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Effects of natural and anthropogenic stressors in the North Pacific ecosystems: Scientific challenges and possible solutions
 
Abstracts
 
Oral (S1-8663), Science Board Session

The Ocean Health Index: Global assessment and future priorities

Benjamin S. Halpern1,2

1 National Center for Ecological Analysis and Synthesis, 735 State St. Santa Barbara, CA, 93101, USA
E-mail: halpern@nceas.ucsb.edu
2 Center for Marine Assessment and Planning, UC Santa Barbara, Santa Barbara, CA, 93106, USA

Recent development of the Ocean Health Index offers a flexible, quantitative and comprehensive tool for assessing the condition of the natural and human dimensions of marine ecosystems. The Index assesses the sustainable delivery of 10 widely-held public goals for healthy oceans, using measures of the current status, relative to a reference point, and likely future state to quantify these goals. I will present results and lessons learned from the initial global assessment and discuss future priorities and opportunities to refine and expand the Index.

 
 
Poster (S1-8), Science Board Session

Decrease of surface water nutrient concentration and nutrient flux from the sediment in Harima-Nada, Eastern Seto Inland Sea, Japan

Kuninao Tada1, Miho Kayama1, Naoto Hirade1, Hitomi Yamaguchi1, Supaporn Yamaguchi1, Kazuhiro Harada2,
Minoru Tanda2, Munehiro Fujiwara3, Kazuhiko Ichimi4 and Tsuneo Honjo4

1 Faculty of Agriculture, Kagawa University, Miki, Kagawa, 761-0795, Japan. E-mail: tada@ag.kagawa-u.ac.jp
2 Fisheries Technology Institute, Hyogo Prefectural Technology Center for Agriculture, Forestry and Fisheries, 22-2 Minami-Futami, Akashi, Hyogo, 674-0097, Japan
3 Kagawa Prefectural Fisheries Experimental Station, Yashima-Higashi, Takamatsu, Kagawa, 761-0111, Japan
4 Seto Inland Sea Regional Research Center, Kagawa University, Takamatsu, Kagawa, 760-8521, Japan

From the 1960s onwards, when Japan achieved high economic growth, the Seto Inland Sea was heavily eutrophicated due to serious water pollution by industrial effluent and urban wastewater. The result was a high occurrences of red tides. Since the Law for Conservation of Environment of the Seto Inland Sea was enacted in 1973, water quality has gradually improved. Since 1990, however, nutrient concentrations in seawater have decreased considerably, which has raised a new problem. With the recent Dissolved Inorganic Nitrogen (DIN) decrease, Nori (Porphyra) yield has declined. The fisheries yield of species such as sardine and short-neck clam has also been affected negatively. We investigated the causes of the nutrient decrease by examining the nutrient concentration of surface water in the eastern part of the Seto Inland Sea. We also surveyed the content of organic matter in the surface sediments and nutrient upward fluxes from the sediments across the overlying water-sediment interface. Our results showed that the organic content and the horizontal distributions in surface sediments were similar to those of 30 years ago. On the other hand, the nutrient fluxes were quite low compared with fluxes examined about 10 and 30 years ago in the same area. In this study, we suggest that the decrease of nutrient upward flux is an important factor for the recent nutrient decrease in the surface seawater in the Seto Inland Sea.

 
 
Oral (BIO-P-8652), BIO Paper Session

Spatial, temporal and dietary overlap between harbour seals and fisheries in Erimo, Japan: Conflict at sea?

Tabitha C.Y. Hui1, Yumi Kobayashi2, Yoko Mitani3, Kei Fujii4, Kei Hayashi5 and Kazushi Miyashita3

1 Graduate School of Environmental Science, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido, 041-8611, Japan. E-mail: tcyhui@ees.hokudai.ac.jp
2 Faculty of Fisheries Sciences, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido, Japan 041-8611
3 Field Science Center for Northern Biosphere, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido, Japan 041-8611
4 Obihiro University of Agriculture and Veterinary Medicine, Kuril Harbor Seal Research Group, Obihiro, Hokkaido, Japan 080-0835
5 Pinniped Research Group, Obihiro, Hokkaido, Japan 080-0835

