|Researched by||Jacqueline Hill & Nicola White||Refereed by||Dr Dagmar Stengel|
|Authority||(Linnaeus) Le Jolis, 1863|
|Other common names||-||Synonyms||-|
A common large brown seaweed, dominant on sheltered rocky shores. The species has long strap like fronds with large egg-shaped air bladders at regular intervals. The fronds of Ascophyllum nodosum are typically between 0.5 and 2m in length. The species often bears tufts of the small reddish-brown filamentous epiphytic algae Polysiphonia lanosa. Ascophyllum nodosum occurs on the middle of the shore, often with Fucus vesiculosus. The species grows slowly and plants can live to be several decades old. Individual fronds can become up to 15 years old before breakage.
Detached forms of Ascophyllum nodosum are known from several habitats. Ascophyllum nodosum var. mackayi is found on very sheltered shores, in sea lochs and is sometimes common on the west coasts of Ireland and Scotland. The frond has extensive dichotomous branching and bears few air bladders. The plants drift in large, spherical masses in sheltered waters. Ascophyllum nodosum var. scorpioides, which is abundant in New Hampshire (U.S.A.), is often associated with the marsh grass Spartina alterniflora. According to Gibb (1957) the major difference between the ecads mackayi and scorpioides is the proportion of apical to lateral branching. If branching is both 'apical and lateral' the algae would be designated as mackayi while if it is 'almost entirely lateral' it would be designated as scorpioides. Unattached forms arise when detached fragments of Ascophyllum nodosum are deposited onto the shore where they continue to multiply and branch independently of the original fragment (Chock & Mathieson, 1976).
Chock & Mathieson (1979) demonstrated the physiological responses of Ascophyllum nodosum and its detached ecad scorpioides were similar under varying conditions of light intensity, temperature and salinity.
Ascophyllum nodosum var. mackayi
The presence of the ecad in any particular situation depends on the combination of a number of conditions applying at a tide level between high and low water neaps:
Very sheltered conditions are often found at loch heads on the west coast of Scotland and in these situations the ecad is sometimes present in great abundance. Sheltered or land-locked bays or situations in the lee of small islands are other favourable positions (Gibb, 1957).
|Phylum||Ochrophyta||Brown and yellow-green seaweeds|
|Authority||(Linnaeus) Le Jolis, 1863|
|Typical abundance||High density|
|Male size range||Up to 2m|
|Male size at maturity|
|Female size range||Large(>50cm)|
|Female size at maturity|
|Growth rate||5 - 15cm/year|
|Characteristic feeding method||Autotroph|
|Typically feeds on|
epiphytic algae Polysiphonia lanosa and ascomycete fungus Mycosphaerella ascophylli.
|Is the species harmful?||No|
Ascophyllum nodosum is an edible species and alginates from the algae are used in a range of edible products. Also widely used as an animal feed, on its own or as a supplement.
|Physiographic preferences||Open coast, Strait / sound, Sea loch / Sea lough, Ria / Voe, Estuary|
|Biological zone preferences||Mid eulittoral, Upper eulittoral|
|Substratum / habitat preferences||Bedrock, Cobbles, Large to very large boulders, Small boulders|
|Tidal strength preferences||Moderately Strong 1 to 3 knots (0.5-1.5 m/sec.), Strong 3 to 6 knots (1.5-3 m/sec.), Very Weak (negligible), Weak < 1 knot (<0.5 m/sec.)|
|Wave exposure preferences||Extremely sheltered, Moderately exposed, Sheltered, Ultra sheltered, Very sheltered|
|Salinity preferences||Full (30-40 psu), Reduced (18-30 psu), Variable (18-40 psu)|
|Depth range||Not relevant|
|Other preferences||No text entered|
|Migration Pattern||Non-migratory / resident|
|Reproductive type||Gonochoristic (dioecious)|
|Reproductive frequency||Annual episodic|
|Fecundity (number of eggs)||No information|
|Generation time||5-10 years|
|Age at maturity||5 years|
|Season||April - June|
|Life span||10-20 years|
|Larval/juvenile development||Spores (sexual / asexual)|
|Duration of larval stage||2-10 days|
|Larval dispersal potential||No information|
|Larval settlement period|
The MarLIN sensitivity assessment approach used below has been superseded by the MarESA (Marine Evidence-based Sensitivity Assessment) approach (see menu). The MarLIN approach was used for assessments from 1999-2010. The MarESA approach reflects the recent conservation imperatives and terminology and is used for sensitivity assessments from 2014 onwards.
