Red Algae (Phylum Rhodophyta, Classes Rhodellophyceae, Compsopogonophyceae, Bangiophyceae, Florideophyceae)
Bladed and branched species of Gigartina showing a range of colours - the axes exposed to higher levels of sunlight have bleached to golden and khak-green tones - growing in the upper subtidal zone on rocky reef covered with pale pink encrusting coralline algae in Taranaki. Photographer K Neill.
Wendy Nelson and Taoho Patuawa
General Description
The red algae, Phylum Rhodophyta, form a very diverse and ancient lineage, characterised by a combination of photosynthetic pigments, as well as the absence of flagella in all life history stages. Although generally pink to purplish in colour, red seaweeds can also range from brown to black, orange and yellow and even appear khaki or green.
Although red algae do not grow as large as brown seaweeds, they display a very wide range of growth forms from single-celled species through to delicate filaments, crusts, densely branched, or expanded blades. Members of the family Delesseriaceae include some of the most delicate thalli found in the red algae. There are many red algal "sheets" which vary in consistency from thick and leathery thalli (eg, Pachymenia, Gigartina spp.) to delicate and membranous blades (eg, Laingia, Pugetia) or to slippery, gelatinous blades (eg, Schizymenia, Kallymenia). There are a number of very mucilaginous red algae-including the pink, inflated branches of Scinaia and the gooey brown-red Helminthocladia. Some red algae are cartilaginous and wiry with growth forms able to withstand wave exposure and sand abrasion (eg, Melanthalia, Gigartina spp.). Finely filamentous species occupy a wide range of niches, growing either directly on rock and other hard substrata such as shells and carapaces of various invertebrates, or growing as epiphytes on other algae. A number of red algae have a prostrate growth form, growing close to the substrate-rock, shells, or other algae. Some of these species are tightly attached, such as Hildenbrandia which forms deep crimson patches on rock surfaces. Others grow as fan-shaped lobes, for example, Peyssonnelia. There are species that form fleshy crusts-the northern Apophlaea sinclairii looks more like tar patches than a red seaweed. There are also species which are not crustose but have a prostrate growth habit and cling to rock surfaces (Rhizopogonia asperata) or wrap around the stipes or axes of large brown algae (Acrosorium decumbens on Xiphophora gladiata, Chlidophyllon kaspar on Sargassum johnsonii). There are red algae that grow as sacs-hollow and filled with watery fluids (bladders of the southern Webervanbossea), or filled with viscous, jelly-like material (eg, Grateloupia intestinalis).
Calcium carbonate is laid down in the cell walls of particular red algae. In some cases this gives the blades a streaky appearance (eg, Curdiea coriacea in northern waters) or a pink to chalky white colour (the soft textured Liagora harveyana of northeastern New Zealand). There is a group of red algae known as corallines that have a solid calcium carbonate framework. Early marine biologists understood this to be a type of skeletal structure and classified these red algae as animals. Some corallines are geniculate or jointed-Haliptilon, Corallina, Jania-while others are non-geniculate and form sheets, discs, or knobbly crusts (Synarthrophyton, Melobesia, Heydrichia). Typically the coralline algae have a distinctive pink to rosy red colour, and when dead they bleach white. Large areas of rocky reefs are covered by pink non-geniculate coralline algae. In some areas of subtidal reefs, sometimes referred to as "barrens" areas, they can cover almost 100% of the reef. It is now realised that these algae play a critical role in the lives of a number of invertebrates by producing certain chemicals that promote the settlement of larvae. These crusts, which have been dismissed as "pink paint" in the past, are now implicated as key settlement and metamorphosis inducers in species of tube worms, chitons, starfish, urchins, hard and soft corals, and paua. Paua (Haliotis sp.) habitats are rich in corallines and research in southern Australia has shown that for at least one species of abalone the larvae settle preferentially on a particular species of coralline. Non-geniculate corallines have also been shown to be a critical food source for juvenile rock lobster.
Some red algae are particularly adapted to live as epiphytes on other algae. Sometimes this is an obligate relationship so that a particular species will grow only on one specific host (eg, Lembergia on Osmundaria, Pleurostichidium on Xiphophora). Many other species, particularly species of finely branched red algae, are capable of growing in a variety of habitats and on a variety of hosts/substrata-living epiphytically, epizoically (eg, on limpet shells, horse mussels) or epilithically on rock substrates. Certain red algae grow only as parasites on other red algae. These parasites are often so reduced in size that they are almost unnoticeable except as pale coloured lumps on the surface of thalli. An interesting feature of these parasites is that they are often very closely related to their hosts and have evolved methods of reproducing to ensure that they can maintain their close relationships with hosts. There are no brown or green algae that are parasitic on other algae.
