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paleontology

Living records of time

New species of marine invertebrates discovered on the coastline of São Paulo help to understand the evolution of the oceans

Every time he has to collect the small marine invertebrate animals used in his research, paleontologist Marcello Guimarães Simões suffers with his trips out to sea. As soon as the Progresso, the shrimp fishing boat adapted for research, leaves Ubatuba, on the north coast of São Paulo, his seasickness begins, only to end when he sets foot on land again. But not even this indisposition makes him give up his goal: catching small invertebrates known as brachiopods – similar to the mollusks found on beaches, with which they have only the shells in common – which are helping to understand the alterations that the marine environment has undergone over the last thousands of years, and in future, should make it possible to propose ways of recovering these areas.

Overcoming their indisposition and often a rough sea, Simões and Adilson Fransozo, both from the Institute of Biosciences (IB) of the São Paulo State University (Unesp), in Botucatu, have managed to collect, between 2001 and this year, some 5,000 specimens of one of the least studied species of brachiopods alive, the Bouchardia rosea – a task in which a team led by Michal Kowalewski, of the Virginia Polytechnic Institute, in the United States, took part. For being morphologically very similar to representatives of the same lineage that lived 60 million years ago, the Bouchardias are regarded as living fossils.

With two almost symmetrical and articulated shells, similar to those that become toys in the hand of children on the beach, these invertebrates are a sort of window that opens simultaneously into the past and into the future. This is due to the fact that they are helping to reconstitute in detail the marine environment in remote eras and to develop applied marine paleoecology, a science focused on assessing the deterioration of the environment and preventing its progress.

Since the beginning of work with the brachiopods collected off the coast of São Paulo, the team from Unesp that Simões is coordinating has overturned a few dogmas. The most recent results, published in July in Palaios, one of the most important magazines of the area, and presented in October at the annual encounter of the Geological Society of America, in Denver, showed that the current fauna of articulated brachiopods from the Brazilian continental platform is more diversified than previously imagined. Besides the Bouchardia rosea, a typically Brazilian invertebrate and the only articulated brachiopod known hitherto, the researchers found representatives of Platidia anomioidesTerebratulina sp and Argyrotheca cuneata, species that show affinities with those from Antarctica, the Caribbean, the Mediterranean and the South African portion of the Atlantic and Indian Oceans.

This diversity poses some queries on the distribution of brachiopods over the planet. Two questions that the researchers intend to answer as soon as possible are why Bouchardia rosea exists only in Brazil, and how the other species arrived here. They now know that distant relatives of Bouchardia rosea – such as B. conspicua, B. antarctica and B. transplatina – have a long geological history: some of them inhabited the oceans some 60 million years ago, after the extinction of the dinosaurs.

At the moment, fossils from the Bouchardia species and other kindred forms, like Bouchardiella , may be found in rocks in Antarctica, Australia, Argentina and Uruguay.Some 15 millimeters long and covered with pink shells of calcium carbonate, sometimes with tiny white stripes, B. rosea is the only known living species from the Bouchardiidae family that still inhabitants the seas, spread along the coastline of the states of São Paulo, Paraná, Rio de Janeiro and Espírito Santo. So far, the researchers do not know exactly when the species appeared.

“For reasons that are still little understood, while the populations of Bouchardia rosea show a distribution more to the north, along the western side of South America, other fossil species of the same genus have a more widespread distribution in the continents of the Southern Hemisphere and are found in Australia, in the Antarctic and, in the South American continent, in Argentina and Uruguay”, Simões points out. “Other studies suggest that the distribution of the species is a result of the modifications in the ocean currents that have taken place over the last few millions of years, during the evolution of the Atlantic”.

Another novelty is the depth at which the populations of Bouchardia may be found, sometimes with thousands of individuals in just 1 square meter. It used to be said that they lived in shallow waters, at a depth of up to 20 meters, with rare occurrences in waters over 100 meters deep. But the researches of the group from Unesp and the samples collected under the Program for Assessment of the Sustainable Potential for Live Resources in the Exclusive Economic Zone (Revizee) have shown that these organisms can live as deep as 550 meters down. The discovery expands the range of future studies, by showing that a species formerly found only in shallow water can occupy deeper and less studied habitats.

There may be a few corrections to the course of the research. On the basis of the sparse data on the biology of Bouchardia rosea , the specialists used to interpret the wayof life of the fossil species of this genus as similar to those of the Bouchardia rosea. Accordingly, they saw many occurrences of fossils as having been generated from being deposited from shallow waters, since until then the distribution of the live species was to a great extent restricted to shallow waters. “As we now know that the species occupies the seabed at depths of around 500 meters, it would be interesting to reexamine the occurrences of fossils in the light of the new data and to compare them with data derived from other sciences, like stratigraphy, which studies the origin and composition of layers of rock”, comments the researcher from Unesp.

Simões’s studies also suggest that the resurgent ocean currents (from very cold waters) may be fundamental for the development of populations of brachiopods. Once more, the evidence is moving in the opposite direction to what was known: it was imagined that these currents, rich in nutrients, would bring damage to these invertebrates, since they could block the filtering apparatus, called the lophophore, which drains the water and selects the nutritive matter. Finally, it was also verified that the brachiopods had a preference for given kinds of substrates – the Bouchardia grow in areas of the seabed where the concentration of calcium carbonate in the sediments varies from 40% to 70%.

