Projection of Pacific saury response to future climate change

Shin-ichi Ito¹, Takeshi Okunishi², Michio J. Kishi^3,4 and Muyin Wang⁵

An ecosystem based bioenergetics model NEMURO.FISH (North Pacific Ecosystem Model for Understanding Regional Oceanography. For Including Saury and Herring) was developed and successfully reproduced realistic growth of Pacific saury with parameters mainly determined based on field observations. The model is composed of three ocean domain boxes and saury is assumed to migrate between those boxes. This model was used to investigate responses of Pacific saury to global warming using the sea surface temperature (SST) of a global warming condition generated by MIROC3.2 coupled atmospheric–ocean model output with the A2 emission scenario. The saury showed a decrease in both wet weight and body length under global warming because of less prey plankton density. The migration pattern was modified by increased SST and reduced size of saury. Higher SST in the mixed water region under global warming prevented southern migration of saury in the first winter and delayed it in the second winter. As a result, egg production was enhanced by higher availability of prey plankton in the mixed water region. To evaluate the robustness of the result, an ensemble projection was conducted with SST outputs from 12 climate models. The results showed considerable uncertainty of the Pacific saury response. We conducted a case study to separate direct temperature effects with those through prey plankton. Model results suggested an SST increase (especially in the mixed water region) directly reduces juvenile growth while a prey plankton density decrease has an influence on the growth of adults and migration pattern, hence egg production.

Spatio-temporal changes in species diversity and assemblage structure of Euphausiids (Oyashio to Oyashio-Kuroshio Transition Region in the western north Pacific)

Sayaka Matsumura¹, Hiroya Sugisaki², Hiroaki Saito³, Yuji Okazaki³ and Tomohiko Kikuchi¹

The spatio-temporal changes in diversity and assemblage structure of the micronektonic euphausiids were analyzed with the physical oceanographic structure in the Oyashio to the Oyashio-Kuroshio Transition Region of the western north Pacific. All the specimens were collected by means of MOCNESS, and physical data were obtained from CTD sensors during eight cruises of the R/V “Wakataka-Maru” of the Fisheries Research Agency of Japan, from May 2004 to March 2006. In total, 40 species representing eight genera were identified from six fixed stations. A clear regional distinction of the euphausiid assemblage structure was observed, associated with temperature and salinity characteristics of water masses. However a seasonal pattern was hardly observed from the two-year survey, with some exceptions. Cluster and multi-dimensional scaling (MDS) ordination analyses based on the Bray-Curtis similarity index and its inverse analysis showed four distinct euphausiid assemblage groups. Group I consisted of the Arctic-Boreal, the Subarctic and the Subarctic-Transition species. Group II mainly consisted of the Subarctic and the Subarctic-Transition species. Group III consisted of the Subarctic- Transition, the Transition and the western Pacific coastal species. Group IV mainly consisted of the Central and the Central-Equatorial species. Euphausia pacifica, the only Subarctic-Transition species, was most abundant in Groups I, II and III. The results of this study suggest that a spatio-temporal change in the assemblage structure of euphausiids was controlled principally by physical factors rather than the seasonal variance in this area.

Feeding rates of adult Euphausia pacifica on natural particle assemblages in the coastal upwelling zone off Oregon, USA

