Grazing Impact of the Copepod <Emphasis Type="Italic">Calanus sinicus</Emphasis> on Phytoplankton in the Northern East China Sea in Late Spring

We investigated the feeding habits of Calanus sinicus during its four developmental stages as copepodite 4 (CIV), copepodite 5 (CV), adult males and females in early June 2015 at 12 sampling stations along the southern coast of Korea to the northern East China Sea, to better understand the role of C. sinicus in controlling phytoplankton stocks. Ingestion rate, daily ration as body carbon, population ingestion rate, and grazing impact were estimated using the gut pigment method. The mean biomass of CVs was the greatest (13.5 mg C m^–3) and that of adult males was the lowest (0.7 mg C m^–3). The ingestion rate per C. sinicus individual tended to increase with developmental stage, with the highest rate in adult females (519 ng chl ind^–1 d^–1) and the lowest rate in CIVs (305 ng chl ind^–1 d^–1). A significant correlation was found between ingestion rate and temperature, but not salinity or chlorophyll-a concentration. The daily ration of C. sinicus as body carbon significantly decreased with increased body weight, with the highest value found in CIVs (66.4%) and the lowest value in adult males (30%). Despite the high ingestion rate of the adults, the mean grazing impact of C. sinicus on phytoplankton biomass, in terms of chlorophyll-a concentration, was the highest in CVs (2.6%), followed by CIVs and adult females, and was the lowest in adult males (0.1%). The higher grazing impact of copepodites than adults underscores the importance of evaluating copepodite stages in the feeding studies of marine food webs.     

Changes in the egg production rate of two copepod species of the genus <Emphasis Type="Italic">Pseudocalanus</Emphasis> in relation to temperature in the White Sea

This study examines changes in egg production rates of two co-occurring Pseudocalanus species, P. acuspes and P. minutus, in response to changing temperatures (0, 3, 6, 9 and 12°C) in the White Sea. The boreal P. acuspes (sample size >650 individuals) increased its reproductive rate gradually across the entire range of temperatures from 0 to 12°C. Significant differences in egg production rates and reaction to temperature were also observed between P. acuspes females incubated during the early vs. the mid-summer season. The sample size of the Arctic P. minutus was significantly smaller due to the low numbers at which this species occurred. However, the results suggest that this species increases its egg production rates from 0 to 3°C from 3.3 to 8.5% dry weight female^–1 day^–1, but at 9° its reproductive rate drops significantly and the animals demonstrate markedly reduced fitness. Our results indicate that closely related co-occurring species, and even different generations within one species, can demonstrate significantly different responses to changes in the physical environment.     

Distribution of ephyrae and polyps of jellyfish <Emphasis Type="Italic">Aurelia</Emphasis><Emphasis Type="Italic">aurita</Emphasis> (Linnaeus 1758) <Emphasis Type="Italic">sensu lato</Emphasis> in Mikawa Bay,Japan

We surveyed the distribution of colonies of polyps of Aurelia aurita sensu lato (s.l.) in Mikawa Bay, Japan. First, we surveyed the distribution of ephyrae of A. aurita s.l. at 75 stations encompassing the whole of Mikawa Bay in early 2008. A total of 37 ephyrae were sampled mostly from fishing ports. Ephyrae were most abundant around the islands located near the mouth of the bay, and decreased from the western part to the eastern part of Mikawa Bay. Next, we selected five fishing ports in Mikawa Bay where ephyrae occurred and surveyed the underside of floating piers and underwater overhangs of wharfs. We found dense colonies of polyps of A. aurita s.l. under nearly all of the floating piers at the two islands located near the mouth of the bay. Fitting a logistic regression model to the dataset showed that the percentage coverage of Aurelia polyps was significantly greater at the two islands compared with the other locations. In addition, the coverage of Aurelia polyps was greater when the coverage of other fouling organisms was in the range of 65–90%, and the coverage of Aurelia polyps was lower on floating piers with a vinyl surface and on concrete wharfs. The combined distribution of polyp colonies of A. aurita s.l. in Ise Bay and Mikawa Bay suggested that A. aurita s.l. in the two bays probably forms a single population and shoals of medusae mainly originate from protected harbors along the mouth-part of the bays.     

