Research > Core research projects > core project description Research: Core research projects Project two: Coastal Ecosystem and Biodiversity DOWNLOAD FULL PROJECT DESCRIPTION [PDF 4.2mb] Investigators CSIRO Marine Research, Floreat, WA: Russ Babcock (Project Leader), Geordie Clapin, Paul Dean, Peter Fearns, Tim Harriden, Matt Kleczkowski, Martin Lourey, Nicole Murphy, Alan Pearce, Julia Phillips, Alison Sampey, Mat Vanderklift, Mark Westera CSIRO Marine Research, Hobart, TAS: Lesley Clementson, Andy Revill, Peter Thompson Curtin University: Wojciech Klonowski University of Western Australia: Marion Cambridge Flinders University: Tim N. Moore Executive summary The aim of the SRFME Coastal project is to characterize the coastal benthic ecosystems of southwestern WA, with particular focus on benthic reef ecosystems, their productivity and dynamics, and the physical, chemical and biological factors driving variability along dominant spatial and temporal scales. To achieve this, we undertook 3-monthly seasonal sampling from 2003 – 2005 at a series of coastal sites situated between Cape Naturaliste in the south and Jurien Bay in the north. Benthic Sampling was integrated with satellite observations of SST, ocean colour and subsurface measurements of other water column properties, as well as sediment biogeochemical sampling. Within this region benthic sampling was nested at Regional (100s km) Local (10s km) and Site (1 km) scales and within each of the regions additional sites were sampled to incorporate site scale variability along cross-shore gradients. The program involved nine core research components: 1) Correlate patterns with physical environmental variables (e.g. light, nutrients, wave energy, transport) 2) Describe biogeographic patterns in benthic community structure 3) Quantify seasonal and inter-annual variability at key sites 4) Determine the effects of nutrient availability in benthic reef communities 5) Describe patterns in community structure determined by ecological interactions 6) Determine principal sources of nitrate supply to the shelf 7) Determine the role of biogeochemical nutrient cycling in pelagic ecosystems 8) Characterise spatial and temporal variability in coastal ocean water column productivity using chlorophyll concentration as a proxy, and SST using remote sensing technology 9) Characterise spatial and temporal variability in coastal sediment transport and benthic habitat distribution using remote sensing technology Standard protocols included sampling to obtain data on: benthic algal species diversity and biomass, benthic invertebrate diversity, abundance and biomass, substratum physical characteristics, depth, invertebrate recruitment, light attenuation, TSS, chlorophyll a, particulate organic carbon, nutrient concentrations, salinity, as well as CTD casts with concurrent measurement of in situ fluorescence, dissolved oxygen and subsurface irradiance; discrete water column samples for analysis of salinity, dissolved nutrients (nitrate+nitrite, ammonium, phosphate and silicate), chlorophyll a, HPLC pigments, particulate organic carbon, phytoplankton and microzooplankton species composition and abundance. Biogeochemical sampling protocols include sampling of sediment cores, and interstitial waters, sampling for microphytobenthos, in situ O2 microprobe sediment measurements and in situ benthic respirometry chamber deployments. The coastal ecology program’s ocean colour group has developed the capability to routinely download, archive and process remote-sensed data from a number of applications. This capacity feeds into all aspects of the SRFME program, and has been extensively validated by a field sampling program including both case 1 and case 2 waters. The remote sensing and concurrent validation have produced time series of SST and chl a for the study area that indicate a clear seasonality in coastal chl a with summer minima and winter maxima in May-August. This seasonal trend in phytoplankton biomass is attributable to an overall increase in phytoplankton rather than to the abundance of any particular taxon. Winter chl a trends are paralleled by a seasonal trend in total suspended solids (likely to be mainly algal detritus) and CDOM. The parallel trends in phytoplankton biomass as well as in re-suspended matter and CDOM suggest that an important seasonal source of N in coastal waters is indeed likely to be from sources in or near the bottom or sediments. Analysis of broad scale spatial and temporal data sets suggests that further offshore an additional source of nutrients is likely to be deeper mixing related to a deepening of the mixed layer mixing nutrients into the euphotic zone. These trends in phytoplankton biomass are relative and WA coastal waters are very low in phytoplankton productivity compared with other coastal waters around the world. Algal and invertebrate communities both display latitudinal trends in community structure between the northern most sites at Greenhead, and the southern most sites at Cape Naturaliste, though this pattern is most clear in the algae. To date over 400 species of algae and seagrasses and 530 taxa of invertebrates have been recorded. There was significant variation in algal community structure within the three study regions of Jurien, Perth and Geographe Bay, as well as among sites within locations. Preliminary analysis suggests that reef topography plays some role in this variation, though further analysis including a wider range of physical variables is still to be completed. The study of this variability holds significant prospects for informing our understanding of physical factors important to algal assemblage structure. Initial analysis of the trends for invertebrates suggests these may follow a similar pattern of variability at small scales. Seasonal trends were apparent in benthic algal biomass, and these appear to stem from both seasonal changes in the physical environment and intrinsic life history attributes of some key brown algal species. Sargassum spp. undergo a seasonal growth, reproduction and senescence with maximum biomass in winter and spring, and sites dominated by this genus showed overall trends in keeping with this. Most sites however were dominated by either the kelp Ecklonia radiata or mixed red and brown algal assemblages, and these sites showed a minimum biomass in winter and spring, correlating with decreased light penetration through the water column and increased storm activity. Thus there appears to be an inverse seasonal relationship between overall benthic algal biomass and phytoplankton biomass, ultimately linked to the same seasonal weather factors of storm activity and wave shear on the inner shelf. Studies of spatial subsidies between reefs and seagrass habitats have established that detached reef algae are exported to adjacent seagrass beds, and are consumed by seagrass-associated fauna. The large quantities of detached algae suggest that this might form a considerable trophic link between reefs and adjacent seagrass habitats. In some places the spatial extent of this trophic link extends more than 300m away from the reefs. The biomass of detached reef algae increased with increasing proximity to the shore, with large accumulations occurring at some inshore reefs. Transport of drift macrophytes (reef algae and seagrass) to inshore reefs is considerable, and forms an important trophic link between inshore reefs and habitats further offshore. The spatial extent of the inshore-offshore linkages appears to be at least several kilometres. Similar trophic linkages are likely to exist between reef predators and prey species found in seagrasses. Studies to date have focused on establishing the existence of gradients in predator density and population structure that can be used to examine the influence of reef-associated predators on seagrass fauna. At the Kingston Reef Sanctuary area on Rottnest Island the population of rock lobster greater than minimum legal size has been shown to be more than ten times greater than in areas outside the sanctuary subjected to recreational fishing. Sampling to assess the relative abundance of prey items has been undertaken at sites across this gradient and holds the potential to increase our understanding of important trophic relationships in Western Australia’s coastal benthic ecosystems. Over the next year the coastal project will concentrate on completing the processing of samples and analysis of data as well as preparing results for publication in refereed scientific journals, though significant amounts of data collection remain in the area of sediment nutrient flux sampling. Plans are being made for follow-up projects to investigate the roles of physical disturbance and recruitment on benthic communities on the temperate west coast and to determine the relative importance of linkages between water column and benthic processes among different regions. Remote sensing of ocean colour may play an important role in this, as well as in more extensive application of remote sensing to mapping of shallow water coastal habitat types. Plans are also underway to experimentally assess the role of both physical (nutrients and sediment) and ecological (herbivory and predation) disturbances to existing ecological processes. The potential for similar research programs at Ningaloo is also under development and may offer the opportunity to better integrate our understanding of ecological processes between the tropics and temperate areas. back to top [core research projects]

 

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