Iakovleva, A., Morov, A.R., Angel, D. & T. Guy-Haim (2024). From ctenophores to scyphozoans: parasitic spillover of a burrowing anemone. Scientific Reports, 14, 20785. https://doi.org/10.1038/s41598-024-72168-7.
The Trouble with the Sessile Lifestyle
One of the most difficult processes of sessile marine organisms, those fixed in one place when adults, is the dispersion of larvae. Larvae are the immature forms of the adults, and sessile organisms usually release larvae into the water column. But a sessile adult has no control over the area where the larvae settle. One way to combat this challenge is by having parasitic larvae. However, scientists believe that parasitism is usually restricted to one or a few hosts within the same group. For example, larvae may only parasitize mammals.
Teams have found a family of burrowing sea anemones, Edwardiidea (genus Edwardsiella), has done just this. When Edwardsiella lineata larvae are dispersed, they parasitize the warty comb jelly (Mnemiopsis leidyi) during the short period of time during early developmental stages. A larva enters and later exits a comb jelly, followed by settling on the seafloor and initiating its adult life, or entering another comb jelly and repeating the process. For the first time, Edwardsiella carnea, a species closely related to E. lineata, was recorded by Iakovleva’s team utilizing two true jellyfish (Scyphozoans) as hosts, in addition to its previously recorded Ctenophore host.
Host, Host, Host
First, Iakovleva and her team identified all three hosts: the Scyphozoans Rhizostoma pulmo (native Mediterranean barrel jellyfish) and Rhopilema nomadica (invasive Indo-Pacific nomad jellyfish), and the Ctenophore M. leidyi. A total of 36 R. nomadica, 17 R. pulmo, and 59 M. leidyi were collected from three locations in the Israeli Southeastern Mediterranean Sea. They recorded any parasites, the parasite’s location in the host, and then removed the parasites to observe behavior and the continued development. Finally, the scientists did DNA extraction of the parasites and compared the DNA to confirmed DNA strands to determine the parasitic species.
The scientists determined that the parasites were 99% likely to be E. carnea. They found a total of 86 larvae in 4 R. nomadica, 7 larvae in 1 R. pulmo, and no larvae in M. leidyi. Iakovleva and her team found all larvae in R. nomadica in late March 2024 (temperature 19.4° C), and all larvae in R. pulmo in late April 2024 (temperature 22.2° C). Once the larvae were removed from the hosts, they swam freely in the lab.
How Switching may have Saved Their Lives
Iakovleva’s team are the first to show parasitic spill-over of the parasitic anemone, E. carnea, from a comb jelly host (Ctenophore, M. leidyi) into a true jelly host (Scyphozoa, R. nomadica and R. pulmo). They are also the first to study the larval developmental stages of E. carnea, and to record a description of a stage that was thought to be pre-parastic, but was determined to be one of the parasitic stages instead. They also determined larvae were integrated into Scyphozoan hosts by ingestion because they were only found throughout the digestion tract of the Scyphozoans. In contrast, E. carnea larvae were found throughout the entire body of the comb jelly hosts. This led the team to conclude that it is easier for E. carnea to burrow in and out of the entire body of comb jellies, and only possible to enter and exit Scyphozoans through means of ingestion and digestion.
Iakovleva reported that E. carnea was, until this study, only recorded in the Northeast Atlantic in the Ctenophore host Bolinopsis. They think by utilizing M. leidyi, the larvae were dispersed into the Mediterranean Sea, and then spilled over into the newly recorded Scyphozoan hosts. But, as none of the M. leidyi specimens had E. carnea larvae, Iakovleva’s team wonders if the Mediterranean population may have abandoned its Ctenophore hosts for good–
One of the biggest questions the team still has is the impact, if any, that climate change will have. R. nomadica and R. pulmo bloom at different times in the Mediterranean based on temperatures. And given the invasive nature of R. nomadica, and the changing of water temperatures, the effect on this parasite is unclear. Additionally, the exact mode of travel of E. carnea from the Northeast Atlantic to the Mediterranean is still unclear.
The team is curious about how exactly the parasitic spill-over occurred. As most parasites are restricted to a few host species, and related parasites are usually restricted to a group, to change from a comb jelly to a true jelly, two species that are extremely unrelated, is certainly a question left over from this study. Iakovleva and her team hope to continue to study E. carnea, answering these questions, and more.
Post Cover Image, is an image captured of an Edwadsiella lineata under a lab microscope. This image was captured by Riley Ann Secor, from Wikimedia Commons.
I am a PhD student in Biological Oceanography at the University of Rhode Island, Graduate School of Oceanography. I completed my M.Res in Ocean Science at the University of Southampton, and completed my B.S. in Biology at Florida State University. I study deep sea coral communities and hydrothermal vent communities, especially with a focus on how physical and geological variable drive organism distribution, diversity, and change over time. When I’m not focused on school, I work with reptiles, and spend a lot of time making art for my friends and family!