Plants are the primary producers of all life on earth and as dormant and sessile as many appear, they are without doubt the most extraordinary of beings with lifestyles that when recognised and understood, are beyond the wildest imaginations of science fiction enthusiasts.
Every life form that ever lived on this planet owes its very existence to the presence of plants - without them, life as we understand it would neither have evolved, nor progressed.
As the primary producers of all life on earth, phytoplankton and sessile algae produce over 60% of earths oxygen. Bubbles of oxygen being formed by the process of photosynthesis from blue - green algae in a rock pool
(Photo Neville Coleman)
Marine plants
Introduction to ALGAE
Dominant green algae species on coral reef at Lord Howe Island. The clear, shallow, well lit water allow for maximum coverage of every bit of bare underwater real estate across the reef.
(Photo Neville Coleman)
There are more than 9000 species of algae in the world's oceans. Of these, the largest and most dominant occur in temperate waters ranging in size from filamentous turfs only millimetres in height, to giant kelps, which can be 30 metres long and may grow at the rate of half a metre a day.
Only found in temperate waters the Giant kelp Macrocystis pyrifera may reach a height of 30 metres and grow at the astounding rate of 1 metre a day.
(Photo Neville Coleman)
Other algae forms are seen merely as a slippery scum on the rocks.
Tropical reefs may support around 1000 species, yet many remain undescribed.
Compared to the higher land plant communities, algae are more primitive in structure and although they have less distinctive features, there are an amazing number of shapes, designs, patterns and textures, far more than the average diver notices, or is aware of.
Lifestyle
Algae grow wherever there is enough light and life-supporting conditions exist. They live on coral reefs, rocky reefs, rubble, sand and mud from above the intertidal zone down to hundreds of metres. Whereas land plants have leaves that extract carbon dioxide from air and roots that absorb moisture and minerals from soil, algae have no true roots; their 'holdfasts' simply anchor them to the bottom.
Like all plants they live by using their photosynthetic pigments (chlorophyll) to convert sunlight, water, carbon dioxide and dissolved nutrients into organic compounds such as starches and sugars which are rich in energy. The by-product of this conversion is oxygen.
Reproduction
Algae have no flowers but reproduce by way of spores in an often complex fashion which includes both sexual and asexual plants.
Female cystocarps of the red algae, Southern Martensia Martensia australis can be seen as minute round balls spread across the surface of the marine plant. Lord Howe Island Jan. 2000.
(Photo Neville Coleman)
Associations
Food to a massive number of herbivores, algae in one form or another supports the existence of every other group of marine life.
Identification
In the past, the identification of algae was entirely based on microscopes and a degree in marine botany. However, although a degree in botany and a specimen is still the most accurate way to go, diving botanist/photographers have made enormous inroads into visual identification over the past 20 years.
In general terms, the subdivision of algae is based on colour: (1) blue-green algae (the most primitive), (2) green algae, (3) brown algae, (4) red algae.
However, although this would appear an easy method of identifying algae it's amazing just how many green-looking species are browns and brown-looking species are reds.
Looking for all the world like a green algae, the rarely seen Herbert Tomaculopsis Tomaculopsis is only found around the northern coast of New South Wales. However, one cannot relate to the colour as an identity key, it is in reality, a brown algae.
(Photo Neville Coleman)
The colours are broadly based in photic zones according to light penetration at depth; blue-green and green algae are found towards the top of the scale (maximum light), browns at the intermediate level (medium light) and reds at the bottom (reduced light).
However, this may not always appear to be the case, especially in tropical waters. As light decreases due to depth, or to increasing turbidity, algae give way to dominant animal communities.
BLUE-GREEN ALGAE - The Slime of Your Life
PHYLUM: Cyanophyta
Living fossils by todays standards, Stromatolites are over three billion years old and have been credited with having created the necessary levels of oxygen that led to the evolvement of higher forms of life as we know it today. Shark Bay, Western Australia.
(Photo Neville Coleman)
These 'Living rocks' were created by the consolidation of sediments into permanent growing rocky structures called stromatolites they are able to convert atmospheric nitrogen into compounds (such as sugars) suitable for plant nutrition. Underwater, they take on a entirey different aspect.
