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

Scientific interests
a typical sea-urchin -

Microcyphus roussoui

Cidaroid test

Growth and Population biology of the short-spined sea-urchin Tripneustes gratilla elatensis

Sea-urchins (classis Echinoida) are a unique kind of invertebrate animals. In one aspect, they show primitive traits -- circular shape, lack of head, eyes and central nervous center. On the other hand, they are equipped with very complex chewing apparatus ("Aristotle's lantern"), very efficient locomotory system, hydraulic tube-feet -- tubular pipes emerging from small hole -- called ambulacra - with vaccum attachment discs at their end; Their skeleton is a symmetrical structure made of close-fitting calcareous plates - which grow in a definte pattern, constantly adding more and more plates - held together by flexible collagenous fibers. They are armed with thick spines, and smaller spines ending with sharp and sometimes poisnous pincers (called pedicellaria)
Tripneustes gratilla is a common indo-pacific regular echinoid of the sea-urchin family Toxopneustidae - bearing toxic pedicellaria. It covers itself with debris from bits of coral to sand grains. Spines are short and harmless so the tube feet are easily observable. Pedicellaria are trigeminous globiferous. Average size in the Red Sea is about 70 mm, reaching 130 mm. I have described a subspecies -- Tripneustes gratilla elatensis -- endemic to the Red Sea (ref. 5, below)

I have studied this sub-species for several years, and found that growth rates depend on available resources - at optimum condition T. g. elatensis obtains the adult size of 60 mm in 150 days, while under limiting condition - low nutrition and presence of predators - they remain stunted for elongated periods. In has been shown that in shores exposed to winter storms they breed in their first year, before being washed-out by the waves, while in an adjacent, more protected shore, they adopt a multi-annual life pattern (ref. 12, 16 below). 

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 elastic 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. 


Eupomatus dafnii
The biology of marine invertebrates

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 invertebrate fauna for over thirty years, and published many semi-popular reports and lists.
The polychaete Eupomatus dafnii Amoureux, Rullier & Fishelson, 1978 was named "in honour of Dr. Ya'aqov Dafni, 1934 -, Israelic marine biologist at the Heinz Steinitz Marine Biological Station, Eilat".
I was also a co-author of the description of the polychaete genus and species Filogranella elatensis Ben-Eliahu & Dafni, 1979 (Ref. 1 below).


Filogranella elatensis
 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). 

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 develop a didactic approach to field teaching and study. I wrote many articles -- in Hebrew -- on this topic.

Dr. Dafni sites: Gulf of Eilat web guides Dafni-sites

Invertebrate web guides
I am the author of several web guides to the invertebrates of the Gulf of Eilat (Aqaba) :

Corals - http://www.dafni.com/corals

Non-Coral Coelenterates - http://www.dafni.com/non-corals

Echinoderms - http://www.dafni.com/echinodermata

mollusca - http://www.dafni.com/mollusca

Crustacea - http://www.dafni.com/crustacea

SCIENTIFIC PUBLICATIONS

1979-1995

  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
Routes and Trails in the Eilat Region
 " Routes and Trails in the Eilat Region"

Gefen Publications, Jerusalem (1995).

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

Gulf of Eilat, From the Red Sea to the Red Line...
 Gulf of Eilat, from the Red Sea to the red line..."

A comprehensive account of the natural and human history of the Gulf of Eilat (Gulf of Aqaba), with reference to its endangered future. (in Hebrew)

Tcherikover Publ. House.,Tel-Aviv