The harbour seal is an endangered species in Japan. Since protection began in the mid-1980s, the total number of harbour seals in Japan has been rebounding. With the increase in seal numbers, increased conflict with fisheries (especially salmon fixed-net fisheries) has occurred through depredation and the belief that seals compete with fisheries for prey. However, competition is unlikely if seals and fisheries take mostly different prey species, obtain prey from different areas or at different times. We studied the foraging ecology of harbour seals in Erimo, site of the largest population of harbour seals in Japan, from 2011-2012. We deployed satellite tags in July 2011 (n=1) and June 2012 (n=4). The foraging ranges (average size of 90% ranges was 30 km2) of all tagged seals overlapped at least one salmon fixed-net (5 total in Erimo). We collected seal scats in summer, fall and spring, identified prey items from hard parts retrieved and compared the results with local fisheries data. Of the 39 scats with identifiable prey remains analysed, none contained salmon remains. The seals’ diet differed greatly from fisheries catches. Gadoids (FO=55%), snailfish (FO=35%) and sculpins (FO=30%) were the main prey items found in seal scats. In contrast, salmonids were the main species caught by fisheries, accounting for >50% of catches by mass, followed by gadoids (15%). Resource overlap between seals and fisheries was <0.01 (Pianka index) in summer, fall and spring. As such, we conclude that competition is highly unlikely between harbour seals and fisheries in Erimo.

 
 
Poster (BIO-P-4), BIO Topic Session

Seasonal occurrence of mesopelagic fish larvae in the onshore side of the Kuroshio off southern Japan

Chiyuki Sassa1 and Yuichi Hirota2

1 Graduate School of Environmental Science, Hokkaido University, 3-1-1 Minato-cho, Hakodate, Hokkaido, 041-8611, Japan. E-mail: tcyhui@ees.hokudai.ac.jp
2 National Research Institute of Fisheries Science, Fisheries Research Agency, 2-12-4 Fukuura, Kanazawa-ku, Yokohama, Kanagawa, 236-8648, Japan

Information on the annual reproductive cycle of mesopelagic fishes has been limited in the western North Pacific, despite their ecological importance.. The Kuroshio region is an important spawning ground for various species of mesopelagic fishes. To describe the reproductive seasonality, we examined the seasonal occurrence patterns of the mesopelagic fish larvae on the continental slope in Tosa Bay which is strongly influenced by the Kuroshio, based on monthly samples collected from January 2001 to December 2004. In total, 2,558 mesopelagic fish larvae occurred, with peak abundance during May to June. Larvae of the dominant families Myctophidae, Sternoptychidae, Gonostomatidae, Bathylagidae, and Phosichthyidae were represented by 26 species (or types) belonging to 18 genera. The twelve most abundant species accounted for 96.9% of the total catch. The seasonal occurrence patterns of these larvae were categorized into five groups in accordance with physical properties of the water column: Winter (Notoscopelus japonicus and Lipolagus ochotensis); Spring (Symbolophorus evermanni and Maurolicus japonicus); Early summer (Myctophum asperum and Diaphus stubby type); Autumn (Lampanyctus sp. A, Cyclothone spp., and Sigmops gracile); and Year-round (Vinciguerria nimbaria, Diaphus slender type, and Diogenichthys atlanticus) groups. No significant difference was observed in the months of peak abundances of these larvae during the four years, suggesting that each species has a fixed seasonal pattern of reproduction. The various patterns of seasonal occurrence would result in seasonal habitat segregation of the larvae among species, possibly reducing intraspecific competition for food resources in the oligotrophic waters of the Kuroshio.

 
Oral (FIS-P-8501), FIS Paper Session

Spatial modeling of the potential fishing zone of Japanese common squid in coastal waters of southwestern Hokkaido, Japan

Xun Zhang, Sei-Ichi Saitoh and Toru Hirawake

Laboratory of Marine Environment and Resource Sensing, Graduate School of Fisheries Sciences, Hokkaido University, 3-1-1 Minato, Hakodate, Hokkaido, 041-8611, Japan. E-mail: xun@salmon.fish.hokudai.ac.jp

Japanese common squid (Todarodes pacificus) is one of the most commercially important fished species in the southwestern Hokkaido coastal region, Japan. Jigging fishing in this region usually occurs at nighttime from June to December and the lights used for fishing can be detected by DMSP (Defense Meteorological Satellite Program) OLS (Operational Linescan System). We used three years of data (2000, 2001 and 2002) on daily fishing vessel distribution derived from the nighttime DMSP/OLS images to identify the presence and absence of Japanese common squid assemblages along the southwestern Hokkaido coastal region. Corresponding environmental factors were considered to explain squid distribution, including bathymetry, SST (sea surface temperature), chlorophyll a concentration and Kd490 (diffuse attenuation coefficients of downwelling irradiance at 490-nm). We tested three different models to predict squid distribution: GAM (Generalized additive model), GLM (Generalized linear model) and BRT (Boosted regression trees). Model performance was validated and compared based on DMSP/OLS data of 2003. The comparisons indicated that the BRT was better than GAM and GLM. Results from the BRT showed that potential fishing zones were closely correlated with the depth of the water. SST and chlorophyll a highly contributed to squid occurrence as well, while Kd490 which is related to the transparency of the water was less associated with the distribution. In addition, we applied BRT to detect monthly potential fishing zones between 2004 and 2009 and mechanisms potentially responsible for the spatial and temporal variation.

