4.1 Population Dynamics and Physical Variability:
Zooplankton Working Group
``To understand the effects of physical processes in predator-prey interactions and population dynamics of zooplankton, and their relation to ocean ecosystems in the context of the global climate system and anthropogenic changes.''
The aims for the Southern Ocean as decided at the La Jolla GLOBEC workshop (U.S. GLOBEC Report No. 5) were re-examined and agreed to be:
These questions do not specifically address the subject of global change. The subject is nevertheless important and is referred to specifically in the overall GLOBEC aim, but it was felt that this aspect was best studied through remote sensing and suitable monitoring studies.
It was recognised that to gain a full understanding of the population dynamics of zooplankton, it is absolutely critical to obtain winter data. This requires ship-board work in winter, but shore bases can make an important input through year-round studies of suitable coastal zooplankton.
The role of physics in influencing biology was deemed to include regional circulation, mesoscale structures and dynamics and the role of sea--ice. Although it is desirable to tackle complex biological questions in an area where the physics is simple, it was recognised that in many areas of the Southern Ocean, the physics is insufficiently understood to decide whether the area is simple or complex.
Work on spawning, larval survival and recruitment to the adult population is at the heart of population dynamics. To resolve these questions will require a close collaboration between modelling, experimental and observational work.
Tackling these questions will require a range of techniques and approaches,
including time-series surveys, process studies at sea and experimental studies
4.1.3 Key Species
Since it is not feasible to study all members of the zooplankton community
at once, it is necessary to select some key species on which to focus
research. These should represent a diversity of life-history strategies
and also include species of direct importance to higher predators. The key
species chosen were:
We reviewed the nature and content of potential studies of birds, mammals
and fish in relation to the aims of SO GLOBEC. (Fish and squid were
considered in general terms but no specialists were present. Subsequent
comments from Dr. I. Everson and Dr. P. Rodhouse are incorporated but
further elaboration of research approaches and priorities for these groups
are required.) We took particular account of: a) the increasing focus of the
overall study onto species and processes intimately associated with the
pack-ice zone; b) the need to concentrate on Antarctic krill because of its
unique role amongst zooplankton as a key prey for a wide range of predator
species; c) the need to ensure that the various predator studies are
conducted at spatial and temporal scales congruent with the research into
the physical and biological environment; d) the requirement that many of the
key process studies must be conducted simultaneously on predators and prey;
e) the requirement that both process and survey studies need to be
underpinned by the continuation and enhancement of existing studies
monitoring trends and variation in population parameters and in aspects of
foraging and reproductive performance of predators; f) the need to conduct
SO GLOBEC studies over several years, at all seasons of the year and
especially to include work in the sea-ice zone in winter.
4.2.1 Target Species
The target species were defined in terms of: degree of association
with ice-cover/ice-edge; degree of dependence on krill; availability of data
from existing and historical studies; and feasibility of study.
The questions below were formulated to try to focus attention on some of these issues and to aid the development of appropriate field and laboratory research, linked to relevant numerical modelling initiatives.
Particularly for this reason the development of outline research programme elements to address each of the key questions will require substantial work by appropriate krill and top predator scientists working together.
Information on the status of current research activities in the
fields below are presented in Table 4.2.1. This is a draft version and the
group recommended that WG-CEMP, the SCAR Group of Specialists on Seals and
the SCAR Bird Biology Subcommittee be asked to review and amend them as soon
126.96.36.199 Definable Populations
We viewed this as comprising two elements.
1. Definition of Unit Populations
This requires studies, using newly developed molecular techniques, of genetic variation within and between breeding units of target species. Definition of population units for crabeater seals and fish are particularly important.
2. Surveys of Population Distribution and Abundance
Some target species, especially seabirds, can be surveyed, at
least locally, by land-based surveys from shore stations. There are quite
extensive existing studies of this kind. For other species, ship, aircraft
and satellite based work will be essential. Remotely-operated vehicles,
especially airborne platforms, could provide invaluable assistance
for studies of seals (and possibly seabirds) also.
