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© Debbie MacKenzie, March 2003

Chondrus crispus (click on photo to enlarge) growing a couple of meters below low water mark where a fair degree of constant water motion exists (near the mouth of Shad Bay, N.S.) The normal summertime color of this seaweed is shown here to be predominantly shades of light green and yellow. This seems unlikely to have been such a common sight in the nineteenth century, when the tendency of this plant to turn green was suspected to be “pathological” and was noted to occur only in marginal habitat such as “pools near high water mark.” See also the eye-catching appearance of white Irish moss in the wave-swept rocky intertidal zone in Nova Scotia last summer.

Abstract:

On the rocky coast of Nova Scotia, in Atlantic Canada, areas that previously supported thick growth of dark red Chondrus crispus now increasingly produce smaller specimens that fade to green and yellow during summer. This color change signals a significant decline in photosynthesis (primary production) by this plant. If this has resulted from a decline in the availability of nitrogen fertilizer in the seawater, a wider and more general decline in marine production is implied. An attempt to discover the prevalence of green and yellow, versus red, Chondrus crispus in the past was made by a literature search, the results of which suggest that recent observations might be part of a significantly longer term trend.

Introduction
My personal experience of the shifting baseline of color in Chondrus crispus (Irish moss)
Discussion
Conclusions
Excerpts from the older scientific literature, including writers’ comments on the color of Chondrus crispus, in chronological order.
References

Introduction:

Why is this important? Briefly, the simplest explanation for the increased fading of these red seaweeds to green is that they are experiencing a drop in the availability of nitrogen-fertilizer in the seawater. The energy (or food) that becomes available to the entire marine ecosystem is ultimately determined by plant growth (photosynthesis) that occurs in the ocean. While the health of the whole ecosystem does not hinge on Chondrus crispus as such, it does depend on marine plant growth. Therefore, a decline in the supply of plant fertilizer in seawater will have a negative impact on the growth of many marine species, certainly including commercial fish stocks. This realization may offer an important insight into the reasons for the extreme slowing of growth rates (FRCC, 2003) that has occurred in many fish species. Growth rates of phytoplankton are notoriously difficult to determine due to their short lived nature, mobility and tendency to be eaten by zooplankton. Therefore, the firmly anchored, long-lived seaweeds such as Chondrus crispus may prove to be more useful monitors of the potential for net photosynthesis in the larger coastal ocean. If moss patches that were red in the past are now fading to green and white, this should at least raise the question of whether marine nutrient cycling in general is slowing.

My personal experience of the shifting baseline of color in Chondrus crispus (Irish moss)

My baseline is established: 1971 - initial encounter at East Dover, Nova Scotia, Canada.

Around this time, in the little fishing village where I grew up, the boys discovered a way to make some money in the summer. My older brother and cousins were collecting, drying and selling Irish moss. I insisted that I be included in this venture and spent a couple of summers working with the moss as well, before moving on to a more lucrative summer job. My mother worried about me raking moss because it was ‘rough’ work done from a small wooden rowboat. ‘Rough’ because the moss was only accessible on rocks that were exposed to noticeable wave action. We used long handled rakes to pull the seaweed from large granite rocks at ‘moderately exposed’ locations, since no useful patches were to be found inside the sheltered coves. Even on a calm day, the little boat moved constantly up and down with the surge of the waves, and I recall many uncontrolled boat-rock collisions. No wonder my mother didn’t like it; I don’t remember particularly liking it either. But I did make a few dollars, and I can still clearly recall what the Irish moss looked like, which rocks it grew on, and the dark purplish mounds of it that we collected.

The baseline shifts: 2001 - my second encounter at East Dover.

For thirty years, Irish moss rarely crossed my mind. I did other things, moved away, moved back, but eventually the summer of 2001 found me meandering along the old familiar shoreline in a sea kayak. By this time my eyes had been opened to the tragic loss of marine life that has occurred during my lifetime, and I was becoming increasingly alarmed by the disastrous trends in commercial fish stocks. But I had not yet fully grasped the idea that it is the entire marine ecosystem that is changing. Until the moment I was daydreaming, drifting in my kayak and awoke to find myself staring into a bed of Irish moss, just a few feet away, that was one of those exact spots where I had raked the stuff 30 years earlier…and it suddenly struck me that not only were the plants no longer large enough to catch with a rake, but that their color had changed dramatically. The “red seaweed” that had grown there 30 years ago in dark shades of brownish to purplish red, was now a bright greenish gold. And no-one has raked moss here for many years. Bizarre, I thought…what happened to the seaweed?

