Olms 鈥� amphibious salamanders that live in the western Balkans and Italy 鈥� are extreme divers, reaching depths in excess of 100 metres in dark lakes inside limestone caves.

A team of divers and biologists has now found the curious creature 113 metres below the surface of such a lake in Croatia.

鈥淭his was the deepest finding of the olm ever recorded,鈥� says team leader Petra Kova膷-Konrad.

Proteus anguinus is commonly dubbed the 鈥渉uman fish鈥� because of its pinkish pale skin, and the creatures were once believed to be baby dragons. They are noted for their slow lifestyle and long lifespan: these blind animals can live up to a century.

Little is known about olms, and it is a race against time to find out more as the salamanders鈥� underground habitat is being contaminated by pollution from human activities on the surface. The animals are notoriously difficult to observe in their natural habitat, except through the complex and dangerous skill of cave diving 鈥� although technology may be about to change that.

Croatian and international cave divers have found five new olm habitats in the past six years as part of the project run by . The lake where the creature was seen at record depth, Zagorska pec, is of particular interest as, unusually, several specimens have turned up there.

鈥淲e spotted specimens at many different depths in the lake, which confirms the assumption that depth of the water isn鈥檛 the stress factor for the olms,鈥� Kova膷-Konrad says. 鈥淲e also noticed that olms prefer specific parts of the cave system with less stressful conditions, such as slower water flow or bigger amount of sediment.鈥�

Recent discoveries of potential new habitats have been made using environmental DNA from cave water once it surfaces, and there are efforts to breed olms in captivity. Most observations of their behaviour involve captive animals, mainly in underground laboratories such as the ones in Postojna or Tular caves in Slovenia.

鈥淪tudy of the olms in greater depths is extremely important, especially when done by divers focused on conservation,鈥� says biologist Gregor Aljan膷i膷, head of the Tular cave laboratory. He suspects the olm will be found even deeper than the current record. 鈥淥ur previous findings indicate that Proteus can withstand significant pressure.鈥�

But it could be that the depths cave divers can reach will be the main determiner of how far down we find olms, says speleologist and biologist Gergely Bal谩zs, of the based in Bosnia and Herzegovina.

As for conserving the animals, information about their geographical spread will be more important than knowledge of the depths they can live at, he says.

鈥淚n some caves all across the olm鈥檚 distribution range you would see only one, and in other places you would see 200 of them during a dive,鈥� says Bal谩zs. 鈥淎nd there are some places where you can鈥檛 find any, but we still don鈥檛 know why.鈥�

Bal谩zs鈥檚 team is now trying to install infrared cameras in the caves to film the olms going about their business.

The fin fanning of damselfish in the聽Red Sea helps boost the rate of聽photosynthesis of the algae that live inside corals.

We already knew that the damselfish (Dascyllus marginatus) lives in symbiosis with the coral Stylophora pistillata. The fish use coral branches as shelters and nests, and in return they remove sediment from the coral surface and excrete nutrients. But it turns out there is more to the relationship.

Nur Garcia-Herrera at the Alfred-Wegener Institute in Germany and colleagues measured oxygen levels inside the branches of聽coral kept in tanks either with or聽without fish.

They found that photosynthesis rates were higher during the day in tanks containing fish, probably helped by the fish鈥檚 fin strokes wafting away water containing high levels of oxygen. The presence of fish increased photosynthesis by 22聽per聽cent.

鈥淭his is the first evidence of positive effects by a coral-associated fish on coral photosynthesis,鈥� says Garcia-Herrera.

Coral ventilation

The effect is probably smaller in the wild, she says, as the fish spend only about a聽third of their time in coral reefs, according to her team鈥檚 field observations. Even so, it may boost the coral鈥檚 photosynthesis by up to 6聽per cent.

鈥淢any corals live in environments where currents are low and the concentration of pollutants and ocean acidification parameters are high,鈥� says Garcia-Herrera. 鈥淭herefore, through the ventilation, the fish are helping the corals to cope with such hard conditions.鈥�

The ventilation by the fish could provide some relief from the build-up of warm water and excess oxygen among the coral branches, says Sebastian Ferse, Garcia-Herrera鈥檚 colleague at the Leibniz Centre for Tropical Marine Research in Germany. This may help to counteract the bleaching risk associated with global warming.

鈥淎nother important point is that fish may spend less time among the branches if their predators are removed, for example if reefs are overfished,鈥� says Ferse. 鈥淚n that case, the damselfish may opt to spend more time foraging outside the coral. Overfishing may thus have previously overlooked negative side-effects on coral physiology.鈥�

鈥淎ll types of fish living alongside corals have some function,鈥� says Petar Kruzic at the University of Zagreb, Croatia. 鈥淚t makes sense that ventilation helps coral.鈥�

But he says that rising sea temperatures and pollution are the main problems facing corals, and the new study doesn鈥檛 necessarily help with solving those.

They鈥檝e cracked it. Small ants carry home large seeds to eat all the time, but no one knew exactly how they managed to break through the seeds鈥� tough exterior.

It turns out that Florida harvester ants, Pogonomyrmex badius, have developed a clever farming strategy to do so 鈥� they plant seeds, wait for them to germinate and then eat the soft spoils.

Some 18 genera of ants harvest seeds, and colonies of some species can store more than 300,000 seeds in their underground granaries.

So far, scientists thought that ants must be able to break the seeds open and just ate them as they were. 鈥淭he reality is a lot more interesting,鈥� says Walter R. Tschinkel at the Florida State University.

鈥淭here are many studies of seed choice by forager harvester ants, but none of the authors asked the question of whether the ants can open the seeds,鈥� says Tschinkel. 鈥淭his may be in part because most of these studies were done on western harvester ants whose deep nests are in hard soil, so the seed chambers are not easily excavated.鈥�

With his team, Tschinkel excavated and studied approximately 200 P. badius nests and found that the ants mostly open and consume small seeds, which are easier to crack. Foragers collect seeds of all sizes, so this leads to the accumulation of larger seeds, which end up forming 70 per cent of stored seeds by weight.

In a series of lab and field experiments Tschinkel and colleagues showed that P. badius doesn鈥檛 seem to be able to open the large seeds unless they have germinated first. Even the caste of ants with large heads and mandibles thought to be specialised for seed opening can鈥檛 crack the big seeds.

Germination, on the other hand, splits the tough husk, making the seed contents available as food for the ants. A single large seed may have nutritional value of 15 smaller seeds, so it makes sense to collect it and wait for it to crack open. Seeds from various species germinate at different times, which may give the ants a steady supply of their 鈥渃rop鈥�.

This is the first example of ants relying on germination to consume large seeds, although some worms seem to do it, too. The only other example of ants farming plants for food is of the Fijian ant Philidris nagasau, which grows Squamellaria plants and harvests their fruit.

Read more: Crops farmed by leafcutter ants show signs of domestication; Ants use herbicide on their gardens; Worms seen farming plants to be eaten later for the first time