Seamount diary: December 2009

An unidentified octopus discovered at a depth of 500m

A new project led by the IUCN (International Union for Conservation of Nature) plans to unveil the mysteries of seamounts in the southern Indian Ocean, and help improve conservation and management of marine resources in the area.

A team of the world's leading experts, paired with scientists from the western Indian Ocean region, has been nominated by the IUCN and its partners to join the Norwegian research vessel Dr Fridtjof Nansen.

Leaving Reunion Island on the evening of November 12, 2009, the vessel is sailing towards the southwest Indian Ocean Ridge, where it will study six seamounts rising from the ocean floor located between 32°00' S and 41°00' S, before ending its voyage in Port Elizabeth, South Africa, on 20 December.

A seamount echogram. The thick blue layer at the summit of the seamount represents the deep scattering layer (see A little background on the science, Tues 1 Dec, below)

Sarah Gotheil, Marine Programme Officer at IUCN, is onboard the vessel, capturing every aspect of the work.

The expedition is supported by expertise and funding supplied by partner organisations including; the United Nations Development Programme, the Global Environment Facility, Zoological Society of London, the EAF-Nansen project, the Institute of Marine Research, Agulhas and Somali Current Large Marine Ecosystems Project, the Marine Ecology Laboratory, University of Reunion and the African Coelacanth Ecosystem Programme.

MONDAY 21 DECEMBER - HOMEWARD BOUND

Land ahead! As we woke on Friday morning, we could see the coast of South Africa and knew the harbour of Port Elizabeth awaited us.

Arrival didn't mean the end of the work, though, and during the few days that separated us from our flights back home people were busy cleaning the ship and packing the samples.

The majority of the species collected will remain in South Africa, while a few will be shipped to England.

Before getting there, however, we had two last stations to study.

After Coral seamount and the "roaring forties", we sailed northward accompanied with a gale force wind towards Melville bank, the last seamount that we investigated on the southwest Indian Ocean Ridge.

A Bean's sawtoothed eel (Serrivomer beanii) captured at 500m

Melville turned out to be very different from Coral, and much more similar to the first seamounts that we studied.

It was a bit like returning to familiar grounds, although it brought its own surprises.

Among the species that we have collected, the barreleye was certainly one of the most special.

Then we finally left the southwest Indian Ocean Ridge and steamed northward for two days to reach the last seamount of this cruise, south of Madagascar.

The area that we reached is called Walters Shoal - an enormous underwater plateau, with areas as shallow as 10 metres from the surface!

For our investigations, though, we went to a much deeper seamount, at about 1200 metres from the surface.

Initially, one of the main reasons for choosing this area was that it was known to attract seabirds, and Barau's petrels in particular, that come to feed here at this time of year.

Unidentified fish caught at 700m

We did not encounter as many seabirds as expected, but at least were back in a pleasant climate.

We also made some great catches, including a scorpionfish, a pelagic butterfish and a shorthorn fangtooth.

The very last trawl came up with the first octopus of the expedition, a ghostly looking squid and a tiny crustacean larva with impressive spikes.

Although the adventure at sea came to an end, the work is really just starting.

Many scientists will be busy analysing the data and working on the specimens collected for the next few years.

The next important step will be the organisation of a scientific workshop to identify all species caught and look at the stomach contents of certain specimens.

A scorpionfish captured 700m above the summit of the final underwater mountain.

We hope that the former work will lead to the discovery of species new to science, while the latter will help us better understand the food chain in the areas surveyed.

Additional analyses will be carried out on the oceanographic work to improve our comprehension of the currents around the seamounts, and on the acoustics data.

All in all, it has been a very successful 40-day expedition over 6000 miles.

We gathered a very rich collection of data and specimens, and encountered a higher diversity of species than expected.

Nearly 7000 individual species or group of the same species have been labelled, and some were recorded for the first time in the region.

A barreleye fish, which has huge eyes within a dome-shaped translucent head

The species collection includes an impressive variety of fish, shrimps, squids and gelatinous marine creatures.

Many more microscopic species of phytoplankton and zooplankton, representing the base of the food chain in the ocean, have also been collected.

The two seabird and marine mammal observers recorded thousands of seabirds from as many as 36 species, and 26 marine mammals.

It was also extremely interesting to discover that the six seamounts we surveyed are very different from each other, and we believe that our findings will certainly improve our global knowledge of seamount ecosystems.

THURSDAY 10 DECEMBER - THE ROARING FORTIES

After nearly two days of steaming, we reached the southernmost station that we have planned to investigate, at about 41° south.

