Pacific Rocky Intertidal Monitoring: Trends and Synthesis
Mastocarpus complex (C.Agardh 1821)
Kingdom Plantae, phylum Rhodophyta, class Florideophyceae, order Gigartinales
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The Mastocarpus complex targeted by MARINe includes morphologies previously identified as Mastocarpus papillatus (Lindstrom et al 2011). Morphology within the complex can be highly variable. Each thallus stands less than15 cm tall, with flattened dark to brownish red blades that are thin yet tough. Blades vary in width, are covered thickly or sparsely with papillae of various sizes, are ribbed along the margin, and have tips which are usually divided dichotomously. Male plants lack papillae and are light rose to greenish or yellowish in color (Abbott and Hollenberg 1976, Kozloff 2000).
Habitat and Geographic Range
Common in the high to mid-intertidal zones, this alga complex often dominates these zones in central and northern California and but is less abundant south of Santa Barbara. Range extends from Alaska to Pta. Baja, Baja California (Abbott and Hollenberg 1976).
Members of another species complex, formerly identified as Mastocarpus jardinii, can be confused with members of the M. papillatus complex. Mazzaella affinis is similar in color and shape to male M. papillatus, but is usually shorter and grows in dense continuous mats rather than as discrete individuals. All Mastocarpus species and another red alga, Pikea have crustose phases in their life histories, making field-identification of the crusts to species level difficult. Hildenbrandia and Ralfisa are other dark crusts but these are thinner than “Petrocelis” (the crustose phase of the M. papillatus complex).
There is great variability in the growth forms of the Mastocarpus papillatus complex. Individuals vary in the size and density of papillae present, amount of branching, and thallus thickness. Surprisingly, Carrington (1990) found that the amount of drag force that an individual was subjected to in high flow environments did not correlate strongly with morphology, including thallus diameter (the area where breakage most commonly occurs). However, Kitzes and Denny (2005) did find a positive relationship between both thallus cross-sectional area and material strength with increasing wave force, indicating a selective force or adaptive ability of individuals living in high wave energy environments.
Mastocarpus exhibits two distinct life cycles: a sexual alternation of generations involving three separate stages, and an asexual direct life cycle that produces only female fronds. The distribution of sexual and asexual populations varies both with latitude, and tidal height within a given site, a pattern of spatial separation called geographic parthenogenesis (Fierst et al.2010). In sexual populations, the upright thallus is the haploid, gametophytic stage, with separate male (typically greenish or yellowish) and female (typically dark red) blades. Males release spermatia, which fertilize ova retained by females. The fertilized diploid zygotes remain attached to the female blades, and are visible as bumps (carposporophytes), on the surface. Carposporophytes release diploid carpospores, which settle and grow into diploid tetrasporophytes, smooth, dark black-red to olive brown crusts typically 2-2.5 mm thick. These crusts were once thought to be a separate species, called “Petrocelis”. “Petrocelis” produces tetraspores via meiosis, which are released and settle to grow into the haploid male or female blades.