Smithsonian at the Poles: Contributions to International Polar

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Interannual and Spatial Variability in Light Attenuation: Evidence from Three Decades of Growth in the Arctic Kelp, Laminaria solidungula Kenneth H. Dunton, Susan V. Schonberg, and Dale W. Funk Kenneth H. Dunton and Susan V. Schonberg, University of Texas Marine Science Institute, 750 Channel View Dr., Port Aransas, TX 78373, USA. Dale W. Funk, LGL Alaska Research Associates, Inc., 1101 East 76th Avenue, Suite B, Anchorage, AK 99516, USA. Corresponding author: K. Dunton (ken.dunton@mail.utexas.edu). Accepted 28 May 2008. ABSTRACT. We examined long-term variations in kelp growth in coincidence with recent (2004– 2006) measurements of underwater photosynthetically active radiation (PAR), light attenuation coeffi cients, chlorophyll concentrations, and total suspended solids (TSS) to determine the impact of sediment resuspension on the productivity of an isolated kelp bed community on the Alaskan Beaufort Sea coast. Attenuation coeffi cients exhibited distinct geographical patterns and interannual variations between 2004 and 2006 that were correlated with temporal and geographical patterns in TSS (range 3.5– 23.8 mg L �1 ). The low chlorophyll levels (�3.0 �g L �1 ) in all three years were unlikely to have contributed signifi cantly to periods of low summer water transparency. Blade elongation rates in the arctic kelp, Laminaria solidungula, are excellent integrators of water transparency since their annual growth is completely dependent on PAR received during the summer open-water period. We noted that blade growth at all sites steadily increased between 2004 and 2006, refl ective of increased underwater PAR in each successive year. Mean blade growth at all sites was clearly lowest in 2003 (�8 cm) compared to 2006 (18– 47 cm). We attribute the low growth in 2003 to reported intense storm activity that likely produced extremely turbid water conditions that resulted in low levels of ambient light. Examination of a 30-year record of annual growth at two sites revealed other periods of low annual growth that were likely related to summers characterized by exceptional strong storm activity. Although kelp growth is expected to be higher at shallower sites, the reverse occurs, since sediment re-suspension is greatest at shallower water depths. The exceptionally low growth of kelp in 2003 indicates that these plants are living near their physiological light limits, but represent excellent indicators of interannual changes in water transparency that result from variations in local climatology. INTRODUCTION Research studies conducted over the past two decades have clearly documented that kelp biomass, growth, and productivity in the Alaskan Beaufort Sea are strongly regulated by light availability (photosynthetically active radiation, PAR). Results from a variety of experimental studies, including the linear growth response of kelp plants to natural changes in the underwater light fi eld (Dunton, 1984; 1990; Dunton and Schell, 1986;), carbon radioisotope tracer experiments (Dunton and Jodwalis, 1988), and laboratory and fi eld physiological work ( Henley and Dunton, 1995; 1997) have been used successfully to develop models of kelp productivity in relation to PAR. Yet, until recently, the relationship
272 SMITHSONIAN AT THE POLES / DUNTON, SCHONBERG, AND FUNK between water turbidity— as measured by total suspended solids (TSS) or optical instruments— and benthic algal production was unknown. Aumack et al. (2007) were the fi rst to establish the quantitative link between water column turbidity, PAR and kelp production through a model that uses TSS data to predict estimates of kelp productivity in an area known as the Stefansson Sound Boulder Patch on the central Alaskan Beaufort Sea coast. This information is essential for evaluating how changes in water transparency are related to higher suspended sediment concentrations from anthropogenic activities near the Boulder Patch, coastal erosion, and increased freshwater infl ow (McClelland et al., 2006). The quantitative measurements of TSS collected by Aumack et al. (2007) in summers 2001 and 2002 were a critical fi rst step in the establishment of