Jacob Dafni, PhD - Marine biologist ; ד"ר יעקב דפני - ביולוג ימי
P.O.box 6469, Eilat, Israel 88105 * 88105 אילת ,6469 ת.ד.
Telefax: 972-8-6372383 טלפקס * Mobile: 972-53-909104 טלפון נייד
E-mail: jdafni@netvision.net.il

To the Hebrew Version ** לגירסה העברית
Dr. J. Dafni
Scientific interests

TEM of sea-urchin spine

Sand dollar

Pneumatic nature of the echinoid skeletons
Sea-urchin skeletons (tests) are unique among vertebrates and invertebrates alike: They are formed as an outer shell, containing inner fluid. It has been suggested that the test is affected by mechanical forces, exerted by inner -- thethering mesenterial threads -- and outer -- tubefeet muscles and the mechanical properties of the collagen fibers that connect the test plates. Under low mechanical activity the test tends to be globular, while under strong adherence the test is flat.

Decalcified sea-urchin skelton A chemically decalcified dead sea-urchin retains its shape, proving that the overall shape of the sea-urchin is supported by the pneumatic properties of the soft tissue.

A special emphasis in my studies were observations and experiments dealing with the skeleton growth and calcification of the test, trying to demonstrate the influence of mechanical pressure and forces applied by the contractile and -- tissues on the final shape. I showed that even without the support of the hard plates, the sea urchin form retains it typical shape, due to the soft tissue envelope, which acts as a matrix to the calcium carbonate plates. An evidence to the pneumatic hypothesis is the "soap-bubble" curvature pattern of the plates' edge, indicating that inner pressure and outer surface tension of the plates' envelope are primary to the calcification process. This and other evidence urged me to propose a "bio- mechanical" model for the growth and morphogenesis of sea urchins (ref. 10). The model was tested experimentally by various scientists.

Soap-bubble pattern in the plate margins Biomechanical components affecting sea-urchin growth Enhanced growth along a gap in living sea-urchin

Left: the reversal curvature pattern of echinoid skeletal plates, showing in the plate edge and earlier growth-lines. Right: a gap between two neighboring plates in a living test, induces rapid growth of needle-like 'trabeculae', proving that available space enhances rapid growth. Middle: graphic presentation of the "mechanical model".

Deformed Tripneustes
Two types of deformed T. gratilla under pollution
Flattened Tripneustes
Deformities of sea-urchin under pollution conditions.

Mass-deformities (up to 70% urchins were affected) of two types were shown in Tripneustes gratilla under pollution conditions, in the Gulf of Eilat. The apparent cause seems to be chemicals aiming to prevent calcium carbonate clogging of pipe systems in a local power-plant (ref. 2) or hotel laundry (6). The deformities are believed to result from less calcification and softening of the mechanical tissues - inter-plate collagen fibers, inner muscles etc. These observations seem to support the proposed model. 


The biology of marine mollusca

The Gulf of Eilat (Aqaba) has a typical Indo-Pacific fauna, with large amount of endemism. Pollution in the northern part of the Gulf limits the number of living species. I have followed the Gulf mollusc fauna for over thirty years, and published semi-popular reports and lists. I have also made a webguide to the mollusca of the region.   .

The effect of pollution on the species diversity

I studied the species diversity of invertebrate community on dead stony corals, aiming to demonstrate the influence of pollution on the community (ref. 11). 

Gulf of Eilat coral guide

Guide to Mollusca of the Eilat Gulf  n

Gulf of Eilat echinoderms

Guiding and teaching nature

I have served many years as warden and guide in the Nature Conservation organization, the Society for the Protection of Nature, I dedicated much effort to the develope a didactic approach to field teaching and study. I wrote many articles -- in Hebrew -- on this topic.

Invertebrate web guides
I wrote several web guides to the invertebrates of the Gulf of Eilat (Aqaba) all included in Dafni-sites:

