Jellyfish blooms are conspicuous demographic events with significant ecological and socio-economic impact, as they alter aquatic food webs. Despite worldwide concern about an increased frequency and intensity of jellyfish outbreaks, we are challenged to predict their booms and busts. To overcome this issue, we need to identify the ecological drivers of jellyfish blooms by taking into account the complex life cycle of scyphozoans (Cnidaria). Here we present demographic rates of all life stages of the cosmopolitan jellyfish Aurelia aurita s. l. within a stage-structured matrix model to investigate the life stage-dynamics of such complex populations under different environments. We illustrate how booms and busts of the medusa stage are highly influenced by non-medusa stage dynamics. We further point out increased food availability as an important ecological driver of jellyfish blooms, as it can shift the population structure of A. aurita away from the benthic polyp stage towards more medusae. Comparatively, our projected climate change scenario caused low fluctuations in population density. Overall, our study reveals ecological and demographic key variables that regulate the intensity and frequency of jellyfish blooms, and thereby contributes to a better understanding of anthropogenic drivers of jellyfish mass occurrence, including habitat eutrophication and climate change.
Species composition, population densities and size of jellyfish and ctenophores were recorded during 5 cruises in the heavily eutrophicated Limfjorden in 2014.No or very few ctenophores (Pleurobrachia pileus) and jellyfish (Aurelia aurita, Cyanea lamarckii) were recorded in April and June 2014, whereas in August and September numerous small individuals of the invasive ctenophore Mnemiopsis leidyi were found on all 4 locations studied, which were strongly reduced in population density during November.M. leidyi exerted a notable predation impact, most pronounced in Løgstør Bredning and Skive Fjord in August when the estimated half-lives of zooplankton were 4.8 and 7.3 d, respectively, and in late September, when the half-life in Skive Fjord was only 2.2 d.Severe oxygen depletion in Løgstør Bredning and Skive Fjord between June and September resulted in a release of nutrients.This was followed by a bloom of the dinoflagellate Noctiluca scintillans and a subsequent peak in the abundance of copepods which decreased rapidly after the introduction of M. leidyi into Limfjorden from the North Sea (between early April and mid-July) to become virtually absent during the rest of the season.This subsequently resulted in starvation and decay of the M. leidyi population.The small predatory ctenophore Beroe gracilis was recorded on most locations during August and September 2014 but although B. gracilis eats small M. leidyi, their low number suggested a negligible predation impact on the M. leidyi population.Our present understanding of the many biological and environmental factors that control the species composition, abundance and predation impact of jellyfish and ctenophore populations in Limfjorden are discussed.
Abstract. Studies investigating the effect of increasing CO2 levels on the phosphorus cycle in natural waters are lacking although phosphorus often controls phytoplankton development in many aquatic systems. The aim of our study was to analyse effects of elevated CO2 levels on phosphorus pool sizes and uptake. The phosphorus dynamic was followed in a CO2-manipulation mesocosm experiment in the Storfjärden (western Gulf of Finland, Baltic Sea) in summer 2012 and was also studied in the surrounding fjord water. In all mesocosms as well as in surface waters of Storfjärden, dissolved organic phosphorus (DOP) concentrations of 0.26 ± 0.03 and 0.23 ± 0.04 µmol L−1, respectively, formed the main fraction of the total P-pool (TP), whereas phosphate (PO4) constituted the lowest fraction with mean concentration of 0.15 ± 0.02 in the mesocosms and 0.17 ± 0.07 µmol L−1 in the fjord. Transformation of PO4 into DOP appeared to be the main pathway of PO4 turnover. About 82 % of PO4 was converted into DOP whereby only 18 % of PO4 was transformed into particulate phosphorus (PP). PO4 uptake rates measured in the mesocosms ranged between 0.6 and 3.9 nmol L−1 h−1. About 86 % of them was realized by the size fraction < 3 µm. Adenosine triphosphate (ATP) uptake revealed that additional P was supplied from organic compounds accounting for 25–27 % of P provided by PO4 only. CO2 additions did not cause significant changes in phosphorus (P) pool sizes, DOP composition, and uptake of PO4 and ATP when the whole study period was taken into account. However, significant short-term effects were observed for PO4 and PP pool sizes in CO2 treatments > 1000 µatm during periods when phytoplankton biomass increased. In addition, we found significant relationships (e.g., between PP and Chl a) in the untreated mesocosms which were not observed under high fCO2 conditions. Consequently, it can be hypothesized that the relationship between PP formation and phytoplankton growth changed with CO2 elevation. It can be deduced from the results, that visible effects of CO2 on P pools are coupled to phytoplankton growth when the transformation of PO4 into POP was stimulated. The transformation of PO4 into DOP on the other hand does not seem to be affected. Additionally, there were some indications that cellular mechanisms of P regulation might be modified under CO2 elevation changing the relationship between cellular constituents.
