2018 Cruise - JC165

Searching for larvae in the deep sea!

So here I am again, about one year later, on the exact same site in the North Atlantic Ocean, the Porcupine Abyssal Plain Sustained Observatory (PAP-SO). This is among the oldest time-series stations in the world, which has been collecting data all the way from the surface of the ocean, across the water column to the seafloor, nearly 5 km deep. During just over three weeks, scientists, engineers and crew are working together to recover old instruments and deploy new ones in the ocean. The data collected with these instruments is transferred to the computers and laboratories onboard the ship, where they can look at the information and compare it with previous years.The kind of data collected are varied and include many chemical and physical parameters of the water, like oxygen, nutrients and temperature. During the cruise several other gear types (e.g. plankton nets, megacore, trawl and towed cameras) are used to collect biological information about small animals swimming around in the water (zooplankton) or buried in the sediment (benthic macrofauna and meiofauna), and larger organisms (megafauna) that live on the seafloor.

From such a comprehensive sampling program, scientists have been able to study patterns in diversity and abundance of the species and relate these patterns with changing ocean characteristics over the years. These long-term studies are very important to understand how natural changes, for example climate and food supply, and human activities (e.g. pollution, and overfishing) can impact the marine environment and its biodiversity. One critical aspect to know how marine animals survive and adapt to changing oceans is called population connectivity. In the same way that people travel around the world and move to new places, marine populations also exchange individuals among different geographic sites. While some of these movements are made by actively swimming between locations, others result from passive transport by oceans’ currents. But, how do species living on the seafloor disperse, and maintain populations across wide geographical areas? Most benthic animals have very limited movement, slowly crawling around (e.g. sea cucumbers and sea stars), or even staying at the same place for most of their life (e.g. mussels, anemones and sponges). However, many benthic species have a larval stage that can live in the water column and be transported hundreds or thousands of kilometres away from their parents.

Studying larvae from deep-sea species is extremely difficult because larvae are minute (a couple tenths of a millimetre) and very hard to collect in deep waters. Ocean observatories provide a great opportunity to test new sampling methods and standardize approaches, which may then be used simultaneously across the world to give us a global view of ocean’s health in space and time. With the goal to know more about larval diversity and distribution in the deep sea, I’ve started to deploy a series of larval traps in several deep-ocean moorings in the North East Atlantic and Mediterranean Sea. I also attached the traps to experimental substrates that larvae could use to settle and grow (see DY077 RRS Discovery cruise 2017), thus giving us a better understanding of population connectivity. Last Sunday, I collected the second set of samples from the sediment trap mooring at PAP-SO and preserved the samples onboard to observe them under the microscope when I return to my land-based laboratory at the University of Aveiro in Portugal.

recovery of larval traps
Figure 1.  Recovery of larval traps and colonization frames from PAP3 mooring

Last year, I also deployed traps attached to the Bathysnap mooring – a metal frame that hosts the time-lapse camera, but yesterday we couldn’t retrieve it. A malfunction of some kind has so far prevented the mooring from coming to the surface, so it is very likely still sitting on the seafloor. Next year, we may be able to bring an additional sonar to aid in locating and recovering the camera and also the larval traps and substrates. This misfortune may in turn reveal exciting new data since a longer time on the bottom will potentially allow more animals to fall in the larval traps and colonize the substrates. A new Bathysnap is now being prepared for deployment and I can’t wait to see what will come back next year.

larval trap recovery
Figure 2. Larval trap sample recovered from PAP3 mooring. 



Written by Luciana Génio.