 
Poster (FIS-P-12), FIS Paper Session

High dispersal of moray eel larvae to the open ocean: Early life history estimated from ocean-wide distribution patterns

Atsushi Tawa1, Taku Yoshimura2 and Noritaka Mochioka1

1 Laboratory of Fisheries Science, Graduate school of Bioresources and Bioenvironmental Science, Kyushu University, 6-10-1 Hakozaki, Higashi-ku, Fukuoka, 812-8581, Japan. E-mail: a-tawa@hotmail.co.jp
2 Seikai National Fisheries Research Institute, Fisheries Research Agency, 1551–8 Taira, Nagasaki, 851–2213, Japan

Information on larval fish ecology and early life history is very important for resource management and the conservation of marine biodiversity. In addition, larval recruitment of demersal fishes determines adult distribution patterns. Moray eels are important elements in tropical to temperate coastal ecosystems due to their role as a higher-level predator. Some species are reported to spawn in coastal areas, however, their larval ecology and early life histories are mostly unknown. Therefore, we first examined the distribution patterns of the leptocephali of different species or types in the Indo-Pacific to estimate the general early life history of moray eels. A total of 914 specimens of muraenid leptocephali were collected across a wide range from the western North Pacific to the western Indian Ocean. They were separated into at least 75 species based on morphology and genetic analysis. All species were distributed in the open ocean. The leptocephali of two species, Gymnothorax minor and G. pseudothyrsoideus were also collected from coastal areas. The specimens collected at moderate distances from coastal areas were small to large size. But the specimens collected at long distances from coastal areas were all large size. Therefore, we estimated that small leptocephali born in the coastal areas were dispersing widely across the open ocean, and then their leptocephali returned to the coastal area after growing. Further research is necessary to clarify their dispersal mechanisms and the timing of when they leave the open ocean, and this will be investigated using otolith microchemistry with LA-ICP-MS.

 

Oral (S10-8429), BIO/MEQ/FUTURE Topic Session

The combined effects of elevated carbon dioxide concentration and temperature on the early development stage of olive flounder Paralichthys olivaceus

Kyung-Su Kim1, JeongHee Shim2 and Suam Kim1

1 Department of Marine Biology, Pukyong National University, Busan, Korea, 608-737
2 National Fisheries Research and Development Institute, 152-1 Haeanro, Gijang-Up, Gijang-Gun, Busan, 619-705, R Korea. E-mail: ks-kim@pknu.ac.kr

Due to a high warming rate and possible local acidification in Korean waters, fishermen and aquaculturists require scientific knowledge on the biological reactions to environmental change for proper management of fisheries. To examine the effects of ocean warming and acidification on the early growth of olive flounder (the most popular fish species in the aquaculture industry), we conducted experiments with larvae reared under different conditions: combination of 400 and 1500 ppm atmospheric CO2 and 18°C and 22°C of seawater temperature. Fertilized eggs of flounder were hatched in the system and larvae were reared for 4 weeks. After 4 weeks, the body weight and length were measured to differentiate the Specific Growth Rate at different rearing conditions. Bone structure and some sensor systems such as the lateral-line and surface porse were examined to compare normal and acidityaffected fish using a scanning electron microscope.

