Mapping the extent of the biotope
Sampling for species diversity and population abundance
Monitoring rates of growth and production of kelp plants
The UK Marine SACs Project is conducting and publishing the proceedings
of a series of workshops devoted to the development of monitoring and management
programmes for marine SACs (Worsfold & Dyer, 1997; Hiscock, 1998a). Methods that
should be included as part of a monitoring programme would include the following.
Mapping the extent of the biotope
At Newcastle University, the BioMar project (Davies et al.,
1997) has developed a survey protocol for mapping the sea floor using acoustic techniques,
validated by biological sampling, with the data stored and analysed using geographic
information systems (GIS). A RoxAnn processor was used for acoustic mapping.
Acoustic data have no biological meaning unless they can be related to biological
assemblages, determined from direct observations or samples of the seabed at predetermined
point locations (see Worsfold et al., 1997 for further discussion).
Based on the video samples, grab samples, diver surveys and previous
detailed records of biological surveys in a Scottish sea-loch (Howson et al.,
1994), a map of the sea-bed showing the predicted distribution of a total of 23
biotopes was constructed. Acoustic mapping using a RoxAnn system provided data on the
physical nature of the sea-bed (depth, smooth/rough, soft/hard), and biological
information was then added to the acoustic data. It was not found practicable to relate
each biologically based biotope classification to a particular acoustic pattern. Instead,
the biotopes determined from a biological approach had to be grouped into 15 much broader
categories in which the species component was generally lost and in which there was no
possibility of indicating a gradual change from one life form to another.
The recent deployment of the RoxAnn method for a few days in
Strangford Lough confirmed its value in mapping the distribution and extent of beds
occupied by different benthic animals (M. Service, pers. comm.) and it is possible that
the RoxAnn method could be further developed to allow the identification of areas
where kelp forests are present. Without subsequent checking by more labour-intensive (and
expensive) methods, the method would not differentiate among different kelp species, and
neither could it provide useful information on density, growth rates or overall health of
the biotope, but it may offer the most cost-effective way of mapping the extent of the
kelp forest in an SAC.
It has often been suggested that subtidal kelp beds could be identified
from aerial photographs. This method could then be used to make a very broad-scale, rapid
assessment of the extent of kelp forests in inshore areas. Attempts to put this idea into
practice in Strangford Lough, Northern Ireland (A. Portig, pers. comm.), have largely
foundered on the virtual impossibility of getting sunny, calm conditions and a low spring
tide to coincide with the availability of an aircraft. The images are also difficult to
interpret quantitatively if the orientation of the photograph departs significantly from
the vertical. In practice, therefore, and especially given the prevailing weather of the
British Isles, it seems that this approach is unlikely to yield detailed, quantitative
information, although it could be used to provide a broad over-view of inaccessible areas
Sampling for species diversity and population
The methods being developed for monitoring marine SACs (Hiscock, 1998a)
which are relevant to kelp biotopes are summarised below but, as with all benthic
habitats, the patchy distribution of flora and fauna creates difficulties for objective
sampling. The main questions
- what is the minimum sample area?
- should samples be distributed randomly or systematically?
- how many samples are needed in order to obtain an adequate representation of the species
diversity and biomass of the site?
Hiscock(1998a) provides a discussion of all of these aspects, with
particular reference to marine habitats, and also covers the additional question of when
is the most appropriate or efficient season to sample a particular type of habitat.
Much of the early work on the extent and biomass of kelp beds in
Scotland and Norway was based on samples obtained with a spring grab lowered from a boat
(see Chapter III). The major disadvantages of this technique are that the surface area
sampled is uncertain, and the grab leaves an unknown (and probably variable) proportion of
the kelp population behind. Nevertheless, several of the ecological relationships
established by this technique have been confirmed in subsequent work by divers, and it may
appear to be a cost-effective way of monitoring kelp plants in relatively dense forests.
However, the limitations mentioned above are so serious as to rule it out for detailed,
quantitative work on the kelps, and the technique also fails to provide useful data on any
of the associated species in the biotope.
In situ surveillance using abundance scales and check lists at
exact sites (ACE surveys)
Quadrats of known size at an exactly located site are surveyed by
divers and the occurrence and abundance of all species on a check list are recorded. This
technique has been developed during the workshops preparing methods for the marine SACs
project (Worsfold & Dyer, 1997), and is described in detail by Hiscock (1998b). Its
efficiency in monitoring sublittoral biotopes has yet to be tested, but it is probably the
only technique available for the quantitative recording and monitoring the species
associated with kelp biotopes on a broad scale. The development of this technique with
specific reference to identifying keystone species in kelp biotopes would make a suitable
topic for a CASE/CAST research studentship.
Quantitative surveillance using photographs
Diver-operated cameras are used to record fixed quadrats at suitable
time intervals, and the percentage cover of the most conspicuous species is subsequently
determined using a grid of point quadrats over the enlarged or projected photographs. The
application of this technique to sublittoral rock biotopes in marine SACs is described in
detail by Hiscock and Bullimore (1998). In kelp biotopes, it would only be practicable for
monitoring the more obvious flora and sedentary fauna of the substratum below a kelp
canopy. The cover of the kelp plants, themselves, could not be determined using this
technique because of their size and mobility in water currents.
Monitoring rates of growth and production of kelp
Measuring the growth rates of individual kelp plants by the
"punched-hole technique (i.e. following the movement of punched holes away from the
base of the blade) is an elegant method of monitoring the performance of plants in situ,
and management agencies would be well advised to make use of it when they are carrying out
underwater surveys. A random sample of 20-25 plants in a representative area of kelp
forest or parkland should be marked by tagging the lower part of the stipe or the
holdfast. A hole (3-5 mm diameter) should then be punched through each blade at a measured
distance above the blade-stipe boundary. At intervals of 2-3 months during the spring and
summer (depending on the growth rates of the plants) and less frequently at other times,
the sites should be re-visited and the distance from the hole to the blade-stipe boundary
re-measured. Once the hole is half-way along the blade, a new hole should be punched near
the base. Using this technique, the growth rates of plants at different depths, or at
different sites, within an SAC can be compared (yielding valuable basic information), and
the effects of environmental changes (e.g. eutrophication, pollution, temperature or
turbidity changes) on growth rate can be quantitatively established.
The productivity of kelp plants can now be measured in the field using
underwater fluorometers ("Diving PAM"; Beer et al., 1998) or submersible
recording oxygen electrodes (Birkett et al., in prep.). Such measurements may
provide a more rapid indicator of environmental change, but the need for technically
elaborate and expensive equipment restricts the number of plants that can be examined.
Nevertheless, academic work is continuing with the aim of modelling kelp productivity from
continuos measurements of surface irradiance, combined with data on light penetration
through the water, and such models may soon require in situ growth data for
validation. Once this stage is reached, a broad picture of kelp performance may be
obtainable from physical measurements made from the surface, verified by spot checks
during diving surveys.