Vol. 4: 263–272, 2013 AQUACULTURE ENVIRONMENT INTERACTIONS Published online December 19 doi: 10.3354/aei00086 Aquacult Environ Interact OPEN ACCESS Identifying potentially harmful jellyfish blooms using shoreline surveys Nicholas E. C. Fleming1,2, Chris Harrod1,3,4, Jonathan D. R. Houghton1,2,* 1School of Biological Sciences, Queen’s University Belfast, Medical Biology Centre, 97 Lisburn Road, Belfast BT9 7BL, UK 2Queen’s University Belfast Marine Laboratory, 12-13 The Strand, Portaferry BT22 1PF, UK 3School of Biological and Chemical Sciences, Queen Mary University of London, Mile End Road, London E1 4NS, UK 4Instituto de Ciencias Naturales Alexander Von Humboldt, Universidad de Antofagasta, Avenida Angamos 601, Antofagasta, Chile ABSTRACT: Interactions between jellyfish and aquaculture operations are frequent around the world, with scyphozoan (in particular Pelagia noctiluca) and hydrozoan species documented as causative agents in major fish kills. Identifying areas of major aggregations or incursions of particular species around a coastline is a good starting point when assessing the threat of jellyfish blooms to ex- isting or potential aquaculture facilities. Here we tested the viability of shoreline surveys to identify areas at risk from coastal and/or oceanic jellyfish species. Surveys were undertaken at over 40 sites around the north of Ireland (covering ~1800 km of coastline) from 2009 to 2011 to test 2 specific hy- potheses: (1) strandings of coastal jellyfish species with life cycles involving production of medusae from benthic polyps or hydroids would display a marked spatial consistency over time, although the magnitude of events may vary inter-annually; and (2) incursions of oceanic jellyfish species (lacking polyps) would impact large areas of coastline and be more episodic in nature. Seven jellyfish species known to harm farmed finfish displayed spatially consistent stranding distributions, with major stranding events evident at several locations. More generally, coastal species stranded throughout the study area at the end of summer, whilst oceanic species were found along the exposed north shore of Ireland, washing ashore during the autumn/winter. The numbers of individuals within stranding events were greater for oceanic species (e.g. P. noctiluca, mean ± SE = 1801 ± 978 ind. km−1) than coastal species (e.g. Aurelia aurita = 112 ± 51 ind. km−1), supporting the idea that large offshore aggregations of P. noctiluca remain a threat to the aquaculture industry across the region. KEY WORDS: Scyphozoan · Hydrozoan · Gelatinous zooplankton · Community composition · Pelagia noctiluca · Ireland INTRODUCTION ding benthic polyps (Arai 1997). As the polyps can persist over many years (Lucas 2001, Purcell et al. Jellyfish blooms are a known threat to coastal 2009, Lucas et al. 2012), it is logical to suggest some industries (e.g. aquaculture on-growing facilities, degree of spatial consistency in the resultant jellyfish recreational beaches and power stations), yet our aggregations from year to year, although long-term ability to predict or even quantify the threat remains data to test this idea are relatively scarce (Colin & an on-going challenge (Nickell et al. 2010). To date, Kremer 2002, Condon et al. 2012, 2013). many studies of such aggregations have focused on A notable exception to this conjecture is the scypho - areas dominated by those jellyfish (i.e. Phylum medusan Pelagia noctiluca (Forsskål 1775), which Cnidaria, Class Scyphozoa) with a metagenic life his- lacks a near-shore polyp stage and can form large tory comprising an alternation of free-swimming and ag gregations in offshore areas (Russell 1967, Purcell sexually reproducing medusae with asexually bud- 2005, Ferraris et al. 2012). Periodic and highly prob- © The authors 2013. Open Access under Creative Commons by *Corresponding author. Email: [email protected] Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 264 Aquacult Environ Interact 4: 263–272, 2013 lematic incursions of P. noctiluca are well docu- lite remote sensing. Each method, in turn, was de - mented in the Mediterranean Sea (Rottini-Sandrini scribed, stating advantages and disadvantages (also et al. 1980, Zavodnik 1987, CIESM 2001), yet the spe- see review by Purcell 2009), and with clear recom- cies had received little attention in the North East mendations for the future including: (1) the develop- Atlantic (NEA) until recently (Doyle et al. 2008, ment of a reporting network, (2) the set-up of sentinel Lican dro et al. 2010). Most notable were the extraor- water monitoring sites and (3) continued trials with dinary abundances recorded around the north of Ire- new and emerging techniques such as the advanced land in November 2007 (spanning more than 4° of molecular identification of jellyfish in continuous latitude along a 1500 km cruise track) that ultimately plankton recorder tows. caused damage worth over £1 million to the Northern One of the key considerations, however, when Irish aquaculture industry in