Brown Algae (Division Heterokontophyta, Class Phaeophyceae)
Brown algae in low intertidal zone-central large thallus of Durvillaea antarctica, beaded thalli of Hormosira banksii-growing on exposed rocky reef at Kaikoura. Photographer K. Neill.
Wendy Nelson, Franz Smith and Taoho Patuawa
General Description
Brown seaweeds are usually brown to olive in colour, owing to their characteristic photosynthetic pigments, and are classified in the division Heterokontophyta (class Phaeophyceae). This group contains most of the large conspicuous algae seen along rocky shores and in shallow-water environments, typically attached to rock or other firm surfaces. The morphology of members of this group varies dramatically-species range in size and form from microscopic filaments, through to sacs, tubes, and blades, to massive leathery kelps that can be metres in length.
Large brown algae create habitats by providing forest structure for fish and invertebrate species and creating conditions in the subcanopy for other algae. Along exposed coasts, thick beds of brown macroalgae help to dampen wave shock, as well as providing habitat and refuge for intertidal and shallow subtidal species. Smaller brown algae can also be important in structuring habitats when they grow as dense mats or extensive areas of crusts.
Brown seaweeds are key primary producers in intertidal, shallow, and deep subtidal reefs. Some species are grazed by herbivorous invertebrates and fishes, whilst others produce compounds which help to deter grazing. Organic materials produced by brown algae are released into the water column as dissolved compounds and particulate fragments and these become food sources for bacteria, and species feeding on detritus, as well as suspension-feeding invertebrates. Drift and beachcast brown algae are also important sources of organic material in coastal food chains. The importance of seaweed production also can extend into deep-sea environments, particularly in higher latitude and polar systems, through drift biomass.
There are many types of life histories found amongst members of the brown algae. In some species the independent stages of the life history have completely different appearances and growth habits. In some species alternating life history stages are cued to particular seasons: the morphologically different phases may also occupy very different ecological niches. In the true kelps such as Ecklonia and Macrocystis, large bladed kelps produce spores which grow into the microscopic, sexual phase of the life history. In other species such as Neptune's necklace, Hormosira, and the bull kelp, Durvillaea, there are no alternative life stages.
Brown algae produce swimming spores, but the dispersal abilities of most species are unknown. In those that have been studied, it appears that spores or gametes settle relatively quickly and thus dispersal is generally within metres of parent. In species that are buoyant, drifting fertile thalli have the potential to increase long-distance dispersal.
Some brown algae are strongly seasonal in their distribution whilst others are perennial. Growth is typically seasonal, with peak production tending to occur during summer months when temperatures are higher and there are more sunlight hours. However, the availability of macronutrients, as well as the physical conditions such as wave exposure and current flow, are also key factors influencing growth and primary production. It has been estimated that species of bull kelp can live for about five to eight years. It is likely that some crustose species are longer lived but there is little known about the longevity or demography of brown algae in New Zealand.
Brown algae are used commercially in a range of products-in human food (as sea vegetables, dietary supplements, food garnish, salt substitute), stock food for feeding to aquacultured paua, and in seaweed-based fertilisers (domestic and agricultural), as well as a source of the polysaccharide alginate. There is research and commercial interest in bioactive compounds found in brown algae.
There are currently 156 species of brown algae recorded in New Zealand waters, representing about 8.5% of the global flora of Phaeophyceae (ie, about 1800 species worldwide). In New Zealand, there are representatives from 10 orders and 24 families. About a third of the species within New Zealand are endemic, exhibiting a relatively high degree of regional endemism, and similar to that recorded for southern Australian brown algae. A number of species in New Zealand are also found in Australia, and there are also relationships with the brown algal floras in southern Africa and southern South America.
Status
About 13 species of brown algae have been identified as examples of range restricted macroalgae, endemic to specific island groups. There are species of Durvillaea, Lessonia, and Landsburgia found only on the Chatham Islands, and on the Three Kings Islands there is an endemic genus, Perisporochnus, as well as endemic species of Sargassum and Landsburgia.
Key Locations
The most distinctive features of the brown macroalgae found on New Zealand shores are the predominance of Fucalean species, many of which are endemic or restricted to Australasia, and the iconic southern bull kelp species in the genus Durvillea which form a conspicuous presence in the low intertidal and subtidal zones. In contrast with northern Pacific shores there is a very low diversity of Laminarian genera in New Zealand.
In warm northern waters around the Kermadec Islands there is not a conspicuous flora of large brown algae, although there is high diversity of members of the Dictyotales. Many of these genera and species are known from other parts of the warm Indian and Pacific Oceans but not found on mainland New Zealand. In the northern North Island, Ecklonia forests predominate along with species of Carpophyllum, whereas from around Cook Strait southwards, large brown algae such as Macrocystis, Lessonia, bull kelps, Cystophora spp. and other Fucales become more conspicuous.
Summary of Threats
Human-induced modifications of seaweed habitats affect brown algae. There are 11 species of brown algae that are considered to have been introduced accidentally into New Zealand waters. Some of these have very restricted distributions and are unlikely to pose any serious threat to coastal systems. However, the large Asian kelp Undaria pinnatifida is proving to be an invasive species, and has spread from its first discovery in Wellington in 1987 to many sites in the North and South islands, and Stewart Island. Research using genetic markers has revealed that this species has been introduced multiple times to New Zealand. As a habitat-shaper Undaria poses a significant threat to New Zealand marine communities. It competes successfully for substrate by producing many spores and recruiting to a wide variety of depths, from the low intertidal through to subtidal, as well as growing in harbours and on the open coast. This capacity to recruit and grow in a wide array of habitats enables Undaria to potentially out-compete and negatively influence native species. Undaria modifies habitats by creating shade and thus altering the light environment for nearby species, and it also appears to modify the sedimentation rate within a stand of kelp.
