Min Jeong Baek

Life history and emergence pattern of cloeon dipterum (Ephemeroptera: Baetidae) in Korea

ABSTRACT Cloeon dipterum (L.) (Ephemeroptera: Baetidae), the common wetland mayfly, emerges and oviposits every season, except winter, and has overlapping generations in the temperate region. We investigated the life history of C. dipterum associated with drought. Field experiments and sampling were conducted in a wetland (25 by 80 m) located in central Korea. Larvae were sampled weekly within two habitat types (a large, deep wetland and a small, shallow wetland) using a dredge sampler, and adults were sampled every 2 d with cube emergence traps, from July 2011 to September 2012 (except winter). C. dipterum had an extended emergence period from late April to early October with four peaks: early May, mid-June, July, and August/September. When the water depth was shallow because of drought, emergence was suppressed and delayed. The accumulated degree-days and body length of the overwintering cohort that emerged in spring 2012 were markedly larger and longer than those of other cohorts. Adults emerged intensively around sunset. C. dipterum has a multivoltine life cycle with four cohorts per year; its life history and population density can be changed by natural disturbances such as drought and fish predation.

Development of Glyptotendipes tokunagai (Diptera: Chironomidae) Under Different Temperature Conditions

ABSTRACT The nonbiting midge, Glyptotendipes tokunagai Sasa (Diptera: Chironomidae), is an organism that can be used as a water quality indicator. Development of this insect under different temperatures was evaluated. The highest egg hatching rate was 99.12 ± 1.47% at 30°C, and the lowest was 84.50 ± 11.09% at 10°C. No eggs hatched at temperatures of 8 and 42°C. Developmental rate (1/h) increased gradually as temperature increased from 10 to 35°C with a peak rate (0.045 ± 0.0079) at 35°C. The estimated lower thermal threshold for egg hatching was 9.3°C. Adult emergence rate was highest (80.6%) at 30°C and lowest (22.2%) at 15°C. The developmental times (egg to adult) for both males and females decreased from 2,102.6 to 457.2 h and from 2,337.1 to 619.8 h as temperatures increased from 10 to 30°C. The estimated lower thermal thresholds for males and females were 11.4 and 10.4°C, respectively. The body sizes of all G. tokunagai decreased as temperature increased from 15 to 35°C. From the results of this study, the approximate rearing temperature for G. tokunagai is suggested to be 25–30°C for egg hatching, larval development, and emergence. Our results demonstrate that G. tokunagai is a potential test insect species that can be reared in the laboratory by providing optimal temperature conditions.

Drought effects on the colonization of benthic macroinvertebrate communities in the early successional phases in experimental mesocosm wetlands

We investigated the drought effects on the colonization rate and pattern of benthic macroinvertebrate communities in newly created mesocosm wetlands in the central Korean Peninsula, from June 2011 to June 2013. The comparison was made between the initial colonization after mesocosm construction (pre-drought) and the recolonization after a drought event (post-drought) with a drought period of 50 days between them. In addition, we categorized communities according to their biological traits in relation to drought. Our results showed that aquatic vegetation abundance and covering degree were higher in post-drought than in pre-drought, thereby influencing rapid colonization. Drought-resistant benthic macroinvertebrates colonized rapidly in post-drought; consequently, the colonization speed was 2.5-fold higher in post-drought than in pre-drought. We classified the benthic macroinvertebrate taxa into three groups: (1) a resistant group which generally emerged after the initial colonization period (e.g., Mollusca, Turbellaria, and Oligochaeta); (2) a sensitive group with diverse life history strategies and biological traits such as active migration or population decline after drought disturbance (e.g., Diptera: Chironominae, Odonata: Orthetrum, Coleoptera: Agabus and Rhantus); and (3) a seasonal group, which emerged only during certain periods and were not markedly influenced by drought (e.g., Ephemeroptera: Cloeon, Diptera: Culicidae, Odonata: Zygoptera and Pantala). Our findings elucidated the effects of drought on benthic macroinvertebrate communities in wetlands by using a mesocosm experiment.

Temporal changes in benthic macroinvertebrates and their interactions with fish predators after restoration in the Cheonggyecheon, a downtown stream in Seoul, Korea

The Cheonggyecheon (Cheonggye stream), a downtown stream in Seoul, Korea, was restored by the historic Cheonggyecheon Restoration Project (2003–2005), and its discharge and other environmental conditions are artificially regulated throughout the year. The aim of this study was to assess temporal changes in benthic macroinvertebrates and their interactions with fish predators in the Cheonggyecheon. Sampling was conducted twice a year (spring and autumn) at three sections of the stream from 2006 to 2010 using a Surber sampler (50 × 50 cm) for benthic macroinvertebrates and a cast net (mesh size, 10 × 10 mm) and a kick net (mesh size, 5 × 5 mm) for fishes. Analyses of annual precipitation and most water quality parameters showed no significant differences across the study period (P > 0.05). The species richness and density of benthic macroinvertebrates and fishes varied across the sampling period. Analyses of functional feeding groups and trophic guilds showed distinct trends, such as an increase in the number of insectivorous fish in the absence of invertebrate predators. Correlation and regression analyses for five major groups of benthic macroinvertebrates and fishes demonstrated that the density of certain groups of benthic macroinvertebrates (e.g. Tubificidae, Erpobdellidae, Baetidae, and Chironomidae) and insectivorous fishes (e.g. Gobioninae, Leuciscinae, Danioninae, and Gobiidae) were negatively correlated. In conclusion, in an artificially regulated stream like the restored Cheonggyecheon, where physical environments are nearly unchanged, fish predation can be a major factor controlling benthic macroinvertebrate communities.

