Asynchronous responses of fish assemblages to climate-driven ocean regime shifts between the upper and deep layer in the Ulleung basin of the East Sea from 1986 to 2010

Past studies suggested that a basin-wide regime shift occurred in 1988–1989, impacting marine ecosystem and fish assemblages in the western North Pacific. However, the detailed mechanisms involved in this phenomenon are still yet unclear. In the Ulleung basin of the East Sea, filefish, anchovy and sardine dominated the commercial fish catches in 1986–1992, but thereafter common squid comprised > 60% of the total catch in 1993–2010. To illuminate the mechanisms causing this dramatic shift in dominant fisheries species, I related changes in depth-specific oceanographic conditions from 0 to 500 m to inter-annual changes in the fish assemblage structure from 1986 to 2010. In the upper layer of 50–100 m depths, water temperature suddenly increased in 1987–1989, and consequently warm-water epi-pelagic species (anchovy, chub mackerel, and common squid) became dominant, while sardine, relatively cold-water epi-pelagic species, nearly disappeared. An annual index of the volume transport by the Korea Strait Bottom Cold Water, originating from the deep water of the Ulleung Basin, displayed a sudden intensification in 1992–1993, accompanied by decreased water temperature and increased water density in the deep water and replacement of dominant bentho-pelagic species from filefish, warm-water species, to herring and cod, cold-water species. The results suggest that climate-driven oceanic changes and the subsequent ecological impacts can occur asynchronously, often with time lags of several years, between the upper and the deep layer, and between epi-pelagic and deepwater fish assemblages.     

Climate-change driven range shifts of anchovy biomass projected by bio-physical coupling individual based model in the marginal seas of East Asia

Recent studies in the western North Pacific reported a declining standing stock biomass of anchovy (Engraulis japonicus) in the Yellow Sea and a climate-driven southward shift of anchovy catch in Korean waters. We investigated the effects of a warming ocean on the latitudinal shift of anchovy catch by developing and applying individual-based models (IBMs) based on a regional ocean circulation model and an IPCC climate change scenario. Despite the greater uncertainty, our two IBMs projected that, by the 2030s, the strengthened Tsushima warm current in the Korea Strait and the East Sea, driven by global warming, and the subsequent confinement of the relatively cold water masses within the Yellow Sea will decrease larval anchovy biomass in the Yellow Sea, but will increase it in the Korea Strait and the East Sea. The decreasing trend of anchovy biomass in the Yellow Sea was reproduced by our models, but further validation and enhancement of the models is required together with extended ichthyoplankton surveys to understand and reliably project range shifts of anchovy and the impacts such range shifts will have on the marine ecosystems and fisheries in the region.     

An assemblage of mollusks associated with the high latitude scleractinian coral <Emphasis Type="Italic">Alveopora japonica</Emphasis> (Eguchi 1968) in Jeju Island,off the south coast of Korea

Corals reefs and communities support a wide range of flora and fauna. The complete richness and abundance of faunal communities in either coral reefs or communities is not fully understood. This is especially true for high-latitude coral communities. In this work, we carried out an analysis of an Alveopora japonica associated mollusk assemblage, in Jeju Island, Korea. A. japonica is one of the major coral species present in high abundance (88–155 colonies m^-2), with a high recruitment rate (7.8 juvenile corals m^-2 yr^-1) in Jeju Island, and may serve as a habitat for other benthic organisms. In 2012, a total number of 579 A. japonica colonies with sizes ranging between 15.1-346.7 cm² in the surface area were collected from a 1m× 10m quadrat installed at a depth of 10 m at Keumneung, on the northwest coast of Jeju Island. Numerous benthic invertebrates were found to be associated with A. japonica colonies. Twenty-seven bivalves and gastropods were identified, including a boring mytilid, Lithophaga curta, and an arcid, Barbatia stearnsi. A zonalgeographical examination of the distribution ranges of these mollusks revealed a majority of warmer water species. Our observations also showed that A. japonica may be providing a habitat to grazing gastropod, Turbo cornutus, and encrusting Spondylidae and Chamidae bivalves. A. japonica forms a coral carpet with a distinct assemblage of bivalves. It is thought that the presence of these mollusks species in the coral indicates its use as a nursery for juvenile species, a ready food supply of organic detritus, and a refuge from predators.     

