Southern Ocean Retrospectives and Perspectives
July 25, 2018
Maggie Amsler, Department of Biology University of Alabama at Birmingham
I recently sailed away from Antarctica on almost the shortest day of the year, plying north through the Southern Ocean to the port city of Punta Arenas, Chile and ultimately flying home to Alabama where I touched down on the longest day (and hottest?!) of the year in Alabama. The four-day transit featured relatively calm seas most of the time, even in the notorious Drake Passage. Island-lifestyle enthusiast Jimmy Buffett would term my relocation a “change in latitude” and as a career polar marine biologist, I have made this drastic hemispheric shift for each of my 27 expeditions to Antarctica. According to my back of the envelope scribbles, I have had the privilege of spending approximately eight years of my life beside, on, in and even above the Southern Ocean. What treasured gifts I have pirated away with over those years. What a bounty of science knowledge the Southern Ocean must still behold.
Initially, I participated in research that focused on the most spectacular and superb denizen of the Southern Ocean – the Antarctic krill, aptly named Euphausia superba. Generically, krill are found in Earth’s every ocean. E. superba however, is only found in the Southern Ocean – the body of water encircling the great white continent. The specific epithet of superba refers to the fact that this species is largest of any the 90-some other euphausiids reaching about 60 mm in length and that it is the most abundant of any of the euphausiids. Massive swarms of the pelagic or ever-swimming individuals are common throughout the Southern Ocean. For a staggering factoid – the estimated total biomass of E. superba exceeds that of the weight of the Earth’s eight billion plus human population!
What accounts for E. superba’s success in waters characterized by year-round near freezing water temperatures and seasonally limited daylight? In short, lots and lots of special adaptations – especially dietary. Krill are basically vegetarians, filter-feeding on small, yet very abundant plant-like organisms – phytoplankton – whose numbers explode in weedy proportions during the long summer days and months of sunshine beaming into the ocean. Krill feed non-stop during these months and devote a great deal of that ingested energy into reproducing and reproducing and reproducing! As the phytoplankton numbers fade with the decreased sunshine of autumn’s shortening days krill basically lapse into a winter fasting.
Ecologically, Euphausia superba is considered a keystone species in the Southern Ocean food web. Fish, seabirds, seals, and whales consume tons and tons and tons of krill on an annual basis. Even invertebrates like sea stars and other crustaceans will feed on this defenseless just-keep swimming and eating critter. Krill is thus considered the ecological driver of the Southern Ocean. If krill are happy and abundant, so too the Southern Ocean.
Krill is also an economic driver for several countries. Such countries send huge factory ships to certain sectors of the Southern Ocean to drag massive nets through the water catching krill to process on-site. The end- product is used in animal feed or marketed as omega-oil nutraceuticals. Though high in protein like their shrimp cousins, krill are uniquely high in fluoride and essentially toxic for human consumption. How is it you wonder when per the Antarctic Treaty, the continent is set aside for science and bans commercial exploitation of it resources like krill? The Treaty, first implemented, signed by and abided by many countries in 1959 applies only to the continent proper. To address exploitation of the continent’s off-shore biological resources, the Commission for the Conservation of Marine Antarctic Living Resources (CCAMLR) was established in 1982.
CCAMLR approves fishing in various sectors around the continent and in doing so effectively controls 10% of the world ocean. Hurrah for conservation – albeit limited. Such controlled, fish-able areas include the southwest Atlantic, waters I have frequented for most of my work along the Western Antarctic Peninsula. I have seen factory ships on occasion and am never comfortable with the sightings. Yet, I find solace in knowing that CCAMLR vigorously controls and monitors catch limits annually. The current total allowable catch of E. superba is 6 million tons annually. A difficult figure to comprehend, yet it is estimated that the tonnage represents around 0.3% of the naturally unexploited – what the whales, seals, penguins, etc. do not eat – biomass of krill. Let’s hope this fishery continues to be sustainable.
Southern Ocean krill have sustained me as a scientist for many years, presenting literal high points and low points in my career. In the early 80’s, courtesy of a US Coast Guard icebreaker helicopter, I conducted a short aerial survey of krill predators in several bays. I felt like Sally Ride dressed in my pumpkin-orange jumpsuit and full helmet striding onto the helo deck to embark on my first helicopter flight. I sat at the edge of the open side door, clipped in by harness, peering over and down at the surface waters below for signs of krill. No luck that day but years later as part of a documentary filming, from the interior comfort of a luxury helicopter, I hovered above and around dozens of whales feeding on countless tons of krill. The orchestrated group feeding technique called bubble-feeding etched short-lived spirals on the water’s surface – the resulting cylinder of bubbles ensnaring krill in a nature-made net.
