INFECTION, GROWTH, AND COMMUNITY‐LEVEL CONSEQUENCES OF A DIATOM PATHOGEN IN A SONORAN DESERT STREAM¹

Abstract

We describe effect of a pathogen that spread through a dense, rapidly growing, benthic diatom community during two infection periods (February and mid‐April 1991) in Sycamore Creek, Arizona. Infected areas appeared as gray rings within a matrix of healthy diatom growth and spread rapidly, eventually covering all benthic substrata and causing algal sloughing (within 2 wk in February and 1 wk in April). Examination of algal material with transmission electron microscopy revealed the presence of invasive bacteria within diatom cells from infected areas, suggesting a pathogenic bacterium as the most probable cause of this phenomenon. Infected area supported lower chlorophyll a concentrations and contained higher percentages of diatom cells with fragmented or reduced chloroplasts than uninfected areas. Spread of the pathogen appeared to be linked most strongly with diatom densities. The infection spread most rapidly in April, when cell densities were highest, and decimated all diatom species populations. The February infection was more species‐specific in its action, affecting large motile and rosetteforming taxa more strongly than small, adnate diatoms. This latter group likely resided at the base of communities and may have been buffered from pathogen transfer by mucilage and/or dentrital particles. Consequently, relative abundance of small, adnate diatom taxa increased in algal communities as a result of the February infection. Pathogen‐induced alteration of diatom species composition and abundance should influence primary production in this ecosystem and affect the dynamics of organisms that exploit algae as a resource.

Seasonal changes of periphytic nutritive quality for Sicyopterus lagocephalus (Pallas, 1770) (gobiidae) in three streams of Reunion Island

“…Many factors interact for controlling development of algal periphytic communities such as nutrient availability, light, flow velocity, pH, temperature, grazing, which can affect abundance, production and community structure (Fairchild et al 1985, Steinman & McIntire 1986, Keithan et al 1988, Bothwell 1988, Peterson et al 1993, Rosemond et al 1993, Pan & Lowe 1994, Pringle & Hamazaki 1997, Rosemond et al 2000. Several experiments of N and P enrichment suggest that nitrogen availability can constitute an essential element in the regulation of primary benthic production (Lohman et al 1991, Perrin & Richardson 1997.…”

Shifts in habitat templates for lotic microalgae linked to interannual variation in snowmelt intensity

“…These taxa also appear to be easily ingested by aquatic herbivores (Lamberti et al 1987), more easily digested (Peterson and Boulton 1999), and more susceptible to invasive infection (Peterson et al 1993) than other algal taxa. Thus, proliferations induced by transient increases in nitrogen from zones of hydrologic upwelling or increased runoff can translate to increased resource availability for primary consumers.…”

“…Nutrient-related changes in algal assemblages in the upstream reach in 1996 were primarily induced by proliferation of large-celled diatoms that are common early colonists of clean substrata or abundant in ungrazed, nitrogen-rich environments (Peterson et al 1993;Stevenson and Pan 1996). These taxa also appear to be easily ingested by aquatic herbivores (Lamberti et al 1987), more easily digested (Peterson and Boulton 1999), and more susceptible to invasive infection (Peterson et al 1993) than other algal taxa.…”

“…This ''habitat template'' shifts within years in response to seasonal changes in the physical/ chemical environment (Duncan and Blinn 1989) and the phenology or timing of visitation by herbivores (Jacoby 1987). Shifts can also be induced by stochastic episodes of physical disturbance (Zimmerman et al 1996) that modify the template on multiple levels or by pathogen outbreaks that alter the biological component (Peterson et al 1993). Variation in global weather, such as the El Niño-Southern Oscillation phenomenon, induces differences among years in seasonal precipitation and temperature and in the frequency and magnitude of flood disturbance (Molles and Dahm 1990).…”

Biological silicon removal from coal seam gas water

“…There are a number of pathogens which can adversely affect diatom growth [31,46] and numerous algae which can compete with diatoms for available light and nutrients. As restricting growth of other algae is not easily managed (algae use the same principal C:N:P macro nutrients) diatoms which are suited to the existing pond and water characteristics will be selected, and their nutrient supply improved so they can out compete other algae.…”