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Distribution of Earth's biomes is structured by the match between climate and plant traits, which in turn shape associated communities and ecosystem processes and services. However, that climate-trait match can be disrupted by historical events, with lasting ecosystem impacts. As Earth's environment changes faster than at any time in human history, critical questions are whether and how organismal traits and ecosystems can adjust to altered conditions. We quantified the relative importance of current environmental forcing versus evolutionary history in shaping the growth form (stature and biomass) and associated community of eelgrass (Zostera marina), a widespread foundation plant of marine ecosystems along Northern Hemisphere coastlines, which experienced major shifts in distribution and genetic composition during the Pleistocene. We found that eelgrass stature and biomass retain a legacy of the Pleistocene colonization of the Atlantic from the ancestral Pacific range and of more recent within-basin bottlenecks and genetic differentiation. This evolutionary legacy in turn influences the biomass of associated algae and invertebrates that fuel coastal food webs, with effects comparable to or stronger than effects of current environmental forcing. Such historical lags in phenotypic acclimatization may constrain ecosystem adjustments to rapid anthropogenic climate change, thus altering predictions about the future functioning of ecosystems., This work was supported by the US NSF (OCE-1031061, OCE-1336206, OCE0-1336741, OCE-1336905) and the Smithsonian Institution. F.T. was supported by José Castillejo Award CAS14/00177. A.H.E. was supported by the FCT (Foundation for Science and Technology) through Project UIDB/04326/2020 and Contract CEECINST/00114/2018. This is Contribution 106 from the Smithsonian’s MarineGEO and Tennenbaum Marine Observatories Network and Contribution 4105 of the Virginia Institute of Marine Science, College of William & Mary.

Protective legislation and management have led to an increase in California’s sea otter Enhydra lutris nereis population. While sea otter recovery has been linked to ecosystem benefits, sea otter predation may negatively affect commercially valuable species. Understanding the potential influence of sea otters is of particular importance as their range expands into estuaries that function as nurseries for commercially valuable species like Dungeness crab Metacarcinus magister. We consider how sea otter predation has affected the abundance and size of juvenile Dungeness crab in Elkhorn Slough, California, USA, and analyzed cancrid crab abundance and size across 4 California estuaries with and without sea otters to understand how biotic and abiotic factors contribute to observed variation in crab size and abundance. We compared trends in southern sea otters relative to Dungeness crab landings in California to assess whether increasing sea otter abundance have negatively impacted landings. In Elkhorn Slough, juvenile Dungeness crab abundance and size have declined since 2012, coinciding with sea otter population growth. However, the impact of sea otters on juvenile Dungeness crab size was habitat-specific and only significant in unvegetated habitat. Across estuaries, we found that cancrid crab abundance and size were negatively associated with sea otter presence. While abiotic factors varied among estuaries, these factors explained little of the observed variation in crab abundance or size. Although we found evidence that sea otters can have localized effects on cancrid crab populations within estuaries, we found no evidence that southern sea otters, at recent population sizes, have negatively impacted Dungeness crab landings in California from 2000-2014.

While considerable evidence exists of biogeographic patterns in the intensity of species interactions, the influence of these patterns on variation in community structure is less clear. Studying how the distributions of traits in communities vary along global gradients can inform how variation in interactions and other factors contribute to the process of community assembly. Using a model selection approach on measures of trait dispersion in crustaceans associated with eelgrass (Zostera marina) spanning 30° of latitude in two oceans, we found that dispersion strongly increased with increasing predation and decreasing latitude. Ocean and epiphyte load appeared as secondary predictors; Pacific communities were more overdispersed while Atlantic communities were more clustered, and increasing epiphytes were associated with increased clustering. By examining how species interactions and environmental filters influence community structure across biogeographic regions, we demonstrate how both latitudinal variation in species interactions and historical contingency shape these responses. Community trait distributions have implications for ecosystem stability and functioning, and integrating large-scale observations of environmental filters, species interactions and traits can help us predict how communities may respond to environmental change., This research was funded by National Science Foundation grants to J.E.D., J.J.S. and K.A.H. (NSF-OCE 1336206, OCE 1336905, and OCE 1336741). C.B. was funded by the Åbo Akademi University Foundation.