Xiuning Du^1,2, William T. Peterson³ and C. Tracy Shaw¹

Feeding experiments on adult Euphausia pacifica were initiated in February 2010 with the plan to determine how feeding rate and selectivity changes during the upwelling season. Incubation experiments were conducted using krill caught at the shelf break 25 miles offshore of Newport, Oregon. We measured the clearance rates and daily rations by feeding the krill on natural plankton assemblages. Feeding rates were calculated from microscopic counts of the phytoplankton and ciliates species. Preliminary rates based on experiments conducted in February and April showed that E. pacifica had higher grazing rates on diatoms (the dominants were Thalassiasira and Chaetoceros) during the spring bloom in February compared to post-bloom conditions in April when plankton biomass was low and E. pacifica had negative clearance rates on total enumerated biomass and extremely low or negative feeding rates based on Chl a data; very low biomass of larger phytoplankton taxa (diatoms and dinoflagellates) in April made it difficult to determine E. pacifica grazing preference. In addition, we found in both months that E. pacifica had a high preference for ciliates and that they did not like eating the smaller flagellates. Our results support the hypothesis that E. pacifica feeds omnivorously on the natural assemblages with ciliates as an important food source and with larger food taxa preferred over the smaller taxa. The above conclusions will be tested further throughout the upwelling season and results of all experiments will be presented at PICES 2010.

Can an introduced parasitic bopyrid isopod Orthione griffenis cause extinction of mud shrimp Upogebia pugettensis populations in U.S. west coast estuaries?

Brett R. Dumbauld¹ and John W. Chapman²

The burrowing mud shrimp, Upogebia pugettensis, is parasitized by an introduced bopyrid isopod, Orthione griffenis, that prevents female egg production. Prevalence of this isopod increased dramatically in Willapa Bay, Washington, between 1998-2001, and the Upogebia population collapsed to below detection limits. We continued to monitor prevalence of Orthione in Upogebia populations in Washington and Oregon estuaries to further document the effects of this invader and determine whether this new parasite was controlling its host populations. Orthione prevalence fluctuated from year to year, but was highest in large female shrimp, greater than 20% in all populations, and prevalence trends were similar among estuaries. Results of a transplant experiment of un-infested shrimp to Willapa Bay, where the shrimp were no longer abundant, suggest that Orthione is extremely effective at finding its host and that these shrimp do not find refuge even at very low population density. Orthione prevalence increased with shrimp size and was highest among reproductive sized females. Upogebia egg production losses to Orthione averaged 68% between 2005 and 2009. Both shrimp and isopods have pelagic larval stages that are greatly affected by coastal nearshore oceanography and estuarine recruitment processes. Despite significant Upogebia recruitment to shrimp populations in Oregon estuaries in some years and recent declines in isopod prevalence, our data suggest that shrimp populations are still declining and this is cause for concern that this introduction and non-coevolved relationship could result in loss of this important ecosystem engineer from US West coast estuaries.

Vertical distribution and reproductive aspects of caridean shrimps in the deep-water of the East Sea, Korea

Hye-Min Park^1,2, Jung Nyun Kim², Hae Won Lee³, Byeong Gyu Hong³, Jin Ho Bae¹, Hyeong Gi Kim¹ and Chul- Woong Oh¹

We investigated distributional patterns of deep-water shrimps in the East Sea. The distribution of the deep-water shrimps showed significant differences by depth. Shallow-dwelling species, Neocrangon communis and Pandalus eous, occurred at similar depths, but the distributional range of the former was wider. Of deep-dwelling species, Argis toyamaensis and Eualus biunguis, the latter exhibited a narrow depth range at the deepest depths of all species in the East Sea. Significant differences in sex ratio by depth were found; more females than males were found at all depths except in the case of P. eous. A size-related bathymetric distribution was observed for all shrimps. For example, large ovigerous females of crangonid species, N. communis and A. toyamaensis were mainly distributed in shallow waters (300-400 m), but for pandalid (e.g., P. eous) and hippolytid species (e.g., E. biunguis), large ovigerous females were distributed in deep water (700 and 800 m, respectively). The percentage of ovigerous females of both N. communis and P. eous females increased at shallow depths during winter. The proportion of females of both species in advanced stages of ovarian development (mainly spent stage) peaked at 300 to 400 m and decreased dramatically with increasing depth. These results suggest that females had already laid eggs at shallow depths (300-400 m) and that ovigerous females migrate to shallow water for hatching. On the other hand, ovigerous females of deep-dwelling species, A. toyamaensis, and E. biunguis, were more widely distributed over all depth ranges. In the case of A. toyamaensis the gonadosomatic index did not vary significantly with depth. We suggest that shrimp life-history strategy is determined by many environmental factors associated with depth and that the four species studied were primarily distributed at optimal depths for their reproductive strategies.

