Blue Green Bacteria Zone   Leave a comment

Blue Green Bacteria Zone

A dark green-black band of living organisms is often visible near the high tide line.Tidal sea water reaches here only at high tide. This green-black zone is formed by the growth of  microscopic plants (Blue green filamentous bacteria, filamentous green algae and red algae are the dominant forms here). Above this zone the environment is essentially terrestrial.

1. Bluegreen Bacteria (Cyanobacteria)

Blue green bacteria produce sugars photosynthetically using water as  a hydrogen source. They may be unicellular or form colonies. One type of colony  is a filament, made up of cells stacked on top of one another. Certain
filamentous species glide over the substratum while others may wave back and forth . Blue green bacteria are an important component of the Bluegreen Zone because of their ability to fix atmospheric nitrogen. They use this  nitrogen to form their own proteins and other important compounds and when they die and decompose, this nitrogen is made available to other organisms for their own use. Several species live in the rocky intertidal. One of the most common, Calothrix spp., attaches for the most part to the rock surface or other green or red algae. Calothrix filaments taper to a point and lie within an obvious sheath. Oscillatoria spp., another common blue green, consists of long uniformly wide filaments without an obvious sheath. Lyngbea spp., on the other hand, looks like Oscillatoria, but is enclosed in a conspicuous sheath.

Most of the microscopic plants from this zone are blue-green bacteria (Cyanophyta) belonging to the genus  Calothrix. Calothrix forms  slippery mats of tangled filaments that attach to rock surfaces. Each filament  is composed of a line of cells that secrete a sticky mucilaginous sheath around
itself. The mucilage reduces contact between the cell and the outside
environment protecting it against drying out and the effects of  rapidly changing  salinity that would occur after a heavy rain. The mucilage in addition to the basal cell holds the filament securely to the rock surface. The mucilage makes the rock surface slippery.

Calothrix spp. X400


Calothrix spp. X400



Oscillatoria spp.  X400


Movement of Oscillatoria

Oscillatoria is capable of slow forward or side to side movement. The video below documents slow forward movement.


2. Red Algae (Rhodophyta)


In addition to Calothrix and Oscillatoria there may be other species of algae living in the mat. Abundant species include filamentous green algae (Ulothrix spp.), tubular green algae (Enteromorpha), filamentous red algae (Bangia), multicellular red algae (Porphyra spp.) and several other types. Populations of Bangia and Porphyra reach their peak from about early March to early May  often forming a reddish mat several millimeters thick.

The red color on the rock surface below  consists of  numerous Bangia  filaments.



Bangia spp. Filament x400


Bangia Filament X400


3. Green Algae (Chlorophyta)

Enteromorpha spp. X100.

Mat forming Enteromorpha create a three dimensional network of filaments that increase the amount of surface area within which organisms can increase population size, hide from predators, and enjoy a greater feeding range. Enteromorpha forms circular tubes that are hollow in the center. Photosynthetically produced oxygen bubbles are released into the center of the tube as shown below. The hollow tube is attached to the rock surface or algal mats by means of a basal holdfast shown below. One species (E. intestinalis) is raised and harvested commercially in Japan. It can be eaten either dried or roasted. Enteromorpha can be pulverized into a powder and used as a flavoring in soups, salads and other dishes.

Enteromorpha spp. X400. The photograph below is focused at the center of

a thin Enteromorpha tube.


Ulothrix spp. X400. Note the horseshoe shaped chloroplast in each cell.


4. Red Algae (Rhodophyta)

Porphyra linearis, shown below, has a holdfast and a short blade  and may form a thin red mat (Third Photograph) on rock surfaces during late winter and early spring months. It is held firmly in  place by a holdfast. It also secretes a mucilaginous substance that sticks the alga  to the rock surface. Small size also makes it more difficult for waves to tear it loose. The entire specimen below is about 25mm in length. The second photograph shows the holdfast with the bluegreen Calothrix spp. attached. A blanket of this species covers the rock surface of the Bluegreen Zone in the third photograph.




 Other macroscopic species of Porphyra may also attach in the Bluegreen Zone. Note the approximately 7 cm  long, purplish specimens  below.


Some of the adaptations  that help these interesting algae

survive in the upper intertidal are:

  1. Secretion of a mucilaginous substance that sticks them to the rock surface making it difficult for pounding waves to dislodge them (Calothrix spp.for example).

  2.  Holdfasts that attach them tightly to the rock surface (Calothrix spp., Cladophora spp., Enteromorpha spp. and  Ulothrix spp. for example).

  3. Small size (Most of the species living here).

  4. Ability to lose over 60% of their water content when exposed to the elements and to quickly rehydrate when covered by seawater again on the incoming tide (Porphyra spp.for example).


5. Diatoms

Phosynthetic unicellular diatoms are abundant in the algal mat. They may be attached to Enteromorpha or lie unattached. 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. The photograph below shows a chain of individual diatoms.



