I completed my PhD in 2010 at the National University of Ireland, Galway. My research focuses on the ecology and distribution of harmful algae and their impact on aquaculture zones.
At UTS, I am an Honorary Associate in the Sustainable Aquaculture Group within the Plant Functional Biology and Climate Change Cluster(C3).
Member of the International Society for the Study of Harmful Algae
NSW Food Authority
NSW Department of Primary Industries, Fisheries
Shellfish aquaculture is a longstanding industry in Australia. A major threat to this immensely valuable sector is the contamination of shellfish product with microalgal toxins. During toxic events harvest zones undergo mandatory closures. This is necessary for the protection of consumers. Understanding the dynamics of how and when harmful blooms occur will enable aquaculture resource managers to make better-informed management decisions.
Farrell, H, Ajani, PA, Murray, S, Baker, P, Webster, G, Brett, S & Zammit, A 2018, 'Diarrhetic Shellfish Toxin Monitoring in Commercial Wild Harvest Bivalve Shellfish in New South Wales, Australia', Toxins, vol. 10, no. 11.View/Download from: Publisher's site
Ajani, PA, Larsson, M, Woodcock, S, Rubio, A, Farrell, H, Brett, S & Murray, S 2018, 'Bloom drivers of the potentially harmful dinoflagellate Prorocentrum minimum (Pavillard) Schiller in a south eastern temperate Australian estuary', Estuarine, Coastal and Shelf Science, vol. 215.View/Download from: Publisher's site
Between 2014 and 2016, five cases of ciguatera fish poisoning (CFP), involving twenty four individuals, were linked to Spanish Mackerel (Scomberomorus commerson) caught in the coastal waters of the state of New South Wales (NSW) on the east coast of Australia. Previously, documented cases of CFP in NSW were few, and primarily linked to fish imported from other regions. Since 2015, thirteen individuals were affected across four additional CFP cases in NSW, linked to fish imported from tropical locations. The apparent increase in CFP in NSW from locally sourced catch, combined with the risk of CFP from imported fish, has highlighted several considerations that should be incorporated into risk management strategies to minimize CFP exposure for seafood consumers.
Farrell, H, Zammit, A, Manning, J, Shadbolt, C, Szabo, L, Harwood, DT, McNabb, P, Turahui, JA & van den Berg, DJ 2016, 'Clinical diagnosis and chemical confirmation of ciguatera fish poisoning in New South Wales, Australia.', Communicable diseases intelligence quarterly report, vol. 40, no. 1, pp. E1-E6.
Ciguatera fish poisoning is common in tropical and sub-tropical areas and larger fish (> 10 kg) are more susceptible to toxin accumulation with age. Although the coastal climate of northern New South Wales is considered sub-tropical, prior to 2014 there has only been 1 documented outbreak of ciguatera fish poisoning from fish caught in the region. During February and March 2014, 2 outbreaks of ciguatera fish poisoning involved 4 and 9 individuals, respectively, both following consumption of Spanish mackerel from northern New South Wales coastal waters (Evans Head and Scotts Head). Affected individuals suffered a combination of gastrointestinal and neurological symptoms requiring hospital treatment. At least 1 individual was symptomatic up to 7 months later. Liquid chromatography-tandem mass spectrometry detected the compound Pacific ciguatoxin-1B at levels up to 1.0 µg kg(-1) in fish tissue from both outbreaks. During April 2015, another outbreak of ciguatera fish poisoning was reported in 4 individuals. The fish implicated in the outbreak was caught further south than the 2014 outbreaks (South West Rocks). Fish tissue was unavailable for analysis; however, symptoms were consistent with ciguatera fish poisoning. To our knowledge, these cases are the southernmost confirmed sources of ciguatera fish poisoning in Australia. Educational outreach to the fishing community, in particular recreational fishers was undertaken after the Evans Head outbreak. This highlighted the outbreak, species of fish involved and the range of symptoms associated with ciguatera fish poisoning. Further assessment of the potential for ciguatoxins to occur in previously unaffected locations need to be considered in terms of food safety.