Genetic population structure of lacustrine sockeye salmon, Oncorhynchus nerka, in Japan

Yuichiro Kogura¹, James E. Seeb², Noriko Azuma¹, Hideaki Kudo¹, Syuiti Abe¹ and Masahide Kaeriyama¹

Lacustrine sockeye salmon (Oncorhynchus nerka) are listed as an endangered species in Japan despite a little genetic information on their population structure. We analyzed the mitochondrial DNA (mtDNA) ND5 region and 45 single nucleotide polymorphisms (SNPs) in 640 lacustrine salmon in Japan and 80 anadromous sockeye salmon from Iliamna Lake, Alaska, USA. The genetic diversities of the Japanese populations in both mtDNA and SNPs were significantly lower than those of the Iliamna Lake populations. In spite of low allelic variability and observed heterozygosity, the SNPs analyses showed that the Japanese populations were significantly divided into three groups. In addition, significant heterozygosity excess was observed in Tachibana Lake and the Abira River populations but not in the Shikotsu Lake within Japanese sockeye salmon. These findings suggest that: (1) all Japanese lacustrine sockeye salmon have extremely lower genetic diversity than anadromous sockeye in the North America and Russia; (2) the Shikotsu Lake population may have a slightly reduced allelic diversity associated with the reduction in population size caused by overpopulation in the 1920s, but a significant bottleneck effect did not occur; and (3) transplants of anadromous sockeye salmon eyed-eggs from the Ulmobetsu Lake population did not affected the population structure of native Japanese lacustrine sockeye salmon.

Oral (S9-6484), MEQ Topic Session

The development of toxigenic Pseudo-nitzschia bloom models in Monterey Bay, California, and their application at a single monitoring site within the model domain

Jenny Q. Lane¹, Peter T. Raimondi² and Raphael M. Kudela¹

Models of regional toxigenic Pseudo-nitzschia blooms have been developed and described for Monterey Bay, California. This modeling exercise provided valuable and useful insight into Pseudo-nitzschia bloom dynamics and the study of those dynamics, including: 1) which regional datasets could be applied towards model development and, more significantly, what factors disqualified the majority of available data; 2) identification of those bloom factors which were recurrent and possibly ‘universal’ (i.e., shared among the Monterey Bay models and models previously described for the Santa Barbara Channel and from a laboratory dataset); and 3) the reconciliation of alternating hypotheses regarding bloom forcing (upwelling versus freshwater discharge) through the consideration of seasonality. Now, over two years after our development of the regional bloom models, we evaluate the applicability of these models towards a ‘real-world’ purpose for which they were not designed: the prediction of localized blooms at a single monitoring site within the model domain – the Santa Cruz Municipal Wharf (SCMW). Model predictions driven by SCMW environmental data will be presented in conjunction with traditional monitoring data (cell counts of toxigenic species, indexed Pseudo-nitzschia [genus] relative abundance, toxin quantification, and sentinel shellfish analysis) and data from a new phycotoxin monitoring tool - Solid Phase Adsorption Toxin Tracking (SPATT). Toxigenic Pseudo-nitzschia bloom events observed in autumn 2009 and spring 2010 are presented as case studies through which we consider the usefulness of model application at SCMW under the circumstances of an ‘unusual’ autumn bloom event (which, as an unusual event, was unanticipated from a regulatory standpoint) and a more ‘classic’ spring bloom event.