It is a site off the southwest Indian Ocean ridge that would allow us to compare it to the other sites on the ridge.

We thus crossed the subtropical front and entered what is known as the roaring forties, an area famous for rough winds and waves.

But thankfully, we were welcomed by calm waters, as well as a thick fog, which rendered the atmosphere surprisingly unearthly.

Scientists hope snowboarding scaleworms will colonise their whale bones

The air was colder and more humid, and the water temperature had dropped by 9°C!

As we had expected and to our great delight, the species were very different from what we saw on the ridge further north.

After a few days of investigations on this site, we went back to the ridge to study a seamount named Coral, also located in the roaring forties.

Like Atlantis seamount, this feature has been set aside on a voluntary basis as a protected area by the Southern Indian Ocean Deepsea Fishers Association.

As its name indicates, deep-sea coral communities are thriving on the seamount, and are thus protected from the potential impact of bottom fishing gear.

We very much look forward to coming back in two years time with the ROV to actually be able to see and film these communities of corals.

Redmouth whalefish (Rondeletia loricata) caught at 900m

As we did on Atlantis, we sunk a stack of whale bones and branches of mango tree onto Coral, which we will recover during the next cruise.

We hope that the bones and wood will have been colonised by communities of scavengers, including snowboarding scale worms, so that we can study these whale fall communities of the Indian Ocean.

We found that the fauna of the waters surrounding Coral Seamount was different to the other seamounts we surveyed.

Species of fish usually associated with seamounts were not caught in our pelagic trawls but instead a species of rattail fish was found that occurs in Australia, New Zealand and the Madagascar Ridge.

A silver spinyfin (Diretmus argenteus) found at 900m

Squids were much less abundant and diverse, and the crustacean fauna was also different with some large prawns taken in deeper trawls.

We had crossed into quite different waters, much colder and more typical of the Sub-Antarctic regions than the waters north of the sub-tropical front.

This also showed in the birds surrounding the ship which were dominated by Southern Ocean species such as wandering albatross, cape pigeons and prions.

The weather also ended up living up to the fearsome reputation of the roaring forties.

After a few days of relative calm we were punished by five days of gale force westerly winds that battered the ship for the last few days at Coral Seamount and pursued us all the way to Melville Bank (140 nautical miles to the north), the last seamount that we will investigate on the ridge, before going further north to Walters shoal, south of Madagascar.

A little background on the management
(by Dr Alex David Rogers)

The other reason we are here - other than the scientific - is that in humankind's search for fish in the oceans, fishers began to target seamounts because of their abundant fish populations.

However, when exploitation of seamounts began there was very limited knowledge about the biology of the fish stocks that were being targeted.

The giant mysid Gnatophausia zoea is among the largest of free-swimming crustaceans (900m)

It came as terrific surprise when it was realised that seamount fish species like orange roughy, oreos and cardinal fish, live for more than 100 years, grow extremely slowly and are very late in maturing to reproduce.

It turned out that many seamount fish stocks were extremely vulnerable to overfishing and given that many of them were located in the high seas where there was no control on fishing effort, many stocks crashed very rapidly.

In addition, it was discovered that the main method of fishing, bottom trawling, was highly destructive to seabed communities on seamounts which were formed by animals like corals.

Some of these have now been aged to more than 4000 years old (although typically ages are tens to hundreds of years old), and are unlikely to recover from severe impacts from fishing.

Phytoplankton (microscopic plants) produce half of the oxygen present in the Earth’s atmosphere

The South West Indian Ocean Ridge was subject to a major boom-bust fishery for deep-sea fish species in 2000 - 2002.

However, fishing still continues on the ridge, although at a lower level than earlier this decade and, furthermore, some of the main fishing companies have got together to voluntarily protect some of the seamounts.

Thus we aim to identify why commercial stocks of fish are found on the South West Indian Ocean Ridge (and therefore elsewhere); how important the seamounts are to other marine life, including birds and whales; and to make our findings available to the fishing industry and managers of fisheries in the region, to help develop ecosystem-based precautionary management of high-seas seamount fisheries.

Our study will help to confirm the conservation benefits of protecting seamount features on the ridge and will inform future management of high seas deep-sea ecosystems globally.

In 2011, we will return again and investigate the seabed communities of the seamounts to examine whether vulnerable marine ecosystems, such as coral reefs, occur on the ridge.

TUESDAY 1 DECEMBER - SAPMER BANK & THE MIDDLE OF WHAT

We reached Sapmer bank, the second seamount we have planned to study, at the beginning of the third week on the ship.

