Algal community structure


Compared to the higher plants, algae may appear simple. But their community structure represents just as much a challenge for marine biologists as our terrestrial counterparts! Algal communities are very complex as they are exposed to a variety of regularly changing cycles, the most predominant being the cycle of the tides and the penetrate of light.

The different forms of algae (as described in seaweed shapes) manifest into several different key life-forms or functional groups. The use of the functional group approach allows biologists to make broad generalisations on the ecology of communities and the interactions that each functional group has with each other. The functional group approach classifies macroalgae into morphologically and functionally similar groups.

Canopy forming algae such as kelp.Canopy

The canopy of a macroalgal dominated shore, consists of the very largest and tallest seaweeds that can inhabit the shore, in areas with reasonably moderate to low wave exposure the canopy community would contain masses of kelp in the lower subtidal zone, and as we move up the vertical axis of the shore the large wracks.

Image > Canopy forming algae such as kelp dominate many other species, including the encrusting algae shown here Lithothamnion.

Understory or turf algae.

Understory / Turf

The smaller seaweeds that are less prone to the effects of wave exposure compared to canopy algae tend to inhabit the understory. Algae such as Cladophora, Chondrus, smaller fucoids etc are generally found below the canopy and exist with lower exposure to light, compared to the fast growing species which shoot up into the canopy.

Image > A mixture of different seaweeds are present in this image, Corralina officinalis dominates with its pinkish and white tone.

Encrusting algae.Encrusting

Encrusting algae is found at the lowest level of the community. These algae are found growing on rocks, forming a layer of cells that spread out over a surface. These species are found on many rocky shores, and are often corraline.

Image > The pink film shown in this rock pool is a large patch of the encrusting algae Lithothamnion. Lithothamnion is the family name used to describe many species, all which are visibly similar and some can only be told apart using genetic techniques!

Epiphytic algae growing on Ascophyllum nodosum.Epiphytic

Epiphytes are found growing on live plants, these may have either a symbiotic or a parasitic relationship with the host. In symbiotic relationships the epiphyte and the host both benefit. In parasitic relationships only the parasite benefits and severe cases of infestation may kill the host plant.

Image > Large amounts of the epiphyte Polysiphonia lanosa are visible on the large leathery macrophyte Ascophyllum nodosum.