Paul van Ruth

El Niño Effects and Upwelling off South Australia

Abstract To determine the possible importance of ENSO events along the coast of South Australia, an exploratory analysis is made of meteorological and oceanographic data and output from a global ocean model. Long time series of coastal sea level and wind stress are used to show that while upwelling favorable winds have been more persistent since 1982, ENSO events (i) are largely driven by signals from the west Pacific Ocean shelf/slope waveguide and not local meteorological conditions, (ii) can account for 10-cm changes in sea level, and (iii) together with wind stress, explain 62% of the variance of annual-averaged sea level. Thus, both local winds and remote forcing from the west Pacific are likely important to the low-frequency shelf edge circulation. Evidence also suggests that, since 1983, wintertime downwelling during the onset of an El Nino is reduced and the following summertime upwelling is enhanced. In situ data show that during the 1998 and 2003 El Nino events anomalously cold (10.5°–11.5°C) wa...

Uptake, distribution and depuration of paralytic shellfish toxins from Alexandrium minutum in Australian greenlip abalone, Haliotis laevigata

Farmed greenlip abalone Haliotis laevigata were fed commercial seaweed-based food pellets or feed pellets supplemented with 8 × 10⁵ Alexandrium minutum dinoflagellate cells g⁻¹ (containing 12 ± 3.0 μg STX-equivalent 100 g⁻¹, which was mainly GTX-1,4) every second day for 50 days. Exposure of abalone to PST supplemented feed for 50 days did not affect behaviour or survival but saw accumulation of up to 1.6 μg STX-equivalent 100 g⁻¹ in the abalone foot tissue (muscle, mouth without oesophagus and epipodial fringe), which is ∼50 times lower than the maximum permissible limit (80 μg 100 g⁻¹ tissue) for PSTs in molluscan shellfish. The PST levels in the foot were reduced to 0.48 μg STX-equivalent 100 g⁻¹ after scrubbing and removal of the pigment surrounding the epithelium of the epipodial fringe (confirmed by both HPLC and LC-MS/MS). Thus, scrubbing the epipodial fringe, a common procedure during commercial abalone canning, reduced PST levels by ∼70%. Only trace levels of PSTs were detected in the viscera (stomach, gut, heart, gonad, gills and mantle) of the abalone. A toxin reduction of approximately 73% was observed in STX-contaminated abalone held in clean water and fed uncontaminated food over 50 days. The low level of PST uptake when abalone were exposed to high numbers of A. minutum cells over a prolonged period may indicate a low risk of PSP poisoning to humans from the consumption of H. laevigata that has been exposed to a bloom of potentially toxic A. minutum in Australia. Further research is required to establish if non-dietary accumulation can result in significant levels of PSTs in abalone.

Meso-Zooplankton Abundance, Distribution and Community Composition in the Eastern Great Australian Bight

Abstract Seasonal meso-zooplankton abundance, distribution and community composition were examined in the eastern Great Australian Bight (EGAB) in 1999 and 2000. Meteorological and oceanographical conditions in the region change markedly with season, with an upwelling circulation dominating the area during summer/autumn, and downwelling prevailing in winter. Highest zooplankton densities occurred in summer in both years of the study, and corresponded to areas of elevated chlorophyll a concentration and cool sea surface temperature, indicative of coastal upwelling. Copepods and cladocerans dominated the zooplankton community, regardless of season. However, a clear difference in zooplankton community composition was identified between the different seasons. During summer/autumn in the EGAB, zooplankton with opportunistic reproductive strategies were significantly more abundant than during winter/spring. It appears that the elevated chlorophyll a concentrations in the EGAB during the summer/autumn upwelling season underpinned the clear seasonal differences in zooplankton community composition observed in this study.

