Benthic jellyfish dominate water mixing in mangrove ecosystems

Water mixing is a critical mechanism in marine habitats that governs many important processes, including nutrient transport. Physical mechanisms, such as winds or tides, are primarily responsible for mixing effects in shallow coastal systems, but the sheltered habitats adjacent to mangroves experience very low turbulence and vertical mixing. The significance of biogenic mixing in pelagic habitats has been investigated but remains unclear. In this study, we show that the upside-down jellyfish Cassiopea sp. plays a significant role with respect to biogenic contributions to water column mixing within its shallow natural habitat (<2 m deep). The mixing contribution was determined by high-resolution flow velocimetry methods in both the laboratory and the natural environment. We demonstrate that Cassiopea sp. continuously pump water from the benthos upward in a vertical jet with flow velocities on the scale of centimeters per second. The volumetric flow rate was calculated to be 212 L⋅h-1 for average-sized animals (8.6 cm bell diameter), which translates to turnover of the entire water column every 15 min for a median population density (29 animals per m2). In addition, we found Cassiopea sp. are capable of releasing porewater into the water column at an average rate of 2.64 mL⋅h−1 per individual. The release of nutrient-rich benthic porewater combined with strong contributions to water column mixing suggests a role for Cassiopea sp. as an ecosystem engineer in mangrove habitats.

Respiration Rates, Metabolic Demands and Feeding of Ephyrae and Young Medusae of the Rhizostome Rhopilema nomadica

Jellyfish (cnidarians and ctenophores) affect the marine food web through high feeding rates and feeding efficiency, but in contrast to their great importance in the ecosystem, our knowledge of their dietary requirements is limited. Here we present the results of respiratory and feeding trials of the rhizostome Rhopilema nomadica, the dominant scyphozoan in the waters of the Eastern Mediterranean, which often establishes massive swarms, mainly in the summer months. Through multiple measurements of oxygen demand in R. nomadica at bell diameters of 3–49 mm, we were able to assess its minimum energetic requirements. These, and the results of the feeding trials on individuals of the same bell diameter range, show that R. nomadica is a very efficient predator. When presented with prey concentrations of 100 prey items per liter, a single hourly feeding session provided between 1.15 and 3 times the estimated daily basal carbon requirement. Our findings suggest that R. nomadica is well adapted to its environment, the hyperoligotrophic waters of the eastern Mediterranean, able to efficiently exploit patches of plankton, possibly at rates even higher than what we observed under laboratory conditions.

Numerical Simulation to Investigate the Occurrence of Vortices at Double Vertical Pumps Intakes

The pumping station is widely used in our modern life. The occurrence of the vortex at pumpsump, which is causing air entering pipe intake, is a common problem in the design of pumps. Thisphenomenon, including surface and sub-surface vortex, may lead to damage to the pumping structure, highpower consumption, and loss in pump performance. In some requirements, the multiple suction pipes areusing to get the required flow. Due to this arrangement, the performance of the suction pipes will influence.This paper is aimed to investigate the occurrence of vortices around the flow pattern of two pumps by usingComputational Fluid Dynamic (CFD) code Fluent. This CFD model is based on solving Navier-Stockequations by finite volume method. The model of double suction pipes was investigated under five differentsubmergence depth (S) and five different suction velocities (v). The SST k-ω turbulence model was selectedfor the turbulence. The results showed that the air entering vortex does not appear when the submergencedepth (S) is equal or greater than 1.5 times from the diameter of the bellmouth for intake pipe (D). Thesurface vortex appeared obviously when the submergence depth (S) equals to 1.25D and the Froude numberat the bell is equal to or greater than 1.028, and appeared clearly when the (S/D=1) and Froude number isequal to or more than 0.77. The nearer attached wall vortex does not appear when the space from the centerof the suction pipe to the sidewall (C) equals 2 times of bell diameter.

