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Historical Abundance and Morphology of Didymosphenia Species in Naknek Lake, Alaska

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Historical Abundance and Morphology of Didymosphenia Species in Naknek Lake, Alaska Color profile: Disabled Composite 150 lpi at 45 degrees Acta Bot. Croat. 68 (2), 183–197, 2009 CODEN: ABCRA25 ISSN 0365–0588 Historical abundance and morphology of Didymosphenia species in Naknek Lake, Alaska DANIELLE P. P ITE1,2,KELLY A. LANE1,ANNA K. HERMANN1,3, SARAH A. SPAULDING1,4*,BRUCE P. F INNEY5 1 INSTAAR Campus Box 450, University of Colorado, 1560 30th Street, Boulder CO 80309, USA 2 Smith College, Northampton MA 01063, USA 3 Tulane University, New Orleans LA 70118, USA 4 U.S. Geological Survey, Fort Collins Science Center, Fort Collins, CO 80526-8118, USA 5 Idaho State University, Department of Biological Sciences, Pocatello ID 83209, USA Since the 1980s, nuisance blooms of Didymosphenia geminata (Lyngbye) M. Schmidt have been documented in sites that are warmer and more mesotrophic than historical re- cords indicate. While the invasion of D. geminata in New Zealand is well documented, it is less clear whether nuisance blooms in North America are a new phenomenon. In order to test the hypothesis that D. geminata blooms have increased in recent years, we exam- ined the historical record of this species in sediments of Naknek Lake, in Katmai National Park, Alaska. Chronological control was established by relating the presence of two ash layers to known volcanic eruptions. We identified two species of Didymosphenia within the sediment record: D. geminata and D. clavaherculis (Ehrenberg) Metzeltin et Lange- -Bertalot. This is the first published record of D. clavaherculis in North America. We found no statistically significant change in the numerical presence of D. geminata or D. clavaherculis, as a group, in Naknek Lake between the years 1218 and 2003. While there has been no sudden, or recent, increase in abundance of Didymosphenia in Naknek Lake, morphological features of D. geminata populations in Naknek Lake are distinct compared to morphological features of D. geminata in streams containing nuisance blooms from sites in North America and New Zealand. Variance in the morphology of Didymosphenia cells may help determine relationships between distinct sub-populations and establish the history of habitat invasion. Key words: diatom, Didymosphenia geminata, Didymosphenia clavaherculis, morphology, counting, bloom, stream, lake, invasion, history, Alaska Introduction Until recently, Didymosphenia geminata (Lyngbye) M. Schmidt was thought to be lim- ited to cold, low-nutrient, well-oxygenated waters in northern latitudes. Nuisance blooms * Corresponding author: e-mail: [email protected] ACTA BOT. CROAT. 68 (2), 2009 183 U:\ACTA BOTANICA\Acta-Botan 2-09\Pite.vp 9. listopad 2009 13:01:38 Color profile: Disabled Composite 150 lpi at 45 degrees PITE D. P., LANE K. A., HERMANN A. K., SPAULDING S. A., FINNEY B. P. of this diatom, however, have been documented in warmer and more mesotrophic sites since the 1980s (NOGA 2003, KAWECKA and SANECKI 2003, SUBAKOV-SIMI] and CVIJAN 2004). Didymosphenia geminata is of concern in stream ecosystems because of its capacity to form thick masses, impacting biological and physical stream conditions. Further, this species is reported in streams and rivers across the United States (KUMAR et al. 2009). This diatom has demonstrated its invasive ability, evidenced by the presence of D. geminata in South Island of New Zealand in 2004 (KILROY et al. 2007). Although some reports assert that the nuisance blooms of D. geminata in North America (KUMAR et al. 2009) and Europe (KAWECKA and SANECKI 2003) are of recent occurrence, there are few to no historical data to establish the historical abundance of D. geminata. The purpose of this study is to exam- ine the historical record of Didymosphenia in order to test the hypothesis that blooms have increased in recent years. This paper documents the record of Didymosphenia over 800 years in the sediments of Naknek Lake, Alaska. Didymosphenia geminata was first recorded from the Faroe Islands in 1819 (LYNGBYE 1819). Other records in the early literature also mention the presence of D. geminata,in- cluding a reference to large masses in the Kanchou region of China (SKVORTZOW 1935). It is possible that extensive blooms are a normal part of this diatom’s life history, but few data exist to quantify stream growth habits. Recognition of the patterns of D. geminata growth is needed to understand the current blooms in North America (KUMAR et al. 2009) and Europe (BELTRAMI et al. 2008) and the expansion to New Zealand. While the invasion of D. geminata in New Zealand is well documented, it is less clear whether nuisance blooms in North America are a new phenomenon. Although several species of Didymosphenia are known from lakes (SKVORTZOW and MEYER 1928, KOCIOLEK et al. 2000), D. geminata is most often recorded in streams and rivers (SHEATH et al. 1986, LAPIERRIERE