an accurate basin-wide production model for the Stefansson Sound Boulder Patch. The productivity of Laminaria solidungula in subtidal coastal ecosystems is an important factor that regulates benthic biodiversity and ultimately, the intensity of biological interactions such as competition, facilitation, predation, recruitment, and system productivity (Petraitis et al., 1989; Worm et al., 1999; Mittelbach et al., 2001; Paine 2002). On a larger scale, biodiversity measurements can serve as an indicator of the balance between speciation and extinction (McKinney, 1998a; 1998b; Rosenzweig, 2001). The interesting biogeographic affi nities of organisms in the Boulder Patch led Dunton (1992) to refer to the area as an “arctic benthic paradox,” based on the Atlantic origin of many of the benthic algae (e.g. the red algae Odonthalia dentata, Phycodrys rubens, Rhodomela confervoides) in contrast to the Pacifi c orientation of many of the invertebrates (most polychaetes and gastropods). This unique character of the biological assemblage, combined with the Boulder Patch’s isolated location (Dunton et al., 1982), suggests the potential of the area as a biogeographic stepping-stone. Thus, the Boulder Patch likely has large biological and ecological roles outside Stefansson Sound. The overarching objective of our study was to use synoptic and long-term measurements of PAR, light attenuation coeffi cients, total suspended solids (TSS; mg L �1 ), and indices of kelp biomass to determine the impact of sediment resuspension on kelp productivity and ecosystem status in the Stefansson Sound Boulder Patch. Between 2004 and 2006, we initiated studies to monitor water quality, light, kelp growth, and the associated invertebrate community in the Boulder Patch. This research program was designed to address ecosystem change as related to anthropogenic activities from oil and gas development. Our initial effort was focused on establishing a quantitative relationship between total suspended solids (TSS) and benthic kelp productivity (see Aumack, 2003; Aumack et al., 2007). Our current objectives included (1) defi ning the spatial variability in annual productivity and biomass of kelp, (2) monitoring incident and in situ ambient light (as PAR) and TSS, and (3) using historical datasets of kelp growth to establish a long-term record of kelp productivity. MATERIALS AND METHODS Our overall sampling strategy during summers 2004, 2005, and 2006 incorporated: (1) semi-synoptic maps of TSS and light attenuation parameters generated through sampling at 30 randomly-selected points in a 300 km 2 area that included the Boulder Patch and the region south of Narwhal Island to Point Brower on the Sagavanirktok Delta (Figure 1; 70°23�N; 147°50�W); (2) long-term variations in underwater PAR at three fi xed sites and incident PAR at one coastal site during the summer open-water period; and (3) kelp growth at several monitoring stations established during the 1984– 1991 Boulder Patch Monitoring Program (LGL Ecological Research Associates and Dunton, 1992). A majority of our study sites were located within the Stefansson Sound Boulder Patch, which is characterized by noncontiguous patches of �10% rock cover. These patches are depicted by gray contour lines in Figures 1–5. SYNOPTIC SAMPLING In order to describe the spatial extent and patterns of TSS, light attenuation, chlorophyll, nutrients, and physiochemical properties across Stefansson Sound, we sampled 30 sites across the monitoring area (Figure 1), which ranges in depth from 3 to 7 m. The location for each site was chosen by laying a probability-based grid over the area and randomly choosing a location within each grid cell. This method allowed sampling locations to be spaced quasi-evenly across the landscape while still maintaining assumptions required for a random sample (i.e., all locations have an equal chance of being sampled). All 30 sites were visited on three separate occasions during summers 2004, 2005, and 2006 using a high-speed vessel (R/V Proteus). We measured TSS, incident PAR, inorganic nutrients (ammonia, phosphate, silicate, nitrogen), water column chlorophyll, and physiochemical parameters (temperature, salinity, dissolved oxygen, and pH) during each synoptic sampling effort.