188.8.131.52 Population Dynamics
For seabirds and fur seals, population age structure, fecundity
rates, productivity and survival rates (both juvenile and adult) are
studied basically by annual capture-mark-recapture studies of individually
identified animals. Offspring production, in relation to breeding
population size, is studied widely throughout the region but there are many
fewer detailed demographic studies of target species and even fewer that
have annual data over more than 10 years.
For ice breeding seals, age structure and vital rates are determined by examination of teeth and reproductive tracts taken from samples of the population. For commercial fish, regular surveys to estimate stock size, population structure, reproductive status and diet are undertaken in support of CCAMLR. Studies on squid are restricted to determining distribution and trophic relationships. In general for fish and squid, age structure and vital rates are determined by examination of otoliths/statoliths and maturity status of the reproductive system taken from samples of the population.
Long-term marking of individuals is not as straightforward in most
top predators as it is for flying birds. The use of passive induction
transponders offers very significant advantages over flipper tags for
penguins but further technological development is required, particularly of
recognition systems to detect tagged individuals, to make maximum effective
use of this new technology.
184.108.40.206 Processes and Mechanisms
220.127.116.11.1 Foraging Ecology
This comprises studies of:
1. Diet composition--including seasonal, interannual and geographical variations in the nature of the prey, including their size, sex and age, where feasible. Diet research is chiefly based on analysis of stomach (and sometimes faecal) samples (increasingly involving lavage methods for seabirds and seals). Serological techniques have provided important confirmation of visual diet observations in squid. Determination of age, size and sex of prey relies extensively on relationships between structures relatively resistant to digestion (e.g. otoliths, statoliths, beaks, mandibles, eyeballs, carapaces) and whole animals. Better, and standardised, relationships are needed for many taxa. Diet studies other than during the summer months are rare and need to be a particular focus of future work.
2. Foraging habitat and area--the physical structure and physical and biological characteristics of the location selected by top predators for feeding activities and how these vary at temporal scales ranging from diel to annual. Once almost entirely dependent either on direct visual observations (seabirds, seals) or net-haul samples with concurrent oceanographic data (fish, squid), the use of satellite telemetry is nowadays revolutionising data acquisition in this field, especially for seabirds and seals. Acquisition of congruent data on the nature of the ice and water habitats is essential and, using conventional methods, more difficult for seabirds and seals than for fish and squid.
3. Foraging behaviour--this comprises all aspects of a) how predators catch
prey, including defining the functional morphology of feeding structures
(e.g. squid), the methods used, the conditions and circumstances involved
(e.g. in terms of the physical (including optical) properties of their
environment); b) when predators catch prey (time of day, etc.); c) how often
and how much prey is caught. For all except flighted seabirds, relevant
quantitative data have only been acquired with the very recent development
of archival and satellite-linked instruments on and inside free ranging
animals. A range of sensors recording continuously or intermittently data
on pressure (= depth), temperature (external and internal), velocity, and
light levels, (and often linked to location and physiological data) are
permitting unique insights into foraging behaviours, patterns and
performance. Requirements for further developing this type of research
include smaller and better instruments (i.e. more efficient with respect to
power utilisation), better data compression and storage, more accurate
sensors to record existing variables (e.g. to collect data on ambient
temperature and conductivity in order to determine water body
characteristics) and especially better data transfer to satellite. The
complementary data on prey distribution and environmental characteristics
need to be collected on equivalently fine scales. Laboratory research on
sensory abilities of predators is also required.
18.104.22.168.2 Energetics and Physiology
Many of the changes in the relationship between top predators and
their environment are ultimately expressed in terms of changes in energy
expenditure and often these are reflected in changes in the physiological
condition of the individuals themselves and/or their offspring. Measurement
of many activity-specific energy costs of air-breathing free-living animals
can be achieved using isotopic techniques. These techniques require
recapture of animals; they integrate the cost of activities between consecutive
sampling periods and can only be used over a relatively short period.
