Roles of clone–clone interactions in building reef frameworks: principles and examples

Abstract

In living and fossil reefs, rapid upward clone growth provides positive topographic relief; the skeletal framework provides rigidity. Clonal organisms have been the chief frame-builders during most of the Phanerozoic; large clone size, growth habit, growth form, and arrangement of these clones in the framework result from rapid growth rates. Dense skeletal packing enhances rigidity and results in live-live interactions between juxtaposed clones. These interactions are both heterospecific and conspecific; the former mostly involve spatial competition whereas the latter involve clone fusion, self-overgrowth, and fission. We describe three types of fusion: (a) inter-clone fusion of two or more clones, each from a separate propagule; (b) intra-clone fusion of parts of the same clone having its origin from a single propagule; it includes recovery from partial clone degradation and self-overgrowth; (c) quasifusion between a live bud/polyp/zooid and a dead part (stem; branch) of the same or a different clone, i.e., a livedead association.

Biological interactions among extant and fossil clonal organisms

“…Such interactions are a vital part of the construction and maintenance of reef frameworks (Fagerstrom and West 2010) and their interplay in such structures is well summarized by WulV and Buss (1979, p. 474) as follows:…”

“…1, 2). Although fusion, Wssion, and diverse interactions would be expected to occur in archaeocyathids as in other hypercalciWed sponges, they have not been documented (see Fagerstrom and West 2010). Apparent inter-clonal fusion in a Silurian stromatoporoid, Denastroma pexisum, is shown by Kershaw (1984, plate 20, Wg.…”

“…ConspeciWc and heterospeciWc interactions between clonal algae and invertebrates are particularly important in the framework construction and enhancement of rigidity of biological reefs (Fagerstrom and West 2010). Such interactions are most easily recognized in extant forms where they can be observed and monitored, but it is possible to infer such interactions in fossils by carefully comparing skeletal features along lines of clonal contact.…”

“…In summary, if the times and distances that coral gametes drift are short and hybridization is rare, mass spawning has great potential for increased reef colonization, enhanced skeletonization/packing density, and rigidity (Fagerstrom and West 2010).…”

“…The growth and survival strategies of clonal organisms are markedly diVerent from those of solitary multicellular organisms and enable clonal algae, sponges, corals and bryozoans to be the dominant frame-builders of both living and fossil reefs (Fagerstrom and West 2010). Our purpose here is to describe, compare, and interpret these strategies among extant clones and use them to recognize and interpret similar strategies among fossil clones.…”