CYTOPLASMIC MASSES PRESERVED IN EARLY HOLOCENE DIATOMS: A POSSIBLE TAPHONOMIC PROCESS AND ITS PALEO‐ECOLOGICAL IMPLICATIONS¹

Abstract

In Lake Suigetsu, central Japan, greenish/lightbrown granules identified as cytoplasmic masses had been preserved in siliceous cell walls of freshwater diatoms in annual layers of lacustrine muds since the early Holocene. The lacustrine muds consisted of alternating dark-colored (rich in diatom valves, clay, and organic matter) and light-colored (mainly diatom valves) laminae. The greenish/lightbrown granules were predominately preserved in frustules of the genus Aulacoseira preserved in the dark-colored laminae. The dark-colored laminae were inferred to have formed annually under stratified water caused by surface water warming in summer that caused the formation of an organicrich anoxic layer on the lake bottom that favored granule preservation. The good preservation of cytoplasmic masses in dark-colored laminae suggested a cause for diatom assemblage periodicity, a phenomenon that was commonly noted in temperate lakes: the cells containing these masses could be potential seed stocks for subsequent spring blooms. Frustules of the most abundant granule-containing species, Aulacoseira nipponica (Skvortzow) Tuji, in the dark-colored laminae of the Early Holocene muds were abundant in the overlying light-colored laminae, suggesting that these species reproduced abundantly in springtime yielding a massive diatom bloom.

On the benefits of being redundant: low compositional fidelity of diatom death assemblages does not hamper the preservation of environmental gradients in shallow lakes

“…Nonetheless, it is impossible to equate robust chloroplasts with a living cell without culturing individual cells (Stockner and Lund 1970), which I did not do in this study. However, in cases where the preservation of cytoplasmic structures in the fossil record is exceptional—often as a result of modern displacement along the sedimentary column due to invertebrate burrowing activity (Stockner and Lund 1970)—the chloroplast are usually condensed (Wolfe et al 2006; Tanimura et al 2006). Moreover, good agreement between chloroplast-bearing cell counts and cultures in some freshwater lakes indicated that at least in these lakes the chloroplast counts are a realistic measure of algal viability in recent sediments (Stockner and Lund 1970).…”

Ultrastructure and Function of Setae of a Planktonic Diatom, Chaetoceros Coarctatus

“…However, we rarely observe deep holes in frustules with the exception of Aulacoseira sp. 25 Chaetoceros is one of the most species-rich genera of diatoms in the marine phytoplankton [26][27][28][29] . The cells of Chaetoceros forming chains have long setae protruding from each of their four corners 30,31 .…”