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Abstract
Three hypotheses to discern the strong positive association between juvenile fish
and mangrove habitat were tested with field and laboratory experiments. Artificial
mangrove structure in the field attracted slightly more juvenile fish than areas without
structure. Artificial structure left to accumulate fouling algae attracted four-times
the total number of juvenile fish than areas without structure or areas with clean
structure. Community composition of fish attracted to structure with fouling algae
was different when compared with areas with no structure or clean structure; five
species were attracted by structure with fouling algae whilst two species were associated
with structure regardless of fouling algae. Algae were linked to increased food availability
and it is suggested that this is an important selection criteria for some species.
Other species were apparently attracted to structure for different reasons, and provision
of shelter appears to be important. Predation pressure influenced habitat choice in
small juvenile fish in laboratory experiments. In the absence of predators, small
juveniles of four out of five species avoided shelter but when predators were introduced
all species actively sought shelter. Large fish were apparently less vulnerable to
predators and did not seek shelter when predators were added to their tank. Feeding
rate was increased in the mangrove habitat for small and medium-sized fish compared
with seagrass beds and mudflats indicating increased food availability or foraging
efficiency within this habitat. Larger fish fed more effectively on the mudflats with
an increased feeding rate in this habitat compared with adjacent habitats. The most
important aspect of the mangrove habitat for small juvenile fish is the complex structure
that provides maximum food availability and minimises the incidence of predation.
As fish grow a shift in habitat from mangroves to mudflat is a response to changes
in diet, foraging efficiency and vulnerability to predators.