Poster (S15-6616), MONITOR Topic Session

Variation of satellite chlorophyll a in the East China Sea based on local satellite algorithm with reduced influence from suspended sediment

Hisashi Yamaguchi¹, Young Beak Son², Eko Siswanto³, Joji Ishizaka³, Sinjae Yoo², Yu-Hwan Ahn⁴, Sang-Woo Kim⁵, Junwu Tang⁶, Hiroshi Kawamura⁷ and Yoko Kiyomoto⁸

Accuracy of standard ocean color (SeaWiFS) chlorophyll a (Chl-a) algotithm (OC) is expected to be low in the East China Sea, especially at high suspended sediment areas. Recently, researchers from Japan, China and Korea shared the sea surface in-situ Chl-a, and bio-optical data of the East China Sea, supporting development of a local satellite algorithm for Chl-a. In this study we combined OC and a new empirical algorithm to minimize the influence of suspended sediment and examine the seasonal and interannual variation of Chl-a in the East China Sea. High suspended sediment areas were defined by high normalized water-leaving radiance of 555 nm (nLw555) greater than 2 (mW cm^-2 um^-1 sr^-1). Empirical local Chl-a algorithm based on Tassan’s model was derived for high suspended sediment region with SeaWiFS remote sensing reflectance (TS2). Combination of OC and TS2 (OC+TS2) Chl-a were lower than OC Chl-a from coastal areas to continental shelf with about 50 m isobath in winter, and near coastal areas with about 10 m isobath in summer. This result indicated that OC+TS2 reduced influence of resuspension of sediment typical of coastal areas. It is possible to analyze the seasonal and interannual variation of Chl-a more quantitatively by using OC+TS2 Chl-a.

Oral (POC-P-6646), POC Paper Session

A numerical study on the winter mixed layer on the shelf-slope region south of Japan

Hiroshi Kuroda, Takashi Setou, Yuichi Hirota, Manabu Shimizu and Kazuhiro Aoki

National Research Institute of Fisheries Science, 2-12-4 Fukuura, Kanazawa, Yokohama, Kanagawa, 236-8648, Japan
E-mail: kurocan@affrc.go.jp

The shelf-slope region between the Kuroshio and the southern coast of Japan has been considered as a significant spawning ground of some pelagic fish. For instance, Japanese sardine spawns over the shelf-slope region primarily in February, when the winter mixed layer (hereafter, “WML”) is expected to develop due to energetic sea surface cooling. Our previous study based on long-term in situ temperature records has inferred that there are predominant intra-monthly variations of the WML, and that three-dimensional structures of the WML are quite difficult to capture only from in situ observations. To further investigate behavior and dynamics of the WML, this study develops a triply nested numerical model with the highest resolution of 1/50 degree (~2 km), forced by monthly climatological mean fluxes at the sea surface. The realistic Kuroshio and tide are also given on lateral boundaries of this model. It is found that the 1/50-degree model can successfully simulate properties of seasonal and intra-monthly variations of the WML that are similar to observed features, whereas the second highestresolution model of 1/10 degree can reproduce less well, particularly the intra-monthly variation. This is because the intra-monthly variations are attributed to dominant submesoscale variability with a spatial scale of 10–20km and a timescale of a few days to a week. In addition, a streak-like distribution of shallow WMLs is frequently simulated and associated with horizontal advection of the shallow WMLs. In our presentation contributions of the horizontal advection to temporal change of the WML will be explained in detail.

Sarah Ann Thompson¹, William J. Sydeman¹, Jarrod A. Santora¹, Robert M. Suryan², Bryan A. Black², William T. Peterson³ and John Calambokidis⁴

