Brown Algal Zone
Immediately below the Barnacle Zone, brown algae (Phaeophyta) of the family Fucaceae (Fucus and Ascophyllum) often form a distinct brownish-greenish colored zone located at about mid-tide level.
Fucus spp. has a plate-like holdfast that attaches to the substratum and a branching thallus. The thallus is relatively flat and dichotomously branched. A mid-rib is located in the middle of the thallus. Fucus vesiculosis has paired gas bladders on its thallus that buoy the plant up in the water column providing maximum exposure to sunlight used in the process of photosynthesis. The bladders may subject the thallus to stress during heavy weave action, resulting in dislodgement. A bladderless form of F. vesiculosis lives on rocky shores that are exposed to especially heavy wave action. On the other hand, the number of bladders tends to increase in estuaries and areas with exceptionally high and low tides that occur in the Bay of Fundy (Refer to the fifth and sixth illustrations below). Each terminal branch of the thallus ends in a swollen receptacle in mature plants. Reproductive organs are found in pits (conceptacles) on the inside walls of receptacles. The life cycle is illustrated below. Motile sperm from male conceptacles fertilize eggs that are released from female conceptacles and the embryos attach to the bottom and grow into a Fucus plant. Refer to the video showing sperm movement in Ascophyllum nodosum.
Conceptacles are the rounded lighter colored dots inside the recptacles above.
Note the group of haploid fucoid eggs above. They are formed in the conceptacles that are nested in the receptacles.
Fucus spp. Antheridia X400 Note the rounded sperm in the antheridia above.
Fucus edentatus (Phaeophyta) shown below is a species common to the lower edge of the brown zone. The green algae (Chlorophyta) Cladophora spp. (Third Photograph) and Ulva spp. (Second Photograph)are often found here.
Fucus spiralis (Phaeophyta) is a species that lives in the upper part of the Brown Algal Zone just above Ascophyllum nodosum. It is much shorter than the fucoids described above and the blade is often eroded away towards the base leaving only the mid rib.
During the winter, Fucus can be damaged by freezing as shown below.
Some of the adaptations that help Fucus survive in the brown algal zone include:
1. Holdfast that secures the plant to the substratum
2. Bladders and or receptacles that allow Fucus to float up into the water column exposing them to more light.
3. Flexible shape that allows Fucus to conform to the shape of the wave and thereby avoid being torn loose.
Ascophyllum nododosum (Phaeophyta) has a more rounded thallus that branches irregularly and has bladders along its length. Short lateral branches arise along the thallus on all but the most distal parts. Each lateral shoot may form a receptacle or another branch. Receptacle formation is initiated in the fall and reproduction occurs in spring. Receptacles are usually shed in May.
Round conceptacles are visible in the receptacles shown above.
Gametes are released into the water where fertilization occurs. The zygotes secrete a sticky substance that enables them to adhere to rock after which they grow into a mature specimen. Fucus and Ascophyllum have similar life cycles and adaptations. The eggs and sperm are similar to those shown above for the genus Fucus. The video below the picture of fucoid eggs shows antheridia and actively moving sperm.
The video above shows antheridia and motile flagellated sperm.
Winter freezing sometimes causes damage to Ascophyllum.Note the reddish tissue damage in the photograph below.
Ascophyllum and Fucus that have established a foothold in the barnacle zone are often damaged by wave action as shown below.
The red alga Polysiphonia lanosa (Rhodophora) is permanently attached to Ascophyllum nodosum. It only attaches to the outside of the brown alga and is not an internal parasite. This is an exclusive relationship. What advantage(s) does Polysiphonia receive from this relationship? Is there any benefit to Ascophyllum?
Many of the algae common to our coastline have been harvested commercially. Significant amounts of potash, soda, ash, and iodine have been extracted from Ascophyllum and Fucus in the brown algal zone and the kelps Alaria and Laminaria in the sub-tidal kelp zone. These genera have also been used as manure and animal fodder. Animal fodder made from dried Ascophyllum and Laminaria, in addition to yielding a high percentage of protein, contains quantities of vitamins B1, B2, B12, C, and E.
Three species of filamentous brown algae (Ectocarpus spp., Elachista spp. and Pilayella spp.) are often attached to the surface of either Fucus or Ascophyllum.
