Searching for jellyfish from space

Jellyfish (gelatinous zooplankton, including Scyphozoa, Cnidaria, and Tunicata) play important roles in marine ecosystems as predators, prey, and contributors to carbon cycling. Their blooms can reshape ecosystem dynamics, alter microbial communities, and, due to rapid sinking detritus, probably present an important component of the biological carbon pump. Despite their ecological significance, observational data on jellyfish abundance and distribution remain scarce, particularly in open waters, as large majority of in situ data are coastal.

Remote sensing offers a promising avenue, but its application is limited. Airplane and unmanned aerial vehicle (UAV) observations provide valuable insights but cover small spatial areas. Current satellite-borne instruments lack the spatial and spectral resolution to directly detect jellyfish. To address this, we utilized laboratory data on jellyfish decay and nutrient release to inform a recently coupled physical-biogeochemical model (CROCO-BFM). The model simulates spatiotemporal phytoplankton response to jellyfish bloom decay, producing sea surface Chlorophyll a (Chl-a) patterns indicative of mass mortality events.

We then analyzed CMEMS (Copernicus Marine Service) multi-satellite daily L3 Chl-a maps (1 km horizontal resolution) using principal component analysis to detect localized Chl-a anomalies. Comparing these anomalies with model predictions and in situ observations allowed us to identify potential matches with jellyfish blooms in the northern Adriatic Sea. This approach highlights the potential of indirect satellite-based methods to track jellyfish bloom dynamics and their ecological impacts on marine ecosystems.