แปลบทความวิจัยboulders, presence of crevices, rock pools, depressions, etc. (McCoy
and Bell, 1991), using the chain link method (Beck, 1998). To this
end, we deployed a heavy iron chain and a tape multiple times
across each transect where the quadrat sampling was conducted
(see above). The chain links (length ¼ 2.5 cm) closely followed the
surface and the tape only touched the highest parts of the rocks.
Thus the ratio between the linear distances (tape) vs. the apparent
distance (chain) can be considered as a measure of the structural
complexity of the substratum (hereafter Complexity Index; Beck,
1998). As the AL sampling consisted of contiguous quadrats (see
above) we followed the same protocol for the chain-tape sampling.
We deployed a 1-m long chain and tape (linear distance) multiple
times along a contiguous path, i.e. the beginning of the chain (and
tape) was placed on the end point of the previous chain placement
(15e20 times for each transect), on the breakwater and natural
adjacent platforms along the same transects (totalling 30 to 40
samples for each habitat) where AL sampling was conducted (see
above). In this way, we obtained 30 to 40 measures for the
complexity index for each habitat. At one of the seven study localities
this sampling could only be partially completed (Vi~na del
Mar), given that the strong and persistent wave surge and slope of
the breakwaters at the sampling time (AugusteDecember 2015)
restricted the access to this site. Thus, we only include partial data
sets (10 measures of the Complexity Index) for this locality for
further spatial analyses (see below).
Given inherent differences between intertidal breakwaters (e.g.
made of granite boulders versus cement tetrapods see Fig. 2), we
first conducted a pilot study using three different chain link size;
2.5 cm, 4 cm, and 6 cm per link.We determined that a chain link of
2.5 cm was sufficient to characterize the spatial distribution of both
granite boulders and tetrapods at the study sites considered, and
consequently all results reported are based on this link size.