The complete mitochondrial genome of Haustorioides koreanus Jo, 1988 (Crustacea: Amphipoda: Dogielinotidae).

The mitochondrial genome of a dogielinotid amphipod, Haustorioides koreanus, was completely sequenced for the first time. The total mitogenome length of H. koreanus was 14,839 bp with 13 protein-coding genes, two ribosomal RNA genes, and 22 transfer RNA genes. The phylogenetic tree confirmed that H. koreanus belongs to the families Hyalellidae in the same clade and to the suborder Senticaudata within Amphipoda. This is the first record of the complete mitochondrial genome sequence of the family Dogielinotidae.

Ocean freshening and acidification differentially influence mortality and behavior of the Antarctic amphipod Gondogeneia antarctica.

The Western Antarctic Peninsula (WAP) has experienced rapid atmospheric and ocean warming over the past few decades and many marine-terminating glaciers have considerably retreated. Glacial retreat is accompanied by fresh meltwater intrusion, which may result in the freshening and acidification of coastal waters. Marian Cove (MC), on King George Island in the WAP, undergoes one of the highest rates of glacial retreat. Intertidal and shallow subtidal waters are likely more susceptible to these processes, and sensitive biological responses are expected from the organisms inhabiting this area. The gammarid amphipod Gondogeneia antarctica is one of the most abundant species in the shallow, nearshore Antarctic waters, and it occupies an essential ecological niche in the coastal marine WAP ecosystem. In this study, we tested the sensitivity of G. antarctica to lowered salinity and pH by meltwater intrusion following glacial retreat. We exposed G. antarctica to four different treatments combining two salinities (34 and 27 psu) and pH (8.0 and 7.6) levels for 26 days. Mortality, excluding cannibalized individuals, increased under low pH but decreased under low salinity conditions. Meanwhile, low salinity increased cannibalism, whereas low pH reduced food detection. Shelter use during the daytime decreased under each low salinity and pH condition, indicating that the two stressors act as disruptors of amphipod behavior. Under low salinity conditions, swimming increased during the daytime but decreased at night. Although interactions between low salinity and low pH were not observed during the experiment, the results suggest that each stressor, likely induced by glacial melting, causes altered behaviors in amphipods. These environmental factors may threaten population persistence in Marian Cove and possibly other similar glacial embayments.

Respiration of the sea urchin Mesocentrotus nudus in response to large temperature fluctuations.

Some subtidal habitats may experience extremely large diel temperature fluctuations. To explore the potential of subtidal animals to regulate their metabolic processes, we investigated how the oxygen consumption rate (MO2) of the sea urchin Mesocentrotus nudus changes in response to extreme temperature fluctuations by mimicking temperature variations recorded at Dokdo Island, Republic of Korea. We compared the MO2 of urchins before and after a temperature fluctuation. MO2 was positively correlated with temperature. There was no change in the mean MO2 values even after exposure to fluctuating temperature. There was no significant difference in mean MO2 between large and small temperature fluctuations. These results indicate that the metabolic activity of M. nudus might be well-adapted to extreme temperature fluctuations. However, given that the temperature coefficient (Q10) values decreased with increasing temperature and Q10 values during the temperature decrease was higher than those during temperature increase, temperature rise may still act as a stressor for these animals.

At the tipping point: Differential influences of warming and deoxygenation on the survival, emergence, and respiration of cosmopolitan clams.

Although warming and low dissolved oxygen (DO) levels are co-occurring significant climatic stressors in the ocean, the combined effects of these stressors on marine benthic animals have not been well established. Here, we tested the effects of elevated temperatures and low dissolved oxygen levels on the survival, emerging behavior from sediment, and the respiration of juvenile cosmopolitan Manila clams (Venerupis philippinarum) by exposing them to two temperatures (20 and 23.5°C) and DO levels (3.5 and 6-7 mg/L). Although within previously described tolerable ranges of temperature and DO, this 3.5°C increase in temperature combined with a 50% decrease in DO had a devastating effect on the survival of clams (85% mortality after 8 days). The mortality of clams under normoxia at 23.5°C appeared to be higher than under the low DO condition at 20°C. On the other hand, more clams emerged from sediment under the low DO condition at 20°C than under any other conditions. Oxygen consumption rates were not significantly affected by different conditions. Our results suggest temperature elevation combined with low oxygen additively increases stress on Manila clams and that warming is at least as stressful as low DO in terms of mortality. However, low DO poses another threat as it may induce emergence from sediment, and, thus increase predation risk. This is the first evidence that a combination of warming and deoxygenation stressors should reduce population survival of clams much more so than changes in a single stressor.

Temporal and spatial differentiation in microhabitat use: Implications for reproductive isolation and ecological niche specification.

Niche differentiation enables ecologically similar species to coexist by lessening competition over food and/or shelters and may be critical for reproductive isolation between closely related species in close proximity. Because no extra traits need to evolve, spatial and temporal differentiation may readily take place to complement other isolating mechanisms. Two closely related treefrog species occur together in Korea: the endangered Hyla suweonensis and the widespread Hyla japonica. Advertisement calls are differentiated, but it is unclear whether call difference is sufficient for reproductive isolation. We tracked individuals of both species to study fine-scale differentiation in microhabitat use in the diel cycle of the breeding season using a harmonic direction finder. tracking male movement patterns of both species revealed spatial and temporal differentiation in microhabitat use for calling and resting during the breeding season. Males of both H. suweonensis and H. japonica occurred in all 5 microhabitats identified in this study: rice paddy, ground, buried, grass and bush. Both treefrog species showed general similarities in calling from rice paddies and resting in grass and bush. However, H. suweonensis moved into rice paddies and produced advertisement calls 3 h earlier than H. japonica. These differences likely minimize contact between the species and provide an additional isolating mechanism. In addition, the activity of H. suweonensis may be contributing to the decline of this species, as resting in grass would increase dangers from predatory birds and habitat disturbance.