Upwelling is an important driver of coastal productivity and an essential mechanism to predator-prey interactions in eastern boundary current systems worldwide. Along the west coast of North America, nutrients supplied by upwelling processes support abundant phytoplankton and zooplankton communities that serve as the basis for trophic interactions leading to upper trophic level marine predators. We hypothesized that 1) predator productivity is indirectly affected by upwelling through intermediate trophic levels, and 2) different upper level predators would show different pathways of response. We tested these hypotheses using path analysis from upwelling (divided into winter and summer seasons) through intermediate trophic levels to the productivity and relative abundance of two species of seabirds (common murre and Cassin’s auklet), chinook salmon, rockfish, and humpback whales. Intermediate levels included phytoplankton, proxied by chlorophyll a concentrations, and mid-trophic level prey, indexed by measurements of copepod biomass and community structure and proxies of euphausiid and juvenile rockfish abundance based on seabird diets. Results confirmed indirect effects and variation in the pathways of response for different predators. Multiple intermediate trophic levels were important to include in the path models, and predators had specific key prey. Contrasting the differential pathways of response of predators to upwelling and intermediate trophic levels enhances understanding of fundamental ecosystem dynamics and mechanisms.

Poster (S8-6725), FIS/POC/BIO Topic Session

Variability of mixed layer depth and its relation with chlorophyll concentration in the North Pacific Ocean

Chan Joo Jang and Sinjae Yoo

Korea Ocean Research and Development Institute, 1270 Sa-dong, Ansan, Gyeonggi-do, 426-170, R Korea
E-mail: cjjang@kordi.re.kr

Mixed layer depth (MLD) affects phytoplankton dynamics through controlling the availability of nutrients and light in the upper ocean. This study investigates variability of MLD and its relation with chlorophyll (CHL) in the North Pacific Ocean on seasonal to year-to-year timescales. The North Pacific MLD field was calculated from 98 SODA (Simple Ocean Data Assimilation) version 2.1.6 covering 51 years from January 1958 to December 2008. MLD was defined as the depth at which the potential density takes the reference depth (10 m) salinity value and the temperature value which is 0.2 degree centigrade lower than the reference value. The variability of maximum MLD is well correlated with CHL variability in some regions in the North Pacific Ocean, including the Kuroshio Extension (KE). For example, increased maximum MLDs in the years of 2003–2007 compared with values in the years of 1998–2002 correspond to enhanced CHLs in the KE. The good correspondence between MLD and CHL suggests that increased maximum MLD helps to entrain deep nutrients into the upper ocean and thus to maintain high CHL in the KE. Changes in primary production based on nutrient entrainment by wind mixing at selected locations in the North Pacific also will be given and compared with observation.

Oral (S12-6510), MEQ/FUTURE Topic Session

Evaluating uncertainty in estimates of how climate change may impact Northeast Pacific marine ecosystems

D. Shallin Busch¹, Cameron H. Ainsworth², Jameal F. Samhouri³, William W.L. Cheung⁴, John Dunne⁵ and
Thomas A. Okey^6,7

Climate change will affect Earth’s physical environment strongly and influence its biota in complex ways. While empirical studies provide valuable information on species’ responses to environmental conditions, modeling exercises can be used to gain insights into the indirect and cascading effects of climate change on whole biological communities. Such modeling exercises can, however, contain a large number of uncertainties, all of which can influence their results. We present a study that addresses how uncertainty in both our knowledge of species responses to climate change (effect size and process uncertainty) and our ability to model them (model uncertainty) influences our understanding of the impacts of climate change. This work is an extension of a modeling exercise undertaken by Ainsworth et al. (in review), which attempts to predict the ecosystem-level impacts of climate change on Northeast Pacific shelf ecosystems using simulations with five Ecopath with Ecosim food web models. The Ainsworth et al. study applies five climate change impacts to these food web models: change in annual mean level of primary production, shifts in distribution of fish and invertebrates, alteration of the size structure of plankton communities, ocean acidification, and deoxygenation of surface waters. We consider and explore the effects of the three types of uncertainty using a variety of analytical techniques. Results of this study focus on data that are relevant to resource managers, namely, biomass of groups that provide important ecosystem services (e.g., harvested species, forage fish) and measures of ecosystem health (e.g., diversity, reorganization).