Red algae have evolved a staggering array of reproductive mechanisms and variations of life-history patterns. Within some species the various stages in the life history have the same appearance, whereas in other species the life history stages have very different appearances. These differences in appearance between stages can be very marked-for example, a large, sheet-like blade alternating with a microscopic filamentous phase. Many of the members of the Rhodophyta have complex life cycles, involving a three-phase life cycle, that includes different phases bearing gametes and spores. Reproductive structures are often important characteristics for taxonomic identification of species. In some species there is a strong seasonal control of reproductive cycles with the various phases of the life histories triggered by changes in temperature, day length, light quality or quantity. There are very marked seasonal differences in the subtidal flora in parts of New Zealand. For example, in springtime in northeastern New Zealand a cluster of red algae appear suddenly, grow rapidly, reproduce, and then disappear again for another 8-10 months-for example, Acrosymphyton, Schmitzia evanescens, and Hummbrella hydra.
The Rhodophyta are divided into five classes, four of which are represented in the NZ marine flora. Globally there are about 8000 species of red algae, most of which are marine. There are 217 genera recorded from New Zealand waters of which 6% are endemic, and 523 species, with 40% of these endemic. However, given the varied evolutionary histories of different orders within the red algae, summary statistics such as these do not convey a full picture of the flora and its relationships. In some orders and families there is very high national or regional endemism. For example, in the Gigartinaceae 21 of the 24 species described from the New Zealand region are endemic and sometimes restricted to particular island groups within the region. Many species of red algae are shared between New Zealand and Australia.
Status
There are species restricted to particular parts of the New Zealand region that are listed as "range restricted" within the Department of Conservation threat classification scheme, such as species of Galaxaura from the Kermadec Islands, Curdiea balthazar from the Three Kings Islands, Pyrophyllon cameronii, an obligate epiphyte found only on Lessonia tholiformis, which is itself restricted to the Chatham Islands. There are also species known from very few collections that are listed as "data deficient", for example Erythrotrichia hunterae and Sebdenia lindaueri.
Key Locations
Red algae can be found throughout the New Zealand region in coastal areas and along the fringe of offshore islands, occurring in intertidal and subtidal areas to a depth of 60 m in offshore areas. Red algae are found from the high to middle intertidal zone (eg, species of Porphyra, Bangia, Apophlaea) through to deep coastal waters where there is sufficient penetration of sunlight to allow photosynthesis to occur. The deepest seaweeds known from the New Zealand region are non-geniculate coralline crusts dredged from 200 m in the clear warm waters around the Kermadec Islands.
On rocky reefs, red algae can comprise the dominant understorey species beneath kelp. The biological structure of fleshy and filamentous red algae represent an important habitat for grazers, such as amphipods, isopods, and gastropods. These algae are also an important food source for a wide range of mobile invertebrate species, such as sea urchins, as well as for herbivorous fishes. Non-geniculate coralline algae are important for the settlement of some mobile invertebrate species such as paua.
In some soft-sediment environments, free-living, non-geniculate coralline algae, or rhodoliths, are found. The locations of rhodolith beds are not well documented in New Zealand. One area where rhodoliths are found is in the channel between Kapiti Island and the Waikanae coast north of Wellington. Internationally these habitats are recognised as being hotspots of biodiversity for many invertebrate species and juvenile fishes.
Summary of Threats
Sustainable harvest of seaweeds requires management based on knowledge of algal biology and ecology. Agar and carrageenan are hydrocolloids that are produced only by certain red seaweeds. The size and complexity of these compounds means that they cannot be made artificially, so they have to be extracted from the cell walls of seaweeds. In New Zealand an agar extraction industry began in the 1940s based on the harvest of the red algae Pterocladia lucida and Pterocladiella capillacea. There are many species of carrageenan seaweeds found in New Zealand: there have been small commercial harvests of Gigartina spp. to make gelling milk puddings and there is interest in the possibility of farming species that produce particular commercially valuable forms of carrageenan. In some species of carrageenan seaweeds the tetrasporophyte and the gametophyte stages produce different forms of carrageenan which have very different industrial properties. In many cases little is known about the ecology of New Zealand agarophytes and carrageenophytes.
