Green Macroalgae (Division Chlorophyta, Classes Ulvophyceae, Trebouxiophyceae, Prasinophyceae pro parte)
Wendy Nelson and Taoho Patuawa
General Description
The phylum Chlorophyta includes both attached and planktonic algae, with terrestrial, freshwater, and marine representatives. The benthic marine macroalgae included in this phylum are readily recognisable by their characteristic green pigmentation, although their growth forms are very diverse, ranging from fine filaments, crusts, sacs, tubes, sheets, cushions, clusters of beads, and thick spongy thalli.
The most commonly recognised green algae are species of sea lettuce or Ulva which grow as either blades or tubes, and can be found intertidally and subtidally. The taxonomy of this common genus is very poorly understood. The spongy textured green Codium comes in a number of forms, growing either as thalli that are divided into dark green finger-like branches, or as crusts, which can be convoluted, glassy and smooth, or form domed circular patches. Despite these different appearances, all species in the genus have very similar coenocytic construction (a continuous cellular matrix without crosswalls in which there are many nuclei and chloroplasts). The genus Caulerpa is well represented in New Zealand, particularly in the north. There are nine species that vary in form, with blades that are either feathery, beaded, or look like young rimu leaves: these species are also coenocytic.
In this treatment, the green seaweeds are placed into three classes. Some placements are provisional. As more data come to hand, and the understanding of green algal phylogeny increases, it is likely that there will be further adjustments to the classification scheme. The Ulvophyceae includes unicellular, multicellular, and siphonocladous non-flagellated green algae, including almost all green seaweeds. There are five orders recognised in the New Zealand flora. The Trebouxiophyceae includes the genera Prasiola and Rosenvingiella (Prasiolales), formerly placed in the Ulvophyceae. The palmelloid crust, Palmophyllum umbracola, found in northern waters (the Kermadec and the Poor Knights islands), is provisionally placed in the Prasinophyceae, although the class and ordinal affinities of this genus remain unclear.
There are 130 species of green marine macroalgae currently recorded in New Zealand, with 38 of them being considered endemic to the region (ie, 27%). There are representatives of 7 orders and 19 families.
Status
There are some interesting regional features in the green algal flora. At the Kermadec Islands warm-water affinities of the flora are reflected in the presence of Caulerpa racemosa, C. webbiana, Codium arabicum, C. geppiorum, Acetabularia parvula and Boodlea composita. These species are widespread in tropical and subtropical waters, but not found on mainland New Zealand, and hence recorded as "range restricted" within the Department of Conservation threat-classification scheme. There are small endophytic green algae, which are poorly known, that are classified as "data deficient", as they have been rarely collected and little studied (eg, Ovillaria-an endemic genus; Acrochaete endostraca-an endemic species).
In some harbours and estuaries excessive growth of species of Ulva results in green meadows, which are sometimes known as "green tides". This phenomenon is associated with areas of enrichment and usually quiet harbour/estuarine environments. One consequence of this rapid growth is a build up of biomass. When this seaweed accumulates and then is washed ashore, the rotting masses create a public nuisance.
Only one green macroalga has been reported as an alien in New Zealand waters-Codium fragile subsp. tomentosoides. The impact and risk presented by this species is far from clear (Nelson 1999): although it has been suggested that it has become widespread in the northeastern North Island (Trowbridge 1995) there are very few specimens in collections or vouchered records to substantiate its spread.
There is no commercial use of green seaweeds harvested in New Zealand at present, although some marine farming sites (from Coromandel through to Stewart Island) have been licensed for farming Ulva (Zemke-White et al. 1999), and Ulva is imported for human food use.
Key Locations
Green algae occur throughout the New Zealand archipelago with the genera Codium and Caulerpa well represented in the north, particularly at the Kermadec and Three Kings islands, but with some species also extending into colder southern waters. The lack of taxonomic understanding of other key genera limits our understanding of their distribution.
Summary of Threats
Human-induced modifications of seaweed habitats affect green algae: there are no threats specific to green algae. There is a single introduced green seaweed in New Zealand-Codium fragile ssp. tomentosoides. This subspecies has been highly invasive in other parts of the world where it has been called "oyster thief". In New Zealand it appears to be restricted to the northeastern North Island.
Typical Habitats
Green macroalgae occur high on the intertidal shore, in tidal pools and channels, as well as in rocky reef environments, sometimes to considerable depths. Some green algae can grow in areas of softer sediments, either growing on shell fragments and small stones, or extending from solid substrata across softer sediments with stolons or runners (eg, species of Caulerpa). A few species are tolerant of brackish conditions and occur in harbours and estuaries. The highest macroalgae found on the shore are species of Prasiola which grow in the spray zone of the upper intertidal amongst the guano of seabird rookeries. The deepest recorded green alga in New Zealand, the prostrate Palmophyllum umbracola, has been found at 70 m in the clear waters of the Kermadec Islands (Nelson and Adams 1984).
