Pacific Rocky Intertidal Monitoring: Trends and Synthesis

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Mazzaella (Iridescent Weed)

Mazzaella splendens, Mazzaella flaccida (Setchell & Gardner 1937)

Division Rhodophyta, class Rhodophyceae, order Gigartinales

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Description

Mazzaella flaccida has rubbery blades 20-30 (140) cm long, 8-20 cm wide that are elongate to heart-shaped and iridescent yellow-green with purple or brown near base of blade. Thallus has a short stipe (<2 cm long) and a perennial discoid holdfast (Abbott and Hollenberg 1976).

Mazzaella splendens blades range from 20-40 cm (2m) long and 12-24 (40) cm wide. Blades are typically heart-shaped, rubbery, and violet to blackish in color, with a blue, iridescent sheen when wet. This alga has a perennial, fleshy holdfast out of which a 3-6 cm stipe grows (Abbott and Hollenberg 1976).

Habitat and Geographic Range

Mazzaella flaccida is abundant in the mid to low intertidal zones. It also grows on mid-shore rocks (saxicolous) and the upper limit is close to mid-tide level (~+1 m). It is the most conspicuous blade-like alga in Central CA.

Mazzaella splendens is a common saxicolous alga found from the low intertidal to subtidal (7m) on exposed coasts. The two subspecies of M. splendens have a combined range that extends from southeast Alaska to Punta Baja, Baja California (Hughey and Hommersand 2010).

Synonyms

Mazzaella flaccida: Iridea flaccida

Mazzaella splendens: Iridea cordata var.cordata, Iridea cordata var. splendens

Similar species

M. flaccida and M. splendens are most similar to one another (see above descriptions) and can be virtually indistinguishable in the field. M. splendens has a slightly longer stipe and occurs lower on the shore. M. flaccida has a shorter stipe and is iridescent yellowish-green with purple or brown only on basal portion of blade (Abbott and Hollenberg 1976). For Long-Term Monitoring purposes M. flaccida and M. splendens are combined into the Mazzaella category.

Natural History

The similarities in thalus shape and color of the many species of Mazzaella have resulted in numerous taxonomic reorganizations within the group with 24 currently recognized species.Within this complex group, the splendens clade currently includes four species (Mazzaella flaccida, Mazzaella linearis, Mazzaella sanguinea and Mazzaella splendens) with recent molecular and morphological work identifying six clades and two subspecies within this taxonomically challenged clade (Hughey and Hommersand 2010).

M. flaccida and M. splendens are red algae with separate male and female thalli and three different life history phases. Within each species, individuals of all phases are isomorphic (the same size and shape) despite differences in tissue ploidy (i.e. 1N gametophyte versus 2N tetrasporophyte). For both M. flaccida and M. splendens, individuals of different phases can be differentiated visually when reproductive—the male gametophyte thallus will be smooth, the 1N female gametophyte thallus will have large, rough bumps, and the tetrasporophyte thallus will have many, closely-packed small bumps (Thornber et al. 2006)—or via chemical analysis when non-reproductive by looking at the carrageenan content (McCandless et al. 1975). In a field study by Thornber et al. (2004) they found M. flaccida and M. splendens gametophytes to be more abundant in the field than the sporophytes, resulting in part from a more fecund sporophyte generation which creates the gametophytes. However, while M. splendens adhered closely to the predicted ratio of ~60% haploid: 40% diploid, M. flaccida exhibited a dramatically higher proportion of gametophytes. This is possibly due to the fact that per capita mortality rates for M. flaccida were 11% greater for haploids than diploids (Thornber 2004). Relative abundances of the different M. flaccida tissue ploidy’s (1N gametophyte versus 2N tetrasporophyte) in the field have also been shown to be impacted by herbivory seeing as herbivores, e.g. the snail Tegula funebralis, have shown preferences for gametophyte over sporophyte, as well as reproductive over non-reproductive, tissue (Thornber 2006).

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