One point of the ‘shifting baselines’ theme is that people, including scientists, first encountering the Irish moss at East Dover in 2001, are apt to accept the current bright green-gold color as “normal,” whereas it strikes me, the ‘oldtimer,’ as being distinctly ‘abnormal.’

My personal observation of a decades-long shift in the color of Irish moss at a particular Nova Scotian location, from summertime shades of purple-brown-red to green-yellow-white, seems to suggest that the habitat regularly occupied by this seaweed species has gradually become less favourable to its growth. It is important to note that mine is not the only observation to suggest a declining growth of Chondrus crispus in Nova Scotia.

Ideal conditions for the harvest of commercial quantities of Chondrus crispus formerly existed in Lobster Bay, on the southwest corner of Nova Scotia, in a large bay full of islands where wave action is damped, but the effects of the nearby Bay of Fundy tides are felt in strong tidal currents. Calm enough at slack low tide to easily collect large quantities of seaweed, Lobster Bay supported a considerable commercial enterprise based on Irish moss. But the production of moss in the bay fell to where the commercial harvest virtually ended a few decades ago. Besides a downturn in the ground fisheries and an upswing in the lobster fishery, local people noted a decline in the quantity of Irish moss growing in Lobster Bay. Former moss harvesters in the area assumed that maybe it had failed because they had “raked it too hard,” and they describe the normal color of the moss they collected as a greenish-yellow (personal communication). However, scientific experiments (MacFarlane, 1952) demonstrated that Chondrus beds damaged by “over-raking” recover in less that two years. Some other factor must have come into play to discourage the seaweed growth. The greenish-yellow color reported by the former moss rakers suggests that the moss inside the bay was long experiencing marginal growth conditions, and a slight downshift in nutrient availability beyond that might have helped tip the balance to end the harvest.

Also, a government scientist employed by the Canadian Department of Fisheries and Oceans who has studied commercial seaweeds, including Chondrus crispus, for decades in Nova Scotia, reports agreement with my basic observation: that in recent years there has been an increasing tendency for Chondrus crispus to lose its red color and become “bleached” in summertime (personal communication, Glyn Sharp).

The healthiest, best fertilized examples of Chondrus crispus have long been known to be the darker, redder plants, but the tendency of this red algae to turn green when poorly fertilized and exposed to direct sunlight has also been recorded in scientific literature dating back over 150 years (Harvey, 1849, Harvey, 1846-1851, Harvey, 1853). The question of whether the prevalence of “bleaching” (turning green) of Irish moss has been increasing over time, however, I have not found addressed in the literature. Seaweed science tends to be very descriptive, but time-series data sets, such as might verify my anecdotal observation, are generally lacking. I therefore looked back through a century and a half of seaweed literature to try to get a sense of how common the sight of “bleached” Irish moss might have been to the earliest observers, in an attempt to discover whether its earlier prevalence was different from what we see today.

What seems to emerge is a longer “shifting baseline” in which bleached Irish moss began as a relative oddity, first noted to occur specifically in “unfavourable” areas such as in “shallow pools near high water mark…exposed to strong sunlight,” (Harvey, 1849). This describes extremely marginal habitat for this species, with conditions of still water (i.e. low fertilizer availability) and high irradiation. This unusual occurrence of green Chondrus crispus plants was at first sometimes omitted from detailed scientific descriptions of the species (most notably by Darbishire, 1902), and was later described in terms that suggest that green was not considered “normal,” not the “true color” of the plant (Farlow, 1891, Taylor, 1957, Kingsbury, 1970). It was commonly acknowledged that the green color appeared in relatively unfavourable habitat. In reference to a century old (German) text, Buggeln and Craigie (1973) commented that green fronds were “at first thought to be pathological.” But more recent descriptions of Chondrus crispus, from both sides of the North Atlantic, describe a summertime tendency to turn green “where exposed to direct sunlight” as a simple matter of course, which agrees with my recent personal observations. The appearance of green Chondrus crispus specimens in the natural habitat seems therefore to have possibly shifted from a minor occurrence in the mid-nineteenth century, something relatively unusual and somewhat “abnormal,” to a very common and "normal" observation today.

