Abstract
Grouping species into functional-form groups and measuring directly their surface area to volume ratio are 2 common approaches to forecast primary production of marine macroalgae. A link between the functional-form model (FFM) and the power-scaling approach (PSA) for a wide vari- ety of marine macroalgae has been attempted for the first time in the present work. To test both approaches, thalli of 44 species of marine benthic macroalgae were collected from intertidal zones adjacent to Cadiz Bay. Metabolic rates, tissue nutrient content, surface area to biomass ratio (SA/B) and specific growth rates were measured for these species. PSA slopes were close to 2/3 power for growth rate, while metabolic rates scaled very close to, or matched, 3/4 power. The FFM descriptive model provided similar results to the PSA when it was transformed to a numerical model through the SA/B ratio. Even though both models appear to be valid, the problems derived from species alloca- tion into morphological groups, and other previous criticisms, make the direct use of SA/B ratios more suitable for representing primary production in macroalgal functional groups in numerical models of coastal ecosystems.
Highlights
Macroalgae are the dominant organisms in most rocky-shore habitats and in certain soft-bottom coastal environments
Even though both models appear to be valid, the problems derived from species allocation into morphological groups, and other previous criticisms, make the direct use of surface area to biomass ratio (SA/B) ratios more suitable for representing primary production in macroalgal functional groups in numerical models of coastal ecosystems
Values of net photosynthesis rate (NP) ranged from 0.5 mg C g–1 C h–1 (Codium adhaerens) to 26.3 mg C g–1 C h–1 (Ulva clathrata), while Rd varied from 0.33 mg C g–1 C h–1 (Codium bursa) to 5.1 mg C g–1 C h–1 (Ulva clathrata)
Summary
Macroalgae are the dominant organisms in most rocky-shore habitats and in certain soft-bottom coastal environments. Models of primary production in the coastal ocean need to include the macroalgal compartment in those habitats dominated by these organisms. The first approach aims at predicting macroalgal ‘productivity-related ecological processes’ by grouping algae according to their morphological attributes (Littler & Littler 1980, Littler & Arnold 1982, Steneck & Watling 1982). This model, the so-called functional-group or functional-form model (FFM), sorts macroalgae into several groups: sheet-like, filamentous, coarsely branched, thick leathery, jointed calcareous, and crustose. The FFM descriptive model has received many criticisms: (1) the potential, high morphological variability within a functional-form group or even for a single species (see Padilla & Allen 2000); (2) the ambiguity associated with the definition of functional-form groups when applied to species (Phillips et al 1997); (3) the variable assignment of certain species to a given group
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