Occurrence of the marine yellow-green algae Vaucheria velutina C. Agardh and Vaucheria longicaulis Hoppaugh (Xanthophyceae: Vaucheriaceae) in Auckland, New Zealand

Abstract

The yellow-green algae Vaucheria velutina and Vaucheria longicaulis are identified using morphological characters of fertile material from the eastern coastline of Auckland. The former species occurs in extensive low intertidal beds on sheltered, muddy shores. The latter species was found in Orakei Basin, and is a new record for New Zealand.

Keywords:

• Vaucheria velutina
• Vaucheria longicaulis
• Xanthophyceae
• soft shores
• New Zealand

Introduction

Vaucheria is a world-wide genus of siphonous yellow-green algae (Heterokontophyta: Xanthophyceae). Most species of the genus are freshwater or terrestrial, though some are marine, of which Chapman (1956) listed four in New Zealand: V. pseudosessilis V.J. Chapm., V. synandra Woronin, V. velutina C. Agardh (as V. thuretii Woronin), and V. bursata (O.F. Müll.) C. Agardh (as V. sessilis [Vaucher] DC.). Adams (1994) listed only two marine species, Vaucheria sp. from mudflats in the North Island and Vaucheria sp. ‘Chathams’ from the Chatham Islands. Sarma (1973, 1974) recorded and illustrated several species of Vaucheria from freshwater habitats on Great Barrier Island and Slipper Island.

Records of two species of Vaucheria are reported here, as part of a comprehensive survey of the marine algae of Auckland. Some other populations of Vaucheria have been observed and sampled from sheltered Auckland seashores, but their identification awaits observation of reproductive structures.

Field observations

Several extensive beds of Vaucheria, identified here as V. velutina, have been observed on low intertidal soft shores of the eastern coastline of Auckland. The most prominent of these are at Scandrett Regional Park in Kawau Bay, at Scott Point and Casnell Island in Mahurangi Harbour, at Bucklands Beach, Karaka Bay and Tahuna Torea Spit in the outer Tamaki Estuary, at Omana Beach near Maraetai, and at Umupuia Beach on the northern coast of Duder Regional Park. These sites are protected coasts, with turbid waters, but are not associated with narrow creeks, salt marshes or mangroves (Fig. 1A). The occurrence of these beds has not previously been reported in the literature on Auckland's coastal ecology.

Figure 1  Vaucheria velutina. A, Beds exposed at low tide, Umupuia, 4 July 2008. B, Tufts above mud surface, Scandrett Bay, 7 May 2008. C, Prostrate siphons on mud surface, Umupuia, 4 July 2008. D, Vegetative siphons, Umupuia, 23 June 2009. E, Oogonia (immature), Scandrett Bay, 25 May 2010. F, Antheridia with globular mass of antherozoids, Scandrett Bay, 25 May 2010.

All observations of V. velutina have been from April to October, suggesting that this alga is most conspicuous in winter. It typically grows on fine, grey mud towards and just below the low tide mark in sheltered embayments, sometimes between rock platforms. It has the general form when exposed by the tide of prominent erect tufts on top of the mud surface and extensive sub-surface siphons which bind the sediment together and stabilise the mudflat (Fig. 1B–C). From a distance, these algal beds are a yellowish green, ageing to brown, and can be conspicuous when uncovered at low spring tides.

Another species, identified as Vaucheria longicaulis Hoppaugh, was found in Orakei Basin in Auckland, in May 2010, growing on stones and attached to old tyres at the edge of the shore. The sample collected was fully fertile, bearing antheridia and oogonia, facilitating identification.

Methods and materials

Collection and examination of samples

Samples from each of the V. velutina sites were collected by hand at low spring tides when the beds were exposed and accessible (Fig. 1A). The sample of V. longicaulis was collected from Orakei Basin on a day in which the normally-closed sea gates had been opened to allow the water level to drop to a low level, exposing the muddy shore line. Photographs in the field were taken with a hand-held Canon PowerShot S5IS digital camera.