Farrell, H, O'Connor, W, Seebacher, F, Harwood, DT & Murray, S 2016, 'Molecular Detection Of The Sxta Gene From Saxitoxin-Producing Alexandrium Minutum In Commercial Oyster', The Journal of Shellfish Research, vol. 35, no. 1, pp. 169-177.View/Download from: Publisher's site
The production of toxic secondary metabolites by marine phytoplankton and their accumulation in molluscs and fish has ecosystem-wide and human health impacts.
Ajani, PA, Larsson, M, Rubio, A, Bush, S, Brett, S & Farrell, H 2016, 'Modelling bloom formation of the toxic dinoflagellates Dinophysis acuminata and Dinophysis caudata in a highly modified estuary, south eastern Australia', Estuarine, Coastal and Shelf Science, vol. 183, pp. 95-106.View/Download from: Publisher's site
Dinoflagellates belonging to the toxigenic genus Dinophysis are increasing in abundance in the Hawkesbury River, south-eastern Australia. This study investigates a twelve year time series of abundance and physico-chemical data to model these blooms. Four species were reported over the sampling campaign - Dinophysis acuminata, Dinophysis caudata, Dinophysis fortii and Dinophysis tripos-with D. acuminata and D. caudata being most abundant. Highest abundance of D. acuminata occurred in the austral spring (max. abundance 4500 cells l−1), whilst highest D. caudata occurred in the summer to autumn (max. 12,000 cells l−1). Generalised additive models revealed abundance of D. acuminata was significantly linked to season, thermal stratification and nutrients, whilst D. caudata was associated with nutrients, salinity and dissolved oxygen. The models' predictive capability was up to 60% for D. acuminata and 53% for D. caudata. Altering sampling strategies during blooms accompanied with in situ high resolution monitoring will further improve Dinophysis bloom prediction capability
Farrell, H, Seebacher, F, O'Connor, W, Zammit, A, Harwood, DT & Murray, S 2015, 'Warm temperature acclimation impacts metabolism of paralytic shellfish toxins from Alexandrium minutum in commercial oysters.', Global Change Biology, vol. 21, no. 9, pp. 3402-3413.View/Download from: Publisher's site
Species of Alexandrium produce potent neurotoxins termed paralytic shellfish toxins and are expanding their ranges worldwide, concurrent with increases in sea surface temperature. The metabolism of molluscs is temperature dependent, and increases in ocean temperature may influence both the abundance and distribution of Alexandrium and the dynamics of toxin uptake and depuration in shellfish. Here, we conducted a large-scale study of the effect of temperature on the uptake and depuration of paralytic shellfish toxins in three commercial oysters (Saccostrea glomerata and diploid and triploid Crassostrea gigas, n = 252 per species/ploidy level). Oysters were acclimated to two constant temperatures, reflecting current and predicted climate scenarios (22 and 27 °C), and fed a diet including the paralytic shellfish toxin-producing species Alexandrium minutum. While the oysters fed on A. minutum in similar quantities, concentrations of the toxin analogue GTX1,4 were significantly lower in warm-acclimated S. glomerata and diploid C. gigas after 12 days. Following exposure to A. minutum, toxicity of triploid C. gigas was not affected by temperature. Generally, detoxification rates were reduced in warm-acclimated oysters. The routine metabolism of the oysters was not affected by the toxins, but a significant effect was found at a cellular level in diploid C. gigas. The increasing incidences of Alexandrium blooms worldwide are a challenge for shellfish food safety regulation. Our findings indicate that rising ocean temperatures may reduce paralytic shellfish toxin accumulation in two of the three oyster types; however, they may persist for longer periods in oyster tissue.
