Red Algal Zone   4 comments

Red Algal Zone

The Red Algal Zone  is dominated by the red algae Chondrus crispus (Irish Moss) and Gigartina stellata. Both singly or in combination they  form a dense turf that adheres closely to the rock surface.  Attachment is achieved by means of a basally situated, disk-shaped holdfast that is glued to the rock surface.  The red algal zone is out of water for only a few hours each day.


Chondrus crispus (Irish Moss) may be found in tide pools located throughout the tidal range; however it is always submerged and located in shaded portions of upper pools. The close cropped algal turf tends to retain water providing a suitable environment for many invertebrates such as amphipods and isopods. Carageenin, a sulfated polysaccharide is extracted from Chondrus crispus (Irish Moss) and several other species of red algae. It is used in hand lotions, chocolate milk, toothpaste, ice-cream, etc. as a stabilizing and gelling agent. Plants are removed from rock ledges below the level of low tide with a long handled rake. They are then piled into boats and taken to a factory for processing.  Certain species of red algae that produce Carageenin are cultured rather than harvested in their natural habitat. Agar, derived from red algae such as Gracilaria and Ahnfeltia, is used among other things as a thickening agent in ice cream and as a medium for culturing bacteria. Alginic acid derived from brown algae such as Alaria, Ascophyllum, Fucus, and Laminaria, may be used as a stabilizer in ice cream and paint and as a vehicle for suspending drugs such as penicillin in solution.


Chondrus and Gigartina belong to the same family and share similar features. The blades (thallus) of Chondrus are generally smooth and flat unlike those of  Gigartina which are gnarled. Gigartina can also withstand drying out more than Chondrus and is generally found on vertical, quickly draining, surfaces. During winter, Chondrus often sustains  damage possibly as a result of exposure to low air temperatures. The ends of the algae lose photosynthetic red pigments and appear white.


Gigartina stellata X3


The lower edge of the red zone generally represents the position of extreme low tide.


Some of the adaptations that allow Chondrus and Gigartina to live in this zone are:

1. Holdfast that holds them securely to the rock.

2.  Formation of a thick turf that covers most of the rock surface and prevents organisms from settling there.

3. The thick turf also retains moisture, keeping Chondrus and Gigartina from drying out and protects plants from being torn loose by heavy wave action.


Other species of algae often colonize this zone depending on their size and the availability of space to attach to. In the late winter and spring opportunistic green algae such as Chaetomorpha spp.,Cladophora spp. and Ulva spp.,attach in large numbers within all but the Lichen Zone. Chaetomorpha spp. is an unbranched flilamentous green alga whose basal cell is modified as a holdfast allowing firm attachment to a solid surface. There are two common  Chaetomorpha  species. The first is shown below and the second in the two following photographs. Cladophora spp.  is pictured last.


Ulva spp.  (thallus) consists of a sheet of cells (two cells thick in Ulva and one cell thick in Monostroma). Dried Sea Lettuce is sometimes used as a flavoring agent in soups, salads and other dishes. They are firmly attached to the substratum by basal rhizoidal outgrowths (Holdfast). Ulva has two morphologically similar forms, sporophyte and gametophyte. Cells along the edge of the sporophyte undergo reduction division to produce haploid spores with 4 flagella. Each spore grows into a haploid gametophyte. Cells on the edge of the gametophyte form bi-flagellated gametes through cell division. The gametes fuse and the resulting diploid cell grows into a sporophyte. Both genera produce large numbers of spores and gametes and therefore can quickly colonize open space in the rocky intertidal.


Occasionally the green alga Codium spp. Can be found attached to rocks or other algae.The brown alga Leathesia spp. is often found in the red zone as well.


Leathesia spp. X3


The Coralline Red Alga  Corallina officinalis  is a common component of the red zone. It is an erect, branching, red alga whose cells are coated with a thick layer of calcium carbonate. In addition to a basal holdfast, it is articulated, giving the alga great flexibility, an adaptation which protects it from heavy wave action.


