Phenotypic plasticity is the ability of an organism to alter its developmental modes in response to changes in the environment. A major challenge, however, is to explore the existence of a stabilized "morphometric code", a morphological set of buffering rules used repeatedly by members of any species, regardless of environmental factors. Budding of polyps in reef-building corals, an accretive process of the asexual growth form, is thought to be a plastic developmental characteristic. However, we found that intra-tentacular polyp budding in the coral genus Favia from the Red Sea (6 colonies, 37 polyps during a period of 3 years) is not correlated with polyp size. It is initiated after reaching an allometric threshold ratio of two stereotypic, radially symmetrical morphometric landmarks, consisting of the surface area of the polyp and its perimeter.

Skeletal tumor formations in the massive coral Pavona clavus were investigated for 3 yr on the northern Pacific coast of Costa Rica in a reef composed almost exclusively of this species. A field survey of tumor incidence showed that more than half of the population presented this phe- nomenon and that frequencies increased with depth. Up to 37 tumors per colony were recorded, and the largest tumor size was 37.5 m 2 , covering the whole colony surface area. Tumors and healthy skeletons and tissues were studied by scanning and transmission electron microscopy, histology, in situ alizarin marking for growth rates, and x-ray radiographs of skeletal slabs. Macroscopic and microscopic analyses of skeletons revealed the presence of 3 types of tumors (Types I to III). No cyto- logical changes or intracellular infection by parasitic agents were recorded. The only cellular change observed was the reduced numbers of zooxanthellae in tumorigenic tissues. Tumors begin their growth as a single polyp and develop for scores of years without any sign of cellular necroses. Tumors grew faster than healthy parts; however, their skeletal density was lower, with a higher Mg content making it less resistant to bioerosion. Two yr of in situ isogeneic and allogeneic contacts between healthy and tumor fragments revealed no infection or transfer of the tumor to the healthy tissue, even following isogeneic fusion combinations of healthy versus tumor fragments. We suggest that the ter- minology often used to characterize tumors in hard corals ('tumor', 'neoplasm', 'hyperplasia') does not reflect the pathogenesis and etiology of this phenomenon. The terms 'skeletal tumor' or 'calicoblastic epithelioma' seem more fitting for this de novo genesis.

Chimerism, the evolutionary perplexing outcome of fusion between conspecific individuals, is widely documented in nature. Several reports assign a variety of benefits to the state of chimerism, especially in cases of fusions between kins, rating a chimera as a congruous entity. For the first time, we describe here a follow-up study on chimeras of soft corals that occur only between ontogenetically immature conspecifics, prior to development of a histocompatibility recognition system. Four soft coral species from the Red Sea were investigated: Nephthea sp., Heteroxenia fuscescens, Parerythropodium fulvum fulvum and Clavularia hamra. Co-settlement of planulae resulted in high frequencies of spontaneous allogenic fusions between primary polyps. Tissue fusion between allogenic partners was confirmed histologically. During the observation periods (up to 450 d) chimeras were detached, or chimerism resulted in the death of 1 or more partners, or in morphological resorption of the partners. The results also document slower growth and growth-retarding disorders such as disruption of the structural patterns of polyp budding and polyp configuration. These cumulative effects were only manifested by individuals comprised of incongruous components. Such chimeras are likely to be less suited to field conditions than genetically homogeneous individuals, raising the ecological-evolutionary question of why soft-coral chimeras arose in the first place. We propose that juvenile cnidarian chimerism represents a case in which ontogenetic allorecognition is not infallible, and that it is further promoted by the gregarious settlement of larvae characteristic of many coral species.

The population genetic profiles of 60 specimens of the common intertidal sea anemone Actinia equina taken from four sampling sites (Peroj, Barbariga and the north and south shores of the Limski Canal), along a 25 kin strip of the coast of the Istra Peninsula, Croatia, were evaluated by AFLP markers (144 loci). All populations were characterized by aggregates of specimens confined within a few square meters. One of the populations (on the north shore of the canal) contained both large and small-sized individuals. Results revealed high within-aggregate genetic heterogeneity (36.1-55.6%). With respect to interpopulation profiles, geographically remote populations from Peroj, Barbariga and the south shore of the canal were more closely related genetically than those on the north and south shores of the canal. The small-sized subpopulation from the north shore exhibits a distinct AFLP pattern, suggesting that it warrants recognition as a cryptic species. (C) 2002 The Linnean Society of London.

The development of standardized and sustainable aquaculture techniques for the cultivation of marine organisms offers many advantages: it would help reduce the quantity of living material harvested from coral reefs; it could be used as an efficient means of rehabilitating impoverished reef ecosystems (e.g. by reseeding depleted natural stocks of corals); it would provide an educational and research tool for the intensive study of marine animal biology under controlled laboratory conditions.

The dioecious Red Sea soft coral Parerythropodium fulvum fulvum breeds its nonsymbiotic planula larvae on the surface of female colonies for less than a week. After completing their development, larvae crawl and settle near maternal colonies. Here we study the genetic polymorphism of developing larvae by the use of amplified fragment-length polymorphism markers. Four reproductive colonies from shallow water populations (two from a dense population and two from a less densely populated area 100 m away) were chosen, and ten larvae were randomly collected from each colony. DNA was analyzed by using three different primer combinations producing 61, 63, 63 polymorphic markers, respectively. All larvae exhibited different banding patterns from one another, illustrating the prominent role of sexual reproduction for the production of larvae. Nei's mean genetic distances for all 12 possible pair-wise combinations for larval origins revealed, in most cases, that sister larvae are genetically closer than larvae from different colonies and that larvae may be grouped into three statistical clusters in accordance with colony origin and population studied. The usefulness of molecular methodologies in coral population genetics is discussed.

The gastrovascular system in the Red Sea soft coral Parerythropodium fulvum fulvum comprises two interconnected networks of canals filled with fluid and circulating cells. The first network is composed of narrow canals (50-80 {mu}m in width) located below the upper ectodermal layer; the second network includes larger canals (300-500 {mu}m in width) that are located deeper in the coral tissue. Particle movement in the second network is faster than in the superficial network, but in both, coral cells with and without healthy zooxanthellae circulate freely. To investigate the movement of metabolites and cellular components within the colony, coral fragments were exposed to 14C-labeled seawater for 24 h in the laboratory and in situ under saturating photosynthetic photon flux and then grafted back to their original colonies. Grafts fused after 24 h. In the laboratory experiment, up to 45% of the fixed 14C was translocated to the unlabeled colony within 48 h after fusion. In the in situ experiment, significant translocation of labeled materials occurred at the furthest parts of the colonies, 390 mm away from the fusion line, in 24 h. Even though the amount of labeling varied between colonies, labeled material spread throughout all the unlabeled parts. It thus appears that the gastrovascular system in Parerythropodium fulvum fulvum functions as an effective circulatory apparatus for fast translocation of organic compounds and cellular components within the colony.