Epibiont communities: Recruitment and competition on North American Carboniferous brachiopods

Abstract

Shell-encrusting assemblages have uniquely high ecological fidelity among paleocommunities because adjacent epibionts coexisted in ecological time, and the abundances and spatial relationships of the various members are accurately preserved. This study presents a quantitative reconstruction of communities on brachiopod shells (Composita and alate spirifers) from the Carboniferous of North America. Thirty-one epibiont communities, comprised of a total of 1180 encrusted brachiopods, are analyzed in terms of epibiont abundance (e.g., percent areal cover), ecological diversity (e.g., Shannon-Wiener Index), and the role of larval recruitment and spatial competition in structuring the communities.Mississippian epibiont communities contain from seven to 14 encrusting taxa that occupy up to 25 percent of host shell surfaces. These communities are spatially dominated by trepostome bryozoans, but also include common lower Paleozoic epibionts, such as encrusting ctenostome bryozoans, hederellids, cornulitids, and edrioasteroids. Pennsylvanian epibiont communities contain between eight and 16 epizoan taxa that occupy up to 34 percent of shell surfaces. They are dominated by fistuliporoid or trepostome bryozoans and increasing proportions of erect bryozoans (e.g., fenestellids), encrusting foraminiferans, and articulate brachiopods.Carboniferous epibionts, like their modern counterparts, exist in loosely organized ecological communities that vary widely in abundance and composition in space and geological time. There is little evidence for tight controls on community structure. Much of the variation is attributed to vagaries in the magnitude and selective nature of larval recruitment. Evidence of competition between community members is rare, except where a high percentage of the shell surface is covered. In these cases, sheetlike bryozoans are usually most abundant. Solitary epibionts are surprisingly successful competitors in one-on-one encounters, but apparently lose areal cover to longer-lived colonial encrusters during ecological succession.

The Temporal Resolution of Epibiont Assemblages: Are They Ecological Snapshots or Overexposures?

“…a p 0.05 Each specimen was measured to the nearest 0.1 mm with electronic calipers and examined under a binocular microscope to evaluate the encrusting fauna. Epibionts were distinguished at the morphospecies level, when possible, and grouped to higher taxonomic levels (e.g., serpulid worms, bryozoans, foraminifera) commonly used in taphonomically oriented encrustation studies (e.g., Lescinsky 1997;Best andKidwell 2000a, 2000b;Lescinsky et al 2002). The epibiont assemblage for each shell was described in terms of abundance and richness (the number of morphospecies present), metrics that are easily measured, easily evaluated from a statistical point of view, and directly relevant to the issue of colonization rates.…”

“…By documenting selective patterns of attachment and growth, it is possible to demonstrate or infer preferential settlement patterns and the existence of interactions (commensalism, parasitism, etc. ) among epibionts or between them and their living hosts (e.g., Bordeaux and Brett 1990;Alexander 1994;Fagerstrom 1996;Lescinsky 1997). However, it can be difficult or impossible to distinguish between live-host colonization and postmortem occupation of skeletal surfaces exposed during life, and similar issues arise in identifying competitive overgrowth among epibionts.…”

“…Terebratulid shells can degrade rapidly in marine settings (Emig 1990), and tumbler experiments suggest that Bouchardia are generally less durable than many co-occurring bivalve molluscs, despite being robust and thick-shelled for brachiopods (Torello et al 2002). The fragility of brachiopod shells has led to the suggestion that their encrustation must occur during the life of the host or within decades after its death (e.g., Lescinsky 1997). If so, then the temporal resolution of encrusting assemblages should be excellent and should provide ecological "snapshots" of coexisting epibionts in the fossil record.…”

Encrustation patterns on Late Cretaceous (Turonian) echinoids from southern Poland

“…The previous types of projections or contour diagrams are frequently used for patterns of encrustation, bioerosion, or drilling predation (e.g., Bottjer 1982;Lescinsky 1997;Nebelsick et al 1997;Santos and Mayoral 2008;Zamora et al 2008;Sørensen and Surlyk 2010) but are inadequate for our material as they are designed for flat substrates in contrast to the nearly spherical echinoids studied here. The only exception is Hammond (1988), who used 3-D stereographic projections and goniometry-based recording of epibionts.…”

“…When compared to other biogenic substrates such as mollusks (e.g., Taylor 1979;Lescinsky 1993;McKinney 1996;Lescinsky et al 2002) or brachiopods (e.g., Bordeaux and Brett 1990;Lescinsky 1997;Rodland et al 2004), echinoids have been rarely studied as potential substrates for encrustation. To date, there have been few studies on encrustation patterns on echinoids in general (e.g., Hammond 1988;Nebelsick et al 1997;Schneider 2003;Santos and Mayoral 2008;Zamora et al 2008).…”