Typical Habitats
Brown algae are found in most coastal situations where there is solid substrate for attachment, and sufficient light for growth. In general brown algae are not well adapted to low-salinity environments and are not typically found in brackish conditions.
State of Information
Although the Phaeophyceae are the best known of all macroalgae in New Zealand, there still remains much to discover about these algae. There is no doubt there are more species to be discovered in the New Zealand region. In the past 13 years new species belonging to some of the largest and most conspicuous genera have been discovered and described, for example two species of Lessonia, and one each of Marginariella, Landsburgia, and Zonaria. Fundamental research on life histories, development, and growth is still required for a number of New Zealand species, as well as research on the demography and ecology of most species.
The contributions of brown seaweeds in nearshore systems, both as habitat formers and as sources of primary production, require further research. This is particularly important where there are proposals for commercial harvest of habitat-forming species. There is a need to consider the time of year of harvest, harvest methods, frequency, and intensity, and the impact these may have on recruitment and recovery of the target species/population, as well as on associated species, other algae, and fish and other invertebrates.
Significance for Maori
Seaweeds are collectively called rimu or rimurimu in the Maori language. Of the brown algae, Durvillaea (ie, bull kelp, Durvillaea antarctica) and Porphyra (karengo) hold special significance for the Maori people. Traditionally, and still to this day, southern Maori used the wide blades of Durvillaea antarctica as storage bags or poha titi to store mutton birds (titi-see chapter on Shearwaters) in their own fat. The blades of the kelp were inflated-blown up like natural balloons-and strengthened externally with totara bark. Durvillaea species are listed as taonga in the Ngai Tahu Claims Settlement Act 1998 and are to be reserved for traditional uses. This settlement prohibits any commercial use of Durvillea within the Ngai Tahu tribal area.
Key References
Adams, N M. 1994. Seaweeds of New Zealand. Canterbury University Press, Christchurch, New Zealand. 360pp.
Habib, G. 1987. Korekore Piri Ki Tangaroa. Maori Involvement in the Fishing Industry. Department of Maori Affairs. 205pp.
Hurd, C. (2003) Bull Kelp. In: The Living Reef: The ecology of New Zealand's rocky reefs. Andrew, N L and Francis, M P (eds). 56-63pp. Craig Potton Publishing, Nelson, New Zealand.
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.
Nelson, W A. 1994. Distribution of macroalgae in New Zealand - An archipelago in space and time. Botanica Marina 37: 221-233.
Orbel, M. 2003. Birds of Aotearoa. A Natural and Cultural History. Reed Publishing. 198pp.
Schiel, D R. (2003) Common kelp. In: The Living Reef: The ecology of New Zealand's rocky reefs. Andrew, N L and M P Francis (eds). 64-71pp. Craig Potton Publishing, Nelson, New Zealand.
Schiel, D R, and Hickford, M J H. (2001) Biological structure of nearshore rocky subtidal habitats in southern New Zealand. Science for Conservation 182. 54 pp.
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 27: Brown Algae (Phylum Phaeophyta) in New Zealand
| Class | Order | Family | Endemic species | Total species |
|---|---|---|---|---|
| Chrysophyceae (?) | Chrysomeridales | ? | 1 | |
| Total | 0 | 1 | ||
| Phaeophyceae | Cutleriales | Cutleriaceae | 1 | 3 |
| Desmarestiales | Desmarestiaceae | 2 | ||
| Dictyotales | Dictyotaceae | 3 | 24 | |
| Durvillaeales | Durvillaeaceae | 3 | 4 | |
| Ectocarpales | Chordariacae | 2 | 5 | |
| Chordariopsidaceae | 1 | |||
| Delamareaceae | 1 | |||
| Ectocarpaceae | 5 | 16 | ||
| Elachistaceae | 1 | 2 | ||
| incertae sedis | 1 | 2 | ||
| Leathesiaceae | 2 | 5 | ||
| Myrionemataceae | 3 | 5 | ||
| Myriotrichiaceae | 1 | |||
| Punctariaceae | 1 | 3 | ||
| Ralfsiaceae | 1 | 3 | ||
| Scytosiphonaceae | 9 | |||
| Spermatochnaceae | 1 | |||
| Striariaceae | 1 | |||
| Fucales | Cystoseiraceae | 4 | 9 | |
| Fucaceae | 1 | 2 | ||
| Hormosiraceae | 1 | |||
| incertae sedis | 1 | 1 | ||
| Notheiaceae | 1 | |||
| Sargassaceae | 7 | 11 | ||
| Seirococcaceae | 3 | 3 | ||
| Laminariales | Alariaceae | 1 | 3 | |
| Lessoniaceae | 4 | 5 | ||
| Scytothamnales | incertae sedis | 2 | ||
| Scytothamnaceae | 2 | |||
| Splachnidiaceae | 1 | |||
| Sphacelariales | Cladostephaceae | 1 | ||
| Sphacelariaceae | 3 | 9 | ||
| Stypocaulaceae | 7 | |||
| Sporochnales | Sporochnaceae | 3 | 7 | |
| Total | 50 | 153 | ||
| Xanthophyceae | Vaucheriales | Vaucheriaceae | 0 | 6 |
| Total | 0 | 6 | ||
| Grand Total | 50 | 160 |
Figure 75: Caulerpa Caulerpa brownii annual distribution.
Figure 76: Bull kelp Durvillaea antarctica annual distribution.
Figure 77: Chatham Islands bull kelp Durvillaea chathemensis annual distribution.
Figure 78: Bull kelp Durvillaea willana annual distribution.
Figure 79: Bladder kelp Macrocystis pyrifera annual distribution.
Figure 80: Lessonia Lessonia variegate annual distribution.