GENETIC PATTERNS IN THE CALCIFIED TROPICAL SEAWEEDS HALIMEDA OPUNTIA, H. DISTORTA, H. HEDERACEA, AND H. MINIMA (BRYOPSIDALES, CHLOROPHYTA) PROVIDE INSIGHTS IN SPECIES BOUNDARIES AND INTEROCEANIC DISPERSAL¹

Abstract

The section Opuntia within the green seaweed genus Halimeda includes sprawling and pendant thalli composed of strongly calcified segments. Within this section, identification of Atlantic material is straightforward, but Indo-Pacific material is often difficult to key out. This is particularly true for specimens resembling H. opuntia, H. distorta, and H. hederacea; many specimens do not fit any type or are morphologically intermediate. The goals of the present study are to define morphologically and genetically distinct groups among such specimens and to assess phylogeographic patterns within these groups. Specimens were collected throughout the geographical and morphological range. Sequences of H. minima and H. gracilis were included as outgroups. Two morphological groups were discerned within the ingroup; the first fit H. opuntia, whereas most specimens in the second group, referred to as the distorta-hederacea complex, did not fit any species description unambiguously. The latter were subdivided into two subgroups corresponding more or less to H. hederacea and H. distorta, yet intermediates between these morphs existed. A phylogeny inferred from partial nuclear rDNA sequences showed one lineage with H. opuntia and a second one containing the distortahederacea complex, thus corroborating the two major morphological groups. The distorta-hederacea complex contained two clades that show only partial correspondence with the morphological subgroups. Therefore, H. hederacea is synonymized with H. distorta. Phylogeographic structure within H. opuntia indicated that this species dispersed from the Indo-Pacific into the Atlantic. Fossil records of the species also show occurrence at Pacific sites throughout the last 10 5 years and a sudden appearance in the Caribbean and Bahamas during the last millennium.

A molecular method for identification of the morphologically plastic invasive algal genera Eucheuma and Kappaphycus (Rhodophyta, Gigartinales) in Hawaii

“…Increasingly, the use of molecular approaches has clarified identification of algal species in which morphological characters are poor or contradictory (e.g., Byrne et al 2002;Kooistra and Verbruggen 2005;Garguilo et al 2006;Guillemin et al 2008). While previous studies have employed a variety of molecular markers (the mitochondrial cox2-3 spacer, the plastidal RuBisCo spacer, and rbcL gene, and the nuclear small-subunit ribosomal gene) to elucidate the systematics and taxonomy of Kappaphycus and Eucheuma (Lluisma and Ragan 1995;Fredericq et al 1999;Zuccarello et al 2006), here we assess the usefulness of the mitochondrial cox2-3 spacer plus a system of three additional short molecular markers to aid identification and clarify the distribution of these species on Oahu.…”

Marine Algae of French Frigate Shoals, Northwestern Hawaiian Islands: Species List and Biogeographic Comparisons

“…The specimen collected at French Frigate Shoals is the first known central Pacific record and greatly increases the known range for this species. Although this study is the first to report H. distorta in Hawai'i, previous phylogenetic studies of the genus Halimeda used a specimen of this species from the island of Hawai'i for molecular analysis (specimen 97-059 in Kooistra et al 1999 andVerbruggen 2005). Because of superficial similarities between H. distorta, H. copiosa Goreau & Graham, and H. gracilis Harvey ex Agardh, past collections of H. distorta from the Hawaiian Islands may have been misidentified.…”

Capturing the dynamics in benthic structures: environmental effects on morphology in the macroalgal genera Halimeda and Dictyota

“…Segment size can vary for both, as well as segment shape and intersegment distances for H. opuntia. H. opuntia are known to exhibit higher intersegment distances and smaller and tri-partite segments that grow up loosely in lower light levels (Kooistra & Verbruggen 2005). For these 2 species, measuring density could have also provided increased distinction of morphologies.…”