212
C. Hily and M. Bernard
matrix. Consequently, at the intertidalscape scale, when the number of overturned
boulders increases, the surface of green color increases (Fig. 13.6).
The hand-fishing activity increased considerably in France these last years and
many sites are disturbed each spring tide (almost each month). Most of the mobile
boulders are overturned and remain upside down at the end of the period of the spring
tide (four consecutive days in general). In order to assess the pressure of this disturbance (i.e. the overturning of boulders under the hand-fishing activity) at the boulder
field scale, we proposed an Intertidalscape Boulder Field Index (IBFI) (Bernard
2012). It is visual, SMART indicator (Simple, Measurable, Achievable, Realistic,
and Time limited) with a protocol calibrated to be operated by non specialists.
1. Definition of the index: In the low mediolittoral and emerged fringe of infralittoral of semi-sheltered and sheltered habitats, rocky substratum is covered by
erected brown and/or red macroalgae under which encrusting algae and fauna
can develop. Without hand-fishing, the intertidalscape of the boulder fields is
brown and locally dark red. The rate of green cover increases with the increasing
of the overturned mobile boulders number. However, those which were overturned few days ago are light colored (mixed white and pale yellow), due to the
fixed fauna. To elaborate such an index, we studied 20 boulder fields in Brittany
to obtain various situations on the largest gradient from 100 % brown/red cover
to 100 % green cover.
The aim is to link the relative cover of green color to a level of the hand-fishing
pressure. The observations showed that this surface must be related to the area
which corresponds to the total of boulders which can really be overturned by handfishermen. Actually, the Total Macroalgal Cover (TMC) is composed of algae
which grow (1) on the mobile boulders (MB) which can be overturned for shellfish
( = algae cover of mobile boulders MBca) and (2) on rocky substrata which are
not concerned by the overturning. Among these latter, four categories can occur:
small boulders not attractive for hand-fishermen, boulders which are deeply buried
in the sediment, boulders which are too big and cannot be overturned and rock.
We could gather these four types in a Fixed Boulder (FB) category (Fig. 13.6).
Because the FB are never overturned, their algae cover (FBca) remain brown/red.
The rate of Green Macroalgal cover (GMC) (including the rate of the white
boulders recently overturned) can be expressed relatively to TMC and the MBca.
If FBca is 0 %, the cover rate of green algae can reach 100 %. However it is a
very rare situation. Thus, the first step is to estimate MBca and FBca values in
one boulder field. These values are relatively stable in time, so after this first
step and for monitoring the hand-fishing pressure, the green macroalgal cover
(GMC) will be the only one variable measured. Our index is referred to the
MBca parameter (Fig. 13.6).
The IBF index is based on a discrete distribution of cover rates in 5 classes;
each class is described to facilitate the reading of the landscape (Table 13.1 and
Fig. 13.7).
2. Description of the biocenosis: to better understand the state of the habitat we
described the general feature of the biocenosis (fauna and flora) under these 5
situations (Table 13.1).
C. Hily and M. Bernard
matrix. Consequently, at the intertidalscape scale, when the number of overturned
boulders increases, the surface of green color increases (Fig. 13.6).
The hand-fishing activity increased considerably in France these last years and
many sites are disturbed each spring tide (almost each month). Most of the mobile
boulders are overturned and remain upside down at the end of the period of the spring
tide (four consecutive days in general). In order to assess the pressure of this disturbance (i.e. the overturning of boulders under the hand-fishing activity) at the boulder
field scale, we proposed an Intertidalscape Boulder Field Index (IBFI) (Bernard
2012). It is visual, SMART indicator (Simple, Measurable, Achievable, Realistic,
and Time limited) with a protocol calibrated to be operated by non specialists.
1. Definition of the index: In the low mediolittoral and emerged fringe of infralittoral of semi-sheltered and sheltered habitats, rocky substratum is covered by
erected brown and/or red macroalgae under which encrusting algae and fauna
can develop. Without hand-fishing, the intertidalscape of the boulder fields is
brown and locally dark red. The rate of green cover increases with the increasing
of the overturned mobile boulders number. However, those which were overturned few days ago are light colored (mixed white and pale yellow), due to the
fixed fauna. To elaborate such an index, we studied 20 boulder fields in Brittany
to obtain various situations on the largest gradient from 100 % brown/red cover
to 100 % green cover.
The aim is to link the relative cover of green color to a level of the hand-fishing
pressure. The observations showed that this surface must be related to the area
which corresponds to the total of boulders which can really be overturned by handfishermen. Actually, the Total Macroalgal Cover (TMC) is composed of algae
which grow (1) on the mobile boulders (MB) which can be overturned for shellfish
( = algae cover of mobile boulders MBca) and (2) on rocky substrata which are
not concerned by the overturning. Among these latter, four categories can occur:
small boulders not attractive for hand-fishermen, boulders which are deeply buried
in the sediment, boulders which are too big and cannot be overturned and rock.
We could gather these four types in a Fixed Boulder (FB) category (Fig. 13.6).
Because the FB are never overturned, their algae cover (FBca) remain brown/red.
The rate of Green Macroalgal cover (GMC) (including the rate of the white
boulders recently overturned) can be expressed relatively to TMC and the MBca.
If FBca is 0 %, the cover rate of green algae can reach 100 %. However it is a
very rare situation. Thus, the first step is to estimate MBca and FBca values in
one boulder field. These values are relatively stable in time, so after this first
step and for monitoring the hand-fishing pressure, the green macroalgal cover
(GMC) will be the only one variable measured. Our index is referred to the
MBca parameter (Fig. 13.6).
The IBF index is based on a discrete distribution of cover rates in 5 classes;
each class is described to facilitate the reading of the landscape (Table 13.1 and
Fig. 13.7).
2. Description of the biocenosis: to better understand the state of the habitat we
described the general feature of the biocenosis (fauna and flora) under these 5
situations (Table 13.1).