The global decline of marine foundation species (kelp forests, mangroves, salt marshes, and seagrasses) has contributed to the degradation of the coastal zone and threatens the loss of critical ecosystem services and functions. Restoration of marine foundation species has had variable success, especially for seagrasses, where a majority of restoration efforts have failed. While most seagrass restorations track structural attributes over time, rarely do restorations assess the suite of ecological functions that may be affected by restoration. Here we report on the results of two small-scale experimental seagrass restoration efforts in a central California estuary where we transplanted 117 0.25-m2 plots (2,340 shoots) of the seagrass species Zostera marina. We quantified restoration success relative to persistent reference beds, and in comparison to unrestored, unvegetated areas. Within three years, our restored plots expanded ˜8,500%, from a total initial area of 29 to 2,513 m2 . The restored beds rapidly began to resemble the reference beds in (1) seagrass structural attributes (canopy height, shoot density, biomass), (2) ecological functions (macrofaunal species richness and abundance, epifaunal species richness, nursery function), and (3) biogeochemical functions (modulation of water quality). We also developed a multifunctionality index to assess cumulative functional performance, which revealed restored plots are intermediate between reference and unvegetated habitats, illustrating how rapidly multiple functions recovered over a short time period. Our comprehensive study is one of few published studies to quantify how seagrass restoration can enhance both biological and biogeochemical functions. Our study serves as a model for quantifying ecosystem services associated with the restoration of a foundation species and demonstrates the potential for rapid functional recovery that can be achieved through targeted restoration of fast-growing foundation species under suitable conditions.

In addition to its high biodiversity, the California Floristic Province contains over 1600 rare taxa, including many endemics restricted to specific soil types and habitats. In the highly urbanized San Francisco Estuary, these narrow endemics face additional limitations from habitat destruction and modification, prompting an interest in their conservation and management. One such taxon, the Federally listed Cirsium hydrophilum (Greene) Jeps. var. hydrophilum (Suisun thistle), is restricted to two or three populations, and may face limitations beyond past habitat loss. In this study, we investigated life history limitations that may contribute to rarity in C. hydrophilum var. hydrophilum. We documented low seed set, high seed predation by beetle larvae, low localized wind dispersal of seeds, and possible inbreeding in smaller patches. Because seeds did not have a stringent germination requirement in the lab, however, restoration or introduction of new populations from seed is possible. Using seeds from larger source populations could increase success of reseeding, as could adding seeds to augment potentially low genetic diversity in existing smaller subpopulations. Further study is needed to understand the ecology of seed predators, the relative importance of seed set and seed germination in the field, and to confirm our potential finding of reduced genetic diversity and inbreeding. Though the causes and consequences of rarity may differ for each species, this study explores several research directions that could be productive for understanding other California endemic Cirsium and rare wetland endemics.

