Predicting marine phytoplankton community size structure from empirical relationships with remotely sensed variables
TL;DR: In this article, the authors describe relationships between the environment and the size composition of phytoplankton communities, using a collation of empirical measurements of size composition from sites that include polar, tropical and upwelling environments.
Abstract: The size composition of primary producers has a potential influence on the length of marine food chains and carbon sinking rates, thus on the proportion of primary production (PP) that is removed from the upper layers and available to higher trophic levels. While total rates of PP are widely reported, it is also necessary to account for the size composition of primary producers when developing food web models that predict consumer biomass and production. Empirical measurement of size composition over large space and time scales is not feasible, so one approach is to predict size composition from environmental variables that are measured and reported on relevant scales. Here, we describe relationships between the environment and the size composition of phytoplankton communities, using a collation of empirical measurements of size composition from sites that include polar, tropical and upwelling environments. The size composition of the phytoplankton communities can be predicted using two remotely sensed variables, chlorophyll-a concentration and sea surface temperature. Applying such relationships in combination allows prediction of the slope and location of phytoplankton size spectra and estimation of the percentage of different sized phytoplankton groups in communities.
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TL;DR: A realistic marine food-web model is used, resolving species over five trophic levels, to study how total fish production changes with species richness, and predicts that BEF relations, on average, follow simple Michaelis–Menten curves when species are randomly deleted.
Abstract: Public concern over biodiversity loss is often rationalized as a threat to ecosystem functioning, but biodiversity-ecosystem functioning (BEF) relations are hard to empirically quantify at large scales. We use a realistic marine food-web model, resolving species over five trophic levels, to study how total fish production changes with species richness. This complex model predicts that BEF relations, on average, follow simple Michaelis–Menten curves when species are randomly deleted. These are shaped mainly by release of fish from predation, rather than the release from competition expected from simpler communities. Ordering species deletions by decreasing body mass or trophic level, representing ‘fishing down the food web’, accentuates prey-release effects and results in unimodal relationships. In contrast, simultaneous unselective harvesting diminishes these effects and produces an almost linear BEF relation, with maximum multispecies fisheries yield at E40% of initial species richness. These findings have important implications for the valuation of marine biodiversity.
33 citations
Cites background from "Predicting marine phytoplankton com..."
...(1); Barnes et al.(18) North Sea, Irminger Sea, Benguela upwelling, Norwegian Sea, 5 unspecified locations in Atlantic Ocean Mmat of fish spp....
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TL;DR: The results suggest that variability in δ15N values were largely driven by nitrogen cycling dynamics in the ETP, which highlights the importance of these processes for the interpretation of δ 15N values in food web studies.
Abstract: The effective evaluation of trophic interactions in pelagic food webs is essential for understanding food web ecology, conservation biology, and management. We tested the applicability of compound-specific isotope analysis of amino acids (CSIA-AA) for (1) characterizing trophic positions (TPs) of nine species from four trophic groups (tunas, squids, myctophids, and euphausiids) within a pelagic food web in the eastern tropical Pacific (ETP) Ocean, (2) evaluating trophic discrimination factors (TDFs) of each trophic group, and (3) detecting spatial changes in TPs and food chain length across a region with heterogeneous productivity. Although δ15N values of bulk tissues generally increased from south-to-north, CSIA-AA revealed that trophic positions were uniform throughout our study area. These results suggest that variability in δ15N values were largely driven by nitrogen cycling dynamics in the ETP, which highlights the importance of these processes for the interpretation of δ15N values in food web studies. Absolute TP estimates were unrealistic for higher-level species, and TDFs (tunas: 4.0‰, squids: 4.6‰, myctophids: 5.0‰, and euphausiids: 7.0‰) were lower than a widely used ecosystem TDF. We used remotely sensed oceanographic data to evaluate the physical oceanography and biological productivity throughout our study area and found significant relationships between δ15N values, nitrate concentrations, and SST across our study area. We did not find a gradient in phytoplankton cell size co-occurring with an expected productivity gradient across our sampling region, which substantiated our isotope results indicating non-significant spatial changes in TP and food chain length across the ETP.
33 citations
TL;DR: Results suggest that the silky shark is an opportunistic predator that forages on a variety of prey, which is essential for populating ecosystem models with space-based food webs, which otherwise suffer from generic representations of food webs.