Dulse (Palmaria palmata)  is often present in the red zone. It has a basal holdfast  connected to a broad branching blade. Dulse is harvested commercially and in its sun dried form can be eaten raw or used as a flavor enhancer in salads, sandwiches, soups, and stirfries.


The filamentous, branching, red alga Ceramium spp. is occasionally abundant here attached to rock or other algae. It has a basal holdfast and many branching filaments. Dumontia spp. and Polysiphonia spp.  as well as a number of less abundant algae add to the diversity of species found here in the red zone .


Dumontia spp.


Polysiphonia spp.

Polysiphonia spp. X100


If Chondrus or Gigartina are removed from rock surfaces due to heavy wave action, excessive exposure to low temperatures or excessive exposure to high temperatures, other organisms will occupy the vacant space. The blue mussel Mytilus edulis often dominates bare areas in the red zone, however, recently it has essentially disappeared in mid-coast Maine and other coastal intertidal locations. It grows well however in the water column, attached for example to rope mooring lines, and lines suspended in the water used to commercially grow mussels.


The red algal zone extends down to about the low water mark. Below this point lies the Sub-tidal kelp Zone. The upper edge of this zone is only exposed during the lowest of tides.


Most of the animals that live here  can also be found  in the  Sub-tidal Kelp Zone.  They are listed below by Phylum. The list is not all inclusive. Written descriptions are provided for only a few of the species listed below.


Phylum Porifera

Sponges, members of the phylum Porifera, are filter feeders that remove small organisms and detritus from the water column. Water is drawn into small openings called ostia and exits from the sponge through larger openings (oscula). Flagellated choanocytes in the sponge interior are responsible for water movement and feeding.

Leucosolenia spp. X2


 Halisarca spp. X1



Halichondria spp. (Breadcrumb Sponge) X1

 Halichondria spp. (Breadcrumb Sponge) X1


Chalina spp. (Finger Sponge) X1.5


Phylum Cnidaria, Class Hydrozoa

Members of the phylum Cnidaria, Class Hydrozoa , form colonies of feeding polyps that prey on small animals in the water column. Each feeding polyp has tentacles that contain stinging cells (nematocysts). The prey is immobilized by the stinging cells and pushed into the mouth by the tentacles.

Obelia spp. X1


Tubularia spp.




Phylum Cnidaria, Class Anthozoa

Sea anemones (Class Anthozoa) are common inhabitants of the rocky intertidal attached to hard surfaces or other organisms such as mussels. Stinging cells (nematocysts) on the tentacles immobilize prey that is then directed by the tentacles into the mouth.

Metridium senile (Frilled Anemone)

Metridium senile (Sea Anemone)


Phylum Mollusca

Phylum Mollusca, Class Amphineura (Chiton)



Phylum Mollusca, Class Bivalvia

Feeding in bivalve molluscs is discussed in the Barnacle Zone using the blue mussel Mytilus edulis as an example.

Anomia simplex (Jingle Shell)


Modiolus modiolus (Horse Mussel)



Mytilus edulis (Blue Mussel)

Discussed  in the Barnacle and Brown Algal Zones



Placopecten magellanicus (Northern Scallop)


Saxicava spp.



Phylum Mollusca, Class Gastropoda

Buccinum undatum (Waved Whelk)


Lacuna vincta (Northern Lacuna)


Littorina littorea (Periwinkle)

This species is profiled in the Brown Algal Zone page


Phylum Mollusca, Class Gastropoda,

Subclass Opisthobranchia (Nudibranchs)

Nudibranchs (Sea Slugs) are Gastropod Molluscs that lack a shell. The species shown below, typified by Aeolidia papillosa, have an anterior, ventrally placed mouth, a smooth ventral foot, and finger-like projections on the dorsal surface called cerata. Most species have a radula and are carnivorous.