 
 

Poster (S10-2), BIO/MEQ/FUTURE Topic Session

Iron as a triggering factor for harmful dinoflagellate blooms

Kanako Naito1, Setsuko Sakamoto2, Mineo Yamaguchi2, Ichiro Imai3 and Ken-ichi Nakamura1

1 Department of Environment Sciences, Faculty of Life and Environmental Sciences, Prefectural University of Hiroshima, Shobara, Hiroshima, 727-0023, Japan. E-mail: naito@pu-hiroshima.ac.jp
2 National Research Institute of Fisheries and Environment of Inland Sea, Fisheries Research Agency, 2-17-5 Maruishi, Hatsukaichi, Hiroshima, 739-0452, Japan
3 Laboratory of Marine Biology (Plankton Laboratory), Division of Marine Bioresource and Environmental Science, Graduate School of Fisheries Sciences, Hokkaido University, Hakodate, Hokkaido, 041-8611, Japan

Iron is an essential element for the biochemical and physiological functioning of microalgae. However, the mechanism of iron uptake by eukaryotic microalgae is not yet fully understood because of the intricate iron chemistry of natural seawater and the difficulty in cultivation of axenic microalgae in uncontaminated conditions. Dissolved iron fractions consist largely of colloidal hydrolysis species and most of those are bound by organic ligands in natural waters. As a result of the above mentioned iron speciation, the concentrations of directly bioavailable iron species are extremely low in natural waters. To clarify utilization of the iron for the harmful algal species, we examined the growth experiments using a newly developed artificial synthetic medium in the presence of different iron species. The present study demonstrated that particulate FePO4 and FeS were bioavailable for the growth of the dinoflagellates Cochlodinium polykrichoides, Heterocapsa circularisquama and Karenia mikimotoi. The differences in concentration of organic ligands in each medium caused the changes of the growth (maximal growth yield and specific growth rate) of harmful algae examined. These results suggest that the iron speciation has significant effects on controlling the harmful algal bloom formation in coastal areas. We point out the possibility that iron is a triggering factor for harmful dinoflagellate blooms showing the expansion in the North Pacific Ocean.

 

Invited (S3-8397), POC Topic Session

Interannual to decadal variability of the Gulf Stream and Kuroshio Extension jets

Yoshi N. Sasaki1, Shoshiro Minobe1 and Niklas Schneider2

1 Graduate School of Science, Hokkaido University, Sapporo, 060-0810, Japan
E-mail: sasakiyo @mail.sci.hokudai.ac.jp
2 IPRC and Department of Oceanography, University of Hawaii at Manoa, Honolulu, 96822, USA

The Gulf Stream and Kuroshio Extension jets not only transport nutrients and biota downstream but also act a barrier for mixing subtropical and subarctic water masses. In this presentation, we review interannual to decadal fluctuations of the latitudes of the Gulf Stream and Kuroshio Extension jets, and then we propose new theory, which extends thin-jet theory for meanders on monthly and seasonal timescales, in order to understand the dynamics of the jet variations on interannual to decadal timescales. In this theory, the low-frequent variability of the jets is attributed to westward propagation of meridional shifts of the jets from east. These westward propagating signals are induced by large-scale wind fluctuations, but are trapped around the jet axis. Using satellite altimeter data and an eddy-resolving ocean general circulation model output, we show that the dynamics in the thin-jet framework accounts for the bulk of interannual to decadal fluctuations of the Gulf Stream and Kuroshio Extension jets. Our results suggest that the Gulf Stream (Kuroshio Extension) jet brings atmospheric signals from the eastern to the western North Atlantic (North Pacific), and the resultant meridional shift of the jet induces the notable oceanic changes, such as sea surface temperature and eddy activity, around the jets.

 
Poster (POC-P-5), POC Paper Session
Strong vertical mixing in the Urup Strait, Kuril Islands

Sachihiko Itoh1, Ichiro Yasuda1, Masahiro Yagi1, Satoshi Osafune2, Hitoshi Kaneko1, Jun Nishioka3, Takeshi
Nakatsuka4 and Yuri N. Volkov5

1 Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, 277-8564, Japan
E-mail: itohsach@aori.u-tokyo.ac.jp
2 Japan Agency for Marine-Earth Science and Technology, Yokosuka, 237-0061, Japan
3 Institute of Low Temperature Science, Hokkaido University, Sapporo, 060-0819, Japan
4 Graduate School of Environmental Studies, Nagoya University, Nagoya, 464-8601, Japan
5 Far Eastern Regional Hydrometeorological Research Institute, Vladivostok, Russia

Microstructure measurements were conducted in one of the Kuril Straits in the summer of 2007. Over the course of 1 day of repeated observations across the Pacific side of the steep sill of the Urup Strait, extremely strong mixing was observed during periods of Pacific-ward (down-sill) flows and during the transition from Pacificward to Okhotsk-ward (up-sill) flows, with a turbulent energy dissipation rate ε of 10–6 to 10–5 W kg–1 and vertical diffusivity of 10–1 to 5 ~ 10–1 m2 s–1. During the period of strong mixing, we observed homogeneous layers with a thickness of 300–600 m and potential density of 26.6–26.7 σθ, occupying the entire water column in one case. High values of ε within this layer indicate the injection of diapycnal flows from the upper and lower layers, possibly contributing to the southward intrusion of intermediate water into the subtropical gyre.