Abstract: Diet studies are an essential component of ecosystem-based approaches to fisheries management. In the eastern Pacific Ocean (EPO), the silky shark (Carcharhinus falciformis) is the most common species of shark in the bycatch of the tuna purse-seine fishery. A rare, comprehensive dataset of stomach contents of 786 silky sharks sampled in mostly tropical regions of the EPO (25°N–15°S; 79°W–162°W) during 1992–1994 and 2003–2005 was analyzed via classification tree and quantile regression methodologies to gain insight into its ecosystem role. Results suggest that the silky shark is an opportunistic predator that forages on a variety of prey. Broad-scale spatial and shark size covariates explained the feeding habits of silky sharks captured in sets on floating objects, primarily drifting fish-aggregating devices (FADs). A strong spatial shift in diet was identified by the tree analysis, with different foraging patterns in the eastern (inshore) and western (offshore) regions. Greater proportions of FAD-associated prey than non-FAD-associated prey were observed in the diet throughout the EPO, with the greatest proportion in the offshore region. Thus, silky sharks appear to take advantage of the associative behavior of prey fishes to increase their probability of encountering and capturing prey. Evaluation of prey–predator size relationships showed that maximum prey size increased with increasing silky shark size, but minimum prey size remained relatively constant across the range of shark sizes. Results such as these from spatially oriented analyses of predator feeding habits are essential for populating ecosystem models with space-based food webs, which otherwise suffer from generic representations of food webs.
33 citations
TL;DR: In this article, the authors review and analyze 115 published phytoplankton trend estimates originating from a wide variety of sampling instruments to explore the underlying patterns and ecological implica- tions of phyto-ankton change over the period of oceanographic measurement (1889 to 2010).
Abstract: There is growing evidence that average global phytoplankton concentrations have been changing over the past century, yet published trajectories of change are highly divergent. Here, we review and analyze 115 published phytoplankton trend estimates originating from a wide variety of sampling instruments to explore the underlying patterns and ecological implica- tions of phytoplankton change over the period of oceanographic measurement (1889 to 2010). We found that published estimates of phytoplankton change were much less variable when estimated over longer time series and consistent spatial scales and from the same sampling instruments. Average phytoplankton concentrations tended to increase over time in near-shore waters and over more recent time periods and declined in the open oceans and over longer time periods. Most published evidence suggests changes in temperature and nutrient supply rates as leading causes of these phytoplankton trends. In near-shore waters, altered coastal runoff and increased nutrient flux from land may primarily explain widespread increases in phytoplankton there. Conversely, in the open oceans, increasing surface temperatures are strengthening water column stratification, reducing nutrient flux from deeper waters and negatively influencing phytoplankton. Phytoplank- ton change is further affected by biological processes, such as changes in grazing regimes and nutrient cycling, but these effects are less well studied at large scales. The possible ecosystem consequences of observed phytoplankton changes include altered species composition and abun- dance across multiple trophic levels, effects on fisheries yield, and changing patterns of export production. We conclude that there is evidence for substantial changes in phytoplankton concen- tration over the past century, but the magnitude of these changes remains uncertain at a global scale; standardized long-term measurements of phytoplankton abundance over time can substan- tially reduce this uncertainty.
32 citations
Cites background from "Predicting marine phytoplankton com..."
...…field, and modeling studies suggest that TDS may also lead to declines in the concentration of larger phytoplankton species such as diatoms and increases in smaller species such as small flagellates and cyanobacteria (Li et al. 2009, Morán et al. 2010, Barnes et al. 2011, Boyce et al. 2015a)....
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TL;DR: The ZooMSSv2 model as mentioned in this paper is a functional size spectrum model that resolves nine major zooplankton functional groups (heterotrophic flagellates, heterotrophic ciliates, larvaceans, omnivorous copepods, carnivorous copeps, chaetognaths, euphausiids, salps and jellyfish).
32 citations
References
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TL;DR: If the organisms are randomly distributed, a single count is sufficient to obtain an estimate of their abundance and confidence limits for this estimate, even if pipetting, dilution or concentration are involved.
Abstract: Various methods for the estimation of populations of algae and other small freshwater organisms are described. A method of counting is described in detail. It is basically that of Utermohl and uses an inverted microscope. If the organisms are randomly distributed, a single count is sufficient to obtain an estimate of their abundance and confidence limits for this estimate, even if pipetting, dilution or concentration are involved. The errors in the actual counting and in converting colony counts to cell numbers are considered and found to be small relative to the random sampling error. Data are also given for a variant of Utermohl's method using a normal microscope and for a method of using a haemocytometer for the larger plankton algae.
2,572 citations
"Predicting marine phytoplankton com..." refers background or methods in this paper
...Sub-samples (100 ml) were settled (Utermıhl technique (Lund et al. 1958)) and individuals counted at the species level with an inverted microscope....
