Application of a Hydrodynamic Model to Jellyfish Transport Modelling in an Irish Fjord

In recent times, jellyfish have gained public noteriety due to beach closures and mass kills of marine-farmed fish arising from the sudden occurrence of jellyfish swarms or `blooms`. Numerous fish-kill events or gill disorders in marine-farmed fish due to jellyfish sting toxins have been reported in Europe, Asia, North America, and Australia. The economic consequences are significant with annual losses of 68–205 million USD and 10 million USD previously estimated for Korea and the Gulf of Mexico, respectively. Computer models that are able to simulate jellyfish movement can play a vital role in understanding how we can prevent these adverse effects. Here, we develop a hydrodynamic coastal model to simulate the transport of jellyfish within Killary Harbour, a fjord-like inlet on the west coast of Ireland.

Killary Harbour is approximately 13 km long and 700 m wide with an average depth of about 20 m. A hydrodynamic model of the harbour was developed using the Environmental Fluid Dynamics Code (EFDC). The seabed terrain model was created using a combination of INFOMAR survey data and digitised Admiralty Charts. The principal freshwater sources are the Erriff River on the eastern shore of the harbour and the Bundorragha River on the northern shore. The spring tidal range is about 2.1 m while the neap is about 0.75 m. The model is resolved at a horizontal spacing of 64 m and uses 20 sigma layers in the vertical direction. The model was validated against current velocities measured using an ADCP and good accuracy was achieved.

Activities of jellyfish within Killary were recorded by releasing tagged jellies in the harbour and tracking their patterns of movement with a number of stationary receivers. The jellyfish are modelled using EFDC’s particle transport module which includes advection and random diffusion. The model was used to simulate the transport of the tagged jellies and relatively good agreement was obtained. The modelled and measured jellyfish transport data have indicated that tidal advection accounts for the majority of their transport; this agrees with the literature. Killary Harbour is home to both salmon and mussel farms and the next phase of the research will involve scenario modelling to investigate potential interactions with aquaculture farms.