(Photo Neville Coleman)
Features
Far more easily seen on rocky shoreline substrates than underwater, blue-green algae appear as black or dark-coloured scum at the water's edge. Blue-green algae are extremely slippery to touch and even more so to walk on sending many an intertidal reef walker, or shore entry diver, skidding. Most blue-green algae occur in fresh water with only 75 of the 200 known species living in the sea.
Rusty scum Blue - green algae Schizothrix calcicola is generally seen on sandy bottom in lagoons with little water movement.(Tropical Indo - Pacific)
(Photo Neville Coleman)
These single-celled microscopic plants form clusters of filamentous cells within a gelatinous mass; their colour generates from their main photosynthetic pigments of chlorophyll and phycocyanin. Although they look insignificant the blue-green algae are related to the oldest recognised life forms on earth. By consolidating sediments into permanent growing rocky structures called stromatolites they are able to convert atmospheric nitrogen into compounds (such as sugars) suitable for plant nutrition.
Hair-mat Blue green algae Microcoleus sp. often seen as a smothering mat killing everything in its path, including stony corals. ( Tropical Indo Pacific)
(Photo Neville Coleman)
Living fossils by today's standards, stromatolites are over three billion years old and have been credited with having created the necessary levels of oxygen that led to the evolvement of higher forms of life as we see it today.
Reproduction
By way of spores.
Associations
Blue green algae in a small intertidal rockpool demonstrates the amount of oxygen bubbles generated. As the tide comes in and washes over the pool the bubbles are released into the surrounding air.
(Photo Neville Coleman)
Identification
Most blue-green algae are very difficult to identify unless they occupy a known micro-habitat, or are subjected to microscopic study by a trained botanist.
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GREEN ALGAE
PHYLUM: Chlorophyta
Features
Turtle weed Chlorodesmis fastigiata generally occurs in small clumps on the tops of reefs on the Great Barrier Reef and east coast of Australia.
( Tropical Indo - Pacific)
(Photo Neville Coleman)
For most people the link between land plants (which are mostly green) and green algae can be easily seen. The phyla name chlorophyta is from the Greek words chloros for green and phyton for plant and although green is green, green algae may vary in colour from light green to yellow and dark green to black.
Quite a few green algae, for example, Ulva and Enteromorpha are cosmopolitan and occur throughout most tropical areas. Both these species flourish where there are high nutrients, or welling fresh water.
Green Slime Enteromorpha Enteromorpha clathrata is usually observed as a sheet of slimy green covering rocks along the intertidal zones of the tropical and temperate shorelines. It is extremely common and found throughout the world. It may live on rough, or sheltered shores and has hair - like branched tubes issuing from the base.
(Photo Neville Coleman)
Tropical green algae have an amazing range of forms from huge single cells to encrusting turfs and those with strange calcified plate-like leaves. The Halimeda alga are extremely important in the production of sand and marine sediments and also play a big part in the construction of beach rock, holding the atolls and reefs together.
Cactus Halimeda Halimeda opuntia is comprised of hard calcium carbonate tri radiating segments connected by flexible joints.
( Tropical Indo - Pacific)
(Photo Neville Coleman)
Lifestyles
Looking more like sponge than algae, the strange Pom Pom Tydemania Tydemania expeditionis can be very common on walls and slopes of reefs. It attracts large quantities of sand and silt.
( Tropical Indo - Pacific)
(Photo Neville Coleman)
Green algae is found mostly in shallow water though in some areas where the water is very clear it may be commonly seen in depths below 30 metres (98 ft). Vast areas across the Indo - Pacific reefs are now covered with various forms of algae, many of them greens and these are eaten by parrotfish, surgeonfish and many molluscs.
Reproduction
Sea lettuce
The green alga Ulva undergoes a cyclic alternation and can be a spore-producing plant or a sexual-producing plant. Though each of these plants may look identical, they can only be identified by a specialist with a microscope.
