Biologic response to environmental stress in tropical reefs: Lessons from modern Polynesian coralgal atolls and Middle Permian sponge and Shamovella-microbe reefs (Capitan Limestone USA)

Abstract

Despite prejudices that comparisons of paleoecological patterns in modern and fossil reef communities are of doubtful validity, we compare the biologic response of living coralgal reefs in French Polynesia to environmental stress with an exceptionally well exposed Middle Permian sponge reef and Shamovella-microbial reef of the Capitan Limestone in New Mexico. In the western Tuamotu Archipelago, reef margins are characterized by depth-related changes of biodiversity. The subtidal basic reefbuilding community contains the highest diversity (23 coral and 6 calcareous algal species). With decreasing water depth and increasing environmental stress, diversity reaches a minimum of five taxa on the reef flat. The Capitan consists of two reef stages. Reefbuilders of the lowermost exposed part of Stage 1 formed a cement-rich sponge reef with 42 taxa (28 sponge species). Decreasing water depth along the reef face is accompanied by loss of five taxa, variations in the gross morphology of sponges and changes in framework architecture. Stage 2, dominated by Shamovella obscura, one bryozoan species and microbes, is sandwiched between two unconformities suggesting much shallower water and higher environmental stress. Despite differences in shelf profile and taxonomy, both the modern and Permian reefbuilders respond to increasing environmental stress with diversity impoverishment and dominance of binders.

Biological interactions among extant and fossil clonal organisms

“…Although speciWc details are not given, the implication is that some type of tissue or at least skeletal fusion occurs in the construction of these ridges (i.e., conspeciWc intra-and inter-clonal). Similar occurrences of algal ridges are noted in other eastern Caribbean islands (Adey and Burke 1975) and in PaciWc reefs (Fagerstrom and Weidlich 2005;Fagerstrom and West 2010, Wg. 4).…”

The problem with the Paleozoic

“…In such settings, high water temperatures, elevated salinity, and rapid salinity changes owing to alternating high evaporation and rainfall probably prevented all but algal and microbial life from becoming established. It is probably for this reason that many platform carbonate successions contain barren, cryptalgal laminated, shallow subtidal to peritidal carbonates that are both devoid of benthic animal remains and similar to those found in salinity-stressed modern tropical carbonate buildups (e.g., Fagerstrom and Weidlich 2005).…”

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

“…Thus, the application of uniformitarian/actualistic principles to ancient reef-building processes must be approached with caution (cf. Fagerstrom et al 2000;Fagerstrom and Weidlich 2005). (3) These differences lead to different interpretations of the roles and importance of biological interactions (spatial competition, self-overgrowth, clone fusion, fission, fragmentation) and the roles of particular taxa, growth forms and guilds in frame-building processes.…”

“…noted above, and because of the great variety of zoarial growth forms and the architecture of the structures they build, there can be little agreement on minimal clone sizes necessary to build a bryozoan-dominated biological reef. Although many lagoonal Porites microatolls (Fagerstrom and Weidlich 2005, fig. 6), built by a single massive clone, are larger than most bryozoan reefs, is each microatoll a true reef?…”