Ectocarpus spp.is an epiphytic, filamentous, branched, brown alga that has terminal reproductive organs. It attaches to both Fucus and Ascophyllum.
Note the darker sporangium at the tip of the filament above.
Elachista spp. is a filamentous, unbranched brown alga that attaches mainly to Fucus.
The specimen above was removed from the surface of Fucus vesiculosis. It is about 1.5 cm high.
Note the crowded short basal filaments and the longer filaments (X400) that extend outward into the water column.
Pilayella spp. is a branched, filamentous brown alga with spore producing sporangia situated in the middle of a filament.
The linear arrangement of the sporangia and movement of flagellated spores are shown in the following video.
Over time, Fucus vesiculosis may be battered and torn by frequent exposure to wave action and other factors. This makes them more susceptible to colonization by epiphytic algae. The photograph below shows a portion of such a Fucus vesiculosis plant colonized by the green alga Enteromorpha and the epiphytic brown alga Ectocarpus spp.
There are several species of Hydrozoan Coelenterates that attach to the surface of fucoid algae in the rocky intertidal. The colonial hydrozoan Sertularia spp. and Clava spp. are shown below attached to Ascophyllum.
Clava spp. X3
Larvae of the polychaete Hydroides spp.(Phylum Annelida, Class Polychaete, Family Serpulidae) leave the plankton after a time and seek out a suitable place to settle. It is attracted to places where adults are found such as rock surfaces or the epidermis of Fucus vesiculosis. After attachment it secretes a white calcareous tube within which it develops into an adult. The worm adds to the tube as it grows. Two groups of ciliated filaments are extended from the tube as it filter feeds.
Photosynthetic, unicellular diatoms are abundant in the Brown Algal Zone. They may be attached to any of the macroscopic or microscopic algae or lie unattached. Certain species form chains of attached cells. They belong to the Bacillariophyceae, a division of the Chrysophyta. The cell is protected by a cell wall (Frustule) impregnated with silicon (Silicon Dioxide). The frustule is made up of two halves (Valves) that fit together like the top and bottom of a shoe box. The valves are often adorned with fine lines as shown below. In addition to the photosynthetic pigments chlorophyll a and b, they have a golden brown pigment that gives them their characteristic color.
Seasonally, the opportunistic, filamentous green alga Cladophora spp. (Chlorophyta) may become a dominant form in the barnacle, brown and red zones. The basal cell forms a holdfast and the filament branches frequently. Cladophora spp. is a preferred food of the periwinkle discussed below.
The unbranched green alga Chaetomorpha spp. (Chlorophyta) may also be found in the Brown Algal Zone.
Ceramium spp.,a filamentous, branching, red alga (Rhodophora), is also an opportunistic species, attaching to bare rock surfaces or other algae in the brown and red zones.
Porphyra spp., a red alga, consists of a flat thallus, attached to the substratum by means of a short holdfast. Porphyra resembles the green alga Ulva (Sea lettuce). They have a broad, thin, flaccid thallus with ruffled margins arising from a short holdfast. Porphyra is extensively cultivated in Japan and sold under the name nori. It is used in a wide variety of foods and is high in protein, minerals and vitamins.
Also found in the brown algal zone is a thin encrusting red alga (Rhodophyta) Hildenbrandia. This genus, that often covers a good portion of the substratum, is difficult to distinguish from the rock surface to which it tightly adheres. Other species of encrusting Blue-green bacteria, green brown and red algae may also be found. I have observed areas where Hildenbrandia has completely overgrown small attached barnacles.
Blue mussels (Mollusca, Bivalvia) discussed in the Barnacle Zone above can be found in all of the zones. Like the great majority of bivalve molluscs they feed by capturing small particles of plankton, organic detritus and bacteria in mucus on the gills as the respiratory current passes over them. The mucus and the food are swept to the lower margin of the gills by special tracts of strong cilia and are then brought anteriorly along the food groove at the gill margin where the palps transfer food to the mouth.