The spore-producing plant produces free swimming zoospores which swim to the bottom and attach, each growing into a complete sexual plant (male or female).
When mature, these sexual plants release either sperm or eggs into the water. The fertilised eggs hatch into zygotes which settle to the bottom and grow into spore-producing plants to complete the cycle.
Sea lettuce Ulva lactuca is a common shallow water species eaten by a number of marine grazers. It is also edible for humans. Throughout this clump the oxygen bubbles created as a by-product of photosynthesis can clearly be seen.
( Tropical and temperate Indo - Pacific)
(Photo Neville Coleman)
Associations
Grape weed Caulerpa Caulerpa racemosa is a very common resident of tropical reefs across the entire Indo - Pacific. It is a major food source for many nudibranchs and opisthobranchs.
(Photo Neville Coleman)
Many smaller molluscs and opisthobranchs are only found on various species of algae. There is no doubt that as interest in the prey and predator associations are studied many new records of associations will be discovered.
Identification
Known as the Sailor's Eyeball, the green algae Ventricaria ventricosa is the largest single celled algae in the world. It occurs throughout the tropical Indo - Pacific and is one of the easiest green algae to identify from an image.
(Photo Neville Coleman)
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BROWN ALGAE
PHYLUM: Phaeophyta
Features
Typical brown algae scene at 10 metres underwater on a reef off Rottnest Island Western Australia. The dominant form is Phyllospora sp. with several clumps of the wider bladed Radiate Ecklonia Ecklonia radiata around the edges.
(Photo Neville Coleman)
While there may be over 1500 species of brown algae most of these occur in sub-temperate and temperate waters with relatively few species living in the tropics. However, what they lack in diversity, browns often make up for in abundance and sometimes entire areas can be covered with filamentous brown algae as well as the larger Turbinarias, Sargassums, and Padinas, while Dicyotas dominate the deeper reef slopes.
Growing in only a few metres of water on a rock in the middle of a sea grass meadow, the Radiate Ecklonia Ecklonia radiata is a dominant form of brown algae on the south east coast of Australia.
(Photo Neville Coleman)
The phylum name comes from the Greek world phaios meaning "brown" and the actual colour is due to the brown pigment fucoxanthin which presumes many shades, from yellow to dark brown verging on black.
Lifestyles
Peacock Lobophora Lobophora variegata can be found along the tropical /temperate coasts of Australia where it can appear as different colour morphs, depending on the conditions it is growing under and vaying from that pictured, to brown all over with no irridescence.
(Photo Neville Coleman)
Brown algae can be found throughout the intertidal zone, the inshore subtidal zone and down to several hundred metres. Most brown algae lives on hard bottom or on pieces of rock, shells or dead coral on sand or rubble. Funnel weed (Padina) is a very common brown algae growing on dead coral heads and patch reefs in lagoonal situations.
Funnel Padina Padina commersonii is very common in some lagoonal situations covering areas up to three square metres. The regular growth pattern recurved fronds and chalky appearance make it fairly easy to identify even though it is generally covered with a fine coating of silt. The chalky appearance is due to the presence of calcium carbonate on the upper surface of the flat circular blade.
Tropical Indo - Pacific.
(Photo Neville Coleman)
Ornate Turbinaria Turbinaria ornata is very common on reef tops throughout the Indo-Pacific this Indian Ocean form is well known and easily identified. It is very firm and quite spiky to touch, has a long stalk, and can occur in large fields.
(Photo Neville Coleman)
Reproduction
More common to the tropics than temperate regions the Sargassum Algae Sargassum flavicans (and most of its related species) are as a whole, are difficult to determine in the field. They all have numerous primary branches coming off short stalks. The plants also have small circular bladders present.
(Photo Neville Coleman)
Quite often branches of Phyllospora spp. are torn from reefs during storms. These float around on the surface of the ocean and are capable of living and growing and in many cases support numbers of planktonic creatures, such as shrimps and crabs and small fish. However, they are not able to reproduce from their drifting habitat.
(Photo Neville Coleman)
Plants can be sexual or asexual and follow the basic method of reproduction described for green algae.
