Body size dictates the pace of processes ranging in scale from cell to ecosystem. The decline in total abundance among increasingly larger pelagic organisms is known as size spectra. The slope of this decline neatly measures the efficiency with which microscopic algae at the base of the food web are transferred to big predators such as tuna.
Compared to taxonomic approaches or complex computer simulation models of the food web, size spectra provides a much simpler approach, built on ecological scaling laws. This size-based approach showed that small declines in phytoplankton amplify into much bigger declines in fish nearer the top of the food web. We found that even a small (16%) decline in phytoplankton would magnify into a serious (38%) reduction in the biomass of fish that could be supported.
This has major implications for managing the world’s major pelagic fisheries – these are often co-located in the hotspots that are most at risk of a decline in supportable fish.