Mussels commonly occur in great numbers, are closely spaced, and form mats or beds that cover much of the exposed rock surface. Grouping together makes it more difficult for waves to dislodge them and holds water thus helping to prevent desiccation and providing a home for a variety of organisms. They have a thick bivalve shell which can remain closed for long periods of time. The principal predators of mussels are carnivorous gastropods, starfish and man.
Blue mussels are held in place by strong byssal threads secreted by a byssal gland near the base of the foot. The byssal substance consists of heavily cross-linked, highly viscid, adhesive collagen like protein that undergoes a quinone-mediated tanning after release from the byssal gland. The gland is applied to the rock, then the protein is secreted and finally the foot is drawn away forming a thread at which point the thread hardens.
Blue mussels have separate sexes and release egg and sperm into the water column simultaneously. The fertilized eggs develop into a trochophore larva that is planktonic. Eventually the larvae leave the plankton and develop into juveniles that move around seeking a place to attach. Large numbers of these juveniles can often be found on fucoid algae. Refer to the video of juvenile mussel movement in the Barnacle Zone section.
Some of the adaptations which allow mussels to successfully live in the rocky intertidal include:
1. Thick heavy protective shell that can remain closed for extended periods.
2. Byssal threads that attach to the substratum.
3. Release of large numbers of egg and sperm.
4. Ability to filter feed from the surrounding water.
5. Ability to form rafts or beds of mussels. This allows the species to occupy and hold space thereby preventing attachment by other species.
The periwinkle Littorina littorea (Mollusca, Gastropoda), a conspicuous member of the brown algal zone, feeds by scraping rock and algal surfaces with its radula. Reactions to light, gravity and wave action help the animal to maintain position in the intertidal zone and to cover a maximal feeding area. The periwinkle is covered with a heavy calcareous shell that protects it from mechanical injury and desiccation. In addition, under adverse conditions it seals the shell opening with a cover (operculum) thus protecting the soft internal parts from contact with the environment.
The periwinkle has separate sexes and internal fertilization. Fertilized eggs are released into the plankton and after a suitable period of development, leave the plankton and settle on the bottom.
The littorine snails constantly scrape rock surfaces clean with their radula providing space for other organisms to settle.
A relative of the periwinkle, Littorina obtusata (Mollusca, Gastropoda), is common in the brown algal zone on the fronds of brown algae, especially Fucus and Ascophylum. It has most of the adaptive features of the periwinkle, except that it has no planktonic phase in its life cycle. It lays egg masses on algae and when the young leave the egg mass they tend to stay in the same area as their parents.
Note the central and lateral teeth that are used to scrape food from the surface of fucoid algae and rock surfaces.
Some of the adaptations which allow littorine snails to live in the brown algal zone and elsewhere are:
1. Hard protective shell
2. Operculum that seals the shell
3. Protective coloration. Light colored L. obtusata look like Fucus receptacles.
4. Internal fertilization.
5. Relatively high reproductive rate.
The limpet, Tectura testudinalis ,a gastropod mollusc commonly found in the brown zone, has a conical rather than spiral shell. Limpets move about and feed on algal films with their radula when covered with water or while the rocks are still wet. Between tides they tend to cling tightly to the rock surface, minimizing desiccation and predation. Constant scraping on rock surfaces subjects the radular teeth to considerable wear. As they are worn down or lost they are replaced by new portions of the radula pushed up from behind.
Note the black central and lateral scraping teeth.
Limpets are adapted to living in the rocky intertidal as follows:
Possession of a broad flat foot that can adhere strongly to the substratum by suction.
A “Chinese hat” shaped shell that allows water to flow around the limpet thus reducing water drag during heavy wave action.
A. Phylum Protozoa
i. Peritrich Ciliate X400
Peritrich Ciliates are characterized by bands of cilia situated at the anterior part of the cell. They are attached to the substratum by a stalk containing a contractile thread. When disturbed they contract as seen in the video below. They feed on small microorganisms that they filter from the water. What appear to be the same species resides in all of the rocky intertidal zones.
ii.Hypotrich Ciliate X400
The hypotrich ciliate shown above literally walks using ventrally located large cilia. Each of the large cilia are actually a group of fused smaller cilia. They are also capable of swimming. They graze on a variety of microorganisms as they move across solid surfaces. The animal moves along what appears to be the outside covering of a dead bluegreen filament filled with small diatoms. It appears in all of the rocky intertidal zones.
