Plastic debris has significant environmental and economic impacts in marine systems. Monitoring is crucial to assess the efficacy of measures implemented to reduce the abundance of plastic debris, but it is complicated by large spatial and temporal heterogeneity in the amounts of plastic debris and by our limited understanding of the pathways followed by plastic debris and its long-term fate. To date, most monitoring has focused on beach surveys of stranded plastics and other litter. Infrequent surveys of the standing stock of litter on beaches provide crude estimates of debris types and abundance, but are biased by differential removal of litter items by beachcombing, cleanups and beach dynamics. Monitoring the accumulation of stranded debris provides an index of debris trends in adjacent waters, but is costly to undertake. At-sea sampling requires large sample sizes for statistical power to detect changes in abundance, given the high spatial and temporal heterogeneity. Another approach is to monitor the impacts of plastics. Seabirds and other marine organisms that accumulate plastics in their stomachs offer a cost-effective way to monitor the abundance and composition of small plastic litter. Changes in entanglement rates are harder to interpret, as they are sensitive to changes in population sizes of affected species. Monitoring waste disposal on ships and plastic debris levels in rivers and storm-water runoff is useful because it identifies the main sources of plastic debris entering the sea and can direct mitigation efforts. Different monitoring approaches are required to answer different questions, but attempts should be made to standardize approaches internationally.

A general, size-based simulation model is developed to investigate the dynamics of carbon and nitrogen flows in plankton communities. In the model, community structure and transfer processes are all size-dependent, and all model parameters are determined by body size, using empirically determined relationships calculated from published data Major flows include carbon fixation, release of photosynthetically produced dissolved organic carbon (PDOC), nitrogen uptake, respiration, excretion, predation, senescence and sinking. Because the model is based on general ecological principles and not on a specific ecosystem or data set, it can be used to simulate interactions within plankton communities of any ecosystem. The structure of the model can easily be altered to incorporate fewer or more size classes, or different size ranges of organisms. The program adjusts interactions between different components to allow for changes in the number of size classes, and new parameters are estimated, based on mean organism size A standard simulation is described, which serves as the basis for comparing output from a sensitivity analysis. The model is robust with respect to most parameters. Important factors which affect model output include estimates of various rate parameters (which may be altered by environmental effects), shapes of initial biomass distributions (seeding effects), and wet mass to carbon conversion functions. The model is a useful tool to assist in analysing and interpreting carbon and nitrogen flows in planktonic ecosystems.

Examples of sympatric speciation in nature are rare and hotly debated. We describe the parallel speciation of finches on two small islands in the Tristan da Cunha archipelago in the South Atlantic Ocean. Nesospiza buntings are a classic example of a simple adaptive radiation, with two species on each island: an abundant small-billed dietary generalist and a scarce large-billed specialist. Their morphological diversity closely matches the available spectrum of seed sizes, and genetic evidence suggests that they evolved independently on each island. Speciation is complete on the smaller island, where there is a single habitat with strongly bimodal seed size abundance, but is incomplete on the larger island, where a greater diversity of habitats has resulted in three lineages. Our study suggests that the buntings have undergone parallel ecological speciation.

General allometric equations are derived for rates of nutrient uptake, ingestion, and respiration by planktonic organisms. Previous studies commonly calculated parameters a and b in the allometric equation R = aMb by linear regressions on log‐transformed data. This practice results in variability between data sets in estimates of both a and b, making meaningful comparisons difficult. This problem is overcome by assuming the mass‐specific form of b to be −0.25, based on accumulated empirical evidence. Values of a arc then recalculated from published data, with log transformations and an assumed regression slope of −0.25. Resulting regressions predict values of a (in pg C0.25 d−1) at 20°C as follows: 3.6 for nutrient uptake by phytoplankton and bacteria; 63 and 13 for ingestion and respiration by particle‐feeding heterotrophs. It is hypothesized that organisms that take up dissolved nutrients from solution (autotrophs and osmotrophs, e.g. phytoplankton and bacteria) have lower specific respiration rates (i.e. smaller a) when compared with organisms (either unicellular or multicellular) that ingest particulate material.

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