Here, I review thermal influences on metabolic rates and aerobic scope; growth; adult body size; and reproductive and behavioural traits, such as tendency and timing of the migration of salmonid ...fishes. A thermal window bounded by the upper and lower incipient lethal temperatures (UILT and LILT) determines where salmonids can survive. For most salmonids, LILT is close to 0 and UILT is between 20 and 30 °C. UILT and LILT are influenced by the acclimation temperature. Thermal tolerance is affected by fish size and ambient oxygen content, which decreases with increasing temperature. Standard metabolic rate (SMR), the energy required to maintain essential functions, increases with temperature, whereas maximum metabolic rate (MMR) increases with temperature until reaching a peak (pejus). Then, it decreases gradually to zero, i.e., the upper critical limit (TCrit). Aerobic scope (AS = MMR-SMR) reaches its maximum at the pejus temperature. Metabolic rates and aerobic scope can be modified by temperatures that the fish experiences during embryogenesis and possibly also as larvae and young fry. At maximum feeding, maximum growth increases to a point at or below the pejus temperature. The optimum temperature for growth decreases with reduced food intake and increased body size. As for metabolic rate, the growth rate is influenced by the temperature during embryonic development. In a warmer climate, adult body size is expected to decrease chiefly because of a younger age at maturity. Parental fish retained at a higher temperature during maturation produce larger eggs, and this change in egg size may also be transferred to next-generation offspring. Furthermore, embryogenesis in warmer water leads to larger gonad and egg sizes at maturity. Water temperature influences locomotion, foraging and migratory activity. In a warmer climate, juveniles migrate to the sea earlier in spring. In addition, higher embryo temperature leads to delayed return of adult salmon from the ocean. Thus, temperature affects life history traits of salmonid fishes, partly as a direct effect on metabolic rates and food consumption and partly induced as a phenotypically plastic effect. The phenotypically plastic response may preadapt offspring to perform better in the expected future thermal environment.
Destruction of habitat is the major cause for loss of biodiversity. This volume presents the population ecology of Atlantic salmon and brown trout and how it is influenced by the environment in terms ...of growth, migration, spawning and recruitment.
The last few decades have seen a decrease in Arctic ice cover, leading to changes in the structure and function of marine ecosystems. Yet sustained long‐term observations of the marine environment ...are difficult to acquire. Harsh environments limit in situ measurements, while low light and high solar angles hinder ocean color observations from satellite. Here we use masks of valid‐invalid ocean color pixels to diagnose ocean conditions and find strong positive trends in the Arctic open‐water season close to the ice sheet, generally consistent with sea ice products from satellites. The North East Atlantic with no seasonal ice cover shows weaker, but significant trends indicative of decreasing winter cloud cover. Decreases in both sea ice and cloud cover will increase light availability at the sea surface and potentially enhance phytoplankton growth. Our method allows the winter light conditions to be studied at temporal and spatial scales relevant for phytoplankton dynamics.
Key Points
In the Arctic, the ocean color‐derived open‐water season is lengthening by up to 2 days per year
Winter ocean color satellite coverage starts to degrade at 52°N for the Northern Hemisphere
Analysis suggests significant decreasing trends in winter cloud cover in sub‐Arctic waters of the northern Atlantic
•A novel method to assess dominant timescales of variability in sparse satellite data.•Applied on Chl and SST, the method shows unexpected global patterns of variability.•Shortest timescales can be ...found in subtropical gyres and upwelling regions.•SST generally have much longer timescales of variability than Chl.
Satellite-derived sea surface temperature (SST) and chlorophyll (Chl) datasets have been invaluable for estimating the oceanic primary production, air-sea heat exchange, and the spatial and seasonal patterns in their variability. However, data gaps, resulting from clouds and other factors, reduce coverage unevenly (to just about 20%) and make it difficult to analyze the temporal variability of Chl and SST on sub-seasonal time scales. Here, we present a MOving Standard deviation Saturation (MOSS) method to enable the analysis of sparse time series (with as little as 10% of the data). We apply the method to identify the dominating (sub-annual) timescales of variability, τd, for SST and Chl in every region. We find that τd values for Chl and SST are not consistent or correlated with each other over large areas, and in general, SST varies on longer timescales than Chl, i.e. τd(SST) >τd(Chl). There is a threefold variability in τd for SST and Chl even within regions that are traditionally considered to be biogeographically homogeneous. The largest τd for Chl is generally found on the equatorial side of the trade wind belts, whereas the smallest τd are found in the tropical Pacific and near coasts, especially where upwelling is common. If the temporal variability in Chl and SST were driven largely by ocean dynamics or advection by the flow, regional patterns of τd for SST and Chl should co-vary. This is seen in coastal upwelling zones, but more broadly, the lack of coherence between τd(Chl) and τd(SST) suggests that biological processes, such as phytoplankton growth and loss, decouple the timescales of Chl variability from those of SST and generate shorter term variability in Chl.
Much is still unknown about the control of oceanic biological production, especially in coastal areas where daily changes can be as large as seasonal variability. Both data scarcity and a lack of ...methods with sufficient coverage in space and time hinder our progress. Here we present a satellite‐derived proxy for net community production where simulated velocity fields are combined with satellite data to create a comprehensive accounting of spatial and temporal scales of biological production in the Southern California Bight. Statistical analyses show that rare events exert a major influence when estimating mean production over seasonal time scales: about 65% of change in biomass is caused by the 10% highest values in our data set. The results suggest that frequencies of rare events might be as important for biological production as seasonal averages. Our work highlights the need for additional data sets sampled at higher frequencies and shorter spatial scales.