Abstract. Studies investigating the effect of increasing CO2 levels on the phosphorus cycle in natural waters are lacking although phosphorus often controls phytoplankton development in aquatic systems. The aim of our study was to analyze effects of elevated CO2 levels on phosphorus pool sizes and uptake. Therefore, we conducted a CO2-manipulation mesocosm experiment in the Storfjärden (western Gulf of Finland, Baltic Sea) in summer 2012. We compared the phosphorus dynamics in different mesocosm treatments but also studied them outside the mesocosms in the surrounding fjord water. In the mesocosms as well as in surface waters of Storfjärden, dissolved organic phosphorus (DOP) concentrations of 0.26 ± 0.03 and 0.23 ± 0.04 μmol L−1, respectively, formed the main fraction of the total P-pool (TP), whereas phosphate (PO4) constituted the lowest fraction with mean concentration of 0.15 ± 0.02 μmol L−1 and 0.17 ± 0.07 μmol L−1 in the mesocosms and in the fjord, respectively. Uptake of PO4 ranged between 0.6 and 3.9 nmol L−1 h−1 of which ~ 86 % (mesocosms) and ~ 72 % (fjord) were realized by the size fraction < 3 μm. Adenosine triphosphate (ATP) uptake revealed that additional P was supplied from organic compounds accounting for 25–27 % of P provided by PO4 only. CO2 additions did not cause significant changes in phosphorus (P) pool sizes, DOP composition, and uptake of PO4 and ATP when the whole study period was taken into account. About 18 % of PO4 was transformed into POP, whereby the major proportion (~ 82 %) was converted into DOP suggesting that the conversion of PO4 to DOP is the main pathway of the PO4 turnover. We observed that significant relationships (e.g., between POP and Chl a) in the untreated mesocosms vanished under increased fCO2 conditions. Consequently, it can be hypothesized that the relationship between POP formation and phytoplankton growth changed under elevated CO2 conditions. Significant short-term effects were observed for PO4 and particulate organic phosphorus (POP) pool sizes in CO2 treatments > 1000 μatm during periods when phytoplankton started to grow.
The individual choanocyte pumping rate in choanocyte chambers (CCs) is important for understanding the hydrodynamics in sponges and has hitherto been based on measured volume-specific filtration rate and estimated CC density. However, the CC density may vary in different regions of the sponge and to circumvent this uncertainty and to get precise measurements of the individual choanocyte pumping rate, a new experimental approach was developed. Here the aim was to measure the individual pumping rate of choanocytes based on live dimensions of CC elements and particle tracking to measure the speed of small particles entering into the CCs. This was done by using combined live-cell imaging in sandwich cultures of the marine demosponge Halichondria panicea and video-tracking of particles. Small 2 μm-beads and cyanobacteria (Cyanobium bacillare) in the incurrent canal enter the CCs via a 3.3 ± 0.9 μm diameter prosopyle to be subsequently captured by the choanocytes whereas larger algal cells (Rhodomonas salina) and 10 μm-beads are captured in the incurrent canals. CC diameters were positively correlated to the diameter of choanocytes, indicating a total of 84 choanocytes per CC with mean diameter 22.9 ± 6.2 μm. The pumping rate per choanocyte (Qc) was estimated to be between 54 and 68 μm3 s−1. Regardless of demosponge species and based on data in the literature, a choanocyte is suggested to pump between 50 and 100 μm3 s−1.
Abstract The aim of the present study was to gain insight into the hydrodynamic characteristics of the relatively simple aquiferous system in specimens of a calcareous syconoid sponge, Urna sp. Data on the morphology and ultrastructure of the sponge combined with measured pumping rates were provided and used for subsequent estimates of the pressure drops of water flow through the aquiferous system. The pumping rates were estimated from microscope video-recordings as the product of osculum-cross sectional area and exhalant jet speed. Estimates are given of the sensitivity of pressure drops to dimensional changes associated with observed dynamic, contractile structures (e.g., osculum, apopyles), as well as possible artefacts introduced in the preparations for ultrastructural studies. The estimated pressure losses showed that the choanocyte pumps provide a pressure of 5.5 ± 3.9 Pa at a pumping rate of 1533 ± 1089 µm 3 s −1 per choanocyte. Such high pumping rates, comparable to those of some choanoflagellates, have not been reported for syconoid and leuconoid sponges before. However, the corresponding sponge volume-specific pumping rates (about 10–30 min −1 ) are comparable to values reported in the literature for small sponges and explants that also have relatively higher pumping rates of choanocytes than larger sponges.
Jellyfish blooms may be important bioindicators for marine ecosystem degradation, including the accumulation of microplastics in pelagic food webs. Here we show growth, respiration and filtration rates of the moon jellyfish (Aurelia aurita s.l.) when fed high concentrations (350 L-1) of zooplankton prey (Artemia salina nauplii) and polystyrene (PS) or reference particles (charcoal; size range 50-500 μm). Our controlled feeding experiments reveal that inedible particles are ingested less efficiently compared to prey (retention efficiency ~60 % for PS) and actively removed from the gastrovascular system of ephyrae and medusae. Increased metabolic demands for excretion of inedible material (up to 76.7 ± 3.1 % of ingested prey biomass) suggest that overloading with microplastics can decelerate growth (observed maxima 26.1 % d-1 and 12.6 % d-1, respectively) and reproductive rates when food is limited. Possible consequences of this selective feeding strategy in response to proceeding microplastic pollution in the world's future oceans are discussed.
Microplastic particles are widespread pollutants in the sea and filter-feeding sponges have been suggested as useful monitoring organisms. However, the fate of microplastic particles in sponges is poorly understood, yet crucial for interpreting monitoring data. Here, we describe the fate of inedible (2 and 10 µm) plastic beads compared to that of edible bacteria and algal cells captured in the demosponge Halichondria panicea. Small Cyanobium bacillare cells entered the choanocyte chambers and were phagocytized by choanocytes, while larger Rhodomonas salina cells were captured in incurrent canals and phagocytized in the mesohyl. Likewise, 2 and 10 µm-beads were captured by choanocytes and in the incurrent canals, respectively, but subsequently expelled into excurrent canals and out of the sponge. SEM observations further indicated engulfment of plastic beads on the outer sponge surface. We conclude that sponges can efficiently capture but also quickly expel particles and therefore are not the ideal monitoring organisms.
