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THE ECOLOGICAL EFFECTS OF Undaria pinnatifida:
A Critical Assessment and Summary of the Literature
6 May 1999
Paul R Dean. BSc, Dip Sci, MSc (Dist).
In todays world, Scientific advice is often used to make decisions that have strong and wide
ranging repercussions. If this advice is poor or inaccurate the results of the decisions can
be costly. While writing my masters thesis on the eco-physiology of the seaweed Undaria
pinnatifida (Harvey) Suringar, I encountered many articles on the ecological effects of the
introduction of this seaweed. Many of the conclusions of these articles were contradictory.
This report is my endeavour to sort out the facts and provide a basis for a scientific
assessment.
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INTRODUCTION
Over the last decade a number of studies and reports on the ecological effects of the
introduced seaweed Undaria pinnatifida and surveys of U. pinnatifida that make
statements about it’s ecological effects have been conducted. Many of these reports and
surveys derive conclusions that are different and opposing to each other. This makes it
difficult to quickly assess what the true ecological effects of U. pinnatifida are. To my
knowledge no one has examined the findings of all these reports and scrutinised the
scientific methods used, or for literature surveys the accuracy and range of references
examined. This is the objective of this report.
Twenty articles making statements on the ecological effects of Undaria pinnatifida dated
up until May 1998 were found (Table 1). It is the information provided by these that I am
critically assessing so that a scientifically valid picture of the ecological effects of U.
pinnatifida may be attained. Of the twenty articles making statements about the ecological
effects, four were pure literature searches with no fieldwork or experimental component.
Fourteen had some form of biological survey work (usually performed by SCUBA) ranging
from very minor surveys to compliment a literature search, to large scale surveys of U.
pinnatifida distribution, with none of the surveys having any experimental component.
The remaining two articles had experimental work examining the ecological effects of U.
pinnatifida.
The main body of this report is divided into 3 sections. The 1st section briefly explains the
basic attributes, as determined by prominent ecologists, that an ecological study on
competitive interactions must possess to be of scientific value. The 2nd section is large, and
progresses through all twenty articles, examining the findings and opinions contained
within the articles, and critically assessing the articles validity in respect of the methods
used and the attributes discussed in section 1. The 3rd and final section combines the
results from section 2 and provides an assessment of Undaria pinnatifida’s ecological
impact based on these results and further scientific literature.
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Table 1. Articles examined.
Houghton, C., Lawrence, B., Lettink, M., Numata, M. 1997: Environmental
Lit
impact assessment: ecological and economic impacts of Undaria pinnatifida
in New Zealand. Project for Diploma in Wildlife Management, Zoology
Department, University of Otago, New Zealand.
Parsons, M J. 1995: Status of the introduced brown seaweed Undaria in New
Lit
Zealand. Conservation Advisory Science Notes No 112. Department of
Conservation, Wellington, New Zealand.
Rueness, J. 1989: Sargassum muticum and other introduced Japanese
Lit
macroalgae: Biological pollution of European coasts. Marine Pollution
Bulletin Vol 20, no 4: 173-176
Walker, D I., Kendrick, G A. 1998: Threats to macroalgal diversity: marine
Lit
habitat destruction and fragmentation, pollution and introduced species.
Botanica Marina 41: 105-112
Battershill, C., Miller, K., and Cole, R. 1998: The understorey of marine
Sur
invasions. Seafood New Zealand, March 1998, pp 31-33
Brown, M T. and Lamare, M D. 1994: The distribution of Undaria pinnatifida
Sur
(Harvey) Suringer within Timaru Harbour, New Zealand. Japanese Journal of
Phycology 42: 63-70
Casas, G N. and Piriz, M L. 1996: Surveys of Undaria pinnatifida
Sur
(Laminariales, Phaeophyta) in Golfo Nuevo, Argentina. Hydrobiologia
326/327: 213-215
Castric-Fey, A., Girard, A., and L’Hardy-Halos, M Th. 1993: The distribution
Sur
of Undaria pinnatifida (Phaeophyceae, Laminariales) on the coast of St Malo
(Brittany, France). Botanica Marina 36: 351-358
Fletcher, R L., Manfredi, C. 1995: The occurrence of Undaria pinnatifida
Sur
(Phaeophyceae, Laminariales) on the south coast of England. Botanica
Marina 38: 355-358
Floc’h, J Y., Pajot, R., and Wallentinus, I. 1991: The Japanese brown alga
Sur
Undaria pinnatifida on the coast of France and its possible establishment in
European waters. Journal du Conseil. Conseil International Pour l’Eploration
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The Ecological Effects of Undaria pinnatifida
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de la Mer. 47: 379-390
Hay, C H. 1990: The dispersal of sporophytes of Undaria pinnatifida by coastal
Sur
shipping in New Zealand, and implications for further dispersal of Undaria in
France. British Phycological Journal 25: 301-313
Hay, C H. 1990/1991: Ecological implications of the adventive kelp Undaria
Sur
pinnatifida. DOC Science Project Summaries 1990/1991. Conservation
Estate Management and Advocacy, Science, and Research Internal Report No
119, pgs 11-12
Hay, C H. and Luckens, P A. 1987: The Asian kelp Undaria pinnatifida
Sur
(Phaeophyta: Laminariales) found in a New Zealand harbour. New Zealand
Journal of Botany 25: 329-332
Hay, C H. and Villouta, E. 1993: Seasonality of the adventive Asian kelp
Sur
Undaria pinnatifida in New Zealand. Botanica Marina 36: 461-476
Miller, K., Cole, R., and Battershill, C. 1997: Marine invasions: the spread of
Sur
the introduced Asian alga, Undaria, in New Zealand waters. Water &
Atmosphere 5(2): 8-9
Sanderson, J C. 1990: A preliminary survey of the distribution of the introduced
Sur
macroalga, Undaria pinnatifida (Harvey) Suringer on the east coast of
Tasmania, Australia. Botanica Marina 33: 153-157
Sanderson, J C. and Barrett, N. 1989: A survey of the distribution of the
Sur
introduced japanese macroalga Undaria pinnatifida (Harvey) Suringer in
Tasmania, December 1988. Department of Sea Fisheries, Tasmania,
Australia, Technical Report 38
Stuart, M D. 1997: The seasonal ecophysiology of Undaria pinnatifida (Harvey)
Sur
Suringar in Otago Harbour, New Zealand. PhD thesis, University of Otago,
Dunedin, New Zealand.