Fresh samples were examined in the laboratory of the Auckland Museum Herbarium, using a Leitz Laborlux S binocular compound microscope. Photographs were taken down the microscope eyepiece using a hand-held Pentax Optio 750Z digital camera, set in macro mode. Dimensions were determined using the graticule in the eyepiece of the microscope, calibrated as follows: 40×lens, 1 small division=2 µm; 10×lens, 1 small division = 8.163 µm; 4×lens, 1 small division = 20.408 µm; 2.5×lens, 1 small division = 32.323 µm.

Scale bars were inserted using Olympus Master 2 Photo editing software.

Culturing was attempted in 50% freshwater:50% seawater to induce fruiting, but without success.

Results and discussion

Description and identity of the Auckland bed-forming Vaucheria

Vaucheria velutina C. Agardh (Fig. 1A–F)

References. Chapman (1956), Gallagher and Humm (1981), Christensen (1987b), Womersley (1987), Entwisle (1988), Guiry and Guiry (2010).

Specimens examined. Scandrett Regional Park, Scandrett Bay, Long 174° 46′E, Lat 36° 26′S, M.D. Wilcox 3536, 7 May 2008, AK 305725

Scandrett Regional Park, Scandrett Bay, Long 174° 46′E, Lat 36° 26′S, M.D. Wilcox 2541, 2 Jul 2008, AK 305722

Mahurangi Harbour, Scott Point, Long 174° 43′E, Lat 36° 29′S, M.D. Wilcox 4060, 25 May 2010, AK 315045

Mahurangi Harbour, Casnell Island, Long 174° 44′E, Lat 36° 29′S, M.D. Wilcox 4061, 25 May 2010, AK 315046

Umupuia, Long 175° 04′E, Lat 36° 54′S, M.D. Wilcox 2539, 4 Jul 2008, AK 305724

Omana, Maraetai, Long 175° 56′E, Lat 36°53′S, M.D. Wilcox 2540, 4 Jul 2008, AK 305721

Tamaki Estuary, Bucklands Beach, Long 174° 54′E, Lat 36° 52′S, M.D. Wilcox 3513, 26 May 2009, AK 305723

Umupuia, Long 175° 04′E, Lat 36° 54′S, M.D. Wilcox 3545, 23 Jun 2009, AK 305761

Tamaki Estuary, Tahuna Torea Spit, Long 174° 54′E, Lat 36° 52′S, M.D. Wilcox 3552, 25 Jun 2009, AK 305762

Description

Vegetative features: Thalli coenocytic, 80–100 µm maximum width, 5–10 cm long. Branching sparse. Siphons commonly hollow and colourless with age (Fig. 1D). Anchoring siphons colourless to pale pink, with slender basal ends, tapered to 10–20 µm, deeply buried; side rhizoids short. Thalli when extracted from the mud substrate coarse and hair-like. Dried specimens adhering strongly to paper, with a glossy sheen.

Reproductive features: Most of the Auckland material examined has been sterile, but samples collected in May 2010 from Scandrett Bay were sparsely fertile, with both oogonia (Fig. 1E) and antheridia (Fig. 1F) present. Gametophores absent. Oogonia sessile, ovoid, 50 µm wide (immature), radially symmetrical; base acute, not associated with antheridia; bent at base. Antheridia sessile, ovoid to ellipsoid, 70 µm long, borne in linear groups of two to three, not obviously on the same siphon as the oogonia.

Identification

This bed-forming, mud-dwelling marine Vaucheria in Auckland is here identified from the descriptions in Womersley (1987) and Entwisle (1988) as V. velutina C. Agardh, a species previously recorded from Auckland by Chapman (1956) as V. thuretii. The sessile disposition and radially symmetrical ovoid shape of the oogonia, point to this Auckland species being in section Woroninia (Entwisle 1988). A rather similar and related species, V. conifera T.A. Chr. (Christensen 1987a), in the same section, is known from South Australia and Victoria (Entwisle 1988). These two species differ in the shape of the antheridia—fusiform in V. conifera and ovoid in V. velutina. The oogonia in V. velutina are generally obovoid with an acute, bent base, while in V. conifera they are generally erect and ellipsoid with an obtuse base.