Corals - https://www.dafni.com/corals/index.htm

non-coral coelenterates - https://www.dafni.com/non-corals/index.htm

Echinodermata - https://www.dafni.com/echinodermata/index.htm

mollusca - https://www.dafni.com/mollusca/index.htm

Crustacea - https://www.dafni.com/crustacea/index.htm

Tunicates - https://www.dafni.com/tunicata/

Worms - https://www.dafni.com/vermes/

Sponges - https://www.dafni.com/spongia/

Sea plants - https://www.dafni.com/plants/

Fishes - https://www.dafni.com/fish/index.html


    1979-2010 = PDF העתקי

    1. Ben-Eliahu, N. & J. Dafni (1979) A new reef building serpulid genus and species from Elat and the Red Sea, with notes on other gregarious tube worms from Israeli waters.Isr. J. Zool. 28:199-208.
    2. Dafni, J.(1980) Abnormal growth patterns in the sea urchin Tripneustes cf. gratilla (L.) under pollution (Echinodermata: Echinoidea). J. Exp. Mar. Biol. Ecol., 47:259-279.
    3. Dafni, J. (1982) Skeletal deformations in the sea urchin Tripneustes gratilla (L.) under pollution conditions in the Gulf of Eilat, Red Sea. in: Echinoderms - Proceeding of the Fourth International Conference,Tampa Bay, September 1981 (Ed. J.M. Lawrence), A.A. Balkema, Rotterdam. pp. 69.
    4. Dafni, J.& J. Erez (1982) Differential growth in Tripneustes gratilla (Echinoidea). in: Echinoderms: Proceeding of the Fourth Intenational Conference, Tampa Bay, September 1981(Ed. J.M. Lawrence), A.A. Balkema, Rotterdam. pp . 71-75.
    5. Dafni, J. (1983a) A new sub-species of Tripneustes gratilla (L.) from the northern Red Sea (Echinodermata: Echinoidea: Toxopneustidae). Isr. J. Zool., 32:1-12.
    6. Dafni, J.(1983b) Aboral depressions in the tests of the sea urchin Tripneustes cf. gratilla (L.) in the Gulf of Eilat, Red Sea. J. Exp. Mar. Biol. Ecol., 67:1-15
    7. Dafni, J.& A. Diamant (1984) School-oriented mimicry, a new type of mimicry in fishes. Mar.Ecol. Prog. Ser., 20:45-50.
    8. Dafni, J. (1985) Effect of mechanical stress on the calcification pattern in regular echinoids. in: Echinodermata - Proceeding of the Fifth International Echinoderm Conference, Galway, September 1984 (Eds. B.E. Keegan and B.D.S. O'Connor), A.A. Balkema, Rotterdam. pp. 233-236.
    9. Dafni, J. (1986a) A biomechanical model for the morphogenesis of echinoid tests. Paleobiology, 12:143-160.
    10. Dafni, J. (1986b) Echinoid Skeletons as Pneu Structures. Konzepte SFB 230, Universitat Tubingen und Stuttgart. Stuttgart, 13:9-96.
    11. Dafni, J.& L. Fishelson (1986) Effect of pollution on the community structure of animals associated with dead corals in Eilat (Gulf of Aqaba, Red Sea). In: Environmental Quality and Ecosystem Stability, Proc. Third Intern. Conf. of the Israeli Ecological Society, (Ed. Z. Dubinsky & Y. Steinberger). Bar Ilan University Press, Ramat Gan, Israel. Vol III/B; pp. 849-858.
    12. Dafni, J.& R. Tobol. (1986/87) Population structure patterns of a common Red Sea echinoid (Tripneustes gratilla elatensis)/Isr. J. Zool., 34:191-204.
    13. Dafni, J.& J. Erez (1987a) Skeletal calcification patterns in the sea urchin Tripneustes gratilla elatensis: I. Basic patterns. Mar. Biol. 95:275-287.
    14. Dafni, J.& J. Erez (1987b) Skeletal calcification patterns in the sea urchin Tripneustes gratilla elatensis: II. Effect of various treatments. Mar. Biol. 95:289-297.
    15. Dafni, J. (1988) A biomechanical approach to the ontogeny and phylogeny of echinoids. in: C.R.C. Paul & A.B. Smith (Eds.)Echinoderm Phylogeny and Evolutionary Biology. Oxford University Press, Oxford. pp. 175-188.
    16. Dafni, J. (1992) Growth rate of the sea urchin Tripneustes gratilla elatensis. Isr. J. Zool., 38:25-33.
    17. Dafni, J. (1995) The need for Damaged Reef Reclamation and Restoration. In: Proc. International Conference: The Ecosystem of the Gulf of Aqaba in Relation to the enhanced Economical Development and the Peace Process II - Eilat, Jan 30th - Feb 2nd, 1995, 84-86
    18. Dafni, J. (2001) Reduced biodiversity in the northern Gulf of Eilat. Paper prepared for the evaluation committee and presented at the IUI seminars on May 2, 2001. 7 pp.
    19. Dafni, J. (2008) Diversity and Recent Changes in the Echinoderm Fauna of the Gulf of Aqaba with emphasis on the Regular Echinoids. in: F. D. Por (Ed.) Aqaba-Eilat, the Improbable Gulf : Environment, Biodiversity and Preservation. Magnes Press Jerusalem 2008 pp. 226-234.
    20. Dafni, J. (2010) Pollution induced mass-deformities in Tripneustes: Biomechanical aspects. in: Echinoderms: Durham Proceedings of the 12th International Echinoderm Conference, Durham, New Hampshire, USA, 7-11 August 2006 (Eds L.G. Harris, S.A. Bottger, C.W. Walker and M.P. Lesser), CRC Press, A Balkema Book,ISBN 978-0-415-40819-6, pp.601-607.

Popular publications
.Routes and Trails in the Eilat Region " Routes and Trails in the Eilat Region"

Gefen Publications, Jerusalem (1995).

A guide book describing 30 foot and car trails in the mountains of Eilat Region: 

.Strange is their middle name "Strange is their middle name - Echinodermata
inernet book (PDF) describing the Echinoderms, and the story of a study made by the author in the years 1979-1988"

book logo "Gulf of Eilat from the Red Sea to the Red Line..."

Cherikover, Tel Aviv (2000).

A comprehensive description of the Gulf of Aqaba-Eilat Gulf including Geology, Biology, history and environmental aspects, (in Hebrew only) 

.Eilat's Coral Reefs " Eilat's Coral Reefs"

Yeela Books, Eilat (2008).

A guide and description of the coral reefs of Eilat, showing > 500 species of corals, invertebrates and fishes