Human activities degrade and fragment coastal marine habitats, reducing their structural complexity and making habitat edges a prevalent seascape feature. Though habitat edges frequently are implicated in reduced faunal survival and biodiversity, results of experiments on edge effects have been inconsistent, calling for a mechanistic approach to the study of edges that explicitly includes indirect and interactive effects of habitat alteration at multiple scales across biogeographic gradients. We used an experimental network spanning 17 eelgrass (Zostera marina) sites across the Atlantic and Pacific oceans and the Mediterranean Sea to determine (1) if eelgrass edges consistently increase faunal predation risk, (2) whether edge effects on predation risk are altered by habitat degradation (shoot thinning), and (3) whether variation in the strength of edge effects among sites can be explained by biogeographical variability in covarying eelgrass habitat features. Contrary to expectations, at most sites, predation risk for tethered crustaceans (crabs or shrimps) was lower along patch edges than in patch interiors, regardless of the extent of habitat degradation. However, the extent to which edges reduced predation risk, compared to the patch interior, was correlated with the extent to which edges supported higher eelgrass structural complexity and prey biomass compared to patch interiors. This suggests an indirect component to edge effects in which the impact of edge proximity on predation risk is mediated by the effect of edges on other key biotic factors. Our results suggest that studies on edge effects should consider structural characteristics of patch edges, which may vary geographically, and multiple ways that humans degrade habitats., This research was funded by National Science Foundation grants to JED, JJS, and KAH (NSF-OCE 1336206, OCE 1336905, and OCE 1336741). CB was funded by the Åbo Akademi University Foundation.

[Aim] Studies on latitudinal patterns in plant defence have traditionally overlooked the potential effect that resource availability may have in shaping plant defence. Likewise, latitudinal patterns of tolerance traits have rarely been studied, yet they can be a critical component of plant defence. Therefore, the aim of our study was to examine latitudinal variation in the production of tolerance and resistance traits against herbivory along a latitudinal range and a natural gradient of resource availability from upwelling conditions., [Location] North America (Canada, USA, Mexico)., [Time period] Summer months of 2015., [Major taxa used] The seagrass Zostera marina., [Methods] We conducted experiments simulating macroherbivore (e.g., bird, fish) damage on the seagrass Z. marina at 10 sites across the Eastern Pacific coast (Canada–Mexico) and Quebec and analysed several traits related to resistance and tolerance strategies against herbivory. In addition, we examined the effects of potential seagrass changes in defence strategies by performing a series of feeding experiments with mesoherbivores in a subset of sites., [Results] We found that eelgrass resistance defences did not follow a linear latitudinal pattern but rather followed a bell-shaped curve which correlated with bottom-up control. In sites with higher nutrient availability, plants allocated resources to tolerance strategies and had lower resistance traits. Furthermore, seagrasses did not respond linearly to increased herbivory pressure; while they tolerated moderate levels of herbivory, they underwent a significant reduction in tolerance and resistance under high herbivory levels, which also made them more susceptible to consumers in feeding experiments., [Main conclusions] Our results highlight the importance that nutrient availability has in shaping latitudinal patterns of plant defence against herbivory and show how these defences may not respond linearly to increased herbivory pressure in seagrasses., GH was supported by the research personnel program co-funded by the European Social Fund and the Government of the Balearic Islands. This study was supported by grants from RESIGRASS (CGL2014-58829-C2-2-R), the Ramón y Cajal and the José Castillejo Programs to FT, and in-kind support from author institutions. JA was supported by a Juan de la Cierva post-doc grant (ref. IJCI-2016-27681). MH-L was supported by the Tula Foundation. The Hakai Institute Nearshore team supported the work on Calvert Island. This work is part of the Zostera Experimental Network (ZEN). Funding for ZEN was provided by the National Science Foundation (BIO-OCE 1336905 and 1336206).

Hawai‘ian ecosystems evolved in relative isolation and support an abundance of native and endemic species. As such, they are particularly vulnerable to introduced species that alter habitat and interfere with species interactions. Although mangroves are valued globally for shoreline protection and other services, their invasion of the Hawai‘ian islands may have negative effects on the abundance and functions of native species. On an island in Kāne‘ohe Bay, O‘ahu, we explored the relationship between invasion of the red mangrove, Rhizophora mangle, and abundance of the native burrowing shrimp Alpheus rapax, which shares its burrows with the endemic goby Psilogobius mainlandi in a mutualism that reduces predation on both. We hypothesized that the abundance of shrimp/goby burrows is reduced beneath mangroves due to increased cover associated with mangrove prop roots, which trap leaves and debris and may harbor the invasive red alga Gracilaria salicornia. At 3 mangrove-invaded sites, we conducted a survey of burrow density and benthic debris and found ~4–5× lower burrow density and 4× greater cover of debris under the mangrove edge compared to sandflats that were 1.5 and 5.0 m away. Burrow density was negatively correlated with total cover of benthic debris and with subgroups of that cover composed of G. salicornia or leaves. We tested the effect of debris removal over 2 weeks, which resulted in 3–8× more burrows. Thus, we provide evidence that invasive red mangroves, through trapping leaves and promoting presence of invasive G. salicornia among their prop roots, have strong negative effects on shrimp/goby burrow density. Although our study was limited in spatial scope, we propose that current efforts to remove mangroves in Hawai‘i, for both cultural and ecological reasons, will mitigate negative effects on endemic goby and native shrimp habitat.