Murray, SA, Kohli, GS, Farrell, H, Spiers, ZB, Place, AR, Dorantes-Aranda, JJ & Ruszczyk, J 2015, 'A fish kill associated with a bloom of Amphidinium carterae in a coastal lagoon in Sydney, Australia.', Harmful Algae, vol. 49, pp. 19-28.View/Download from: Publisher's site
We report on a dense bloom (1.80 105 cells mL 1
) of the marine dinoflagellate species Amphidinium
carterae (Genotype 2) in a shallow, small intermittently open coastal lagoon in south eastern Australia.
This bloom co-occurred with the deaths of >300 individuals of three different species of fish. The
opening of the lagoon to the ocean, as well as localized high nutrient levels, preceded the observations of
very high cell numbers. A. carterae is usually benthic and sediment-dwelling, but temporarily became
abundant throughout the water column in this shallow (<2 m) sandy habitat. Histopathological results
showed that the Anguilla reinhardtii individuals examined had damage to epithelial and gill epithelial
cells. An analysis of the bloom water indicated the presence of a compound with a retention time and UV
spectra similar to Luteophanol A, a compound known from a strain of Amphidinium. Assays with a fish gill
cell line were conducted using a purified compound from cells concentrated from the bloom, and was
found to cause a loss of 87% in cell viability in 6 h. The fish deaths were likely due to the low dissolved
oxygen levels in the water and/or the presence of Luteophanol A-like compounds released during the
Farrell, H, Gentien, P, Fernand, L, Lazure, P, Lunven, M, Youenou, A, Reguera, B & Raine, R 2014, 'Vertical and horizontal controls of a haptophyte thin layer in the Bay of Biscay, France', Deep Sea Research Part II: Topical Studies in Oceanography, vol. 101, pp. 80-94.View/Download from: Publisher's site
Investigations into the phytoplankton of the Bay of Biscay in July 2006 revealed an extensive bloom of an unidentified haptophyte species. High-resolution sampling techniques identified the region in the vicinity of the mouth of the Loire estuary as an area of high (10 6 -10 7 cellsl -1 ) cell densities of the haptophyte in a thin sub-surface layer. This organism dominated the phytoplankton population regionally. Measurements of the vertical distribution of horizontal shear showed that the population, located at ca. 20m depth, was confined to a layer lying between two density discontinuities with high shear. Physical measurements indicated that the population was being advected southeastwards, along the coast. Seaward spreading of the population was also noted during the survey. Horizontal diffusion could be derived from the changes in the offshore gradient in the population's distribution with time, with estimates of Kx, the horizontal diffusion coefficient, of the order of 100m 2 s -1 . The magnitude of horizontal dispersion is compared with that of horizontal advective flux, vertical dispersion and growth. © 2013 Elsevier Ltd.
Farrell, H, Velo-Suarez, L, Reguera, B & Raine, R 2014, 'Phased cell division, specific division rates and other biological observations of Dinophysis populations in sub-surface layers off the south coast of Ireland', Deep Sea Research Part II: Topical Studies in Oceanography, vol. 101, pp. 249-254.View/Download from: Publisher's site
The proportions of viable cells of Dinophysis spp. that were paired (dividing) and recently divided during a cell cycle were measured on populations of D. acuta and D. acuminata observed off the south coast of Ireland in July 2007 and July 2009. Both species exhibited phased cell division in 2009 with maximum frequency of division (f max ) 2h after sunrise. Different patterns of division (timing of f max ) were shown by D. acuta in 2007, when the population aggregated in a thin layer was transported by a coastal jet flow. High resolution (decimetre-scale) profiles within the thin layer showed large differences in the vertical distribution of biological properties (feeding status, mortality). Values of the specific growth rate μ were compared to estimates derived in similar fashion from observations on Dinophysis populations elsewhere. Different patterns exhibited by the same species in different regions may be attributed to adaptations to latitudinal differences (length of photoperiod). The question of whether phased cell division always occurs in Dinophysis populations, and the incorporation of the potential specific division rate into models of Dinophysis growth are discussed. Comprehensive field data sets demonstrate the impact of the results on the coherence of Dinophysis populations during their transport along the Irish coast in jet-like flows towards sites of intensive shellfish culture. © 2013 Elsevier Ltd.