Comparison of anchovy biomass estimates measured by trawls,egg production methods and hydro-acoustics in the Chesapeake Bay and the Korea Strait

We compared estimates of anchovy biomass derived from trawl surveys, egg production method (EPM) and acoustic surveys, conducted in two remote regions. Biomass density of bay anchovy Anchoa mitchilli was estimated in Chesapeake Bay, USA, by trawls, EPM and acoustics from 1989 to 2000. Biomass density of Pacific anchovy Engraulis japonicus was estimated in the Korea Strait using EPM, simulation-based daily cohort analysis and acoustics from 1984 to 2006. Most of the existing estimates already had considered body-size-dependent gear selectivity, highlyvariable instantaneous natural mortality of anchovy eggs, and avoidance of trawl nets by adult anchovy. Despite great variability in the ratio of trawl to acoustic biomass estimates (0.034–8.35), annually-averaged biomass density of young-ofthe-year individuals derived by the two methods were similar for bay anchovy in Chesapeake Bay and Pacific anchovy in the Korea Strait (0.83 and 0.70 g m^?3, respectively). Results suggested that, despite substantial uncertainty, anchovy biomass estimates are generally compatible between EPM and acoustics. However, reported estimates of biomass density derived from the two acoustic surveys in the Korea Strait differed by a factor of 28, suggesting that further improvements in calibrations are required to reliably estimate anchovy biomass. The comparisons suggested that all biomass estimates could be biased and will require comparison and validation by other, independent sampling methods.     

A Temperature-Dependent Growth Equation for Larval Chub Mackerel (Scomber japonicus)

Ocean Science Journal - Chub mackerel are commercially one of the most important species in the western North Pacific. Variations in water temperature and growth during the early life stages are...     

Fish biomass size spectra in Chesapeake Bay

Biomass size spectra of pelagic fish were modeled to describe community structure, estimate potential fish production, and delineate trophic relationships in Chesapeake Bay. Spectra were constructed from midwater trawl collections each year in April, June–August, and October 1995–2000. The size spectra were bimodal: the first spectral dome corresponded to small zooplanktivorous fish, primarily bay anchovyAnchoa mitchilli; the second dome consisted of larger fish from several feeding guilds that are supported by multiple prey-predator linkages. Annual production estimates of pelagic fish, derived from a mean production to biomass ratio, varied nearly three-fold, ranging from 162 × 109 kcal (125 × 103 tons) in 1996 to 457 × 109 kcal (352 × 103 tons) in 2000. Seasonally, the biomass level and mean individual sizes of fish in the first dome increased from April to October, while the biomass level of the second dome was relatively stable. Regionally, biomass levels in the second dome were higher than biomasses in the first dome for the upper and lower Bay, but were minimal in the middle Bay where seasonal and episodic hypoxia occurs. To test a benthic-pelagic coupling hypothesis that could explain the higher biomass in the second domes for the lower and upper Bay, a cyclic size-spectrum model was fit that included only species in the zooplanktivorous-piscivorous fish guilds. The mean, normalized slope equaled ?1, indicating that zooplanktivorous fish may support piscivore production, but that a benthic-pelagic linkage is required to fully support fish production in the second dome. Interannual variability in slopes and intercepts of modeled size spectra was related to salinity, recruitment level of bay anchovy, and the primary axis of a correspondence analysis (salinity effect) on fish community structure. The spectral slope and intercept of normalized spectra were lowest in 1996, a near-record wet year. Results suggest that fish size spectra can be developed as useful indicators of ecosystem state and response to perturbations, especially if prey-predator relationships are explicitly represented.     

Decadal changes in fish assemblages in waters near the Ieodo ocean research station (East China Sea) in relation to climate change from 1984 to 2010

We compiled and analyzed past time-series data to evaluate changes in oceanographic conditions and marine ecosystems near the Ieodo ocean research station (IORS) in the East China Sea (N 31°15??C33°45??, E 124°15??C127°45??) in relation to longterm changes in climate and global warming. The environment data we used was a depth-specific time-series of temperature and salinity for the water columns at 175 fixed stations along 22 oceanographic lines in Korean waters, based on bimonthly measurements since 1961 taken by the National Fisheries Research & Development Institute. As an indicator for the ecosystem status of the waters off Ieodo, we analyzed species composition in biomass of fishes caught by Korean fishing vessels in the waters near the IORS (1984?C2010) and summarized the data in relation to the environmental changes using canonical correspondence analysis (CCA). To detect step changes in the time-series of environmental factors, we applied a sequential t-test analysis of regime shift. Correspondence analysis detected a major shift in fish assemblage structure between 1990 and 1993: the dominant species was filefish during 1981?C1992, but chub mackerel during 1992?C2007. This shift in fish assemblage structure seemed to be related to the well-established 1989 regime shift in the North Pacific, which was confirmed again with respect to temperature in the Yellow Sea and the Korea Strait (but not in the waters off the IORS). In overall from 1984 to 2010, salinity was more important than water temperature in CCA, implying that the fluctuation of the Tsushima warm current is a most important force driving the long-term changes in fish assemblage structure in the waters off the IORS. Further multidisciplinary researches are required to identify oceanographic and biological processes that link climate-driven physical changes to fish recruitment and habitat range fluctuations.