Since Chondrus crispus, an extremely common seaweed in North Atlantic temperate zones, forms a band on rocky shorelines and is commonly exposed to air at low tide, many of the plants observed by the earlier writers were also necessarily exposed to “direct sunlight.” However, Otto Darbishire, in his 42 page scientific account of the species, Chondrus (1902), makes no mention of any natural occurrence of green or yellow specimens. Undoubtedly Darbishire was aware that Chondrus crispus occasionally bleached to green in nature, since he was considered to be highly knowledgeable on the subject, and in his text he made reference to Harvey’s earlier publications which include a description of the color of bleached specimens. But perhaps Darbishire did not include bleaching of Chondrus crispus in his description of the species because he did not extend the scope of his work to the inclusion of ‘pathologies’ that might occasionally affect the plant.

In Nova Scotia today a generalized tendency of Chondrus crispus to bleach to green, yellow or white where exposed to direct light is routinely seen across the range of its habitat. Far from an occasional phenomenon limited to “high, shallow tide pools” (i.e. still water) summertime bleaching now routinely affects sunlit subtidal plants exposed to moderately strong water movement as well as intertidal specimens exposed to more intense wave action. Modern observers of the species cannot fail to see this. (See recent photos and description of a white Irish moss belt and gallery of Irish moss photos.)

It has been shown experimentally that the intensity of color in Chondrus crispus (whether it tends toward red or green) is largely determined by the balance between the degree of light stimulation and the availability of fertilizer, specifically nitrogen. (Buggeln and Craigie, 1973) With adequate fertilization, Chondrus crispus can maintain a deep red color despite continuous direct light exposure. (Neish and Shacklock, 1971, cited by Buggeln and Craigie, 1973)

This suggests two initial hypotheses for the shifting baseline in moss color:

(1) There has been a change in the quality of sunlight (for example, increased ultraviolet radiation) such that the seaweed is now more easily light-stressed.

(2) There has been a decline in the availability of nitrogen fertilizer to these plants, with the result that they have a lowered resistance to light-stress.

My preferred hypothesis is the second one, because declining trends in other associated organisms such as rockweeds, mussels, and barnacles (unaffected directly by UVR) also seem to suggest a generalized lowering of marine organic production, or nutrient cycling. Regardless of the cause, however, the color change in Chondrus crispus reflects a substantial decline in the rate of photosynthesis (or primary production) by the plant. (Wurmser and Dulceaux (1921) reported that the rate of photosynthesis in red fronds was 50 - 85% higher than that in green fronds. (cited by Buggeln and Craigie, 1973))

A long-term shift in the ‘normal’ color of Irish moss from red towards green may be an important observation. If this seaweed, dependent for its growth on the availability of plant fertilizers in coastal water, is experiencing a gradual growth decline due to a mounting nitrogen shortage in seawater, then it becomes a reasonable assumption that free floating algae in the same area, the phytoplankton, is similarly affected. A general declining trend in phytoplankton production will predictably translate into a decline in total marine food production, that will ultimately be felt by all marine consumers. Beyond the implications for fish stocks (where frank starvation is now easily observed: e.g. see Atlantic cod), such a decline in marine plant growth rates will inevitably limit the food availability for all other larger marine life forms, such as whales and seabirds…as everything is connected.

Darbishire’s failure to describe the bleaching of Chondrus crispus does not prove that it was less common in his time than it is today, but to observe this species today and the frequency with which it displays shades of green, yellow and white, it is hard to imagine any scientist writing a comprehensive description of the species and describing the color of the plant only as “dark red to light pink, and a brownish colour with a dash of pink.”

