The Water of the Sea, Rich in Jellyfish and Ctenophores

It is one of the most surprising findings of a study led by researchers from the Institute of Evolutionary Biology (IBE) and the Institute of Marine Sciences (ICM) (Spain). The gametes could have a relevant ecological role as a source of nutrients for marine microorganisms and zooplankton, and, therefore, in the carbon cycle. The study identifies a new group of animals and confirms that at least 85% of animal biodiversity is yet to be known.

As every summer, it is very likely that we dive into the sea and swallow some water by accident. A study led by researchers from the Institute of Evolutionary Biology (IBE) -a joint center of the CSIC and the Pompeu Fabra University (UPF) – and the Institute of Marine Sciences (ICM-CSIC) has discovered that, in addition to swallowing chemical compounds such as the sodium and magnesium chlorides and hundreds of unknown microorganisms, with each swallow of seawater we could be ingesting a large quantity of cnidarians (jellyfish) and ctenophores – some animals very similar to jellyfish. Also, researchers have identified a new group of urocordados, animals that are usually fixed on the seabed and are often confused with anemones.

The study is part of the European project BioMarKs, whose purpose is to study the diversity of eukaryotic unicellular organisms – that is, cellular organisms with a differentiated nucleus. Under the project, water columns and sediments of oxygen and oxygen-free environments were sampled at six sampling points scattered along the European coast: Oslo (Norway), Roscoff (France), Gijón and Blanes (Spain), Naples (Italy) and Varna (Bulgaria). The samples were filtered in order to separate the microorganisms according to their size; Then, the genetic material was extracted, which was sequenced.

Large amounts of the 18S gene, ubiquitous in eukaryotic cells and commonly used to identify them, were found in all samples as if they were a barcode. When studying the genetic material, it was observed that a large part of the 18S gene belonged to unidentified organisms. It would be acellmorphs, flatworms, quetognatos and nematodes. On the other hand, a new group of urocordados was identified.

The results confirm what many studies have already pointed out: although there are more than 1.5 million animal species described, it is estimated that there are at least 8.5 million more unidentified. Thus, most of the animal diversity is unknown, mainly microscopic animals, with a size less than 2mm3, and known as micrometazoos. “The results show that biologists still have a lot of work to do to understand marine animal diversity,” says Iñaki Ruiz-Trillo, ICREA research professor at the IBE, and also a member of the Faculty of Biology and the Research Institute of the Biodiversity of the University of Barcelona

The researchers observed a high percentage of genetic material in the smallest filtered fraction. Taking into account the small size of some animal gametes, they estimated that the genetic material most likely comes from the sperm of some metazoans with external fertilization, above all ctenophores and cnidarians. The proportion of sperm genetic material is especially abundant (33%) in samples without oxygen.

The water of the sea, rich in jellyfish and ctenophores

Given their abundance, the scientists point out that sperm could have an important role as a source of food for microorganisms and zooplankton, and that, therefore, it would have a notable impact on marine trophic networks that until now had gone unnoticed. “We ecologists have to seriously consider the role of sperm as a source of nutrients in the food web, especially during spawning periods, in which gametes are released into the environment in huge amounts,” explains Javier del Campo, ICM researcher.


Source: Noticias de la Ciencia


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