186
P. Thiriet et al.
2011). A seascape has therefore two main features, its composition in term of patch
types (e.g. combined total percent cover per patch type) and its spatial configuration,
i.e. the spatial arrangement of all the patches, which may be synthesized using metrics
such as number, sizes and perimeters of patches, inter-patch distances, contiguity
(Wedding et al. 2011).
Patch typology intends to break down the seascape into ecologically meaningful
and workable sub-units for facilitating ecological studies of the whole. Hence, each
patch-type refers to a given set of environmental conditions, such as depth, type
of primary substrate, availability of resources (e.g. food and shelter), and so gives
insight on local ecological functioning. Therefore, patch types may be seen as benthic
habitats (Fraschetti et al. 2008), the term they are usually referred as.
Ecological functioning of the whole mosaic does not simply rely on the sum
of every habitat-specific ecological functioning. Patches interact together and some
specific proprieties may emerge by synergy (e.g. edge effect), depending on seascape
configuration (e.g. amount of ecotones) (Macreadie et al. 2010; Bostrom et al.
2011). Other environmental factors affect ecological processes (e.g. water temperature, salinity and oxygenation affect growth) and they may vary at a spatial
scale distinct from patch scale, usually at broader spatial scales (Ordines et al.
2011). Hence, multiple spatial scales have to be considered for a better understanding of the ecological processes that drive organisms’ distribution patterns within a
seascape.
12.2 From Macrophyte Assemblages to Seascape Configuration
Some benthic organisms greatly modify local 3D-architectural complexity. They
provide habitat to many other organisms and ultimately structure the whole benthic community through “habitat cascade” (Thomsen et al. 2010). Such species
are called biogenic habitat formers and include for instance corals, oysters, mangroves, seagrasses and some macroalgae (Bostrom et al. 2011). In coastal temperate
seascapes, biogenic habitats include mainly seagrass meadows on soft bottom and
macroalgal communities on hard bottom (Fraschetti et al. 2008). Indeed, marine
macrophytes (i.e. both seagrasses and macroalgae) are tri-dimensional structures
at a spatial scale from 10
−2 to 10
1 m (www.algaebase.org). The architectural
complexity of a macrophyte-formed habitat often depends on density and complexity of tri-dimensionnal structure of a dominant species/taxonomical group.
Macrophyte-formed habitats with high architectural complexity include, for instances in the Mediterranean Sea: 1/the Posidonia oceanica meadows due to
very high density of shoots (around 600 shoots m
−2 ) (Terrados and Medina-Pons
2011) that are made of ribbon-like leaves, and 2/the Cystoseira forests due to
the very high degree of branching of Cystoseira species (Chemello and Milazzo
P. Thiriet et al.
2011). A seascape has therefore two main features, its composition in term of patch
types (e.g. combined total percent cover per patch type) and its spatial configuration,
i.e. the spatial arrangement of all the patches, which may be synthesized using metrics
such as number, sizes and perimeters of patches, inter-patch distances, contiguity
(Wedding et al. 2011).
Patch typology intends to break down the seascape into ecologically meaningful
and workable sub-units for facilitating ecological studies of the whole. Hence, each
patch-type refers to a given set of environmental conditions, such as depth, type
of primary substrate, availability of resources (e.g. food and shelter), and so gives
insight on local ecological functioning. Therefore, patch types may be seen as benthic
habitats (Fraschetti et al. 2008), the term they are usually referred as.
Ecological functioning of the whole mosaic does not simply rely on the sum
of every habitat-specific ecological functioning. Patches interact together and some
specific proprieties may emerge by synergy (e.g. edge effect), depending on seascape
configuration (e.g. amount of ecotones) (Macreadie et al. 2010; Bostrom et al.
2011). Other environmental factors affect ecological processes (e.g. water temperature, salinity and oxygenation affect growth) and they may vary at a spatial
scale distinct from patch scale, usually at broader spatial scales (Ordines et al.
2011). Hence, multiple spatial scales have to be considered for a better understanding of the ecological processes that drive organisms’ distribution patterns within a
seascape.
12.2 From Macrophyte Assemblages to Seascape Configuration
Some benthic organisms greatly modify local 3D-architectural complexity. They
provide habitat to many other organisms and ultimately structure the whole benthic community through “habitat cascade” (Thomsen et al. 2010). Such species
are called biogenic habitat formers and include for instance corals, oysters, mangroves, seagrasses and some macroalgae (Bostrom et al. 2011). In coastal temperate
seascapes, biogenic habitats include mainly seagrass meadows on soft bottom and
macroalgal communities on hard bottom (Fraschetti et al. 2008). Indeed, marine
macrophytes (i.e. both seagrasses and macroalgae) are tri-dimensional structures
at a spatial scale from 10
−2 to 10
1 m (www.algaebase.org). The architectural
complexity of a macrophyte-formed habitat often depends on density and complexity of tri-dimensionnal structure of a dominant species/taxonomical group.
Macrophyte-formed habitats with high architectural complexity include, for instances in the Mediterranean Sea: 1/the Posidonia oceanica meadows due to
very high density of shoots (around 600 shoots m
−2 ) (Terrados and Medina-Pons
2011) that are made of ribbon-like leaves, and 2/the Cystoseira forests due to
the very high degree of branching of Cystoseira species (Chemello and Milazzo