Hi all, this is Dr. Edwards, project PI Our second cruise to the Aleutian Islands has come to a close. On July 23, we finished our last set of dives at Yunaska. Yesterday’s rocking and rolling swell was non-existent; the winds had died down completely, and the sun had come out. Yes... the sun. It had been almost two weeks since we saw a clear view of that yellow star that warms us. We went in and hauled our chambers and the hundreds of pounds of chain to the boat and picked up the sensors. The water was so calm, you could set things down and they did not move. The thick kelp that only the day before had snagged on every edge of our tanks, BCs and regulators, now cooperated as if we were in harmony. You could move through it with ease, but only if you respected it...danced with it. If you took it for granted, tried to change the dance, it would still snag and pull on you, slowing every movement. But with respect, it was like gliding through a photograph. The kelp was so thick and full of life. There was an understory of kelp so dense you could not see the bottom. There were sponges that covered square meters of rock bottom. Red, yellow, white. There were large nudibranchs plowing through the sponges and eating their fill. There were snails, and bottom fishes of every color you could imagine. Visibility was so good that the only thing that limited your vision was the scenery in front of you. Though you could if you wanted to, it was hard to pass up an infinite number of scenes in front of you that you almost forgot there was a horizon beyond. It made me completely forget the 41 degree water and the holes in my gloves’ fingertips that appeared after two-weeks of deploying benthic chambers, hauling chain, and collecting urchins. Afterwards we had a day of cleaning gear, packing research equipment, and preparing to disembark from the Oceanus. This is my last shipboard blog for Brenda's and my NSF 2016 and 2017 cruises. In reflection, I look back at what we accomplished. In the past two years, we dove at 15 of the Aleutian Islands (from west to east: Attu, Nizki, Allaid, Shemya, Kiska, Amchitka, Ogliuga, Tanaga, Adak, Atka, Yunaska, Chuginadak, Umnak, Anangula, and Unalaska). My students (Scotty, Tristin, Pike, Sadie and Genoa) and my collaborator Ju-Hyoung pulled off a Herculean amount of work. We deployed nine benthic respiration chambers at each of 11 of the islands; three each in the kelp beds, urchin barren grounds, and in the transition zones between the two. This equated to 99 chamber deployments in total. Each chamber was held down with about 40 pounds of chain, so you can do the math; we deployed and retrieved about 3960 pounds of chain from small inflatables. This, plus the chambers and the sensors…again…Herculean. Together, we did about 250 dives on each of the cruises (about 500 dives total on the project). Conditions ranged from Atka last year where we endured smashing waves and blowing winds in our sites to the calm clear beauty of Yunaska. Water temperatures ranged from 41 degrees to a balmy 46. My students (the SDSU BEERPIGS) more than conquered these tasks and I am grateful and impressed by their abilities, energy, and attitudes. A job well done. On the ship, Ju-Hyoung and Sadie conducted controlled measurements of invertebrate respiration and algal photosynthesis. Generating photosynthesis versus irradiance (P vs I) measurements requires careful and methodical work. The instruments we use are sensitive to even a single degree of change in water temperature, and to differences in light intensity so small that the human eye cannot make them out. Each measurement for each species requires up to 90 minutes to fully evaluate the photosynthetic responses of the algae to changes in irradiance. Between the two of them, they conducted a total of 150 P vs I measurements across 26 species. In total, this equates to about 225 hours of measurement time (and that’s in just four weeks of ship time). Further, they conducted respiration measurements on dozens of species of invertebrates, and evaluated the relationship between urchin respiration and urchin size across nearly 20 size classes. They also examined the carbon uptake kinetics of 10 species of algae, and helped parameterize our field irradiance measurements with light casts. Another job well done. On top of deploying and retrieving chambers, Scotty collected tissue samples from about 400 invertebrates, and 101 water samples that were filtered for phytoplankton. Over the next year, he will analyze these for their isotopic signatures to better understand how food webs and trophic energy flow has changed with the widespread kelp loss. Together with the benthic respiration chamber data I see my next several months of work analyzing and interpreting the results. And then writing up the papers. Not as fun as being underwater, but just as important and rewarding. The crew of the Oceanus was amazing. From the captain on down, everyone was friendly and incredibly helpful. Our skiff drivers navigated the dense kelp beds, and helped haul heavy chain and chambers into the boats. They were both our drivers and our surface support. The food was awesome, from fresh-caught baked halibut to hot out-of-the-oven cookies waiting for us when we returned from our dives, worn out and cold. We could not have asked for a better crew or ship. I thank the National Science Foundation for providing both the ship and the funding for this research. So, as I close this blog, I think about the next time Brenda and I will bring our labs here. It has been almost 25 years since I first came here to live for a few months on Shemya; this place is as beautiful and new as the day I first stepped on that tiny island (though I am a little greyer and maybe a step slower). The ecosystem offers an endless avenue of research questions and our research (as most research does) has resulted in as many new questions as it provided answers. So, I think of the last dive at Yunaska, sitting mid-water and looking at the dense kelp teaming with life. I think of the urchin barrens, which at one time looked to me to be devoid of anything other than urchins, but now have revealed themselves to be diverse and full of their own life. What will happen next? How long will the urchin barrens persist? What might cause them to switch back to kelp beds? New predators? Disease? Some as-of-yet unknown factor? The questions remain. I think about the last dive, and I believe the Aleutians are calling me back. Sincerely, Dr. Matthew Edwards Project PI
