Prey fractionation in the Archaeocyatha and its implication for the ecology of the first animal reef systems

Abstract

Archaeocyaths are the most abundant sponges from the Cambrian period, having formed the first animal reef communities more than 500 million years ago. The Archaeocyatha are index fossils for correlating rocks of similar ages globally because of their abundance, extensive geographic distribution, detailed anatomy, and well-established taxonomy. Their ecological significance remains incompletely explored, yet they are known to have strongly competitively interacted, unlike modern sponges. This study examines the feeding ecology of the fossil remains of Siberian archaeocyath assemblages. As suspension feeders, archaeocyaths filtered plankton from the water column through pores in their outer wall. Here we outline a new method to estimate the limit on the upper size of plankton that could be consumed by an archaeocyath during life. The archaeocyaths examined were predominantly feeding on nanoplankton and microplankton such as phytoplankton and protozooplankton. Size-frequency distributions of pore sizes from six different Siberian archaeocyath assemblages, ranging from Tommotian to Botoman in age, reveal significantly different upper limits to the prey consumed at each locality. Some of the assemblages contain specimens that could have fed on larger organisms extending into the mesoplankton, including micro-invertebrates as a possible food resource. These results show that during the establishment of the first animal reef systems, prey partitioning was established as a way of reducing competition. This method has applicability for understanding the construction and the functioning of the first reef systems, as well as helping to understand modern reef systems and their development though time and space.

Cochleatina: an enigmatic Ediacaran–Cambrian survivor among small carbonaceous fossils (SCFs)

“…Trapping of protistan prey may be seen as part of a broader stepwise escalation of eukaryovory and predation running from the Tonian to the Cambrian (Porter ; Cohen & Riedman ; Antcliffe et al . ). Sponges (and angiosperms and fungi) also display rare instances of trap‐based carnivory (Vacelet & Boury‐Esnault ), but this style of hunting would have declined in importance in a world of increasingly motile eumetazoan predators.…”

Branching archaeocyaths as ecosystem engineers during the Cambrian radiation

“…Previous workers have presented data indicative of prey partitioning among archaeocyaths, which reduces competition between reef builders and is a strategy seen in modern corals (Antcliffe et al, 2019). Our results add efficient suspension feeding in oscillatory flow regimes and the harboring of photosymbionts as further convergent adaptations displayed by archaeocyathides and modern corals.…”

“…Previous workers have presented data indicative of prey partitioning among archaeocyaths, which reduces competition between reef builders and is a strategy seen in modern corals (Antcliffe et al, 2019).…”

“…However, another potential shift in the physical characteristics of shelfal environments likely occurred due to the rise of Earth's first framework reefs built by calcifying animals-the archaeocyath sponges (Class Archaeocyatha). To date, studies of these reefs have focused on taxonomy, paleoecology, and biostratigraphy (Antcliffe et al, 2019;Debrenne, 2007;Erwin & Tweedt, 2012;Pratt et al, 2001;Pruss et al, 2012Pruss et al, , 2021Rowland & Gangloff, 1988;Wood et al, 1992;Zhuravlev, 2001;Zhuravlev & Wood, 1995), but the substrate geometries of these structures and their potential environmental impacts have yet to be constrained.…”

Vertically migrating Isoxys and the early Cambrian biological pump

“…As active suspension feeders, sponges were able to transport large volumes of water between benthic and pelagic realms (e.g. [54]), and the most abundant sponges from the Cambrian, the reef building archaeocyaths, display pore size differentiation within reef systems [55], presumed to be evidence of prey size-selectivity. This illustrates that predator–prey feedbacks were present in the Cambrian Stage 2 (figure 2), presenting a potential driver towards a larger size of plankton, increasing the sinking speed and efficiency of this part of the biological pump, and ventilating the water column.…”