In the world of living organisms, few manage to combine natural elegance, biological uniqueness, and scientific value. Acetabularia, a marine green alga, belongs to this rare category. Visually striking, biologically intriguing, and historically pivotal, this unicellular alga profoundly influenced 20th-century cell biology. In Tunisia, the Kerkennah Islands host several species of Acetabularia, offering an invaluable observation site for both scientists and educators.
We had the opportunity to conduct several field expeditions there, alongside my two colleagues and friends: the late Frej Kartas, whose memory continues to inspire us, and Sadok Dridi, a loyal companion in our explorations. These expeditions allowed us to study Acetabularia in its natural habitat, observe its morphological diversity, and deepen our understanding of its pedagogical potential.
This article explores not only the biological characteristics of this remarkable alga but also its role in research, its importance in science education, and its value in popularizing biological knowledge.
I. Portrait of an Extraordinary Organism
1. A Giant Cell
Acetabularia belongs to the class Ulvophyceae, family Polyphysaceae. Although unicellular, it can reach an impressive size of 5 to 10 cm, making it a cell visible to the naked eye. This unusual trait places it at the frontier between the microscopic and macroscopic, immediately sparking curiosity.
Its general morphology is tripartite:
- A rhizoid, anchored in the marine substrate, containing the nucleus.
- An elongated stipe (stem) providing support.
- An umbrella or “cap”, shaped like a parasol, which appears at the end of development.
Its aesthetic appeal makes it a favorite subject for nature photographers and school textbooks.
2. Unicellular Yet Complex
Beneath its apparent simplicity lies a sophisticated cellular organization. Acetabularia contains active chloroplasts, a single nucleus (in young individuals), a functional cytoskeleton, and an efficient intracellular transport system. This complexity, combined with its unicellular nature, made it the subject of many landmark experiments in cell biology.
II. Acetabularia in Tunisia: The Kerkennah Islands as a Haven
1. A Favorable Habitat
The Kerkennah Islands, off the coast of Sfax, form a discreet but biologically rich archipelago. Their shallow waters, stable temperatures, and limited industrialization provide favorable conditions for the development of many marine species, including Acetabularia. The sandy substrate, clear waters, and presence of seagrass beds create ideal conditions for its growth.
The presence of Acetabularia in this Mediterranean microcosm has been documented by several field studies conducted by Tunisian marine biologists. Species such as Acetabularia acetabulum have been regularly observed there.
2. An Ecological Potential to Protect
Coastal urbanization and marine pollution threaten this fragile ecosystem. Preserving coastal marine zones where Acetabularia thrives means protecting a valuable scientific and educational resource. Including this species in local biodiversity conservation programs—alongside seagrasses—would help raise awareness among younger generations about the richness of their natural heritage.
III. A Star of Experimental Biology
1. Joachim Hämmerling’s Experiments
The name Acetabularia is inseparable from that of Joachim Hämmerling, the German-Danish biologist who used it in the 1930s for a series of landmark experiments. By grafting stems and rhizoids from different Acetabularia species, he demonstrated that the shape of the cap depended on the nucleus located in the rhizoid.
He thus showed that morphogenetic information resides in the nucleus rather than in the cytoplasm. This conclusion—reached even before the full identification of DNA as the carrier of heredity—was a decisive advance.
2. The Lifespan of mRNA
One of Acetabularia’s advantages is the significant physical distance between its nucleus (in the rhizoid) and its cap, where cellular structures form. This feature made it possible to study the lifespan of messenger RNA (mRNA), revealing that proteins could continue to be synthesized in the cap even after the nucleus was removed. This was a major step in understanding genetic translation and mRNA stability.
3. A Model for Intracellular Transport
Thanks to its large size, Acetabularia allows direct observation of intracellular mechanisms such as organelle movement, vesicle transport, and cytoplasmic streaming (cyclosis). It remains a model organism for visualizing living processes under the microscope.
IV. An Exceptional Educational Tool
1. A Cell Visible to the Naked Eye
The primary pedagogical value of Acetabularia lies in its size. It demonstrates to students that a cell can be enormous, breaking the common misconception that cells must be microscopic. This realization is particularly striking in secondary education, where “cell” is often associated with “invisible.”
By handling it in laboratories or observing it in the field, students discover the diversity of life forms and gain a sense of biological scale.
2. A Cell with Multiple Functions
Acetabularia can also be used in higher education to illustrate:
- Cellular compartmentalization
- The role of the nucleus
- Transcription and translation
- Morphogenesis
- Mitosis and the cell cycle (in young cells)
It fits naturally into curricula in cell biology, genetics, plant embryology, and physiology.
3. Stimulating Curiosity
In Tunisia, incorporating Acetabularia into university curricula (marine biology, biotechnology, science education) or preparatory classes would bring students closer to their immediate ecological heritage. Organizing field trips to Kerkennah to observe the alga in its natural habitat is a unique opportunity to link theoretical science with lived experience.
V. Popularizing Science Through the Beauty of Life
1. An Alga that Fascinates
Its elegant shape, resembling a tiny parasol on a stem, is visually captivating. This aesthetic dimension makes it an ideal subject for scientific or artistic exhibitions. It has appeared in botanical illustrations, educational videos, and even bioart.
Sharing its story, uniqueness, and scientific contributions can captivate audiences far beyond specialized circles.
2. A Subject for Media
Acetabularia could be highlighted in science outreach programs, magazines, or traveling school exhibitions. A large 3D model or interactive animations of its cellular functions would attract interest from students and the general public alike.
3. An Ambassador of Mediterranean Life
Positioning Acetabularia as a symbol of Tunisian marine biodiversity would strengthen citizens’ connection to their environment. It could feature in awareness campaigns alongside dolphins, sea turtles, and seagrasses.
VI. An Interdisciplinary Approach
1. Art and Science
Tunisian artists could draw inspiration from Acetabularia’s structure to create installations or educational objects. Combining science and art often sparks unexpected vocations and makes biology more accessible to non-specialists.
2. Philosophy and Biology
The uniqueness of Acetabularia also raises philosophical questions: What defines a living individual? Where does complexity begin? Can a single cell take on an “organized” form comparable to a multicellular organism? These questions open the door to dialogue between science and philosophy, both in classrooms and in science outreach forums.
VII. Perspectives for Tunisia
1. Toward National Educational Valorization
Including Acetabularia in Tunisian school textbooks, organizing workshops in high schools and science clubs, or launching a pilot project in Kerkennah in collaboration with universities (Sfax, Monastir, Tunis El Manar) would reinforce Tunisia’s place in innovative life-science education.
2. Training Teachers in its Use
Training sessions could be offered to biology teachers, including observation kits, teaching sheets, videos, and simple experimental protocols. This would make Acetabularia a concrete example for teaching core biological functions.
Conclusion
Acetabularia is far more than a simple alga. It is a mystery turned solution, a tool turned symbol. From Joachim Hämmerling to tomorrow’s Tunisian educators, it continues to bridge research, education, and science outreach.
Encountering it in the clear waters of the Kerkennah Islands is not merely a biological curiosity; it is an opportunity to root science in a territory, reconnect students with their environment, and remind us that sometimes, a single cell is enough to explain everything.
