Jellyfish on the menu: mtDNA assay reveals scyphozoan predation in the Irish Sea

Abstract

Localized outbreaks of jellyfish, known as blooms, cause a variety of adverse ecological and economic effects. However, fundamental aspects of their ecology remain unknown. Notably, there is scant information on the role jellyfish occupy in food webs: in many ecosystems, few or no predators are known. To identify jellyfish consumers in the Irish Sea, we conducted a molecular gut content assessment of 50 potential predators using cnidarian-specific mtDNA primers and sequencing. We show that jellyfish predation may be more common than previously acknowledged: uncovering many previously unknown jellyfish predators. A substantial proportion of herring and whiting were found to have consumed jellyfish. Rare ingestion was also detected in a variety of other species. Given the phenology of jellyfish in the region, we suggest that the predation was probably targeting juvenile stages of the jellyfish life cycle.

Cryptic diets of forage fish: jellyfish consumption observed in the Celtic Sea and western English Channel

“…The most frequent consumer of jellyfish in the early season (February–March) was C. harengus (Lamb et al , ), however none were captured in October and we were unable to draw comparison between early and late season. Seasonal comparisons in the other detected predators also presented challenges: in the early season a large sample size and a variety of trawling techniques were employed to capture both benthic and pelagic communities of fish (Fox et al , ), facilitating the detection of rare predation.…”

“…Jellyfish predation as a function of bell area (bar height). Predation of ephyrae is inferred using data from 2008–2009 (Lamb et al , ), medusae predation was inferred using 2015 data presented in this paper. n.b .…”

“…The protocol developed previously by Lamb et al () was used here. In brief, the cnidarian‐specific 16s mitochondrial (mt)DNA primers Scy_16s_f4 and Scy_16s_r4 were used to amplify a 135 bp amplicon in a PCR.…”

“…PCR conditions were identical to those described here. Details of sampling approach, DNA extraction techniques and DNA sequences are available in full in Lamb et al ().…”

“…The significance of jellyfish in marine food webs has become clear through the application of stable‐isotope analysis (Cardona et al , ; Utne‐Palm et al , ), stationary underwater cameras (Sweetman & Chapman, ), remote operated vehicles (Hoving & Haddock, ) and acoustic surveys (Utne‐Palm et al , ). Commercially‐important fish species such as herring Clupea harengus L. 1758 and whiting Merlangius merlangus L. 1758 were shown to consume jellyfish in the Irish Sea using a molecular assay (Lamb et al , ). However, the observed scyphomedusae consumption occurred when jellyfish in the Irish Sea were juvenile and lacked the size or defensive structures to deter predation; it remains unknown if they are consumed throughout the year or used as a seasonal resource.…”