We were looking forward to being able to discover another underwater mountain and compare it to the first one.

Sapmer turned out to be a really exciting site, with many animals and a great diversity of species, cephalopods in particular.

An anglerfish (Melanocetus johnsoni) which lives 1000m down

We were thrilled to see our first anglerfish, the famous "black devilfish" portrayed as the monster of the deep.

Sapmer is very different from Atlantis seamount.

While Atlantis looks like the ideal cone-shaped seamount with one summit plateau, Sapmer is a rugged structure with many pinnacles and a complex topography.

Its plateau is also much larger than Atlantis's and rock falls can be quite clearly seen along its flanks.

We've gathered some initial evidence that the tides may be washing deep cold currents up the slopes of the seamount and bringing rich and productive water to its top, acting like an upwelling.

This may explain why we have seen such a high diversity of creatures, including predators such as seabirds and whales.

A leaping humpback whale spotted

Once done with our work on Sapmer, we went on to visit a seamount named Middle of What.

This site turned out to be equally exciting in terms of species diversity.

However, the highlight of our little stay on Middle of What remains the two humpback whales that jumped around just a few metres from the ship for 30 minutes.

A wonderful and unforgettable show!

A little background on the science (by Dr Alex David Rogers)

Why are seamounts important and why are we studying them in the South West Indian Ocean, hundreds of nautical miles from the nearest land?

Most of the deep-sea is inhabited by a very sparse (but diverse) community of animals.

This is because most of them rely on particles of food raining down from the sea surface where photosynthesis takes place.

Gigantocypris (rear view), caught at 700m

As this food - known as marine snow, because it looks like snowflakes - sinks it gets consumed and so only a small part reaches the seafloor.

Seamounts are different, as some of them harbour striking communities of animals living on the seabed as well as an abundance of fish.

They also appear to be hotspots for ocean predators such as sharks, tuna, whales, seabirds and seals.

Scientists have proposed several mechanisms for why this happens.

Early theories suggested that because seamounts act as an obstruction to the flow of ocean currents they could cause nutrient rich deep waters to rise to the ocean surface, acting like fertiliser to stimulate production by microscopic marine plants called phytoplankton.

Rosenblattia rubustus caught at 700m

However, early work using echosounders around seamounts, suggested that layers of animals that live in oceanic waters may act as a food source to the animals on seamounts.

These layers - known as the deep-scattering layer (DSL), because they reflect sound and are visible on echosounders - undergo the world's largest daily migration, rising towards the sea surface at night to feed, and then sinking back into the dark depths by day to avoid being eaten themselves.

It has been suggested that these layers of animals may drift over seamounts at night when they are shallow.

Then when they try to migrate downwards at or before dawn they are set upon by the seamount residents.

The amphipod Eurythenes gryllus (700m)

One of the reasons we are studying the South West Indian Ocean Ridge is that the seamounts along it occur at a variety of depths and in different currents and provide us with a range of environments to try and understand what is making seamounts biological hotspots.

Is it enhanced productivity, or is trapping of the DSL, or is there some other mechanism at work?

To investigate the different aspects of seamount ecosystems we need to include very different types of scientific observations.

Thus we have on board specialists working on phytoplankton, planktonic animals, fish, echosounders (acoustics), and on ocean currents (oceanographers).

Portraits of each cruise participants will soon be available on the cruise blog!

TUESDAY 24 NOVEMBER - OUR FIRST SEAMOUNT

At 6am on the morning of the 17 November, we reach our first seamount, named Atlantis.

We can tell we've been travelling southward: the temperature has dropped by a few degrees, the wind is stronger, the sky more cloudy and waves higher.

The visible wildlife is also different: we've identified four different species of albatrosses (Shy, Wandering, Indian yellow-nose and Northern royal).

They may have travelled all the way from the Antarctic, and some of the birds have been following the ship for a few days, probably in the hope of a meal.

On the hunt for a bone-eating snotflower worm (Osedax mucofloris)

Atlantis seamount has an interesting history. It used to be an actual island some 100,000 years ago before it became submerged.

If closely observed, fossil beaches can even be noticed!

Atlantis, a 15 kilometres long feature, has its summit at 700m from the surface and goes as deep as 4000m.

It has been set aside on a voluntary basis as a benthic protected area (i.e. a non-fishing zone) by the Southern Indian Ocean Deepsea Fishers Association.

Before our arrival, very little information on the species thriving on and around Atlantis was available.

As seamounts are known to be hotspots of biodiversity, we had rather high expectations as regards the variety and the multitude of species we would collect above Atlantis.