Human actions that result in changes to coastal reefs may be having more profound impacts than realised. Corallines are very sensitive to excess nutrients from human interventions. Sewage pollution decreases coralline algal cover and there is an inverse relationship between corallines and sedimentation: terrestrial runoff smothers corallines. This not only kills the algae but also will inhibit the recruitment of invertebrates, and thus have far-reaching impacts on the whole reef community. The maintenance of healthy coralline communities is an imperative for maintaining recruitment and sustainability throughout the community.
Understorey algal species provide habitat and structure within rocky reef communities as well as contributing significantly to the biomass and food supplies for herbivorous fishes and invertebrates. Unfortunately, species of subtidal red algae have received little direct study in New Zealand, and there has been little research on the ecological processes affecting the organisation of algal assemblages. There are complex interactions between predators, herbivores, canopy, and understorey species. In order to understand the interactions between different components of the community, information is required about the specific life histories and seasonal behaviours of particular species.
Of the 24 invasive species of seaweed currently recognised in New Zealand, 12 are red algae (Nelson 1999; McIvor et al. 2001). None of these is considered to pose a serious risk to native flora or fauna. In some cases they are locally abundant but restricted in their distribution (eg, Chondria harveyana). One species appears to form a substantial biomass in the Auckland region (Orakei Basin and Manukau Harbour), but it is not clear how long the populations have been present in these habitats or how widespread the species has become. Investigations of polysaccharide chemistry and rbcL sequences place this species within the Solieriaceae. In addition, there is a species of Gracilaria in Manukau Harbour that is very similar in appearance to G. chilensis but which differs from this species in its chemistry (Wilcox et al. 2001).
Typical Habitats
Although not as conspicuous as the large brown algae, the red algae play integral roles in nearshore rocky reefs as primary producers, habitat formers, and as determiners of invertebrate settlement and recruitment. Red algae are found in most coastal situations where there is solid substrate for attachment, and sufficient light for growth. In general, red algae are not well adapted to low salinity environments and are not typically found in brackish conditions.
State of Information
There is a critical need for taxonomic studies of genera and families of New Zealand red algae. It is difficult to select the most problematic groups-there are serious shortfalls in virtually all families. As so few taxa have received detailed attention, it is not clear how the current estimates of species numbers reflect the actual biodiversity of New Zealand red algae.
The non-geniculate coralline algae have been acknowledged as poorly known in New Zealand and recent attention has been directed both to coralline taxonomy and to the identification of non-geniculate species (Harvey et al. 2005). Non-geniculate corallines are present throughout low intertidal and subtidal shores and have been clearly implicated in the settlement and development of invertebrates such as paua. Given their apparent ecological significance and ubiquity, it is important that we have a better understanding of the distribution and regional and ecological variability in the species diversity of this group.
The New Zealand members of the Gigartinaceae are very diverse and their systematics is very poorly understood at present. This is at a time when there are world shortages of particular isomers of carrageenan and strong interest in the potential for aquaculture of these seaweeds. At present the lack of systematic, biological, and ecological information is a serious bottleneck in the development of the economic potential of these algae. Research on the Bangiales in New Zealand has uncovered unexpected diversity (eg, Nelson et al. in press). Given the cultural significance of karengo (see below) and its use internationally as a food crop, there is a need to gain a fuller understanding of these species.
Significance for Maori
Karengo, Porphyra, is highly prized by the Maori community but is little known to most other New Zealanders. Porphyra species are listed as taonga or treasures in the Ngai Tahu Claims Settlement Act 1998 and are to be reserved for traditional uses. This settlement prohibits any commercial use of Porphyra within the Ngai Tahu tribal area. The genus of red seaweed grows throughout the world and is highly valued as a food. In Japan it is known as nori and is extensively farmed. The seaweed sheets that wrap around Japanese sushi are made from Porphyra.
Key References
Adams, N M. 1994. The seaweeds of New Zealand. An illustrated guide. Canterbury University Press. 360pp.
Francis, M P and Nelson, W A. 2003. Biogeography. In: The living reef. The ecology of New Zealand's rocky reefs. (eds) Andrew, N L and Francis, M P. Craig Potton Publishing, Nelson.
Harvey, A, Woelkerling, W, Farr, T, Neill, K and W Nelson. 2005. Coralline algae of central New Zealand: an identification guide to common 'crustose' species. NIWA Information Series No. 57. 145pp.