Interannual and seasonal variation of the population structure,abundance, and biomass of the arctic copepod <Emphasis Type="Italic">Calanus glacialis</Emphasis> in the White Sea

The results of multiyear observations of the seasonal and inter-annual variability of the population structure, abundance, and biomass of the arctic calanoids copepod Calanus glacialis in the White Sea are presented. The spring season represents the most crucial period for the population’s seasonal dynamics. During the spring, the maximal abundance, biomass, and contribution of C. glacialis to the total zooplankton biomass is observed. The interannual variability of the abundance is closely related to the timing of the spring warming of the upper water column and the respective shifts of the onset of reproduction and the offspring development. The development of a new generation to the overwintering copepodite stage IV is usually completed three to four weeks later in the cold years compared to the warm ones. Our multiyear observations suggest that C. glacialis could be more tolerant of Arctic warming than it is usually believed. The high abundance of the C. glacialis population in the White Sea indicates that this arctic species is able to cope with the seasonal surface warming and should continue to do so, being provided with the cold water “refuge” in the deep sea.     

Molecular phylogeny of the genus <Emphasis Type="Italic">Chondracanthus</Emphasis> (Rhodophyta), focusing on the resurrection of <Emphasis Type="Italic">C. okamurae</Emphasis> and the description of <Emphasis Type="Italic">C. cincinnus</Emphasis> sp. nov.

Determining the taxonomic status of the red algal genus Chondracanthus based on morphological characters is challenging due to the similarity and high degree of plasticity of the thallus. Since the taxonomic history of several Chondracanthus species remains unclear, we analyzed the plastid rbcL and mitochondrial COI genes of the specimens from Korea and Japan, in combination with morphological observations, to examine their phylogenetic relationships. Our results confirmed the distinction of C. okamurae, which is separated from C. intermedius, and identified a novel species, C. cincinnus sp. nov. Three species (C. okamurae, C. intermedius and C. cincinnus) formed a monophyletic clade with C. tenellus. C. okamurae is distinguished by linear, narrow, cylindrical to compressed, slightly recurved axes, and a high-intertidal to subtidal distribution. It was collected from Korea and Japan, while C. intermedius was identified from Japan only. A new species, Chondracanthus cincinnus sp. nov., is characterized by linear, compressed, strongly recurved axes, and a low-intertidal to subtidal distiribution. Based on the molecular phylogeny using rbcL and COI data, we herein resurrect C. okamurae as a distinct species and identify C. cincinnus as a new species.     

Temporal changes in the geographic distribution of two clam species <Emphasis Type="Italic">Meretrix lusoria</Emphasis> and <Emphasis Type="Italic">M. petechialis</Emphasis> along the coast of Japan and South Korea

The objectives of this study were to distinguish fossil specimens of Meretrix (Bivalvia, Veneridae) using discriminant score and multivariate analysis, and to examine temporal changes in the geographical distributions of M. lusoria and M. petechialis in Japan and South Korea. Fossil shells of Meretrix were collected from Miyagi, Fukui, Aichi and Kumamoto in Japan, and Gimhae, Seosan, Siheung and Ganghwa-do in South Korea. The outside of the right valve was photographed with a digital camera, and ten characteristics of the shell morphology, such as shell height and shell length, were measured using image analysis software and a digital slide caliper. The discriminant score and multivariate analysis of the shell morphology identified all of the examined fossils as M. lusoria, while living individuals collected from the western coast of South Korea were identified as M. petechialis. These results suggest that the fossil shells excavated from the western coast of South Korea are a different species from the living individuals collected from the same areas. Radioactive carbon isotopic results revealed that the ages of the four fossil shells collected from tidal flats in Ganghwa-do ranged between 3,270 ± 30 and 1,830 ± 30 Cal BP. These results suggest that M. lusoria inhabited the western coast of South Korea until at least 2,000 years ago, but was replaced by M. petechialis during the last 2,000 years. Therefore, we propose that either M. petechialis spats were introduced artificially, or planktonic larvae migrated naturally from China to the western coast of South Korea during the last 2,000 years.     