The reality turned out to live up to our hopes!

Amazing creatures, from tiny transparent animals that look like terrestrial scorpions to a 2-metre-long dealfish, including fish, larvae, squids, crustaceans and jellyfish were captured.

A Stemonosudis fish species caught at a depth of 700m

We also gathered our first evidence of how seamounts are different to the open ocean.

During the night many predators rise into the waters above the seamount preying on the creatures from the surrounding ocean.

Atlantis appears to be a biological hotspot, an oasis in the ocean!

We've spent three full days fishing and taking oceanographic measurements, including during the night. Operations on a research vessel usually take place 24 hours per day, 7 days a week, weather permitting…

Heteropod with shell caught at 350m

A stack of whale bones, mingled with thick branches of mango tree, were also sunk by one of our scientists onto the seamount.

As we did, you may wonder why this was done?

Fascinating communities, mainly made of worms, develop and thrive on whale bones.

They live in conditions that are comparable to those found on hydrothermal vents: they do not live off solar energy, like the great majority of ecosystems on earth, but exploit chemically-based energy.

The discovery of these so-called chemosynthetic habitats in the 1970s shattered the conviction that life was impossible without sunlight.

While we start to have a database of these worms from around the world, we don't know anything about them in the Indian Ocean.

A white-chinned petrel and storm petrel dance on the waves

The plan is to come and collect the colonised bones and wood back in two years time, when the second cruise is in the area.

One of our birdwatchers was also lucky enough to see a whale, live this time, a sperm whale that was quietly roaming around, just a few metres from the ship.

Towards the end of the week, we started making our way down to the second seamount called Sapmer bank. We even passed above several seamounts that we believe to be unnamed features.

To our knowledge, Sapmer has been fished in the past, and is still targeted by the deep-sea fishing industry.

It will be interesting to see whether there is a difference in biodiversity and biomass between a fished and a protected seamount.

TUESDAY 17 NOVEMBER - HITTING THE HIGH SEAS

This first week - half of which was spent on land and the other half on the vessel - may well have been the most hectic week out of the whole expedition.

The first part of the scientific team arrived on Reunion Island on November 7, followed a day later by the other part of the team coming from South Africa and Madagascar.

It was the first time that we all met - 15 people of eight different nationalities (French, Swiss, South African, Malagasy, Mauritian, German, British and Norwegian) who were going to spend six weeks together on a vessel in the middle of the Indian Ocean.

We spent Sunday and Monday discussing the finalisation of the cruise plans, including the location and number of stations we would survey and the surveying methods we would use at each investigation point.

An unknown species of squid, caught at a depth of between 45-70m

The meeting ran really smoothly. But our arrival at the port on Tuesday morning was a bit chaotic.

Traffic delays meant that as we arrived at the dock, we just had enough time to throw our luggage into our respective cabins, and welcome a group of local schoolchildren, showing them everything from the laboratories, the acoustic room, the research equipment, the kitchen, the dining room, the wheelhouse, to the TV/library area and the gym.

After a few intense hours, we finally got a chance to get familiar with our new home and its friendly Norwegian crew.

But it didn't take long before a black cloud spoiled this beautiful sunny day.

We got informed that we wouldn't be able to leave the next day, as planned, as the ethanol that we were expecting from South Africa had not yet arrived.

Unknown species...

The alcohol is a key product, as it is used for species preservation, thus it was not thinkable leaving without it.

We ended up losing a precious day and half, out of a tight 40 day schedule.

At last, at 7pm on November 12, we left the port of Reunion Island.

It was a very particular and moving moment, as we realised that we were leaving land and civilisation behind us for quite some time, and that we were all together sharing an adventure, in this confined habitat in the middle of nowhere.

The work started slowly but surely, as it will take a few days before getting to the first seamount.

The first experts on duty were the birdwatchers, who were lucky enough to see about 1000 sooty terns - the most common species of seabirds in the western Indian Ocean area - on their first day of watch.

An unknown species of lightfish

We also took some initial oceanographic measurements.

The week ended with the launch of the first fish net and the first catches of marine species (pictured).

They give us a little glimpse into the biodiversity of the Indian Ocean and a foretaste of what we might find around the seamounts.

We are all thrilled about this adventure, as we know that very few people have been in this area before.

We are conscious about the pioneering dimension of this cruise, as very little biological studies have been undertaken to date in the high seas of the Indian Ocean.

We are also excited to think that we will most certainly come across species that are new to science - maybe we have already collected some?