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Kelp loss, urchin barrens, and food web comparisonsHey everyone, Scott Gabara here to describe part of my dissertation working on creating food webs of nearshore and offshore subtidal communities across the Aleutians Islands. In the marine environment, kelps can create the understory and canopy that comprise most of the biomass of kelp forests, providing structure and food resources for their associated communities and can even deliver material to adjacent areas supporting consumers many kilometers away! This is very similar to the plants, bushes, and trees that comprise forests on land (and can deliver leaf litter to adjacent areas). With the loss of sea otters and subsequent formation of urchin barrens across many locations of the Aleutian Island archipelago, kelp is lost and organisms will either not be able to deal with the loss of food that kelps provided, or they may change their diet to another source of food locally, or rely on food from other locations that drift in. At some locations urchin barrens were formed long ago, but most formed during the late 1990s- early 2000s, giving us communities that lost kelp long ago, many that have lost kelp for about 20 years, and some locations that have had kelp continuously. I wanted to better understand the long term impacts of kelp loss on the trophic ecology of these kelp forest communities that still have kelp or have lost kelp over different amounts of time. To do this I will create and compare food webs using stable isotopes of the dominant community members (producers and consumers) among urchin barrens, kelp forests, and offshore communities at islands across the Aleutian archipelago.
Stable isotopes of carbon and nitrogen are stored in tissues and help us to understand how energy flows through food webs. Stable isotopes act as a hidden tracer that can reveal both where energy is coming from, and the trophic level of a consumer. For example, we can sample the fingernails or hair of people, and using carbon stable isotope values, be able to tell differences of diets based more on rice versus those based more on corn because of the differences in the way rice and corn take carbon up during photosynthesis. We can also identify differences in the diet of people that are vegan, vegetarian, or those that eat more meat, because of differences in the trophic level of the foods that they eat. All of this information is stored in the nitrogen stable isotopes of the food we eat and is then left as a signature in our fingernails and hair. Food webs help us to understand the connections among organisms and reveal the potential impacts of removing certain food resources (primary producers) that comprise the base of the food web or the impacts of removing the food web members (consumers). Potential food web resources for kelp forest and urchin barren associated organisms are things in the water such as phytoplankton (that live in the water column) or pieces of algae that break off while algae grow or get ripped off the bottom and drift around, multiple attached algae such as the lower lying green and red algae in kelp forests, and the larger subcanopy and canopy forming brown algae. To estimate a water column isotopic signature, water was filtered from urchin barrens, kelp forests, and offshore. Filtering water for phytoplankton or algae particulates is no easy task. Water is collected and then needs to either be pushed or pulled through a filter to concentrate the material from the water. To do this I modeled a water filtration setup after the Rohwer lab at SDSU/Smith lab at Scripps developed by Mark Hatay at SDSU. Clear PVC was cut to fit 5 Liters of water, 4 inch adjustable plumbing plugs were used to seal the ends, and tapped plastic valved fittings onto the plugs were used to create a tube that could collect water and be pressurized. A propane pressure regulator and a SCUBA tank was used to create pressure that would push the water through the clear collection tube and then through a glass fiber filter in a holder, concentrating the material from the water on the filter, to be dried and later run for stable isotope analysis. Locations of nearshore and offshore (grey), kelp forest (green), and urchin barren (blue) water samples.
To estimate algal isotopic signatures, tissues of algae that were living in urchin barrens and kelp forests were collected. To estimate the isotopic signature of nearshore and offshore consumers, invertebrates were collected from surveys or offshore trawls done in collaboration with the Konar lab at University of Alaska Fairbanks. To estimate fish isotopic signatures, pole spears were used to catch fish that were in urchin barrens and kelp forests by divers and by using the trawl to get fish that were living in the deeper offshore areas.
Tissues were prepped and dried on the R/V Oceanus and will be run for carbon and nitrogen stable isotope analysis. The ratio of the heavier to lighter stable isotopes of carbon and nitrogen will help us trace how important local and/or drifting kelp is for organisms in urchins barrens, kelp forests, and offshore areas. By creating food webs of these different communities we may have a better understanding of why certain organisms can survive the transition from kelp forests to urchins barrens and if and how kelp loss in the nearshore affects offshore food webs.
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