Diet composition and some observations on the feeding ecology of the rhizostome Rhopilema nomadica in Israeli coastal waters

Since the mid-1980s, swarms of the rhizostome Rhopilema nomadica have been an annual phenomenon in Israeli Mediterranean coastal waters during the summer months. Despite its annual prominence and the potential impact on food webs and ecosystem services, studies concerning its feeding ecology and its interactions with other biota in the marine food web have not been conducted. During summer 2015 gut contents of 41 R. nomadica were analysed as well as ambient plankton assemblages. More than 60% of the medusae diet was found to consist of microzooplankton <150 μm. Size correlations revealed that larger R. nomadica consumed faster swimming prey while smaller medusae relied more on the slower swimming taxa. The medusan diet reflected most of the ambient plankton taxa, but no statistically significant correlations between the relative abundance in diet and ambient plankton were found. As summer progressed, there was a gradual decrease in both mean medusa bell diameter (from 42.2–16 cm) and integrity of feeding structures. These findings suggest that R. nomadica, at least at the time of its appearance in Israeli coastal waters, may exert less predatory pressure on the plankton than we might otherwise expect.

Benthic jellyfish dominate water mixing in mangrove ecosystems

Water mixing is a critical mechanism in marine habitats that governs many important processes, including nutrient transport. Physical mechanisms, such as winds or tides, are primarily responsible for mixing effects in shallow coastal systems, but the sheltered habitats adjacent to mangroves experience very low turbulence and vertical mixing. The significance of biogenic mixing in pelagic habitats has been investigated but remains unclear. In this study we show that the upside-down jellyfish Cassiopea sp. plays a significant role with respect to biogenic contributions to water column mixing within its shallow natural habitat (< 2 m deep). The mixing contribution was determined by means of high-resolution flow velocimetry methods in both the laboratory and in the natural environment. We demonstrate that Cassiopea sp. continuously pumps water from the benthos upward in a vertical jet with flow velocities on the scale of centimeters per second. The volumetric flow rate was calculated to be 212 l h−1 for average sized animals (8.6 cm bell diameter), which translates to turnover of the entire water column every 15 minutes for a median population density (29 animals m−2). In addition, we found Cassiopea sp. are capable of releasing porewater into the water column at an average rate of 2.64 ml h−1 per individual. The release of nutrient-rich benthic porewater combined with strong contributions to water column mixing, suggest a role for Cassiopea sp. as an ecosystem engineer in mangrove habitats.Significance StatementWater mixing is a critical process for aquatic life. Coastal mangrove habitats are vital nurseries for commercially and ecologically important species, but these sheltered habitats experience little water mixing. The upside-down jellyfish, Cassiopea sp., occurs in circumtropical mangrove habitats at high densities. They are epibenthic and pulse nearly continuously, producing a vertical current that transports hundreds of liters of seawater per hour. This results in turnover of the entire water column every 15 minutes for an average population. Additionally, Cassiopea sp. can greatly expedite the transport of nutrient-rich water from sediments into the water column. Thus, Cassiopea sp. represents a previously unrecognized ecosystem engineer that can affect primary productivity, nutrient distribution, and alter new habitats as their range is expanding.

Record of Aggregation of Alien Tropical Schyphozoan Rhopilema nomadica Galil, 1990 in the Mediterranean Coast of Egypt

Recently, annual swarm of invasive Erythrean schyphozoan RhopilemanomadicaGalil, 1990 appeared along Egyptian Mediterranean coasts causing beach closures and fishing problems. The present study conducted survey and field monitoring on R. nomadica during blooming season in the Egyptian Mediterranean coast throughout three consecutive years (2015-2017). Three main features of R. nomadica bloom were addressed; viz starting date, duration and maximum density of aggregation. In 2015, the bloom started on 28 July, and over the following two years the bloom starting date shifted earlier being 19 July in 2016 and 15 June in 2017. The duration of the bloom varied yearly giving the longest duration in 2017 when the bloom continued in high density for a month. The highest density of R. nomadica was about 896 medusae/1000 m3 in 2017. The medusae diameter ranged between 21 to 112 cm. The average bell diameter for each year displayed gradual increasing values over the years. The consistent annual R. nomadica blooming was attributed to the high level of eutrophication and ecosystem degradation occurred along the Mediterranean coast since last decades. The shifting in the annual bloom starting date and duration may reflect the adaptation of R. nomadica to the climate change effect on the Mediterranean Sea temperature.

