Establishing baselines: eighty years of phytoplankton diversity and biomass in south-eastern Australia

Establishing trends in phytoplankton diversity and biomass, particularly in relation to climate change, is challenging and requires reference to baseline observations. Detecting changes over seasonal, inter annual, and interdecadal timescales requires the collection of long-term datasets. Australian marine ecosystems and their constituent phytoplankton have been studied only in the last approximately 100 years, focused on the south-eastern coast of Australia, as this is the site of the major population centres. The coastline of south-eastern Australia is dominated by the dynamic East Australian Current, as well as a diverse range of estuaries, each with its own distinct riverine inputs, tidal cycles, and flushing times. Warming of the East Australian Current over the past century at two to three times the global average, combined with increased nutrient loads and encroaching coastal urbanization, is likely to have had an impact on the coastal environment, ecosystems, and supported phytoplankton communities. Even though sporadic research has been undertaken into the diversity, distribution, and ecology of marine and estuarine phytoplankton over the past 80 years, the first long-term time-series investigations have only recently been completed. In this review, we conducted a meta-analysis of 90 phytoplankton studies from 1933 to 2015 and examined the major themes covered and methodologies used. We examined five datasets spanning the past 50 years from the long-term coastal station off shore from Port Hacking, Sydney. Whilst species composition and distribution appear to have changed over time, our knowledge of their systematics and identification has also expanded. Sixty-three species, 5 genera, and about 19 potentially harmful species have been described from south-eastern Australian waters over the past 30 years, and many represent first-time Australian records. The emerging use of next-generation sequencing and quantitative molecular methods for phytoplankton identification and enumeration is likely to enable us to identify significantly more diversity than previously considered present in these waters, as well as enable faster and more reliable enumeration methods. The baseline information presented in this review provides a valuable reference point to determine future research directions and assess future changes in phytoplankton communities in south-eastern Australia