Bloom and bust: Why do blooms of jellyfish collapse?

Abstract

Research on jellyfish blooms has focused heavily on the factors influencing the production of blooms. Identifying the factors that cause blooms to collapse, however, is important for predicting the duration of blooms and when they are likely to disappear. We assembled studies from the literature to assess the persistence of populations of medusae, the timing of the disappearance of the populations and the potential cause of the populations' declines. We found 76 observations that met our criteria for inclusion that were derived from 33 studies and included 47 different taxa. Most populations exhibited strongly seasonal patterns of occurrence, but the population dynamics of the same or closely related species varied greatly across small spatial and temporal scales. Duration of occurrence was negatively related to latitude, but latitude explained only 8 % of the total variability, and no relationship existed when tropical species were excluded from the analysis. Senescence after spawning, infestations of parasites, food limitation, disease, low salinity, extreme water temperatures, predation and intertidal stranding were most commonly cited as causing blooms to collapse. Improving understanding of when and why blooms collapse will benefit coastal industries that are affected by blooms and greatly improve our understanding of how jellyfish blooms impact the ecology of the systems they inhabit.