Monitoring and Surveillance Options
Introduction to Monitoring
Introduction to Methods
Intoduction to Monitoring
This chapter discusses the options available for monitoring and
surveillance of biogenic reefs, but does not make detailed recommendations for monitoring
programmes as these would need to be tailored carefully to the needs of the individual
SACs, and will be prepared by the relevant authorities. The information presented here
relates mainly to available methods.
There are two types of monitoring which need to be considered by SAC
managers: condition monitoring, which is synonymous with surveillance monitoring; and
compliance monitoring. These can be defined as follows:
Condition monitoring (surveillance monitoring): monitoring designed to
determine whether or not the feature is maintaining favourable condition
status (Burt, pers. comm.). Essentially this sort of monitoring must attempt to
detect unanticipated impacts, including those which may be wide ranging, subtle or which
only slowly become obvious (Hartnoll, in prep).
Compliance monitoring: monitoring designed to detect whether particular
activities or disturbances are or are not having negative impacts upon the feature (Burt,
In many instances the methods available for the two types of monitoring
are essentially the same, particularly where effects at the level of populations or
communities are being investigated (looking for changes in the extent of beds or in
population structure, for example). However, the area covered may vary greatly. It may,
for example, be possible to limit compliance monitoring for fishing impacts to a small
area of biogenic reef in the safe knowledge that fishing does not occur elsewhere, while
surveillance monitoring may have to be carried out over a much wider area.
In other cases compliance monitoring can be more focused than
surveillance monitoring, for example where levels of contaminants (such as heavy metals in
mussels) or physiological changes (such as imposex in gastropods caused by TBT
contamination) are being investigated.
Choosing what monitoring methods are most suitable for any given area
of SAC requires a more detailed level of knowledge of distribution (of both biotopes and
human activities) and other circumstances than can be entered into in this report.
However, a range of possible monitoring methods, some quite general and some more specific
to the five main biogenic reef species, is given here.
Introduction to Methods
Assessment of the reliability and practicalities of a variety of
monitoring methods which might be useful for monitoring in SACs is presently underway
(Hiscock, 1998a; Hiscock, 1998b). A report summarising two recent workshops on this
subject, including interesting field exercises investigating consistency of methods
between survey teams, together with a literature survey of methods, is also available
(Worsfold & Dyer, 1997).
Details of monitoring options are given for each biogenic reef species
in the subsequent sections (B-F). Since subtidal communities will be much more difficult
to monitor than intertidal ones, and are more likely to rely on modern technology, a brief
overview of some of the available methods is given here.
For many of the subtidal reefs, their distinctive topography and
texture renders it likely that modern acoustic monitoring methods such as RoxAnnÔ and sidescan sonar may be useful, and these are referred to
several times in this chapter. RoxAnnÔ interprets the signals
from an ordinary shipboard echosounder of the type routinely used for measuring depth, and
gives information on the hardness/softness and
roughness/smoothness of the bottom, which by calibration against known seabed
types can be used to rapidly collect information on seabed type over large areas (for
detailed technical information see Chivers et al., 1990). Information is obtained only
from the seabed directly below the boat. Sidescan sonar uses a dedicated sonar source
towed on a wire behind the boat, relatively near to the seabottom, which scans
out a signal to either side many times per second. By interpretation of the signal
bounced back from the seabed an image of the seabed, which is based upon both topography
and hardness/softness of the bottom, can be produced. This image can typically
cover an area of up to a few hundred metres on either side of the boat.
Worsfold & Dyer (1997) contains a useful overview of the use and
limitations of RoxAnnÔ bottom discrimination, (although for
more detailed assessment of the techniques application see Davies et al., 1997).
There was no detailed discussion of sidescan, although it was pointed out that no
references to its use in the mapping of biological features or biotopes had been found. In
fact, use of sidescan for mapping biological features has been successfully used where the
features are physically distinct and/or obvious, including for a number of biogenic reef
features, particularly Modiolus reef areas. Other features such as maerl beds in
Scottish sea lochs have also been mapped (Foster-Smith & Davies, in prep). Holt et al.
(unpublished) were able to map unusual reef structures formed by Modiolus off the
north end of the Isle of Man, as well as nearby Ophiothrix beds; Magorrian et al.
(1995) were able to map Modiolus reefs in Strangford Lough. Very large Modiolus
bioherms have been mapped in Canada using relatively long range sidescan (Wildish et al.,
in press). Subtidally, areas of semi-infaunal Mytilus in the Tay Estuary have
recently been mapped by sidescan (Silke Wewetzer, pers. comm.). Rees and co-workers had
considerable success in mapping Modiolus beds off the Lleyn Peninsula using
acoustic methods, particularly RoxAnnÔ .
Monitoring of the population structure of the reef forming species and
the associated flora and fauna in subtidal communities will be problematical. Options
include broadscale surveys using towed video or ROV, although the former might in some
cases cause physical damage, hand held diver video, fixed quadrat photography, or diver
surveys using Abundance scale Checklist at Exact locations (ACE surveys) or
transect/quadrat counts. Video surveys cover larger areas than fixed quadrat photography
or diver surveys but only limited conspicuous organisms can confidently be quantified. ACE
surveys and transect/quadrat surveys are expensive but more likely to detect change. All
of these methods would be limited to macrobiota. Monitoring of infauna and cryptic fauna
can only be carried out with destructive sampling techniques which are expensive to
process and, given the state of present knowledge of biogenic reef communities, should
take a lower priority for now.
Hartnoll (in prep) notes that likely improvements to methodology for
work in the sublittoral in the near future will be of great value for survey and
monitoring of circalittoral hard substrata, and similar arguments apply in respect of
sublittoral biogenic reefs. These improvements relate mainly to increased dive times due,
for example, to increasing use of nitrox gas mixtures and rebreathing apparatus, improved
location, communication, site marking and recording equipment for divers, and further
development and use of non diving technologies including ROV and automatic dataloggers.
Problems associated with determining acceptable
limits of change