Floc’h, J Y., Pajot, R., and Mouret, V. 1996: Undaria pinnatifida
Exp
(Laminariales, Phaeophyta) 12 years after its introduction into the Atlantic
Ocean. Hydrobiologia 326/327: 217-222
Russell, L. 1997: Community ecology and nutrient ecophysiology of Undaria
Exp
pinnatifida (Harvey Suringar) in Otago Harbour. BSc (Hons) dissertation,
University of Otago, Dunedin, New Zealand.
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SECTION 1. EXPERIMENTAL DESIGN
To attain scientifically valid data on competitive interactions well designed manipulative
experiments must be carried out (Connell 1975, Underwood and Denley 1984, Wiens
1984). These experiments must be manipulative and not “natural experiments”
(Underwood 1986). There is general agreement among ecologists that “natural
experiments” are of little or no value in examining processes such as competition, as the
nature of these studies makes it likely that non-competitive interactions are the cause of the
differences observed (Underwood 1986). “Natural experiments” are studies where an area
where a supposed competitor is naturally absent is compared to an area where the supposed
competitor is present, and conclusions drawn from the differences observed.
The type of measurements made of the experimental sites to quantify the effects of
competition also affect the validity of the data. Schiel and Foster (1986) conclude that
questions concerning the recruitment and longevity of a species and change in size
composition of algal communities can only be addressed by enumerating individuals. I.e.
the number of individuals in the study site has to be assessed; standing crop measurements
e.g. biomass and percent cover estimates can not be used for any consideration of the
population biology or demography of algal species and therefore have little use in assessing
interactions (Schiel and Foster 1986).
The commonest method used to detect the effects of one algal species on another is the
removal of canopies, with observations on the subsequent recruitment of each species
(Schiel 1990). This manipulative experiment mimics the natural clearances by storms or
grazing. The enumeration of individuals is highly important in these canopy clearance
experiments as it would otherwise be unclear whether new recruitment has occurred or if
small juveniles already present have grown to replace the canopy (Schiel and Foster 1986).
Replication and controls are also important factors in the design of a valid experiment
(Kingsford 1998). This is especially important where dealing with seaweeds, as seaweed
stands show great natural variation both spatially and temporally (Choat and Schiel 1982,
Dayton 1985, Schiel and Foster 1986, Schiel 1988, Foster 1990).
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SECTION 2. SUMMARIES OF PREVIOUS WORK
LITERATURE SURVEYS
The use of information from pure literature searches must be used with caution. The
validity of the conclusions in literature searches must be assessed by examining the variety,
quality, and number of references used to back up their conclusions and the accuracy with
which statements from these references have been reported. Unfortunately literature
searches can not provide any new basic facts about the topic examined, but can identify
areas where there appear to be contradicting results and further research is needed. The
findings of the four literature surveys along with a critical assessment of the articles
follows.
Houghton et al. (1997)
In their Environmental Impact Assessment report, Houghton et al. (1997) concluded that
Undaria pinnatifida had many characteristics of an invasive species and would
dramatically alter the marine ecosystem having a predominantly negative effect. They also
state that Undaria has a window from May - September in which it may recruit into
disturbed patches while other large brown seaweeds can not. A check of this article shows
that it is of extremely poor quality. Containing a number of erroneous references to back
up the conclusions in which the referred to articles do not support the statements of
Houghton et al. (1997) or do not even cover the subject being discussed.
These erroneous references are: Pg 7 “Colonisation is extremely aggressive in high
disturbance and erosion prone areas (Miller et al. 1997)”, Miller et al. (1997) does not
suggest this; Pg 11, Figure 4 of Houghton et al. (1997) is attributed to be after the data
presented in Hay and Villouta (1993), but the length representation shown does not at all
follow the seasonal changes found in Wellington, Timaru, or Oamaru by Hay and Villouta
(1993); Pg 22 “Undaria is able to colonise disturbed areas (McShane et al. 1996)”, the
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article McShane et al. (1996) does not even mention Undaria; Pg 24 “Indigenous fauna
potentially affected include chitons, limpets, snails, and small molluscan grazers in cobbled
areas (Creese 1988)”, Creese (1988) does not say these invertebrates are potentially
affected, Houghton et al. (1997) suggest this.
Houghton et al. (1997) also state, without reference, that paua settle in “coralline barrens”
and that Undaria invades coralline barrens, hence will lessen the settlement of paua. This
is in complete contrast to the experimental literature discussed later in section 3. The
presentation of conclusions from the articles in the bibliography appeared to be highly
biased. Six of the articles examined by the authors concluded that Undaria would not have
detrimental environmental effects; Hay 1990/1991, Floc’h et al. 1991, Hay and Villouta
1993, Brown and Lamare 1994, Parsons 1995, Floc’h et al. 1996. Of these six only one
was reported in the text, Brown and Lamare (1994). Houghton et al. (1997) stated that the
conclusions reached by Brown and Lamare (1994) were incorrect. From communication
with the authors it was found that the report was part of the course work for a 4th year
Diploma Course and that the authors did not have a Marine botany or Marine ecology
background.
Parsons (1995)
The conclusions reached by the Department of Conservation report Parsons (1995) were:

Undaria will become part of the natural community of marine organisms, and will not
displace any other species completely.

Since the initial introduction of the sporophyte, plants of Undaria have become part of
the natural community of algae and marine animals in nearby habitats, successfully
maintaining themselves without excluding any particular native species.

Although Undaria will compete for space with the algae in this community it does not
to date seem to have occupied any natural communities to the exclusion of other
species.

Undaria plants are more fragile than tough native brown algal species such as
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Carpophyllum. Suggesting that Undaria would not readily grow in the conditions
favoured by Carpophyllum.

Drift is not likely to be a factor in the spread of Undaria in New Zealand.
