Biodiversity & Conservation

LR.LR.Ov.RhoCv

Explanation of sensitivity and recoverability


Physical Factors

Substratum Loss
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The community is dominated by algae which form permanent attachments to the substratum. Removal of the substratum would remove these species and slow moving species associated with them. Intolerance has been assessed to be high. Recoverability is likely to be high (see additional information below).
Smothering
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A 5cm covering of sediment is likely to be washed away with the wave motion against the cave walls. Whilst smothering is generally unlikely on the vertical walls of caves, it may occur at the base of the walls. Impermeable materials, such as concrete, oil, or tar, are likely to have a greater effect. An intolerance of intermediate is recorded. A recoverability of high is recorded (see additional information below).
Increase in suspended sediment
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As the species in the biotope are probably adapted to high suspended sediment concentrations a sensitivity of 'not sensitive' has been recorded.
Decrease in suspended sediment
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Rhodothamniella floridula needs sediment to bind to and will therefore need enough available to do so. If less suspended sediment is available for the species to bind to then it is likely that colonization of bare substratum would be prevented and a reduction in the abundance of Rhodothamniella floridula may occur. Other algae will probably not be affected. Intolerance has been assessed to be low. Recoverability is likely to be high (see additional information below).
Desiccation
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Caves are kept moist, due to wave splash and lack of direct sunlight. However if wave splash was stopped due to coastal defences desiccation is likely to occur. Little is known of the desiccation tolerance of Rhodothamniella floridula, it may be protected further from desiccation by the water held in the sand it binds with. Intolerance has been assessed as intermediate.
Increase in emergence regime
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An increase in emergence is likely to shift the distribution of Rhodothamniella floridula lower down the shore if suitable habitats exist. Replacement may occur by other flora and fauna more tolerant of desiccation. Some mortality of key species is likely, so an intolerance of intermediate has been recorded. Recoverability is likely to be high (see additional information below).
Decrease in emergence regime
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Decreases in emergence may put the algal species in competition with species that typically remain submerged (e.g. laminarians). This could result in a depression in the limits of the LR.RhoCv biotope or a shift of the biotope. An intermediate intolerance has been recorded. Recoverability has been assessed to be high (see additional information below).
Increase in water flow rate
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Moderate water movement is beneficial to seaweeds as it carries a supply of nutrients and gases to the plants and removes waste products. No information has been found on tolerance of the biotope to water flow rates. This biotope occurs in wave exposed situations (Connor et al., 1997b) where the forces of wave surge are likely to be much more damaging than an increase in tidal flow. However, an increase to stronger flows may inhibit settlement of spores and remove adults or germlings. Water flow would probably be reduced inside the enclosed caves compared to outside. It is unlikely therefore that the benchmark increase in water flow rate would result in mortality. Therefore, the biotope is probably relatively tolerant of increases in water flow.
Decrease in water flow rate
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Moderate water movement is beneficial to algae, mussels and barnacles as it provides a supply of food and nutrients to the organism and also helps to remove waste products. A decrease in water flow rate would also mean that scour decreased and it is possible that Rhodothamniella floridula could be out-competed by other species that thrive in environments lacking scour. In areas where wave energy is low, tidal flow may be important in supplying suspended sediment to the biotope and encouraging growth of Rhodothamniella floridula over other species. In such situations a decrease in water flow rate may cause a different biotope to develop. Mortality of key species is likely to occur and a decrease in growth and respiration/photosynthesis is probable. Intolerance has been assessed to be intermediate. Recoverability has been assessed to be high (see additional information below).
Increase in temperature
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Maximum sea surface temperatures around the British Isles rarely exceed 20 C (Hiscock, 1998) and, as Rhodothamniella floridula occurs south of the British Isles, an increase in temperature is not likely to cause mortality. An acute change in temperature may cause photosynthesis and growth to be impaired, compensating for increased spore production. For instance, spore production of Rhodothamniella floridula is higher at higher temperatures (Stegenga, 1978). Increase in air temperature may cause desiccation, bleaching or death to at least the outer fronds.