 

Oral (S11-8594), MONITOR/POC Topic Session

Tsunami disaster and nuclear power plant accident effects on fishery facilities and marine products in Fukushima Prefecture: Present conditions and prospects

Toshihiro Wada1, Yoshiharu Nemoto2, Shinya Shimamura2 and Satoshi Igarashi2

1 Soma branch, Fukushima Prefectural Fisheries Experimental Station, 100 Azagoro, Soma, 979-2542, Japan
E-mail: wada385@yahoo.co.jp
2 Fukushima Prefectural Fisheries Experimental Station, 13-2 Aza-Matsusita, Shimokajiro, Onahama, Iwaki, Fukushima, 970-0316, Japan

The Tohoku earthquake tsunami disaster of 11 March 2011 severely damaged Fukushima’s coastal areas. Parts of all 10 fishing ports were destroyed, and 873 fishing vessels (74% of all registered vessels) were damaged. Regarding prefectural facilities, the Soma branch office of the Fukushima Prefectural Fisheries Experimental Station (FPFES) was destroyed, and its research vessel, the Iwaki-maru (150 tons) sank in Onahama Port. The Fukushima Prefecture Fish Farming Station, located 3 km south of Fukushima No. 1 Nuclear Power Plant, was destroyed. Moreover, contamination of marine products by radioactive substances has prevented fishermen from commencing commercial fishing. As of June 2012, the Fukushima prefectural government has inspected the concentrations of radioactive substances (cesium-134/137 and iodine-131) from 4,450 specimens within 165 marine species. From April 2011 – March 2012, 24 species exceeded the tentative regulation limit of cesium (500 Bq/kg). From January – June 2012, 36 species exceeded the new legal limit of cesium (100 Bq/kg) enforced in April 2012. The specimens exceeding the legal limit were mostly found in shallower waters south of the nuclear power plant. Concentrations decreased gradually in some pelagic fishes, seaweed, abalone, and surf clams. However, most fish, especially demersal fish species, have not shown a clear declining tendency, suggesting that radioactive cesium is continuing to pass through the food web. FPFES and other cooperative organizations continue to monitor marine products, seeking to clarify the intake/discharge mechanisms for radioactive substances between the environment and marine products, to restore fishery operations quickly, and to safeguard the safety of fishery product consumers.

 

Poster (S11-6), MONITOR/POC Topic Session

Oceanic dispersion of radioactive cesium around Japan and western North Pacific after the Fukushima Dai-ichi Nuclear Power Plant accident

Hideki Kaeriyama1, Daisuke Ambe1, Masachika Masujima1, Kou Nishiuchi2, Ken Fujimoto1, Tsuneo Ono1 and
Tomowo Watanabe1

1 National Research Institute of Fisheries Science, FRA, Kanazawa-Ku, Yokohama, Kanagawa, 236-8648, Japan
E-mail: kaeriyama@affrc.go.jp
2 Seikai National Fisheries Research Institute, FRA, 148, 1551-8, Taira-machi, Nagasaki-shi Nagasaki, 851-2213, Japan

The Fukushima Dai-ichi Nuclear Power Plant (FDNPP) accident after the Great East Japan Earthquake and tsunami on 11 March 2011 resulted in the elevation of the level of anthropogenic radioactivity in the marine environment in the western North Pacific from atmospheric fallout and direct discharges of highly radioactive waters. Intensive monitoring of iodine-131, cesium-134 (Cs-134) and cesium-137 (Cs-137) in seawater near offshore FDNPP, and in marine organisms in the broader area around Japan, was conducted during the time when information of radioactive contamination in the seawater around western part of Japan and western North Pacific was quite limited. In this study, we report the concentrations of Cs-134 and Cs-137 in seawater collected from the western North Pacific, Japan Sea and East China Sea during 2011. Although high concentrations of Cs-134 and Cs-137 were detected off the coast of eastern Japan, an almost background level of Cs-137 was detected from the samples collected off the coast of western Japan, Japan Sea and East China Sea. In the western North Pacific, both Cs-134 and Cs-137 were detected from the sample collected along 155˚E, but Cs-134 was not detected at almost all stations along 175˚E in June and July 2011. The Kuroshio extension seemed to prevent the southward dispersion of radioactive cesium. The vertical distributions of radioactive cesium off the coast of northern Japan around FDNPP revealed complex patterns mainly due to the water mass interaction between Oyashio water and Kuroshio water.

