Strange Trends: Jellyfish Biomass Doubles

The Bering Aleutian Salmon International Survey, or BASIS, has been conducting a study on Bering Sea jellyfish since 2004.  As the name suggest, BASIS is concerned primarily with Bering salmon populations.  However, the data produced by scientists monitoring the bycatch of the BASIS-coordinated surface trawls have revealed much about indigenous jellyfish populations.  Once the trawl nets are full, they are hauled aboard.  The jellyfish medusae (the non-polyp form of cnidarians) are then sorted by species.  Weight and bell diameter are recorded and biomass is calculated for each species.

Interestingly, the jellyfish biomass doubled from 2012 to 2013.  This was also the year of the highest recorded biomass since the beginning of the study.  It is important to note that in 2012, distribution was patchy, as half of the total catch came from one particular station.  In the 2013 portion of the study, however, the findings were more uniform across sampling areas. This may mean that there were actually more or less jellyfish than accounted for in the 2012 portion, because the densely populated patches may not have been indicative of overall biomass.

The study suggests that this sharp increase in biomass cannot be fully accounted for by changes in temperature and salinity.  The variation may be a result of environmental forcing, which can be defined as changes in an ecosystem’s abiotic factors, like climate, trophic interactions, and hydrodynamics (the movements of the ocean).

This substantial increase in the jellyfish population could seriously disrupt the Bering food chain.  Jellies feed on zooplankton and larval fish so their biomass stands to decrease, potentially with adverse effects on the entire ecosystem.


Lion’s Mane Jellyfish – the species with the largest biomass in the study

Photo copyright: Tim Nicholson at SCUBA Travel


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