It seems clear that Chondrus has always turned green in marginal habitat, but the older literature describes this as being spots such as “shallow pools near high water mark.” In contrast, a characterization of the typical habitat in which Chondrus turns green today would include almost everywhere that sunlight hits it…except in situations where fertilization is augmented by extreme water motion, for instance. (An example of this can be seen at Peggy’s Cove.) There would seem to be a substantial difference now, as in the past, between the growth possibilities of this plant in high tide pools as opposed to the prime habitat from which I once raked the stuff. From my observations over the last few summers, I would be hard pressed to say that I have ever seen Chondrus crispus, of any color, growing in a “pool near high water mark.” Survival in such locations may no longer be possible.

It would be interesting to try to reassess the exact sites where the early scientists made their seaweed observations. I wonder, for instance, if those “pools near high water mark” which provided marginal habitat for Chondrus crispus in the mid-nineteenth century, still support the growth of the species at all. In several recent summers of close observation, I have seen specimens of Chondrus growing in tide pools, but not in any that were “near high water mark.” A gradual declining trend in the availability of fertilizer in seawater would render marginal habitat too poor to continue to be used, and richer natural habitat less favourable than it was previously. The change in many seaweed species might be so subtle as not to be noticed, as they just gradually slowed their growth rates. It is fortunate, perhaps, that a red algae such a Chondrus crispus in this situation will at some point pass a fertilization threshold which will trigger a highly visible color change from red to green or yellow. But, due to the superimposition of such a slow shifting baseline on the typically short human attention span, it seems that we may have missed this important signal.

The validity of my explanatory hypothesis (that a long term decline in the rate of marine primary production is what is reflected by the changing hues of Chondrus crispus) needs to be assessed in the context of changes in other species…i.e. how does everything, all the changing trends in marine life, fit together? Do other marine plant species show signs of abandoning marginal habitat? (Yes, see rockweed.) What about marine animal life; are there indications of a slow decline in their food supply? Are those species slowing their growth rates and abandoning the least favourable parts of their former ranges? (Yes, see barnacles, and codfish.)

What else was different in the North Atlantic coastal ocean in William Harvey’s and Otto Darbishire’s time? For one thing, it can be stated with certainty that there were a lot more fish swimming in the water in those days. Has a decline in marine photosynthesis accompanied, and maybe been causally associated with, the decline in the numbers of fish? Unexpected, to be sure, but this is the type of question that needs consideration today.

Unfortunately, our fractured approach to the scientific study of marine life seems to have prevented us from appreciating how intensely interconnected all marine life forms are. We have not fully appreciated the extent of the reciprocal nature of plant-animal relationships in the sea. And scientific efforts to monitor the health of the ocean, a photosynthesis-dependent ecosystem, have largely neglected to include health assessments of the largest plants, the seaweeds.

1. 1846-1851 Phycologia Britannica by William Henry Harvey (Volume 3)

“Habitat. On rocky sea shores, extending from three quarters tide level to low water mark, and beyond it…Very abundant on the shores of the British Islands.

Geog. distr. Shores of Europe from North Cape to Gibraltar. Not found in the Mediterranean? Eastern shores of North America.

Descr.…the colour is extremely variable, ranging from a yellowish green to a livid purple, or a purplish-brown.”

2. 1849. Manual of the British Marine Algae. by William Henry Harvey.

“But the young student must be careful not to place too absolute dependence on colour alone, in referring plants which he may gather to their place in the system; for some species, which in their healthy state are red, or of that class of colour, become, when grown under unfavourable circumstances, of an orange, yellowish, whitish, or greenish shade…Chondrus crispus too, when found in shallow water, exposed to strong sunlight, is often of a bright herbaceous green…”

“Chondrus crispus, L. …Colour, various shades of purple or greenish; in shallow pools near high-water mark, generally yellow or pale green.”

3. 1853. Nereis Boreali-Americana: or, Contributions to a history of the Marine Algae of North America Part II - Rhodospermeae. by William Henry Harvey.

Regarding Chondrus crispus: “Colour varying from a dull livid purple to greenish and yellowish.” And, from his notes on red algae in general: “colour varies through every shade of red and purple into red brown, or pure brown; and degenerates under the influences of sun-light and shallow water, into orange, yellow, or dull green.”

