ENVIRONMENTAL CONTROL OF STALK LENGTH IN THE BLOOM‐FORMING, FRESHWATER BENTHIC DIATOM DIDYMOSPHENIA GEMINATA (BACILLARIOPHYCEAE)¹

Abstract

Blooms of the freshwater stalked diatom Didymosphenia geminata (Lyngb.) M. Schmidt in A. Schmidt typically occur in oligotrophic, unshaded streams and rivers. Observations that proliferations comprise primarily stalk material composed of extracellular polymeric substances (EPS) led us to ask whether or not the production of excessive EPS is favored under nutrient-limited, high-light conditions. We conducted experiments in outdoor flumes colonized by D. geminata using water from the oligotrophic, D. geminata-affected Waitaki River, South Island, New Zealand, to determine the relationship between D. geminata stalk length, cell division rates, and light intensity under ambient and nutrient-enriched conditions. Stalk lengths were measured in situ, and cell division rates were estimated as the frequency of dividing cells (FDC). FDC responded positively to increasing light intensity and to nutrient additions (N+P and P). Under ambient conditions, stalk length increased as light level increased except at low ambient light levels and temperature. Nutrient enrichment resulted in decreased stalk length and negative correlations with FDC, with this effect most evident under high light. Our results are consistent with the hypothesis that extensive stalk production in D. geminata occurs when cell division rates are nutrient limited and light levels are high. Thus, photosynthetically driven EPS production in the form of stalks, under nutrient-limited conditions, may explain the development of very high biomass in this species in oligotrophic rivers. The responses of FDC and stalk length under nutrient-replete conditions are also consistent with occurrences of D. geminata as a nondominant component of mixed periphyton communities in high-nutrient streams.

Harmful Algal Blooms

“…Like many other HABs taxa, D. geminata exploits both inorganic and organic sources of P to support growth. This is supported by evidence from other studies; Kilroy and Bothwell (2011) showed that when a period of nutrient enrichment was followed by unenriched conditions, D. geminata division rates declined by 60% while mean stalk length increased by 250%. During low ambient supplies of inorganic P (i.e., phosphate), D. geminata cell division is P-limited Kilroy and Bothwell, 2011), and under such conditions, the upper parts of stalks stain strongly for organic P-scavenging phosphomonoesterase activity (Ellwood and Whitton, 2007;Aboal et al, 2012).…”

Evidence from checklists for a Holarctic (circumboreal) kingdom of diatoms

“…Native means occurring before European settlement or before intercontinental travel and commerce became common and widespread. Documented cases of freshwater diatoms introduced from other continents since European settlement are not common (e.g., Edlund et al 2000, Spaulding et al 2010, Reid et al 2012, Kilroy and Bothwell 2011). If one accepts evolution and vicariance or “historical biogeography” as the prevailing mechanisms that explain diatom distributions (as opposed to unrestricted dispersal and “ecological biogeography”), then one must assume that all taxa are native, unless there is evidence to the contrary of their recent introduction.…”

Environmental DNA genetic monitoring of the nuisance freshwater diatom, Didymosphenia geminata, in eastern North American streams

“…In addition to plankton drift net samples for eDNA, we collected water chemistry data that included total phosphorus, soluble reactive phosphorus (SRP), pH, nitrate, sulphate, chloride and specific conductance, which are thought to be predictive of D. geminata distribution or abundance (Kilroy & Bothwell, 2011;Bothwell et al, 2014;Bray et al, 2016). At Maryland sites, a 1 L grab sample of stream water was collected for laboratory chemical analyses at the Appalachian Laboratory (University of Maryland Center for Environmental Science), using standard protocols for each analyte (American Public Health Association (APHA), 2005).…”