Gelatinous zooplankton—such as jellyfish and salps—have fragile, soft bodies and have lived in the world’s oceans for 500 million years. They consume food in the upper levels of the ocean, trapping carbon at the same time. Jelly-falls (or mass jellyfish deaths) occur when food sources become depleted. These jelly-falls are found on ocean floors. We studied the role that gelatinous zooplankton play in the carbon cycle, as well as the degree to which they trap carbon at different ocean depths.

 

Using multiple data sources, we estimated the biomass (mass of a community of organisms) of the three main gelatinous zooplankton: pelagic tunicates, cnidarians, and ctenophores. We mapped our results on a grid, averaged them by month and year, and identified four biomes (large communities of plants and animals). We then evaluated the carbon flux, which is the amount of carbon exchanged between the upper and lower levels of the ocean. The carbon flux we modeled consisted of particulate organic carbon, which is slightly larger than dissolved organic carbon.

 

Our modeling variables included assimilation efficiency (a measure of consumption), exudation and egestion (waste production), ingestion (consumed fuel), mortality (death rate), predation (being consumed by another organism), respiration (carbon dioxide release), and reproductive losses (death of offspring).

 

Key Findings:

• We revised the global mean biomass estimates for gelatinous zooplankton to be 13 times higher than previous estimates.

• The biome-based biomass analysis showed variable results based on the type of gelatinous zooplankton and the biome.

• There were significant carbon fluxes in the top 200 meters of the ocean due to gelatinous zooplankton.

• Of the three gelatinous zooplankton groups, pelagic tunicates contributed the majority (72%) of particulate organic carbon modeled because of their large fecal pellet production.

• Pelagic tunicate carcass production was much smaller, only 22% compared to 48% by cnidarians.

 

In line with other research, our model shows that the high sinking rates of gelatinous zooplankton-associated carbon, as compared to other forms of organic carbon, lead to fairly high transfer efficiencies from the surface of the ocean to the ocean floor. To validate our model, we compared the growth rates of the three gelatinous zooplankton types to existing research. We also compared values at point sites against known jelly-falls. According to our model, gelatinous zooplankton-mediated carbon flows produce globally significant outcomes.

 

Luo, Jessica Y., Robert H. Condon, Charles A. Stock, Carlos M. Duarte, Cathy H. Lucas, Kylie A. Pitt, and Robert K. Cowen. "Gelatinous Zooplankton‐mediated Carbon Flows in the Global Oceans: A Data‐driven Modeling Study." Global Biogeochemical Cycles 34, no. 9 (August 2020): 1-23. https://doi.org/10.1029/2020gb006704.

 

Salp colony

Photo by Peter Southwood, CC BY-SA 3.0