Dendronotus frondosus X4


Aeolidia papillosa X5 Ventral View

Aeolidia papillosa Dorsal View X5


Coryphella spp. X4



Phylum Arthropoda, Class Crustacea, Order Amphipoda

Amphipods  so named because they have appendages that can be used for walking and swimming, are flattened from side to side. They are important scavengers, consuming dead or almost dead animals and plants.  



Phylum Arthropoda, Class Crustacea, Order Isopoda


Isopods, named because their appendages are of equal length and size, are flattened from top to bottom (dorsal to ventral)  Most are scavengers and are consumed often by polychaete worms and juvenile fishes.




Phylum Arthropoda, Class Crustacea, Order Decapoda

Crabs  feed for the most part on blue mussels and Littorina snails. They can crush smaller animals with their claws and directly consume them. Larger prey require more effort. They generally chip away at the shell until they reach the inside or in some cases chip off the shell spire and pull the animal from its shell. They, along with starfish, restrict the distribution of their blue mussel prey especially in the red algal and subtidal kelp zones.

Carcinus maenas (Green Crab) X2


Cancer spp. (Rock Crab)



Homarus americanus (Lobster)

Lobsters generally are nocturnal scavengers. Typical food would include algae, eelgrass, and dead and dying animals. In crowded quarters they often cannibalize themselves. Lobsters in turn are consumed by humans and larger fish such as cod.  These crustaceans build burrows 2-3 feet deep in the sediment where they lie protected during the day. They back into the burrow and face outward. Males introduce sperm into the sperm storage sac of the female. When the female is ready she releases the eggs.Eggs in turn are fertilized by the stored sperm and literally glued to abdominal appendages where they develop into small larvae. Eventually the larvae hatch and are released into the water column where they further develop and then metamorphose into small lobsters.



Phylum Annelida, Class Polychaeta, Family Serpulidae

Serpulids live within  coiled, calcium carbonate tubes which are permanently attached to  solid surfaces such as rock or the epidermis  of algae, especially Chondrus crispus. They extend ciliated tentacles into the water column, as shown in the second photograph, and filter feed on small organisms.

Hydoides spp. X3




Phylum Annelida, Class Polychaeta, Family

Polynoidae(Scale Worms)

Scale worms are dorso-ventrally compressed (flattened). The scales, present on the dorsal surface, are overlapping thin plates (Elytra). Most scale worms are predators capturing prey with pointed jaws. The jaws are located on the inner surface of the first portion of the digestive tract (Pharynx). When the pharynx is turned inside out (Everted), the jaws are visible. They grab small prey and the pharynx is retracted and at that point the prey lie in the digestive tract.

Lepidonotus squamatus  (Scale Worm) X4




Phylum Annelida, Class Polychaeta, Family Terebellidae

Terebellid worms are generally sedentary, tube dwelling polychaetes with a body divided into a head with tentacles, a long thorax and a short coiled abdomen. The ventrally grooved, ciliated tentacles, can be extended over the sediment surface. The tentacle tip is pressed down against the sediment. Mucus secreted here traps organic matter forming a “ball” which is passed through ciliary action down the ventral ciliated groove to the mouth. Red branchiae. that have a respiratory function,arise from the head region.



Phylum Bryozoa

Bryozoans for the most part are sedentary, colonial animals that attach and grow on solid objects such as rock, blue mussel shells, and kelp. They are filter feeders that capture small organisms with their ciliated tentacles (Lophophore). Each individual (Zooid) secretes a calcium carbonate “shell” that is connected to surrounding individuals thrrough small pores. They are preyed on by organisms such as crustaceans, mites, Sea urchins and starfish.


The following videos shows the lophophore emerging from the “shell”. Note the ciliated tentacles that make up the lophophore.



Phylum Echinodermata, Class Asteroidea(Starfish)

The common starfish Asterias spp. (Phylum Echinodermata) are important predators of bivalve molluscs such as the blue mussel Mytilus edulis. They wrap their arms around prey, hold themselves in place with tube feet, and evert the stomach between the shells of the bivalve, digesting  the mussel in its own shell.