W. H. Harvey documented seaweed growth on both sides of the North Atlantic, and made no notes of any difference between the characteristic color of Chondrus crispus growing on the eastern and western shores.

4. 1867. British Sea-Weeds: And Introduction to the study of the Marine Algae of Great Britain, Ireland, and the Channel Islands. by Samuel Octavus Gray

This author’s description of Chondrus crispus includes no notes on color, other than classifying it as a red seaweed, but describes in some detail its variable morphology.

5. 1891. The Marine Algae of New England. by W. G. Farlow.

Regarding the Florideae, the group of species including Chondrus crispus: “Their color is always some shade of red or purple when they are growing in their normal condition. When, however, they grow in positions where they are much exposed to light they become green, and in decaying they pass through various shades of orange and yellow to green. Their favorite place of growth is below low-water mark and in deeper water, but some species grow in tide-pools.”

Regarding Chondrus crispus: “Fronds purple…Common from New York northward…When growing exposed to the light, the color is a yellow-green.”

(At this point, green and yellow specimens were thought to be “decaying,” not in “their normal condition.” Contrast this with photos posted on a commercial seaweed website in 2000, in which the normal appearance of the plant is shown to be markedly yellowed: http://www.seaweed.ie/isio/Companies/Seaweed%20Ltd./SeaweedLtd.html )

6. 1902. Chondrus. by Otto V. Darbishire

This 42 page text, with 7 plates, was written by Otto V. Darbishire of the Liverpool Marine Biology Committee. Unlike the previous sources cited here, in which Chondrus crispus was briefly described in books which catalogued many other species, this work was devoted to just this single species.

Beginning in 1885, the LMBC organized “dredging, trawling and other collecting expeditions,” and eventually produced the “LMBC Memoirs,” described as “a series of special studies, written by those who are thoroughly familiar with the forms of which they treat.” Darbishire’s “Chondrus” was No. 9 in this series.

Darbishire offers a detailed description of the state of scientific knowledge about Irish moss a century ago, based on, it would seem, at least 15 years of observations. He included much detail on the extent and variation of habitat occupied, the varied morphology of Chondrus plants at different levels of the intertidal zone, as well as seasonal growth and reproductive cycles, and microscopic details of structure. Nowhere in his text does Darbishire describe seeing green or yellow Irish moss in nature. He describes studying both fresh, live specimens and those “thrown up after a gale” but recommends using the fresh ones. Here are the total of his comments on the color of Chondrus crispus:

“The color of the frond varies from dark red to light pink, and a brownish colour with a dash of pink.”

Microscopic histology: “…the central cells of the shoot are easily distinguished by their red contents…the external cells, distinguished by their dark red colouring…” Regarding the holdfast: “The cells of the attachment organ…are reddish in colour, but the latter is not as dark as in the assimilating cells of the upright shoot.” “The Rhodoplastids are best developed in the assimilating cells. They are seen here to be of a dark red colour. The red colour is made up of a mixture of chlorophyll and phycoerythrin, the latter completely obscuring the former. The latter may be extracted by submersion in fresh water for some time, preferably in warm water. The plant will remain green, the chlorophyll being insoluble in water.”

Darbishire obviously observed Chondrus exposed to relatively high degrees of light: “Chondrus crispus, as a plant lying quite exposed when the tide recedes, extends from 3(feet) to 4(feet) above 0 downwards (0 is dead low water mark of an ordinary spring tide)…As a general rule the upper plants are shorter, broader and thinner than the lower ones. The latter are stouter, very much longer, and the frond is divided into narrower lobes than are found higher up When growing in pools Chondrus crispus has been found up to a height of 9(feet) above 0, being often fairly broad, but never very high. It is a plant which is completely exposed only for a short time.”

