Boring bivalve traces in modern reef and deeper-water macroid and rhodolith beds
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(2020) 7:41
Progress in Earth and Planetary Science
RESEARCH ARTICLE
Open Access
Boring bivalve traces in modern reef and deeper-water macroid and rhodolith beds Davide Bassi1* , Juan C. Braga2, Masato Owada3, Julio Aguirre2, Jere H. Lipps4, Hideko Takayanagi5 and Yasufumi Iryu5
Abstract Macroids and rhodoliths, made by encrusting acervulinid foraminifera and coralline algae, are widely recognized as bioengineers providing relatively stable microhabitats and increasing biodiversity for other species. Macroid and rhodolith beds occur in different depositional settings at various localities and bathymetries worldwide. Six case studies of macroid/rhodolith beds from 0 to 117 m water depth in the Pacific Ocean (northern Central Ryukyu Islands, French Polynesia), eastern Australia (Fraser Island, One Tree Reef, Lizard Island), and the Mediterranean Sea (southeastern Spain) show that nodules in the beds are perforated by small-sized boring bivalve traces (Gastrochanolites). On average, boring bivalve shells (gastrochaenids and mytilids) are more slender and smaller than those living inside shallow-water rocky substrates. In the Pacific, Gastrochaena cuneiformis, Gastrochaena sp., Leiosolenus malaccanus, L. mucronatus, L. spp., and Lithophaga/Leiosolenus sp., for the first time identified below 20 m water depth, occur as juvenile forms along with rare small-sized adults. In deep-water macroids and rhodoliths the boring bivalves are larger than the shallower counterparts in which growth of juveniles is probably restrained by higher overturn rates of host nodules. In general, most boring bivalves are juveniles that grew faster than the acervulinid foraminiferal and coralline red algal hosts and rarely reached the adult stage. As a consequence of phenotypic plasticity, small-sized adults with slow growth rates coexist with juveniles. Below wave base macroids and rhodoliths had the highest amounts of bioerosion, mainly produced by sponges and polychaete worms. These modern observations provide bases for paleobiological inferences in fossil occurrences. Keywords: Rhodoliths, Macroids, Bioerosion, Phenotypic plasticity, Bivalves, Pacific Ocean, Mediterranean Sea, Recent
1 Introduction Macroids and rhodoliths form extensive beds in marine waters from shallow subtidal and coral reef areas down to outer platforms (e.g., Foster 2001; Amado-Filho et al. 2012; Foster et al. 2013). Macroids are coated grains, larger than 10 mm, made up of encrusting metazoans or protozoans (Hottinger 1983). Coralline red algae are dominant components of free-living nodules which are named rhodoliths (Bosellini and Ginsburg 1971). Macroids and rhodoliths form a habitat for many other organisms, from protists to fish and including boring bivalves * Correspondence: [email protected] 1 Dipartimento di Fisica e Scienze della Terra, Università degli Studi di Ferrara, Via Saragat 1, I-44122 Ferrara, Italy Full list of author information is available at the end of the article
that inhabit the nodules themselves, and they contribute to the benthic primary pr
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