Recent developments in the use of heart-rate as an index of energy
expenditure are very promising. However this technique generates very large
quantities of data (requiring extreme compression of data for storage and/or
transmission) and needs accurate calibration studies (involving use of
respirometric and other techniques on live animals in flumes, wind tunnels,
For seabirds and seals the most widely used measures of condition are still those of mass, or size-corrected mass. Use of electronic weighing platforms is greatly enhancing: a) the range and quality of such data; b) the ability to make regular records from individuals with minimum disturbance; c) the feasibility of estimating body energy stores/reserves; and d) linking such data to simultaneous studies of reproductive performance and survival of both adults and/or offspring.
Sampling populations via collected samples offers a range of additional
physiological indices and condition (e.g. blubber thickness, fat and protein
reserves, chemical composition, nucleic acid ratios, gonadosomatic and
hepatosomatic indices (fish), etc.). Almost none of these techniques have
been used successfully on a routine basis on animals captured and released
alive. Considerable development, both in laboratory and field, in
acquisition and interpretation of data using ultrasound, biological
impedance and blood chemistry techniques will be required before these
techniques can have widespread use.
Various aspects of growth reflect different aspects of interactions between
predators and their environment. Growth (in mass and/or morphometrics) of
dependent offspring reflects parental performance over the breeding season.
Growth rates of juveniles and adults (chiefly accessible via annual or daily
growth layers revealed by analysis of sections of teeth otoliths and
statoliths) integrate a range of interactions over daily to annual time
4.2.4 Sampling and Observation Systems
A full definition of the sampling and observation systems required
to address the predator-prey interaction element of SO GLOBEC will need to
await the definition of the research programmes required to address the key
questions. However, it may be helpful at this stage to summarise some
aspects of likely sampling requirements and to note those methods and
sampling systems that are being, or will need to be, developed in order to
have effective field programmes. Table 4.2.2 summarises some relevant details
and highlights several key requirements in the field of development of new
It was recognised in plenary discussion that a major difficulty was posed by the requirement to study different organisms on a single cruise. A sampling protocol designed solely around, for example, the population dynamics of a fast-growing copepod would not provide any meaningful data on, again for example, adult Euphausia superba or predatory behaviour by Cape Petrels, Daption capense.
The detailed planning of cruises would need to be undertaken by a separate implementation workshop. Nevertheless the major types of study could be clearly identified. These were:
This type of cruise was seen as essential to tackle the following questions:
In each matrix the abbreviations representing types of study are:
4.4 Historical Data and Data Management Working
The recommendations for modelling studies that arose from the U.S. GLOBEC
Southern Ocean Workshop that was held in 1991 focused on the need for
modelling prior to a field programme, the need for sea-ice models, and the
need for models of aggregation behavior. Our modelling group endorsed these
recommendations and took the next step in making more specific
recommendations for a Southern Ocean modelling programme. These are discussed
in the following sections.
4.5.2 Modelling Issues
The working group recognised the need for general modelling efforts that
will result in the development of circulation, biological and
physical-biological models. These models should address important issues
that are of general interest to a Southern Ocean modelling programme,
including issues of how Southern Ocean models could fit into global models,
the use of data assimilation techniques for biological data, and the matching
of space and time scales between circulation and biological models. However,
the working group focused the majority of its discussion on the unique
characteristics of the Antarctic that must be included in models.
Circulation models of the Southern Ocean will be affected by inclusion of sea-ice processes, mixed layer dynamics and buoyancy-driven flows. In particular, models of sea-ice processes were considered to be critically important since many of the components of the Antarctic marine food web depend on sea-ice during all or part of their life history.
Two unique aspects of the Antarctic ecosystem which will influence
biological modelling studies are the aggregation (swarming) behavior of
Antarctic krill (Euphausia superba) and the importance of top
predators, such as penguins and seals. The working group felt that the
understanding and modelling of krill swarming behavior was critical to the
understanding of krill population dynamics as well as understanding the
population dynamics of the top predators. The working group also discussed
the need for resource modelling studies that could be used to determine how
krill is allocated among its many predators.
4.5.3 Conceptual Model
The GLOBEC programme endorses the development of modelling studies prior
to implementation of field programmes. The working group felt that efforts
in this regard could be helped by the existence of a conceptual model
that could be used as a framework for the Southern Ocean programme and
around which Southern Ocean field programmes could be developed. This
conceputal model should consist of modules that describe the physical
environment, food resources and top predator effects on a target species,
such as Antarctic krill. Other target species, such as copepods, can be used
in place of krill.
