Researchers describe five new species of marine invertebrates

Animals found on Brazilian coast belong to the family Didemnidae; research paves the way to discovery of chemical compounds.

By Noêmia Lopes

Agência FAPESP – In a paper published in the January issue of the journal Zootaxa, Brazilian researchers described five new species of ascidians. Commonly known as sea squirts, ascidians are marine invertebrates that generally form permanently submerged colonies.

When the larval stage of the animals is completed, they attach themselves to rocks, shells and shipwrecks, losing the ability to swim or move. Their best defense against predators is the production of chemical substances.

What attracts researchers, besides the opportunity to enhance taxonomic knowledge of the group, are the potential uses of these natural compounds, which can contribute to the development of new medical drugs and pesticides, among other products.

Some 120 species of ascidians had previously been described on the basis of exemplars found in Brazil. The five new species come from the coast of Bahia State; one of the five was also found off the coast of Espírito Santo. The team members who made the discovery are affiliated with the Federal University of Paraná’s Zoology Department (DZ-UFPR).

The researchers’ taxonomic analysis of the samples was supported by FAPESP through the Thematic Project “Investigation of metabolic and biotechnological potential of marine organisms in bioremediation processes and for the production of substances with anti-viral, anti-inflammatory and anti-Leishmania activities,” coordinated by Roberto Gomes de Souza Berlinck, a professor at the University of São Paulo’s São Carlos Chemistry Institute (IQSC-USP).

“Back in the 1990s, Professor Berlinck invited us to join his group in a partnership to look for marine invertebrates with interesting chemical properties. Some research had been done along these lines on sponges. Our focus, however, was on ascidians, which are less well known and have plenty of potential,” said Rosana Moreira da Rocha, a researcher at DZ-UFPR and coordinator of the studies that resulted in the paper published in Zootaxa.

There are some 3,000 known species of ascidians worldwide, 20% of them in the family Didemnidae, including the exemplars from coastal Brazil. Four of the five new species belong to the genus Didemnum and were found in Bahia (D. aurantium, D. flammacolor, D. lambertae, and D. longigaster). The other new species belongs to the genus Diplosoma (D. citrinum) and was found in both Bahia and Espírito Santo.

“Members of Didemnidae are generally promising in terms of chemical compounds, which are their only defense against predators,” Moreira da Rocha said.

“Exotic molecules obtained from research on ascidians have been explored worldwide for use in combating cancer,” she added. “However, preclinical trials are often aborted because of these animals’ high toxicity. The substances they produce can eliminate cancer cells, but they also destroy healthy cells. Nowadays there are different, more diversified targets, such as Parkinson’s, Alzheimer’s, leishmaniasis and malaria.”

With regard to ascidians specifically, Moreira da Rocha believes much remains to be discovered in Brazilian territory because vast areas of the coast have not yet been visited by researchers interested in these marine animals.

“Some of our coastal waters are naturally oligotrophic, deficient in nutrients, compared with the Pacific coast, for example. Nevertheless, we expect to continue finding new species,” she said.

Expeditions and analysis

The researchers from DZ-UFPR chose Bahia for logistical reasons (a partnership with the Federal University of Bahia provided the necessary support) and because the sea there is rich in biodiversity.

With support from FAPESP, their diving took place in 2004 and 2007, at depths of up to 15 meters.

The sites visited included shallow reefs off Salvador and the entrance to Baía de Todos os Santos (BTS): Ondina, Porto da Barra, Boião da Barra and Iate Clube.

Samples were also collected from points deeper inside BTS (Canal Madre Deus), the wreck of the Germania and artificial structures (North and South Breakwaters). “We photographed the ascidian colonies in situ and collected samples with and without substrate removal,” Moreira da Rocha said. “We then placed them in menthol dissolved in seawater for about two hours. This is because ascidians have bands of strong muscles, which have to be relaxed in menthol. Otherwise the material changes into compact tissue, which can’t be analyzed.”

The next step was to fix the ascidians in formalin and add dye because otherwise the characteristic transparency of zooids (the individual members of a colony), each measuring approximately 1 mm, would hinder observation under a microscope.

“Colonies are formed by a common tissue that covers groups of individuals and is sometimes pigmented, giving them all a certain color, such as red, yellow or orange. But each zooid inside this blob or layer is transparent and independent, filtering its own water, breathing and reproducing. It’s this tiny animal that we have to dissect and identify,” she explained.

For research purposes, ascidians must be collected during the reproductive cycle. “This isn’t a convention, but we know gonads are the structures that best typify species and differentiate them from each other,” she said.

Taxonomic classification took a number of years. Samples of the new species were then deposited at the University of São Paulo’s Zoology Museum, which holds one of Brazil’s main collections of ascidians, and with the Federal University of Paraná’s Zoology Department.

“We also shared the material with Professor Berlinck’s research group,” Moreira da Rocha said. “They’re working on extraction of chemicals, which will be tested to evaluate potential industrial applications.”

If interest arises in specific substances, they will not be obtained directly from ascidians. “We’re looking for models,” she said. “Once the biochemists understand the structure of a specific molecule, the next step will be to synthesize it by imitating its chemistry and hence its physiological effects.”

Other collection sites

Once or twice a year, the researchers from DZ-UFPR choose a site at which to dive repeatedly for a week, performing new surveys of ascidian biodiversity.

To date, they have surveyed locations on the coast of São Paulo State in partnership with the University of São Paulo’s Marine Biology Center (CEBIMAR-USP), Rio de Janeiro State with UERJ, the state university, and Paraná State, where research is ongoing.

“We also know about groups who are diving to survey this fauna in the states of Paraíba, Ceará and Pernambuco. So we’re confident that plenty of discoveries will be made in the Northeast of Brazil in the years ahead,” Moreira da Rocha said.

Collection dives performed in 2012 at Escalvada Island, Espírito Santo state, in partnership with Vila Velha University (UVV), resulted in the identification of an exemplar of Diplosoma citrinum, mentioned in the Zootaxa paper alongside the exemplar found on the coast of Bahia. “As we identify more widely distributed species, we compile all the occurrences and publish them in a single paper as evidence of ascidians’ territorial range,” Moreira da Rocha said.

Before the new discoveries, Bahia and Espírito Santo were each the source of 11 described species of ascidians.