Hydrobiologia (2007) 579:29–39 DOI 10.1007/s10750-006-0362-2 PRIMARY RESEARCH PAPER The broad-scale distribution of five jellyfish species across a temperate coastal environment Thomas K. Doyle Æ Jonathan D. R. Houghton Æ Sarah M. Buckley Æ Graeme C. Hays Æ John Davenport Received: 9 March 2006 / Revised: 10 July 2006 / Accepted: 11 July 2006 / Published online: 2 November 2006 Ó Springer Science+Business Media B.V. 2006 Abstract Jellyfish (medusae) are sometimes the stranding events over three consecutive years. most noticeable and abundant members of coastal Jellyfish species displayed distinct species-specific planktonic communities, yet ironically, this high distributions, with an apparent segregation of conspicuousness is not reflected in our overall some species. Furthermore, a different species understanding of their spatial distributions across composition was noticeable between the northern large expanses of water. Here, we set out to elu- and southern parts of the study area. Most cidate the spatial (and temporal) patterns for five importantly, our data suggests that jellyfish dis- jellyfish species (Phylum Cnidaria, Orders tributions broadly reflect the major hydrographic Rhizostomeae and Semaeostomeae) across the regimes (and associated physical discontinuities) Irish & Celtic Seas, an extensive shelf-sea area at of the study area, with mixed water masses pos- Europe’s northwesterly margin encompassing sibly acting as a trophic barrier or non-favourable several thousand square kilometers. Data were environment for the successful growth and gathered using two independent methods: (1) reproduction of jellyfish species. surface-counts of jellyfish from ships of opportu- nity, and (2) regular shoreline surveys for Keywords Irish Sea Æ Hydrographic regimes Æ Rhizostomeae Æ Semaeostomeae Handling editor: K. Martens T. K. Doyle (&) Introduction Environmental Research Institute, University College Cork, Lee Road, The ecological role of jellyfish (more specifically Cork, Ireland e-mail: [email protected] medusae of the Phylum Cnidaria: Orders Rhizo- stomeae and Semaeostomeae) within coastal J. D. R. Houghton Æ G. C. Hays marine systems has received much recent atten- Institute of Environmental Sustainability, tion. This interest has been largely driven by the School of the Environment and Society, University of Wales Swansea, Singleton Park, propensity of jellyfish to form extensive nuisance SA2 8PP Swansea, UK blooms and their associated socio-economic effects (CIESM, 2001). For example, during the S. M. Buckley Æ J. Davenport Æ T. K. Doyle 1980s blooms of Pelagia noctiluca occurred Department of Zoology, Ecology and Plant Sciences, University College Cork, Distillery Fields, throughout the Mediterranean and caused wide- North Mall Cork, Ireland spread concern to both fishermen and tourists 123 30 Hydrobiologia (2007) 579:29–39 (CIESM, 2001). Since then, many other examples temperate coastal environment, and comment of jellyfish blooms impacting negatively on econ- upon the factors that may ultimately drive omies have been reported worldwide (e.g. Graham observed patterns. et al., 2003; Kawahara et al., 2006). This was recently illustrated by the outbreak of Sanderia malayensis in the Yangtze Estuary for the first time Methods in 2004 that resulted in fisheries being dominated by a 98% jellyfish by-catch (Xian et al., 2005). Study area There is also a concern that jellyfish might capitalise upon the niche left by the removal of The Irish & Celtic Seas form part of the northeast top predators (e.g. planktivorous fish), with once Atlantic shelf seas, represent a network of abundant fish stocks being replaced by jellyfish- extensive shallows and have a long and complex dominated communities (Brierley et al., 2005). coastline (Le Fe`vre, 1986). The majority of this Such regime shifts might be further exacerbated seaboard is within the 100 m-depth contour of the by increased eutrophication and climate change continental shelf. Jellyfish data were collected that are intrinsically linked to global human from the southern and central Irish Sea and the population trends (Cloern, 2001), suggesting that northern extreme of the Celtic Sea to the south this issue may remain highly topical for the fore- (51.0° N to 53.5° N and –3.0° W to –11.0° W) seeable future. However, our ability to respond to (Fig. 1). these globally important issues is often hampered by a lack of baseline data. Indeed, Mills (2001) Shoreline surveys remarked that research efforts should be redi- rected towards the study of the population Regular shoreline surveys were carried out dynamics of some of the common and abundant across the study area during the period June jellyfish species, about which we know next to 2003–September 2005, to record the presence or nothing