Crustose Coralline Algae Species Studied

Appendix

Crustose Coralline Algae Species Studied

Most Caribbean algae are relatively easy to identify due to the existing taxonomic literature and guides (e.g., Littler and Littler 2000). Tropical non-geniculate coralline algae, or “crustose coralline algae” (CCA), are different. Coralline taxonomy has been in flux almost since its modern inception in the late 1800s. Since the 1970s two schools developed with very different taxonomic schemes. In the 1980s many taxa were synonomized based on their original descriptions (e.g., Woelkerling 1988). However, the most recent revisions using molecular genetics (Bittner et al. 2011; Kato et al. 2011) revealed that some important genera that had been synonomized are in fact phylogenetically distinct and thus should be reinstated. One conspicuous example was the genus Porolithon that had been synonomized with Hydrolithon. Molecular genetic studies determined them to be distinct, and thus, reinstated Porolithon (Bittner et al 2011). Several biogeographically disparate species have also been synonomized, such as Neogoniolithon solubile (type location Jamaica in the Caribbean), Neogoniolithon fosleii (type location Mediterranean Egypt) and Neogoniolithon brassica-florida (type location southern most (temperate) region of South Africa). This synonomy suggests a coralline flora that is without thermogeographic or biogeographic limits, despite coralline literature to the contrary (Adey and Adey 1973; Adey and Steneck 2001). Molecular studies on N. brassica-florida concluded that this taxa appears “to be polyphyletic, suggesting the presence of several cryptic species…” (Kato et al. 2011). To avoid including such cryptic species, we followed Adey’s taxonomic schemes (Adey 1970; Adey et al. 1982) and follow many of the original descriptions because they conform well with recent studies that use genetic data (Bittner et al. 2011; Kato et al. 2011). Accordingly, we use currently under-valued characteristics such as branching propensity and morphology, thallus surface features, arrangements of unique cells (e.g., trichocytes, described below), anatomical characteristics of epithallial, perithallial (cortical) and hypothallial (medulla or basal) cell layers.

A specialized anatomical character that has received little attention in recent decades is the size and arrangement of trichocyte cells. These were described by Foslie in the early 1900s and were recently used for coralline taxonomy in Guam and the Hawaiian islands (Gordon et al 1976; Adey et al 1982, respectively) where they were called “heterocysts”. “Heterocysts” is a term used for cyanobacteria and since these are hair cells, “trichocyte” is a better descriptor (e.g., Woelkerling 1988). The arrangement of trichocyte fields is a taxonomic characteristic that corresponds well with recent molecular-based phylogenies. Porolithon’s distinctive tightly packed horizontal trichocyte fields make this genus easy to identify. The closely related taxon Pneophyllum conicum was originally described as the genus Paragoniolithon, which had loosely grouped horizontal trichocyte fields. The more distantly related Hydrolithon (sensu Adey 1970) has widely spaced trichocytes. Thus, within the mastophoroids, there exists a gradient of trichocyte arrangement that corresponds well with genetically based phylogenetic trees.

Nongeniculate coralline algae are characterized by three distinct cell layers. The outer most layer is the epithallus that is usually one cell layer thick but can be multilayered in some taxa. The cells typically shed from the thallus taking epibionts with them (with one notable exception described below). Epithallial cells are produced by the region of growth called the meristem (or subepithallial initials). The meristem also produces cells that comprise the majority of the crust’s thickness in a layer called “perithallus” but is roughly homologous with the cortex of typical erect fleshy macroalgae. The basal layer of CCA is called the “hypothallus”, which is homologous with the medulla of typical erect fleshy algae. Each of these tissue layers are composed with different arrangements of cells that can be characteristic of taxonomic affinities. Beyond the anatomy we just described are several morphological characters such as propensity to form protuberances (i.e., “branches”), thallus thickness, degree of adherence to hard substrates and reproductive characters such as size, shape and pore characteristics of the reproductive structured called conceptacles. Specifically the size and shape of asexual (tetrasporangial) conceptacle pores used to release spores are often diagnostic for CCA taxa.

It is well beyond the scope of this paper to resolve taxonomic confusion surrounding CCA since the taxonomic literature relevant for the Caribbean corallines is lacking or in need of a revision (Taylor 1960). Littler and Littler (2000) is a good field guide with excellent photographs, but it does not use the diagnostic taxonomic characters necessary to reliably determine coralline species. For our study, we define taxa on multiple independent characters that relate to regionally relevant described species. For this reason, we provide the species names and descriptions of key anatomical and morphological characteristics we used to identify the species used for the larval settlement and metamorphosis assays. We describe the CCA in sufficient detail so others could arrive at the same determination using a dissecting microscope and when genetic studies have been completed, revisions can be made of these taxa. To be conservative, we only describe taxa whose type locality is relevant to the tropical western Atlantic. Our approach in effect resurrects some taxa that have been synonomized based on relatively few currently accepted taxonomic characters. While it is correct that many characters used in past coralline taxonomic studies are variable, when several characters are considered simultaneously, the likelihood of identifying either genetically unique or remarkably convergent taxa increase.