Effects of temperature on growth,photophysiology, Rubisco gene expression in <Emphasis Type="Italic">Prorocentrum donghaiense</Emphasis> and <Emphasis Type="Italic">Karenia mikimotoi</Emphasis>

To explore the effects of temperature changes on dinoflagellate bloom succession in the coastal waters of the East China Sea, changes in the growth, photophysiology, and Rubisco gene expression of Prorocentrum donghaiense and Karenia mikimotoi, two harmful algal species, were investigated at different temperatures (16 to 28°C). The maximal specific growth rate and the maximal mRNA expression of Rubisco gene in P. donghaiense and K. mikimotoi occurred at 20 and 24°C, respectively. The photosynthetic activity of P. donghaiense was generally stable, but K. mikimotoi photosynthesis increased when temperatures rose from 16 to 28°C. The effective photochemical efficiency (F _q ^′ /F _m ^′ ) and the maximal relative electron transfer rate (rETR_max) of K. mikimotoi increased significantly with increasing temperature, and the lowest and highest values occurred at 16 and 28°C, respectively. It seems that P. donghaiense has higher photosynthetic capacity than K. mikimotoi due to its higher F _q ^′ /F _m ^′ , rETR_max, and photosynthetic efficiency (α). However, K. mikimotoi has a higher growth rate than P. donghaiense. These results suggest that the photosynthetic activity and genetic responses of dinoflagellates are species-dependent. It is likely that temperature changes affect species composition during blooms, leading to the observed patterns of bloom succession.     

Morphological differences between three groups of <Emphasis Type="Italic">Luciogobius guttatus</Emphasis> on the Korean Peninsula

Three ecological and geographical forms of Luciogobius guttatus from the western and eastern coasts of the Korean Peninsula as well as the coasts of, Jeju Island which is located to the south of the peninsula are described and compared based on morphological characteristics. The environments of these three coastal areas are different, and the morphometrics show a clear pattern of differentiation and reveal the discreteness of the western, eastern and Jeju groups. In addition, a discriminant analysis (DA), a principal component analysis (PCA) of morphometric characteristics, and a t-test for meristic characteristics all show that the three populations of L. guttatus differ from each other. Three divergent lineages of L. guttatus are described with the possibility of niche differentiation between the western, eastern and Jeju coastal habitats. The standard length of eastern populations was greater than that of western and Jeju populations, and those with morphometric characteristics had a longer body. In addition, eastern populations had a higher number of vertebrae. We speculate that the characteristics of eastern populations evolved through the difference in tide level and gravel density, whereas the difference between western and Jeju populations is due to geographical distance.     

<Emphasis Type="Italic">Zostera marina</Emphasis> seed burial can be enhanced by Manila clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis>: A microcosm study

Seagrass seed bank plays a key role in the regeneration of new vegetation when seagrasses are removed by the natural or man-made disaster. Various factors may affect the development of sediment seed bank. We conducted a microcosm experiment to test the effects of burrowing and feeding activities of Manila clam, Ruditapes philippinarum on the burial of Zostera marina seeds in sediments. The effects of lasting time (3-hour, 1-day, 3-day, 7-day, 14-day and 28-day), clam density (0, 2, 4 and 8 clams with shell length of 3 cm in each microcosm) and clam size (shell length of 2, 3 and 4 cm at 4-clam density) on seed burial were examined in plastic microcosm cores (30 cm high × 10 in inner diameter) in a 28-day period. Results showed that the seed burial depth significantly increased with time, the density and the size of clams. No seeds were buried in the sediment in the cores without clams during the whole experiment period. For the 3-cm clams, about 91.61% of the seeds were buried in the sediment at the end of the experiment in the high-density treatment (8 clams at each core); while in the medium and low-density treatments (4 and 2 clams in each core, respectively), about 76.93% and 60.61% of the seeds were buried in the sediment, respectively. For the size treatments, large (4 cm) clams buried 89.56% of the seeds at the end of the experiment, much more than those of medium (3 cm, 76.93%) and small (2 cm, 61.50%) size clams. During the whole experiment period, nearly all of the buried seeds were at a depth of from 0 cm to 5 cm. These results suggested that Manila clam Ruditapes philippinarum may play an important positive role in seagrass seed bank dynamics in the field.     