The DoC report by Parsons (1995) was a large scale survey with 27 cited references and 40
additional references in a separate bibliography. A check of all references found no
misquotation of references. The conclusions of the report were supported by and based on
correctly quoted references.
Rueness (1989)
Rueness (1989) only mentions Undaria briefly (2 paragraphs) and says that Undaria may
be potentially harmful. The four references used were all correctly quoted.
Walker and Kendrick (1998)
Walker and Kendrick (1998) in their section on Undaria suggests that there is a high
probability of Undaria colonising the temperate shores of Australia, and there may be a
resulting change in community structure and food webs as a result. The section in Walker
and Kendrick (1998) on Undaria is of a low standard. The other sections in Walker and
Kendrick (1998) were not critically assessed and have not been commented on.
The major problem was misquotation, where possibilities talked about by the authors
Walker and Kendrick (1998) reference are presented as scientific fact by Walker and
Kendrick (1998): Pg 108 “Once established it has proven impossible to eradicate (Hay
1990, Sanderson 1990)”, Hay (1990) and Sanderson (1990) do not report on any attempts
to eradicate Undaria as attempts to eradicate Undaria have only occurred from 1997
onwards; Pg 108 “Undaria grows faster than the grazing rates of the urchins (Sanderson
and Barrett 1989)”, Sanderson and Barrett (1989) state that one reason Undaria may be
plentiful is that it may grow faster that the grazing rates of the urchins, although no
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experiments have been performed to examine this. This section on Undaria in Walker and
Kendrick (1998) appears to be based on a very small literature survey (total of 6 references)
with 2/3 rds of citations coming from Sanderson and Barrett (1989).
BIOLOGICAL SURVEYS
Biological surveys are able to provide us with a range of facts about an organism, i.e.
where it is found, the conditions that it has been found in, and how many there are. But can
not tell us why they are found where they are or about their interactions with other
organisms. The findings of the fourteen surveys, the opinions of the authors, and a critical
assessment of the articles follows.
Battershill et al. (1998)
Battershill et al. (1988) suggests that Undaria is displacing Carpophyllum spp’s from a
rocky edge of Wellington Harbour. Also suggested is that the sub canopy is substantially
changed by the presence of Undaria. This is based on the examinations of five 1 m2
quadrates in three densities of Undaria at two sites
Battershill et al. (1998) is a small-scale semi quantitative survey of the distribution of
Undaria and other marine species in Wellington Harbour and the Marlborough Sounds.
This study is a classic example of a “natural experiment”. The authors must have
recognised this and have included a one-sentence caveat in their article explaining that
nothing can be shown by a study of this design. Their “evidence” for Undaria displacing
Carpophyllum is that there are separate patches of Undaria and Carpophyllum and that the
denser the Undaria the less Carpophyllum is found, and visa-versa. The densities in this
study were not measured but were only estimated by those in the field (R Cole pers. com.).
The use of % cover when examining the algal abundance is another serious mistake in this
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study, as the actual no of individuals should have been used, as explained in section one.
Many of the changes to the sub canopy species that Battershill et al. (1998) say occur in
Wellington Harbour are not evident from their figures. Figure 3, pg 33 does not show a
significant change (=0.05) in the % cover of Lithothamnion or encrusting coralline algae
in December or in March from outside to inside of patches. The % cover of turfing algal
species also does not show a significant change (=0.05) from outside to inside or low to
dense in December, or from outside to inside in March. The only change that is
statistically significant is the increase in solitary ascidians.
The poor quality of the experimental design of this study is concerning as it was carried out
by NIWA staff who should know more about experimental design than what has been
shown in this study (one of the authors has recently co-edited a book on Marine
experimental design). No misquotation of references was found.
Brown and Lamare (1994)
Brown and Lamare (1994) performed a large-scale 7 month survey of Undaria in Timaru
Harbour. The following facts can be taken from Brown and Lamare’s survey.

Rocks in the harbour of 3-5 cm dia or smaller had no growth of Undaria, where as
rocks from 5-10 cm dia did have growth of Undaria.

Maximum depth plants were found down too was 5m. At 5m depth the light level was
100 E with a surface PFD of 1100 E per m2. I.e. over 90% of the light was
attenuated at this depth. There was suitable substrate below this depth.

Larger plants were at the more exposed Harbour sites. Exposure was measured with
plaster balls.

The sporophytes disappeared by late summer.
Brown and Lamare (1994) also concluded that Undaria colonises disturbed substrata like
an opportunist, but lacks other attributes associated with opportunists such as several
generations per year, high fecundity and high net primary productivity. They also feel that
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a low competitive ability of the species is implied by its low abundance among large
seaweeds, although it could possibly compete with the fucalean seaweeds, Sargassum,
Cystophora, and Carpophyllum. No misquotation of references was found and statements
not based on the surveys results were backed up by appropriate references.
Casas and Piriz (1996)
Casas and Piriz (1996) surveyed wharfs and ports of Puerto Madryn, Argentina, from 1992
and stated that they found that Undaria attached to substrates not covered by native
seaweeds, and one of these substrata were ascidians. No misquotation of references was
found and statements not based on the surveys results were backed up by appropriate
references.
Castric- Fey et al. (1993)
The conclusions Castric-Fey et al. (1993) made were that Undaria pinnatifida will become
introduced into indigenous settlements without generating major problems to the
environment. Undaria behaves relatively non aggressively against the native flora, but
may compete with Sargassum polysacharides for similar habitats. Castric-Fey et al. (1993)
appears to be a large scale survey of the coast of St Malo, France. Unfortunately the
methods used are not well documented so an in depth critical appraisal is hard to perform.
The measurements in the survey were of numbers of algae per meter squared, which is the
suggested measurement to use (see section one). No misquotation of references was found
and statements not based on the surveys results were backed up by appropriate references.
Fletcher and Manfredi (1995)
Fletcher and Manfredi (1995) make the conclusion that Undaria possesses a number of
biological features that might give it a competitive edge over some of the native North
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Atlantic laminarians and may impose significant long-term effects. These are:

It is an opportunistic species and can rapidly colonise new/disturbed substrata and
artificial/floating structures.

