[[en/index|English]] · [[zh/index|中文]] · [[en/frustule_硅藻壳/diatom-frustule|EN]] · [[zh/frustule_硅藻壳/diatom-frustule|中文]] # Diatoms and their frustules — the survival strategy of diatoms Diatom frustules are glassy and hard; their design is simply to keep you from eating them. In the beginning, the ocean was rich in silicon, and diatom frustules did not care much about shape. Later, silicon in the ocean became scarce — with no raw material, diatoms could not make thick frustules, yet they could not afford to be eaten either. So diatoms began to work on the shape of their glass shells, becoming longer and thinner. The aim: to stab you. The aim: to keep you from eating them. ## Unique things of diatoms: frustule and large vacuole - Behrenfeld, Michael J., Kimberly H. Halsey, Emmanuel Boss, Lee Karp-Boss, Allen J. Milligan, and Graham Peers. 2021. "Thoughts on the Evolution and Ecological Niche of Diatoms." Ecological Monographs 91(3). https://doi.org/10.1002/ecm.1457. > (diatoms are) the only photosynthetic protistan lineage expressing external siliceous cell wall structures called frustules. Many diatoms also have large internal vacuoles, and a common assumption in the literature is that success of the diatoms is largely attributable to these two morphological inventions: the frustule for defense and vacuole for luxury nutrient uptake. > While a thin and fused silica cell wall provides an energetically cheap barrier to pathogens compared to the cellulose plates of dinoflagellates, it was also accompanied by some significant challenges. First, vegetative diatom cells lack flagellae, so frustules not only decreased available surface area for nutrient uptake, but the loss of active swimming diminishes nutrient acquisition in patchy environments and limits options for grazer avoidance. A second challenge is that the opal encasement increased cell density and this increased propensity to sink could not be counteracted by flagellar swimming. > The greater requirement for sex in diatoms (a fortuitous consequence of the frustule) compared to other photosynthetic protists has the very significant advantage of promoting speciation. ### Two limits for frustules - Too thick --- the diatom will sink - Too thin --- the diatom will easily be cracked by predators and eaten > By providing an instrument for buoyancy control, expansion of the vacuole both created and eventually solved the sinking problem associated with the rise of large diatom frustules. The presence of a large vacuole has also been repeatedly linked in the literature to diatom success for another reason: luxury nutrient uptake. > ...the diatoms' two unique morphological inventions: the frustule and large vacuole. ## Ballast (镇流器) > In a vessel that travels on the water, the ballast will remain below the water level, to counteract the effects of weight above the water level. ## Diatoms and their grazer — copepod (桡足类) - Grønning, Josephine, and Thomas Kiørboe. 2020. "Diatom Defence: Grazer Induction and Cost of Shell-thickening." Functional Ecology 34(9): 1790–1801. Diatom shells thicken with copepod cues, at a cost of reduced growth rate and/or cell volume. > Diatoms account for 40% of the ocean primary production and play a key role in the oceans' ability to sequester carbon. The evolutionary success of diatoms and their role in ocean biogeochemistry are related to the siliceous shell that provide partial protection against grazing. No wonder it is a hot topic these days — diatoms in carbon neutrality. > Diatoms are a diverse and important group of phytoplankton. They account for about 20% of the Earth's photosynthesis (Armbrust, 2009) and are a major contributor to the biological carbon pump (Smetacek, 1999). Diatoms are characterized by an external silica shell, the frustule, that has many hypothesized functions, ranging from enhancement of light and nutrient harvesting to mechanical protection of the cell against grazing. The shell has the highest mechanical strength relative to its density of any known biological material, and the consequent force required to crush the cell wall is remarkable. ### Silicon in diatoms AND in terrestrial plants > The role of silicon in diatoms resembles its role in many terrestrial plants. It serves multiple purposes, both as a cheap structural element and as a defence agent, and plays many other possible roles, both in plants and in diatoms. In terrestrial plants, silicification is inducible by grazers and highly variable, both within and between species, just as shown here for diatoms. ## Pennates vs. centric diatoms - Petrucciani, Alessandra, Peter Chaerle, and Alessandra Norici. 2022. "Diatoms Versus Copepods: Could Frustule Traits Have a Role in Avoiding Predation?" Frontiers in Marine Science. https://doi.org/10.3389/fmars.2021.804960. > Evolution led to an explosion of morphological varieties of diatom cells, from a radial to an elongated geometry, with a significant change in the frustule silicification. This change in silicification is consistent with a decreasing availability of silicic acid in oceans through geologic eras. > When pennates were co-cultured with centric diatoms, their growth was unaffected by predators. Our data suggested that the frustule morphology contributes to long-term prey-predator interaction since the elongated thinner frustule, which evolved more recently, benefited cells in escaping from predators also when facing competition for resources. ## Silver carp (鲢鱼) can crush Cyclotella (小环藻属) - Xie, Ping. 1999. "Gut Contents of Silver Carp, Hypophthalmichthys Molitrix, and the Disruption of a Centric Diatom, Cyclotella, on Passage through the Esophagus and Intestine." Aquaculture 180(3): 295–305. > The present results indicate that some 67% of the intact Cyclotella cells were more or less damaged as a result of ingestion and digestion by silver carp, of which as much as 52% occurred in the esophagus while only 15% could be attributed to digestion in the intestine. In other words, mechanical crushing of a sufficient proportion of ingested algal cells occurred apparently as a result of grinding by the pharyngeal teeth in the esophagus. > Cyclotella was chosen as an indicator of the digestion process of silver carp: first, Cyclotella has a hard, less digestible silicated frustule, and is thus easily recognized under microscope; second, Cyclotella constituted the major part of the total algal biomass during the study period. > The present study shows that only ca. 1/3 of the ingested Cyclotella remained intact in the feces.