non-Indigenous Species surveys (black arrows). Prior to commencing the survey, it was necessary baseline species list of indigenous and non- to design a sampling protocol that was cost- indigenous species inhabiting Barrow Island which effective, while still being adequate to sample the was subsequently used in conjunction with the species present. A transect-based approach formed potential NIS threats to the island to develop the the basis of the protocol, and built upon a design surveillance program, described in the papers by that had been used for many years in rehabilitated Whittle et al. (2013 a, b). mine sites for sampling invertebrates from all strata; ranging from the litter layer up to the trees PILOT STUDY (shrubs in the case of Barrow Island) (Allen 1989). The pilot study was performed twice, once Once the sampling protocol had been agreed upon, during the week beginning 22 April 2005 and once two separate, but complementary surveys were during the week of 1 May 2005, immediately after performed. The Gas Plant (GP) survey targeted a significant rain event (Figure 1). Seven native the area where the gas processing plant was to vegetation sites and three disturbed sites (airport, be built and was designed to sample the species old rubbish dump and accommodation camp) were most likely to be affected by the development. sampled. Sampling was based upon a 90 m transect This positioning of the transects was designed to and included pitfall trapping, herb and shrub enable us to elucidate the major determinants of vacuum sampling (10 swathes at 90o to the transect), the composition of the invertebrate fauna, including shrub beating (10 small trees or shrubs close to soil type, vegetation association, distance from the each pitfall trap), litter sampling using Winkler coast, and season. Paired transects were set up both sacks (Agosti et al. 2000) and hand collecting for close to and distant from the proposed gas plant in one hour during both daytime and night. Pitfall order to provide a basis for ecological monitoring trap configurations included small (43 mm internal of potential edge effects. The second survey was diameter) versus large (110 mm) traps, 10 versus 20 designed to detect whether any non-indigenous small diameter traps, and 5 versus 10 days of small species (NIS) already exist on the island and diameter trapping. targeted areas of current or previous disturbance – The resulting material was sorted to areas where NIS are most likely to be found. morphospecies and individual groups were sent The results of the two surveys have been to the relevant taxonomists for determination, comprehensively reported on by Callan et al. (2011). resulting in a list of approximately 550 The results are summarised here and findings have morphospecies. Then, for selected groups, the been updated in the light of further taxonomic number of species per sampling technique was information being provided. This formed the summed, the estimated total number of species TERRESTRIAL INVERTEBRATE FAUNA OF BARROW ISLAND 15 was calculated from species accumulation curves, Finally, invertebrates were hand collected from a the efficacy of each method was compared, and the range of microhabitats in a 100 m radius around complementarity between the different methods each transect for 1 person-hour during the day and was assessed. From this, a standardised sampling 2 person-hours during the night. Light traps were protocol was agreed upon, and is summarised in also run at a third of the GP and NIS sites, selected Figure 2. to maximise their spread across the island. The finalized protocol was once again based on a 90 m transect, with 10 small-diameter pitfall traps GAS PLANT (GP) SURVEY with ethylene glycol preservative, run for 5 day periods following a 12 hour digging-in period. Leaf Twelve sites were sampled during this survey, litter was taken from close to each pitfall trap and representing coastal dunes, floodplain vegetation, coarse-sieved to remove large litter fragments. The and a range of limestone sites ranging from flats resulting material was placed in Winkler sacks and to ridges. Wherever possible, sites of comparable invertebrates were extracted over a 4-day period. vegetation were in duplicate pairs, with one site Three vegetation vacuum swathes were taken in 30 proximal to the future gas plant and the other some x 15 m areas parallel with the sampling transect. distance away (Figure 3a). This was designed to To complement this, 10 small trees or shrubs were characterise the fauna close to the areas that will sampled by beating with a stout stick over a net. be disturbed and to enable monitoring of any spill- FIGURE 2 Standardised sampling protocol used for the GP and NIS surveys. Further details are explained in the text; design of the protocol was modified in some of the NIS sites to allow for irregular shape of the areas and the existence of structures of interest, such as buildings. 16 J.D. MAJER, S. K. CALLAN, K. EDWARDS, N. R. GUNAWARDENE AND C. K. TAYLOR AB ,19(57(%5$7(678'<6,7(6 ,19(57(%5$7(678'<29(59,(: m 7HUPLQDO7DQNV m %DUURZ,V %DUURZ,V 0HWUHV .LORPHWUHV &RRUGLQDWH6\VWHP*'$0*$=RQH