532
ANDREAS OSCHLIES
3.
Observations
A trivial statement is that the ocean is severly undersampled and that
we need more data to better understand what is going on out there. We
also have data of very different quality. There is a large number of
data which are difficult to interpret in terms of ecological variables or
processes resolved by dynamical models. Examples include wet zooplankton weight, satellite ocean colour data (which contain information
on water-leaving radiance at a few wavelengths, but not immediately
on surface chlorophyll or even primary production), or uptake of carbon
isotopes into particulate matter (which is related but not identical to
primary production, e.g., Dring and Jewson [1982]). Particular care has
to be taken when different measurement methods that attempt – and
often claim – to measure the same quantity (e.g., chlorophyll concentration, primary production) in fact measure different things . In contrast to
more straightforward measurements of concentrations of standing stocks
of organic or inorganic matter, direct observations of processes or rates
(e.g., growth, grazing, sinking, exudation, mortality) are usually difficult
to carry out without perturbing the system under investigation and, accordingly, are very limited in number and often have large random and
systematic errors.
Available observations are also often biased towards the spring and
summer season, with generally very few ship-based winter or autumn
observations, particularly in mid and high latitudes. The same sampling
bias holds for measurements of physical variables, but may be more
critical for ecological properties for which the amplitude of the local
seasonal cycle can be as large as the global range of the respective annual
mean property.
Valuable observational information can also be taken from laboratory
studies. Investigations using cultured species may, for example, help to
reveal physiological information on the impact of environmental conditions like nutrient concentrations, light intensity, turbulence levels, or
temperature on growth rates. A caveat to be kept in mind is that those
species that have been cultured so far are not necessarily representative
of the open-ocean plankton community. Considering that the number
of generations separating our domestic plants and animals from their
wild ancestors is reached by phytoplankton in only a few years, culture
species may also be affected by selection and mutation.
It appears that information on the loss side (e.g., grazing, mortality)
is more difficult to obtain than on the production side (growth). There is
a (perhaps related?) tendency of marine ecosystem modellers to increase
model complexity preferentially on the production side rather than on
ANDREAS OSCHLIES
3.
Observations
A trivial statement is that the ocean is severly undersampled and that
we need more data to better understand what is going on out there. We
also have data of very different quality. There is a large number of
data which are difficult to interpret in terms of ecological variables or
processes resolved by dynamical models. Examples include wet zooplankton weight, satellite ocean colour data (which contain information
on water-leaving radiance at a few wavelengths, but not immediately
on surface chlorophyll or even primary production), or uptake of carbon
isotopes into particulate matter (which is related but not identical to
primary production, e.g., Dring and Jewson [1982]). Particular care has
to be taken when different measurement methods that attempt – and
often claim – to measure the same quantity (e.g., chlorophyll concentration, primary production) in fact measure different things . In contrast to
more straightforward measurements of concentrations of standing stocks
of organic or inorganic matter, direct observations of processes or rates
(e.g., growth, grazing, sinking, exudation, mortality) are usually difficult
to carry out without perturbing the system under investigation and, accordingly, are very limited in number and often have large random and
systematic errors.
Available observations are also often biased towards the spring and
summer season, with generally very few ship-based winter or autumn
observations, particularly in mid and high latitudes. The same sampling
bias holds for measurements of physical variables, but may be more
critical for ecological properties for which the amplitude of the local
seasonal cycle can be as large as the global range of the respective annual
mean property.
Valuable observational information can also be taken from laboratory
studies. Investigations using cultured species may, for example, help to
reveal physiological information on the impact of environmental conditions like nutrient concentrations, light intensity, turbulence levels, or
temperature on growth rates. A caveat to be kept in mind is that those
species that have been cultured so far are not necessarily representative
of the open-ocean plankton community. Considering that the number
of generations separating our domestic plants and animals from their
wild ancestors is reached by phytoplankton in only a few years, culture
species may also be affected by selection and mutation.
It appears that information on the loss side (e.g., grazing, mortality)
is more difficult to obtain than on the production side (growth). There is
a (perhaps related?) tendency of marine ecosystem modellers to increase
model complexity preferentially on the production side rather than on