ecological effects of marine protected areas empafish project ...

EMPAFISH Booklet no. 1 Ecological effects of Atlanto-Mediterranean MPAs in the EU
remote sensing, marine circulation modelling, tagging, including external
(natural or artificial), chemical (trace elements or stable isotopes in otholiths)
or genetic (Pérez Ruzafa et al. 2006) methods, and Geographical Information
Systems (GIS).
1.3 The importance of habitat structure
The habitat of an organism can be intuitively defined as the place where it
lives and which provides food, shelter and living space to the organism
(Chabanet et al. 2005). More formally, a habitat can be defined as a spatiallybounded
area, with a subset of physical and biotic conditions, within which the
density of interacting individuals, and at least one of the parameters of
population growth, is different than in adjacent subsets (Morris 2003). Habitat
must be defined in relation to the species and populations of interest, and in a
manner that reflects underlying processes operating at appropriate spatial and
temporal scales.
Potential habitats for a species (at a given spatial scale) vary with respect to
both quality and quantity of available resources (food, refuge, etc.), predation
risk, or resource requirements by organisms from the same or different
species leading to competitive interactions. Therefore, the question to address
is: what habitat features are relevant for these organisms and what are the
ecological functions provided by these features, which are to be measured
and, ultimately, protected (García Charton et al. 2000). The concept ‘habitat’
encompasses not only the substratum (rock, sand, etc.), but also habitat
‘formers’ (e.g. coral reefs, seagrass meadows, gorgonians, vermetid reefs,
maërl beds, or macroalgae); moreover, habitat ‘determiners’, i.e. organisms
able to modify the physical structure of habitat by their individual activity
(e.g. by grazing, scratching, scavenging), should be considerded.
In studies of habitat structure, the distinction is often made between habitat
complexity – the absolute quantity of each element type, which represents
the degree of variation in the orientation of the three-dimensional surface per
unit of seabed area (vertical component), and heterogeneity – variation
attributable to the relative abundance of the different structural elements of
habitat (horizontal component), at each spatial scale of interest (García
Charton & Pérez Ruzafa 2001; García Charton et al. 2004).
Marine habitats can be classified according to the ecological function they
provide (e.g. habitat for spawning, recruitment, nursery, etc.). Futhermore, a
particular organism can occupy different types of habitat during the day (e.g.
for resting and feeding), and particularly at different stages of their life cycle.
On the other hand, habitats can be described at different spatial scales of
observation, which will also depend on the organism of interest (García
Charton et al. 2000; Chabanet et al. 2005).
Marine habitats are being altered by physical disturbances of human origin
(coastal works, dredging, dumping, spilling, trampling and other tourist
impacts, trawl fishing, anchoring, etc.), which generate a variety of negative
effects (siltation, occupation of the coastal fringe, destruction of erect
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