We estimated the production of the copepod Calanus sinicus, including somatic production of copepodite stage 1 (CI) to copepodite stage 5 (CV) and egg production of adult females, to elucidate the role of C. sinicus during spring in the northern East China Sea, including the southern waters of Korea. To estimate the somatic production of the copepodites, an empirical equation for broadcasters (Hirst & Bunker 2003) was used. The total biomass of the C. sinicus population, including CI to adult males and females, ranged from 0.11 to 30.23 mg C m−3, with a mean of 8.69 mg C m−3. The egg production rate (EPR) of adult females of C. sinicus, measured over 24 h of shipboard incubation, ranged from 0 to 14.9 eggs female−1 day−1 (mean 5.8 eggs female−1 day−1), equivalent to mean 33.6 µg C m−3 day−1. The weight-specific EPR (WSEPR) of adult females averaged 0.023 day−1, and significantly increased with increasing water temperature at 5 m depth and surface chlorophyll a concentration, respectively. WSEPR decreased with increasing body mass of individual adult females. The total production of the C. sinicus population ranged from 0.02 to 3.67 mg C m−3 day−1 (mean 0.91 mg C m−3 day−1) and the depth-integrated mean total production was estimated to be 52.72 mg C m−2 day−1. CV production accounted for 54% of the total production. By contrast, EPR contributed on average only 3.7% of the total production rate. Our estimate of the production of C. sinicus can be applied for potential comparisons of region-specific copepod production.
Species composition and quantitative characteristics of the macrozoobenthos in the Kytai Lake were studied. During 2006–2012, 272 macrozoobenthic samples were collected from the littoral and sublittoral zones of the lake. A total of 66 species were identified in the collected samples. In 2006–2009, the number of species increased from the upper to the lower reaches of the lake, with all 66 species recorded in the latter. However, with increasing salinity and decreasing dissolved oxygen content, the total number of macrozoobenthic species dropped up to 12 in 2012, with the highest number observed at the lower reaches. The average annual macrozoobenthic abundance and biomass in the littoral zone (836±33.08 ind. m−2 and 19.7±0.78 g m−2, respectively) were comparable to those in the sublittoral zone (879±35.16 ind. m−2 and 9.19±0.36 g m−2, respectively). In summer 2012, during the period of maximum development, the macrozoobenthic abundance and biomass in the littoral zone were 346 ind. m−2 and 3.26 g m−2, respectively. The Shannon-Weaver diversity index reached 3.26 bits ind−1 in the littoral zone in 2006–2008 and then decreased to 2.34 bits ind−1 in 2010–2012. The Pielou evenness indices during these periods were 0.66 and 0.61, respectively. In August 2009–2012, the correlation coefficient between salinity and macrozoobenthic abundance was −0.97. In July 2006–2012, the correlation coefficient between dissolved oxygen content and macrozoobenthic biomass was 0.89, whereas that between dissolved oxygen content and macrozoobenthic species number was 0.95. Results of the correlation and multiple regression analyses revealed the key role of oxygen depletion in decreasing the macrozoobenthic species richness and its development. Principal component analysis indicated that the first two principal components, related to transparency, oxygen, salinity, and temperature, explained most of the total variance of the data. Transparency, oxygen, and temperature positively influenced the macrozoobenthic species composition and quantitative characteristics, whereas salinity exerted a negative influence.
The San Jorge Gulf, and the littoral to its north, is one of the most important fishing grounds for Argentina. Nevertheless, phytoplankton production has been scarcely studied. Here we analyzed during spring (2008) and summer (2009) the phytoplankton biomass, production, and the composition of phytoplankton and protozooplankton; their possible trophic relationships, and physical conditioners. At the south coast of the gulf during spring micro-nano-plankton (diatoms and dinoflagellates) were predominant and responsible for the maximum integrated production, comparable to that reported for the rich Argentinian shelf-break. Part of the organic carbon produced there was consumed by heterotrophic dinoflagellates, adding a trophic level to the food web. While at the center of the gulf, a conspicuous deep chlorophyll maximum would probably add organic matter to the bottom. During the following summer (2009), the ultra-fraction represented the largest contribution to total phytoplankton biomass, and was dominated by Synechococcus sp. This, plus the abundance of ciliates, indicate the prevalence of a microbial food web during summer. It has been found that the frontal zones in the north and south of the gulf, favoring high phytoplankton biomass and its maintenance due to high primary production, provide a favorable food environment for impregnated female shrimp in spring, and for larvae during summer.
