“Indirect development” increases reproductive plasticity and contributes to the success of scyphozoan jellyfish in the oceans

Ecologists and evolutionary biologists have been looking for the key(s) to the success of scyphomedusae through their long evolutionary history in multiple habitats. Their ability to generate young medusae (ephyrae) via two distinct reproductive strategies, strobilation or direct development from planula into ephyra without a polyp stage, has been a potential explanation. In addition to these reproductive modes, here we provide evidence of a third ephyral production which has been rarely observed and often confused with direct development from planula into ephyra. Planulae of Aurelia relicta Scorrano et al. 2017 and Cotylorhiza tuberculata (Macri 1778) settled and formed fully-grown polyps which transformed into ephyrae within several days. In distinction to monodisk strobilation, the basal polyp of indirect development was merely a non-tentaculate stalk that dissolved shortly after detachment of the ephyra. We provide a fully detailed description of this variant that increases reproductive plasticity within scyphozoan life cycles and is different than either true direct development or the monodisk strobilation. Our observations of this pattern in co-occurrence with mono- and polydisk strobilation in Aurelia spp. suggest that this reproductive mode may be crucial for the survival of some scyphozoan populations within the frame of a bet-hedging strategy and contribute to their long evolutionary success throughout the varied conditions of past and future oceans.

New Records of Cubozoan and Scyphozoan Jellyfish from Sabah Waters, Malaysia

Jellyfish play a vital role in the ocean’s ecosystem, acting as a nursery for young fishes, crabs, and brittle stars, as well as a source of food for certain charismatic megafauna, such as sunfish and sea turtles. They also pose a threat to human activities, with jellyfish blooms negatively impacting fisheries, power generation, and tourism. However, very little information is available on the biodiversity of jellyfish within the waters of Borneo. Here, we present new records of jellyfish found along the coast of Sabah, Malaysia, located in northern Borneo, bordering the megadiverse region of the Coral Triangle. A total of six species belonging to two classes and six families hitherto not recorded to the state are reported, Chironex yamaguchii, Acromitus maculosus, Crambione mastigophora, Linuche aquila, Netrostoma sp., and Phyllorhiza punctata. Of these, two species (C. yamaguchii and L. aquila) are harmful to humans, with C. yamaguchii capable of causing human fatalities. Reports of harmful jellyfish are useful to the medical and tourism industry, as some of these species may inflict stings and adverse reactions to humans ranging from rashes and skin irritation to fatal envenomation. A checklist has also been provided for all collected jellyfish species from Sabah waters of Borneo, Malaysia.

Citizens’ Eyes on Mnemiopsis: How to Multiply Sightings with a Click!

Monitoring the spreading of marine invasive species represents one of the most relevant challenges for marine scientists in order to understand their impact on the environment. In recent years, citizen science is becoming more and more involved in research programs, especially taking advantage of new digital technologies. Here, we present the results obtained in the first 20 months (from 12 July 2019 to 8 March 2021) since launching avvistAPP. This new app was conceived to track the spreading of the invasive ctenophore Mnemiopsis leidyi in the Adriatic Sea; it was also designed to collect sightings of 18 additional marine taxa (ctenophores, jellyfish, sea turtles, dolphins, salps and noble pen shell). A total of 1224 sightings were recorded, of which 530 referred to Mnemiopsis, followed by the scyphozoan jellyfish Rhizostoma pulmo (22%), Cotylorhiza tuberculata (11%) and Aurelia spp. (8%). avvistAPP produced data confirming the presence of Mnemiopsis (often in abundances > 20 individuals m−2) along almost the entire Italian coast in the summer of 2019 and 2020.

Population Structures and Levels of Connectivity for Scyphozoan and Cubozoan Jellyfish

Understanding the hierarchy of populations from the scale of metapopulations to mesopopulations and member local populations is fundamental to understanding the population dynamics of any species. Jellyfish by definition are planktonic and it would be assumed that connectivity would be high among local populations, and that populations would minimally vary in both ecological and genetic clade-level differences over broad spatial scales (i.e., hundreds to thousands of km). Although data exists on the connectivity of scyphozoan jellyfish, there are few data on cubozoans. Cubozoans are capable swimmers and have more complex and sophisticated visual abilities than scyphozoans. We predict, therefore, that cubozoans have the potential to have finer spatial scale differences in population structure than their relatives, the scyphozoans. Here we review the data available on the population structures of scyphozoans and what is known about cubozoans. The evidence from realized connectivity and estimates of potential connectivity for scyphozoans indicates the following. Some jellyfish taxa have a large metapopulation and very large stocks (>1000 s of km), while others have clade-level differences on the scale of tens of km. Data on distributions, genetics of medusa and polyps, statolith shape, elemental chemistry of statoliths and biophysical modelling of connectivity suggest that some of the ~50 species of cubozoans have populations of surprisingly small spatial scales and low levels of connectivity. Despite their classification as plankton, therefore, some scyphozoans and cubozoans have stocks of small spatial scales. Causal factors that influence the population structure in many taxa include the distribution of polyps, behavior of medusa, local geomorphology and hydrodynamics. Finally, the resolution of patterns of connectivity and population structures will be greatest when multiple methods are used.

Observations on the Feeding of Drymonema dalmatinum in the Gulf of Trieste

The largest scyphozoan jellyfish of the Mediterranean Sea, Drymonema dalmatinum was first described by Haeckel [1] from material collected off the Dalmatian coast of the Adriatic Sea [...]