|Ascophyllum nodosum is permanently attached to the substratum so would be removed upon substratum loss. The species has poor recruitment rates and is slow growing, limiting recovery (Holt et al., 1997). The lack of recovery of Ascophyllum nodosum from harvesting is well documented. For example, in their work on fucoid recolonization of cleared areas at Port Erin, Knight and Parke (1950) observed that even eight years after the original clearance there was still no sign of the establishment of an Ascophyllum nodosum population. The species is extremely fertile every year and Printz (1959) suggests it must be assumed that some special combination of climatic or environmental conditions is needed for an effective recolonization.|
|If smothering occurred while the tide was out, the whole plant would be covered in sediment preventing photosynthesis and damaging the plant. If smothering occurred while the plant was immersed, fewer surfaces would be covered allowing some surfaces to be unaffected. Recovery is slow in Ascophyllum nodosum due to its slow growth rate and poor recruitment (Holt et al., 1997).|
|Siltation may cover some surfaces of the plant, reducing photosynthesis rates which may reduce growth rates. However, the species naturally occurs in places of high siltation, such as estuaries and very sheltered areas, so is likely to be tolerant of this factor. Upon return to normal conditions the photosynthesis rate would quickly return to normal.|
|Ascophyllum nodosum regularly becomes exposed to air during tidal cycles and so is tolerant of some desiccation. Brinkhuis et al. (1976) concluded that productivity is affected by desiccation, but only when water loss exceeds 50%. Stengel & Dring (1997) found that growth was lowest in those plants highest up the shore. In transplantation experiments Stengel & Dring (1997) found that 80% of plants moved from the lower shore to the upper shore died within 3 months, whereas all transplants from the upper to the lower shore and all controls survived. However, the photosynthetic and growth rates of those plants that survived on the upper shore had acclimated to the new conditions, but whether the plants survived or not seemed to be determined by thallus morphology which may be genetically fixed. An increase in desiccation at the level of the benchmark, equivalent to a change in position of one vertical biological zone on the shore, will kill a large proportion of plants at the upper end of the populations range depressing the upper limit. Other species, which are better able to tolerate desiccation are likely to competitively displace Ascophyllum nodosum. However, some plants are likely to be able to acclimate to the new conditions and survive so intolerance is assessed as intermediate. Conversely, a decrease in the level of desiccation may result in the upper limit of the species extending further up the shore. Recovery would be slow due to the slow growth rate and poor recruitment of the species (Holt et al., 1997).|
|Ascophyllum nodosum is normally exposed to air for no more than a few hours (Lüning, 1990). An increase in the period of emersion would subject the species to greater desiccation and nutrient stress, leading to a depression in the upper limit of the species distribution on the shore. A reduction in the period of emersion may result in the species being competitively displaced by faster growing species and may allow the upper limit of the population of Ascophyllum nodosum to extend up the shore. Recovery would be slow due to the slow growth rate and poor recruitment of the species (Holt et al., 1997).|
|An increase in water flow rate may cause plants to be torn off the substratum or the plant with the substratum will be mobilised and may be moved to conditions unsuitable for the growth of the species. However, a certain degree of water flow is required to supply nutrients and remove waste products so a reduction in the water flow below a certain level may have an adverse effect on the species. Recovery would be slow due to the slow growth rate and poor recruitment of the species (Holt et al., 1997).|
|Intertidal algae, such as Ascophyllum nodosum, are regularly exposed to rapid and short-term variations in temperature. Both exposure at low tide or rising tide on a sun-heated shore may involve considerable temperature changes, and during winter the air temperature may be far below freezing point. Growth has been measured between 2.5 and 35°C with an optimum between 10 and 17°C (Strömgren, 1977). In the North Sea Ascophyllum nodosum can tolerate a maximum temperature of 28°C and the optimum growth rate is at 15°C (Lüning, 1990). Laboratory experiments in New Hampshire showed that Ascophyllum nodosum exhibits a eurythermal response to temperature with a more pronounced optimum occurring during the summer than the winter (Chock & Mathieson, 1979). Overall, summer plants showed a higher rate of net photosynthesis than winter specimens. Therefore, the species is likely to be quite tolerant of a long term change in temperature of 2°C. The species is unlikely to