Within each module of the conceptual model are submodules that consider specific processes, for example:
circulation model (including three-dimensional flow fields and hydrographic structure), sea-ice model (including dynamic and thermodynamic processes), mixed layer model
bio-optical models for pelagic phytoplankton production and sea-ice algal production
heterotrophic production models, including pelagic and sea-ice components
energy requirements to support steady state populations
foraging behavior, impact on krill processes
swarming--mechanisms of formation and maintenance, spatial, and temporal variability
Ocean currents from large-scale dynamic topography, and from instrumented drifters
Quantification of ice-melt fresh water production
However, for some of these satellites, there is a significant delay in data availability.
Global scale ice cover-
DMSP (SSMI) passive microwave
resolution 30 km, daily maps of globe
ERS-1 SAR Ice coverage
5 degree coverage (100 km) every 3 days (planned coverage)
Cloud independent, resolution 30 m.
AVHRR ice cover and sea surface temperature variations and current movements can be obtained from time-series analysis of these images.
Interference by cloud coverage
1 km temperature and sea-ice resolution, at 1500 km coverage
Possibility of sensing aggregations of birds and seals?
Landsat 6 visible image of sea-ice cover
(rookeries?), etc. at 35 m resolution every 15 days, 800 km coverage. Expensive
SPOT visible-15 m every 15 days, swath width 800 km
MOS1B Japanese system launched, but data availability unknown
SeaWiFS-April 1994, 8 channels likely, data availability-3 days after satellite pass
4 km resolution available with receiver anywhere in world.
1 km resolution available only when receiver is in quadrant of interest
Need to calibrate pigment concentrations for Southern Ocean. GLOBEC could provide major contribution here.
ADEOS-High resolution OCS with high resolution data acquisition accessible anywhere in the world. Has memory capability and 12 channels.
There is a significant potential for the application of small remotely
piloted, or programmed aircraft to carry sensors or cameras over
specific areas of interest. These aircraft have been used by the military
for pilotless reconnaissance. These could be used for mammal and bird
population surveys, determination of fine scale oceanographic features, and
4.6.3 Problems That Need Attention
Satellite data is often difficult to acquire (Landsat, SPOT) or can only be
acquired in near real time if the investigator has access to a dedicated
data acquisition and processing facility. In addition, some systems require
local receivers to acquire high resolution data of that area. A major
contribution of GLOBEC.INT would be to develop a site or sites in the core
Southern Ocean study sites which have dedicated satellite data acquisition
and processing capabilities that could supply researchers with satellite
images and data in real or near real time.
Currently studies of the behavior of mammal and bird behavior while at sea
is limited by the data bandwidth of the ARGOS satellite system. The
potential exists to acquire data on the diving behavior (swim velocity,
depth and feeding rate) that can be correlated with physical features
(location, depth, salinity, and temperature). This limitation is based on
the limited time available for data uplinks to ARGOS and the small bandwidth
available (8 bytes).
4.6.4 Local Level Data and Sample Acquisition
Same as other GLOBEC.INT programmes except:
Develop the capability to use newly developed sampling schemes in ice.
Apply genetic techniques to Southern Ocean systems. State-of-the art approaches have yet to be implemented for population genetic studies with higher trophic levels.
Need further refinement and/or development of PIT tags (transponder identification tags) that can incorporate greater ranges and can be coupled with automatic weighing and counting devices.
Development of data loggers with sensors capable of collecting data (pressure, temperature, salinity) valuable to oceanographers.
Develop data loggers and/or satellite tags that can measure:
Use R.O.V.'s to observe behavior of predator-prey interactions.
Develop capability to place cameras on predators to observe their behavior in relation to prey.
Develop acoustic and/or optical sensing methods to correlate prey abundance with predator behavior.
Develop ability to telemeter behavioral data on top predators by acoustic transmission to moorings coupled to ARGOS satellites or directly to ship. (This includes fish, mammals, and birds.)