Freshwater bryozoan from the northern hemisphere

Freshwater bryozoans, such as this variety from the northern hemisphere, are little studied animals  © Lebendkulturen.de/Shutterstock

New arrivals of Amazonian moss animals boost the world's largest collection

After travelling to the Amazon rainforest to search for a group of animals known as bryozoans, Merit Researcher Prof Beth Okamura and colleagues at the Museum have brought back hundreds of new freshwater specimens, adding to what is now the world's biggest collection of these little-known creatures. 

Bryozoans are an ancient group of organisms, having diverged from the rest of the animal kingdom at least half a billion years ago.

They are colonies of individual creatures known as zooids. Typically half a millimetre in length, the tiny zooids use a crown of tentacles to filter food particles from the water before passing it on to a mouth that sits in the centre.

While at first glance bryozoans can look very similar to coral, this is where the likeness ends. The individual polyps that make up corals are incredibly simple animals effectively containing just a mouth and stomach. By comparison, zooids are far more complex.

Despite their diminutive size the little creatures pack a lot in. Not only do they have a mouth and a stomach, they have many other well-defined organs, including intestines and sex organs, as well as a distinct body cavity, muscles and even a separate anus. The individual animals are also able to share food with neighbouring zooids in the colony if one hasn't had enough to eat.

Bryozoan growing in the water

Freshwater bryozoans, such as this one from Florida, grow on submerged branches and vegetation © Flordia Fish and Wildlife/Flickr CC BY-ND 2.0 

Bryozoans are incredibly diverse and boast a global distribution. There are roughly 15,000 species known from the fossil record alone, with another 6,500 recognised today. The majority of these live in marine environments, usually found in warm, tropical waters to a depth of around 100 metres, although there are some deep-sea varieties known from oceanic trenches.

Species of freshwater bryozoans, however, are far less numerous. They are found in all freshwater habitats, ranging from lakes and ponds to flowing rivers and estuaries.   

'We don't really know very much about these freshwater bryozoans, particularly tropical freshwater species,' explains Beth. 'We are starting to get a better understanding of these animals, but there are still big gaps in our knowledge, particularly of those from Central Africa and South America.'

Into the Amazon

To redress this lack of knowledge, Beth and her colleagues have been out on multiple trips to the Amazon basin in the search of bryozoans in the flooded forests and waterways.

One of the main reasons for investigating the Amazonian region is that it is a cradle of diversification for many groups of plants and animals. Diversification of freshwater animals is especially well documented for fishes, but also for amphibians, aquatic mammals and birds. The stability of a warm, tropical environment during climate cooling in other places may have helped plants and animals to diversify in the Amazon.  

This has resulted in hundreds of thousands of species - including bryozoans - evolving right across the Amazon basin, from Colombia down to Bolivia and Peru across to Brazil.

The boat on which beth and her colleagues lived

Beth and her colleagues turned a boat into a floating laboratory © Beth Okamura

'The first trip that we took a couple of years ago was really successful,' says Beth. 'We found around four new species, including two new families. There was one species that is so amazingly different it suggested that this was just the tip of the iceberg of bryozoan diversity.'

On a return trip last year, the researchers set out to find even more. 

Uncovering more species

The Amazon rainforest has two major seasons: wet and dry. During the dry season, the water level drops and is restricted to the main river channels and streams, while in the rainy season so much water flows into the Amazon basin that the rivers such as the Amazon and Tapajós flood the surrounding rainforest.

While this is bad news for the terrestrial animals that are forced to climb trees or find higher ground as the water level rises, for the aquatic bryozoans the conditions are ideal, as colonies can then take advantage of new territory high up on tree trunks.

Going out on small boats into the flooded forests, Beth searched for the colonial animals on submerged branches and surfaces. These were then taken back to the boat on which the team were living, where the researchers were able to fully examine the specimens under a microscope in what was in effect a floating laboratory.

Examining bryozoans with a microscope

Beth was able to examine the bryozoans they collected using microscopes on the boat © Tim Wood

'We collected many hundreds of specimens,' says Beth. 'And already in this new material it looks as if we have at least six - and maybe more - new species.

'This material, together with that collected on our previous trip, makes the first real, substantial collection of bryozoans from Amazonia, which is of course shared with our Brazilian colleagues.' 

Implications for disease

Going through these samples, which arrived in the Museum at the beginning of the year, will help to answer questions about the animals' diversity and evolution in freshwater environments, something which has long been neglected.

But it could also help in research investigating certain diseases.

Some species of freshwater bryozoans are known to be hosts for worm-like parasites with complex life cycles, in which they exploit both freshwater bryozoans and fish. In North America and Europe, some of these parasites are known to cause a devastating kidney disease in farmed and wild fish.

'We haven't detected any parasites in the Amazonian bryozoans yet,' explains Beth, 'but evidence of infection in either the host bryozoans or fish could be of interest. Some Amazonian fishes are important food items, and biodiversity conservation is an increasing concern in the face of environmental changes in Brazil.

'Ultimately, by clarifying how bryozoans and their parasites have diversified within Amazonia, our research will both expand our general knowledge of the tree of life and reveal how these animals have radiated in this under-sampled and hyperdiverse region of the world.'

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