be affected by a short term change of 5°C, as it was not damaged during the unusually hot summer of 1983 when the average temperature was 8.3°C higher than normal (Hawkins & Hartnoll, 1985). However, the species has been found to be damaged by thermal pollution if the water temperature is above 24°C for several weeks (Lobban & Harrison, 1997) and the southern limit of the species distribution is controlled by the maximum summer temperature of about 22°C (Baardseth, 1970). The species can tolerate freezing as it has been observed to survive in a block of ice for several days. However, temperature is important for reproduction in Ascophyllum nodosum. David (1943) suggests that temperature could provide the stimulus for gamete release. Studies in Maine, USA (Bacon & Vadas, 1991) and in Norway (Printz, 1959) have shown that gamete release in both countries commences at 6°C and in Maine terminated at about 15°C. Provided the temperature has not exceeded the critical limits it will soon recover on return to normal conditions.|
|Changes in turbidity would alter the light available for photosynthesis during immersion. In laboratory experiments Strömgren & Nielsen (1986) observed that there was a strong correlation between the total radiant energy during the day and the average daily growth rates and Ramus et al., (1977) observed reduced growth rates of fucoid algae with depth. However, at low tide, when the plants are emersed, Ascophyllum nodosum can continue to photosynthesize as long as the plant has a sufficiently high water content and so will be unaffected during this period. Upon return to previous turbidity levels the photosynthesis rate would return immediately to normal.|
|Ascophyllum nodosum cannot resist very heavy wave action so exposure to wave action is an important factor controlling the distribution of the species. In moving from protected sites to the open sea the number of plants become progressively reduced, and individual plants become increasingly short and stumpy (Baardseth, 1970) and with a higher percentage of injured tissue (Levin & Mathieson, 1991). Thus, the species is only present in sheltered or moderately exposed locations and increased wave exposure causes plants to be torn off the substratum and replaced by Fucus vesiculosus. Intolerance to wave exposure is therefore high. In moderately exposed locations all Ascophyllum nodosum fronds produce few vegetative laterals, but are prolific reproducers even at an early age. Such an allocation of resources is to be expected in habitats where environmental severity is extreme and life expectancy of fronds is likely to be short (Cousens, 1985). In populations sheltered from wave action reproduction does not occur until they have reached a greater age and size. Recovery is slow due to the poor recruitment and slow growth rate of the species (Holt et al., 1997). Wave exposure may also be important in preventing settlement of zygotes and therefore recruitment.|
|Tolerant||Not relevant||Not sensitive||Not relevant|
|Seaweeds have no known mechanism for the perception of noise.|
|Tolerant||Not relevant||Not sensitive||Not relevant|
|Seaweeds have no known mechanism for visual perception.|
|Abrasion may damage the fronds and kill germlings of seaweeds. Ascophyllum nodosum is particularly intolerant of abrasion from trampling (Holt et al., 1997). It is also likely to be removed if shores are mechanically cleaned following oil spills. Recovery would be slow due to the slow growth rate and poor recruitment of the species.|
|Ascophyllum nodosum is normally permanently attached to the substratum and cannot re-establish itself if detached. Only the unattached forms, such as Ascophyllum nodosum var. mackaii, can tolerate displacement. Recovery would be slow due to the slow growth rate and poor recruitment of the species. The lack of recovery of Ascophyllum nodosum from harvesting is well documented. For example, in their work on fucoid recolonization of cleared areas at Port Erin, Knight and Parke (1950) observed that even eight years after the original clearance there was still no sign of the establishment of an Ascophyllum nodosum population. The species is extremely fertile every year and Printz (1959) suggests it must be assumed that some special combination of climatic or environmental conditions is needed for an effective recolonization.|
|The disappearance of Ascophyllum nodosum from Oslofjord has been attributed to the reduced ability of germlings to recruit at highly polluted sites (Sjoetun & Lein, 1993). However, Hoare & Hiscock (1974) observed that Ascophyllum nodosum was found within 100m of an acidified, halogenated effluent discharge, although plants had abnormal and retarded growth. Recovery is slow due to the low growth rate and poor recruitment levels of this species (Holt et al., 1997).|
