Hypothesized resource relationships among African planktonic diatoms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109870/1/lno19863161169.pd

Differences in silica content between marine and freshwater diatoms

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/109821/1/lno19893410205.pd

Diatom responses to microenvironment structure within metaphyton mats

Microscale conditions within metaphyton mats affected the distribution of diatom genera. We investigated the conditions within layers of floating filamentous algal mats and changes in diatom genera over 57 days using microprobes every 2, 4, and 6 cm down through mats held in floating nets. Mats were then collected, frozen, and sliced into 2 cm layers for analysis. Filamentous algae and their diatom epiphytes were identified, counted, and analyzed for nitrogen, phosphorus, carbon, silicon, ash-free dry mass (AFDM), and chlorophyll a. Light intensity, temperature, dissolved oxygen, dry mass, and AFDM all fell significantly with increasing depth in the mat. Diatom coverage per filament was calculated as an epiphyte area index (EAI) and was significantly higher at the edge versus the center of the mat. The uppermost 2 cm layer showed the greatest downward trend in EAI over the sampling period. The density of Gomphonema, Cocconeis and Fragilaria were significantly positively correlated with lower light intensity and lower layers of the mat. Cymbella/Encyonema density was significantly correlated with higher light intensity. Gomphonema, Cocconeis and Nitzschia were positively correlated with filaments with higher chlorophyll a content. Achnanthidium, Cymbella/Encyonema and Nitzschia required higher levels of silicon. Diatoms with different growth habits responded similarly to measured variables. Stalk-forming Gomphonema and adnate Cocconeis both occurred in lower light areas and grew well under low nitrogen and phosphorus conditions

Evidence for the Persistence of Food Web Structure After Amphibian Extirpation in a Neotropical Stream

Species losses are predicted to simplify food web structure, and disease‐driven amphibian declines in Central America offer an opportunity to test this prediction. Assessment of insect community composition, combined with gut content analyses, was used to generate periphyton–insect food webs for a Panamanian stream, both pre‐ and post‐amphibian decline. We then used network analysis to assess the effects of amphibian declines on food web structure. Although 48% of consumer taxa, including many insect taxa, were lost between pre‐ and post‐amphibian decline sampling dates, connectance declined by less than 3%. We then quantified the resilience of food web structure by calculating the number of expected cascading extirpations from the loss of tadpoles. This analysis showed the expected effects of species loss on connectance and linkage density to be more than 60% and 40%, respectively, than were actually observed. Instead, new trophic linkages in the post‐decline food web reorganized the food web topology, changing the identity of “hub” taxa, and consequently reducing the effects of amphibian declines on many food web attributes. Resilience of food web attributes was driven by a combination of changes in consumer diets, particularly those of insect predators, as well as the appearance of generalist insect consumers, suggesting that food web structure is maintained by factors independent of the original trophic linkages

The effect of pH, aluminum, and chelator manipulations on the growth of acidic and circumneutral species of Asterionella

The growth rates of two diatoms, acidophilic Asterionella ralfsii and circumneutral A. formosa , were differentially affected by varying pH, Al, and EDTA in chemically defined media. Free Al ion concentration increased as pH and EDTA concentration decreased. Free trace metal ion concentration decreased as EDTA levels increased but increased by orders of magnitude upon addition of Al. pH had an overriding species specific effect on growth rate; at low pH A. ralfsii had higher growth rates than A. formosa and vice versa at high pH. For both species higher EDTA levels depressed growth rates. Moderate additions of Al generally resulted in growth stimulation. The growth rate stimulations, especially at 200 and 400 μg L −1 Al additions, correlate to increases in free trace metal ion concentrations. The EDTA-AI interaction effects on growth rate were both pH and concentration dependent: at pH 7 both species were stimulated by addition of Al at all EDTA levels (except A. ralfsii at 5.0 mM EDTA and A. formosa at 0.5 mNM EDTA); at pH 6 Al addition either stimulated or had no effect on the growth rates of both species (except at low EDTA and high Al levels); at pH 5 A. formosa did not grow and additions of 200 μg L −1 Al stimulated growth of A. ralfsii . It is likely that the effect of pH, Al, and EDTA on speciation of essential or toxic trace metals affects growth rates of these diatoms in a species specific manner.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43905/1/11270_2004_Article_BF00282626.pd

Linking planktonic diatoms and climate change in the large lakes of the Yellowstone ecosystem using resource theory

Resource-based physiology of the eight important planktonic diatom species in the large lakes of the Yellowstone region can be used to explain their relative abundances and seasonal changes. The diatoms are ranked along resource ratio gradients according to their relative abilities to grow under limitation by Si, N, P, and light. Hypotheses based on resource physiology can be integrated with observations on seasonal changes in diatom assemblages to explain the present distributions of diatoms and to test the causal factors proposed to explain diatom distributions over the Holocene. Knowledge of the limnology of these lakes and process-oriented physiology provide the basis for a more detailed interpretation of the paleorecord and a firmer basis for landscape-level transfer functions for fine-scale climate reconstruction