Thus, the only mention made of green Chondrus by Darbishire is in his description of how to extract the red pigment by soaking plants fresh water (establishing at least than he was not colour blind). It appears that Darbishire had written the most comprehensive scientific description of the species until his time, having “surveyed more or less in detail the development, structure and ecology of Chondrus crispus,” without noting the occurrence of bleached plants in nature. But he surely knew of the occasional occurrence of green Chondrus as described decades earlier, since he refers in his text to “The very good Phycologia Britannica of Harvey.” At one point Darbishire comments that “The forms and varieties mentioned here and there in the literature are of no special value”…seemingly dismissing the tendency of previous authors to assign many different names to the different growth patterns assumed by this plant under different conditions, especially when occurring at different levels of the intertidal zone, and under differing degrees of wave exposure. But Darbishire may also have been dismissing the early accounts of color changes in the species as being not particularly noteworthy.

7. 1931. A Handbook of the British Seaweeds. by Lily Newton.

“The Rhodophyhceae are red or deep purple when growing normally. In shallow bays where very few genera are able to exist the plants become greenish, as e.g. Chondrus crispus, which will grow in shallow pools exposed to a great deal of light.”

8. 1933. Observations of the seasonal changes in the marine algae in the vicinity of Halifax, with particular reference to winter conditions. by Constance MacFarlane and Hugh P. Bell, published in the Proceedings of the Nova Scotia Institute of Science, xviii, pt 3.

Observations were made about 20 kilometres from the East Dover shoreline, and the description of Chondrus crispus includes: “Colour varies from deep fluorescent purplish red to a light green,” without elaborating on the characteristics of the habitat where the green specimens were found.

9. 1949. A Study of certain British Seaweeds and their utilization in the preparation of Agar. by S. M. Marshall, L. Newton, and A. P. Orr.

Chondrus crispus is simply described as “deep red” in colour; there is no mention of seasonal bleaching in this text.

10. 1957. Marine Algae of the Northeastern coast of North America. by William Randolph Taylor.

“…New Jersey to Nova Scotia, P.E.I. and Newfoundland, growing throughout the year on rocks, shells, or woodwork, in tide pools and the intertidal belt, descending to moderate depths, often exceedingly common, particularly on exposed stations, where shaded developing normal coloration, but where exposed to the light bleached and greenish, yet actively growing, through the year…”

11. 1963. British Seaweeds. by Carola I. Dickinson.

“Purplish-red plants with a tendency to turn green in strong sunlight.”

12. 1970. The Rocky Shore by John M. Kingsbury.

“In fully exposed, sunny locations, especially near its upper limit, Irish moss is often bleached. Its true color is a deep burgundy red (look for plants growing in the shade of overhanging rockweeds), but bleached plants have yellowish or greenish branches.”

13. 1973 - Chondrus crispus. by M. J. Harvey and J. McLachlan.

“Seasonal greening of natural Chondrus populations has long been noted…” “Abrupt decline in phycoerythrin occurred during April in plants exposed to direct sunlight…It was shown by Haxo and Strout (1950) that bleached (= green) thalli of Chondrus, collected in late summer, would respond to treatment with 0.01 - 5.0 mM KNO3, NH4Cl, NaNO3, and NH4NO3 with the reappearance of phycobilins. These results suggest that, in some cases, loss of phycobilins may result from a nitrogen deficiency…Neish and Shacklock (1971) have also found that additions of NH4+ or NO3- salts will prevent bleaching of Chondrus growing under continuous irradiation.” (This quote included here in support of my mounting nitrogen deficiency hypothesis to explain the increasing extent of Chondrus bleaching seen today.)

14. 1977 - Seaweeds of the British Isles. by Peter S. Dixon and Linda M. Irvine, British Museum (Natural History) London.

The color of Chondrus crispus is described as “dark reddish or purplish brown, bleaching to a greenish yellow, frequently iridescent at the tips.”

15. 1977. Seaweeds A Color-Coded, Illustrated guide to Common Marine Plants of the East Coast of the United States. by C. J. Hillson.

“Color varies from deep reddish purple, almost black tones in shaded or deep growing plants, to a yellow-green or pinkish green color in plants exposed to strong light.”

16. 1977. The Seaweed Handbook, An Illustrated guide to seaweeds from North Carolina to the Arctic. by Thomas F. Lee.