Two new species of Hydromedusae from Queensland, Australia (Hydrozoa, Leptothecata)

Two new species of small hydromedusae were found during routine monitoring in coastal waters of eastern Australia and are here described. The first,MelicertissaantrichardsoniUribe-Palomino &amp; Gershwin,sp. n., from Moreton Bay, Queensland, is placed in its genus because of its possession of both cordyli and eight-fold symmetry. It differs from its congeners in two conspicuous features: firstly, having small, oval split gonads located adjacent to the base of the stomach, and secondly, in its extremely small size at maturity (2 mm bell diameter, compared to the next smallest species at 7 mm). Moreover, it possesses a unique combination of other characters. This species appears to be endemic to Moreton Bay. The second new species,ParaloveniayongalensisGershwin &amp; Uribe-Palomino,sp. n., from the Great Barrier Reef, Queensland, is placed in its genus because of its two opposite normal tentacles and two opposite marginal clusters of cirri. It differs from its congeners primarily in a more rounded body than the others; the shape, length, and position of its short spindle-shaped, distal gonads; possession of subumbrellar nematocyst clusters; and possession of statocysts. These discoveries bring the total number ofMelicertissaspecies to eight and the total number ofParaloveniaspecies to three. The discovery of these two micromedusae underscores the need for further examination of the often-ignored minute and/or gelatinous fauna.

Floating nurseries? Scyphozoan jellyfish, their food and their rich symbiotic fauna in a tropical estuary

Background The anthropogenic modification of trophic pathways is seemingly prompting the increase of jellyfish populations at the expense of planktivorous fishes. However, gross generalizations are often made because the most basic aspects of trophic ecology and the diverse interactions of jellyfish with fishes remain poorly described. Here we inquire on the dynamics of food consumption of the medusoid stage of the scyphozoan jellyfish Stomolophus meleagris and characterize the traits and diversity of its symbiotic community. Methods S. meleagris and their associated fauna were sampled in surface waters between November 2015 and April 2017 in Málaga Bay, an estuarine system at the Colombian Pacific. Stomach contents of medusae were examined and changes in prey composition and abundance over time analysed using a multivariate approach. The associated fauna was identified and the relationship between the size of medusae and the size those organisms tested using least-square fitting procedures. Results The presence of S. meleagris medusa in surface waters was seasonal. The gut contents analysis revealed that algae, copepods and fish early life stages were the more abundant items, and PERMANOVA analysis showed that the diet differed within the seasons (P(perm) = 0.001) but not between seasons (P(perm) = 0.134). The majority of the collected medusae (50.4%) were associated with individuals of 11 symbiotic species, 95.3% of them fishes, 3.1% crustaceans and 1.6% molluscs. Therefore, this study reports 10 previously unknown associations. The bell diameter of S. meleagris was positively related to the body sizes of their symbionts. However, a stronger fit was observed when the size relationship between S. meleagris and the fish Hemicaranx zelotes was modelled. Discussion The occurrence of S. meleagris was highly seasonal, and the observed patterns of mean body size through the seasons suggested the arrival of adult medusae to the estuary from adjacent waters. The diet of S. meleagris in the study area showed differences with previous reports, chiefly because of the abundance of algae that are seemingly ingested but not digested. The low number of zooplanktonic items in gut contents suggest the contribution of alternative food sources not easily identifiable. The observed changes in the composition of food in the guts probably reflect seasonal changes in the availability of prey items. The regular pattern in the distribution of symbionts among medusae (a single symbiont per host) and the positive host-symbiont size relationship reflects antagonistic intraspecific and interspecific behaviour of the symbiont. This strongly suggest that medusa represent an “economically defendable resource” that potentially increases the survival and recruitment of the symbionts to the adult population. We argue that, if this outcome of the symbiotic association can be proven, scyphozoan jellyfish can be regarded as floating nurseries.

Floating nurseries? Scyphozoan jellyfish, their food and their rich symbiotic fauna in a tropical estuary