Associations
An easily recognised temperate water species seen along the southern intertidal coastlines of Australia, Bank's Hormosira Hormosira banksii forms dense mats.
(Photo Neville Coleman)
There are not as many animals which feed on or are associated with brown algae as there are with greens and reds.
Identification
Some browns are easy to identify visually while others still require a specimen and a trained botanist.
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RED ALGAE
PHYLUM: Rhodophyta
Features
Asparagas Asparagopsis Asparagopsis taxiformis occurs in large groves across a large part of the tropical reef regions of the Indo - Pacific. It is stable in colour and has a fairly well formed shape which makes it reasonable easy to identify to at least genus. Very common in Moreton Bay Queensland.
(Photo Neville Coleman)
Pink mat Jania Jania sp. is found in places of high energy wave action. This algae has hard calcified, jointed branches which are generally forked at the ends. The branches grow quite close together forming dense clumps of mat-like turf over large areas. This genus is widespread throughout the tropical Indo-Pacific.
(Photo Neville Coleman)
With more than 4000 species known from tropical reefs the red algae are the most diverse in shape, pattern and design and are found from the intertidal area down to at least 100 metres. They may appear in almost any colour though their phylum name Rhodophyta comes from the Greek rhodon meaning 'red' rose. The red colour itself comes from having large quantities of the pigment phycoerythrin in the cells which absorbs the green and blue components of the sun's rays.
Some red algae are so calcified that they grow upright in clumps and appear as brittle pink skeletons with articulating joints.
Lifestyle
Found along the inshore reefs of central/south east coast of New South Wales, the Official Corallina Corallina officinalis is very common and forms low mats in the intertidal areas.
(Photo Neville Coleman)
Coral reefs or tropical biotic reefs are constructed by lime-secreting animals and plants, corals and red coralline algae that live in vast communities under optimum conditions of moderately stable temperatures, good aeration, maximum sunlight, limited nutrients and carbonates. A coral reef is just a large mound of solidified skeletal debris covered by a thin veneer of living coral.
The Congested Lithophyllum Lithophyllum conjestum covers wide areas of intertidal coral reef and helps in cementing the reef crests together, therby protecting the Great Barrier Reefs and the coral cays.
(Photo Neville Coleman)
The corals contribute the major bulk of building materials to the reef and may be likened to providing the foundations, or the bricks. Holding the bricks together are various types of red coralline algae which bind and solidify, anchoring the larger formations against the forces of nature. Red coralline algae may not get much attention due to their insignificant appearance, yet they are as important to the function of a true coral reef as are the corals themselves. In fact, red algae dominate and at times exceed corals in importance as reef-building organisms.
Fungi-form Red Peyssonelia Peyssonelia capensis is a widespread Indo-Pacific genus. This interesting red algae generally lives on shady drop offs, reef walls, slopes and terraces where it grows under ledge edges and on vertical surfaces. The purple, pink, green or yellow fronds have radial striations.
(Photo Neville Coleman)
Often referred to as lithothamnians, these red coralline algae extract calcium carbonate from sea water and are found all over the reef. Their hard encrusting layers cover the reef rock rim, cementing the living and dead corals together to form protective ramparts against the ever-erosive ocean and making it possible for other life forms to exist.
Reproduction
By spores similar to others previously described.
Associations
Many types of fish and invertebrates feed on red algae and there are some species of crabs and molluscs that mimic it.
Identification
My first photograph of an algae taken in 1968, this Delicate Nitophyllum Nitiphyllum delicatum was from Botany Bay New South Wales. It also occurs as far north as Byron Bay.
(Photo Neville Coleman)
With so many species and variations red algae present a challenge to visual identificationists. However, many have very characteristic forms, patterns and shapes and will prove easy in the future. The coralline encrusting forms may always require a specialised botanist to separate species on specimen based material.
The Combination Halichrysis Halichrysis coalascens is a low profile red algae that looks similar to a green algae, (with the exception of the other colours present). It is a magnificent species and may be found on rocky reef beneath the skirts of other algae. It is rarely seen and must be searched for.
(Photo Neville Coleman)