Feeding,egg production,and respiration rate of pteropods <Emphasis Type="Italic">Limacina</Emphasis> in Arctic seas

The feeding, egg production, and respiration rate of the dominant pteropod Limacina helicina have been studied in Russia’s Arctic seas. The sinking rates of fecal pellets and dead individuals have been measured to estimate their role in vertical carbon flux. As has been shown, the rate of ecophysiological processes taking place in the pteropods is higher than that of copepods, the main consumers of phytoplankton. The gut pigment content in Limacina (3084 ng ind^–1 as a maximum) was two orders of magnitude higher than in copepods. The egg production rate in Limacina even without feeding reached 4000 eggs ind^–1 versus 350–450 egg ind^–1 typical of the dominant copepods even with excess food. A close correlation between the pteropod feeding rate and individual body weight was observed for Limacina rather than a correlation with food concentration. The experimentally estimated sinking rate of Limacina fecal pellets was 270 m day^–1, higher than for most copepods. The sinking rate of dead pteropods reaches 2000 m day^–1. According to the literature, discarded mucous feeding nets sink at a rate of 80 to 1080 m day^–1. Evidently, pteropods play a significant role in biogeochemical cycles by accelerating sedimentation. High rates of all studied processes suggest that Limacina are an important component of plankton communities and play the most important role in trophodynamics at sites of their accumulation.     

Distribution of the primary production and chlorophyll <Emphasis Type="Italic">a</Emphasis> in the Kara Sea in September of 2007

The studies were performed from September 10 to 29 of 2007 in the Kara Sea in transects westward of the Yamal Peninsula, near the St. Anna Trough, in the Ob River’s estuary, and on the adjacent shelf. The concentration of chlorophyll a in the euphotic layer changed from 0.02 to 4.37 mg/m³, amounting on the average to 0.76 mg/m³. The primary production in the water column varied from 10.9 to 148.0 mg C/m² per day (the mean was 56.9 mg C/m² per day). It was shown that frontal zones divided the Kara Sea into distinct areas with different productivities. The maximum levels of the primary production were measured in the deep part of the Yamal transect (132.4 mg C/m² per day) and the shallow Kara Sea shelf near the Ob River’s estuary (74.9 mg C/m² per day). The characteristics of these regions were the low salinity of the surface water layer (19–25 psu) and the elevated silicon content (12.8–28.1 μg-atom Si/l), which is explainable by the river water inflow. The frontal zones of the Yamal Current in the Yamal and Ob transects displayed high values of the assimilation numbers, amounting to 2.32 and 1.49 mg C/mg of chlorophyll per h, respectively (the maximal for the studied regions).     

Pathologic survey on the Manila clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> (Adams and Reeve 1850) from Haeju off the western coastal Yellow Sea

Pathologic condition of Manila clam, Ruditapes philippinarum collected from Haeju off the west coast of North Korea in February and March 2007 was investigated in this study. The diagnostics included a protozoan parasite, Perkinsus olseni, the brown ring disease (BRD) caused by bacteria Vibrio tapetis and metazoan parasites Trematod and Cestod. P. olseni infection was examined using histology and Ray’s fluid thioglycollate medium (RFTM) assay along with Choi’s NaOH digestion technique. Trematode and cestode infection was also examined from the histology. A total of 140 clams with 35–45 mm in shell length (2–3 years old) were analyzed. Condition factor (CF), a ratio of the wet tissue weight to the shell dry weight, ranged from 0.445±0.074 (February) to 0.544±0.132 (March). Total body burden of P. olseni (i.e. infection intensity) ranged from 18,644±37,755 (February) to 26,933±80,611 cells/g wet tissue (March) with the prevalence of 76.7–43.3% (March) respectively. Prevalence of trematode and cestode infection in February and March varied 22.5–25.0 and 15.0–22.5% respectively. Infection intensity of V. tapetis ranged 1–2 and the prevalence was 1.4 (February) and 5.7% (March). Prevalence and infection intensity of P. olseni in clams from Haeju was comparatively lower than those of clams reported on the west coast of Korea. BRD and the other metazoan parasite infection were also relatively lower or similar to the condition of the clams reported previously. CF of Haeju clams was also relatively higher than the clams in Gyeonggi Bay and Taean, suggesting that Haeju clams had relatively better pathologic and health condition.     

