A new record of Percursaria percursa (Ulvaceae, Ulvales) on the North Island, New Zealand

Abstract

The filamentous green alga Percursaria percursa (Ulvaceae, Ulvales) was recorded for the first time on the North Island of New Zealand at Ōmokoroa Estuary, Tauranga Harbour. This species is previously known within New Zealand from only two records, both from the South Island. In Tauranga Harbour, this species was restricted to anoxic estuarine sediments where mangrove forests had been mulched, and mulchate left in situ. Percursaria percursa was found intertwined with Ulva spp. and Rhizoclonium spp. Surveys of other North and South Island estuaries suggest that this alga, although occurring as part of nuisance green algal blooms in Tauranga Harbour, has only colonized human-impacted locations, and has not yet been observed in ‘natural’ estuarine ecosystems in New Zealand. As this species was found intertwined with other mat-forming filamentous green algae, it can easily be misidentified in the field, leading to both over- and under-reporting of species occurrence.

Keywords:

• Percursaria percursa
• Ulvaceae
• Tauranga Harbour
• mangrove
• macroalgal blooms
• New Zealand

Introduction

Here we report a new record of the macroalgal species Percursaria percursa (C. Agardh) Rosenv. (Ulvaceae) at Ōmokoroa Estuary, Tauranga Harbour, North Island, New Zealand. Percursaria percursa has previously been recorded only twice in New Zealand waters from South Island localities. Laing (1927, 1932) recorded it from Kaikorai, Dunedin, but this record was questioned by Naylor (1954) as no authenticated voucher was found in Laing's herbarium. Percursaria percursa has also been found from highly modified hypersaline lagoons and channels adjacent to Lake Grassmere, Marlborough (Adams 1994). Based on the few records available for this species, it is currently difficult to determine whether it is an uncommon or cryptic indigenous species or an introduced non-indigenous species.

The genus Percursaria Bory (Ulvaceae) is monotypic and is comprised currently of the single recognized species P. percursa (Guiry & Guiry 2012). The species is widely distributed globally with extensive representation throughout the coastal margins of the Pacific and Atlantic oceans (Garbary et al. 1985; South 1984; Wynne 1986), usually in sheltered bays and inlets in the upper intertidal region (Londry et al. 2005). Percursaria percursa is a filamentous green alga that forms dense, bright green clumped mats on the substrate. While this alga is virtually indistinguishable in the field from other filamentous green algae such as Rhizoclonium spp., it is readily identified in the laboratory with the aid of a compound microscope.

The first documented record of P. percursa on the North Island of New Zealand was at Ōmokoroa Estuary, Tauranga Harbour, in April 2010 (Table 1). Large patches (>1 ha) of filamentous green algae were also observed colonizing disturbed substrates where mangroves were removed in four other estuaries in Tauranga Harbour (Waikareao, Waikaraka, Te Puna and Matua estuaries); however, P. percursa has not yet been documented at these sites. All putative records have been associated with localized disturbances due to deposition of post-removal mulched mangrove (Avicennia marina subsp. australasica (Walp.) J.Everett). Large seasonal blooms of filamentous green algae, similar in timing to blooms of other Ulvaceae such as sea lettuce (Ulva sp.) and other filamentous green algae such as Rhizoclonium spp. (Cladophoraceae), have formed at most mangrove clearing sites; these blooms are probably fuelled by high nutrient availability at these disturbed sites, although in situ nutrient release associated with mangrove mulchate has not been quantified.

Table 1  Collection sites of Percursaria percursa at Ōmokoroa Estuary, Tauranga Harbour, Bay of Plenty, North Island, New Zealand.

Sample ID	Date collected	GPS coordinates	Det.	Voucher
ASK204	10 November 2010	37°39.006′S 176°02.235′E	W. Nelson	WELT A032066
ASK205	10 November 2010	37°39.006′S 176°02.235′E	W. Nelson	WELT A032067
SJP15	23 January 2012	37°39.056′S 176°02.310′E	S. Pratt	WAIK 22539

Distribution and habitat

Percursaria percursa presence in the North Island of New Zealand was confirmed from three collections at Ōmokoroa Estuary, Tauranga Harbour, made in 2010 and 2012. The locality is described as an upper intertidal mudflat of the greater Tauranga Harbour (Table 1). The site is inundated with harbour water twice daily for <6 h per tidal cycle.

We observed P. percursa only on the highly anoxic (oxic layer generally <5 mm deep) mangrove mulchate along with Ulvaceae and other filamentous green algae. These multispecies macroalgal blooms (C. J. Lundquist, NIWA, pers. obs.), including P. percursa, Rhizoclonium spp. and Ulva spp., were found in highest abundance in spring months. Large patches of filamentous green algae were recorded in Ōmokoroa in 2010, and sub-samples confirmed the presence of P. percursa, and did not confirm presence of other filamentous green algae such as Rhizoclonium spp. Detailed sampling in 2012 found macroalgal blooms to be comprised of multispecies aggregations at all locations, suggesting that the large patches of filamentous green algae observed in 2010 were likely to also be multispecies aggregations.

