Fatty acids have been used as qualitative markers to trace or confirm predator-prey relationships in the marine environment for more than thirty years. More recently, they have also been used to identify key processes impacting the dynamics of some of the world's major ecosystems. The fatty acid trophic marker (FATM) concept is based on the observation that marine primary producers lay down certain fatty acid patterns that may be transferred conservatively to, and hence can be recognized in, primary consumers. To identify these fatty acid patterns the literature was surveyed and a partial least squares (PLS) regression analysis of the data was performed, validating the specificity of particular microalgal FATM. Microalgal group specific FATM have been traced in various primary consumers, particularly in herbivorous calanoid copepods, which accumulate large lipid reserves, and which dominate the zooplankton biomass in high latitude ecosystems. At higher trophic levels these markers of herbivory are obscured as the degree of carnivory increases, and as the fatty acids originate from a variety of dietary sources. Such differences are highlighted in a PLS regression analysis of fatty acid and fatty alcohol compositional data (the components of wax esters accumulated by many marine organisms) of key Arctic and Antarctic herbivorous, omnivorous and carnivorous copepod species. The analysis emphasizes how calanoid copepods separate from other copepods not only by their content of microalgal group specific FATM, but also by their large content of long-chain monounsaturated fatty acids and alcohols. These monounsaturates have been used to trace and resolve food web relationships in, for example, hyperiid amphipods, euphausiids and fish, which may consume large numbers of calanoid copepods. Results like these are extremely valuable for enabling the discrimination of specific prey species utilized by higher trophic level omnivores and carnivores without the employment of invasive techniques, and thereby for identifying the sources of energetic reserves. A conceptual model of the spatial and temporal dominance of group-specific primary producers, and hence the basic fatty acid patterns available to higher trophic levels is presented. The model is based on stratification, which acts on phytoplankton group dominance through the availability of light and nutrients. It predicts the seasonal and ecosystem specific contribution of diatom and flagellate/microbial loop FATM to food webs as a function of water column stability. Future prospects for the application of FATM in resolving dynamic ecosystem processes are assessed.

Fatty acid trophic markers in the pelagic marine environment.

Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology. Levy walks are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators-sharks, bony fishes, sea turtles and penguins-exhibit Levy-walk-like behaviour close to a theoretical optimum. Prey density distributions also display Levy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Levy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Levy-like behaviour seems to be widespread among diverse organisms, from microbes to humans, as a 'rule' that evolved in response to patchy resource distributions.

Scaling laws of marine predator search behaviour

Dynamical aspects of animal grouping: Swarms, schools, flocks, and herds

We investigated the effects of three sizes of polystyrene (PS) microbeads (0.05, 0.5, and 6-μm diameter) on the survival, development, and fecundity of the copepod Tigriopus japonicus using acute and chronic toxicity tests. T. japonicus ingested and egested all three sizes of PS beads used and exhibited no selective feeding when phytoplankton were added. The copepods (nauplius and adult females) survived all sizes of PS beads and the various concentrations tested in the acute toxicity test for 96 h. In the two-generation chronic toxicity test, 0.05-μm PS beads at a concentration greater than 12.5 μg/mL caused the mortality of nauplii and copepodites in the F0 generation and even triggered mortality at a concentration of 1.25 μg/mL in the next generation. In the 0.5-μm PS bead treatment, despite there being no significant effect on the F0 generation, the highest concentration (25 μg/mL) induced a significant decrease in survival compared with the control population in the F1 generation. The 6-μm PS beads d...

Size-Dependent Effects of Micro Polystyrene Particles in the Marine Copepod Tigriopus japonicus

