Phytoplankton blooms are prominent features of biological variability in shallow coastal ecosystems such as estuaries, lagoons, bays, and tidal rivers. Long-term observation and research in San Francisco Bay illustrates some patterns of phytoplankton spatial and temporal variability and the underlying mechanisms of this variability. Blooms are events of rapid production and accumulation of phytoplankton biomass that are usually responses to changing physical forcings originating in the coastal ocean (e.g., tides), the atmosphere (wind), or on the land surface (precipitation and river runoff). These physical forcings have different timescales of variability, so algal blooms can be short-term episodic events, recurrent seasonal phenomena, or rare events associated with exceptional climatic or hydrologic conditions. The biogeochemical role of phytoplankton primary production is to transform and incorporate reactive inorganic elements into organic forms, and these transformations are rapid and lead to measurable geochemical change during blooms. Examples include the depletion of inorganic nutrients (N, P, Si), supersaturation of oxygen and removal of carbon dioxide, shifts in the isotopic composition of reactive elements (C, N), production of climatically active trace gases (methyl bromide, dimethylsulfide), changes in the chemical form and toxicity of trace metals (As, Cd, Ni, Zn), changes in the biochemical composition and reactivity of the suspended particulate matter, and synthesis of organic matter required for the reproduction and growth of heterotrophs, including bacteria, zooplankton, and benthic consumer animals. Some classes of phytoplankton play special roles in the cycling of elements or synthesis of specific organic molecules, but we have only rudimentary understanding of the forces that select for and promote blooms of these species. Mounting evidence suggests that the natural cycles of bloom variability are being altered on a global scale by human activities including the input of toxic contaminants and nutrients, manipulation of river flows, and translocation of species. This hypothesis will be a key component of our effort to understand global change at the land-sea interface. Pursuit of this hypothesis will require creative approaches for distinguishing natural and anthropogenic sources of phytoplankton population variability, as well as recognition that the modes of human disturbance of coastal bloom cycles operate interactively and cannot be studied as isolated processes.

Phytoplankton bloom dynamics in coastal ecosystems: A review with some general lessons from sustained investigation of San Francisco Bay, California

Growth physiology and fate of diatoms in the ocean: a review

Organisms differ in the proportions of major elements that they contain, including N and P, which are known to be highly dynamic and potentially limiting to production of aquatic ecosystems. Such contrasting elemental composition between, for example, algae and herbivores, or between different herbivores, generates a suite of ecological predictions and opens up new dynamical possibilities. Here we review studies relating to the nutritional physiology of aquatic herbivores, especially freshwater pelagic species, and we relate element content to secondary production and nutrient recycling. A variety of evidence from many types of studies-physiological modelling, whole-ecosystem surveys, laboratory growth studies, etc-is assembled into an internally consistent picture of mineral limitation of aquatic herbivores. Herbivores with high nutrient demands (the best example is probably Daphnia and phosphorus) appear frequently to be limited not by the food quantity or energy available to them but by the quantity of mineral elements in their food.

Algal nutrient limitation and the nutrition of aquatic herbivores

The productive regions of the ocean are characterized by seasonal blooms of phytoplankton which are generally dominated by diatoms. This algal class has, therefore, traditionally been regarded as providing the bulk of the food that sustains the marine food chain to top consumers and important fisheries. However, this beneficial role has recently been questioned on the basis of laboratory studies showing that although dominant zooplankton grazers such as copepods feed extensively on diatoms, the hatching success of eggs thus produced is seriously impaired1. Here we present evidence from the field showing that the hatching success of wild copepods feeding on a diatom-dominated bloom is also heavily compromised, with only 12% of the eggs hatching compared with 90% in post-bloom conditions. We report on the structure of the three aldehydes isolated from diatoms that are responsible for this biological activity, and show that these compounds arrest embryonic development in copepod and sea urchin bioassays and have antiproliferative and apoptotic effects on human carcinoma cells.