Humans are changing the Earth's surface at an accelerating pace, with significant consequences for ecosystems and their biodiversity. Landscape transformation has far-reaching implications including reduced net primary production (NPP) available to support ecosystems, reduced energy supplies to consumers, and disruption of ecosystem services such as carbon storage. Anthropogenic activities have reduced global NPP available to terrestrial ecosystems by nearly 25%, but the loss of NPP from wetland ecosystems is unknown. We used a simple approach to estimate aquatic NPP from measured habitat areas and habitat-specific areal productivity in the largest wetland complex on the USA west coast, comparing historical and modern landscapes and a scenario of wetland restoration. Results show that a 77% loss of wetland habitats (primarily marshes) has reduced ecosystem NPP by 94%, C (energy) flow to herbivores by 89%, and detritus production by 94%. Our results also show that attainment of habitat restoration goals could recover 12% of lost NPP and measurably increase carbon flow to consumers, including at-risk species and their food resources. This case study illustrates how a simple approach for quantifying the loss of NPP from measured habitat losses can guide wetland conservation plans by establishing historical baselines, projecting functional outcomes of different restoration scenarios, and establishing performance metrics to gauge success.

The San Francisco Bay-Delta estuary, the largest estuary on the west coast of North America, has lost over 90% of its tidal wetlands through conversion to agriculture, grazing or urban development. Accelerated sea-level rise poses an additional threat to the remaining wetlands, and keeping pace requires that they increase in relative elevation through trapping of suspended sediment or increasing organic productivity in the root zone. Suspended sediment concentrations (SSC) have been declining in rivers and deep channels, and although little is known about sediment dynamics in shallow areas, sediment supply to tidal wetlands may not be sufficient to maintain their elevations in the future. Wetlands will be constrained by existing development and mountainous terrain. Increases in tidal wetland salinity have been occurring in saline, brackish and the western edges of freshwater tidal wetlands. To mitigate for sea-level rise, considerable acreages currently are being restored, with and without active management practices. Restoration techniques are being piloted to increase shoreline protection, resiliency, and high tide refuge in adaptation to current and projected sea level rise. We recommend additional research into plant physiological responses to combinations of climate change impacts, as well as suggest potential practical policy positions.

The extensive loss of tidal marsh habitat surrounding the San Francisco Bay has led to numerous restoration projects to restore ecosystem function. Native cordgrass (Spartina foliosa) is important for sediment accumulation and nesting habitat for endangered California Ridgway’s Rail (Rallus obsoletus obsoletus), and because salt marshes are typically nitrogen-limited ecosystems, previous restoration studies in California have used nitrogen fertilizers to increase plant growth. This study compared the use of two low-nitrogen, high-carbon fertilizers (Macrosystis pyrifera (kelp) and sodium alginate) to stimulate N2-fixing bacteria inhabiting the S. foliosa rhizosphere in a historic and recently restored marsh in San Francisco Bay. Alginate increased N2-fixation, though there was no observed S. foliosa growth response. Kelp suppressed N2-fixation, and increased the foliar nitrogen content of Salicornia pacifica in mixed Spartina-Salicornia stands. The restored marsh had less than 0.5 μM phosphate in porewaters, suggesting phosphorus, not nitrogen, limits S. foliosa growth in this marsh. Alginate increased rates of N2-fixation and may promote plant growth in marshes exhibiting nitrogen limitation. Phosphate limitation was a surprise considering numerous previous studies indicate nitrogen as the primary limiting nutrient of tidal marsh plants. We recommend first assessing nutrient stoichiometry when considering manipulations to promote plant growth in restored marshes.