Key Points
We have a proxy for oceanic biological production with unpredecented spatiotemporal resolution
Biological production in the South California Bight show high episodicity
Frequencies of rare events might be as important for biological production as seasonal averages
The region of the South Pacific Subtropical Gyre (SPSG) at 20°–30°S, 140°–110°W is the oceanic area with the lowest chlorophyll concentration and the deepest nutricline, O2 saturation horizon, and ...euphotic zone. We analyze the limited available data from this region to determine if rates of net community production (NCP) are systematically lower than elsewhere. We present limited mixed layer O2/Ar data constraining mixed layer NCP, examine hydrographic data from the CLIVAR repeat hydrography P18 line to assess seasonal dissolved inorganic carbon drawdown, and review results from the literature. While it is not possible to formalize uncertainties, the evidence suggests that euphotic zone NCP is around the lower end (~1 mol m−2 yr−1) of rates observed elsewhere. However, NCP is shifted to unusually deep depths, a change enabled by the very low extinction coefficients of these waters.
Key Points
Net community production in the South Pacific is “normal” despite highly oligotrophic conditions
Production in the South Pacific extends to unusually deep depths in the water column
Sea surface irradiance appears to be an important control on NCP throughout the oceans
By analyzing otolith microchemistry, we examined the use of freshwater and marine environments by brown trout Salmo trutta L. that spawn in the Swedish River Emån and migrate to the Baltic Sea. We ...estimated the time juveniles spent in freshwater and the number of times the fish returned to freshwater, presumably to spawn. Twenty-six percent of the fish migrated to sea by 1 year of age. However, 13% spent less than one year in the river. Most brown trout (48%) migrated to the sea between 1 and 2 years of age. On average, brown trout, which averaged 4.4 years in age (range 3–6 years), returned to freshwater 2.3 times, and there was an inverse relationship between time spent in freshwater after hatching and the number of visits to freshwater. Our results do not support the classical life history pattern, where brown trout spend one or more years in freshwater before migrating to the sea. Here, we found evidence that part of the population leaves freshwater during their first year. While the cause for precocial migration in the River Emån is not known, our results from this permanently flowing river do not support the idea proposed for other Baltic Sea populations, where the risk of drought has been suggested to be the cause.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
9.
Ocean Biology Studied from Space Sathyendranath, Shubha; Brewin, Robert J. W.; Ciavatta, Stefano ...
Surveys in geophysics,
10/2023, Letnik:
44, Številka:
5
Journal Article
Recenzirano
Odprti dostop
Visible spectral radiometric measurements from space, commonly referred to as ocean-colour measurements, provide a rich stream of information on ocean biota as well as on biological and ecosystem ...processes. The strength of the ocean-colour technology for observing marine life lies in its global reach, combined with its ability to sample the field at a variety of spatial and temporal scales that match the scales of the processes themselves. Another advantage lies in the growing length of the time series of ocean-colour-derived products, enabiling investigations into any long-term changes, if present. This paper presents an overview of the principles and applications of ocean-colour data. The concentration of chlorophyll-a, the major pigment present in phytoplankton–single-celled, free-floating plants that are present in the sunlit layers of the ocean–was the first, and remains the most common, biological variable derived from ocean-colour data. Over the years, the list of ocean-colour products have grown to encompass many measures of the marine ecosystem and its functions, including primary production, phenology and ecosystem structure. Applications that exploit the data are many and varied, and include ecosystem-based fisheries management, biogeochemical cycles in the ocean, ecosystem health and climate change. An integrated approach, incorporating other modes of ocean observations and models with satellite observations, is needed to investigate the mysteries of the marine ecosystem.
Questions of whether diurnal changes in carbon fixation affect the global carbon budget cannot be answered using the present generation of polar orbiting ocean color sensors that can only retrieve ...one image daily. Here, we present novel satellite‐derived indices of chlorophyll‐based production based on the Geostationary Ocean Color Imager (GOCI), whose hourly imaging capability offer the potential for direct estimates of net phytoplankton growth over hourly to seasonal time scales. Our results reveal large variations in net chlorophyll growth in the GOCI study region, both over the day and between seasons. Hourly changes in chlorophyll concentration are highest during spring while growth rates show maxima during the winter. We show seasonal relationships between growth and photon flux. Our study suggests that Geostationary Ocean Color data can be used to constrain phytoplankton productivity on diurnal time scales and be an essential tool to better understand diurnal growth patterns over large spatial regions.
Plain Language Summary
The rate at which microscopic ocean plants, or phytoplankton, consume carbon dioxide represents a gap in scientific knowledge that needs to be filled in order to better model the earth system. To aid in this understanding we use a novel technique that allows us to track the growth behavior of phytoplankton in the Yellow Sea and the East Sea‐Japan Sea. This is enabled by using satellite data from the Geostationary Ocean Color Imager, which has the unprecedented ability to collect quality biological information from the ocean surface each daylight hour. We find that the results, while in agreement with local observations and other satellite studies, also contain information about how phytoplankton change over daily to annual cycles and how native communities adapt in response to the annual solar cycle. This information is useful to the ocean modeling community, that seeks to understand various ways in which phytoplankton communities affect the cycling of Earth’s carbon.
Key Points
The Geostationary Ocean Color Instrument tracks changes in net phytoplankton growth at hourly intervals
Gains, losses, and net accumulations of chlorophyll show strong diurnal and seasonal variability
Seasonality in net growth versus light provides evidence for seasonal evolution in phytoplankton community composition
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