Rosenvingea (Ectocarpales, Scytosiphonaceae) – a new brown macroalgal record for New Zealand

Abstract

The brown alga Rosenvingea sanctae-crucis (Ectocarpales, Scytosiphonaceae) is recorded from New Zealand for the first time. It was found in the Tamaki Estuary, Auckland in May 2009, and is considered to be a very recent introduction to the New Zealand region.

Keywords:

• non-indigenous macroalga
• Rosenvingea
• Scytosiphonaceae
• New Zealand

Introduction

Despite its geographic isolation, New Zealand has received a steady influx of introduced macroalgae. Adams (1983) published the first list of macroalgae presumed to have reached New Zealand as a result of human-mediated pathways, with 14 taxa treated. Sixteen years later, Nelson (1999) listed 20 species considered to be introductions, of which 9 were brown algae. Subsequently, an additional two species of brown algae presumed to be introduced to New Zealand have been found: Dictyota furcellata (C.Agardh) Grev. (Nelson et al. 2004) and Asperococcus ensiformis (Chiaje) M.J.Wynne (D'Archino & Nelson 2006).

In this paper, the occurrence of the brown algal genus Rosenvingea Børgesen (Ectocarpales, Scytosiphonaceae) in New Zealand waters is recorded for the first time.

Observations

Numerous thalli of a brown alga (Fig. 1) were found in May 2009 on the Tahuna Torea spit and shell bank which extends across the Tamaki Estuary, opposite Bucklands Beach, Auckland. This shell bank is ~ 1 km from Half Moon Bay marina, where predominantly recreational craft are moored.

Fig. 1  Rosenvingea sanctae-crucis – WELT A024346; scale bar = 2 cm.

The shell bank is largely exposed at low tides, and comprises muddy sand and shells of bivalve molluscs, principally Austrovenus stutchburyi, Cyclomactra ovata, Macomona liliana and Paphies australis. Thalli were found attached to shells of the common cockle (A. stutchburyi), nestled on the muddy surface, with the majority of thalli stranded by the low tide and lying loose (unattached). Dozens of thalli were present. Other algae in this habitat were Codium fragile (Suringar) Har., Dictyota sp. and Hincksia sordida (Harv.) P.C.Silva.

Morphological observations

Thalli were golden brown in colour, ~ 15 cm in height and ~ 2 mm in width. The axes were cylindrical and irregularly branched with a somewhat antler-like appearance at the tips. In cross-section, thalli were found to be hollow, with three to four cell layers, the outer cortical layer cuboidal and the inner cells large and rounded. The thalli were fertile with plurilocular sporangia in ovoid sori, and colourless (phaeophycean) hairs were present scattered over the thallus surface.

The specimens were identified as belonging to the genus Rosenvingea Børgesen (Scytosiphonaceae), possessing hollow, branched axes with tapering apices, and with a cortex of small pigmented cuboidal cells and a medulla of large colourless cells. Based on the presence of hairs, the height and width of the thalli, as well as the appearance of the apices of the branches, we have identified these specimens as Rosenvingea sanctae-crucis Børgesen. This species was originally described from the Virgin Islands (Børgesen 1914) where it was recorded to grow to ~ 20 cm in height, and has been subsequently reported from the Canary Islands, eastern North and Central America, the Caribbean, Pacific Mexico, Brazil, Venezuela, Mauritania, Bangladesh and India (Guiry & Guiry 2010).

Reference specimens: North Island, Auckland, Tamaki Estuary, Tahuna Torea Spit, 36°52.27′S 74°53.93′E, M.D. Wilcox, 11 May 2009, AK 304900, also WELT A024346; Tamaki Estuary, Bucklands Beach, M.D. Wilcox, 26 May 2009, AK 305056. (for herbarium codes see Thiers 2010).

Discussion

The genus Rosenvingea was erected for tubular branched brown algae previously included in the genera Asperococcus J.Agardh and Encoelium C.Agardh, and was considered to be closely related to the genus Chnoospora J.Agardh (Børgesen 1914). Other species that have been subsequently transferred to Rosenvingea were initially placed in the genera Cladosiphon Kütz. and Stilophora J.Agardh (Taylor 1955; Wynne 1997).

Rosenvingea sanctae-crucis is very similar to Rosenvingea orientalis (J.Agardh) Børgesen, a species described originally from the Philippines and which is reported to have a wide distribution in warm-water regions (Guiry & Guiry 2010). Børgesen distinguished these two species on the basis of the presence (R. sanctae-crucis) or absence (R. orientalis) of hairs, the smaller size of cells in R. orientalis, and also noted that R. orientalis had much finer apices and reached greater heights (to ~ 40 cm). Currently, seven species of mainly tropical or subtropical distribution are recognized in Rosenvingea (Guiry & Guiry 2010). Abbott and Huisman (2004) considered that a detailed study of upright Rosenvingea species would result in changes in this genus, but there has been no such study published to date. Earle (1969) and Littler and Littler (2000) suggested that R. sanctae-crucis and R. orientalis may be conspecific, with Earle pointing to the need for study of the type material of R. sanctae-crucis. Silva et al. (1996) and Wynne (2005) recorded both of these species from the Indian Ocean and the tropical and subtropical western Atlantic, Wynne (2005) noting that if these species are ‘to be regarded as taxonomic synonyms, R. orientalis has priority’. Although Dawes and Mathieson (2008) recorded R. sanctae-crucis as a synonym of R. orientalis, Guiry and Guiry (2010) continue to record both species. In the absence of a detailed comparative study of type specimens and collections from the vicinity of the type localities, we are applying the name R. sanctae-crucis to the specimens from Auckland, given that the material collected in the Tamaki Estuary closely conforms to Børgesen's original description, and exhibits the characters that he considered to distinguish this species from R. orientalis.

The origin of the population in the Tamaki Estuary is unknown. This species was not recorded during surveys of the Tamaki Estuary carried out 2002–2004 (January, October) (Hayward & Morley 2005) and thus we conclude that it is a recent arrival. The proximity of the collection site to a large marina suggests that the species could have arrived attached to a vessel arriving from tropical or subtropical ports.

It is interesting to observe that two thirds of the 12 species of brown algae reported to be introduced to New Zealand waters (including Rosenvingea) belong to the Ectocarpales, with four species in the family Scytosiphonaceae [Chnoospora minima (Hering) Papenf. (Nelson & Duffy 1991), Colpomenia bullosa (D.A.Saunders) Yamada (Parsons 1982), Hydroclathrus clathratus (C.Agardh) M.Howe (Johnson & Dromgoole 1977) and Rosenvingea]. Heteromorphic life histories are typical of members of the Scytosiphonaceae and the switch between life history phases has been documented to be influenced by such environmental stimuli as day length and temperature (van den Hoek et al. 1995). Such life histories may enable the transport of these species by various vectors, either as a microscopic or crustose phase, or as the macroscopic phase. The differing tolerances of these heteromorphic phases may also provide physiological ‘flexibility’ enabling these taxa to survive a range of physical conditions. Unlike various other invasive brown algae, e.g. the kelp Undaria pinnatifida (Harv.) Suringar, no members of the Scytosiphonaceae have been identified internationally as ecologically or economically significant invasive species, although they are frequently recorded internationally as non-indigenous species.

Acknowledgements

Jenn Dalen (Herbarium, Museum of New Zealand Te Papa Tongarewa) is thanked for assistance. The New Zealand Foundation for Research Science and Technology is thanked for funding (CO1X0502 – WAN).