As for krill lows – think Jules Verne and of course, Sylvia Earle! A submersible view to krill – also as part of the documentary filming. Most of my cumulative 33 hours in Nadir, (the same sub and even seat Sylvia has occupied) a three-person submersible operating in waters around the Antarctic Peninsula, included krill sightings. From the surface, all the way down to 1000m! My most memorable krill submersible moments included being engulfed in a’ krill blizzard’ at 450 m deep – the density of surrounding krill school engulfing my sphered world was so thick it was hard to see water! And – seeing in person all the organisms that catch and eat krill! Goodness what predation pressure E. superba endures!
Excitingly, one of those krill predators seen was most unexpected in peninsular waters – a juvenile Antarctic toothfish (Dissostichus mawsoni)! The youngster was spotted by the submersible’s cameraman as it peered out from beneath a rocky ledge. The near-vicinity was blanketed with a deep, easily stirred layer of undigestable and excreted krill exoskeletons. Toothfish scat. The scene was similar to that of an octopus lair – the surrounding yard littered with crushed clamshells. Like most Antarctic fish, the toothfish lacks a swim bladder and thus lives primarily on the bottom. However, fattening up on krill as a juvenile results in a neutrally buoyant adult toothfish. The fish grow huge (5 feet in length), are long-lived and reproduce late in life. It is the top predatory fish in the Southern Ocean – sort of the shark of the Southern Ocean.
I have had one other sighting of a toothfish. I participated in three cruises devoted to imaging the seafloor in parts of the Southern Ocean. Our research vessel towed a paired-camera array and recorded literally hundreds of thousands of images of life on the seafloor down to 1600m. Reviewing all those snapshot images was enthralling, not to mention time-consuming and resulted in deepening our understanding of community dynamics in the dark depths of the Southern Ocean. Findings include documenting the abundance and distribution of a deep sea crab threatening to move shallow as the Southern Ocean waters rapidly warm, the first known skate (cousin of sting rays and sharks) nursery in Antarctic waters, and numerous natural history observations including the sighting of a beautiful, juvenile Antarctic toothfish. Hopefully, that individual, like its brethren sighted from the submersible, continues to lead a long and ultimately prosperous life.
Many Antarctic toothfish lead an unnaturally short life. Its northern and very tasty cousin, the Patagonia toothfish has been severely overfished. You may be more familiar with its restaurant (pricey) entrée name – Chilean seabass. Years of unregulated longline fishing in the south Atlantic for this prized catch have drastically lowered yields so efforts turned to equally tasty Antarctic toothfish. It is referred to as “white gold” in the illegal trade and it is feared that illegal, unregulated and unlicensed fishing vessels are taking unsustainable numbers of this long-lived species despite regulatory efforts by CCAMLR. Through the efforts of CCAMLR, toothfish in sectors south of New Zealand – in the Ross Sea – have a better chance for long life. In 2016 CCAMLR declared 1.5 million km2 of the Ross Sea a Marine Protected Area (MPA). Huge hurrah! At roughly twice the size of Texas, the celebrated Ross Sea Preserve is the largest MPA on the planet. Very limited fishing will be allowed and we can hope, the preserve will preserve Antarctic toothfish populations for many generations to come.
Yet, the Southern Ocean, like the rest of the world ocean, remains susceptible to overfishing. Improved processing technology puts increasing pressures on krill and toothfish. Climate change-influenced decrease in ice cover or duration means vessels can reach and fish more remote areas. Hopefully, through the continuing efforts of CCAMLR additional sectors of Antarctica’s waters will be aside as preserves with limited fishing activity like the Ross Sea now enjoys. Since 2012, negotiations have been underway to establish a 1 million km2 MPA in East Antarctica. The October 2017 annual CCAMLR meeting fell two votes short as China and Russia tabled objections. Perhaps with additional negotiations over the coming months both countries will be satisfied and next year’s meeting will celebrate unanimous approval of another Antarctic MPA. CCAMLR will then set sights on MPA proposals in the Weddell Sea and even waters of the Antarctic Peninsula. Hope for the Southern Ocean and consequently hope for the world ocean.