It can form dense vigorous stands that form a thick canopy over the subordinate biota.

It can occupy a wide range of shores varying in exposure.

It has an extensive vertical distribution, low tide to 15 (18) m depth in suitably clear
water.

It has an extended period of spore formation and release.
Fletcher and Manfredi (1995) performed a small-scale qualitative survey to report the
presence of Undaria in Britain for the first time. This was complemented by a medium
sized literature search. No misquotation of references was found and statements not based
on the surveys results were backed up by appropriate references.
Floc’h et al. (1991)
Floc’h et al. (1991) concluded that Undaria does not seem to be very competitive, and the
fact that it is often found in small numbers among large seaweeds or sessile macrofauna in
other studies implies a low competitive ability. Floc’h et al. (1991) was a large scale
survey of the French coast which used the correct methods of individual numbers and size
classes to measure the abundance of seaweeds over an approximately two year period. An
extensive literature search was also evident in this paper. No misquotation of references
was found and statements not based on the surveys results were backed up by appropriate
references.
Hay (1990)
The main finding of this article is that Undaria is most likely transported on the hulls of
vessels between New Zealand ports for hundreds of kilometres. In the discussion a small
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mention of Undaria’s competitiveness is made. Hay (1990) says that Undaria has three
biological features that may help its competitive ability:
 Ability to colonise new or disturbed substrates.
 The possibility that there are Undaria propagules in the water of Wellington year round.
 Ability to colonise floating or suspended objects.
Hay (1990) is a small qualitative though wide ranging (New Zealand to France) survey
combined with a literature search and research on vessel movements between New Zealand
wharves so that an idea of the movement of Undaria is attained. No misquotation of
references was found and statements not based on the surveys results were backed up by
appropriate references, although mention was made of unpublished experimental results.
Hay 1990/1991 DoC Science Project Summaries
Hay 1990/1991 DoC Science Project Summaries is a short report on C. Hay’s investigation
into the ecological implications of the adventive kelp Undaria pinnatifida for the
Department of Conservation Science and Research Division. As this report was a
summary it is not possible to evaluate the methods and conclusions obtained. The interim
conclusions in this summary were that Undaria:
 Was one of up to 20 seaweeds introduced by shipping.
 Does not appear particularly aggressive.
 Is mostly found in areas where there is little native seaweed growth.
 Effects on the native flora will become apparent when it spreads.
 Behaves like a weed colonising recently bared rock.
 Is unlikely to invade established beds of Carpophyllum, Cystophora, or Lessonia, but if
it does colonise bare patches other seaweeds could be excluded for a long time.
 Probably has beneficial effects on animals, i.e. the production of blade material coated
with microbes is possibly a new source of food for filter feeders. There are also signs
that paua and sea slugs concentrate in areas where Undaria is abundant.
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 Will probably increase species diversity in areas like the Marlborough Sounds where
there is naturally little seaweed.
Hay and Luckens (1987)
Hay and Luckens (1987) say that Undaria pinnatifida may compete for light and space
with large native brown seaweeds such as Carpophyllum and Cystophora. This study is a
small-scale qualitative survey of Wellington Harbour reporting the presence of U.
pinnatifida in the southern hemisphere for the first time. No misquotation of references
was found and statements not based on the surveys results were backed up by appropriate
references.
Hay and Villouta (1993)
Hay and Villouta (1993) showed that Undaria grew rapidly in winter with a large die off in
late summer in Wellington, Timaru and Oamaru Harbours. Hay and Villouta (1993) say
that by shading and covering much of the substrate Undaria is potentially able to exclude
smaller seaweeds e.g. Ulva and Codium. However they found a very high diversity of
native seaweeds growing among Undaria, even in spring when the biomass of Undaria
was highest. They also say that Undaria appears to colonise bare areas where there is little
competition from perennial brown seaweeds, and that there is no obvious sign of Undaria
displacing Carpophyllum maschalocarpum or Carpophyllum flexuosum in Wellington
Harbour. It is mentioned that Undaria may be able to invade areas of perennial kelp that
are cleared by storms, grazing, abrasion by gravel or sand, and perhaps by pollution in
summer or autumn. In areas cleared in winter Undaria would have to compete with the
native seaweeds, although Undaria may have a faster growth rate than some seaweeds.
However if the native seaweeds survive until summer they may be advantaged by the
autumnal decline of Undaria. They also mentioned unpublished experiments by C H Hay
that are said to show the presence of zoospores in Wellington Harbour water column
through out the year.
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Hay and Villouta (1993) performed a large-scale survey of Wellington, Timaru, and
Oamaru Harbours. Sampling was conducted at various times from late 1987 until late
1992. Not enough information is provided in this paper to assess the unpublished
experiment.
No misquotation of references was found and statements not based on the surveys results
were backed up by appropriate references, although mention was made of unpublished
experimental results.
Miller et al. (1997)
This article shows that the distribution of Undaria in Wellington Harbour has increased
from 1989 to 1997. Also shown is that Undaria is present in the Marlborough Sounds.
Miller et al. (1997) says that there is a possibility Undaria is competing for space with
native species. Miller et al. (1997) is a small article in the in-house NIWA magazine
‘Water and Atmosphere’. No misquotation of references was found.
Sanderson (1990)
Sanderson (1990) is basically a brief description of the report Sanderson and Barrett
(1989). Reiterating the fact that Undaria was most prevalent on rocky reefs that normally
support few macroalgae such as urchin barrens. Sanderson (1990) stated that it was the
authors opinion that the introduction of Undaria will have a long term impact, and an
assessment of these possible impacts is required. No misquotation of references was found
and statements not based on the surveys results were backed up by appropriate references.
Sanderson and Barrett (1989)
Sanderson and Barrett (1989) found that the cover of Undaria was patchy and that where
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there was an abundance of native vegetation there were only isolated individuals of
Undaria. Undaria growth in high water movement areas was restricted due to the more
prolific growth of native macroalgae. Sanderson and Barrett (1989) concluded that
Undaria will affect similar annual macrophytes that occupy the same ecological niche e.g.