ROV dive surveys were carried out inside and outside the Sumisu Caldera, located in the Izu-Bonin Arc. The caldera is hydrothermally active and nourishes a unique chemosynthetic ecosystem, which includes Bathymodiolus mussel beds and vestimentiferan tubeworms. Sixty-one gelatinous zooplankton morphotaxa were observed (21 ctenophores, 16 siphonophores, 10 hydromedusae, 4 scyphozoans and 10 thaliaceans), and notes on their taxonomy and fine-scale distributional data are presented. The vertical distribution patterns of gelatinous zooplankton clearly differed inside and outside the caldera: three gelatinous zooplankton morphotaxa, the ctenophores Lobata sp. “Boli” and undescribed Lobata “No auricles”, and the hydromedusa Earleria bruuni, were highly abundant inside, but not outside, of the caldera. Thaliaceans and Solmissusincisa s.l. (Narcomedusae) were distributed over a wider vertical range inside the caldera than outside. The utility of ROV video records for investigating midwater gelatinous zooplankton taxonomy and ecology is discussed, and the efficacy of ROV investigations for this type of research is shown.
Mass mortality of fish (∼8,500 fishes), mainly Oreochromis placidus, was noted in a man-made lake located at Kuching, Sarawak (Malaysia). A field investigation was conducted to collect water samples and fishes. Patches of discoloration in brick red were observed in the lake and clear oil layer was found on the surface of the water. Microscopic observation and enumeration of the water samples showed that the plankton composition was dominated by a green algal species Botryococcus sp., with the colony densities ranging 1.2×103–7.4×106 colonies L−1. Detailed morphological assessment by light microscopy revealed the dominant species as Botryococcusbraunii Kützing. Molecular characterization using an rDNA marker further supported the species identity as B. braunii in the L race. Fish gill observation showed that cells of B. braunii and the oily substances were found in the dead fish gills. The race-L B. braunii bloom was reported, for the first time, to be associated with a fish kill event in a freshwater lake in Malaysia and confirmed the species as one of the algal types causing harmful effects to the environment.
The family Vitrinellidae is a group of tiny marine snails that generally occur in shallow waters of temperate and tropical seas. The biology of most vitrinellid species remains poorly understood. In this study, we report that Circulus cinguliferus (A. Adams, 1850) (Vitrinellidae), distributed widely in the warm shallow waters of the Pacific, inhabit crustacean burrows, including those of the mud shrimp Neaxius acanthus (Strahlaxiidae) and snapping shrimp Alpheus rapax (Alpheidae), in the intertidal and subtidal flats of the Okinawa Islands, southern Japan. They exhibited highly clumped distribution among the host burrows, suggesting that they are attracted by conspecifics. Although the biology of most Circulus species remains unknown, Circulus texanus (D. R. Moore, 1965) is known to inhabit stomatopod burrows in the western Atlantic. Our findings suggest that such a commensal habit may be more widespread in this genus than previously thought.
Phyllochaetopterus (Annelida: Chaetopteridae) is a diverse genus of tube-dwelling polychaetes found in a wide range of marine environments from subtidal to abyssal depths, including chemosynthesis-based ecosystems. The Shinkai Seep Field (SSF) is a serpentinite-hosted system in the Mariana Trench, where the deepest-known Phyllochaetopterus polychaetes inhabit the surfaces of brucite/carbonate chimneys. Despite all specimens collected from SSF being morphologically consistent with P. polus originally described from a deep-sea hot vent on the Mid-Atlantic Ridge, molecular barcoding using the mitochondrial cytochrome c oxidase subunit I (COI) gene revealed at least three cryptic lineages, none of which corresponded to P. polus. Phylogenetic reconstruction recovered P. polus embedded among the three SSF lineages, confirming their close relationship. These results warrant careful examination of Phyllochaetopterus from other regions using integrative taxonomy in order to understand its true diversity and pinpoint further taxonomically informative morphological characters.