Species groups: Phytoplankton Part 2 – Key Species Groups 4 Species groups 4.1 Phytoplankton Principal contributors Luke Twomey Paul Van Ruth Other contributors Anya Waite Peter Thompson Species group name and description The term phytoplankton usually refers to autotrophic planktonic organisms in the euphotic zone (surface lit waters) of an aquatic ecosystem. Phytoplankton communities are largely comprised of protists from a diverse range of taxonomic classes including; glaucophytes, green algae, cryptomonads, chrysophytes, haptophytes, diatoms, dinoflagellates, apicomplexa, euglenoids and cerozoa. Prokaryotic Cyanobacteria are also included in the phytoplankton. The definition of phytoplankton however, is not straight forward, complicated by the ability of some taxa to change their modes of nutrition. Many dinoflagellates for example, are heterotrophic able to obtain nutrients through phagocytosis. Additionally, mixotrophs have the ability to combine heterotrophy and autotrophy (Jansson et al. 1996). Generally the decision whether on not to include particular organisms within the phytoplankton is subjective, typically left to the individual researcher to determine whether or not the organism is autotrophic or not. More often than not, the whole protist community are included as phytoplankton if they are filterable on a glass fibre filter or equivalent. Traditionally taxonomists have identified phytoplankton using light microscopy and in more recent decades electron microscopy. Modern techniques enable resolution of individual cells down to about 5 μm. Phytoplankton are generally defined by three size classes, microplankton (20-200μm), nanoplankton (2- 20μm) and picoplankton (0.2-2μm) (Sieburth et al. 1978). Diatoms and dinoflagellates are the most abundant of the micro and nanoplankton size classes (Jeffrey and Vesk 1997), and were for many years thought to be responsible for the majority of oceanic primary production. More recent studies have suggested that photosynthetic picoplankton may also play an important role in carbon fixation in the ocean, especially in oligotrophic waters where they may be responsible for up to 90% of primary production (Stockner 1988). 144 Species groups: Phytoplankton In more recent years High Performance Liquid Chromatography (HPLC) has been used to supplement traditional light microscopy by evaluating the relative concentration of photosynthetic pigments (chlorophylls, carotenoids etc.) in the phytoplankton community, which can be used as markers of phytoplankton taxa (Mantoura and Llewellyn 1983). HPLC methods are very useful in regions where there are large proportions of nano- and pico-plankton that would otherwise go undetected. Recent data from shelf, slope and open- ocean off Western Australia suggest that the phytoplankton are dominated by nano- and pico-plankton, which comprise ca. 90% of the biomass (Thompson, unpublished data). While measurements of phytoplankton photo-pigments would appear to be a more accurate method to evaluate phytoplankton community composition and relative biomass, there are still serious issues regarding the conversion of pigments to phytoplankton species groups. Primarily, software such as the well-developed CHEMTAX program depend on initial ratios between pigments and cell counts to initialize their analysis. Studies have shown that proper initialization is crucial for accurate estimation, but that ratios are highly variable between water masses and need to be determined separately for different oceanographic regions. Phytoplankton are the start of the food chain in the ocean, and provide the organic compounds required for the survival of higher trophic levels through photosynthesis. As micro-organisms in a dynamic environment, phytoplankton are dependent on oceanographic processes like upwelling and vertical mixing to bring nutrients from great depths to levels where they may be utilized for photosynthesis. The dynamic nature of these processes means both nutrients and phytoplankton are distributed randomly through the water column, and phytoplankton are exposed to constantly fluctuating nutrient supplies and light intensities. The following report is divided into two separate sections which describe the phytoplankton of (1) the Western Australian and (2) South Australian regions. 