Four-year successive rearing of Glyptotendipes tokunagai Sasa (Diptera: Chironomidae) under laboratory condition

The dipteran Chironomidae have been commonly used as water quality indicators and toxicity test organisms. Two chironomids, Chironomus riparius Meigan and C. tentans Fabricius, are standard test organisms for toxicity (OECD), but their distribution is limited in Korea. The purpose of this study was to establish a Korean native chironomid species as a toxicity test organism. Glyptotendipes tokunagai Sasa, distributed widely in Korean streams, was selected and reared successively under laboratory conditions for over 30 generations over 4 years.

Biological and Genetic Characteristics of Glyptotendipes tokunagai (Diptera: Chironomidae) on the Basis of Successive Rearing of Forty-Two Generations Over Seven Years Under Laboratory Conditions

ABSTRACT Members of the nonbiting midge family Chironomidae have been used worldwide as water-quality indicators or toxicity test organisms. The purpose of this study was to establish the chironomid Glyptotendipes tokunagai Sasa as a new test species by conducting successive rearing under laboratory conditions. We monitored biological and genetic aspects of >42 successive generations over 7 yr, and also compared the development of the 39th generation with the fourth generation under five constant temperatures of 15, 20, 25, 30, and 35°C. We observed that the number of eggs in an egg mass and the adult body sizes decreased rapidly in the early generations, and thereafter tended to stabilize from the fifth generation to the 42nd generation. In all generations, the mean hatching rate was >75%. Males were predominant in the early generations, but the sex ratio increased to 0.5 (ranged 0.24–0.61) in later generations. The genetic divergence of the reared generations, analyzed by using the mitochondrial cytochrome c oxidase subunit I gene, decreased from 0.0049 to 0.0004 as the generations progressed. In comparison with the fourth generation, the mortality and developmental time of the 39th generation were generally greater, and the adult body sizes were generally smaller. The estimated low developmental threshold temperatures of eggs, male larvae to male adults, and female larvae to female adults were 9.6, 11.3, and 9.7°C, respectively. The optimal rearing temperature was determined to be 25°C. This is the first record of domesticated rearing of a wild chironomid species under laboratory conditions for >7 yr.

Life history differences of Psilotreta locumtenens (Trichoptera: Odontoceridae) in two reaches of a mountain stream in Korea

The life history traits of the caddisfly, Psilotreta locumtenens Botosaneanu (Odontoceridae), were studied in two stream reaches with different thermal ranges (main and branch streams) of the Gapyeong Stream, a typical mountain stream located in the central Korean Peninsula. Psilotreta locumtenens larvae were quantitatively sampled monthly from November 2008 to July 2010, and biweekly during the emergence period (late April to early July), using a Surber sampler (30 × 30 cm). Adults were quantitatively sampled with a sweep net. Larval density in the main stream (324.21 ± 38.59 m−2) was higher than that in the branch stream (60.48 ± 10.86 m−2). The larvae hatched in the early summer and overwintered as 5th and 3rd instars in the main and branch streams, respectively. The emergence peak at the main stream was approximately 2 weeks earlier. The sex ratio at both sites was approximately 0.3. The life history in both streams was univoltine. Secondary production in the main stream was much higher than in the branch stream, owing to high larval densities, and the P/B ratios at the two sites were similar. This study demonstrated remarkable differences in larval growth patterns and emergence peaks in P. locumtenens between the two stream reaches due to differences in accumulated degree days (230.30 DD) and other phenological cues such as daily mean threshold water temperature (9°C) during the ascending phase, despite their relatively small mean annual water temperature difference of 0.58°C.

A long‐term change of benthic macroinvertebrate communities in the Cheonggye stream, a restored urban stream in Seoul, Korea

Stream restoration affects stream biodiversity by improving water quality and habitat environments. Benthic macroinvertebrates are used as indicators of changes in stream environment, and, therefore, the effects of restoration can be evaluated by a long‐term monitoring of benthic macroinvertebrates. Cheonggye stream is an urban stream in Seoul, Korea, and a restoration project was conducted from July 2003 to September 2005. The purpose of this study was to investigate the long‐term changes in the benthic macroinvertebrate communities in Cheonggye stream after the restoration project in 2005.

Impact of flood intensity on aquatic insect communities in a Korean stream under monsoonal climate

As a consequence of climate change, localized torrential rainfall has increased in intensity and frequency in Northeast Asia under the influence of the monsoonal climate. The purpose of this study was to evaluate the impact of flood intensity on aquatic insect communities in a Korean stream, where the summer monsoonal flood is normal. Quantitative sampling was conducted according to stream reaches (upstream, midstream, and downstream sites) in Gapyeong stream, located in the central Korean peninsula, during July 2008–October 2009. Sampling was conducted within 48 hours after every rain event during the rainy season, and flood intensity was evaluated using the total amount of precipitation for 3 days before sampling. Precipitation was categorized in 100 mm increments. Water velocity and Froude number (Fr) were measured, and mean species abundance and species richness were determined. Habitat orientation groups (HOGs) were analyzed. Data were analyzed using nonmetric multidimensional scaling (NMS) ordination and two‐way analyses of variance .