The Power of Biofilm Colonization as an Educational Engagement Tool

As biofilms start to develop, they are an excellent tool for educators to draw in students and then keep them engaged. An understanding of how biofilms develop under different conditions can provide students with real-world scenarios of how changes in variables like temperature, sunlight, or salinity can affect biodiversity.

Biofilm Colonization Progression

A key element to explore as biofilms develop is the progression of organisms on substrates such as PET / PET-G or aluminum discs immersed in your local marine or aquatic environment. This is known as biofilm colonization; it is the process from the first few hours after initial colonization by bacterial biofilm species to the days and months afterwards (Baier, 1984). An understanding of how the fundamental principles of ecology and biology are involved in this process and how colonization proceeds in different scenarios, helps to guide student participation and engage them in developing research questions.

In field sites and in classrooms around the world, the species progression will vary depending on the marine environment and the physical conditions, but there will be similar organisms observed and methods shared for counting or enumerating their biodiversity.

One focus of the BiodivOcean Project is the biodiversity that can be observed with basic microscopy and photography techniques and the process of colonization by various marine organisms. This is a great opportunity for students to engage with microscopy and participate in biodiversity assessments of the discs throughout the colonization process.

Student research questions can include: How do organisms find the disc? How long did colonization take? Is there a pattern to colonization? All of these are good questions, so let’s dig into them!

After the biofilm has established itself on the disc, chemical signals diffuse into the surrounding water from the bacteria that show that there is now an established bacterial food supply and a community, and that colonization is beginning!

Retrieval of the discs takes place after they have been in the water somewhere between a few weeks to a few months. Biological growth on the discs can be seen with the naked eye as a community of what is usually a variety of species depending on the location and time of year. It is best to take the time to observe the disc under a microscope as well because there are always interesting biological interactions happening on a scale that can only be seen under magnification.

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Community Building

Here is a representation of species progression observed in the VIRTUE-s Project, broken down by single-celled, or bacterial colonization, vs. multi-celled colonization. 

Single-Celled Colonization

Bacterial Biofilm- cellular colonization and deposition of minerals and other sediment on the disc.
    Protista and Algae – cellular and multicellular or colonial algal species.

Multi-Celled Colonization- Invertebrates, both sessile and free-living. This order may vary from location to location. 

The progression below is similar to that of the Baltimore Harbour, USA. 

• Cnidaria- hydroids, anemones, jellies
  • Bryozoa- colonial and tube dwelling
    • Platyhelminthes and Annelida- free living and tube dwelling species
      • Mollusca- mussels, oysters, sea slugs, nudibranchs
        • Arthropoda- copepods(?), barnacles, amphipods, and crabs
          • Echinodermata- sea stars
            • Chordata- tunicates or sea squirts, ascidians 

The taxonomic complexity can be ordered fairly easily, however, the colonization does not necessarily follow this neat and orderly pattern. Once the colonization has passed the point of the initial bacterial and algal colonization larvae begin the colonization process and this will be determined by the time of year and larval recruitment at that time of year.  

It may be that in early to late spring barnacle larvae are heavily recruited to the discs prior to their less complex counterparts like polychaetes and molluscs. For example, if discs are placed into the water in midsummer there could be a lack of barnacles since larval recruitment and patterns have already been completed. In some areas there may be larval recruitment until late autumn, so that discs placed in the water during this time may have full-grown barnacles and/or mussels in spring despite the early time of the year. There are many opportunities for student engagement (with regard to experimental design appropriate for fieldwork and lab work) that can power investigations that become student-driven.

Further Reading

Baier, Robert E. 1984. Initial Events in Microbial Film Formation in Marine Biodeterioration: An Interdisciplinary Study, Proceedings of the Symposium on Marine Biodeterioration, pp. 57-62. Uniformed Services University of Health Sciences, 20-23 April 1981.

University of California, Museum of Paleontology at Berkeley, Taxon Lift. https://ucmp.berkeley.edu/help/taxaform.html, accessed on February 12, 2026.