Family: Peyssonneliaceae

Species: Peyssonnelia sp. (Decaisne 1841)

Distinguishing characteristics are described in Littler and Littler (2000).

Order Corallinales

Family: Corallinaceae

Subfamily Lithophylloideae (tetrasporangial conceptacles single pored, secondary pits between adjacent cells; recent molecular genetic study found the articulated coralline Amphiroa is a lithophylloid and so it is included here (Bittner et al 2001))

Species Amphiroa tribulus (J. Ellis & Solander)

Distinguishing characteristics are described in Littler and Littler (2000).

Species Titanoderma prototypum (Foslie) Woelkerling, Y.M.Chamberlain & P.C.Silva.

Distinguishing characteristics: Pink to red coloration with a thin overgrowing thallus in which overall thickness is achieved by single layered vertical (“palisade”) hypothallus repeatedly overgrows itself usually showing distinct arcuate pattern over overgrowth (called “aplanate branching”). Epithallial cells are uniquely retained and are visible in cross section under overgrowing portion of the thallus. Another much rarer Titanoderma species (T. bermudense) has a distinct white margin on its very regular overgrowing thallus and it does not retain epithallial cells. T. prototypum has single pored tetrasporangial conceptacles that are raised with an outside diameter ranging between 400 – 600 µm. Type locality: St. Croix, U.S. Virgin Islands. It is important to note this name is for the Caribbean species, but has been applied to an undescribed, morphologically similar species found in the Pacific Ocean.

Subfamily Mastophoroideae (Tetrasporangial conceptacles single pored, vegetative cell fusions between adjacent cells)

Species Neogoniolithon affine (Foslie & Howe) Setchell and Mason

Distinguishing characteristics: Irregular relatively thin dark red-brown thallus, coaxial (acruate and aligned cells) hypothallus, raised tetrasporangial conceptacles 500 – 600 µm OD. Trichocytes are small and often not visible with dissecting microscope. Type locality: Culebra, Puerto Rico

Species Neogoniolithon mamillare (Harvey) Setchell and Mason

Distinguishing characteristics: Smooth yellow-brown-pink crust that develops irregular mammalate (wider than they are high protuberances) thallus that often has conspicuous curved sloughing or flaking of epithallial cells. Strongly raised large conceptacles 800 – 1800 µm OD. Hypothallus parallel. Large trichocytes with a scattered distribution are very distinct with a dissecting microscope. Type locality: Brazil

Species Neogoniolithon munitum (Foslie & Howe) Adey

Distinguishing characteristics: Red-brown or yellow brown, rugulose (irregular, rough surface with no pattern), subtesslate (distinct raised surface patches, “subtesselate” refers to less distinct tessellations), medium thickness (ca 500µm) crust with a growing margin that may be nonadherent (“leafy”), tetrasporangial conceptacles raised dome (very abundant) conceptacles 275 – 475 µm OD. Trichocytes are small and inconspicuous when using dissecting microscope.

Species Hydrolithon boergesenii (Foslie) Foslie

Distinguishing characteristics: Purple coloration, strongly tessellated surface texture with an adherent thallus margin that is not white. Tetrasporangial conceptacles abundant, distinctly raised, rounded dome-shaped 300 – 400 µm OD. Single layered hypothallus is rarely visible with dissecting microscope.

Species Paragoniolithon solubile (Foslie & Howe in Foslie) Adey, Townsend and Boykins

Distinguishing characteristics: Expansive and often moderately thick crust > 500 µm. The hypothallus is strongly coaxial. The conceptacles are readily visible with dissecting microscopes, strongly raised and large 900 – 1800 µm. Type locality: Jamaica

Species Porolithon pachydermum (Foslie) Foslie

Distinguishing characteristics: Blue to purple coloration, smooth surface texture, chalky very thick thallus that usually grows on upper facing convex hard substrates in shallow zones < 10 m deep. Conceptacles slightly raised or flush and small, 100 – 200 µm OD. Hypothallus parallel and moderately thin (50 – 200 µm) which is sometimes visible with dissecting microscopes.

Species Lithoporella atlantica (Foslie) Foslie

Distinguishing characteristics: Pink to red coloration with thin leafy over-growing thallus with conspicuous fan-like arrangement of the cells. The hypothallus is single layered with a vertical (palisade) orientation, and the conceptacles are raised (500 – 800 µm OD).