< POS520: Searching For Traces in the Open Ocean
01.03.2018 13:53 Age: 138 days

POS520: Exciting Discoveries

Bruce Robison, MBARI, climbing out of JAGO after a dive down to 350 m, welcomed back on board by the two technicians Peter and Ede / Bruce Robinson (MBARI) verlässt nach einem Tauchgang bis in 350 Metern Tiefe das Tauchboot JAGO. Die beiden Techniker Peter und Ede begrüßen ihn zurück an Deck. Photo: Karen Hissmann/JAGO-Team

Oceanographic pioneer Maurice Ewing is reported to have advised his students that the key to discovery is to take a new instrument to a place where no one has explored before. The midwater research conducted off the Cape Verde Islands during Poseidon Cruise 520 is a fine example of that research philosophy. The unique combination of technologies employed to examine the deep pelagic fauna of this poorly known region has yielded significant new perspectives and understanding of midwater ecology. The reason for this advance is pretty clear – we are using a unique combination of technologies: a manned submersible, a towed video profiler, and a multi-sample, discrete depth net system. These three tools, each with ancillary hydrographic instrumentation, provide an unprecedented data set with which to examine biodiversity, vertical structure, and ecology.

We are using these tools to conduct a comprehensive initial survey of the animals that inhabit oceanic waters surrounding the Cape Verde Islands. Integrated data streams will allow us to develop a picture of midwater community composition and structure. We will compare this picture with a reference community we have studied in the Pacific, off California. We will examine similarities and differences between the two communities in order to determine which environmental factors influence the community off Cape Verde, and how those influences are expressed. Much of the data for the reference community were collected there by three of the participants in Poseidon Cruise 520: Hoving, Osborn and Robison.

Many marine scientists believe that there is no substitute for the human eye and mind making direct observations in the habitat they wish to understand, whether it’s on a coral reef using scuba, or in deep water using a submersible. Despite major advances in imaging technology there is still nothing that can match the depth perception, continual focus, and wide field of view of a human observer. Our experiences working with JAGO in midwater certainly verified this conclusion. I will focus here on a few of the many discoveries we made during our JAGO dives.

Much of what we observed from JAGO was new; patterns, behaviors, and animals we had never seen before. Some of these were of considerable significance while others were simply interesting; although we have learned that seemingly elementary observations can lead to big surprises as more data become available. One surprise occurred at a depth of 351 m when we stopped to observe a handful of Phronima, amphipod crustaceans that lay their eggs inside a barrel that they fashion from the hard gelatinous bodies of pyrosome tunicates. The mother Phronima pushes the barrel around like a deep-sea baby buggy, protecting her eggs and making sure they are well oxygenated. As time went by the number of Phronima increased until a large aggregation of at least 200 individuals were swarming beneath JAGO’s lights. A second swarm of thousands of very small animals joined the melee that we took at first to be krill, until we realized that these were small, just-hatched Phronima. We witnessed a mass hatching event and were able to watch as these babies attached themselves to passing pyrosomes and salps, perhaps to ride and feed on them until big enough to make a barrel and produce their own eggs.

An exciting discovery (for me, at least) is that giant larvaceans of the genus Bathochordaeus have been observed and collected for the first time in the eastern tropical North Atlantic. These animals have been studied extensively in the Pacific off California, where they are known to play a highly significant role in the flux of organic carbon from the ocean’s productive upper layers to the hungry residents of the deep seafloor below. Because these invertebrates and their complex feeding filters are quite fragile, it is virtually impossible to observe or sample them with nets. The only way to study them is through direct intervention by manned submersibles like JAGO, or with ROVs. The discovery of numerous examples of Bathochordaeus during POSEIDON cruise 520, means that we can now correctly put into place an important segment of the oceanic food web of the waters around the Cape Verde Islands.

One further event involved a fearsome-looking fish called a fangtooth that came up in one of our trawl nets. The specimen was in perfect condition and was actively swimming around in a container of water in the laboratory refrigerator. We all wanted to help it resume its life in the deep sea. So, on that evening’s JAGO dive we took it back home to deep water and released it, watching as it first seemed stunned to be free — then it swam quickly off into the darkness.

Between 14 Feb and 1 March expedition POS520 with RV POSEIDON and the submersible JAGO takes place off the coast of the Cape Verdean islands of Santo Antão and Fogo.  The chief scientist, the JAGO team and participants of the cruise write here as guest writers. Today: Bruce Robison, Midwater Ecologists at the Monterey Bay Aquarium Research Institute (MBARI) in California.