beyond their names. absence of stranded jellyfish. Surveys were An area where this problem has recently come timed to coincide with low tide and constituted to light is the Irish and Celtic Seas, an extensive an outward leg along the high water mark and a shelf-sea area at Europe’s northwesterly margin return leg along the waters edge. Jellyfish were spanning several thousand square kilometers. identified to species level and tallied using the Despite being one of the most intensively studied following categories to give an indication of bodies of water in the world (Allen et al., 1998; relative abundance: 0, 1–10, 11–50, 51–100, 101– Evans et al., 2003), our overall knowledge of jel- 500, and >500 per length of coastline surveyed. lyfish biogeography within the region remains Data were additionally converted to numbers of largely dependent on the classic studies of Delap individuals per 100 m of coastline. Lastly, to (1905) and Russell (1970). Although invaluable, derive an indirect measure of seasonality, (and the findings of these previous studies are gener- provide baseline data for the Celtic and Irish ally limited to generic statements, with jellyfish Seas) shoreline surveys were conducted during described in such terms as northern or southern each month with the presence of stranded jel- boreal species (Russell, 1970). To elucidate these lyfish taken as evidence that individuals were patterns further, we collected data for five scy- also present within the water column at that phozoan species over three consecutive years time. (2003–2005). Given the extensive spatial and temporal coverage of our study, data were gath- ered using two independent methods: (1) surface- Visual counts from ships of opportunity counts of jellyfish from ships of opportunity, and (2) regular shoreline surveys for stranding events. Visual counts of jellyfish were made from ships of From this, we provide an empirical account of opportunity (ShOps) traversing the Irish & Celtic how jellyfish may be distributed across a large, Seas during the summer months (June–September) 123 Hydrobiologia (2007) 579:29–39 31 Fig. 1 Hydrographic map of the main water bodies, and frontal systems within the Celtic and Irish Seas. In respective order, the labels (A), (B) and (C) correspond to the Celtic Sea, Irish Sea and Bristol Channel. CSF, Celtic Sea Front; WISF, Western Irish Sea Front. Figure reproduced from Golding et al. (2004) of 2004 and 2005. Three independent ferry identified from the ferry observation deck crossings were utilised that roughly followed the (Fig. 2). Angle of inclination (degrees from 51.5°, 52.0° and 53.5° N parallels (termed tran- horizontal) for each object was measured using sects T1, T2, and T3). During the entire study an inclinometer, and converted to horizontal period a total of 20 crossings were made (2004: distance from the vessel using simple trigo- N = 5; 2005: N = 15). All observations nometry. Distance of objects from the vessel (N = 4,265 min) were made from an elevated was plotted on frequency histograms and the position from the beam of the ShOps, during spread of data tested for normality (Anderson– daylight hours (07:00–21:00 h) (Fig. 2). Jellyfish Darling normality test). This revealed an inter- were identified to species level, and their numbers esting pattern with sightings of objects at low estimated per 5-min intervals using the following sea states (i.e. calm weather £ force 3 on the categories: 0, 1–10, 11–50, 51–100, 101–500, and Beaufort) being skewed and non-parametric >500 (Note: jellyfish abundance was on occasion (Anderson–Darling; P > 0.05); yet during ele- so great that estimates beyond this resolution vated sea states (‡force 4 on the Beaufort were impractical). Sample periods were 15 min scale), the distance of sighted objects was nor- long with 5-min breaks between successive sam- mally distributed (Anderson–Darling; P > 0.05). ples. After three successive sample periods a Where necessary, data were then normalised, 20 min break was taken, and after every 3–4 h a and for all sea states mean distance of objects 1-h rest period was taken. Location (latitude and from vessel calculated (Fig. 2). By use of two longitude), time, sea state (Beaufort Scale) standard deviations (±) as outer limits, the and glare, were recorded every 15 min. Glare observational field (m) was calculated for each was determined using a system of arbitrary oc- sea state (Fig. 2). Use of this value as width, tares whereby the field of view is visually divided and the distance travelled in 5-min (calculated into eight equal sections, and the number of from latitude and longitude) as length, jellyfish sections obscured by glare taken as an estimate count data were converted to a density value (Houghton et al., 2006). (indiv./m2). To aid analysis,