Habitat structure is known to influence the abundance of fishes on temperate reefs.
Biotic interactions play a major role in determining the distribution and abundance of
species. The significance of these forces in affecting the abundance of fishes may
hinge on the presence of organisms that either create or alter habitat. On temperate
reefs, for example, macroalgae are considered autogenic ecosystem engineers because
they control resource availability to other species through their physical structure and
provide much of the structure used by fish.
On both coral and temperate reefs, small cryptic reef fishes may comprise up to half
of the fish numbers and constitute a diverse community containing many specialized
species. Small cryptic fishes (<100 mm total length) may be responsible for the
passage of 57% of the energy flow and constitute ca. 35% of the overall reef fish
biomass on coral reefs. These benthic fish exploit restricted habitats where food and
shelter are obtained in, or in relation to, conditions of substrate complexity and/or
restricted living space. A range of mechanisms has been proposed to account for the
diversity and the abundance of small fishes: (1) lifehistory strategies that promote
short generation times, (2) habitat associations and behaviour that reduce predation
and (3) resource partitioning that allows small species to coexist with larger
competitors. Despite their abundance and potential importance within reef systems,
little is known of the community ecology of cryptic fishes. Specifically on habitat
associations many theories suggested a not clear direction on this subject.
My research contributes to the development of marine fish ecology by addressing the
effects of habitat characteristics upon distribution of cryptobenthic fish assemblages.
My focus was on the important shallow, coastal ecosystems that often serve as
nursery habitat for many fish and where different type of habitat is likely to both play
important roles in organism distribution and survival.
My research included three related studies: (1) identification of structuring forces on
cryptic fish assemblages, such as physical and biological forcing; (2) macroalgae as
potential tools for cryptic fish and identification of different habitat feature that could
explain cryptic fish assemblages distribution; (3) canopy formers loss: consequences
on cryptic fish and relationship with benthos modifications.
I found that: (1) cryptic fish assemblages differ between landward and seaward sides
of coastal breakwaters in Adriatic Sea. These differences are explained by 50% of the
habitat characteristics on two sides, mainly due to presence of the Codium fragile,
sand and oyster assemblages. Microhabitat structure influence cryptic fish
assemblages. (2) Different habitat support different cryptic fish assemblages. High
heterogeneity on benthic assemblages reflect different fish assemblages. Biogenic
components that explain different and diverse cryptic fish assemblages are: anemonia
bed, mussel bed, macroalgal stands and Cystoseira barbata, as canopy formers. (3)
Canopy forming loss is not relevant in structuring directly cryptic fish assemblages. A
removal of canopy forming algae did not affect the structure of cryptic fish
assemblages. Canopy formers algae on Conero cliff, does not seem to act as
structuring force, probably due to its regressive status.
In conclusion, cryptic fish have been shown to have species-specific associations with
habitat features relating to the biological and non biological components afforded by
fish. Canopy formers algae do not explain cryptic fish assemblages distribution and
the results of this study and information from the literature (both from the
Mediterranean Sea and elsewhere) show that there are no univocal responses of fish
assemblages. Further exanimations on an non regressive status of Cystoseira canopy
habitat are needed to define and evaluate the relationship between canopy formers and
fish on Mediterranean sea