“In deep water the fronds are quite long and dark purple-red, while in shallow water or in tide pools they are short, compact and of a pale green-red hue. Sunlight striking the fronds often gives them a curious iridescent metallic sheen.”

17. 2000. An Irish company, Seaweed Limited, that markets Chondrus crispus includes two photographs of the live plant on its webpage. In both instances the Irish moss shows clear signs of bleaching, suggesting that these yellowish tones now typify the ‘normal’ appearance of this seaweed. See: http://www.seaweed.ie/isio/Companies/Seaweed%20Ltd./SeaweedLtd.html

18. 2002 - Description of Chondrus crispus on the website of the Marine Life Information Network for Britain and Ireland ( http://www.marlin.ac.uk/demo/chocri.htm )

“Chondrus crispus is a small purplish-red seaweed (up to 22 cm long) found on rocky shores and in pools…This seaweed is highly variable in appearance depending on the level of wave exposure of the shore and has a tendency to turn green in strong sunlight.”

See gallery of Irish moss photos.

Buggeln, R. G. and J. S. Craigie. 1973. The Physiology and Biochemistry of Chondrus crispus Stackhouse. In M. J. Harvey and J. McLachlan (eds) 1973. Chondrus crispus. Nova Scotia Institute of Science.

Darbishire, Otto V. 1902. Chondrus. Liverpool Marine Biology Committee, Memoir 9.

Dickinson, Carola I. 1963. British Seaweeds. London: Eyre and Spottiswoode.

Dixon, Peter S. and Linda M. Irvine. 1977. Seaweeds of the British Isles. London: British Museum (Natural History).

Farlow, W. G. 1891. The Marine Algae of New England. Washington: Government Printing Office.

FRCC, 2003. 2003/2004 Conservation Requirements for Groundfish Stocks on the Scotian Shelf and in the Bay of Fundy (4VWX5Z), in Subareas 0, 2+ 3 and Redfish Stocks. Ottawa: Fisheries Resource Conservation Council ( http://www.frcc-ccrh.ca )

Gray, Samuel Octavus. 1867. British Sea-Weeds: And Introduction to the study of the Marine Algae of Great Britain, Ireland, and the Channel Islands. London: L. Reeve & Co.

Harvey, M. J. and J. McLachlan. 1973. Chondrus crispus. Nova Scotian Institute of Science, Halifax, Nova Scotia.(155 pp)

Harvey, William Henry. 1846-1851. Phycologia Britannica (Vol. III) London: Reeve and Benham.

Harvey, William Henry. 1849. Manual of the British Marine Algae. London: John Van Voorst.

Harvey, William Henry. 1853. Nereis Boreali-Americana: or, Contributions to a History of the Marine Algae of North America. Part II - Rhodospermeae. Published by the Smithsonian Institute. New York: G.P. Putnam & Co.

Hillson, C. J. 1977. Seaweeds A Color-Coded, Illustrated Buide to Common Marine Plants of the East Coast of the United States. The Pennsylvania State University Press.

Kingsbury, John M. 1970. The Rocky Shore. Connecticut: The Chatham Press.

Lee, Thomas F. 1977. The Seaweed Handbook, An Illustrated Guide to Seaweeds from North Carolina to the Arctic. New York: Dover Publications.

Lobban, Christopher S. and Paul J. Harrison. 1994. Seaweed Ecology and Physiology. Cambridge University Press.

MacFarlane, Constance. 1952. A Survey of Certain Seaweeds of Commercial Importance in Southwest Nova Scotia. Can. J. Bot. 30:78 - 97.

MacFarlane, Constance and Hugh P. Bell. 1933. Observations of the seasonal changes in the marine algae in the vicinity of Halifax, with particular reference to winter conditions. Proceedings of the Nova

Marshall, S. M., L. Newton and A. P. Orr. 1949. A study of certain British seaweeds and their utilization in the preparation of agar. London: His Majesty’s Stationary Office.

Newton, Lily. 1931. A Handbook of the British Seaweeds. London: British Museum (Natural History).

Taylor, William Randolph. 1937. Marine Algae of the Northeastern coast of North America. University of Michigan Press.