A beachgoer who closely examines a handful of sand from the ocean might be lucky enough to find tiny, curved disks just a few millimeters in diameter that look like umbrellas without shafts as they move about in the sediment with the help of transparent bristles around the edges. These disks—bryozoans of the genus Discoporella—are colonies of nearly transparent creatures that, when in a safe environment, extend their tentacles to capture food. Apparently uprooted since it moves along the bottom, a recently discovered species of this genus, Discoporella gemmulifera, is part of a universe in miniature ignored by specialists until now: a grain of sand. In this strange habitat, researchers from Brazil and the United States have identified some twenty new species.
“Here is the grain,” says biologist Leandro Vieira of the Center for Marine Biology at the University of São Paulo (CEBIMar/USP), pointing out a nearly imperceptible irregularity in a photo of Discoporella. The first larva to attach itself there secretes an exoskeleton of calcium carbonate and starts reproducing asexually, forming a colony of clones. Then, when it reaches the proper size, the bryozoan can reproduce sexually, releasing spermatozoa into the water to fertilize other colonies. Having grown away from the grain of sand that served as the anchoring point for the larva, Discoporella chooses a habitat that is favorable but not typical of fauna that are being uncovered.
When he dives into the ocean 10 to 30 meters down and fills a glass flask with sand from the bottom, Vieira knows there will be a lot of work ahead. Once back in the laboratory, he spreads the sand around in trays containing seawater from spigots at CEBIMar. He then begins to examine it on a small plate under a powerful magnifying glass, of the kind that look like a microscope, using a painter’s brush to separate and turn the sand over one grain at a time. On the few millimeters of each grain could be a diversity of fauna that might include hydrozoans (related to jellyfish) and tubes secreted by polychaete worms, among other creatures. But they are not what he is looking for. Vieira is searching for somewhat indistinct, translucent clusters resembling groups of tiny compartments that are hard to detect even by a trained pair of eyes.
From Florida to Brazil
The idea of looking for bryozoans attached to grains of sand and shell fragments rather than rocks was suggested by American Marine Biologist Judith Winston of the Virginia Museum of Natural History. In 2002, Winston was at CEBIMar at the invitation of Alvaro Migotto, who at the time was in charge of coordinating the study of bryozoans as part of a project under the Biota-FAPESP program that was researching the biodiversity of the organisms that live close to the substrate.
Years earlier in Florida, Winston had discovered bryozoans attached to sand, but that observation was viewed as accidental. When she arrived in Brazil and examined the samples of sand that had been collected around Caraguatatuba and São Sebastião on the north coast of the state of São Paulo and stored in the Biota collection, she again came upon the tiny bryozoans, which she described along with Migotto in a 2005 article in Invertebrate Biology. “Even so, a lot of people did not believe it,” says Vieira, “but every time we went back to the same locations, we found those fauna, regardless of the time of year.”
When Vieira arrived at CEBIMar to work on bryozoans, he himself did not believe that this tiny fauna could spend its whole life clinging to grains of sand. Now he is convinced: in an article published in September 2013 in the journal Zootaxa, he and Winston identified 22 species of sand-dwelling bryozoans. “And we’ve already found more species since then. It’s a never-ending job!”
The resistance from the community of specialists also appears to have been overcome. At the conference of the International Bryozoology Association held in Italy in June 2013, Winston presented the findings and showed videos of bryozoans in action, feeding as they clung to grains of sand (available at cifonauta.cebimar.usp.br). At that same conference, there was a surprise: a presentation on bryozoans living in the sands of Australia. One of the authors, Eckart Håkansson, had worked with Winston on the article that revealed the life form in Florida in 1986. It took almost 30 years for similar studies to be conducted, on nearly opposite ends of the globe. “After that we exchanged emails and photos: the species have very similar features,” Vieira notes.
The 2013 publication is an initial catalog that includes 17 new species, 3 new genera and even a previously unknown family of bryozoans. We already know a little about the conditions favorable to the life of these animals. The size of the grains needs to be sufficient to host the visitors, and there must be little sediment on the seabed, since bryozoans have no way of choosing what falls into their tentacles. Coarse, irregular sand with abundant shell fragments appears to be a paradise. But the knowledge of ecology ends there.
All around the ocean
The current plans are to expand the catalog and our understanding of how these bryozoans live, migrate and diversify. One key tool will be the DNA sequencing of each of these species to form a large database. This will make it possible to examine the genetic material present in samples of sand—without the grain-by-grain process—and discover what organisms are living there. With this kind of wholesale approach, the researchers will be able to examine other points on the ocean floor, perhaps at greater depths and farther from the coast, and get an idea of the actual distribution of this sand-dwelling fauna. “We’re going to select new areas and examine parameters that can affect the occurrence of the animals, such as granulometry, pH, amount of dissolved oxygen, organic content in the sediment and movement of the water,” says Vieira, who in 2013 began post-doctoral research at CEBIMar and intends to learn about the factors that can influence the diversity of these organisms.
In any event, the findings could change the procedures used by those who specialize in fauna of the ocean floor, who are accustomed to washing the sand to collect the organisms of interest and then discarding it. It is worthwhile to look closer and not let any discoveries that could be attached to the grains escape.
Benthic marine biodiversity in the state of São Paulo (No. 1998/07090-3); Grant Mechanism Biota Program – Thematic Project; Coord. Antonia Cecilia Zacagnini Amaral; Investment R$2,047,637.90 (FAPESP).
WINSTON, J. E. and VIEIRA, L. M. Systematics of interstitial encrusting bryozoans from southeastern Brazil. Zootaxa. V. 3.710, No. 2, p. 101-46. Sept. 2013.
WINSTON, J. E. and MIGOTTO, A. E. A new encrusting interstitial marine fauna from Brazil. Invertebrate Biology. V. 124, No. 1, p. 79-87. 2005.