Rebecca J. Bixby

The effects of amphibian population declines on the structure and function of Neotropical stream ecosystems

Amphibians can be important consumers in both aquatic and terrestrial habitats and may represent an important energetic link between the two, particularly in the tropics, where amphibian species richness and abundance are high. In the past 20 years, amphibian populations have declined dramatically around the world; numbers have decreased catastrophically in protected upland sites throughout the neotropics, usually resulting in the disappearance of over 75% of amphibians at a given site, particularly those species that breed in streams. Most studies of amphibian declines have focused on identifying causes and documenting changes in adult abundance, rather than on their ecological consequences. Here, we review evidence for the potential ecological effects of catastrophic amphibian declines, focusing on neotropical highland streams, where impacts will likely be greatest. Evidence to date suggests that amphibian declines will have large-scale and lasting ecosystem-level effects, including changes in algal com...

Relationships of stream algal community structure to catchment deforestation in eastern Madagascar

Abstract Approximately 0.5 million km of tropical stream channel are modified by catchment deforestation annually, but the consequences of this process for community structure are poorly understood because of a dearth of data from tropical regions. We compared the algal communities of epilithic biofilms from 3 tropical rainforest streams draining Ranomafana National Park (RNP) in eastern Madagascar and 3 open-canopy streams draining RNPs deforested peripheral zone. Forest and open-canopy streams differed in canopy cover and mean water temperature but did not differ in substrate composition or major nutrient chemistry. We recorded 137 algal taxa, of which ∼45% can be considered endemic or potentially endemic. Deforestation had significant effects on algal community structure. Complete separation between forest and open-canopy streams was observed in nonmetric multidimensional scaling ordinations based on species cell densities, species presence–absence, and cell densities of algal growth forms. Forest streams were characterized by higher species richness and cell densities of motile and solitary growth forms (e.g., Navicula spp.) than were open canopy streams. Open-canopy streams had more variable community structure than forest streams and were characterized by prostrate and solitary (e.g., Planothidium spp.) and chain-forming/stalked growth forms (e.g., Gomphonema spp.). Community shifts and reductions in species richness observed in open-canopy streams show that diatom biodiversity might be affected adversely by vegetation removal in the catchments we studied. Given that Madagascar has lost most of its rainforest in recent centuries, it is reasonable to assume that historical deforestation has led to shifts in algal assemblages at broader regional scales. Our results also suggest that global algal diversity could be affected by tropical deforestation if similar patterns of endemism and alteration of algal assemblages occur in the 0.5 million km of stream channel affected by tropical deforestation annually.

HANNAEA SUPERIORENSIS SP. NOV., AN ENDEMIC DIATOM FROM THE LAURENTIAN GREAT LAKES

Hannaea superiorensis sp. nov. is formally described from benthic and tychoplanktonic locations in the North American (Laurentian) Great Lakes, primarily from Lake Superior. This taxon has previously been reported as Ceratoneis arcus (Ehrenb.) Kütz., Hannaea arcus (Ehrenberg) Patrick or Hannaea arcus var. linearis (Holmboe) Ross in Hartley; however, significant morphological and ecological differences support the separation of Hannaea superiorensis as a new species. Length-width-curvature triplots demonstrate the greater length and length: width ratio of this taxon compared with other Hannaea populations. Morphologically, H. superiorensis most closely resembles H. arcus var. linearis. Finally, the habitat preferences of H. superiorensis are distinctive compared to the riverine nature of H. arcus and its varieties; Hannaea superiorensis is primarily found as epilithon in the littoral wave zone of Lake Superior. This species can also be found secondarily in the tychoplankton of Lake Superior and is occasionally transported as tychoplankton to other Laurentian Great Lakes. Hannaea superiorensis does not appear to be sympatric with H. arcus in the modern Great Lakes, but it may have speciated from local river populations of H. arcus during the Late Pleistocene-Early Holocene to become adapted to the cold, high-energy wave zone of Lake Superior.

HANNAEA ARCUS (EHRENBERG) R. M. PATRICK: LECTOTYPIFICATION AND NOMENCLATURAL HISTORY

The original material of Navicula arcus Ehrenberg (the type of Hannaea R. M. Patrick) was studied and two specimens have been selected as the lectotype and the isolectotype. Since the generic placement of this taxon has been misunderstood for one and a half centuries, its nomenclatural and taxonomic histories are reviewed.

Abundance and size change of Hannaea baicalensis in Lake Baikal

Abstract Hannaea baicalensis is a benthic pennate diatom that predominantly grows at depths of less than a metre attached to rocks and filamentous algae in Lake Baikal, Russia. This narrow zone at the edge of the lake is subject to frequent wave action and lake level fluctuations, which combine with other factors to affect seasonal abundance. During ice cover from January to May in 2008, when lake levels decreased from 42 to 14 cm above datum, H. baicalensis cell abundance remained low (0.39 × 106 cells cm–2). The main period of net cell increase occurred in autumn, when there was a period of stable lake level (±10 cm changes in water depth) that coincided with the return of nutrients during autumn overturn. Cell abundance reached 1.52 × 106 cells cm–2 on 31 October. Alongside the changes in abundance, cyclic size changes in cell apical lengths were found (40 to 144 µm), which were associated with timing of the length of the life cycle. Size decline occurred in both spring and autumn, with an average decrease in apical length of 36 µm per year. It took two years for the mean apical length of a single cohort to decrease from 128 µm to 56 µm, which was then below the threshold (< 65 µm) for initiation of size regeneration.

Metal reactivity in laboratory burned wood from a watershed affected by wildfires

We investigated interfacial processes affecting metal mobility by wood ash under laboratory-controlled conditions using aqueous chemistry, microscopy, and spectroscopy. The Valles Caldera National Preserve in New Mexico experiences catastrophic wildfires of devastating effects. Wood samples of Ponderosa Pine, Colorado Blue Spruce, and Quaking Aspen collected from this site were exposed to temperatures of 60, 350, and 550 °C. The 350 °C Pine ash had the highest content of Cu (4997 ± 262 mg kg-1), Cr (543 ± 124 mg kg-1), and labile dissolved organic carbon (DOC, 11.3 ± 0.28 mg L-1). Sorption experiments were conducted by reacting 350 °C Pine, Spruce, and Aspen ashes separately with 10 μM Cu(II) and Cr(VI) solutions. Up to a 94% decrease in Cu(II) concentration was observed in solution while Cr(VI) concentration showed a limited decrease (up to 13%) after 180 min of reaction. X-ray photoelectron spectroscopy (XPS) analyses detected increased association of Cu(II) on the near surface region of the reacted 350 °C Pine ash from the sorption experiments compared to the unreacted ash. The results suggest that dissolution and sorption processes should be considered to better understand the potential effects of metals transported by wood ash on water quality that have important implications for postfire recovery and response strategies.