The majority of my Southern Ocean perspective is not that of waves rocking the ship’s deck, or sweeping panoramas aloft in a jumpseat or what’s that in the high beams beyond the submersible bubble, but simply viewing life through my scuba mask. My research focus has narrowed to bottom dwelling shallow water communities along the Antarctic Peninsula. Rather than studying the role of one particular species in the community, I study how the myriad of organisms within the community interact – the ecology of the community. More specifically, I work in the field of marine chemical ecology which is the study of chemically-mediated interactions between organisms or between organisms and their environment. With biology colleagues from my home institution the University of Alabama at Birmingham in collaboration with chemistry colleagues at the University of South Florida, we investigate how benthic and sessile organisms – those that are literally stuck in place for life, e.g., macroalgae, sponges, etc. – defend themselves from predation. Turns out many of the organisms in the rich and diverse communities along the Antarctic Peninsula produce unique chemicals that apparently make their tissue taste bad and in turn protect them from being eaten. No doubt such chemical warfare shapes, develops and likely maintains these communities.
In fact, it appears that chemical interactions do indeed structure communities in the subtidal communities around Palmer Station – a research base where I have lived and worked during most of my expeditions to Antarctica. The local waters teem with life including underwater forests of macroalgae: towering kelp-like algae, massive branched and widely bladed browns carpet the bottom along with more delicate feathery red algae. The biomass of these forests rival mature Pacific kelp forests. After years of scuba-based observations and sampling coupled with laboratory experiments we have learned that most seaweeds in Antarctica are chemically defended – they taste bad so do not get eaten. Yet, many of the algae are covered with hordes of shrimplike crustaceans much, much smaller than krill called amphipods. Why hang out on something you apparently cannot eat? Simple, the algae protect the amphipods from being eaten by their main predator – fish. We then asked if the macroalgae are paid back for their indirect largesse. The answer appears to be yes – the amphipods feed on diatoms (small celled plant-like organisms) and smaller, filamentous algae that live inside and on the surfaces of macroalgae both of which would compete with the host macroalga for light (needed for photosynthesis) and nutrients. We have recently added a few more levels of interaction to this dynamic, further enforcing our understanding of how chemistry orchestrates what we call a community-wide mutualism.
The defensive chemicals that play in this subtidal symphony may also someday benefit society. One of my favorite findings to come out of our work is from that of a very distant relative of mine (and yours!) – a tunicate. Tunicates, like us are chordates but most chordates have a backbone and are thus vertebrates. The tunicate though is spineless and thus an invertebrate. As the tunicate metamorphoses from a free-swimming larva to an attached, benthic adult, its rudimentary spinal cord is lost. Once attached the tunicate is sort of barrel-shaped with two siphons: one that draws water and nutrients into the body and the other that expels the water. Some tunicates are solitary representing a single individual and bearing just one set of siphons. These can get baseball-sized and often wash up on the beach. Many a beachcomber has discovered why the common name for a solitary tunicate is sea squirt as upon a gentle squeeze of the tunic the water inside shoots out. Mother Nature’s water pistol.
From one particular Antarctic tunicate (Synoicum adareanum) the project chemists have isolated several unique chemical compounds. The compounds were sent to the National Cancer Institute for testing on a bunch of different lines of human cancer cells. One compound, Palmerolide, is very toxic to skin cancer cells. No tunicates do not get skin cancer and we have yet to determine why the tunicate produces such a compound. But years from now after lots of clinical trials, a synthetic version of Palmerolide may be used in the fight against melanoma. A gift of sorts from the Southern Ocean. Other possible gifts from the sea our studies have revealed come from sponges. In particular, a compound isolated from the cactus sponge (Dendrilla membranosa) and termed Darwinolide shows promising antibacterial activity against the biofilm form of MRSA. Numerous other compounds of interest have been isolated from other sponges, soft corals and even algae with activity against herpes, the Zika virus, even the parasite causing Leishmania. Who knows how many other drugs from the sea the Southern Ocean inhabitants may be harboring.
Over the years I have sailed many of the Southern Ocean’s seas. A most memorable cruise began in the waters south of South America and ended in the Ross Sea, south of New Zealand. During that voyage, which included seafloor imaging and during two other intensive seafloor imaging cruises, not one shred of anthropogenic input was observed. The only ‘litter’ noted was dropstones, seal bones and whale falls. No garbage, ghost traps, or stranded nets – not even ‘hairballs’ of copper wire from xbt casts – a commonly used oceanographic expendable instrument thrown into the sea to profile water temperature with depth. Additionally, my observations from submersibles yielded no signs of human footprints. The only errant material was algal drift (still identifiable to species) down to 1000m. Admittedly, when at Palmer Station our project does an annual Earth Day dive around the station pier to collect stuff blown overboard, washed offshore, dropped, etc. Yet, hundreds of other scuba dives in the station’s vicinity (except for a nearby location that served as a staging area in the late ‘60s while building the existing station) we see no manmade artifacts. I hope that one day through concerted efforts, like Mission Blue, all the world oceans will be as pristine as I have witnessed of the Southern Ocean.