The same species, shown below, moves over the surface of a Cladophora filament. Note the feeding pattern.
B. Phylum Platyhelminthes ( Class Turbellaria Order
This unidentified species glides over solid surfaces in the Brown Algal Zone. The video below shows a specimen held in place by a glass coverslip.
C. Phylum Nematoda
Nematodes are found throughout all of the rocky intertidal zones. The video below shows typical nematode movement.
D. Phylum Rotifera
A few rotifers have been observed in all of the rocky intertidal zones, however they are too small and too active to photograph clearly.
E. Phylum Mollusca, Class Gastropoda
Juvenile Littorina obtusata are common in the Barnacle and Brown Algal Zones. They can be seen on the surface of barnacles in the photograph below and are common on the surfaces of Ascophylum and Fucus.
A small juvenile (X40) is shown in the video below moving in and out of its shell. The tentacle, black eyespot, foot and operculum are visible.
F. Annelida: Class Polychaeta
Fabricia spp. is a small filter feeding polychaete species, about 6 mm long, with an obvious tentacular crown of ciliated filaments. It can form a temporary mud tube and is capable of leaving the tube and moving around. It has a pair of anterior and posterior eyespots that are sensitive to light. The first video features an adult while the second highlights a juvenile worm. This species is common throughout the rocky intertidal.
F. Phylum Arthropoda (Class Arachnida, Mite)
The mites, about 3 mm long, have four pairs of legs attached to a stubby, oval body. Mites have been found in all of the rocky intertidal zones.
G. Phylum Arthropoda (Class Crustacea, Order
The 10 mm long gammarid amphipod in the above photograph was moving in and out of crevices in the Bluegreen Zone at low tide, presumably feeding on algae. They are also found in the Barnacle and Brown Algal Zones.
The following paragraph features a description of the anatomy of the much smaller salt marsh pool/rocky intertidal amphipod shown in the video below. The head bears a pair of compound eyes, a pair of antennules slightly above the eyes, two antennae below the eyes, and two maxillipeds underneath the mouth. The thorax, consisting of 8 segments, is attached to the head followed by the abdomen. The maxillipeds are the first thoracic appendages, followed by 2 pairs of gnathopods (2nd and 3rd thoracic appendages). The gnathopods are followed by 5 pairs of pereiopods (4th to the 8th thoracic appendages). The abdomen has 6 pairs of abdominal appendages. The first three are periopods; they are constantly waving back and forth. The remaining three pairs are uropods.Amphipods can crawl as shown in the photographs above, swim sideways or tuck their abdomen under their body and flick it backward creating forward movement.
H. Phylum Arthropoda (Class Crustacea, Order Isopoda)
Isopods are generally flattened from top to bottom while amphipods are flattened from side to side.
I. Phylum Arthropoda (Class Crustacea, Order
Several species of copepods live in the Barnacle Zone . They are a common component of marine ecosystems, especially planktonic communities. A long (sometimes short) pair of antennules are visible extending laterally from the head. These are used to propel the animal forward as shown in the second video. Between the two antennae lies a single median eye. Thoracic appendages are visible along the wide portion of the body. The thorax narrows and joins a thinner abdomen. In the photographs below the cephalothorax is the region of the body from the point of the thorax arrow to the right; the thorax is the section of the body from the point of the thorax arrow to the tip of the abdomen arrow and the abdomen comprises the rest.
Note the movement of the harpactcoid copepod using its antennae in the first video while the second video shows movement by dorso-ventral contractions of the body. The specimen highlighted in the third video was collected from the Brown Algal Zone.
K. Phylum Arthropoda (Class Insecta, Family
Chironomidae, Sub-Family Orthocladinae)
This species is a non-biting midge that in the larval stage scrapes food using its labial plate, from the bluegreen mat or the surface of small algae attached to barnacles or large brown algae such as Fucus or Ascophyllum. The adults mate as shown below and deposit their eggs in intertidal areas. The eggs develop into larvae also shown below, that after several molts reach a length of about 8 mm. It is also found in the Red Algal Zone. This species is also described in the Bluegreen and Barnacle Zones.