Dietary shift and feeding intensity of <Emphasis Type="Italic">Stenobrachius leucopsarus</Emphasis> in the Bering Sea

The food habits of the dominant myctophid Stenobrachius leucopsarus were examined in the central basin of the Bering Sea in relation to oceanographic conditions, in summer 2002 and 2003 and spring 2006. S. leucopsarus exhibited an ontogenetic and seasonal dietary shift. In spring, small fish (≤40 mm) preyed mainly on Neocalanus flemingeri/plumchrus whereas large fish fed mainly on Neocalanus cristatus. In summer, small fish preyed mainly on Metridia pacifica whereas large fish fed mainly on euphausiids (Thysanoessa spp.). In the summer of 2003, when water temperature in the epipelagic layer (≤100 m) was warmer, reflecting the prevalence of the Alaskan Stream, small-sized S. leucopsarus showed a higher stomach content index, perhaps reflecting the greater abundance of M. pacifica. Thus, the present study shows that the physical variability in the epipelagic layer affects not only diets but also feeding performance of micronekton.     

High mortality and poor growth of green mussels, <Emphasis Type="Italic">Perna viridis</Emphasis>, in high chlorophyll-<Emphasis Type="Italic">a</Emphasis> environment

The current study was carried out from May 2014 to April 2015 to estimate the stock status of P. viridis in Marudu Bay. The gonad development was monitored by histological examination, while the population parameters including asymptotic length (L_∞), growth coefficient (K), mortality rate (Z, F and M), exploitation level (E) and recruitment of P. viridis were estimated using the lengthfrequency data. Results of the current study demonstrated that P. viridis in Marudu Bay spawned throughout the year with two major peaks, one in April to May and another one in October to December. The recruitment pattern was continuous with the peak in May to June 2014, which corresponded to the first spawning peak in April. However, no significant recruitment was observed from the second spawning peak due to the difference in spawning timing between male and female populations. The estimated asymptotic length (L_∞), growth coefficient (K), total mortality (Z), natural mortality (M), fishing mortality (F) and growth performance (ф) of P. viridis in Marudu Bay were estimate to be 117 mm, 0.97 yr^-1, 4.39 yr^-1, 1.23 yr^-1, 3.16 yr^-1 and 4.123, respectively. The exponent b of the lengthweight relationship was 2.4 and exploitation level (E) was 0.72. The high mortality, low condition indices and negative allometric of P. viridis in Marudu Bay is caused by a lack of suitable food in the surrounding water.     

Role of the <Emphasis Type="Italic">Noctiluca scintillans</Emphasis> population in the trophic dynamics of the Black Sea plankton over the spring period

Noctiluca scintillans is a common and numerous component of the heterotrophic plankton living in the Black Sea. It can play a significant role in the trophic dynamics of the pelagial community. The ingestion rate for the Black Sea Noctiluca is experimentally measured in this article, and its influence on the plankton community over the spring period is estimated. The average grazing of phytoplankton by the N. scintillans population made up about 0.8% in March. In local swarms, it was up to 11%. Noctiluca grazed 4.6% of the primary production per day in June. The grazing of Calanus euxinus eggs by the Noctiluca population varied from 1% to 42% in March. Then, it was 16% in April and 23% in June. The grazing of Acartia clausi eggs was from 1% to 7% in March–April (up to 80% in Noctiluca swarms), from 60% to 817% in May, and 45% in June. The grazing of Calanus faecal pellets was less than 1% in March–April and more than 20% in the beginning of June. It is the first time when the cumulative daily ration (subject to its various food components) for N. scintillans has been measured. The size of the ration was significantly higher than the energy expenditures on metabolism both in March (0.21 μg of C/ind/day) and in the beginning of June (0.28 μg of C/ind/day). Thus, the rapid growth of the population was enabled.     