This paper explores the notion that the theoretical basis for contemporary research concerning the structure and function of marine pelagic ecosystems is self-limiting. While some findings such as the microbial food web have extended our knowledge of the biological components of the upper water column and their relationships to fluxes of materials and energy, they have not advanced our understanding of why specific pelagic forms occur in time and space, and why only some attain dominant status and contribute the bulk of biogenic fluxes emanating from the mixed layer. It is argued here that a major impediment to improved conceptual models is the historic focus on resource-driven or 'bottom-up' factors as being the dominant variables structuring planktonic ecosystems. Evidence is presented that predation or 'top-down' trophic effects may be equally important in specifying the occurrence of particular taxa, the biomass within adjacent trophic levels, and the morphology of dominant herbivores and carnivores. It is suggested that key species, because of unique combinations of life history strategies, metabolic demands, and physiological performance, may exert a dominant role in the extent to which predatory interactions cascade through pelagic food webs. There is considerable evidence of evolution of predation avoidance strategies among phytoplankton and zooplankton. It is proposed that future research might profitably be directed toward the question of how the pelagic environment selects for life histories and morphologies of organisms under conditions when resource availability and predation are both significant structural buttresses. Methodological approaches should include detailed studies of dominant key taxa from different environments, with the goal of identifying the critical aspects of life history, behavior, or morphology which account for their success.

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Organism life cycles, predation, and the structure of marine pelagic ecosystems

https://aslopubs.onlinelibrary.wiley.com/doi/epdf/10.4319/lo.1980.25.4.0583

Grazing patterns of copepods in the upwelling system off Peru

Continuous estimates were obtained of zooplankton abundance, chlorophyll fluorescence, and water temperature along 10-to 100-kilometer transects of the North Sea. Spectral analysis methods were applied to the data. The "patchiness" of the plankton was distributed over all the length scales resolved with no indication of a characteristic patch size. The relative intensity of the zooplankton patchiness was greater than that of the phytoplankton at all spatial scales, with this difference becoming progressively greater for finer-scale features. In the North Sea data, the concentrations of phytoplankton and zooplankton consistently showed negative spatial correlations.

http://science.sciencemag.org/content/sci/204/4388/62.full.pdf

Spectral analysis of zooplankton spatial heterogeneity.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1976.21.1.0175

Selection of particle sizes by filter-feeding copepods: A plea for reason

Feeding experiments were conducted at Palmer Station from December 1985 to February 1986 to examine the potential role of copepod prey as an alternative food source for Euphausia superba. Copepod concentration, copepod size, phytoplankton concentration, the duration of krill starvation and the volume of experimental vessels were altered to determine effects on ingestion and clearance rates. Krill allowed to feed on phytoplankton and copepods in 50-litre tubs showed greatly increased feeding rates relative to animals feeding in the much smaller volumes of water traditionally used for krill-feeding studies. Clearance rates on copepods remained constant over the range of concentrations offered, but clearance rates on phytoplankton increased linearly with phytoplankton concentration. Feeding rates increased when larger copepods were offered and when krill were starved for two weeks prior to experiments. Clearance rates of krill feeding on copepods were higher than, but not correlated with, their clearance rates on phytoplankton in the same vessel. E. superba may have a distinct mechanism for capturing copepods, perhaps through mechanoreception. Although our observed clearance rate of 1055 ml krill-1 h-1 indicates that krill can feed very efficiently on copepod prey, such feeding would meet less than 10% of their minimum metabolic requirements at the “typical” copepod concentrations reported for Antarctic waters. However, substantial energy could be gained if krill fed on the patches of high copepod concentrations occasionally reported during the austral summer, or if krill and copepods were concentrated beneath the sea ice during the winter or spring months. Our results, indicating efficient feeding on zooplankton and higher clearance rates on phytoplankton than previously believed, represent a step towards balancing the energy budget of E. superba in Antarctic waters.

Omnivorous feeding behavior of the antarctic krill Euphausia superba

Measurements of rates of feeding indicate that Euphausia superba can feed on particles ranging from nanophytoplankton to macrozooplankton; a typical animal of 120 mg dry weight processes about 450 ml water per h and ingests at a maximum about 10% of its body carbon per day A food concentration of about 100 µg carbon 1–1 allows the animal to ingest its minimum food requirement of 23% body carbon per day Measurements of 210Po and 210Pb indicate krill from Bransfield Strait in February 1982 were feeding herbivorously Photographic analysis of the thoracic legs employed by E superba for feeding indicates that the mechanical power required to extract phytoplankton from the water ranges up to about 30% of its total respiratory energy

Carl M. Boyd

Papers

Grazing patterns of copepods in the upwelling system off Peru

Spectral analysis of zooplankton spatial heterogeneity.

Selection of particle sizes by filter-feeding copepods: A plea for reason

Omnivorous feeding behavior of the antarctic krill Euphausia superba

Feeding of the antarctic krill euphausia superba