Ulva, Cladophora, Polysiphonia and Ectocarpus. Sanderson and Barrett (1989) also feel
that there may be an effect on some perennial algae. The rapid growth and canopy forming
ability of Undaria may cut out some of these species at an establishment phase. They also
say that Macrocystis occupies a similar ecological niche and could possibly be threatened
by Undaria. In Tasmania Undaria grows to a depth of 12 m where small red algae are
found. Undaria could compete with and shade these algae.
Sanderson and Barrett (1989) was a large scale survey of Tasmanian waters over a one year
time period together with a comprehensive literature search. A small laboratory
experiment on zoospore settlement was also conducted, but none of the resulting
gametophytes produced sexual structures. A good question that Sanderson and Barrett
(1989) bring up is will urchin numbers increase with the presence of Undaria, then when
the Undaria dies off will they eat other algae? One statement made, that Undaria cover of
the ocean floor often exceeded 100% in some sites, made me question how over 100%
cover can be obtained. No misquotation of references was found and statements not based
on the surveys results were backed up by appropriate references.
Stuart (1997)
Stuart (1997) states that Undaria dispersal is mainly by humans, e.g. boat hulls etc.
Undaria may become a problematic fouling organism on mussel and salmon aquaculture
structures, and that Undaria may colonise substrata in regions of clear water and low
densities of native seaweeds.
Further findings of Stuart (1997) are that in sheltered shallow waters with poor water
clarity, the vertical distribution of U. pinnatifida is limited from MLW to 5.5-7 m (Hay and
Luckens 1987, Brown and Lamare 1994) and would be confined to depths occupied by
fucalean seaweeds such as Carpophyllum spp, Sargassum spp, and Cystophora spp. In
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regions of shallow water and strong tidal current, U. pinnatifida would occur with
Macrocystis pyrifera as is already apparent at Aquarium point in Otago Harbour. At wave
exposed sites the vertical distribution of U. pinnatifida is depressed 6-12+m (Sanderson
and Barrett 1989) and would place U. pinnatifida within a zone inhabited by Ecklonia
radiata, M. pyrifiera, Carpophyllum spp, and Sargassum spp. At various sites about New
Zealand U. pinnatifida may also cohabit with Lessonia spp e.g. L. variegata. Several
authors have suggested that U. pinnatifida may compete with other large laminarian and
fucalean kelps. But U. pinnatifida is more likely to compete with seaweeds occupying a
similar ecological niche such as annual or ephemeral seaweeds. Competition between U.
pinnatifida and understory seaweeds for substrata, nutrients, and light may represent the
major impact on indigenous benthic communities.
Stuart (1997) also states that the higher PFD requirements for gametogenesis and
gametophyte growth in Undaria pinnatifida would limit the recruitment to areas which
have been cleared of competitors and to unstable environments where new substratum is
always available for colonisation. Based on his findings and the findings of other
researchers (Suto 1950, Saito 1956 , Vadas et al. 1992 , Arakawa and Morinaga 1994),
Stuart (1997) also states that at his study site the duration of successful spore settlement
and germination only occurs from December to March. If U. pinnatifida gametophytes
were present under a seaweed canopy and were not removed with the canopy during an
event resulting in the clearance of the seaweed canopy from May-September, when other
large brown seaweeds do not recruit, U. pinnatifida would be the only seaweed to recruit in
to the patch. Regular grazing of patches within a stable stand of perennial kelps may allow
U. pinnatifida and other ephemeral seaweeds to invade and persist in a seaweed
community. However successful colonisation of cleared substratum by U. pinnatifida
depends on its ability to out compete other colonising seaweeds. Evidence from Venice
Lagoon Italy, and Port Philip Bay Australia suggests that U. pinnatifida may have a
competitive advantage in disturbed eutrophic environments.
Stuart (1997) also says that no experimental manipulation has been used to examine the
impact of Undaria pinnatifida on native seaweed communities, and such an approach
would be beneficial. Stuart (1997) missed Floc’h et al. (1996) and the results from Russell
(1997), both of which were manipulative experiments.
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Stuart (1997) is a PhD thesis on Undaria eco-physiology, with a section inferring
ecological possibilities. No misquotation of references was found and statements not based
on the surveys results were backed up by appropriate references. Unfortunately Stuart
(1997) did not include the paper Floc’h et al. (1996), that showed the results of a long term
manipulative experiment on Undaria’s ecological effects. This paper would appear to be
an important reference for inclusion in the ecological effects section of the thesis.
MANIPULATIVE EXPERIMENTS
The last two articles are manipulative experiments performed to examine the ecological
effects of Undaria pinnatifida on native seaweeds. It is these manipulative experiments
that are likely to show what is actually occurring in the marine environment.
Floc’h et al. (1996)
Floc’h et al. (1996) performed a large-scale long term manipulative experiment to
investigate the competitive ability of Undaria. The experiment started in June 1988 at
Ushant Island, Brittany, France. Ushant Island was a site where Undaria is cultivated on a
seaweed farm. In 1987 a survey found 20,000 mature Undaria plants growing on the
seaweed farm, a nearby (50 m away) mussel farm and the rocky bottom beneath the
seaweed and mussel farms. Three 50 m long transects were chosen in the bay of Lampaul,
Ushant Island, between approx 100 m and 1 km away from the seaweed farm. Along each
of these transects were two lanes 10 m apart, one was untouched with a thick forest of
kelps and the other had the rocky bottom denuded by the removal of all the kelps in a 2 m
wide strip along the lane. Sporophylls from near the Undaria seaweed farm site were
harvested and after checking that they were mature and able to release spores in great
quantities were placed in nets attached every 0.5 m to 50 m long ropes which were placed
along each lane of each transect. Hence a total of 600 sporophylls were placed on the
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bottom, 100 attached to each of the six 50 m ropes. Each transect had one end at +1.5 m
(the low water mark of neap tide) and the other end at 15 m below the low water mark of
spring tide. Every 2 months from June 1988 until June 1989 the two lanes in each of the
three transects were examined for the settlement of Undaria sporophytes. After June 1989
the transects were examined once a year in spring until 1993. Three control sites in the Bay
of Lampaul with no Undaria were also monitored at the same times as the transects.