145 Species groups: Phytoplankton Western Australia Data available A detailed guide to dominant dinoflagellate species throughout Australia is provided by (Wood 1954). The dominant dinoflagellate flora of SW planning area is outlined in this publication. Early Russian cruises documented phytoplankton community composition in the oceanic waters off the coast of Western Australia (Markina 1974; Markina 1976). A comprehensive study of phytoplankton and zooplankton dynamics were conducted in Cockburn Sound and Warnbro Sound, adjacent to Perth from 1991-1994 (Helleren and John 1997). This study presents the most comprehensive and taxonomically sound list of phytoplankton taxa for the coastal waters of Western Australia. The 1995 mass mortality of pilchards (Sardinops sagax) prompted an investigation of the water quality and phytoplankton community composition in the waters of Rottnest Island off the coast of Perth, and Dongara and Geraldton north of the SW planning area in June 1995 (Griffin et al. 1997a). In their recent report on phytoplankton biomass levels of Western Australian coastal and estuarine waters, (Pearce et al. 2000) clearly demonstrate that there is a paucity of near-shore, coastal and oceanic data in south-west Australia. However, in the past 5 years there has been an increased focus on continental shelf, shelf-break and deep water phytoplankton dynamics off the coast of Western Australia, led by research teams from CSIRO Marine Research and the University of Western Australia, Centre from Water Research. A four year study of phytoplankton response to wastewater discharge on inshore shelf-waters was conducted near Perth provided a detailed phytoplankton taxonomy of integrated water column samples from 8 sites, including sites near waste-water outfalls and distal control sites (Figure 4.1.1) (Thompson and Waite 2003). A detailed phytoplankton species list was generated using light microscopy of preserved samples collected from 1996- 2000 (Table 4.1.1). An honours dissertation by Congdon (2003) from the Centre for Water Research at the University of Western Australia investigated nitrogen fixation along a transect from Fremantle to Rottnest in May and August 2003. The study reported the presence several organisms capable of N fixation including the ubiquitous non-heterocystous cyanobacteria Trichodesmium genus. Importantly the pico-planktonic size fraction was responsible for the majority of N-fixation off the WA coast (Congdon 2003). 146 Species groups: Phytoplankton (Fearns et al. 2005) conducted a study to validate ocean colour products derived from SeaWiFS satellite data along a 40 km offshore transect located 20 km north of Perth at Hillarys Marina (31°49.9' S, 115°19.0' E). Physical, chemical and biological measurements were take at a total of nine sampling stations at 5 km intervals along the transect from October 1996 to December 1998. A limited phytoplankton data set was generated from this study, which included the spatial and temporal dynamics of diatoms, dinoflagellates and cyanobacteria. A preliminary one-year study on phytoplankton diversity and production off Bunbury was conducted as part of a baseline survey for the Water Corporation (Waite and Alexander 2000). This showed that production rates were overall 2-3 times higher off Bunbury than off Perth, and that there was a very diverse phytoplankton assemblage present. In 2002 – 2004, a detailed study across the continental shelf north of Perth was conducted in a collaborative project led by Tony Koslow (CSIRO Marine Research) (Keesing and Heine 2005). The aim of the project was to characterise the continental shelf/slope pelagic ecosystem off southwestern Australia. Monthly sampling was conducted from inshore to the outer continental shelf (100 m water depth), extended quarterly to offshore waters (1000 m depth). Taxonomic analysis was conducted with light microscopy and supplemented with High Performance Liquid Chromatography (HPLC). An expedition by the research vessel Southern Surveyor (SS0803) was conducted in 2003 to assess the physical, chemical and biological dynamics associated with 2 eddies off the coast of south-west Australia (Figure 4.1.1). A series of transects were established across the two eddies which included collection of surface and water column phytoplankton samples. Phytoplankton taxonomy was provided by light microscopy (Table 4.1.2) and supplemented with diagnostic pigment analysis via HPLC (Thompson et. al in preparation). Immediately following the Eddy’s cruise, the RV Southern Surveyor (SS0903) was employed to sample a series of cross-shelf transects from the Houtman Abrolhos Islands to Cape Leeuwin. Several sites were sampled at the surface and deep chlorophyll maximum (DCM) depth for phytoplankton taxonomy via light microscopy (Figure 4.1.1, Table 4.1.2) and via HPLC photopigment analysis (Twomey, Pez & Waite in preparation) The Southern Surveyor cruise details and data sets from cruises SS0803 and SS0903 are accessible through the CSIRO Division of Marine Research MarLIN data base www.marine.csiro.au/marlin/ 147 Species groups: Phytoplankton Figure 4.1.1. Location of phytoplankton sampling stations for Table 4.1.2 . 148 Species groups: Phytoplankton Table 4.1.2 Phytoplankton