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Fishery Bulletin 109(3) 
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CIS 
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Rockpool 
Rockpool 
Figure 4 
Mean (±1 standard error) of (A) number of individuals, (B) number of taxa, (C) 
Shannon diversity, (D) Pielou’s evenness, (E) total length, and (F) total wet weight 
of all fish. The results of the Friedman (A-D) or Kruskal-Wallis (E-F) tests for 
differences among pools are inserted in the graphs. n = 8; NS=not significant. 
the number of interspecific competitors and preda- 
tors also is regulated by physiologic stress. Moreover, 
equivalent-size pools at the reef’s higher fringe hold 
more individuals than those at lower levels because 
of the overwhelming numerical dominance of thermal 
and saline stress-adapted species. In that case, low 
substrate heterogeneity and environmental complexity, 
held as important factors for community structuring, 
do not necessarily translate into low fish abundance as 
commonly thought (Griffiths et al., 2006). Immediately 
below this upper zone, the middle zone is much less 
affected by external influences (e.g., groundwater seep- 
age) and consequently even small pools present less ex- 
treme and less stressful conditions. Thus, species with 
little or no adaptation to intertidal life (opportunistic 
and transient fish) are more common in this zone and 
differences in fish community structure among pools 
would be directly related to pool morphometry because 
it will determine the number of available niches. The 
last zone (unstudied) is close to the sea, and a high 
number of pools, if not all, are extensively connected 
to it through a pipe and cave system; at low tide, water 
circulation remains intense in these pools because it is 
driven by waves on the forereef from a meter to tens 
of meters away. Occurring in these pools are juveniles 
and small-size adults of infralittoral species not found 
elsewhere on the reef flat. 
According to Mahon and Mahon (1994), large tidepools 
have higher numbers of individuals, species richness, 
and biomass because of higher availability of resources 
and niches. Such a pattern was clearly distinguishable 
at Praia dos Castelhanos and presented some interest- 
ing twists that shed some light on the mechanisms re- 
sponsible for pool-specific community structure. Instead 
of being strongly structured by the physicochemical 
setting, middle zone communities were finely tuned by 
minor differences in pool characteristics and ecological 
effects such as competition, predation, and territorial- 
ism. In particular, the abundance of territorial species 
is related to their need to establish territory and, be- 
cause larger pools provide more space, they also offer 
an opportunity for a larger number of territories. Nev- 
ertheless, for territorial herbivores (such as S. fuscus, 
pattern A) the ultimate factor is sufficient consolidated 
substrate in sunlit areas for these species to maintain 
their “gardens”. In a similar way, roving herbivores such 
as A. bahianus (pattern A) are particularly abundant in 
large pools filled with rocks because schooling behavior 
(schools usually contain 5-20 individuals) and her- 
bivory create a demand for ample space and adequate 
substrate (Lawson et al., 1999). Finally, a number of 
discrete and solitary species, such as the roving her- 
bivore S. axillare (pattern C) and the carnivores L. 
nuchipinnis (pattern D) and M. delalandei (pattern C), 
