II. C. Defining Function |
Ecological functions are natural attributes of a given habitat that “serve” the resources that rely upon that habitat. Ecological functions are defined by the structure (i.e., size, shape, substrate, and species composition) of the habitat, and the species interactions that occur therein. For example, bull kelp, found in the shallow subtidal zone of Puget Sound, provides a variety of functions to the nearshore ecosystem that are derived from its complex forest-like structure. These functions include refuge and feeding habitat for fishes (especially rockfish), spawning habitat for herring, and buffering of wave and current energy (Williams and Thom 2001). As ecosystems grow increasingly complex, functions that are provided by one habitat may also be beneficial to other habitats, resulting in a broad network of interactions. From a landscape perspective, the presence of a variety of nearshore habitats contributes a wider range of potential ecological functions (e.g., biodiversity maintenance) to the ecosystem as a whole.
To help evaluate the ecological functions of individual habitats for fish and wildlife within Puget Sound, standardized protocols have been developed that describe recommended techniques for quantitatively measuring habitat attributes that characterize these potential functions (Simenstad et al. 1991). Expert- and literature-derived guidance was used during this process to develop habitat-specific lists of representative fish and wildlife species, and their primary functional mechanisms (i.e., reproduction, feeding, refuge, and physiological adaptation). Specific examples of typical nearshore species and aspects of habitat functional dependence are discussed in Chapter V of this document.
It should be noted that within the Puget Sound ecoregion, the nearshore zone provides a number of necessary functional benefits to salmon, a key species that indicates local watershed health and provides cultural and economic resources to communities region-wide. Some of these functions include prey production (i.e., food for juvenile and adult salmon), migratory corridors, refuge for juveniles from predators, and juvenile rearing. In addition, salmon transport marine-derived nutrients back into freshwater streams and forests as they spawn and become prey for wildlife (see Cederholm et al. 2000), thus linking the functions of the nearshore ecosystem to the health of the entire watershed. The specific functional benefits of the nearshore to salmon are further explored in Chapter V.
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