The results of this study showed that after removal of the kelp canopy the denuded lanes
became clearer due to the disappearance of the algae that were previously protected by the
shade of the kelps. In Autumn 1988 20 Undaria plants were found growing in the
transects. These were all in a denuded lane, and of these, 15 were attached to the rope
holding the sporophylls and 5 to the rocky bottom close to the rope. In June 1989 one year
after starting the experiment no Undaria plants were found in any of the transects, while
Undaria from the same sporophyll source was still abundant on the mussel farm nearby.
After five years in 1993 the denuded areas had recovered and showed no discernible
difference between the flora in the denuded and non denuded areas. In 1993 a total of 26
Undaria sporophytes were again found in the experimental transects, in both the denuded
and non denuded lanes. Of these 17 were found in the region +1.5 m to 0 m above low
water spring. 19 of the sporophytes were in the transect approximately 100 m away from
the seaweed farm and only 2 sporophytes in the transect approximately 1 km away from the
seaweed farm.
The findings of Floc’h et al. (1996) were that Saccorhiza polyschides was the most
opportunistic alga to settle on the denuded areas and it appears that Undaria is less
competitive vis-à-vis the native kelps. Floc’h et al. (1996) say that this hypothesis is
enhanced by the fact that Undaria propagation from the seaweed farm occurred better in
the Himanthalia zone (Low Water Spring (LWS) to Low Water Neap (LWN)) than in the
kelp zone along the transects as well as the control sites. Floc’h et al. (1996) state that
whatever the reasons, the above observations lead to the conclusion that the new species
did not supersede the indigenous species and Undaria seems to have a preference for
artificial structures.
This manipulative experiment follows the guidelines for examining competitve interactions
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as set out in section one, and the results were followed for a long time (five years). The
examination of clearances during different seasons would have been an informative
addition to the experiment. The canopy clearance for this experiment was only carried out
during one season (the time of natural Undaria reproduction in the northern hemisphere),
and to be completely sure the results are applicable to the rest of the year, clearances and
spore seeding should also be carried out during the other three seasons. Although this may
require the use of laboratory grown spores or gametophytes to distribute when the natural
populations are not reproducing.
Russell (1997)
The results of Russell (1997) showed that removal of Undaria had no significant effect on
the community composition or relative abundance of prominent species. These results
suggest that Undaria may be exploiting an unfilled niche in Otago Harbour. Russell
(1997) states that the results of this experiment are tentative due to the high variability both
spatially and temporally of seaweed species, and to provide conclusive data would require
more than the five replicates used in this study.
The sub canopy community consisted of a number of red and green sheet and filamentous
macroalgal species, and a number of marine invertebrates, primarily anthozoans and
sponges. A species list showing the two green and seven red seaweeds examined in this
study and the invertebrates is provided by Russell (1997) and is included in this report
(Appendix 1).
Russell (1997) performed an experiment examining the effect on the sub canopy biota of
removing the Undaria canopy on wharf piles at a site in Otago Harbour. A total of fifteen
0.5 x 0.5 m quadrats were studied on ten piles. Five piles had Undaria removed each
month from quadrates at 1 m depth. Five piles did not have Undaria removed from
quadrates at 1 m depth. A further five piles did not have Undaria removed from quadrates
at 2 m depth to enable the examination of depth differences. The percent cover of the
species on the piles was recorded each month for twenty weeks starting in May.
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One problem with this study was that percent cover was used instead of numbers of
individuals of each species. This was explained in the text as being used due to the
inability of determining distinct individuals of some of the species studied while
underwater, and due to the time constraints of diving in cold water. The question, is the
Undaria canopy affecting the understory biota, was actively investigated in this experiment
with an appropriate experimental design (forgiving the constraints discussed by the author).
The author also recognises the necessity for high numbers of replication when working
with seaweeds due to their naturally large spatial and temporal variation.
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SECTION 3. DISCUSSION
Competitive Interactions and Colonisation
COMPETITION
Undaria pinnatifida does not appear to compete with or detrimentally affect other native
seaweeds. The experimental results from France and New Zealand both support this
conclusion. Stuart (1997) states that the main area of competition is likely to be between
Undaria and its understorey of annual or ephemeral seaweeds. The results of Russell
(1997) showed that the Undaria canopy did not affect the native understorey seaweeds or
fauna. The results of Floc’h et al. (1996) showed that in France Undaria was not
competitive against the native French seaweeds and was pushed into a narrow band just
above LWS. The temperature range of the French coast is very similar to that of the South
Island of New Zealand, 5-18°C (J Jillet pers. Com., Desprez et al.1991), but the
composition of the seaweed community is different. In the Northern Hemisphere the
dominant seaweeds are laminarians where as in the Southern Hemisphere fucalean
seaweeds are more abundant (Schiel and Foster 1986). Laminarian seaweeds have a
greater reproductive potential than fucalean seaweeds. But due to the fucalean germlings
advanced development, greater size and higher survival rates, fucalean seaweeds are likely
to produce more viable recruits than laminarian seaweeds (Schiel 1988). Calculations in
Schiel (1988) show the fucalean seaweed Sargassum sinclairii producing approximately
100 adult recruits per m2 per year, compared to the laminarian seaweed Laminaria
longicruris producing approximately 1 adult recruit per m2 per year. As Undaria was
shown to be out competed in France by laminarian seaweeds, it is logical to suggest
Undaria would have less chance at competing with native Southern Hemisphere seaweeds
that have a higher proportion of fucaleans which are likely to have more competitive
reproductive propagals than the Northern Hemisphere laminarians.
A few authors also state that Undaria may compete with the laminarian Macrocystis
pyrifera, (Houghton et al. 1997, Walker and Kendrick 1998, Sanderson and Barrett 1989,
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Stuart 1997) although none have suggested mechanisms by which Undaria would
outcompete Macrocystis. I do not feel this is a likely scenario due to the much larger size
Macrocystis attains (20m, Adams 1994) compared to Undaria (1-2m, Adams 1994), and
the much greater frond growth rate Macrocystis has (7-13 cm d-1 , Zimmerman and Kremer
1984) compared to Undaria (0.9cm d-1, Dean 1998). Also of interest is that a similar
growth rate to Undaria is obtained by the fucalean Sargassum sinclairii (10 mm d-1, Schiel
1990).
