Whale-guided research reveals the oceans’ true biology.

By Dave Armstrong - 18 Feb 2016 11:42:0 GMT
Whale-guided research reveals the oceans’ true biology.

Researchers have used the predatory foraging off whales to help assess the biota and biomass of deep sea organisms. This first could provide even more information on the unexpected great variety and interesting distribution of life at these little-known depthsZiphius cavirostris image; Credit: © Shutterstock

Kelly J. Benoit-Bird, Brandon L. Southall and Mark A. Moline followed the well-known deep dives of foraging Cuvier’s beaked whales to uncover the structure of ocean communities. As a paper, the writing hardly stands out on the page, but the meaning of this aided research is in how the whales helped out and how it can be interpreted.

New technology forever offers insights into areas that were previously unreached by science. The bathypelagic zone is that part of the sea that stretches as far as 50km deep. The surprise in the results is that the ecology is diverse all the way down! The predator/prey relationship is critical in this study because of the animal’s preferences, but the whole of the energy cycle and all of its transfers from primary production upward are involved. Many pieces of research have patently assumed the whole zone was uniform. How wrong can you be?

The biggest communities of animal and plant life on the planet live in the bathypelagic zone, in terms of biomass, numbers or simply the space involved. Distribution is indeed according to which ocean you are in. But the diversity and activity that remote vehicles have revealed in the mid and deep areas were only clues as to the real world under the surface. The AUV dives to only 600m for example. Fishing nets reveal some specimens and remotes give valuable data, but essentially we have been blinkered.

Seals and odontocete (toothed) whales have previously given us valuable evidence of the biota. They have invested heavily in body modification to go down more than 1000m., meaning there must have been great value in gaining their prey from these depths.

Ziphius cavirostris (Cuvier’s beaked whale) dives to extreme depths off southern California, beaten to the record only by the incredible sperm whales chasing their squid. The US Navy’s SOAR data provided basic satellite-linked tagging, hydrophone and visual information on these dives so that the research could be targeted on specific strata within the sea. Then an echosounder was placed in a 3.5m long (250kg) REMUS 600 AUV that dived to 600m and critically does not make any bubbles! Many dangers surround the possibility of contamination and disruption by these remotes We note in our article on deep sea vents being contaminated by vehicles that new restrictions are necessary on size and sampling are important for conservation. The echosounder made the depth measurable by commendably remote means extend down as far as 1200m. Measurements of temperatures, pressure, oxygen concentrations, fluorescence, etc. were detected from a ship overhead. Biomass and the abundance of different phyla and classes were measured from rapidly-towed net samples.

The challenge of studying deep waters necessitates inventive approaches. Kelly Benoit-Bird and her associates from Southall Environmental Associates, University of Delaware and Oregon State University demonstrate sampling is an art form as far as original thought is concerned. You can read it up in The Proceedings of the Royal Society B’s Predator-guided sampling reveals biotic structure in the bathypelagic zone.

The key results demonstrated the location of individual animals down to 1200m, classified them according to their frequency responses, sized them up and explored distribution patterns on a scale ranging from 10m to a magnificent 50km, without taking them from their habitat. Whether these creatures were prey for the whales or not became irrelevant. The historic habitat usage and the prey selections of beaked whales simply paved the way for the investigation.

The uneven distribution of various squid species is a new finding that places the whale/squid interaction in new contexts. Even slower swimming animals may have to be considered as less homogeneous in their distribution than previously thought. Many fish such as the mesopelagic myctophids (lantern fish), jellyfish, euphasiid and amphipod crustaceans were much more abundant in the eastern part of the survey, reflecting great differences in productivity by phytoplankton and zooplankton. The squid distribution varied even when their prescribed zones were 6.5km apart. What this means for the whole ecosystem goes dee and meaningful. Whether speedy squid distribute according to predator attacks, or slow movers can adjust to their own level of fatalities, can now be worked out with new figures that prove how much more productive the deeper levels were than we thought. The phytoplanktonic energy is transferred not only to close-to-surface fish that fishermen have always caught, but also to deeper levels where biogeochemical cycling and unimaginable new ecologies (and huge communities) are being revealed to us on this giant scale.