Evidence of nitrification associated with globally distributed pelagic jellyfish

Abstract

Often considered detrimental to the environment and human activities, jellyfish blooms are increasing in several coastal regions worldwide. Yet, the overall effect of these outbreaks on ecosystem productivity and structure are not fully understood. Here we provide evidence for a so far unanticipated role of jellyfish in marine nitrogen cycling. Pelagic jellyfish release nitrogen as a metabolic waste product in form of ammonium. Yet, we observed high rates of nitrification (NH4+ → NO3−, 5.7–40.8 nM gWW−1 [wet weight] h−1) associated with the scyphomedusae Aurelia aurita, Chrysaora hysoscella, and Chrysaora pacifica and low rates of incomplete nitrification (NH4+ → NO2−, 1.0–2.8 nM gWW−1 h−1) associated with Chrysaora fulgida, C. hysoscella, and C. pacifica. These observations indicate that microbes living in association with these jellyfish thrive by oxidizing the readily available ammonia to nitrite and nitrate. The four studied species have a large geographic distribution and exhibit frequent population outbreaks. We show that, during such outbreaks, jellyfish‐associated release of nitrogen can provide more than 100% of the nitrogen required for primary production. These findings reveal a so far overlooked pathway when assessing pelagic nitrification rates that might be of particular relevance in nitrogen depleted surface waters and at high jellyfish population densities.

Similarities between the biochemical composition of jellyfish body and mucus

“…Adult medusae of five scyphomedusae species ( A. aurita , C. fulgida , C. pacifica , E. inexpectata and R. pulmo ) were collected, following the protocol by Hubot et al. (2021 ), from Horsea Lake (UK), Walvis Bay (Namibia), the London Aquarium (UK), Port Elizabeth (South Africa) and the Isle of Portland (UK), respectively.…”

“…Our jellyfish organic matter (body and mucus) was rich in nitrogen (C:N = 3.7) compared with the global medians (6.6–7.4, Martiny et al., 2014 ) and to other marine zooplankton organisms (4.8–6.2 for crustacean zooplankton; Pitt et al., 2013 ). Jellyfish, particularly in high abundances such as during blooms, represent a storage of nitrogen-rich organic matter that can be supplied to the environment through excretion of inorganic nutrients ( Hubot et al., 2021 ) and mucus production ( Condon et al., 2011 ) or reach higher trophic levels through predation ( Hays et al., 2018 ). Subsequently, when a jellyfish dies and starts decaying, its body mass will be available for bacterial degradation.…”