COLONISATION
One condition under which some authors (Stuart 1997, Hay 1990, Fletcher and Manfredi
1995) feel Undaria may compete with other seaweeds is in the race to recolonise substrata
that has been cleared. Floc’h et al. (1996) showed that Undaria was not competitive in the
recolonisation of cleared areas in France. Houghton et al. (1997) and Stuart (1997) state
that in New Zealand there is a time period from May to September when large brown
seaweeds are not recruiting while Undaria may possibly be able to recruit. Undaria would
then be the only seaweed to colonise patches cleared during this time period. This
statement may be misleading as if seaweeds other than large browns are included, at least
seven other seaweeds could colonise bare patches during this window (see Appendix 2 for
seaweeds found settled on the lines of a seaweed test farm in Otago Harbour between May
and September 1997). There are two mechanisms by which Undaria could recruit during
this window. The first is by the normal settlement of zoospores into the bare patches with
the subsequent development and fertilisation of the gametophytes. The second
unexamined mechanism is by the possible settlement of zoospores under the canopy of
other seaweeds with subsequent vegetative growth of the gametophytes until the clearance
of the canopy. With development then able to continue due to the greater light levels
reaching the substrate.
The ability of Undaria to release spores in great number during this window is at present a
question that has not been directly addressed. Hay and Villouta (1993) mention an
unpublished experiment that shows the presence of Undaria zoospores in the Wellington
Harbour water column through out the year. As the success of colonising bare patches
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during this window would be highly dependent on the number of spores present in the
water column, the number of spores present during this period needs to be quantified to
determine the probability of Undaria colonising bare patches in this window.
Unfortunately Hay and Villouta (1993) make no mention of spore numbers found through
out the year. A rough comparison of the possible number of spores that would be available
inside and outside of the May - September window can be made by examining the
development of the sporophylls (reproductive structures) of Undaria. Stuart (1997)
measured the dry weight of the ten largest sporophylls from his study site each month.
This showed that over the period May - September the average sporophyll dry weight was
around 4.4 g. While in October when the sporophylls are mature, outside of the window,
the average weight was around 16 g. Hence the possible number of spores released during
the period May- September is much less than outside of this period. Stuart (1997) also
states that based on his findings and the findings of other researchers (Suto 1950, Saito
1956 , Vadas et al. 1992 , Arakawa and Morinaga 1994), that at his study site the duration
of successful spore settlement and germination only occurs from December to March,
which is outside of the May - September window discussed. Hence it does not appear
likely that Undaria will be able to colonise bare patches due to zoospore release and
settlement during this May - September window. The possibility of algal colonisation by
waiting under the canopy as a gametophyte for a clearance in the canopy has not been
strongly investigated (Schiel 1985). If the zoospores managed to settle under a canopy and
develop in to gametophytes, they would have to survive grazing by sea urchins, gastropods
and micro-crustaceans (Schiel and Foster 1986), smothering and abrasion by silt or sand
(Devinny and Volse 1978), and resist the clearance phenomenon that removed the canopy.
The time period they would need to survive under the canopy would be three to ten
months, assuming the zoospores successfully settled in the period December - March. The
probability of surviving under the canopy for this time period appears slim. Although until
experiments to examine the survival of gametophytes under these conditions are performed
it is impossible to determine the likely hood of this occurring.
Effects on Fauna
The literature would suggest that the settlement of paua would be increased by the presence
of the kelp Undaria, and that the notion of Houghton et al. (1997) that Undaria would
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inhibit paua settlement by overcrowding coralline algae is completely against findings
presented in the literature. McShane et al. (1988) concluded that the presence of kelp
slows water motion allowing more paua (which have a limited swimming rate and can not
settle in high velocity water motion) to settle, the more kelp present the greater the
settlement of paua. Kaspar and Mountfort (1995) have shown that in the natural New
Zealand environment, GABA (settlement inducing chemical produced by some coralline
algae) is not likely to play a significant role in Haliotis (paua) settlement. Naylor and
McShane (1997) have also shown that predators like polychaete worms that live in the
coralline algae eat many settling larvae, greatly lowering the number of paua that survive in
coralline algae. Observation of the size of holdfasts of Undaria and native seaweeds shows
that many native seaweeds have holdfasts much more damaging and larger than those of
Undaria. The holdfasts of Undaria are small enough to be pulled off by hand, where as the
holdfasts of individuals of Macrocystis, Ecklonia and Durvillaea may cover an area 10 –
20 times greater than an Undaria holdfast, and prove nearly impossible to remove (Pers.
obs.). Undaria may also provide a source of food for paua, snails, kina (sea urchins),
mussels, sea cucumbers, mud snails and esturine fauna (Roberts et al. 1997, Fletcher and
Farrell 1999). Undaria has also been found to be the prefered diet of many paua species
(Floreto, Teshima, and Ishikawa 1996; Floreto, Teshima, and Koshio 1996). Battershill et
al. (1998) found large numbers of green lipped mussels, blue mussels, kina (sea urchins),
and whelks under Undaria patches in the Marlborough Sounds. Manipulative experiments
need to be performed to find out whether Undaria settles around these species or these
species are attracted to Undaria cover after Undaria settlement.
Battershill et al. (1998) shows an increase in solitary ascidians under patches of Undaria in
Wellington Harbour. This is interesting as Casas and Piriz (1996) found Undaria attached
to substrata not covered by native seaweeds, one of these substrata were ascidians. Hence
it is likely that Undaria settles on ascidians which other native seaweeds do not settle on.
Therefore it is likely that this ability of Undaria to settle on ascidians is the reason why
large numbers of ascidians can be found under the Undaria patches of Battershill et al.
(1998). This highlights the point made by Underwood (1986) that “natural experiments”
make it likely that non competitive interactions are the cause of the differences observed
(see section one).
