Major human activities affecting Norwegian coastal marine ecosystems: Present status and challenges

Erlend Moksness

The Norwegian coastal zone encompasses approximately 90,000 km2 and has a coastline of 57,000 km (incl islets and islands). The coastal zone with its many fjords and habitats is inhabited by numerous of species. Cod (Gadus morhua) is one of the key species, and each fjord has their local unique stock. The area is annually used by several abundant oceanic fish such as Norwegian spring-spawning herring (Clupea harengus), capelin (Mallotus villosus) and Arctic cod and haddock (Mellanogrammus agelefinus) for spawning and as nursery grounds.

Historically, the transport and fishing industries have been the major stakeholders in the coastal zone. Over the past 40 years, however, the number of stakeholders has increased and now includes new stakeholders such as aquaculture, oil and gas exploration and different forms of tourism. This development has resulted in increased user conflicts, and higher pressure and impact on the different coastal ecosystems, affecting both habitats and living resources. The increased public attention on the coastal zone in general has led to demand for better knowledge and understanding of the content and functions of the different ecosystems. This has resulted in increased mapping and research activities, and implementation of new regulations. Because there are now many stakeholders and a need to keep the monitoring cost at a low level, there is a requirement to develop management models that include environmental, social and economical components. Such models should be a significant part of a future toolbox to be applied in the management of the coastal zone.

Growth-increment chronologies reflect ecosystem responses to climate variability in the northeast Pacific

Bryan A. Black

In recent years, traditional tree-ring techniques (dendrochronology) have been increasingly applied to growth increments that occur in long-lived fish and bivalve species in the northeastern Pacific. Resulting chronologies are annually resolved, span from decades to centuries, and can be used to i) establish the effects of climate on growth and recruitment, ii) reconstruct climate prior to the start of instrumental records, and iii) establish climate-driven linkages across diverse species and ecosystems. For example, rockfish (Sebastes spp.) growth-increment chronologies in the California Current Ecosystem (CCE) positively relate with climatic indicators of cool, upwelling-favorable conditions during the winter months. On a broader spatial scale, these CCE chronologies inversely relate with rockfish chronologies above Vancouver Island, consistent with an inverse productivity regime between the CCE and Gulf of Alaska. Moreover, chronologies from Pacific geoduck (Panopea abrupta) along the British Columbia coast also relate to rockfish chronologies as well as high-elevation tree-ring chronologies, illustrating climate-driven synchrony from the continental shelf to alpine forests. With respect to describing past climate variability, combinations of tree-ring and geoduck chronologies can be used to reconstruct up to 70% of the variance in regional sea surface temperatures, more than doubling the length of the existing instrumental record. Ultimately, methods from dendrochronology could be applied in a variety of systems to address biological response to climate, develop high-resolution climate reconstructions, and inform estimates of ecosystem response to future climate change.

Time-series observation of phytoplankton productivity in the western subarctic gyre of the North Pacific

Tetsuichi Fujiki¹, Kazuhiko Matsumoto¹, Shuichi Watanabe¹, Takuji Hosaka² and Toshiro Saino³

The western subarctic Pacific plays a role as a sink of anthropogenic carbon dioxide (CO₂) from the atmosphere. Phytoplankton can contribute to the efficient uptake of atmospheric CO₂ in this ocean. Thus, knowledge of the variability in phytoplankton productivity is needed to understand the carbon cycle dynamics in the western subarctic Pacific. However, in ship-based studies of the open ocean, the time-series observations for understanding of variability in primary productivity have been restricted. In the previous study (Fujiki et al. 2008), we developed an underwater profiling buoy system that uses a fast repetition rate fluorometer. The profiling buoy system can estimate in situ primary productivity at high vertical and temporal resolutions. In this study, we deployed the profiling buoy system at the time-series station K2 (47^oN, 160^oE) in the western subarctic gyre of the North Pacific during the early summer (June-July) of 2006 and succeeded in observing day-to-day variations in primary productivity for about 40 days. Here, we show the results of observations and also discuss the relationship between primary productivity and organic carbon flux.

Maturity and spawning of small yellow croaker, Larimichthys polyactis

Hyunjung Kang¹, Yeonghye Kim¹, Jinkoo Kim², Sungyeon Kim³, Sukgeun Jung¹, Dongwoo Lee¹ and Daesoo Chang¹

The small yellow croaker, Larimichthys polyactis, is a commercially important fish species in the Yellow and East China Seas. It is actively targeted by both Chinese and Korean fishing vessels. Past studies suggested that overfishing has led to a decline in its maturation size (norms of reaction), but catches of this species have dramatically rebounded since 2006. To obtain recent estimates of growth and maturity parameters and to re-evaluate the long-term change in its reproductive biology, we investigated monthly changes in maturity, gonadosomatic index, gonad weight, mean length at maturity, and sex ratio based on croaker samples caught by trawl, lift and gill nets from January 2006 to December 2008. We compare our estimates of these parameters to those previously reported to evaluate long-term changes in maturity of small yellow croaker.

