A UNIQUELY CALCIFIED BROWN ALGA FROM HAWAII:NEWHOUSIA IMBRICATAGEN. ET SP. NOV. (DICTYOTALES, PHAEOPHYCEAE)¹

Abstract

An encrusting brown alga from subtidal habitats around the island of Oahu (Hawaiian Islands) represents only the second genus of the class Phaeophyceae to form calcium carbonate, which it deposits primarily as both extracellular and intracellular aragonite, admixed with small (3.3%) amounts of calcite. Plants form expanses 15–100+ cm in extent consisting of horizontally aligned imbricating tiers of distromatic blades 1–4 mm in diameter that are separated from one another by cementing layers of extracellular aragonite, the tiers forming stacks of dozens of laminae and anchored to coral substrata by a basement layer that adheres tightly without haptera or rhizoids. The hypodermal layer of each blade consists of lightly pigmented rectilinear cells bearing either one or two smaller deeply pigmented epidermal cells in cross‐sectional profiles and three or four in long‐sectional profiles, the cells of both layers becoming encased in rigid carbonate skeletons laid down in their outer wall matrices. The successive tiers become stacked by either overgrowing marginal proliferations or new blade primordia that arise from the hypodermal layer of surface laminae and initially spread centrifugally by means of continuous marginal meristems. Neither plurilocular nor unilocular reproductive structures are known. The alga is described as the new genus and species Newhousia imbricata Kraft, G.W. Saunders, Abbott et Haroun and is assigned on the basis of small subunit rDNA gene sequence analyses to the order Dictyotales, family Dictyotaceae, within a strongly supported monophyletic clade that includes Distromium, Lobophora, and Zonaria.

An Overview of Marine Biodiversity in United States Waters

“…The largest gaps in our understanding of the Hawaiian marine flora are linked to (a) a lack of trained algal taxonomists, (b) public and government apathy toward the study of marine plants, and (c) difficulty of access to many environments. When trained phycologists explore underexamined reef areas, even on the heavily populated island of Oahu, species new to science are regularly discovered [183], [188], [189], [190], and suspected cryptic diversity is only beginning to be investigated [191], [192].…”

Ocean acidification effects on calcifying macroalgae

“…The aragonite crystals are deposited externally in a semi-enclosed space formed by infolding of the margin of the thalli (Okazaki et al 1986). Newhousia imbricata is a calcified encrusting species that deposits mostly aragonite both extracellularly between frond layers and intercellularly within the cell wall matrices (Kraft et al 2004).…”

First report of the Hawaiian genus Newhousia (Dictyotales, Phaeophyceae) from Madang, Papua New Guinea and description of the new species N. yhaga sp. nov.

“…The rbcL sequence clustered together with the N. imbricata sequence in the rbcL based ML and BI phylogenetic trees. The Bayesian phylogeny inferred from the smallsubunit rDNA in Kraft et al (2004) positioned N. imbricata as a sister taxon to the genus Zonaria and the authors recommended that the phylogenetic position of Newhousia be refined by further investigation with more variable genes. The Bayesian and ML phylogenies (Figure 3) based on the concatenation of the rbcL+psbA+cox3 genes positioned Newhousia as sister species to Lobophora, with support values of 100% for the BI phylogeny but only 56% for the ML phylogeny (Figure 3).…”

“…Indeed, Kraft et al (2004) already commented that "the frond structure of Newhousia is closest to tightly adherent forms of Lobophora". Both Lobophora and Zonaria have cortical layer on all surfaces and tiers of regularly aligned rectilinear medullary cells, those in Zonaria consisting of 5-8 layers of cells that are of uniform size (Womersley 1987), whereas Lobophora has a 3-25 layered medulla of stacked and aligned cells, in which those of the central layer are twice or more the height of medullary cells on both sides (Vieira et al 2014).…”

“…At that time endemic to Oahu in the Hawaiian Islands, it was only the second genus of calcified species in the Phaeophyceae, although in a form differing from that of any other alga. Unique was the laying down of calcium carbonate as both an extracellular horizontal layer between the overlapping frond and as intracellular deposits laid down within the cell-wall matrix, an additional unique feature being the production of calcium carbonate in the form of both calcite and aragonite (Kraft et al 2004). Based on small and large subunit rDNA phylogenies, Kraft et al (2004) determined that Newhousia was in a strongly supported monophyletic clade that includes Distromium, Lobophora and Zonaria.…”