The findings about the currents and the substrate in which they grow more easily are important clues for a global mapping of these populations, indicating in a clearer way where they may manifest themselves and the areas they may help to recover. “The shells provide reliable records about the recent history and the environmental and biological modifications experienced by that region of the Brazilian platform”, Kowalewski repeats. “Using data from the past, we have achieved information on the damage caused to nature by human action, giving a new direction to the activities of ecologists, geologists, paleontologists, biologists and environmental agencies”.

Kowalewski cites as an example a work by the University of Arizona, also in the United States, which in the mid-90’s and in collaboration with the team from Virginia, threw some light on the potential for so-called applied marine paleoecology, an area of research where live fossils like the brachiopods and the records from past ages have served as a point of reference for projects for recovering degraded areas.

With this kind of information, it has now, for example, been possible to develop a recovery plan for the delta of the Colorado River, near to the frontier of the United States with Mexico, an area that has suffered an intense environmental transformation with the construction of hydroelectric power stations. The dams put up since 1930 have greatly reduced the quantity of water that reaches the mouth of the Colorado River.

As a consequence, there has also been an increase in salinity, which has brought the risk of extinction to species of invertebrates like the Mulinia coloradoensis , a mollusk that used to serve as food for small fish, birds, and for the local population. To make things more complicated, there were few historical records of the environmental parameters of the river’s delta in the period prior to the dams.

This was the point where paleoecology went into action. The researchers collected samples of shells of the threatened invertebrates, which formed dense accumulations (surface deposits) along the delta. Next, in the laboratory, they determined the age of these shells, which varied between recent ones and up to 7,300 years ago. This is an essential detail, because it makes it possible for the researchers to access the geochemical information in shells formed at different epochs, as the animals secrete the calcium carbonate and form their shells in chemical equilibrium with the sea water. This analysis reveals, for example, how the environmental conditions – the temperature and salinity, amongst others – varied from hundreds to thousands of years ago.

This is how it became clear what the quantity of water to be discharged in the delta should be, so as to maintain suitable conditions for the survival of the Mulinia. The team from Unesp sought to follow a similar path. Although still at the embryonic stage, the researches are just as ambitious as the work carried out by the Americans. “Applied marine paleoecology is an area of enormous social importance that has only recently started to receive the attention it deserves”, explains Simões. “The study of the Colorado River is a landmark”. His laboratory holds samples of heaps of dead Bouchardia rosea shells and bivalve mollusks found in accumulations with thousands of specimens.

They were collected at 46 maritime stations, with depths of up to 45 meters, located at some 40 kilometers off the coast of Ubatuba, Caraguatatuba and São Sebastião, where they would arrive only after a four hour boat trip. Back to the laboratory, the researchers analyzed the shells from the point of view of an area of science that studies the preservation standards for organic remains, such as the degree of articulation of the shells and of fragmentation, alterations in color, or the rates of incrustation taking place during life or acquired after the death of these invertebrates – known as taphonomy. This was how they succeeded in discovering how these accumulations were formed and the origins of the shells deposits on the seabed.

Afterwards, the shells went on to the University of Virginia team, which checked the basic taphonomic characteristics. From there, they were sent to the Woods Hole Oceanographic Institution’s National Ocean Sciences Accelerator Mass Spectrometry Facility (Nosams) and dated with the carbon 14 technique, more suitable for dating substances up to 70,000 years old. Another batch went from Virginia to the George Washington University, where researchers took care of datings with amino acids, which work like biological clocks and indicate the time passed since the death of the organism.

“Although it has its limitations, dating by amino acids is a cheaper and quicker method than carbon 14”, Simões comments. The conclusion: the ages of the Bouchardia shells found on the north coast of São Paulo varied from zero (the organism had just died) to 20,000 years, with those that had up to 500 years predominating absolutely. Surprisingly, it is possible to establish complete series of ages at every 50 years, up to the range of around 500 years or more, and to determine how the environmental standards varied”, says the researcher.

In the next stage of work, the teams from Unesp and Virginia intend to invest in the geochemical study of the shells already dated, within the series of ages of up to 500 years or more – and they secrets they keep should be revealed by the analysis of stable isotopes. The specialists are going to compare the proportions amongst the chemical elements – such as carbon 13 and 12 and oxygen 18 and 16 – from the waters of the ocean with those recorded with Bouchardia shells from different epochs (today, and 500, 3,000 and 20,000 years old, for example).

The objective is to build up a historical line of environmental parameters, like salinity and temperature. Simões knows that there will more than storms and seasickness along this route. “If we were talking of a new species of dinosaur, the theme would be recognized rapidly”, he explains. “In the case of such small shells, the process is slower”.

The Project
Taphonomy of Brachiopods and Bivalves in Siliciclastic Environments of the North Coast of the State of São Paulo: Environmental Variation in the Taphonomic Signatures, Biostratinomic Style and Temporal Mixture amongst Taphocenoses
Modality
Regular Research Benefit Line
Coordinator
Marcello Guimarães Simões – Institute of Biosciences/Unesp
Investment
R$ 137,658.43

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