Trophic BATS: Post # 5 (Day 3)

Foreground: (left) Stardboard A-frame - used for deploying the CTD. (right) Stern A-frame - used for array deployments, net tows, and in-situ pumping.

Background: (left) The Sun - used to provide life for the entire planet.

This is what we’ve had to deal with all day. Rough isn’t it. I checked the weather report for the next week (we return Friday 3/23) and laughed out loud at what I read. Over the next 7 days no winds are supposed to break 15 kts, while averaging below 10 and with a wave height of a whooping 2-4ft. This has made all the ship operations go as smoothly as possible, allowing us to stay on schedule even getting ahead of ourselves.

Right now (2300) Dr. Rob Condon and his research technicians are performing several net tows. Zooplankton net tows are done both during the day and at night. Zooplankton perform what is termed diel vertical migration. During the night, certain species of zooplankton will ascend to the surface for optimal foraging, thus differences in tow composition will likely be observed between day and night. From the tow collections, Rob will separate half the tow and dedicate it to species identification by microscopy. The other half is size fractionated and then measured for carbon. Other times, plankton collections from the tow will be hand picked and individual swimmers will be used in experiments for grazing and for fecal pellet/DOM production.

To fill us in on a little more detail on the research of zooplankton’s role in the food web, Dr. Rob Condon, Research Senior Marine Scientist from Alabama's Dauphin Island Sea Lab, has kindly agreed to answer of our few questions.

Q: How does one measure the flux of carbon transfer through zooplankton?

Rob: Our understanding of the open ocean food web is based on classical food web paradigm of a phytoplankton being eaten by copepods being eaten by a fish. As we develop new techniques and become more multidisciplinary in our approach, we are discovering that food webs are not simple but rather very complex, with interactions between many trophic levels. One way to determine the structure of the pelagic food web is to use stable isotopes (13C and 15N) as a way of interpreting energy source and what eats what based on these elemental signatures in organic matter, plankton and fish. Rate processes such as grazing, excretion, respiration and fecal pellet production are also important metrics in understanding of how food webs function. We are conducting experiments measuring the source-sink dynamics of carbon in zooplankton and how this feeds into the bioavailability of carbon to higher trophic levels vs the loss of carbon from surface waters through flux (e.g., fecal pellets).

Q: What are the major differences between zooplankton groups with respect to carbon transfer?

Rob: Zooplankton encompasses a wide range of organisms ranging from microzooplankton that consume very small particles and phytoplankton to crustacean zooplankton such as copepods that are important food for fish and gelatinous plankton. My research team is focusing on the crustacean and gelatinous zooplankton. Most studies to date have focused on copepods but the jellies are of particular interest as very little is known about them but are potentially important for carbon transfer in food webs. Some jellies, such as salps, produce very large fecal pellets that can sink rapidly to the deep ocean, which may be important means of transporting carbon via the biological pump (the process whereby oceans sequester carbon at depth). Other groups, such as medusae and ctenophores, can be voracious predators that produce and release a lot of organic carbon as mucus. This mucus is rapidly utilized by microbes for respiration, a process that converts energy back into a form (carbon dioxide) that can't be used by higher organisms, thus these gelatinous organisms may act as a shunt energy in food webs.

Q: What are the challenges that exist when performing your measurements and experiments?

Rob: There are inherent problems associated with dealing with animals that makes experiments a challenge. For example, we know that gelatinous plankton are abundant in open ocean environments but many kinds are extremely delicate, such as ctenophores (comb jellies) that will explode on touch. We have to use blue water diving techniques to examine these type of animals. Many of these organisms live in deep waters and migrate to the surface at night but are likely important components of the open ocean and mesopelagic food webs. To study these animals requires use of ROVs or submersibles which are expensive and hard to come by in oceanographic expeditions.

Q: From a zooplankton perspective what are the major implications of this research?

Rob: There are several significant implications from this research. The first centers on the implications of food web structure for fisheries production vs carbon flux. If primary production is linked to copepods then this represents potentially more energy for fisheries production, which in turn has consequences for fisheries management in the open ocean. By contrast, not very much is known about what predators consume gelatinous plankton, and what their overall role is in biogeochemical cycles. Do jellies reduce carbon flow to fish or make food webs more complex? And do they increase carbon export to depth? There is also a paradigm that jellyfish are increasing in the world's oceans as a response to a variety of human insults to the sea. Most studies have focused on coastal and estuarine systems with very little focus on the gelatinous species that exist in the open ocean that cover 70% of our planet. Understanding how energy is partitioned between crustacean and gelatinous plankton will help us better manage ecosystems and resources in this delicate marine environment.

Awesome! Thanks, so much Rob.

Emily, Molly, and Rob await the approaching net tow. Copepods dominate the zooplankton community composition at 50-70%, followed by euphausids, ostracods, and then gelatinous zooplankton. However, estimating the real contribution of gelatinous zooplankton is a major focus of Rob's. The organisms are very delicate and prone to disruption during recovery, thus proving difficult to accurately measure its abundance.

Rob and Molly hover over the recovered net tow, quickly eyeing their catch.

This is a single organism recovered from a a net tow. Nicknamed the spaghetti monster by Dr. Stephanie Wilson it is actually a siphonophore, a type of jelly. In the same tow, the zoop team discovered an amphipod that was the inspiration of design for the alien in the movie Alien. When someone informed me, I expected the lab to be littered with bodies and imagined a tail escaping through the ceiling covers, but alas the little creature was about the size of my fingernail and was simply hiding inside of an another gelatinuous zoop called a Salp.

Well, that is all for tonight. Catch everybody tomorrow!

Doug Bell

Research Technician, Phytoplankton Ecology Lab

Oceanographic Filterer: Level 17