Using classification trees to capture a manager's interpretation of Bayesian projections

Tatiana Tunon and Gottfried Pestal

Terminal fisheries targeting Atnarko River, British Columbia, chinook salmon (Oncorhynchus tshawytscha) are managed based on weekly projections of total escapement to the spawning grounds. A projection model using Bayesian updating was developed with the local manager in 2001, and has been used since the 2002 fishing season.

A crucial step in the development was to explore and document the end-user’s interpretation of Bayesian projections. We presented the manager with observed and simulated sets of in-season data, elicited his assessments of stock status based on the model output, and fit a simple classification tree of binary choices to the responses. The resulting classification trees capture both the characteristics of the quantitative projection model and the subjective judgments of the fisheries manager (e.g. choices of prior assumptions, approach to reconciling projections based on alternate model structures, decisions based on a range of projections relative to management reference points).

The impact of climate change on the development of marine aquaculture: A case study on Japanese scallop aquaculture in Funka Bay, Hokkaido, Japan

I Nyoman Radiarta^1,2, Sei-Ichi Saitoh¹ and Toru Hirawake¹

Evidence has been accumulating in recent years that suggest climate change might drive changes in aquaculture development. Sustainability of scallop production is also influenced by changes of environmental conditions. Climate change presents unquantifiable threats in the forms of increased temperatures, extreme weather and diminishing water supplies. In this study, to model the potential impact of climate change on the scallop aquaculture, we carried out a two-step analysis. First, we analyzed the suitability of sites for Japanese scallop aquaculture using an integrated remote sensing and geographic information system (GIS)-based model. Multi-criteria evaluation was adapted to the GIS models in order to rank sites on a 1 (least suitable)-to-8 (most suitable) scale. Second, in the site selection analysis, we examined the potential climate change impacts using the sea surface temperature (SST) values of 1^oC, 2^oC, or 4^oC. These three SST values were selected based on the fourth assessment report of the IPCC. By increasing the SST values, we found that the most suitable sites (score 8) indicated slight (26.4%), significant (14%) and drastic (0.01%) changes compared with the original model (29%), respectively. These prediction models showed that climate change, by altering the physical characteristics of suitable cultivation areas, can have detectable impacts on the development of scallop aquaculture. The models also indicated that climate change might have an important impact on the future development of marine aquaculture in this region, a prospect that will need to be considered.

Growth and photosynthetic characteristics of three Zostera spp. (Z. japonica, Z. marina and Z. caespitosa) along vertical gradient: Implications for seagrass zonation

Sang Rul Park and Kun-Seop Lee

Department of Biological Sciences, Pusan National University, Geumjeong-gu, Busan, 609-735, Korea. E-mail: srv99park@pusan.ac.kr

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Trophic cascades in Hawaii's nearshore ecosystem: Using observing technology to understand ecological interactions

Kelly J. Benoit-Bird

Moored single and multi-frequency echosounders were used to describe zooplankton, micronekton, and spinner dolphin distributions off the leeward coast of Oahu Hawaii while a moored acoustic Doppler current profiler (ADCP), thermistor chains, point current meters, and an autonomous vertical profiler provided a description of the physical circulation, and optical sensors on the autonomous profiler were used to characterize the distribution of phytoplankton. Intensive sampling with a 4-frequency echosounder, ADCP, vertical profiling package, and nets were used to examine specific ecological interactions. During the study, extremely thin, dense layers of phytoplankton were optically identified. Dense acoustic scattering layers comprised primarily of copepods were often identified just beneath phytoplankton layers, but were not found when phytoplankton were more diffusely distributed. The presence of zooplankton layers reduced the extent of the diel migration of mesopelagic micronekton leading to changes in the nocturnal behavior of spinner dolphins foraging on these micronekton. This ecosystem shows a strong, bottom-up trophic cascade where the physical environment affects the formation and persistence of thin phytoplankton layers which influence the formation of thin layers of zooplankton. The presence of zooplankton layers modifies the behavior of micronekton that serve as prey for spinner dolphins and, in turn, affects the nighttime behavior of dolphins. Sampling of these interactions was greatly facilitated by continuous observations of the physical habitat and four trophic levels as well as near real-time data on the physical and optical characteristics of the habitat that permitted intensive ship-based sampling when phytoplankton layers were detected.