a matter of days (Doyle seeking to establish a long-term monitoring protocol et al. 2008). This species was also a suspected causa - is financial outlay (e.g. aircraft, ship time) or the tive agent of over 1 million Atlantic salmon Salmo requirement for specialised equipment and training. salar killed off northwest Ireland in 2003 (Cronin et Within this context, an additional method that shows al. 2004), and aquaculture companies still ex press promise is the monitoring of jellyfish strandings grave concern over this ongoing threat (Nickell et al. along the shoreline, which has been used previously 2010). Moreover, as the drivers of oceanic jellyfish to identify the broad-scale distribution patterns incursions in the NEA are poorly understood (Doyle (Doyle et al. 2007) and reproductive seasonality et al. 2008), insurance companies have, in the past, (Hough ton et al. 2007) of jellyfish medusae. Natu- had no other option than to classify such events as rally, this method comes with its own caveats, as ‘acts of God’, with subsequent marked negative eco- strandings data do not indicate the duration that a nomic impacts for the marine aquaculture sector. species is present in the water column in a particular Such high-profile case studies of jellyfish-induced area, nor do they take into account those species fish kills (see review by Rodger et al. 2011 for exam- which are very small, fragile and quick to decompose ples) can sometimes lead to the perception that jelly- (e.g. ctenophores and small hydromedusae). Such fish represent a recent or rapidly increasing threat to species are more readily identified by in situ monitor- the industry. For example, the events of 2007 were ing at aquaculture facilities (see Baxter et al. 2011a). reported throughout the international media as un - Here, the focus is on the broad-scale distribution of precedented and indicative of a regime shift within larger scyphozoan jellyfish which have proved prob- the NEA, yet these claims were purely speculative. lematic in Irish/UK waters over recent years. Strand- Indeed, a follow-up study by Doyle et al. (2008) ings, in the main, reflect the end of season fall-out revealed that such incursions of oceanic jellyfish into which retrospectively provides an indication of what UK/Irish waters were far from rare, with Pelagia species ‘were’ present in an area in a given year as noctiluca reported anecdotally in 21 out of a possible well as inter-annual variation in the magnitude of 95 years between 1890 and 1985. This assertion was blooms. Although of limited direct utility in the short supported further by Licandro et al. (2010) and Bast- term, such data when viewed over consecutive years ian et al. (2011), who revealed that major aggrega- provide invaluable information regarding the loca- tions of this species can frequently occur between the tion and persistence of threats. Amongst ecologists, Bay of Biscay and the north of Scotland. this method is gaining recognition, as highlighted by Effective threat assessment of jellyfish blooms re- the recent National Centre for Ecological Analysis quires data to be gathered over a number of years in and Synthesis jellyfish working group which incor- a cost effective manner that can be easily replicated porated such data into a global synthesis of reports of at different locations. In terms of mapping the distri- jellyfish abundance (e.g. Condon et al. 2012, 2013). bution of jellyfish, a number of potential methods are To assess the efficacy of shoreline surveys from a available. The UK Crown Estate recently commis- coastal stakeholder perspective including aquacul- sioned a study in response to the Scottish salmon ture, the Northern Ireland Government funded a pro- mariculture industry’s concerns about mortalities gramme in 2007 (prompted by the County Antrim related to jellyfish blooms (Nickell et al. 2010). This fish kill) to record jellyfish strandings around the project aimed to develop the capacity to monitor the north of Ireland (>1800 km of coastline between spatial and temporal distributions of jellyfish in west- Counties Donegal in the west and Down in the east). ern Scottish waters. Several techniques were suc- More than 500 surveys were conducted across 40 cessfully tested, ranging from reporting networks at sites (2009 to 2011), with data gathered for an assem- fish farms through to coastal aerial surveys and satel- blage of scyphozoan and hydrozoan jellyfish (i.e. Fleming et al.: Patterns of jellyfish strandings 265 documented threats to aquaculture on-growing facil- both of its life stages in the pelagic environment ities; Rodger et al. 2011). Here we report the findings (‘oce anic’; Purcell et al. 2012). The remaining taxa of this programme and highlight a method that has (including the hydrozoan Aequorea sp.) encountered broad applicability to the expanding aquaculture in the surveys all have a benthic polyp or hydroid sector in UK/Irish waters (FAO 2012). More specifi- stage that require substrate for settlement (‘coastal’).