Animals living in the Bluegreen Zone

1. Littorina saxatilus

The snail Littorina saxatilus, about 6mm tall,  lives in rock crevices in and above this zone. It feeds for the  most part on algae scraped from the rock surface with its radula. During periods of excessively high or low temperatures it moves into rock crevices. The snail  is able to seal its shell against rock surfaces with mucus from the leading edge of its foot and  survive for extended periods with little or no atmospheric oxygen, using anaerobic metabolic pathways to obtain energy.


Note the tentacle, the round, black eyespot at the tentacle base and the flat, white, foot to the left. The edge of the operculum  lies just below the foot.


Snails move actively over moist rock surfaces throughout the tidal cycle.


Littorina saxatilus Anatomy. 6 mm in Length


Note the trail created by a moving, feeding snail


Note the radular teeth (X100)above and at 400X below, that are used to scrape algae from rock surfaces.

Some of the adaptations that allow Littorina saxatilus to

live high in the rocky intertidal are:


1.  Internal fertilization and internal development. Note the juvenile snails in an internal brood sac pictured below.

2.Ability to glue itself to rock surfaces. Mucus applied by the front edge of the foot can literally glue the shell to solid surfaces making it harder to dislodge them. What other advantages might this practice confer to the snails?

3.Ability to return to its original position if dislodged (Littorina saxatilus for example)

2. Other Animals

The intertwined filaments in the bacterial and algal mats provide 3-dimensional space within which other, mostly microscopic species,  can find shelter, food, and a relatively safe place to reproduce. Examine the video below.

 This is a fascinating world that few have viewed. I therefore decided to include microscopic videos of some of the more common forms. In the spring (2012), when the mats reach full development I will provide more of them. Many of the animal types found here are identical to those found in Salt Marsh Pools.

A. Phylum Protozoa

1. Flagellated Protozoans

There are several species of flagellated protozoans in the Bluegreen Zone. Most of them are extremely small and difficult to photograph. Flagellates tend to move in a jerky side to side movement. Note the flagellum extending from the specimen on the far right.

The video below shows the general movement of both flagellated and ciliated protozoans. The erratically moving flagellates jerk from side to side while the larger, oval ciliates have more directed movement.

2. Ciliated Protozoans


i. Peritrich Ciliates 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.


ii. Peritrich Ciliate with a Covering called a Lorica


iii.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. In the video below,the animal moves along what appears to be the outside covering of a dead blue green filament filled with small diatoms.

The same species, shown below, moves over the surface of a Cladophora filament. Note the feeding pattern.


iv. Hypotrich Ciliate (Elongated Species) X400


3. Amoeboid Protozoans

The small amoeba shown in the video below is a common inhabitant of the Bluegreen Zone.


B. Phylum Nematoda


Nematodes (Round Worms) are  multi-cellular organisms that live in large numbers in almost every freshwater and marine habitat. Longitudinal muscles that run the length of the animal contract on one side and then on the other generally moving the animal forward or backward. Nematodes have a complete digestive system with mouth and anus and most species living in marsh pools feed on microscopic organisms such as bacteria that they suck into their mouths using a muscular pharyngeal bulb (similar to drawing liquid into an eyedropper by squeezing and releasing the bulb) located between the pharynx and intestine.

A developing nematode worm is shown in the first video while the second shows nematode movement.


C. Phylum Rotifera


A few rotifers have been observed, however they are too small and too active to photograph.


D. Annelida: Class Polychaeta

Fabricia spp.

Fabricia spp. is a small species, about 6 mm long, with an obvious tentacular crown  of ciliated filaments. It can form a temporary 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.


E. Phylum Tartigrada (Water Bears)


Two unidentified types of water bears are relatively common in the Bluegreen Zone. They are about 0.3 mm long with a more or less cylindrical body with four pairs of short legs each with a number of terminal claws.


F. Phylum Arthropoda (Class Arachnida, Mite)

Two unidentified types  of mites are relatively common in the Bluegreen Zone. They are about 3 mm long and  have four pairs of legs attached to a stubby, oval body.


G. Phylum Arthropoda  (Class Crustacea, Order



The 10 mm long gammarid  amphipod in the above photograph was moving in and out of crevaces in the Bluegreen Zone at low tide, presumably feeding on algae.

The following paragraph features a description of the anatomy of the much smaller 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



Several species of copepods live in the Bluegreen 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 harpacticoid copepod  in the video below.


I. Phylum Arthropoda (Class Insecta, Family

Chironomidae, Sub-Family Orthocladinae)

Halocladius variabilis


This species is a non-biting midge that in the larval stage scrapes food using it’s labial plate from the bluegreen mat or the surface of small algae attached to larger 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.This species is also found in the Barnacle and Brown Zones. Additional photographs of Halcladius are provided in each of these zones.


Posted November 14, 2011 by zottoli

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