A profiling mooring buoy to observe mixed layer formations in the western North Pacific and its combination with a deeper type underwater glider

Shin-ichi Ito¹, Yugo Shimizu¹, Shigeho Kakehi¹, Fumitake Shido¹, Taku Wagawa¹, Kazuyuki Uehara², Toshiya Nakano³, Masafumi Kamachi⁴

From climatological analysis, the deepest mixed layer was found in the region 40-42N and 152-160E in the North Pacific. In this region, weak stratified thick layer was found from summer hydrographic observations and the thick layer was referred to as Transition Region Mode Water (TRMW). For the formation of TRMW, supply of saltier water by quasi-steady warm streamers is considered to play an important role. However, the observations in this region have been limited to summer season because of rough sea condition in other seasons. Accompanied with the deep mixed layer formation, a large nutrient supply is expected and the existence of TRMW is considered to intensify the formation of the mixed layer. Indeed, recently, a large nursery ground for mackerel, anchovy and sardine was found near the TRMW region. Therefore, it is important to observe the actual mixed layer formation process in the TRMW region. We deployed a profiling mooring buoy in the TRMW region. An underwater winch was mounted on the mooring (at a depth of 250m to avoid hazards from purse seining), and a CTD sensor buoy moves up and down from the winch. The profiling mooring buoy can make high-resolution time-series observations at a specific location, but the horizontal spatial coverage is limited. Underwater gliders have possibility to overcome this weak point. A deeper type underwater glider, equipped with CTD, DO-sensor and fluorometer, is now on test in the TRMW region.

Oral (W8-5741), POC Topic Session

Influence of reducing weather noise on ENSO prediction

Xiaohui Tang¹, Ping Chang² and Fan Wang¹

El Niño-Southern Oscillation (ENSO) is the strongest interannual fluctuation in the tropical atmosphere-ocean system. Many studies showed that atmospheric noise forcing can affect ENSO predictability, but there is yet no discussion on how the weather noise impact ENSO forecast skills.

In this study, retrospective predictions of tropical sea surface temperature anomalies (SSTA) were conducted using an atmospheric general circulation model coupled to a 1-1/2 layer reduced gravity ocean model. A novel atmospheric noise filter is introduced into the coupled model to suppress weather noise in wind stresses and surface heat fluxes before they pass to the ocean, in order to test the impact of weather noise on ENSO-related SST prediction.

Results show that suppressing weather noise leads to a general improvement in model forecast skills. With appropriate initial conditions, reducing weather noise can alleviate drop of ENSO forecast skill caused by the so called “spring predictability barrier”, and help maintaining considerably high skill in 3-4 leading seasons. Further analyses show that the improved ENSO forecast skill is mainly attributed to reducing weather noise in wind stresses. It is hypothesized that reducing weather noise boosts the signal-to-noise ratio in the tropical Pacific and improves the model’s response to Bjerknes feedbacks between wind stress, thermocline and SST, resulting in an enhanced ENSO forecast skill.

Numerical study of bidecadal water mass variations in the subarctic North Pacific related to the 18.6-year tidal cycle

Satoshi Osafune and Ichiro Yasuda

Bidecadal variations of water mass, such as salinity in the surface layer and isopycnal potential temperature in the intermediate layer, have been observed around or downstream of the strong tidal mixing region like the Kuril Islands and the Aleutian Islands. It is shown that those variations can be explained by modification of the water mass by vertical mixing, which should be modulated, related to the 18.6-year tidal cycle. We conducted a series of numerical experiments using an Ocean General Circulation Model, in which tidal mixing in the localized sites is represented by elevating vertical diffusivity up to 20, 50 and 200 cm²/s. An 18.6-year oscillation of the elevated diffusivity induced bidecadal water mass variations similar to those observed. A budget analysis of salinity in the surface layer suggested that the water mass variation in this model is induced in a simple balance. The anomaly caused by the anomalous mixing in the strong mixing region spreads by the mean current. The amplitude of the anomaly is related not only to the amplitude of the diffusivity, but also to the mean profile, which is affected by the mean value of the diffusivity. As a result, large diffusivity does not necessarily lead to large water mass variation, and relatively small diffusivity can cause water mass variation effectively. This result indicates the importance of tidally induced vertical mixing, and emphasizes the necessity to clarify spatial and temporal variations of tidal mixing.