Christensen (1987b) has suggested that European material with antheridia and oogonia on separate filaments and with most of the oogonia upright, as in the Auckland samples, is referable to V. velutina var. separata Christensen, which is probably the same as V. dichotoma var. submarina Lyngbye.

Distribution and habitat

Vaucheria velutina is widely distributed in Europe (Christensen 1987b; Guiry & Guiry 2010) and North America (Schneider et al. 1993). Gallagher and Humm (1981) have described Vaucheria beds in Tampa Bay, FL, USA, noting three species (Vaucheria velutina, Vaucheria longicaulis, and Vaucheria litorea C. Agardh), their presence in the cooler months of the year, and their occurrence in the low intertidal on soft, unconsolidated sediments. As here observed in the Auckland populations, Gallagher and Humm (1981) note in Florida that the emergent filaments of V. velutina form a dense, green turf that accumulates and stabilises fine sediment, and that a system of colourless rhizoidal filaments penetrate 4–6 cm into the substrate.

As described by Chapman (1962) and Guiry and Guiry (2010), reproduction in Vaucheria can be by vegetative fragmentation of the filaments, by asexual multi-flagellate zoospores produced in club-shaped sporangia, or by oogamous sexual reproduction through the fertilisation of large non-motile egg cells produced in oogonia by motile antherozoids produced in antheridia. The very sparse occurrence of reproductive structures in the Auckland beds of V. velutina suggested that vegetative fragmentation is the common mode of reproduction for bed maintenance and expansion at these sites.

Description and identity of the Vaucheria sample from Orakei Basin

Vaucheria longicaulis Hoppaugh

References. Gallagher and Humm (1981), Christensen (1987b), Entwisle (1988).

Specimen examined. Waitemata Harbour, Orakei Basin, Long 174° 49′, Lat 36° 52′, M.D. Wilcox 4052, 10 May 2010, AK 313152

Description

Vegetative features: Thalli coenocytic, 25–60 µm wide and 100–200 mm long (Fig. 2A). Siphon branching sparse.

Figure 2  Vaucheria longicaulis. A, Vegetative siphons, Orakei Basin, 10 May 2010. B, Antheridium, Orakei Basin, 10 May 2010. C, Developing oogonium, Orakei Basin, 10 May 2010. D, Mature oospore, Orakei Basin, 10 May 2010.

Reproductive features

Dioecious. Oogonia clavate to pyriform, not subtended by a cell (Fig. 2C). Ripe oospores spherical (Fig. 2D). Antheridia (Fig. 2B) subtended by a basal, empty cell, opening by one or several pores on lateral protuberances.

Identification

All the features observed in this sample point to Orakei Basin alga being Vaucheria longicaulis Hoppaugh. It is illustrated by Entwisle (1988), and Womersley (1987) states that this is probably the commonest marine Vaucheria in southern Australia. It also occurs in the USA, and is illustrated from there in Abbott and Hollenberg (1976), Gallagher and Humm (1981), and Dawes and Mathieson (2008). Vaucheria longicaulis is in the Section Piloboloideae. It does not appear to have been recognised before in New Zealand.

Distribution and habitat

Orakei Basin is a 700 m-wide, shallow, saltwater lake, cut off from the sea at Hobson Bay by control gates constructed in the 1920s, and is flushed out on the highest tide every two weeks (Hayward et al. 2008). Two freshwater streams, the Waiatarua and Purewa Creeks, flow into it, and salinities are likely to fluctuate from c. 2.5% to c. 3.5%. Vaucheria longicaulis was found sparsely on the eastern side of the flushed basin attached to stones at the base of tuffaceous banks, and old tyres.

Acknowledgements

Thanks to Tim Entwisle, to Phil Novis and to other referees for helpful advice, and to Bruce Hayward for information about the salinity and flushing regime of Orakei Basin.