Farrell, H, Brett, S, Ajani, P & Murray, SA 2013, 'Distribution of the genus Alexandrium (Halim) and paralytic shellfish toxins along the coastline of New South Wales, Australia', Marine Pollution Bulletin, vol. 72, no. 1, pp. 133-145.View/Download from: Publisher's site
Blooms of Alexandrium species, in particular the species Alexandrium catenella, accounted for more than 50% of algal related, shellfish aquaculture harvest zone closures in New South Wales (NSW) Australia since 2005. While there are indications that species of Alexandrium are more abundant than they were formerly, there is little data available on the spatial and temporal distribution and abundance of the genus in NSW. A six and a half year dataset comprising a total of 8649 fortnightly samples from 31 estuaries spread over 2000 km of NSW coastline was analysed. The greatest abundances of Alexandrium spp. were observed during the austral Spring and Summer, in estuaries in the mid and southern latitudes of the state. In identifying these high risk zones, we propose variables such as season, temperature, rainfall and estuarine flushing to be targeted in intensive site specific studies, to support the development of predictive tools for resource managers.
Farrell, H, Gentien, P, Fernand, L, Lunven, M, Reguera, B, González-Gil, S & Raine, R 2012, 'Scales characterising a high density thin layer of Dinophysis acuta Ehrenberg and its transport within a coastal jet', Harmful Algae, vol. 15, pp. 36-46.View/Download from: Publisher's site
An investigation into the distribution of Dinophysis spp. in coastal waters off the south coast of Ireland was carried out in July 2007. Dinophysis acuta was present as a sub surface layer containing up to 55,000cellsL -1. The population had a high percentage of viable cells (mean: 89%; median: 94%; n=24) with a high specific division rate (∼0.55d -1). The layer, of approximately 5m thickness, did not coincide with the fluorescence maximum and was present as a patch of horizontal dimension less than 10km×7km. Both conventional and towed undulating CTD used in conjunction with high vertical resolution sampling methods showed the patch of Dinophysis to move with a similar speed and direction as the coastal flow, which ran parallel to the coast in the form of a coastal jet with speed of the order of 6.5-7kmday -1. The implications of the alongshore transport of populations of harmful species in coastal jets for monitoring programmes and predictive models are discussed. © 2011 Elsevier B.V.
Touzet, N, Farrell, H, Rathaille, A, Rodriguez, P, Alfonso, A, Botana, L & Raine, R 2010, 'Dynamics of co-occurring Alexandrium minutum (Global Clade) and A. tamarense (West European) (Dinophyceae) during a summer bloom in Cork Harbour, Ireland (2006)', Deep-sea Research Part Ii-topical Studies In Oceanography, vol. 57, no. 3-4, pp. 268-278.View/Download from: Publisher's site
The dinoflagellate genus Alexandrium contains neurotoxin-producing species, which have adversely affected the aquaculture industry and fisheries worldwide. Seasonal toxic blooms of Alexandrium spp. occur on an annual basis in the North Channel area of Co
Farrell, H, Ajani, P, Brett, S, Zammit, A & Murray, S 2013, 'Alexandrium species in New South Wales (NSW) coastal waters: historical distributions and identification of high-risk zones', Proc. 9th Int. Conf. Molluscan Shellfish Safety, International Conference on Molluscan Shellfish Safety, United Nations FAO, Sydney Australia, pp. 107-110.
Accumulation of paralytic shellfish poisoning (PSP) toxins, produced by marine planktonic dinoflagellates, can occur in all major commercial shellfish species. Aside from the potential risk to human health, aquaculture industries have reported severe economic losses due to regulatory closures. Members of the dinoflagellate genus Alexandrium are known PSP producers. Since 2005, there has been an apparent increase in reports of Alexandrium blooms in New South Wales (NSW), with species causing over 50% of algal related shellfish harvest zone closures. Our current knowledge of the distribution of the species in NSW is examined with an emphasis on high-risk zones.