Catactotoechus instabilis, Berkowski, 2008
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publication ID |
https://doi.org/ 10.4202/app.2010.0048 |
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persistent identifier |
https://treatment.plazi.org/id/039787BF-4E10-FF98-A3E8-8BF3FAA1FA44 |
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treatment provided by |
Felipe |
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scientific name |
Catactotoechus instabilis |
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Analysis of Catactotoechus instabilis life strategy
The studied association of Catactotoechus instabilis displays a strong diversity of size and shape ( Fig. 2 View Fig ). The average size of the most studied mature corallites are 0.5–4 cm. Typically, their shapes are ceratoid to trochoid, but in many cases they are irregular due to frequent changes of growth direction and may become strongly cornute or scolecoid (i.e., wormshaped). Their calices are relatively shallow, in most studied specimens with typically developed calices, their depth, i.e., height/diameter ratio varies between 0.4–0.8. On the other hand, they reveal strong diversity in diameter dimension due to frequent process of constriction resulting mostly from various type of rejuvenescence phenomena and extensions of corallites in times of favourable conditions. Measured diameters vary from 0.4 to 2.2 cm, but typically are 0.8–1.5 cm. The strong variation in the shape of the specimens belonging to the association seems to result from four biologically and ecologically controlled factors: the strength of the attachment structures of the corallite, the stability of the host hard particles (mostly of biogenic origin), stability of the sediment and the rate of sediment influx.
Settlement strategy and initial growth.—The process of settlement of the larvae (planulae) is one of the most important stages of the coral life determining its future success or failure in growth and development. For the successful settlement of planulae a stable and relatively hard substrate is needed. Neuman (1988) suggests that the rugose coral larvae were not able to survive if settling strictly on soft unstable substrates devoid of at least small hard grains for their attachment.
The settling larvae in majority of the individuals in the studied association seems to adapt a fixosessile, apically cementing life strategy (sensu Neuman 1988). Typically the initial parts of the corallites are firmly attached by talon structures to detrital hard particles i.e., tabulate coenostea ( Fig. 2A View Fig ), fragments of crinoids stems ( Fig. 2B View Fig ), molluscan shells or trilobite carapaces. In many cases they used the external walls of the corallites of dead or alive individuals ( Fig. 2C, F View Fig ), forming gregaria (pseudocolonies) composed of corallites of this same population. Some of them settled on the remaining part of the calicular rim of the alive specimen, after the rejuvenation process and inflicting further competition between the host specimen and newly settled juvenile corals ( Fig. 2G View Fig ). Others, less common in the studied assemblage, in which the larvae settled on small grains embedded in soft sediment did not develop talons ( Fig. 2D, E View Fig ). They either grew upward rooted in the soft sediment or floated on it, rapidly extending their width. Both types of settlement and growth are typical for soft, argillaceous sediments with embedded, here and there, hard particles of mostly biogenic origin, which had been fully exploited by sessile organisms as the base of their attachment.
Growth strategies.—Many of these specimens reveal a marked diversity of corallite shape after an initial growth period. This is the result of varied ecological factors that caused important skeletal modifications during corallite growth. Among these, the most prominent are: expansions and constrictions of the corallite diameter, rejuvenescence, and deflection of growth direction. Although the differences between these
http://dx.doi.org/10.4202/app.2010.0048
modifications are easily distinguished, the boundaries between them are not sharp and it is possible to find intermediates. These have been observed both in well attached, fixosessile forms and others, which lay directly on or were rooted within the soft sediment and therefore lack any attachment structures.
Expansion, constriction, and rejuvenescence.—Constriction and expansion of the corallite diameter reflect contraction and expansion of the polyp, which in turn apparently reflect changes (sometimes cyclic) in the ecological conditions influencing polyp health. The external wall of the corallite is marked by growth wrinkles that reflect expansion of coral diameter. Thus, the calice became broader or reduced, more or less rapidly. Extensional growth phases are characterized by relatively slow, mostly gradual and undisturbed growth. In this case the expansion of the polyp was restricted by the width of the calicular rim used by the polyp as the base for the newly−formed skeletal structures. This phenomenon is closely connected with initial growth of the polyp in its brephic and juvenile stages of growth, but may also proceed after constriction phases ( Fig. 2C, D View Fig ). On the other hand constrictive phases probably happened rapidly, thus the contracted polyp used various parts of previously formed calice. There are two main types of contraction phenomena ( Fig. 3 View Fig ). (i) Weak and slow, marked only by narrowing of the corallite diameter. In this case, the polyp gradually reduced its diameter without leaving any part of the calice, and as a result, the external wall remained continuous. (ii) Marked and relatively abrupt, where a portion of the calice is left outside of a newly−formed external wall. In the latter case, the polyp axial lateral axial lateral constriction rejuvenescence withdrew completely or partly from the calicular rim and began to form a new wall interiorly to the previously formed calice. As a result it abandoned the calicular rim and some of the inner calicular skeletal elements, which were no longer used to form new skeletal structures. This process is often called rejuvenescence.