No mortality of key species is likely to occur, although physiological compensation may take place. Therefore, intolerance has been assessed to be low. When temperatures return to normal, respiration, reproduction and growth will quickly recover. Recoverability has been assessed to be very high.

Decrease in temperature
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Minimum surface sea water temperatures rarely fall below 5 C around the British Isles (Hiscock, 1998). The distribution of Rhodothamniella floridula has not been recorded north of the British Isles and may not be able to survive a chronic decrease in temperature. However, Dixon & Irvine (1977) observed that Rhodothamniella floridula (as Audouinella floridula) grows much faster in winter, but low temperatures may delay or slow reproduction (Stegenga, 1978).

As mortality of characterizing species may occur if chronic changes in temperature occur, intolerance has been assessed to be intermediate. When temperature returns to normal, respiration, reproduction and growth will quickly recover in surviving species. Recoverability has been assessed to be high (see additional information below).

Increase in turbidity
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An increase in turbidity will probably have little direct effect on the key species within this biotope. However, it may cause a reduction in the photosynthetic capability and growth of algae, but will probably not result in any mortality. Intolerance has been assessed to be low. On return to normal conditions recoverability is likely to be high.
Decrease in turbidity
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A decrease in turbidity may mean that more light is available for photosynthesis. However, as the biotope occurs at <10% of natural daylight (Anand, 1937c) and has been recorded near Flamborough Head (George et al., 1998) , where low turbidity is usually present (Marine Task Force, 1993), it has been assessed to be 'not sensitive'.
Increase in wave exposure
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The LR.RhoCv biotope occurs on moderately exposed coasts (Connor et al., 1997b). Increased wave action above this level may cause damage to individual plants, breaking fronds and removing entire plants from the substratum. There may also be increased erosion of the substrate and growths of Rhodothamniella floridula may become dislodged, leading to susceptible patchiness. Therefore, intolerance has been assessed to be high. Recoverability is likely to be high (see additional information below).
Decrease in wave exposure
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Chalk caves are carved into the shoreline by wave action. The LR.RhoCv biotope only occurs on wave exposed shores (Connor et al., 1997b) within these caves. However, characteristic species within the biotope are unlikely to be intolerance of a decrease in wave exposure and may actually benefit. The biotope has been assessed to be being 'not sensitive*' to a decrease in wave exposure.
Noise
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Seaweeds have no known mechanism for detection of noise vibrations. The biotope has been assessed to be not sensitive to noise.
Visual Presence
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Seaweeds are unable to detect visual presence. An assessment of 'not sensitive' has been made.
Abrasion & physical disturbance
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Upper littoral fringe caves are unlikely to be impacted by physical disturbance from anchorage or dredging. However, soft rocks are friable, and physical disturbance may be caused by pebbles, rocks, or marine debris, which accumulates in caves when moved by wave action. Although algal species are highly flexible, abrasion is likely to cause damage to and removal of fronds and may even remove entire plants from the substratum. The cushion-like base of turf forming algae (such as Rhodothamniella floridula) may offer some protection against abrasion but if a portion is removed, the sharp edges may be subject to lifting by wave action. Intolerance has been assessed to be intermediate. Recoverability is likely to be high (see additional information below).
Displacement
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Rhodothamniella floridula and other algae are permanently attached to the substratum. If removed, the attachment cannot be reformed. Therefore, intolerance has been assessed to be high. Recoverability is likely to be high (see additional information below).

Chemical Factors

Synthetic compound contamination
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Rhodothamniella floridula is likely to be highly intolerant of synthetic chemical contamination. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/dispersant mixtures, with little difference between adults, sporelings, diploid or haploid stages (Grandy, 1984, cited in Holt et al., 1995). Cole et al. (1999) suggested that herbicides, such as simazine and atrazine were very toxic to macrophytes. Therefore, a high intolerance has been recorded. Recovery is likely to be high (see additional information below).
Heavy metal contamination
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Bryan (1984) suggested that the general order for heavy metal toxicity in seaweeds is: Organic Hg > inorganic Hg > Cu > Ag > Zn > Cd > Pb. Cole et al. (1999) reported that Hg was very toxic to macrophytes. The sub-lethal effects of Hg (organic and inorganic) on the sporelings of an intertidal red algae, Plumaria elegans, were reported by Boney (1971). 100% growth inhibition was caused by 1 ppm Hg. Intolerance has been assessed to be intermediate. Recoverability is likely to be high (assuming deterioration of contaminants) (see additional information below).

