Influence of in situ temperature and maternal provisioning on the medusa-to-polyp transition in a year-round population of the scyphozoan Aurelia aurita

Abstract

Abstract We investigated how environmental conditions translate into reproductive success or failure in Aurelia aurita from the medusa to the polyp life stage. This study examined how: (i) settlement success and development of planula larvae and polyps vary across the year, (ii) the role of temperature in determining the successful settlement of larvae and growth of polyps, and (iii) the influence of maternal provisioning in the successful settlement of larvae and growth of polyps. Medusae were collected monthly from February to December 2019 from Horsea Lake, UK. Planula larvae were settled in conditions mimicking the in situ temperature and salinity of collection. For the individual treatments, planula collected in August settled most rapidly. Early development rates (<8 tentacles) were significantly higher than later growth rates (>8 tentacles) and were positively correlated with temperature, unlike later growth rates. Planula length, used as an indicator of maternal provisioning, varied significantly across the year. In July 2019, a high temperature anomaly coincided with an increased time spent by planula larvae in the water column. Increasing temperatures past thermal limits through the increasing occurrence of temperature anomalies is likely to be detrimental to larval settlement and indirectly to the replenishment of temperate polyp populations.