Title
Coastal Lagoon Monitoring in the Southern Chukchi Sea National Park Units: Fieldwork Summary 2021
Author(s)
Kevin Fraley; Martin Robards; Michael Lunde
Published
2022
Abstract
Wildlife Conservation Society (WCS) has worked with the National Park Service since 2012 to design and implement the Coastal Lagoon Vital Signs component of the Arctic Inventory and Monitoring Network. This program is intended to establish biotic and abiotic reference conditions for assessing long-term changes in the coastal lagoons of Cape Krusenstern National Monument and Bering Land Bridge National Preserve. The Vital Signs program focuses on monitoring both the structure and ecological function of lagoons, as well as the fish resources used for subsistence by coastal communities. A standardized Vital Signs Protocol was developed for these lagoons, informed by our field efforts throughout 2015-2018. Our 2021 Vital Signs fieldwork sought to build upon the pre-existing database of in-depth temporal and spatial information on lagoon ecology. There are nine coastal lagoons described in the boundary of Cape Krusenstern National Monument – Aukulak, Imik, Ipiavik, Kotlik, Krusenstern, Port, Sisualik, Tasaycheck, and Atilagauraq. We collected seasonal physical and biological data at three Cape Krusenstern lagoons including Kotlik, Krusenstern and Aukulak, which have been previously sampled in 2012 and 2015-2018. We measured physical and chemical water properties, primary productivity, and performed benthic Mysidae tows at all three lagoons. We also assessed lagoon fish assemblage diversity and abundance, sampled a variety of fish to evaluate contaminant loads in subsistence-harvested species, and collected stickleback species for proximate composition and food web analyses. Additionally, we conducted sampling at the mouth of the Tukrok River, a riverine matrix which acts as the connection between Krusenstern Lagoon and the Chukchi Sea, with the outlet to the marine environment located 14 km away from the main body of the lagoon. Given the significant distance between the two sampling locations we treated the Tukrok River mouth as an entirely different sampling site than Krusenstern Lagoon. While ease of access and logistics allowed for two sampling efforts at Cape Krusenstern lagoons via wheeled airplanes (June and August), the lack of a floatplane or a helicopter prevented sampling efforts at Bering Land Bridge lagoons during the 2021 field season. We generally accessed the various Park unit lagoons via fixed-wing plane equipped with tundra tires. Within and among each visited lagoon, we used a small inflatable boat equipped with a 9.9 horsepower outboard motor. Four long-term stations (center, outflow, inflow, and marine edge) and three random sampling stations were sampled at each lagoon. At each station and during each season we collected water quality and primary productivity data (YSI Sonde instrumentation) at all long-term and random sites. Fish sampling occurred at the outflow, marine edge, and inflow sites during both seasons, including a total of 40 beach seine pulls, 14 2-hour fyke net sets, and 74 gillnet sets (varying durations). Additionally, certain stations were sampled for Mysidae diversity and abundance using a benthic tow net. These investigations will supplement results from ongoing and future laboratory analyses of fish and Mysidae samples in collaboration with the University of Alaska Fairbanks. Lagoons varied in their seasonal connectivity with the ocean. Krusenstern and Kotlik Lagoons were open to the marine environment during the first round of sampling in June, and closed during the second round of sampling in August. Aukulak Lagoon remained closed throughout the 2021 summer season. Evaluation of water quality data indicates that physical water properties varied by lagoon and season. Seasonal salinity levels tracked those of previous years, and were related to a lagoon’s connection with the marine environment; the more directly connected the lagoon is to the Chukchi Sea, the higher its salinity. Average salinity levels at all lagoons dropped between the first and second sampling rounds, likely because of closure to the marine environment and significant rainfall that preceded the final sampling excursion. Because Aukulak Lagoon remained closed to the ocean, and Krusenstern is 14 km distant from the marine opening, they exhibited low salinity throughout the year. Mean water temperatures at all three lagoons decreased over the course of the field season and were largely comparable to temperatures from previous years. However, average temperatures in Aukulak and Kotlik Lagoons in the early season (20.30 and 16.47 C, respectively) were higher than any from 2012-2018, indicating a warmer-than-average June in 2021. Dissolved oxygen saturation decreased at all lagoons over the course of the season, but saturation was higher than 96% at all times, indicating normoxic conditions. Lagoon pH was lower in 2021 compared to previous years, and lower in the late season. This indicates a shift towards greater acidity, yet levels are comparable to adjacent environments and remain well above thresholds of concern for biota. Turbidity of lagoons was low overall (0.71-11.44 FNU), and increased from the early to late sampling season, likely a result of suspended sediment entrained by persistent storms in August 2021. As in previous years, Krusenstern Lagoon exhibited the highest turbidity, likely due to wind-driven turbation caused by the lagoon’s considerable fetch. Primary productivity was low during the 2021 season, likely due to an uncommonly stormy and cloudy summer that was not conducive for optimal autotrophic growth and reproduction. Total chlorophyll ranged from 1.01 – 3.56 RFU and blue-green algae concentration ranged from 0.17 – 0.92 RFU. Algal blooms were not observed visually like they had been during previous sampling years. Experimental Mysidae sampling with a benthic tow net was effective in lagoons where Mysidae were present (Krusenstern and Kotlik) and yielded ample sample volumes, which have been frozen and are being held by WCS for future taxonomic sorting, counting, proximate composition analyses, and food web studies. We captured and processed 1,726 fish at the lagoons and the Tukrok River mouth, which represented much lower overall abundance than previous years. We attribute this to fewer small-bodied forage fish being present across sites, and the near-absence of fish in Aukulak Lagoon due to winterkill. Species richness of fishes and their abundance in lagoons fluctuated during the course of each field season with population composition and relative abundance varying between both season and lagoon. We recorded a total of 20 different fish species, including the typical suite of key forage and important subsistence species. This was similar to species diversity in 2018, but lower than the most speciose year in 2016 (25 species). Diversity was highest at Kotlik Lagoon, and diversity and abundance were lowest at Aukulak Lagoon with only four individuals of two species encountered because of winterkill and lack of lagoon marine connectivity. Several species that had rarely or never been encountered in previous lagoons investigations were caught, including broad whitefish, yellowfin sole, Arctic grayling, Alaska blackfish, and slimy sculpin. Conversely, notable absent taxa included Pacific salmon species, belligerent sculpin, capelin, and sand lance. Interestingly, the largest Dolly Varden and Arctic grayling ever recorded in the lagoons by WCS were captured in Kotlik Lagoon in June 2021. Overall, our research builds on prior lagoon ecology monitoring and research, providing information vital for understanding long-term change, monitoring and managing Arctic lagoons of these Park units. This data will help prioritize spill contingency planning (by establishing the most productive lagoons), and will continue to inform a comprehensive understanding of the Story of the Lagoons – a key priority for the Native Village of Kotzebue, Wildlife Conservation Society, and the National Park Service. Future planned efforts include evaluation of lagoon basal prey resource taxonomy and food web ecology, fish seasonal movements and life history chronology investigations, and community outreach efforts through film and other media.
With thanks to our partner organizations the Native Village of Kotzebue Environmental Program and the National Park Service Arctic Inventory and Monitoring Network.
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