The anthropogenic modification of basal trophic pathways is seemingly prompting the increase of jellyfish populations at the expense of planktivorous fishes. However, gross generalizations are often made because the most basic aspects of trophic ecology and the diverse interactions of jellyfish with fishes remain poorly described. Here we inquire on the dynamics of food consumption of the medusoid stage of the scyphozoan jellyfish Stomolophus meleagris and characterize the traits and diversity of its symbiotic community. S. meleagris and their associated fauna were sampled in surface waters between November 2015 and April 2017 in Málaga Bay, an estuarine system at the Colombian Pacific. Stomach contents of medusae were examined and changes in prey composition and abundance over time analysed using a multivariate approach. The associated fauna was identified and the relationship between the size of medusae and the size their symbionts tested using least-square fitting procedures. The presence of S. meleagris medusa in surface waters was seasonal. The gut contents analysis revealed that algae, copepods and fish early life stages were the more abundant items, and PERMANOVA analysis showed that the diet differed within the seasons (P(perm)=0.001) but not between seasons (P(perm)=0.134). The majority of the collected medusae (50.4 %) were associated to individuals of 11 symbiotic species, 95.3% of them fishes, 3.1% crustaceans and 1.6% molluscs. Thereby, this study reports 10 previously unknown associations. The bell diameter of S. meleagris was positively related to the body sizes of their symbionts. However, a stronger fit was observed when the size relationship between S. meleagris and the fish Hemicaranx zelotes was modelled. The ocurrence of S. meleagris was highly seasonal, and the observed patterns of mean body size through the seasons suggested the arrival of adult medusae to the estuary from adjacent waters. The diet of S. meleagris in the study area showed differences with previous reports, chiefly because of the consistent abundance of algae that are seemingly ingested but not digested. The low number of zooplanktonic items in gut contents suggest the contribution of alternative food sources not easily identifiable. The observed changes in the composition of food in the guts probably reflect seasonal changes in the availability of prey items. The regular pattern in the distribution of symbionts among medusae (a single symbiont per host) and the positive host-symbiont size relationship reflects antagonistic intraspecific and interspecific behaviour of the symbiont. This strongly suggest that medusa represent an “economically defendable resource” that potentially increases the survival and recruitment of the symbionts to the adult population. We argue that, if this outcome of the symbiotic association can be proven, scyphozoan jellyfish can be regarded as floating nurseries.

Floating nurseries? Scyphozoan jellyfish, their food and their rich symbiotic fauna in a tropical estuary

The anthropogenic modification of basal trophic pathways is seemingly prompting the increase of jellyfish populations at the expense of planktivorous fishes. However, gross generalizations are often made because the most basic aspects of trophic ecology and the diverse interactions of jellyfish with fishes remain poorly described. Here we inquire on the dynamics of food consumption of the medusoid stage of the scyphozoan jellyfish Stomolophus meleagris and characterize the traits and diversity of its symbiotic community. S. meleagris and their associated fauna were sampled in surface waters between November 2015 and April 2017 in Málaga Bay, an estuarine system at the Colombian Pacific. Stomach contents of medusae were examined and changes in prey composition and abundance over time analysed using a multivariate approach. The associated fauna was identified and the relationship between the size of medusae and the size their symbionts tested using least-square fitting procedures. The presence of S. meleagris medusa in surface waters was seasonal. The gut contents analysis revealed that algae, copepods and fish early life stages were the more abundant items, and PERMANOVA analysis showed that the diet differed within the seasons (P(perm)=0.001) but not between seasons (P(perm)=0.134). The majority of the collected medusae (50.4 %) were associated to individuals of 11 symbiotic species, 95.3% of them fishes, 3.1% crustaceans and 1.6% molluscs. Thereby, this study reports 10 previously unknown associations. The bell diameter of S. meleagris was positively related to the body sizes of their symbionts. However, a stronger fit was observed when the size relationship between S. meleagris and the fish Hemicaranx zelotes was modelled. The ocurrence of S. meleagris was highly seasonal, and the observed patterns of mean body size through the seasons suggested the arrival of adult medusae to the estuary from adjacent waters. The diet of S. meleagris in the study area showed differences with previous reports, chiefly because of the consistent abundance of algae that are seemingly ingested but not digested. The low number of zooplanktonic items in gut contents suggest the contribution of alternative food sources not easily identifiable. The observed changes in the composition of food in the guts probably reflect seasonal changes in the availability of prey items. The regular pattern in the distribution of symbionts among medusae (a single symbiont per host) and the positive host-symbiont size relationship reflects antagonistic intraspecific and interspecific behaviour of the symbiont. This strongly suggest that medusa represent an “economically defendable resource” that potentially increases the survival and recruitment of the symbionts to the adult population. We argue that, if this outcome of the symbiotic association can be proven, scyphozoan jellyfish can be regarded as floating nurseries.