The Production of Particles in the Surface Waters of the Ocean With Particular Reference to the Sargasso Sea1

Abstract

In the surface waters of the ocean particle production and consumption are in balance. The structure of the pelagic food chain and the morphological limitations dictated by the environment are such that, in general, large particles have to consume smaller ones. If the large particles are removed the small particles cannot be consumed and their production rate can be measured, A state of exponential growth stems to be normal. The rate of production, as revealed by small particle growth following predation release, is much greater than the apparent rate of primary production indicated by radiocarbon uptake.It is quite obvious that the ocean is not like the land, but it is not generally appreciated that oceanic food chains are also quite unlike those of most terrestrial ecosystems. This is particularly true of the pelagic environment. The basic structure of the pelagic food chain in the open ocean is relatively simple, and this simplicity is largely determined by the nature of the environment, There are three main reasons for this. The first is that all the components are floating (or swimming) particles-a fairly obvious requirement.The second is that primary production occurs only as small particles. It is not immediately obvious why this should be, but it is certainly true that large photosynthetic organisms are rare in the pelagic environment. The third is that at each link in the food chain large particles take up smaller ones. In general, when one oceanic organism feeds on another it does so by engulfing it. This means that the predator has to be larger than the prey. There is no common pelagic equivalent of a small goat browsing on a large tree. These three factors are quite fundamental and they place limits on the structure of a pelagic ecosystem.In when taken over logarithmically equal size intervals, tends to be roughly the same at all sizes ( Sheldon et al. 1972). To maintain this state the rate of particle production should vary inversely with particle size. At any link of the food chain the relative production of the two components must also be inversely proportional to the ccological efficiency, more or less. In practical terms this means that if the ecological efficiency of an alga-herbivore relationship is 10% then the rate of algal production must be at least 10x the rate of herbivore production.This corresponds to the situation where all the algal production is consumed by the herbivores. Similar considerations will apply to other links of the food chain.It is fundamental to our understanding of oceanic production to realize that over long periods of time the total biomass of the open ocean is fairly constant. Therefore, all the organic material that is built up into particles is ultimately consumed or broken down again. In this paper we describe a series of observations and experiments which show that it is possible to increase our understanding of marine production simply by looking at particle formation.We would like to thank N. Prouse for making 14C determinations of production.

Herbivory as a factor in patterns of nutrient utilization in the sea1

“…1960;Voronina 1972) and speciation in low latitudes to biologically expand the number of niches in a relatively stable physical habitat with a wide diversity of herbivores to crop all size classes of phytoplankton (Sheldon et al 1973); the larger diversity of zooplankton carnivores in the horizontal interior of the ocean may also rcfleet the above diffcrcnces in the kinetic energy variance spectra. It is then possible that, in contrast to the continental shelves, the phytoplankton-herbivore interfact (Steele 1974) is an extremely efficient control mechanism within the gyres and, perhaps, offshore divergences, such that most phytoplankton are always consumed by herbivores in both systems, without blooms or full utilization of the nutrients in the offshort divergences.…”

A random encounter model for the microbial planktonic community

“…He assumes a steady state in which net growth rate of the population at trophic level 1 equals the sum of the net growth rate and respiration rate of the population at trophic level 2. He then invokes a relationship between specific rates of growth, here u (Sheldon et al 1972(Sheldon et al , 1973 h, of its prey. Given the assumption of constant cell density, Kerr found that such relationships yield a predicted ratio of the concentration of total cell volume for adjacent trophic levels:…”

“…The size distribution of cells must, therefore, satisfy this condition. In particular, a mathematical statement of the hypothesis is based on the following relationships: volume of a cell varies as the cube of its diameter; clearance rate (L3T-I) by a predator varies as the square of its diameter; and, for a given population, its range of possible prey sizes varies with its prey diameter at the same time that the range of predator sizes able to capture the given population varies with its predator diameter.Measurements at sea of the distribution of particle sizes by electronic detection (Sheldon et al 1972(Sheldon et al , 1973 and by phase contrast microscopy have shown that there is a characteristic distribution for particles in the size range between 2 and 100 pm. Samples collected from diverse regions of the open ocean are all characterized by a steep and continuous decrease in the particle concentration with increasing particle size.…”

“…Measurements at sea of the distribution of particle sizes by electronic detection (Sheldon et al 1972(Sheldon et al , 1973 and by phase contrast microscopy have shown that there is a characteristic distribution for particles in the size range between 2 and 100 pm. Samples collected from diverse regions of the open ocean are all characterized by a steep and continuous decrease in the particle concentration with increasing particle size.…”

The use of track autoradiography to determine species-specific phytoplankton productivity

“…Methodologies for estimating biomass concentrations are numerous: cell numbers, wet or dry weight, chlorophyll ~ concentrations, mineral content, and others (Vollenweider, 1969). As the size of the standing crop is a result of an i~terplay between growth rate, predation and sinking rates, biomass is a measure of the net amount of energy capital in the community (Cooper, 1973;Sheldon and Sutcliffe,!, 1973). There does not appear to be a straightforward relationship between the size of the standing crop and its productivity (Findenegg, 1969;Malone, 1971).…”