Spatial variability of the primary production and chlorophyll <Emphasis Type="Italic">a</Emphasis> concentration in the drake passage in the austral spring

The spatial distribution of the primary production (PP) and the chlorophyll a concentration (Chl) were investigated during two research cruises in the Drake Passage area in October–November of 2007 and 2008. The algorithm evaluating the integral PP (PP_int) for the water column in this area was developed based on the data on the surface chlorophyll (Chl_s) and the incident solar irradiance obtained in 2004–2008 in the Atlantic Sector of the Southern Ocean. The results obtained both by the experimental and model approaches suggested that the Polar Front (PF) region of the Drake Passage was characterized by low values of both the PP_int (<100 mg C/m² per day) and Chl_s (0.08–0.20 mg/m³) in October–November. Low values of the Chl_s and relatively high phaeophytine a concentrations indicated the winter succession state of the phytoplankton community in the Antarctic Ocean and the southern Polar Frontal Zone (PFZ). The seasonal warming of the surface water layers and the developing pycnocline resulted in a phytoplankton bloom and a Chl_s concentration of more than 1 mg/m³ in mid-November in this area and the Subantarctic waters.     

New polymorphic microsatellite markers derived from hemocyte cDNA library of Manila clam <Emphasis Type="Italic">Ruditapes philippinarum</Emphasis> challenged by the protozoan parasite <Emphasis Type="Italic">Perkinsus olseni</Emphasis>

Manila clam Ruditapes philippinarum is one of the most important benthic animals in the coastal north Pacific region, where clam populations have been mixed genetically through trade and aquaculture activities. Accordingly, identification of the genetically different clam populations has become one of the most important issues to manage interbreeding of the local and introduced clam populations. To identify genetically different populations of clam populations, we developed 11 expressed sequence tag (EST)-microsatellite loci (i.e., simple sequence repeat, SSR) from 1,128 clam hemocyte cDNA clones challenged by the protozoan parasite Perkinsus olseni. Genotype analysis using the markers developed in this study demonstrated that clams from a tidal flat on the west coast contained 6 to 19 alleles per locus, and a population from Jeju Island had 4 to 20 alleles per locus. The expected heterozygosity of the 2 clam populations ranged from 0.472 to 0.919 for clams from the west coast, and 0.494 to 0.919 for clams from Jeju Island, respectively. Among the 11 loci discovered in this study, 7 loci significantly deviated from the Hardy-Weinberg equilibrium after Bonferroni correction. The 5 loci developed in this study also successfully amplified the SSRs of R. variegatus, a clam species taxonomically very close to R. philippinarum, from Hong Kong and Jeju Island. We believe that the 11 novel polymorphic SSR developed in this study can be utilized successfully in Manila clam genetic diversity analysis, as well as in genetic discrimination of different clam populations.     

Carbon and nitrogen dynamics of the intertidal seagrass, <Emphasis Type="Italic">Zostera japonica</Emphasis>, on the southern coast of the Korean peninsula

Seagrasses require a large amount of nutrient assimilation to support high levels of production, and thus nutrient limitation for growth often occurs in seagrass habitats. Seagrasses can take up nutrients from both the water column and sediments. However, since seagrasses inhabiting in the intertidal zones are exposed to the air during low tide, the intertidal species may exhibit significantly different carbon (C) and nitrogen (N) dynamics compared to the subtidal species. To examine C and N dynamics of the intertidal seagrass, Zostera japonica, C and N content and stable isotope ratios of above- and below-ground tissues were measured monthly at the three intertidal zones in Koje Bay on the southern coast of Korea. The C and N content and stable isotope (δ¹³C and δ¹⁵N) ratios of seagrass tissues exhibited significant seasonal variations. Both leaf and rhizome C content were not significantly correlated with productivity. Leaf δ¹³C values usually exhibited negative correlations with leaf productivity. These results of tissue C content and δ¹³C values suggest that photosynthesis of Z. japonica in the study site was not limited by inorganic C supply, and sufficient inorganic C was provided from the atmosphere. The tissue N content usually exhibited negative correlations with leaf productivity except at the upper intertidal zone, suggesting that Z. japonica growth was probably limited by N availability during high growing season. In the upper intertidal zone, no correlations between leaf productivity and tissue elemental content and stable isotope ratios were observed due to the severely suppressed growth caused by strong desiccation stress.