The elusive life cycle of scyphozoan jellyfish – metagenesis revisited

Abstract

Massive proliferations of scyphozoan jellyfish considerably affect human industries and irreversibly change food webs. Efforts to understand the role of jellyfish in marine ecosystems are based on a life cycle model described 200 years ago. According to this paradigm the pelagic medusae is considered seasonal and alternates with the benthic polyp stage from which it derives. However, we provide evidence that a) the occurrence of several species of medusae is not restricted to a season in the year, they overwinter, b) polyp- and medusa generations are neither temporally nor spatially separated, and c) “metagenesis” which is defined as the alternation between sexual and asexual generations does not always occur. Hence we recommend additions to the current model and argue that the scyphozoan life cycle should be considered multi-modal, rather than metagenetic. The implications of these findings for jellyfish proliferations, including possible consequences and associated environmental drivers, are discussed.

Trophic relationships between the large scyphomedusa Chrysaora plocamia and the parasitic amphipod Hyperia curticephala

“…Conversely, our comparison of C:N ratios in the two tissues indicates that at the time of sampling, lipid contents were similar. This may be explained by the finding that in the study area, sexually mature C. plocamia mainly occurs between October and December, with their numbers decreasing rapidly thereafter (Ceh et al 2015). Therefore, gonad tissue of medusae collected in January may be relatively depleted in lipids.…”

“…In Mejillones Bay, the medusa stage of C. plocamia generally occurs between late in the Austral spring and early autumn (November-March; Riascos et al 2013). At the start of the pelagic season, the population is comprised mainly of large adult medusae; at the end, juvenile medusae are more common due to high adult mortality (Ceh et al 2015). Additionally, the burden of hyperiids was found to be high in the middle of the pelagic season of C. plocamia (Riascos et al 2012).…”

“…Adult, sexually mature medusae (bell diameter ≥27 cm; N = 8) were collected in surface waters up to 9 m depth, and juvenile medusae (bell diameter <27 cm; N = 11) were collected in deeper waters (15-25 m depth). The relationship between sexual maturity and body size of C. plocamia, described by a logistic model [% of maturity = 0.098/1 + e (15.855−0.551 bell diameter) ] (see Ceh et al 2015 for details), was used to classify individuals as adults or juveniles. Each animal was captured using a plastic bag to preserve associated hyperiids, stored on ice and immediately transported to the laboratory.…”

“…Considering that pelagic phytoplankton, macroalgae and benthic microalgae are the main sources of primary production in this area (Reddin et al 2015) and the fact that C. plocamia (Ceh et al 2015) and hyperiid amphiods (Fleming et al 2014) may use benthic resources, samples of macroalgae, particulate organic matter (POM) and benthic algae/biofilm were collected from subtidal locations on the Mejillones peninsula adjacent to Mejillones Bay to include them as potential energy sources in our analysis. Epilithic biofilm was scraped from rocks using a metal spatula, a 5 l water sample was collected for POM, and fronds of the dominant brown alga (Lessonia nigrescens) were collected, with tissue taken from frond areas of recent growth.…”

“…Apart from zooplankton, only three trophic levels of consumers are typically distinguished: small-size planktivorous fish (mainly the anchovy Engraulis ringens and the Pacific sardine Sardinops sagax), larger fish predators (including the jack mackerel Trachurus murphyi, the hake Merluccius gayi and cephalopods) and top predators (mainly tuna Thunnus orientalis, swordfish Xiphias gladius, southern sea lions Otaria flavescens and seabirds) (see Thiel et al 2007 and references therein). Although jellyfish may form dense aggregations and exert significant trophic impacts on copepods (Pagès et al 2001), fish eggs (Riascos et al 2014) and benthic fauna (Ceh et al 2015), they are rarely considered in trophic web models (Pauly et al 2009). Among schyphozoan jellyfish, Chrysaora plocamia is the most conspicuous and abundant in the HCS, whose seasonal proliferation affect human activities, including fisheries, aquaculture, desalination plants and tourism (Mianzan et al 2014).…”