Dr. A. SankaranarayananC.G. Bhakta Institute of BiotechnologyUka Tarsadia University, Surat District.

Gujarat state. INDIA.e-mail: drsankarkamal@gmail.com

ECOLOGY OF BACILLARIOPYCEAE

• Diatoms comprise the main component of the open-water marine flora and freshwater flora.

• Attached diatoms can be characterized by the brown scums found on various kinds of substrate; fluffy growth caused by abundant epiphytic diatoms.

• Pennate algae are equal in freshwater and marine habitats; centric and gonoid algae are present in marine;

• pennate algae that has bilateral symmetry. ; Centric algae are radially• symmetrical ;

General habitat featuresMarine environment, colder more diatom

population; open oceans have larger number of species with a low organisms;

Near to the shore, the total number of diatoms are very high but species diversity is low.

Un enriched water and enriched water (coastal water receiving enrichment from the land).

Regarding Bacillariophyceae, two aquatic habitats: i. Marine environment ii. Freshwater environment

Marine Environmenti* In general, marine enviornment, algae have some

adaptations to make them buoyant. • Density of sea water varies from 1.021 to 1.028, algae

have lighter cellular components than sea water, to achieve buoyancy.

• But cytoplasm little heavier than sea water, vacoule as a source of positive buoyancy.

• Vacoular sap being isotonic. • Vacoule of the algae have lighter ions than the

surrounding sea water; concentration of Na+ relative to K+

• Algae vary in density during day time. They can move up and down in surface of water absorb more nutrients. Eg. Ditylum brightwelli.

• In dark hours (night) sedimentation rates are more.

Marine environment• Surface area relative to the volume of the cell,

placing a role in drag of cell to water. • Discs, ribbon elongate forms; aggregation of

cells into chains increase the dragging rate. • Increase the size of algal cells results increase in

the ascension rate. • Planktonic diatoms can vary in density during

the day, moving up and down in the water column, enabling better absorption of nutrients.

• Ascension rate – how deep it go inside

Centric Diatoms (Centrales)

• Radial symmetry• Primitive • Raphe Absent• Almost immoblie• Large vacuole with

many discoid cloroplasts

Pennate Diatoms (Pennales)

• Bilateral symmetry• Boat-shaped• Raphe/pseudoraphe

is present• Few elongated

chloroplasts• advanced

The Raphe

Freshwater Environment• Large in spring and less in autumn. Reason is temperature; • Presence of silica• Silica level reaches 0.5 mg / litre algae growth ceases. • Enrichment in freshwater by inputs from industry and

agricultural run off. (Richardson et al. 1996). • Diatoms in streams having two factors. • i. Increasing in currents retard the attachment of diatoms

to the substrate. • Ii. Increase in water current increase the growth of

organisms (long term) but initially fast flowing remove the algae from the substratum.

Attached diatoms in standing water have a good growth. Silica 0.5 mg/l or less good growth; but too less decrease

the population. Epiphytic good growth but benthic less growth in winter

– due to production of some organic products. In freshwater habitats, diatoms often comprise the

dominant algal flora in thermal waters between 30 and 40 °C. Fairchild and Sheriden (1974) showed that Achnanthes exigua isolated from a hot spring showed optimum photosynthesis at 42 °C, with maximum and minimum temperatures for growth at 44 and 10 °C, respectively – characteristics of a thermophilic organism.

Other ecological features

• wide range of pH levels, temperatures and organic pollution.

• This variety of living conditions can help tell pollution or other ecological levels of the water.

• They also vary in their lifestyle, living singly or in a colony. They do not always float freely in the water, they will attach themselves to a rock or another animal in the water.

• Diatoms may just seem like they are just part of the plankton that feed that fish and animals.

Further Readings

• Phycology by Robert Edward Lee ; 2008 Cambridge University Press.

• Richardson, J. L., Mody, N. S., and Stacey, M. E. (1996). Diatoms and water quality in Lancaster County (PA) streams: a 45-year perspective. Pennsylvania Acad. Sci. 70:30–9.