et al. 1989, MILLER et al. 1992, SHEATH et al. 1996, ELLWOOD and WHITTON 2007) where it appears to reach its greatest biomass (KILROY et al. 2007). Determining the history of diatoms in streams and rivers, however, is more prob- lematic than in lakes, as streams are high flow systems that typically do not leave a continu- ous sedimentary record that can be interpreted (SMOL 2002). Even so, reconstruction of en- vironmental change in rivers by examining stream diatoms deposited in the sediments of lakes has been shown to be successful (SMOL 2002). In sites where streams or rivers flow into lakes, records of historical change in river systems may be archived in lake sediments. For example, the relative abundance of stream diatoms [Hannaea arcus (Ehrenberg) Pat- rick and Meridion circulare (Greville) Agardh] found in lake sediments was used to recon- struct historical river discharge in the high arctic (LUDLAM et al. 1996, ANTONIADES and DOUGLAS 2002). Because Didymosphenia reaches its greatest abundance in streams and rivers, we propose that the concentration of cells in lake sediments is directly related to the concentration of cells in stream inflows. The presence of diatom cells preserved in lake sediments and the accurate dating of those sediments provide that opportunity to examine changes in cell abundance over time. Differences in valve morphology of D. geminata cells from different regions of Europe and Asia have been noted (ANTOINE and BENSON-EVANS 1983, STOERMER et al. 1986, METZELTIN and LANGE-BERTALOT 1995) and these morphological differences are thought to reflect distinct sub-populations. Although differences in the valve margins of diatoms are easily recognized visually, until recently few tools have existed to evaluate statistically sig- 184 ACTA BOT. CROAT. 68 (2), 2009 U:\ACTA BOTANICA\Acta-Botan 2-09\Pite.vp 5. listopad 2009 13:22:37 Color profile: Disabled Composite 150 lpi at 45 degrees DIDYMOSPHENIA IN NAKNEK LAKE nificant differences in shape (STOERMER et al. 1986). Diatoms, in particular, are a group of organisms whose species concepts and boundaries are based largely on differences in valve shape (STOERMER et al. 1986). Qualitative evaluation of valve morphology of cells of Didymosphenia may provide insights into the nature of the relatedness of populations and the history of range expansion and invasion into new habitats. Furthermore, preliminary evaluation of molecular markers in the internal transcribed spacer (ITS) regions of the 18S rRNA gene shows a distinction between populations of D. geminata from different geo- graphic regions (CARY et al. 2008). These results not only indicate a marked separation be- tween the European and North American populations of D. geminata, but the close affilia- tion of North American and New Zealand populations. The second objective of this paper is to examine the morphology of D. geminata cells preserved in sediments dating to 800 years B.P. and compare valve shape to modern, bloom-forming populations of D. geminata from around the world. Materials and methods Naknek Lake is located in Katmai National Park, Alaska, near the base of the Alaskan Peninsula (latitude 58°40’N and longitude 156°12’W) (Fig. 1). The lake is 64 km long and up to 13 km wide and has a maximum depth of 173 m (LAPERRIERE 1997). The lake is fed Fig. 1. Map showing Alaska (inset) with the Naknek Lake Watershed in Katmai National Park. Bathymetric map of Naknek and Brooks Lakes with contours at 10 m intervals. The site where the sediment core was taken is marked by an »X«. Brooks Lake flows into Naknek Lake via Brooks River, providing much of the clear water inflow. The Savanoski and Utak Rivers and Margot Creek are the major inflows to the southern arm of Naknek Lake. The outlet of Naknek Lake is the Naknek River. Map courtesy of the National Park Service, based on 1963 data. ACTA BOT. CROAT. 68 (2), 2009 185 U:\ACTA BOTANICA\Acta-Botan 2-09\Pite.vp 5. listopad 2009 13:22:37 Color profile: Disabled Composite 150 lpi at 45 degrees PITE D. P., LANE K. A., HERMANN A. K., SPAULDING S. A., FINNEY B. P. both by glacial meltwater and clearwater streams such as the major inflowing tributary, Brooks River. Naknek Lake drains west into Bristol Bay through the Naknek River. Naknek Lake is bounded by terminal moraines that were deposited by glaciers that flowed from east to west during the last glaciation. Based on dating of the terminal moraines, Naknek Lake is estimated to have formed approximately 14,000 years BP. The lake today receives a large input of silt particles from active glaciers in its watershed. The sediments are grey in color and suspended silt particles prevent light penetration in much of the lake (LAPERRIERE and EDMUNDSON 2000). Nutrient concentrations are low and the lakes are considered oligotrophic (GOLDMAN 1960, LAPERRIERE and JONES 2002). Cores were obtained from Naknek Lake in 2003 using both a hammer core and piston core. The coring location, at a water depth of 61 m, is shown in figure 1.
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