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Smithsonian at the Poles Contributi
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Contents FOREWORD by Ira Rubinoff i
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Elaina Jorgensen, Alaska Fisheries
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CONTENTS vii Watching Star Birth fr
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x SMITHSONIAN AT THE POLES blooms i
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xii SMITHSONIAN AT THE POLES Change
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xiv SMITHSONIAN AT THE POLES Museum
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Advancing Polar Research and Commun
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James P. Espy (1785- 1860), the fi
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ology fueled hopes that the scienti
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Meteorologists also provided critic
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visualize weather patterns remotely
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in ice sheets. The latest collapse
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Cooperation at the Poles? Placing t
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British Association for the Advance
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cations, in which the Smithsonian s
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ence” (Robinson, 2006: 76), he ha
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Taylor, C. J. 1981. First Internati
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24 SMITHSONIAN AT THE POLES / KORSM
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36 SMITHSONIAN AT THE POLES / De VO
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From Ballooning in the Arctic to 10
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ern Svalbard in 1896 (Capelotti, 19
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FIGURE 2. The Andrée campsite in 1
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National Zoo in Washington, D.C.—
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FROM BALLOONING TO 10,000-FOOT RUNW
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e rapidly deployed to South America
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“Of No Ordinary Importance”: Re
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1942). Ethnological collecting had
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group. More importantly, Murdoch’
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gan to study the question of Indian
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small museums and culture centers i
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fer of Alaskan objects and informat
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fi rst time in polar research— di
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Boas, Franz. 1888a. “The Central
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Lindsay, Debra. 1993. Science in th
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80 SMITHSONIAN AT THE POLES / FIENU
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90 SMITHSONIAN AT THE POLES / BURCH
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100 SMITHSONIAN AT THE POLES / CROW
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From Tent to Trading Post and Back
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in befriending an extraordinary Inu
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The Smithsonian Institution’s pre
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of departure for research during th
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FIGURE 8. A drawing of the so-calle
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situated experiential education and
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the Past: Archaeologists, Native Am
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130 SMITHSONIAN AT THE POLES / KRUP
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144 SMITHSONIAN AT THE POLES / PARK
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Brooding and Species Diversity in t
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iefl y consider below some of the i
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ment. Consequently, the selective e
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ated from the Antarctic. Strong cur
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the four main genera of brooding sc
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ing such cryptic speciation suggest
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LITERATURE CITED Absher, T. M., G.
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Madon-Senez, C. 1998. Disparité Mo
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Persistent Elevated Abundance of Oc
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ABUNDANCE OF ANTARCTIC OCTOPODS 199
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206 SMITHSONIAN AT THE POLES / WINS
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Page 240 and 241: Considerations of Anatomy, Morpholo
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Page 244 and 245: FIGURE 4. A three dimensional recon
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Page 252 and 253: DISCUSSION Imaging and dissection o
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Page 258 and 259: Scientifi c Diving Under Ice: A 40-
Page 260 and 261: TABLE 2. Principal Investigators an
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Page 266 and 267: MARINE LIFE HAZARDS Few polar anima
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Page 270 and 271: Environmental and Molecular Mechani
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322 SMITHSONIAN AT THE POLES / KIEB
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Capital Expenditure and Income (For
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tal breeding systems (Boyd, 1998; T
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FIGURE 3. Pup mass gain in relation
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MONITORING FOOD CONSUMPTION DURING
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primary productivity in McMurdo Sou
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Non-steady-State Systems. Journal o
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Latitudinal Patterns of Biological
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and perhaps others, may have invade
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colonizing the Arctic Ocean under c
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due in part to the great distances
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and (2) human-mediated responses to
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Lewis, P. N., M. Riddle, and C. L.
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Cosmology from Antarctica Robert W.
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There they found better observing c
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TELESCOPES AND INSTRUMENTS AT THE S
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Gaier, T., J. Schuster, and P. Lubi
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J. M. Kovac, C. L. Kuo, A. E. Lange
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Watching Star Birth from the Antarc
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STAR BIRTH FROM THE ANTARCTIC PLATE
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is constructing and deploying the P
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Antarctic Meteorites: Exploring the
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at the Field Museum, and pieces wer
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the description and curation of Ant
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led these committees throughout the
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Index AAUS. See American Academy of
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temperature, 350-355 tourism, 354 B
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Fishing. See also Biological invasi
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McMurdo Station, xiv, 265-267, 393
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Rogick, Mary, 206 Ronne, Finn, 55 R
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U.S. Naval Support Force Antarctica
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