Systematic, continental scale temporal monitoring of marine pelagic microbiota by the Australian Marine Microbial Biodiversity Initiative

Sustained observations of microbial dynamics are rare, especially in southern hemisphere waters. The Australian Marine Microbial Biodiversity Initiative (AMMBI) provides methodologically standardized, continental scale, temporal phylogenetic amplicon sequencing data describing Bacteria, Archaea and microbial Eukarya assemblages. Sequence data is linked to extensive physical, biological and chemical oceanographic contextual information. Samples are collected monthly to seasonally from multiple depths at seven sites: Darwin Harbour (Northern Territory), Yongala (Queensland), North Stradbroke Island (Queensland), Port Hacking (New South Wales), Maria Island (Tasmania), Kangaroo Island (South Australia), Rottnest Island (Western Australia). These sites span ~30° of latitude and ~38° longitude, range from tropical to cold temperate zones, and are influenced by both local and globally significant oceanographic and climatic features. All sequence datasets are provided in both raw and processed fashion. Currently 952 samples are publically available for bacteria and archaea which include 88,951,761 bacterial (72,435 unique) and 70,463,079 archaeal (24,205 unique) 16 S rRNA v1-3 gene sequences, and 388 samples are available for eukaryotes which include 39,801,050 (78,463 unique) 18 S rRNA v4 gene sequences.

A database of marine larval fish assemblages in Australian temperate and subtropical waters

Larval fishes are a useful metric of marine ecosystem state and change, as well as species-specific patterns in phenology. The high level of taxonomic expertise required to identify larval fishes to species level, and the considerable effort required to collect samples, make these data very valuable. Here we collate 3178 samples of larval fish assemblages, from 12 research projects from 1983-present, from temperate and subtropical Australian pelagic waters. This forms a benchmark for the larval fish assemblage for the region, and includes recent monitoring of larval fishes at coastal oceanographic reference stations. Comparing larval fishes among projects can be problematic due to differences in taxonomic resolution, and identifying all taxa to species is challenging, so this study reports a standard taxonomic resolution (of 218 taxa) for this region to help guide future research. This larval fish database serves as a data repository for surveys of larval fish assemblages in the region, and can contribute to analysis of climate-driven changes in the location and timing of the spawning of marine fishes.

A database of chlorophyll a in Australian waters

Chlorophyll a is the most commonly used indicator of phytoplankton biomass in the marine environment. It is relatively simple and cost effective to measure when compared to phytoplankton abundance and is thus routinely included in many surveys. Here we collate 173, 333 records of chlorophyll a collected since 1965 from Australian waters gathered from researchers on regular coastal monitoring surveys and ocean voyages into a single repository. This dataset includes the chlorophyll a values as measured from samples analysed using spectrophotometry, fluorometry and high performance liquid chromatography (HPLC). The Australian Chlorophyll a database is freely available through the Australian Ocean Data Network portal (https://portal.aodn.org.au/). These data can be used in isolation as an index of phytoplankton biomass or in combination with other data to provide insight into water quality, ecosystem state, and relationships with other trophic levels such as zooplankton or fish.

Evaluation of MODIS Products in the Great Australian Bight and Adjacent Coastal Waters

Satellite remote sensing data can produce global environmental data and is easily accessible and widely used by the scientific and non-scientific community. However, to use satellite data, it is important to know its limitations and how it validates against in situ measurements for the different regions. Here, field measurements of chlorophyll-a concentration and euphotic depth within the Great Australian Bight, Gulf St Vincent and Spencer Gulf were used to validate ocean colour products derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the Aqua satellite. The field data include in situ and in vivo chlorophyll-a concentration, which were compared against MODIS chlorophyll-a products derived from three algorithms (OC3M, Carder, and Garver-Siegel-Maritorena (GSM)), as well as euphotic depth measurements derived from photosynthetically active radiation (PAR) profiles, which were compared against two MODIS euphotic depth products (derived semi-analytically and from surface chlorophyll-a). The OC3M product performed well in open waters, with errors below the 35% NASA accepted limit, but it overestimated chlorophyll-a values in shallow (<50 m) waters. The GSM product produced the lowest errors, but also showed a smaller dynamic range, while the Carder product produced higher errors than GSM and it also showed small dynamic range. The relationships between the MODIS and in situ euphotic depth were robust, with errors lower than 20%. MODIS products showed weaker or no significant relationships to in situ measurements in the Eastern Great Australian Bight. This is thought to be due to the summertime subsurface upwelling pool that is characteristic of the area. Based on these results, the OC3M product provides the most reliable estimates of chlorophyll-a, and is recommended for further applications of MODIS imagery, if the limitations in shallow waters are taken into account. Alternatively, the GSM product could be a better option if the algorithm were locally adjusted. Changes in the sampling methodology to improve the algorithms are discussed. Derived euphotic depth products can be used with confidence in applying MODIS products for monitoring water clarity, ecosystem health or primary productivity in the region.