Abstract
Abstract. Photosynthetically active foraminifera are prolific carbonate producers in warm, sunlit, surface waters of the oceans. Foraminifera have repeatedly developed mixotrophic strategies (i.e., the ability of an organism or holobiont to both feed and photosynthesize) by facultative or obligate endosymbiosis with microalgae or by sequestering plastids (kleptoplasts) of ingested algae. Mixotrophy provides access to essential nutrients (e.g., N, P) through feeding while providing carbohydrates and lipids produced through photosynthesis, resulting in substantial energetic advantage in warm, sunlit environments where food and dissolved nutrients are scarce. Our morphological as well as stable carbon isotope data provide, as of now, the earliest (Mid-Devonian) evidence for photosynthetic activity in the first advanced, multichambered, calcareous foraminifera, Semitextularia, from the tropical shelf of the Laurussia paleocontinent. This adaptation likely influenced the evolutionary radiation of calcareous Foraminifera in the Devonian (“Givetian revolution”), one of the most important evolutionary events in foraminiferal history, that coincided with the worldwide development of diverse calcifying marine communities inhabiting shelf environments linked with Devonian stromatoporoid coral reefs.
Highlights
Among photosynthetically active protists, symbiont-bearing benthic Foraminifera (SBBF) are important carbonate producers (e.g., Prazeres and Renema, 2019, and references therein), contributing nearly 1 % of global calcium carbonate budgets (Hohenegger, 2006; Langer et al, 1997)
We examined a total of 25 samples from the upper Eifelian (Middle Devonian) Skały beds of the Holy Cross Mountains in central Poland
Lack of diagenetic alternation of the Skały samples can be supported by uniquely preserved brachiopods with preserved brachidia, primary shell structures (Biernat, 1966), and in some cases relicts of the original color pattern (Biernat, 1984)
Summary
Symbiont-bearing benthic Foraminifera (SBBF) are important carbonate producers (e.g., Prazeres and Renema, 2019, and references therein), contributing nearly 1 % of global calcium carbonate budgets (Hohenegger, 2006; Langer et al, 1997). The occurrence of modern SBBF is limited to tropical and warm temperate zones and is related to the light requirements of the hosted symbiotic microalgae (e.g., Hallock, 1979; Larsen and Drooger, 1977; Renema, 2018). Shallow, euphotic environments enables hosts to use their tests as “glass houses” suitable for the husbandry of endosymbiotic algae (e.g., Hohenegger, 2009; Hottinger, 1982). SBBF inhabit mainly upper euphotic shallow-reef and lagoon environments, though some groups hosting diatoms can be found along reef slopes in highly transparent water down to 130 m depth of the lower euphotic zone (e.g., Hallock, 1999; Hohenegger, 2000). Benefits for the algal symbionts may include protection afforded by the host tests (Hohenegger, 2000, 2018) if the symbionts do benefit (Wooldridge, 2010)
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