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

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 a maximal 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). 

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.

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".

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 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. Lately I created a website, as data base of the mollusca of the Gulf of Aqaba (Eilat Gulf):

םינימ ןווגמ לע םוהיז תעפשה

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

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.

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

Gefen Publications, Jerusalem (1995).

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

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

Tcherikover Publ. House.,Tel-Aviv

In Hebrew: "...ופוס דעו ףוס-םימ ,תליא ץרפמ"