Further Research
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Fletcher and Manfredi (1995) listed a number of features of Undaria that might provide it
with a competitive advantage over other seaweeds. A good addition to this article would
have been if Fletcher and Manfredi (1995) explained how these features would assist
Undaria out compete specific examples of native seaweed, as the literature shows other
seaweeds in the region also posses a number of these features. E.g. Laminaria hyperborea
and Saccorhiza polyschides (Castric-Fey et al. 1993). No studies have taken an extensive
species by species approach, examining the different habitats, physiology, and recruitment
of a wide range of specific species and proposed how competition with Undaria may affect
them. Instead there have only been general statements that different groups may be
affected due to a list of various reasons. A study examining the specifics of how
competition may occur for a wide range of specific seaweed species is likely to show areas
where further competition may occur and where manipulative experiments should be
performed to determine the extent of competition.
The question posed by Sanderson and Barrett (1989), of whether the number of sea urchins
would dramatically increase in areas where Undaria flourishes, then start decimating other
algae when the Undaria dies off needs investigating. Areas with only a moderate
proportion of Undaria biomass are unlikely to be detrimentally affected as any alteration of
the seasonal seaweed biomass would be minor. The availability of native algal material to
urchins and other grazers already undergoes cyclic seasonal changes with no reported
detrimental effect. E.g. in California the availability of algal biomass to grazers is greatest
in summer and decreases greatly in winter (Harrold and Reed 1985). Areas where Undaria
would make up a large proportion of the algal biomass, e.g. the Marlborough Sounds which
has little native macroalgae, may be affected by this phenomenon. The additional grazing
that may occur would probably be restricted to near the Undaria patch due to the limited
mobility of sea urchins. Strongylocentrotus franciscanus the Californian red sea urchin
was found to move 0.80 m per day when looking for food in barren areas (Harrold and
Reed 1985). A worthy start to this investigation would be to identify areas where Undaria
makes up a large proportion of the algal biomass. Experiments to investigate the effects
Undaria has on urchin populations and the subsequent effects on other algae after the
summer disappearance of Undaria may be difficult and costly to perform. To be
ecologically relevant the effects of predation on the urchins, whether by fish or man, would
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The Ecological Effects of Undaria pinnatifida
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also have to be investigated. It is possible that an abundance of grazing urchins could
devour the gametophytes and small sporophytes that would make up the next generation of
Undaria, leaving a barren patch where the Undaria patch was. A discussion of patch
dynamics and algae/herbivore interactions, even a brief study, is beyond the scope of this
report, and will not be entered into due to the inherent complexity of the subject which
would require extensive research and experimentation.
Effects on Salmon and Mussel Farming
Stuart (1997) suggests that Undaria may become a problematic fouling organism on
mariculture structures. The economic costs of this fouling is likely to be small or
negligible for Salmon farms. The main problem faced by Salmon farms is seaweed growth
on the cages lowering water flow. Undaria is unlikely to be a problem due to the regular
cage cleaning that is already performed to remove the native seaweeds that foul the cages.
The worst offenders are the filamentous seaweeds which regrow from fragments left on
the cage structure after cleaning (C Harrison pers. com.).
The effect Undaria may have on Mussel farms is not as clear. The Cawthron Institute is
growing a trial crop of Undaria on Marlborough Mussel Co Mussel farm main lines. A
recent article reporting on the research did not mention any detrimental effects of Undaria
on the mussels of this farm (Gibbs and Hay 1998). There may be a positive benefit to filter
feeders like mussels due to the production of microbe rich detritus (Roberts et al. 1997).
Also work by Battershill et al. (1998) showed that under Undaria canopies in the
Marlborough Sounds there are dramatically higher densities of Mytilus edulis (blue mussel)
and Perna canaliculus (green-lip mussel). These higher densities may be caused by the
presence of Undaria, although proper experimental work is required to verify or refute this.
Because of the almost neutral buoancy of Undaria, fouling is unlikely to cause the sinking
of any marine structures. Measurements have shown that 15 kg of Undaria ( weighed out
of the water) has an apparent weight of only 800 g in the water.
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SUMMARY
 Undaria appears to be less competitive than the seaweed flora of New Zealand and
France.
 Experiments have shown Undaria had no observable effects on its understory biota.
 The timing of zoospore release and the gametophyte life history of Undaria does not
appear to offer Undaria advantages over other native seaweeds in the colonisation of
bare patches.
 The effects on fauna are likely to be advantageous.
 Paua settlement and growth is likely to be enhanced by the presence of Undaria.
 Areas of little natural algal cover, like the Marlborough Sounds, may be subjected to
intense localised grazing pressure for the scarce native algal cover following the annual
die off of Undaria.
 Salmon farms are unlikely to suffer any adverse effects from Undaria. No detrimental
effects on Mussel farms have been reported and observations infer possible
advantageous interactions.
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Appendix 1:
Macroalgal and marine invertebrate species in the understory of Russell (1997)
Chlorophyta
Cladophora feredayi
Ulva rigida
Rhodophyta
Ceramium spp.
Grifflesia crassiuscula
Mediothamnium lylli
Phycodrys quercifolia
Rhodymenia leptophylla
Sarcodia flabellata
Schizocerus dichotoma
Marine invertebrates
Aplidium phortax
Bostryllus leachi
Didemnum candidum
Dysidea fragilis
Pyura pachydermatina
Unidentified sponge species
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Appendix 2:
Seaweeds settled on seaweed test farm lines in Otago Harbour May - September 1997
From “Keeping Seaweed on Seaweed Farms” a report for the Department of Marine
Science, University of Otago, By P R Dean 1998. Report available from P Dean (03) 455
0533.
Ulva spp. (Most likely stenophylla)
Macrocystis pyrifera
Porphyra spp.
Scytosiphon lomentaria
Colpomenia peregrina
Punctatia latifolia
Filamentous brown Ectocarpus like seaweed, possibly Pilayella littoralis
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Personal communications
John Jillet. Portobello Marine Laboratory, University of Otago, Dunedin.
Russell Cole. NIWA, Nelson.
Chris Harrison. Salmon maintenance diver, Nelson.
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