Hurd, C L, Nelson, W A, Falshaw, R and K Neill. 2004. History, current status and future of marine macroalgae research in New Zealand: taxonomy, ecology, physiology and human uses. Phycological Research 52: 80-106.
McIvor, L, Maggs, C A, Provan, J and M J Stanhope. 2001: rbcL sequences reveal multiple cryptic introductions of the Japanese red alga Polysiphonia harveyi. Molecular Ecology 10: 911-919.
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 N. Andrew and M. Francis, (eds). The Living Reef. The ecology of New Zealand's rocky reefs. Craig Potton Publishing, Nelson, New Zealand. 283pp.
Nelson, W A, Farr, T J and J E S Broom. In press a: Phylogenetic relationships and generic concepts in the red order Bangiales: challenges ahead. Phycologia.
Wilcox, S J, Bloor, S, Hemmingson, J A, Furneaux, R H and W A Nelson. 2001. The presence of gigartinine in New Zealand Gracilaria. Journal of Applied Phycology13: 409-413.
Also: www.seaweed.ie
Table 28: Red Algae (Phylum Rhodophyta) in New Zealand
| Class | Order | Family | Endemic species | Total species |
|---|---|---|---|---|
| Bangiophyceae | Bangiales | Bangiaceae | 7 | |
| Erythropeltidiales | Erythrotrichiaceae | 5 | 9 | |
| Porphyridiales | Porphyridiaceae | 3 | ||
| 5 | 19 | |||
| Rhodophyceae | Acrochaetiales | Acrochaetiaceae | 2 | 10 |
| Batrachospermales | Psilosiphonaceae | 1 | ||
| Bonnemaisoniales | Bonnemaisoniaceae | 3 | 8 | |
| Ceramiales | Ceramiaceae | 24 | 74 | |
| Dasyaceae | 6 | 12 | ||
| Delesseriaceae | 8 | 37 | ||
| Rhodomelaceae | 26 | 78 | ||
| Corallinales | Corallinaceae | 11 | 28 | |
| Gelidiales | Gelidiaceae | 6 | 10 | |
| Gigartinales | Acrosymphytaceae | 1 | 1 | |
| Calosiphoniaceae | 1 | 1 | ||
| Caulacanthaceae | 1 | 4 | ||
| Cystocloniaceae | 1 | 6 | ||
| Gigartinaceae | 16 | 24 | ||
| Gloiosiphoniaceae | 1 | |||
| Hypnaceae | 3 | |||
| incertae sedis | 1 | 1 | ||
| Kallymeniaceae | 8 | 15 | ||
| Nemastomaceae | 2 | 5 | ||
| Peyssonneliaceae | 1 | 5 | ||
| Phacelocarpaceae | 2 | |||
| Phyllophoraceae | 2 | 4 | ||
| Pseudoanemoniaceae | 1 | |||
| Rhizophyllidaceae | 1 | |||
| Sarcodiaceae | 3 | 4 | ||
| Schizymeniaceae | 1 | 5 | ||
| Solieriaceae | 1 | 2 | ||
| Gracilariales | Gracilariceae | 6 | 9 | |
| Pterocladiophilaceae | 1 | |||
| Halymeniales | Halymeniaceae | 9 | 20 | |
| Sebdeniaceae | 1 | 1 | ||
| Hildenbrandiales | Hildenbrandiaceae | 2 | 6 | |
| Nemaliales | Galaxauraceae | 4 | 11 | |
| Liagoraceae | 10 | |||
| Palmariales | Palmariaceae | 1 | ||
| Rhodothamniellaceae | 2 | |||
| Plocamiales | Plocamiaceae | 1 | 7 | |
| Rhodymeniales | Champiaceae | 3 | 6 | |
| Faucheaeceae | 2 | 6 | ||
| Lomentariaceae | 4 | 5 | ||
| Rhodymeniaceae | 4 | 18 | ||
| 161 | 446 | |||
| Grand Total | 166 | 465 |
Figure 81: Agar weed Pterocladia capillacea annual distribution.
Figure 82: Agar weed Pterocladia lucida annual distribution.
Figure 83: Bronze karengo Porphyra cinnomomea annual distribution.
Figure 84: High golden karengo Porphyra coleana annual distribution.
Figure 85: Gracilaria Gracilaria chilensis annual distribution.