The insidious effect of diatoms on copepod reproduction

A review of the literature (ca 1900 to 1992) on copepod feeding indicates that combinations of stochashc and deterministic processes result in behaviors, or feeding strategies, that optirnize nutritional gain from the food environment, and further, that strategies change in response to environmental variability. Because the diet is the product of a feeding strategy, one may gain insight into the ways in which copepods respond to their food environments by measuring their diets. Investigations of the hnks between copepod feeding and production suggest that dietary diversity is often a key to the procurement of a nutritionally complete ration, and the optimization of secondary production within constraints dictated by the physical environment. The ability to eat different kinds of foods (ornnivory) and the tendency to include a variety of foods in the daily ration may enhance the probabhty of obtaining a nutritionally complete ration in variable, nutritionally dilute, food environments. The notion that the relationshp between feeding and production in copepods is driven by clletary diversity is derived in part from a recent recognition of the diversity of microplanktonic organisms that potentially or actually contribute to the diet. Further, the concept is consistent with current trophic dynamic models in which food webs are envisioned as complex interwoven systems rather than short, simple chains.

/pdf/on-the-diets-of-calanoid-copepods-4wh7tnn19e.pdf

On the diets of calanoid copepods

Relationships among microplankton composition, copepod diet, and egg production are examined with data from gut content analysis of copepods from California coastal waters and from the Irish Sea, feeding and egg production experiments on Acartia tonsa off southern California, and egg production measurements on copepods from a subtropical estuary (Port Everglades, Florida), temperate shelf waters (southern California, Irish Sea), and the open ocean (Gulf Stream). The copepod species studied appeared to feed preferentially on dinoflagellates and microzooplankton relative to diatoms. Patterns of variability in egg production conform, generally, to changes in dinoflagellate and microzooplankton biomass, but seem to be independent of changes in diatom biomass.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1991.36.1.0172

Trophic interactions between copepods and microplankton: A question about the role of diatoms

High-frequency acoustical technology is used to measure the spatial distributions of small zooplankton with meter-scale resolution in the vertical, resolutions of hundreds of meters or better in the horizontal, and with temporal resolutions of minutes. Both size and abundance measurements can be made by using sensors in a cast mode from a ship, from undulating towed bodies and by placing instruments on moorings. This presentation includes an overview of some of the technical concepts that are involved, examples of the use of the sensors and systems that have been developed and brief discussions related to the algorithms used to convert acoustical measures to biologically relevant estimates for small zooplankton.

Bioacoustical oceanography at high frequencies

Determination of zooplankton size and distribution with multifrequency acoustic technology

Plant and animal carotenoid pigments were isolated from the guts of the copepods Calanus pacificus and Clausocalanus sp, and the cladocerans Evadne spp. by high performance Liquid chromatography. Measured carotenoid concentrations were converted to eshmates of class-specific phytoplankton biomass and total microzooplankton biomass In the zooplankton diets. Different pigments were present in the guts at dfferent times of day and night and the tllnmg of peak gut fullness var~ed between species. In C. pacificus, pigment concentrat~ons were highest during the period from evening twilight to midnight. Evadne spp. exhibited a midnight peak In gut pigmentation. Clausocalanus sp. contained elevated levels of pigments between midnight and noon. The gut contents of C. pacificus and Evadne spp. were dominated by animal carbon when phytoplankton biomass and productivity were relatively low, and by algal carbon when phytoplankton biomass and productivity were high. Clausocalanus sp. did not follow this pattern. Our observations are consistent with the hypothesis that carnivory may represent an important mode of feeding among small zooplankton and, further, that the diets of some species of zooplankton vary in response to quantitative and qualitative attributes of the food environment.

https://www.int-res.com/articles/meps/49/m049p231.pdf

R. E. Pieper

Papers

Trophic interactions between copepods and microplankton: A question about the role of diatoms

Bioacoustical oceanography at high frequencies

Bioacoustical oceanography at high frequencies

Determination of zooplankton size and distribution with multifrequency acoustic technology

Natural diets of zooplankton off southern California