|The disappearance of Ascophyllum nodosum from Oslofjord has been attributed to an increase in pollution and copper at concentrations of 1039nM (66µg/L) have been found to inhibit the growth of Ascophyllum nodosum (Strömgren, 1979a). However, adult plants appear to be fairly robust in the face of heavy metal pollution (Holt et al., 1997) and so intolerance is reported to be low. For example, the species penetrates into the metal polluted middle reaches of Restronguet Creek in the Fal estuary system where concentrations of both copper and zinc are in the region of 1000-2000µg/g in the sediment and 10-100µg/l in seawater (Bryan & Gibbs, 1983). Although Ascophyllum nodosum accumulates copper this can be removed because the species naturally sheds its epidermis at regular intervals (Stengel & Dring, 2000). Earlier life stages of Ascophyllum nodosum are probably more sensitive than adult plants. Therefore on return to normal conditions growth rates should gradually return to normal.|
|Experimental studies have found that long-term exposure to low levels of diesel reduces the growth rate in Ascophyllum nodosum. For example, in mesocosm experiments, Bokn (1987) observed growth inhibition at a diesel concentration of 130 ppb and that inhibition stops when the oil is removed. Thus, a limited amount of oil pollution need not be detrimental to a population with good recruitment (Sjoetun & Lein, 1993). However, Ascophyllum nodosum generally has poor recruitment so populations may take a long time to recover and hydrocarbon contamination may also prevent fertilization and germination and hence recruitment. If plants are heavily oiled the fronds can become severely overweighted by oil and be broken by waves. This may be no more detrimental than a severe storm if a few blades are lost, but the loss of too many blades can be harmful (Lobban & Harrison, 1997).|
|No information||No information||No information||Not relevant|
|Ascophyllum nodosum, like several other intertidal algae, is able to accumulate nitrogen in its tissues in response to seasonal availability. A reduction in the level of nutrients could reduce growth rates in Ascophyllum nodosum. A slight increase in nutrients may enhance growth rates but high nutrient concentrations could lead to the overgrowth of the algae by ephemeral green algae. Ascophyllum nodosum plants, when transplanted into sewage-stressed areas have become heavily infested with epiphytes and frequently overgrown by Ulva species and there are reports of a decline in populations of the species in the North Atlantic as a result of increased eutrophication (Fletcher, 1996). On return to normal nutrient levels the growth rate would be quickly restored.|
|Ascophyllum nodosum is euryhaline with a salinity tolerance of about 15 to 37 psu (Baardseth, 1970). The species can also withstand periodic emersion in freshwater (Baardseth, 1970) and frequently inhabits estuaries where salinity is variable. Doty & Newhouse (1954) reported Ascophyllum nodosum from estuarine waters with a maximum salinity of 17.3psu and a minimum of 0psu. Further evidence is provided by Chock & Mathieson (1979) who found Ascophyllum nodosum plants in the laboratory exhibited net photosynthesis at salinities from 0 to 40 psu although the long term effects within this range were not evaluated. Intolerance to salinity changes is therefore assessed at low. Once salinity levels have returned to normal the seaweed will rapidly recover.|
|No information||No information||No information||Not relevant|
|There is insufficient information to make an assessment.|
|No information||Not relevant||No information||Not relevant|
|Although bacteria and fungi are associated with Ascophyllum nodosum no information could be found on any disease causing microbes. Nematodes have been associated with small, round galls, usually located near the air vesicles in Ascophyllum nodosum (Barton, 1892).|
|No information||Not relevant||No information||Not relevant|
|Harvesting of Ascophyllum nodosum will severely affect the population if the whole plant is removed. If stumps 10-20cm high are left the plants will re-sprout and harvesting is possible in 3 to 6 years (Baardseth, 1970). Where the whole plant is removed recovery is slow due to the slow growth rate and poor recruitment of Ascophyllum nodosum. In their work on fucoid recolonization of cleared areas at Port Erin, Knight and Parke (1950) observed that even eight years after the original clearance there was still no sign of the establishment of an Ascophyllum nodosum population. Even in an area where many plants remained after harvesting no repopulation was seen for several years (Printz, 1959). The species is extremely fertile every year and Printz (1959) suggests it must be assumed that some special combination of climatic or environmental conditions is needed for an effective recolonization. Recovery of the population to original abundance and biomass is therefore, likely to take a very long time.|
|Tolerant||Not relevant||Not sensitive||Not relevant|
|There are no other species that are required as a host or prey for Ascophyllum nodosum.|
|Northern Ireland Priority Species|
|National (GB) importance||Not rare/scarce||Global red list (IUCN) category||-|
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This review can be cited as:
Last Updated: 29/05/2008