Modern active microbialite-metazoan relationships in peritidal systems on the eastern cape coast of South Africa: ecological significance and implication for the palaeontological record

Abstract

Modern microbialites are useful partial analogues of their ancient counterparts and especially can provide clues on the conditions to which they were once exposed to. One of the conundrums which has been slow to solve is the role that grazing and burrowing metazoans had towards disrupting the Phanerozoic microbial mats that formed microbialites, especially those of the laminar variety, stromatolites. Here we use a modern occurrence where rare active microbialites along the southern African coastline are forming in direct association with a metazoan community. We show that these associations demonstrate clear evidence of burrows and trace marks from the metazoans, reflecting direct occupation of the microbialite matrix by some taxa. Importantly, these permanent burrows appear to form (mostly) without disruption to the microbialite consolidation, but rather are constructed along the same axis of that of the microbialite. Furthermore, stromatolitic layering is also observed in direct association with active metazoans. This provides further evidence for the refugia hypothesis which suggests that under certain conditions metazoans are not necessarily restrictive of microbialite integrity. This is explained by the selective forces acting against the destructive influence of metazoans because of the refugia benefits (oxygen, predation, exposure) that they accrue from this habitat. This calls for a reinterpretation of some palaeontological observations.