Rejuvenescence is a common phenomenon observed in all groups of fossil (for a review see Scrutton 1998) and living (e.g., Chevalier and Beauvais 1987) corals. Fedorowski (1978: 180) redefined the term as “an action of a polyp leading to reduction of dimensions by leaving part of some skeletal structures in a calice outside its new external wall”. Both types, weak and strong contraction (rejuvenescence), may proceed axially or laterally ( Fig. 3 View Fig ). Axial contraction (or rejuvenescence) occurs when the central part of the calice and also the central part of the polyp remain in place almost unchanged, whereas their marginal parts are narrowed. In contrast to this, lateral rejuvenescence takes place when a polyp leaves only a part of the calicular periphery on a given side of the calice, whereas the other side remains unchanged.
Polyp contraction, which is manifested by constriction of skeleton growth, may be connected to various reasons: extrinsic, related to surrounding physical, chemical and biological environmental conditions or intrinsic, related to the overall condition of the polyp. It is possible to speculate that the axial contraction is an effect of decreasing diameter of the pedal disc due to its resorption, caused by e.g., lack of food sources. On the other hand, lateral contraction is in most cases relatively rapid and seems to be an effect of extrinsic factors. Among them the most prominent are: partial burial of the calicular part of the skeleton, falling and a resulting recumbent posture of the corallite, injury caused by other organisms, competition between coral and other incrusting fauna etc.
Most examples of constriction and rejuvenescence in the studied association display the lateral types. They were observed on the external wall and in longitudinal sections ( Fig. 4) but also on well preserved calices ( Fig. 5 View Fig ).
Weak constriction is manifested by delicate narrowing of the corallite diameter on the external wall ( Fig. 4B, D). In this case the wall is continuous on each side of the corallite but in the lateral type it can be narrowed only on one side. In longitudinal section it is clearly distinguishable by increasing size and/or number of dissepiments, which in first stage caused narrowing of the tabularium ( Fig. 4B 2, D 2 View Fig ), and reflects gradual contraction of the polyp. This type was also observed on well preserved calices ( Fig. 5B View Fig ), where it is manifested by narrowing of the tabularium by lonsdaleoid dissepiments.
Strong constriction i.e., rejuvenescence is clearly distinguishable on external wall ( Fig. 4A, C, E) in places where the part of the wall is destroyed on a given side of the corallite. It is often easy to identify an abandoned portion of septa and dissepiments inside well preserved calices ( Fig. 5C View Fig ). In longitudinal section it is well distinguishable by the remaining part of the calicular floor on a given side ( Fig. 4E: on the left
BERKOWSKI—LIFE STRATEGIES OF DEVONIAN RUGOSE CORAL FROM MOROCCO 395
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side), which was often invaded by sediment. The process of rejuvenescence thus is characterized by narrowing and/or shifting of the tabularium and formation of a new wall with dissepiments ( Fig. 4 A 2, C 2, E 2 View Fig ).
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Deflection of growth direction.—As upward growth is typical for corals, any deflections of the corallite reflect changes of growth direction during the polyp’s life. Such deviations in most cases are caused by extrinsic factors such as bottom currents, soft and unstable sediment, or interactions with other organisms. The phenomenon of deflection of growth direction may occur very early in the ontogeny, especially in specimens not attached firmly to stable objects and also in later ontogenetic stages. Juvenile specimens previously attached only to small grains often became recumbent on soft sediment, and again formed skeletons trying to recover an up−facing position. A similar recovery process is represented in mature specimens by the scolecoid shape of corallites, where several deflections can be traced during the complete growth of the corallite. Growth deflections can also co−occur with phenomenon of lateral rejuvenescence. In fact, most specimens revealing lateral rejuvenescence caused by partial burial of the calicular part of the corallite commonly changed growth direction soon thereafter.
The majority of specimens of the investigated Catactotoechus instabilis association show frequent changes of corallite growth direction. These changes are clearly marked by growth wrinkles (rugae) on the corallite external wall and reflect past positions of the calicular rim, i.e., the edge of the calice ( Fig. 4C–F). Hence, it is easy to trace periods of stable upward growth of the corallite, as well as the events of their reaction to extrinsic factors causing deflections of their growth direction. This is evident in longer, ceratoid and scolecoid forms. Here several successive deflections of the corallite appear during their growth history. External surfaces and longitudinal sections of most specimens studied show that repeated deflections proceed in this same direction ( Fig. 4C–E), making corallites cornute rather than scolecoid. This suggests they were subject to one repeated, unidirectional process. Taking into account bottom topography of the sea floor, and the character of its sediment, it would seem that these corals lived on the slopes of mud mounds, within and upon the soft and unstable sediment had simply gradually moved downslope, causing this recumbence. This process, when relatively strong and abrupt, may have caused the partial burial of their calices and polyps and resultant lateral rejuvenescence ( Fig. 4E).
Deflections of growth direction have been also observed in specimens, that interacted with other organisms exploiting their skeletons for attachment. Among these organisms, rugose corals of the same species and tabulate corals predominate as incrusting fauna ( Figs. 2F, G View Fig , 4E).
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