Environmentally induced phenotypic variation in jellyfish polyps and medusae: Ecological implications.

摘要

Pelagic cnidarians (i.e., "jellyfish") are conspicuous components of marine coastal and shelf ecosystems worldwide. These gelatinous predators are receiving special attention due to their fluctuations in abundance often resulting in mass occurrences (i.e., blooms, swarms, aggregations) that can considerably affect the trophic ecology of marine systems worldwide and negatively affect human enterprise, including fishing by clogging nets aquaculture by causing fish death in pens, power generation and desalination by blocking intake screens, and tourism by causing injuries or death to bathers. Despite the negative socio-economic impacts of jellyfish blooms, the causes and mechanism of bloom formation remain poorly understood. Considering that the world's ocean conditions are changing (e.g., warming temperatures, eutrophication, acidification), by assessing the mechanisms and extent of environmentally induced responses in the benthic and pelagic phases of the life cycle of these cnidarians, we can further our knowledge of jellyfish ecology and better predict mass occurrences in space and time, as well as evaluate ecological strategies in response to environmental change. Thus, the overall goal of this research was to quantify the extent of environmentally induced effects on the phenotype of polyps and medusae, with emphasis on morphology and reproduction, in response to changes in the abiotic and biotic environment. Major findings included: 1) Size and shape of jellyfish polyps (Aurelia sp.9) was highly plastic to variation in temperature and food quantity. Environmentally induced polyp morphology had a significant effect on asexual fecundity, since polyp size positively correlated with the number of buds attached, and the number of new polyps produced and ephyrae stacked per polyp. These findings suggested that polyp asexual fecundity is likely ultimately limited by body size, which can be environmentally induced. In addition, polyp and ephyra traits are linked, and environmentally-induced variation in polyp morphology can be carried into the next life-cycle phase and affect the size and shape of ephyrae at release. 2) Jellyfish medusae exhibited environmentally induced geographic morphological variation; however, the extent of the response differed between species. Molecular analysis detected two distantly related Aurelia medusae co-occurring in the Gulf of Mexico. Morphology of individuals of Aurelia sp.9 was geographically structured, while morphology of medusae of Aurelia sp.12 was geographically invariant. These findings suggest that jellyfish have evolved different ecological strategies to cope with environmental change. 3) Morphology, behavior, and fecundity of medusae can be mediated by interactions with other species. Medusae of Aurelia sp.5 infected by parasitic larvae of the anemone Edwardsiella sp. were more abundant higher in the water-column, smaller, and had lower fecundity than healthy counterparts. These findings highlight the potential crucial role of parasites at mediating medusa population size in ecosystems worldwide.