 

Oral (S14-8651), POC/TCODE Topic Session

Quantification of BDOC (bio-available dissolved organic carbon) of different water masses in East China Sea

Shuchai Gan and Ying Wu

State Key Laboratory of Estuarine and Coastal Research, East China Normal University, 3663 North Zhongshan Rd., Shanghai, 200062, PR China. E-mail: ganshuchai@163.com

Bioavailability of dissolved organic carbon (DOC) has garnered recent attention for its potential impacts on carbon sink and source capacity. As a major ‘food’ and excrement of micro-organisms, BDOC is important for the microbial food web. In order to verify the importance of BDOC in regional carbon cycle modeling of the East China Sea, a 10-day cultivation experiment was carried out focusing on the major water masses in the East China Sea—Yangtze river plume, bloom, Taiwan Warm Current and Kuroshio Current. Excitation emission matrix fluorescence spectroscopy (EEMs), which we applied in our study, has recently been used to characterize the sources, transformation and behavior of CDOM (the light absorbing fraction of DOM) in aquatic environments. Combined with parallel factor analysis (PARAFAC), 5 individual fluorescent components have been identified: 3 humic-like and 2 protein-like components (P1, P2), which suggest different sources and bioavailability. We have found that P1 and P2 are responsible for the BDOC. The percentage of bio-available DOC ranges from 0 to 31.1% with different P1 and P2 fluorescence, highest in the bloom event in coastal water, lowest in the Yangtze Estuary with lowest P1 and P2. Estimated from the degradation process, the inorganic carbon output of different water masses was calculated. It is important to elucidate that the biological processes (both DOC degradation and production) are ‘visible’ by 3-D fluorescence (EEMs), which verifies that the microbial food web plays an important role in the carbon cycle of aquatic ecosystems.

 

Poster (S14-5), POC/TCODE Topic Session

Active carbon flux by diel migrant zooplankton in the eutrophic and oligotrophic waters of the Canary Current

Sébastien Putzeys1,3, Carlos Almeida2, Pierrick Bécognée1, Lidia Yebra3, Ángeles Marrero Diaz4 and Santiago Hernández-León1

1 Institute of Oceanography and Global Change. Universidad de Las Palmas de Gran Canaria, Tafira Baja, 35017, Las Palmas, Spain. E-mail: sebastien.putzeys@ma.ieo.es
2 Centro de Biotecnología Marina, Universidad de Las Palmas de Gran Canaria, Muelle de Taliarte s/n, Telde, 35214, Las Palmas, Spain
3 Instituto Español de Oceanografía, Centro Oceanográfico de Málaga, Puerto Pesquero s/n, 29640, Fuengirola, Málaga, Spain
4 Department of Physic. Universidad de Las Palmas de Gran Canaria, Tafira Baja, 35017, Las Palmas, Spain

The Canary Current is characterized by a strong disruption of its flow by the Canary archipelago, forming a downstream region of high mesoscale activity. This Canaries-African coastal transition zone connects the NW African upwelling system with the oligotrophic open ocean waters of the Eastern North Atlantic subtropical gyre. Further south, the Cape Vert Frontal zone is a highly productive area influenced by a quasi-permanent upwelling and a thermohaline front. To assess the role of zooplankton in the vertical export of carbon in those areas, we studied zooplankton biomass distribution and metabolism from the coast to the open ocean in an oligotrophic zone (26ºN) and in a meso- or eutrophic one (21ºN). Zooplankton biomass followed the same pattern in both transects, presenting two dense layers of organisms. The upper layer was located above 200 m and the second one below 400 m depth coincident with the deep scattering layer. However, the average migrant biomass (0-200 m) was 2.6-fold higher at 21ºN (71.4±51.4 mmolC·m-2) than at 26ºN (27.1±12.4 mmolC·m-2). This was reflected in the downward export of respiratory carbon (0-900 m depth) which was 10-fold higher in the southern than in the northern transect (0.54±0.42 and 0.05±0.05 mmolC·m-2·d-1, respectively). Moreover, the estimated pigmented gut flux was 20-fold higher in the south than in the north (0.85±0.98 and 0.04±0.26 mmolC·m-2·d-1). The total contribution of zooplankton metabolism to the particulate organic carbon flux was 4% in the oligotrophic transect, contrasting with the 92% observed in the eutrophic transect.

 
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