In addition to growing epilithically, green algae can be found growing within the lamellae of mollusc shells and within some types of rock (Nielsen 1987), Other species grow as epiphytes or endophytes, such as the green alga Sporocladopsis novae-zelandiae, which is an obligate epiphyte of species of the brown kelp Lessonia. No green algae have flotation devices as found in some brown algae, and few species of green algae can survive free-living for more than a very short period adrift on open coasts, as they are tossed ashore or sink into subtidal drifts. The exception to this is in sheltered estuaries and harbours where unattached species of Ulva can grow very large (in excess of 1.5 metres in length).
State of Information
The systematic knowledge of the New Zealand green macroalgae is seriously deficient. The most speciose genera are also the ones with the most serious taxonomic problems (eg, Ulva sensu lato, Monostroma, Cladophora, Bryopsis, Chaetomorpha). Genera such as Gemina, Lobata, Letterstedtia need serious examination. In addition, type specimens of some taxa described by Chapman have not been located. For example, Bryopsis kermadecensis V J Chapm., described as endemic to the Kermadec Islands and known only from the type collection cannot be verified because the specimen is missing.
Some genera and/or species are well represented in collections because they are readily distinguished in the field and thus the distributional information about them may be considered to be sound (eg. some species of Codium, Caulerpa, Chaetomorpha). In some other genera (eg, Ulva sensu lato, Cladophora) the current knowledge cannot be regarded as reliable.
In the absence of modern systematic studies it is very hard to assess the total number of green macroalgae present in New Zealand waters. Although there have been collections made throughout the region, without a sound systematic framework it is difficult to know how well the existing collections encompass the actual diversity. The more remote parts of the New Zealand region (the Kermadec and the Chatham islands, the subantarctic islands) have been relatively infrequently visited, and seasonally representative collections have not been made. Parsons (1985) considered that once the green algae are revised fewer species will be recognised in New Zealand, although there are also unrecorded species and new species that will require description.
Significance for Maori
Sea lettuce, Ulva spp., is listed as a taonga species in the Ngai Tahu Deed of Settlement within the claim area, and also in the Ngati Tama protocol area (North Taranaki).
Key References
Adams, N M. 1994. Seaweeds of New Zealand. Canterbury University Press. 360pp.
Nelson, W A. 1999. A revised checklist of marine algae naturalised in New Zealand. New Zealand Journal of Botany 37: 355-359.
Nelson, W. 2004. Chapter 6. Green and red seaweeds. 48-55pp in Andrew, N and Francis M, editors. The Living Reef: The ecology of New Zealand's rocky reefs. Craig Potton Publishing, Nelson, New Zealand. 283pp.
Nelson, W A, and Adams, N M. 1984. Marine algae of the Kermadec Islands. National Museum of New Zealand, Miscellaneous Series 10: 1-29.
Nielsen, R. 1987. Marine algae within calcareous shells from New Zealand. New Zealand Journal of Botany 25: 425-438.
Parsons, M J. 1985. New Zealand seaweed flora and its relationships. New Zealand Journal of Marine and Freshwater Research 19: 131-138.
Trowbridge, C D. 1995. Establishment of the green alga Codium fragile ssp. tomentosoides on New Zealand rocky shores: current distribution and invertebrate grazers. Journal of Ecology 83: 949-965.
Zemke-White, W L, Bremner, G and C L Hurd. 1999. The status of commercial algal utilization in New Zealand. Hydrobiologia 398/399: 487-494.
Also www.seaweed.ie
Table 29: Green Macroalgae (Division Chlorophyta, Classes Ulvophyceae, Trebouxiophyceae, Prasinophyceae pro parte) in New Zealand
| Class | Order | Family | Genera | Endemic species | Total species |
|---|---|---|---|---|---|
| Ulvophyceae | Ulotrichales | Acrosiphonaceae | 2 | 0 | 2 |
| Endosphaeraceae | 1 | 1 | 2 | ||
| Monostromaceae | 2 | 4 | 9 | ||
| Ulotrichaceae | 1 | 1 | 2 | ||
| Capsosiphonaceae | 1 | 1 | 1 | ||
| Ulvales | Gomontiaceae | 1 | 0 | 1 | |
| Phaeopilaceae | 1 | 0 | 1 | ||
| Ulvaceae | 6 | 12 | 33 | ||
| Ulvellaceae | 7* | 4 | 11 | ||
| Cladophorales | Anadyomenaceae | 1 | 0 | 1 | |
| Cladophoraceae | 4 | 5 | 26 | ||
| Siphonocladaceae | 2 | 1 | 3 | ||
| Bryopsidales | Bryopsidaceae | 4 | 6 | 11 | |
| Caulerpaceae | 1 | 0 | 9 | ||
| Codiaceae | 1 | 1 | 11 | ||
| Ostreobiaceae | 1 | 0 | 1 | ||
| Dasycladales | Polyphysaceae | 1 | 0 | 1 | |
| 37 | 36 | 125 | |||
| Trebouxiophyceae | Prasiolales | Prasiolaceae | 2 | 1 | 4 |
| 2 | 1 | 4 | |||
| Prasinophyceae | incertae sedis | incertae sedis | 1 | 1 | 1 |
| 1 | 1 | 1 | |||
| Grand Total | 40 | 38 | 130 |
*Family contains one endemic genus