Hydrocarbon contamination
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No evidence was found specifically relating to the intolerance of Rhodothamniella floridula to hydrocarbon contamination. However, inferences may be drawn from the sensitivities of red algal species generally. O'Brien & Dixon (1976) suggested that red algae were the most sensitive group of algae to oil or dispersant contamination. Laboratory studies of the effects of oil and dispersants on several red algal species concluded that they were all sensitive to oil/dispersant mixtures, with little difference between adults, sporelings, diploid or haploid life stages (Grandy, 1984, cited in Holt et al., 1995). Therefore intolerance has been assessed to be high. Recoverability has been assessed to be high (see additional information below).

Radionuclide contamination
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No information concerning the effects of radionuclides on species within the biotope was found and 'insufficient information' has been recorded.
Changes in nutrient levels
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Nutrient availability is the most important factor controlling algal germling growth. Plants under low nutrient regimes achieve smaller sizes and may be out-competed. A moderate increase in nutrient levels may enhance their growth. However, if nutrient loading is excessive this can have a detrimental effect on algal productivity. Therefore, intolerance has been assessed to be intermediate. Recoverability is likely to be high ( see additional information below).
Increase in salinity
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The LR.RhoCv biotope occurs in full salinity. Therefore a low intolerance has been recorded. Recoverability is likely to be very high.
Decrease in salinity
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The LR.RhoCv biotope occurs only in full salinity conditions. It is probable that a proportion of the population would die in lower salinities, or at least be out-competed by brackish water tolerant species. Intolerance has been recorded to be high. Recoverability is likely to be high (see additional information below).
Changes in oxygenation
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The effects of reduced oxygenation on algae are not well studied. Plants require oxygen for respiration, but this may be provided by production of oxygen during periods of photosynthesis. Lack of oxygen may impair both respiration and photosynthesis (see review by Vidaver, 1972). A study of the effects of anoxia on Delesseria sanguinea (a red algae), revealed that specimens died after 24 hours at 15C but that some survived at 5C (Hammer, 1972). Cole et al. (1999) suggest possible adverse effects on marine species below 4 mg/l and probable adverse effects below 2mg/l. As some important species within the biotope may die, an intermediate intolerance has been recorded. Recoverability is likely to be high (see additional information below).

Biological Factors

Introduction of microbial pathogens/parasites
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No information relating to the effects of microbial pathogens on the key species within the biotope was found.
Introduction of non-native species
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No information was found on alien species that may compete with species within the biotope.
Extraction
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It is extremely unlikely that any of the species indicative of sensitivity would be targeted for extraction and we have no evidence for the indirect effects of extraction of other species on this biotope.

Additional information icon Additional information

Recoverability
Following a major loss of the main characterizing species there will be a colonization succession. No information was found relating to colonization or recolonization rates of Rhodothamniella floridula, however, sand-binding algal species, such as Rhodothamniella floridulaare able to colonize soft or crumbly rock more successfully than fucoids (Lewis, 1964). Red algae are typically highly fecund, but their spores are non-motile (Norton, 1992) and therefore highly reliant on the hydrodynamic regime for dispersal. Kain (1975) reported that after displacement some Rhodophyceae were present after 11 weeks, and after 41 weeks, in June, Rhodophyceae species predominated. However, Stegenga (1978) noted that tetrasporangia of Rhodothamniella floridula (as Rhodochorton floridulum) germinated in 'rather low numbers'. Recoverability of the biotope has been assessed as high, although recovery of remote populations will be more protracted and dependent upon favourable currents bringing spores.

This review can be cited as follows:

Riley, K. 2007. Rhodothamniella floridula in upper littoral fringe soft rock caves. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 25/11/2014]. Available from: <http://www.marlin.ac.uk/habitatbenchmarks.php?habitatid=39&code=1997>