Exploring the Deep Ocean off Tobago

There’s more sea than meets the eye off Tobago. Enter the depths with Diva Amon, a deep-sea biologist who has explored the deep ocean in Antarctica, the Atlantic and the Pacific. She has experience in chemosynthetic habitats and anthropogenic impacts on the deep sea. You can find out more via her Twitter (https://twitter.com/DivaAmon) and her website (https://divaamon.com/). This feature was first published in the Tobago Newsday on June 22, 2017

                   

When you imagine Tobago, you see turquoise waters on the shores of beautiful white-sand beaches or glimpses of coral reefs teeming with colourful fishes. Few people ever give thought to what exists further out to sea from Tobago’s coast, where the sea turns from turquoise to deep blue. This is surprising given that most of the ocean surrounding our twin-island state is actually far below the reach of scuba divers; it extends to depths of nearly four kilometres. Our deep ocean is out of sight and out of mind but it is a place where weird and wonderful animals thrive in freezing temperatures, crushing pressures and in the absence of any sunlight. And just like on land, there are mountains, valleys, plains and coral gardens.

Diva Amon on board a research ship

Very little is known about the deep ocean around Trinidad and Tobago. To date it has not been mapped in its entirety! Apart from oil and gas companies, there have been only a handful of deep-sea research expeditions, with two having actually imaged the deep seafloor with Remotely Operated Vehicles (ROVs) or Human Operated Vehicles (HOVs or submersibles). The first of the two research expeditions was in the 1980s, led by a team of French scientists, and their findings were extraordinary. They discovered cold seeps southeast of Tobago, a type of deep-sea habitat that no one knew existed before 1983 when they were first discovered in the Gulf of Mexico. There were huge patches of 20-cm long Bathymodiolus mussels with 3-foot long tubeworms and ghost-like shrimp dotted between them. At the time of this discovery, nearly all of the species encountered were new to science and many were endemic to these cold-seep habitats.

The majority of life on the planet is part of a food web that is reliant on plants using light energy to create food (photosynthesis). There is no light or plants in the deep sea, so most deep-sea animals rely on food in the form of marine snow, dead plants, animals and fecal matter, that must drift thousands of metres from the sea surface to the seafloor. But at some deep-sea habitats such as cold seeps and hydrothermal vents, there is another way to get food: chemosynthesis! Bacteria use chemical energy from hydrocarbon fluids seeping from the seafloor to make food. These bacteria can be found inside or on the surfaces of animals, or growing in thick mats on the seafloor and are the basis of the food chain at cold seeps, like plants are on land and in shallow waters. Cold seeps are unique because they have a plentiful food source (bacteria) so animals living there can grow to large sizes rapidly and reproduce quickly, unlike in the rest of the deep sea which is very food limited. As a result, cold seeps are oases of life, patchy areas of huge abundances of unique endemic animals.

Thousands of deep-sea Bathymodiolus mussels and many Lamellibranchia tubeworms are seen at one of the cold seeps visited by the EV Nautilus in 2014. Photo credit: Ocean Exploration Trust.

An octopus surrounded by many sponges on the outskirts of one of the seeps. Both the octopus and sponge are thought to be new species. Photo credit: Ocean Exploration Trust.

There was no further exploration off Trinidad and Tobago until 2014, when Dr. Judith Gobin (University of the West Indies) and I ventured out on the EV Nautilus with other scientists from the Ocean Exploration Trust. We visited four sites with the ROV Hercules, two previously visited in the 1980s and two that had never been explored before. It was a humbling experience to have the privilege of seeing parts of not only Trinidad and Tobago but also the planet for the first time. At over 1.5 kilometres depth, we found fields of Bathymodiolus mussels and shrimp that stretched as far as the eye could see, as well as thickets of tubeworms. But there were other remarkable discoveries including several tentative new species such as a large species of sponge that fringed the mussel beds. There were also eel-like white fish that live among the mussels, since named Pachycara caribbaeum as they are only known from two small sites in the Caribbean. Several adorable purple octopuses were also spotted, so new to science that they do not even have a name! There were bizarre Hydrolagus ghost sharks, orange crabs, white squat lobsters and tree-like pink and purple corals. In total, there were at least 44 species observed in this small area, with over 20 being new records for our waters and many new to science.

Three of the main inhabitants of the deep-sea seeps southeast of Tobago, Bathymodiolus mussels, Alvinocaris shrimp and the eel-like fish, Pachycara caribbaeum.

Unfortunately, these newly discovered areas are already under threat. The economy of Trinidad and Tobago currently relies on oil and gas, and our reserves on land and in shallow waters are running low. As a result, we are being forced to explore deeper waters for new reserves, with exploitation expected to begin later this year. These cold seeps are Vulnerable Marine Ecosystems (VMEs) that will likely be irreparably damaged by drilling. This is especially tragic as science is struggling to catch up and we may lose species and habitats before we can study them. 95% of the deep ocean around Trinidad and Tobago has not been explored and we cannot know how best to protect the animals living there until we understand what exactly exists in the depths.