Morphology

We observed mats, both fresh and rehydrated, under×400 magnification on a compound microscope; this was the minimum magnification at which we could make reliable determinations. The thalli of P. percursa are generally unbranched, biseriate filaments (Londry et al. 2005; Guiry & Guiry 2012) (Fig. 1). The filaments are also typically contorted in appearance. The filament cells are square to slightly elongate, typically 10–25 µm wide×10–40 µm in length (Guiry & Guiry 2012). The two rows of cells are more or less symmetrical, with each cell containing a single parietal chloroplast (Londry et al. 2005). It is not uncommon for filaments to become uniseriate for short lengths (Bliding 1963; Londry et al. 2005). The life history of this species alternates between isomorphic gametophytes and sporophytes (Bliding 1963). The species is capable of both asexual and sexual reproduction, producing quadriflagellated zoospores and biflagellated anisogametes, respectively.

Figure 1  Low-light photomicrograph of a biseriate filament of Percursaria percursa (not stained). Sample SJP15, Ōmokoroa Estuary, Tauranga Harbour, Bay of Plenty, North Island, New Zealand.

Percursaria percursa can be easily distinguished under×40 magnification from other filamentous green algae and Ulvaceae with which it often co-occurs, due to its biseriate filaments; Rhizoclonium has uniseriate filaments with square to rectangular-shaped cells and Ulva spp. have two layers of cells (Guiry & Guiry 2012).

Discussion

This record of P. percursa from the North Island of New Zealand adds to the current records of the distribution of this species both in New Zealand and internationally. We refer to the species as non-indigenous given its restricted distribution records which are all associated with sites that have been modified by human activity, however, it is possible that this species is a cryptic and uncommon indigenous species that has evaded detection until recently.

The origin(s) of the population of P. percursa at Ōmokoroa is unknown at this time and monitoring should continue to estimate the extent and frequency of occurrence of this species. Small-scale sampling of macroalgal blooms associated with mangrove removals at selected sites in Auckland and Whangamatā harbours, as well as other sites within Tauranga Harbour (Waikaraka, Waikareao, Te Puna and Welcome Bay estuaries) has not found any P. percursa present. Extensive field sampling in Auckland estuaries in unmodified habitats did not detect this species, and it was not recorded in a national survey of soft sediment habitats in Whāngārei, Otago and Kaipara harbours, though Ulva spp. and Rhizoclonium spp. were recorded in all harbours (Neill et al. 2012). Elsewhere P. percursa is generally found within upper tide-pools and salt marshes (Londry et al. 2005). We observed P. percursa only in association with highly anoxic substrate, generally as part of multispecies blooms with Ulvaceae and other filamentous green algae. This environmental condition is associated with the human modification of the harbour through consented mangrove removal by mulching. In Tauranga Harbour, mangrove management has occurred as a response to increasing mangrove distributions, which are linked to changes in land-based inputs to the harbour (Green et al. 2003). Mangroves in Tauranga Harbour have increased substantially from <20 ha aerial coverage in 1943 to c. 550 ha in 2001 (Park 2004).

Percursaria percursa is not recognized as a nuisance species in the worldwide literature, in comparison with Ulva spp. that form extensive blooms in European and North American estuaries, as well as extensive blooms in Tauranga Harbour (de Winton et al. 1998). Because macroalgal blooms often require management action to mitigate smothering of benthic communities and anoxic conditions, it is likely that the presence of macroalgal blooms on mangrove removal may be delaying return of these managed areas to a healthy ecosystem state (e.g. oxic layer reinstated and macrofauna re-establishment).

Accurate identification of P. percursa requires microscopic examination as this species can easily be mistaken for other filamentous green algae (and vice versa) in the field. Care must be taken to tease apart the mats that commonly consist of tangled filaments of multiple species. Ecologists must be cautious in this regard if their surveys are to be accurate. Identification of P. percursa and Rhizoclonium can also be confirmed via molecular identification, i.e. DNA-barcoding (C.E.C. Gemmill and S. Pratt, University of Waikato, unpublished data).

Acknowledgements

This research was funded in part by a grant to National Institute of Water and Atmosphere Research (NIWA) by the New Zealand Ministry of Science and Innovation (Rehabilitation of Aquatic Ecosystems #C01X1002). Steven Pratt was funded by a University of Waikato Summer Research Scholarship. We are also grateful to the two referees for their constructive comments and suggestions for this manuscript. We thank Dr Svenja Heesch for providing a cultured sample, Dr Barry O'Brien (University of Waikato, UoW) for assistance with photography, and Rebecca Gladstone-Gallagher (UoW), Marenka Weis (NIWA) and Kelly Carter (UoW) for their assistance in the field.