Abstract
Causes and consequences of jellyfish bloom formation are subject to controversial discussions worldwide. While medusae have been studied to a broader extent, the knowledge on polyp stages of scyphozoans is limited thus hampering reliable prediction of jellyfish bloom formation. This study describes the occurrence, abundance, habitat characteristics and interactions of scyphozoan Aurelia sp. polyp colonies with other fouling organisms in intertidal and subtidal sectors of Trondheimsfjorden (Norway). In total, 982 polyps were found on 70 substrata of varying material types during a field survey in spring-summer 2018 along a longitudinal gradient within and outside Trondheimsfjorden. The polyps were identified as Aurelia sp. based on molecular species identification. Most polyps were found in bays with macroalgae canopy on the down facing side of artificial and natural substrata (rocks, concrete, iron) and inside rock cracks. Polyp microhabitats included the surface of Ascidia mentula (solitary ascidian), increments of Pomatoceros triqueter (polychete) tubes and dead Balanus balanoides (barnacle) shells. Based on the deployment of settling plates, abundance of Aurelia sp. polyps ranged from 1.2 (± 0.7) to 0.12 (± 0.07) polyps cm–2. Settlement occurred either directly on the PVC settling plates or as epibionts on the ascidian Ascidia mentula and on barnacle shells of Balanus balanoides. This study provides insights into the potential of local Aurelia sp. polyps contributing to the seasonal occurrence and abundance of Aurelia sp. in fjord systems, where intensive blooms occur annually.
Highlights
Jellyfish blooms vary from weekly changes to decadal cycles (Lucas et al, 2012; Hosia et al, 2014; Licandro et al, 2015)
Polyp Counts The field survey provided a qualitative overview of the Aurelia sp. polyp colonies within and outside Trondheimsfjorden (Table 1)
Polyps were found on 70 substrata of varying material types at nine stations along the longitudinal gradient within and outside Trondheimsfjorden
Summary
Jellyfish blooms vary from weekly changes to decadal cycles (Lucas et al, 2012; Hosia et al, 2014; Licandro et al, 2015). Has a metagenetic life cycle, alternating between pelagic (ephyrae, sexually reproducing medusae, planulae) and benthic (asexually reproducing polyps/scyphistoma, podocysts, planulocysts) stages (Arai, 1997). Aurelia aurita can produce 1–18 ephyra per strobila within 18–60 days after settlement (Lucas et al, 2012). Benthic scyphozoan life stages as drivers of jellyfish blooms have received more attention (Marcus, 1998; Lucas et al, 2012; Duarte et al, 2013).
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