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Fishery Bulletin 109(3) 
Figure 1 
Location of study area (Praia dos Castelhanos) off the coast of Espirito Santo, Brazil. The spatial distribution of the 
rockpools on the reef flat is shown in the map on the right. 
tion from the sea; e.g., Gibson, 1972), the abundance 
and distribution of fishes on a flat reef are expected 
to be affected by less complex interactions between 
environmental and ecological variables and that there 
would be a lower disparity in fish community structure 
among pools. Such natural simplification of environ- 
mental complexity could also shed some light on how 
the current tendency of habitat homogenization driven 
by modern anthropogenic activities (Thompson et al., 
2002) may affect the divergence of fish communities 
(Villeger et al., 2010). 
Materials and methods 
Study area 
The study was conducted at Praia dos Castelhanos 
(20°49'S, 40°36'W), in the state of Espirito Santo in 
southeastern Brazil (Fig. 1). The mean water level rela- 
tive to the reference datum of zero-level of Brazilian 
marine charts is 0.82 m. The reef is a complex of carbon- 
ate material composed of encrusting coralline algae and 
stony coral skeletons with sparse lateritic (ferruginous) 
rocks and is essentially flat. During the ebb tide a large 
number of pools become isolated. Pool substrates often 
consist of sand and gravel and pool walls are charac- 
teristically irregular, almost vertical, and are covered 
by algal turf, soft macro-algae, crustose coralline algae, 
encrusting soft-coral, and a few stony corals. 
Morphological characterizations of tidepools 
Six isolated tidepools (without connectivity to the sea 
or other pools during the ebb tide) were selected: two 
located near the sand beach (pools 1 and 2), two in an 
intermediary position (pools 3 and 4), and two closer to 
the water edge (pools 5 and 6; Fig. 1). The mean time 
of exposure to air was about three hours per day. The 
height of the reef flat was located at about 6 cm (pool 2), 
11 cm (pool 3), 10 cm (pool 4), 20 cm (pool 5), and 13 cm 
(pool 6), below that near pool 1. The pools were charac- 
terized on a single occasion relative to their surface area, 
depth, and bottom rugosity. Surface area was estimated 
by using a 3x 1-m grid of 10 x 10-cm squares. Depth was 
measured with a ruler at randomly chosen intersections 
of the grid. Volume was derived from surface area and 
mean depth. Rugosity was measured by the chain-and- 
tape technique (Wilding et al., 2010). 
Sampling 
Sampling was conducted every three months between 
August 2005 and June 2007 (n = 8) during the mornings 
of two consecutive days. During the first day, water 
temperature and salinity were measured with a mercury 
thermometer (0.5°C precision) and a refractometer (1 psu 
precision). Measurements were taken at three separate 
times in each pool: immediately after isolation of the 
pool from the sea (“beginning”); when the water level fell 
below reef level (“middle”); and at the time correspond- 
ing to the lowest level of the tide and immediately before 
the pool was connected to the rising sea (“end”). Algal 
cover and bottom composition were visually estimated 
on a scale ranging between 0 and 100 (Bennett and 
Griffiths, 1984). Algal cover was estimated only for pool 
walls and consolidated bottom areas and refers exclu- 
sively to macroalgae. Substrate types were categorized 
as sand (less than 1 mm diameter), gravel, or rock (diam- 
eter greater than 50 mm), and the sum of all categories 
