A feast of the dead is taking place in the chilly, dark depths of the Arctic Ocean. Marine sponges may not appear to be very interesting, yet these animals (yes, animals) are intriguing organisms. Today we’ll look at their morphology, reproduction, and diet. Sponge habitats not only provide homes for a variety of creatures but also provide ingredients for medications. However, these exceptionally tough creatures are in danger.
Researchers report in Nature Communications, that a massive community of sponges, the densest population of these organisms seen in the Arctic, is consuming the remains of an old ecosystem to survive.
According to Jasper de Goeij, a deep-sea ecologist at the University of Amsterdam who was not involved with this research, the discovery demonstrates how opportunistic sponges are. Sponge evolutionarily “is more than 600 million years old, and they inhabit all sections of our world,” he said. Scientists may not be aware of all of them because many sponge habitats are difficult to access, he adds.
Sponges are mostly filter feeders that play an important role in nutrient recycling throughout the oceans. The presence of this colony, found by a research ship in 2016, has remained a mystery.
Sponges frequently appear to take advantage of the most abundant carbon sources, which may change when global warming changes the composition of the oceans. One key question will be how adaptable sponge-microbe associations are, and how quickly they evolve to exploit new carbon sources.Stephanie Archer
The sponges, which include the species Geodia parva, G. hentscheli, and Stelletta rhaphidiophora, reside between 700 and 1,000 meters below sea level in the central Arctic Ocean, where there are no currents to give food and sea ice covers the water year-round. Furthermore, sponges are largely immobile, but in 2021, researchers led by Teresa Morganti, a marine biologist at the Max Planck Institute for Marine Microbiology in Bremen, Germany, reported that these ones move slowly, using their spicules — microscopic skeletal structures — and leaving thick brown trails in their wake.
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Morganti and colleagues focused their attention in the current study on the matted layer beneath the sponge colony, which was a buffet of abandoned spicules and blackened petrified life, including empty worm tubes and mollusc shells. The scientists examined samples of sponges, mat material, and nearby water to see whether this dense mat was a food source. The researchers also looked at the genetic makeup of the bacteria that dwell within the sponge tissues as well as those that live in the sediment.
Carbon and nitrogen isotopes — atoms with differing amounts of neutrons — in sponge tissues closely matched those in the dead stuff below, indicating that the animals ate it. The bacteria’ genetic fingerprints revealed that they have enzymes capable of breaking down the substance and were most likely dissolving the dead organic stuff into food for the sponges.
The matted layer is up to 15 centimeters deep in spots, according to the experts. The team calculates that if the layer is more than 4 cm thick on average, it may give nearly five times the carbon that the sponges would require to survive.
The discovery that the sponges are feeding from below means they are likely moving to access more food, Morganti and colleagues suggest. The scientists also found many sponges to be budding, or breaking off parts to form new individuals, showing active reproduction.
Radiocarbon dating revealed that the adult sponges, which covered more than 15 square kilometers on the peaks of an underwater volcanic mountain range, were over 300 years old on average, a “truly outstanding” discovery, according to Paco Cardenas, a sponge expert at Uppsala University in Sweden who was not involved in the new study. “We expected sponges to grow very slowly,” he says, “but this had never been measured in the deep sea.”
According to the researchers, the dead ecosystem beneath the sponges is roughly 2,000 to 3,000 years old, a once-thriving population of organisms that lived in the nutrient-rich conditions established when the volcanoes were last active.
Sponges frequently appear to take advantage of the most abundant carbon sources, which may change when global warming changes the composition of the oceans, according to ecologist Stephanie Archer of the Louisiana Universities Marine Consortium in Chauvin, who was not involved in the research. “One key question will be how adaptable sponge-microbe associations are, and how quickly they evolve to exploit new carbon sources,” she says.
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