Fecundity and early life of the deep-water jellyfish Periphylla periphylla

Comparisons over 6 years of three Norwegian fjord populations of the deep-water scyphomedusa Periphylla periphylla are presented. A minor part of the population in Lurefjord is migrating to the surface during night, which benefits mating encounters by increasing abundance per unit volume and decreasing the distance between individuals. Simulations using a typical water-column density profile and Stoke’s law show that fertilized eggs released in the surface quickly reach a depth where light is insufficient for visual predators. Consequently, the distribution of the smallest juveniles was strongly skewed towards higher depths in all three fjords studied. Mature females in Sognefjord were 4–5 times less abundant than in Lurefjord and Halsafjord, but due to a larger size and strong exponential relationship between size and number of mature oocytes, the potential recruitment rate as recruits m−2 year−1 was not much different from the other two fjords. Nevertheless, the observed number of small (<1 cm) juveniles was 18–31 times higher in Sognefjord than in the other two fjords, and it is assumed that the deeper habitat (up to 1300 m) compared to the other fjords (up to 440 and 530 m) is a superior habitat for the early development of P. periphylla.publishedVersio

Assessment of investigation techniques for scyphozoan statoliths, with focus on early development of the jellyfish Sanderia malayensis

Statolith ageing techniques provide a useful tool in the study of age, growth, and population structure of several marine organisms. Previous investigations on scyphozoan statoliths demonstrated increased statolith numbers and size with increasing medusa size, as well as taxon-specific variations in statolith shape. Thus, statoliths are potentially useful for age determination and taxonomic studies on medusae. Unfortunately, studies on statoliths are difficult because of the fragile structure of the numerous tiny crystals and their hygroscopic nature. We evaluated the potential of various modified study techniques for scyphozoan statocysts and statoliths applied to early medusa stages of Sanderia malayensis Goette, 1886. Light microscopy was suitable to follow the increase of statolith numbers and sizes with age and allowed differentiation of various statolith shape types, which were confirmed by scanning electron microscopy. The use of the fluorescent marker calcein provided direct evidence for measurable statolith growth. Our results indicated that statoliths stopped growing after reaching a certain size while additional statoliths developed in the basal region of the statocyst. Micro-computed tomography data allowed visualization and morphometric measurements of statoliths, revealing interspecific differences that may be useful for phylogenetic studies. Statolith numbers were positively correlated with medusa age and bell diameter. Thus, statolith analyses could provide information on medusa age or size, both of which are important parameters for population structure analyses that are difficult to assess with currently applied techniques. Our study provides methodological bases for future studies to reveal further potential of scyphozoan statolith investigations for phylogenetic and ecological studies

Fecundity and early life of the deep-water jellyfish Periphylla periphylla

Comparisons over 6 years of three Norwegian fjord populations of the deep-water scyphomedusa Periphylla periphylla are presented. A minor part of the population in Lurefjord is migrating to the surface during night, which benefits mating encounters by increasing abundance per unit volume and decreasing the distance between individuals. Simulations using a typical water-column density profile and Stoke’s law show that fertilized eggs released in the surface quickly reach a depth where light is insufficient for visual predators. Consequently, the distribution of the smallest juveniles was strongly skewed towards higher depths in all three fjords studied. Mature females in Sognefjord were 4–5 times less abundant than in Lurefjord and Halsafjord, but due to a larger size and strong exponential relationship between size and number of mature oocytes, the potential recruitment rate as recruits m−2 year−1 was not much different from the other two fjords. Nevertheless, the observed number of small (<1 cm) juveniles was 18–31 times higher in Sognefjord than in the other two fjords, and it is assumed that the deeper habitat (up to 1300 m) compared to the other fjords (up to 440 and 530 m) is a superior habitat for the early development of P. periphylla