Recent Portuguese technological advances benefiting deep-sea biological research

  ^{(1) Portuguese Institute for the Sea and Atmosphere (IPMA), Lisbon, Portugal}

  ^{(2) CIIMAR - Interdisciplinary Centre of Marine and Environmental Research, University of Porto, Matosinhos, Portugal}

The deep sea and the mesopelagic zone (between 200 and 1000 m deep) in particular comprises more than 60% of the planet's surface and 20% of the ocean's volume, constituting a large part of the total biosphere and still representing an unknown world. Most of the world's fish species live in the mesopelagic zone, both in terms of number and biomass. Moreover, the mesopelagic zone presents a great diversity, with the dominant groups being crustaceans, gelatinous organisms, and cephalopods, in addition to fish. These species are generally small, dark in colour (black or red), have luminescent organs and/or, large eyes and mouths. Recent studies indicate that the globally calculated total mesopelagic fish biomass has been grossly underestimated, possibly by a factor of 10. The new assessment suggests a biomass around 10,000 million tons, roughly equivalent to 100 times the annual catch from the fishery (about 100 million tons).

Although much is known about the mesopelagic and the deep-sea communities and their functioning in marine ecosystems, much remains unknown, especially the role of many species in deep sea carbon sequestration. Advances in knowledge are relatively recent. For example, the discovery of hydrothermal vents and cold vents with unique ecosystems, which was only made in 1971. These hydrothermal ecosystems studies have revolutionised the knowledge of marine biology, by discovering modes of life different from those existing at low depths, and their potential for economic exploitation.

This advance in knowledge is only feasible due to the development of technologies that can take humans to depths where they cannot survive and/or technologies that make it possible to bring specimens from the deep sea and provide a set of conditions to keep them alive at the surface, so that studies and experiments can be carried out. Technologies for studying deep-sea organisms have improved significantly in recent years. Remotely operated vehicles (ROV) or autonomous underwater vehicles (AUV) are equipped with vision systems (cameras and light) and other mechanical systems, that allows them to acquire data, capture specimens, and perform in situ experiments.

A major difficulty preventing studies, on environmental and biological traits, of deep-sea species, is the low hydrostatic pressure at surface, causing that specimens captured at deep sea and brought to the surface usually arrive dead or dying. In this sense, one of the main needs identified was the development of a hyperbaric system with controlled high hydrostatic pressures, capable of simulating the environmental conditions unique to deep sea organisms allowing said experiments.

This need led to the HiperSea hyperbaric system, developed by a multidisciplinary team consisting of biologists from the Portuguese Institute of the Sea and Atmosphere (IPMA) and the Interdisciplinary Center for Marine and Environmental Research (CIIMAR), as well as electrotechnical engineers in the field of robotics and autonomous systems from the Institute for Systems and Computers Engineering, Technology and Science (INESC TEC), the Polytechnic of Porto - School of Engineering (ISEP) and by the company A. Silva Matos Metalomecânica, which led the technological development project.

With the objective of capturing deep-sea species and keeping them in good physiological conditions in the laboratory, allowing their reproduction in captivity at the surface, the project proposed to develop a mobile hyperbaric infrastructure. The hyperbaric infrastructure collects the specimens in the deep sea (to 1000 m deep) and transports them to surface, where another hyperbaric chamber mimics (high pressure, low temperature or extremely high, in the case of proximity to active volcanoes, and low luminosity) their habitat. The system developed will allow the survival, maintenance, and reproduction in captivity, at the surface.

The HiperSea hyperbaric mobile chamber, the transfer chamber and the hyperbaric aquarium, developed under the project “HIPERSEA - Hyperbaric System for Collection and Maintenance of Deep Sea Organisms”, was built and tested to be used on the bottom of the sea and/or coupled to a mesopelagic trawl, to capture mesopelagic species as well.

We started with the biological requirements and technical specifications that the hyperbaric chambers should have. The planning and construction of the hyperbaric system was carried out at the premises of the company A. Silva Matos Metalomecânica, in Aveiro.

The hyperbaric aquarium can support a small number (up to six) of medium-sized species (up to 400 g), maintaining a specific pressure, the desired temperature, the adequate physical-chemical parameters of the water (pH, PCO2, PO2 and ammonia) and the control of photoperiod. It also enables the administration of food.

The hyperbaric diving chamber is versatile and can be used to capture deep-sea pelagic and benthic species. When capturing benthic species, the diving chamber acts as a trap on the seabed. When capturing pelagic animals, the system is placed at the end of a mesopelagic trawl. The fabric of the net is luminescent to attract species. The depth at which the net is operated is decided with the help of an acoustic probe.

The entire prototype system was tested at sea on board the NI Mário Ruivo (Figure 2), in the Lisbon and Setúbal canyons, at depths that varied between 40 and 906m. All the captured species were deep-sea crustaceans (Figure 3), using the HiperSea prototype system on the seabed. Organic and luminous baits were tested, the latter using different frequencies and light intensity to attract the species. The mesopelagic trawls we were not so successful to capture species. The crustaceans captured in the two benthic dives were successfully transferred to the HiperSea prototype aquarium and remained very active after the transfer. Later, unexpected problems related to changes in the voltage of the electric current supplied to the prototype led to difficulties in maintaining the temperature of the water inside the chamber, which rose unexpectedly and led to the death of the animals.

After the at sea tests, we verified that the first prototype of the HiperSea hyperbaric system supports depths of up to 1000 m. In fact, we were able to place it on the sea floor at a depth of 906 m, corresponding to a pressure of 92 bar, always maintaining communication with the system and properly monitoring the environmental and biological parameters. Therefore, the tests at sea were extremely positive. Finally, it was also possible to verify the aspects that we can improve, such as the transportation of the system, its format, and the conditions for capturing and maintaining the species. Thus, the survey was crucial to assess the work and technological development carried out and to plan future developments.

The project is now concluded, but the prototype built is still operational. It is now imperative to find a way (research funds and/or opportunities) to pursue this technological development.