Asterias vulgaris (Northern Seastar)X1



Asterias forbsei (Forbs’ Seastar)



Henricia sanquinolenta (Blood Star)

Henricia sanquinolenta feeds on sponge tissue.



Solaster endeca (Northern Sunstar)


The Northern Sunstar, about 15 cm in diameter, feeds for the most part on  green sea urchins.



Phylum Echinodermata, Class Echinoidea (SeaUrchins)

The green sea urchin Strongylocentrotus droehbachiensis  (Phylum Echinodermata) has been responsible for destroying kelp beds along the New England and Canadian coasts. The urchins use their five teeth to scrape tissue from the living alga. Often they scrape away the holdfast, releasing the kelp from its point of attachment. Once kelp has been removed, the browsing activity of the urchins tends to prevent the establishment of new plants. Harvesting of sea urchins for their gonads has greatly reduced populations of these herbivores along the entire New England coast.

Strongtlocentrotus drobachiensis (Green Sea Urchin)



Phylum Echinodermata, Class Ophiuroidea (Brittlestars)




Phylum Urochordata, Class Ascidiacea (Tunicates)

Tunicates are filter feeders. They draw water, containing prey,  into an internal branchial chamber through an upper opening called the incurrent siphon. The water passes through small slits (Gill Slits) in the branchial chamber and is directed to the outside through the lower excurrent siphon. Cilia in the branchial chamber and muscle contractions are responsible for water movement. As the water exits to the outside, prey organisms are left behind and are directed into the digestive tract. The siphons are visible in photographs  3 and 4.


Botryllus schlosseri  (Star Tunicate)



Ciona intestinalis (Vase  Tunicate)



Molgula spp. (Sea Squirt) X6


Posted December 8, 2011 by zottoli

4 responses to “Red Algal Zone

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  1. Mr. Razottoli

    What wonderful pages you have put together. The photographs astonish me.

    I poke around Penobscot Bay a lot and I have a very narrow question for you. In your photo in the Sub tidal chapter you have a marvelous photo whose (hidden) tittle is “Subtidal in Pool Hendricks Point”. And there is a pink formation in there which you did not label but which I have been staring at because it is similar to coral-like formations I found on a beach on a small island at a very low tide. In the photo it is just to the left of the Porphyra spa. and a tiny bit northwest (so to speak) of Littorina littorea. It is pink and white and knobby and may be the product of a former coraline red algae. Do you by chance know what it is?

    Perhaps you know of good sites or books for learning these things?

    Is Hendricks Point on South port island?

    Thank you very much for putting your beautiful work out on the web for the rest of us

    • Hi Mary:
      Thank you for your kind comments. Hendrick’s Point is in Southport- you may need a GPS to find it, but it is worth visiting. The tide pools are outstanding. The owner of the lighthouse doesn’t mind people visiting the intertidal in front of the lighthouse. Another neat site is on the eastern shore of Baileys Island, especially at a minus 1.0 or more tide. To get there, take a left just after passing Mackerel Cove on your right. Park facing the small church on any day except Sunday. Follow the road to the shore. The coral-like formations are a type of calcareous red algae-probably Lithothamnion spp.. Unfortunately-from my point of view-there are no really good books out there. This is the main reason why I created the web site. There are a number of eye popping sites in Lubec Maine-If you plan to visit let me know and I will give directions. Also don’t hesitate to call me at 442-0609.

      Have a great day.

      Bob Zottoli

  2. Dear Mr. Zottoli,

    fist of all…many thanks for these wonderful and amazing pictures!!!

    I have a question regarding one picture (red algae zone) of Palmaria palmata. In the first picture of Palmaria some fronds are partly covered by small, fussy looking algae. Do you know by any chance what kind of algae this is?

    Many many thanks in advance!

    Best regards

  3. Pingback: Coast Walk 8: Great Head | The Coast Walk Project

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