SCUBA belt transects for abundance data H. cochlea and H. aequicostatus

Marine symbioses are integral to the persistence of ecosystem functioning
in coral reefs. Solitary corals of the species Heteropsammia cochlea and
Heterocyathus aequicostatus have been observed to live in symbiosis with
the sipunculan worm Aspidosiphon muelleri muelleri, which inhabits a
cavity within the coral, in Zanzibar (Tanzania). The symbiosis of these
photosymbiotic corals enables the coral holobiont to move, in fine to
coarse unconsolidated substrata, a process termed as “walking”. This
allows the coral to escape sediment cover in turbid conditions which is
crucial for these light-dependent species. An additional commensalistic
symbiosis of this coral-worm holobiont is found between the Aspidosiphon
worm and the cryptoendolithic bivalve Jousseaumiella sp., which resides
within the cavity of the coral skeleton. To understand the morphological
alterations caused by these symbioses, interspecific relationships, with
respect to the carbonate structures between these three organisms, are
documented using high-resolution imaging techniques (scanning electron
microscopy and µCT scanning). Documenting multi-layered symbioses can shed
light on how morphological plasticity interacts with environmental
conditions to contribute to species persistence.