Interannual variability in abundance of North Sea jellyfish and links to the North Atlantic Oscillation

Abstract

Pronounced interannual variability in the abundance of medusae of the jellyfish species Aurelia aurita, Cyanea lamarckii, and Cyanea capillata (Phylum Cnidaria, Class Scyphozoa) in the North Sea was evident in data arising from the International Council for the Exploration of the Seas International 0-group Gadoid Surveys between 1971 and 1986. Possible climatic forcing of jellyfish abundance, via the North Atlantic Oscillation (NAO), was investigated with data on medusae from four areas of the North Sea (east of Scotland, north of Scotland, east of Shetland, and west of northern Denmark). There were significant inverse relationships between medusa abundance and the NAO Index (December-March) in two regions: west of northern Denmark (A. aurita r 2 ϭ 0.70, P ϭ 0.003, n ϭ 10; C. lamarckii r 2 ϭ 0.74, P ϭ 0.002, n ϭ 10) and east of Scotland (A. aurita r 2 ϭ 0.53, P ϭ 0.008, n ϭ 12). Fluctuations in the abundance of A. aurita and C. lamarckii medusae might be linked to hydroclimatic changes induced through atmospheric effects (as encapsulated in the NAO Index) on wind stress, temperature, and currents. These fundamental hydroclimatic changes alter the timing of spring phytoplankton blooms and zooplankton community composition. Predation by an abundance of medusae on zooplankton and ichthyoplankton could affect the North Sea ecosystem through top-down and bottom-up mechanisms. Because the NAO is presently in a high phase, climatic conditions could be serving to depress the abundance of medusae: a future reversal of the NAO might favor jellyfish and weaken the persistence or recovery of fisheries.

Energy budget calculations indicate resource limitation in Eastern Pacific leatherback turtles

“…To our knowledge, no data are available on abundances of gelatinous animals in the EP and their responses to ENSO-driven climate change. However, jellyfish abundances and distributions in other regions are affected by climatic forcing (Lynam et al 2004) on broad temporal and geographic scales (Mills 2001), and productivity in areas where leatherbacks are presumed to forage in the EP (Morreale et al 1996, Eckert & Sarti 1997 is patchy and unstable due to ENSO (Glantz 2001). Such ENSO-related decreases in primary productivity would trigger bottom-up trophic cascade effects resulting in decreased jellyfish abundances, since jellyfish and related organisms are chiefly secondary consumers.…”

“…Such oceanographic fluctuations cause abundances and distributions of leatherback prey (e.g. jellyfish, ctenophores and other gelatinous animals) (Bjorndal 1997, James & Herman 2001 to vary greatly in time and space (Mills 2001, Lynam et al 2004.…”

Preservation methods alter stable isotope values in gelatinous zooplankton: implications for interpreting trophic ecology

“…Lynam et al 2004;Doyle et al 2008;Kirby et al 2009), the need to assess the role of jellyWsh within marine systems is paramount. ReWning and standardising SIA methodology is an important step to achieving this goal.…”

Development, biological regulation, and fate of ctenophore blooms in the York River estuary, Chesapeake Bay

“…In particular, the North Atlantic Oscillation Index (NAO) has been used as an environmental variable to explain increases in medusae (Brodeur et al 2002, Lynam et al 2004, including Chesapeake Bay scyphomedusae (Purcell & Decker 2005). Our limited time-series restricts similar comparisons, although Mnemiopsis leidyi blooms could be connected with NAO as York River water temperature is positively correlated to positive phases of NAO (Austin 2002).…”