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...technique (Lund et al. 1958)) and individuals counted at the species level with an inverted...
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TL;DR: Cellular carbon and nitrogen content and cell volume of nutritionally and morphologically diverse dinoflagellate species were measured to determine carbon to volume and nitrogen to volume relationships.
Abstract: Cellular carbon and nitrogen content and cell volume of nutritionally and morphologically diverse dinoflagellate species were measured to determine carbon to volume (C : vol) and nitrogen to volume (N : vol) relationships. Cellular C and N content ranged from 48 to 3.0 3 10 4 pgC cell 21 21 5
2,137 citations
"Predicting marine phytoplankton com..." refers background in this paper
...0 −− = µvolumeyearCpg Equation 5 reported for taxonomically diverse protist plankton (Menden-Deuer and Lessard 2000)....
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...reported for taxonomically diverse protist plankton (Menden-Deuer and Lessard 2000)....
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TL;DR: In this paper, an estimate of global net primary production in the ocean has been computed from the monthly mean near-surface chlorophyll fields for 1979-1986 obtained by the Nimbus 7 CZCS radiometer.
Abstract: An estimate of global net primary production in the ocean has been computed from the monthly mean near-surface chlorophyll fields for 1979-1986 obtained by the Nimbus 7 CZCS radiometer. Our model required information about the subsurface distribution of chlorophyll, the parameters of the photosynthesis-light relationship, the sun angle and cloudiness. The computations were partitioned among 57 biogeochemical provinces that were specified from regional oceanography and by examination of the chlorophyll fields. Making different assumptions about the overestimation of chlorophyll by the CZCS in turbid coastal areas, the global net primary production from phytoplankton is given as 45-50 Gt C year"1. This may be compared with current published estimates for land plants of 45-68 Gt C year"' and for coastal vegetation of 1.9 Gt C year"1.
1,381 citations
"Predicting marine phytoplankton com..." refers background or methods in this paper
...All changes from the implementation of Longhurst et al. (Longhurst et al. 1995) are detailed in Mélin (Mélin 2003)....
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...ocean area (Longhurst et al. 1995), and to regional differences in phytoplankton community...
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...PP was computed from a wavelength- and depthresolved model (Mélin 2003), building on the approach of Longhurst et al. (Longhurst et al. 1995)....
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...This is due to variations in absolute productivity among regions, with 50% of production estimated to come from 27% of ocean area (Longhurst et al. 1995), and to regional differences in phytoplankton community structure....
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...(Longhurst et al. 1995) are detailed in Mélin (Mélin 2003)....
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TL;DR: This study provides evidence that reduced body size is the third universal ecological response to global warming in aquatic systems besides the shift of species ranges toward higher altitudes and latitudes and the seasonal shifts in life cycle events.
Abstract: Understanding the ecological impacts of climate change is a crucial challenge of the twenty-first century. There is a clear lack of general rules regarding the impacts of global warming on biota. Here, we present a metaanalysis of the effect of climate change on body size of ectothermic aquatic organisms (bacteria, phyto- and zooplankton, and fish) from the community to the individual level. Using long-term surveys, experimental data and published results, we show a significant increase in the proportion of small-sized species and young age classes and a decrease in size-at-age. These results are in accordance with the ecological rules dealing with the temperature–size relationships (i.e., Bergmann's rule, James' rule and Temperature–Size Rule). Our study provides evidence that reduced body size is the third universal ecological response to global warming in aquatic systems besides the shift of species ranges toward higher altitudes and latitudes and the seasonal shifts in life cycle events.
1,292 citations
"Predicting marine phytoplankton com..." refers background in this paper
...There is evidence that reduced body size is the third universal ecological response to global warming besides the shift of species ranges toward higher altitudes and latitudes and the seasonal shifts in life-cycle events (Daufresne et al. 2009)....
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...higher altitudes and latitudes and the seasonal shifts in life-cycle events (Daufresne et al. 2009)....
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TL;DR: In this paper, the frequency distributions of particIe size between sizes of about I and 100 p are given for both surface and deep water of the Atlantic and Pacific Oceans.
Abstract: Frequency distributions of particIe size between sizes of about I and 100 p are given for both surface and deep water of the Atlantic and Pacific Oceans. The form of the size spectra varies predictably both geographically and with depth. A hypothesis is presented to show that, to a first approximation, roughly equal concentrations of material occur at all particle sizes within the range from 1 p to about 10” p, i.e. from bacteria to whales.
1,116 citations