Recovering species are often limited to much smaller areas than they historically occupied. Conservation planning for the recovering species is often based on this limited range, which may simply be an artifact of where the surviving population persisted. Southern sea otters (Enhydra lutris nereis) were hunted nearly to extinction but recovered from a small remnant population on a remote stretch of the California outer coast, where most of their recovery has occurred. However, studies of recently-recolonized estuaries have revealed that estuaries can provide southern sea otters with high quality habitats featuring shallow waters, high production and ample food, limited predators, and protected haul-out opportunities. Moreover, sea otters can have strong effects on estuarine ecosystems, fostering seagrass resilience through their consumption of invertebrate prey. Using a combination of literature reviews, population modeling, and prey surveys we explored the former estuarine habitats outside the current southern sea otter range to determine if these estuarine habitats can support healthy sea otter populations. We found the majority of studies and conservation efforts have focused on populations in exposed, rocky coastal habitats. Yet historical evidence indicates that sea otters were also formerly ubiquitous in estuaries. Our habitat-specific population growth model for California’s largest estuary—San Francisco Bay—determined that it alone can support about 6,600 sea otters, more than double the 2018 California population. Prey surveys in estuaries currently with (Elkhorn Slough and Morro Bay) and without (San Francisco Bay and Drakes Estero) sea otters indicated that the availability of prey, especially crabs, is sufficient to support healthy sea otter populations. Combining historical evidence with our results, we show that conservation practitioners could consider former estuarine habitats as targets for sea otter and ecosystem restoration. This study reveals the importance of understanding how recovering species interact with all the ecosystems they historically occupied, both for improved conservation of the recovering species and for successful restoration of ecosystem functions and processes.

Microclimatic variation has emerged as an important driver of many ecological and evolutionary processes. Nonetheless, fine-scale temperature data are still rare in most habitats, limiting our ability to understand the consequences of microclimatic variation under current and future conditions. We measured fine-scale thermal variation in a common, species-rich, but rarely studied habitat with respect to temperature: the airspaces under rocks on intertidal zone boulder shores. The effects of thermal variation were investigated using physiological, behavioral, and demographic responses of the porcelain crabRocas calientes y rocas no tan calientes en la orilla del mar: patrones y consecuencias dependientes del tamaño del cuerpo de la variación microclimática en el hábitat de rocas intermareales (Hot rocks and not-so-hot rocks on the seashore: patterns and body-size dependent consequences of microclimatic variation in intertidal zone boulder habitat) La variación microclimática se ha convertido en un importante impulsor de muchos procesos ecológicos y evolutivos. No obstante, los datos de temperatura a pequeña escala aún son raros en la mayoría de los hábitats, lo que limita nuestra capacidad de comprender las consecuencias de la variación microclimática en las condiciones actuales y futuras. Medimos la variación térmica a pequeña escala en un hábitat común, rico en especies, pero rara vez estudiado con respecto a la temperatura: los espacios aéreos debajo de las rocas en las costas de rocas de zonas intermareales. Los efectos de la variación térmica se investigaron utilizando respuestas fisiológicas, conductuales y demográficas de los cangrejos de porcelanaRochas quentes e rochas não-tão-quentes à beira-mar: padrões e conseqüências dependentes do tamanho coporal para a variação microclimática no habitat de rochas da zona entremarés (Hot rocks and not-so-hot rocks on the seashore: patterns and body-size dependent consequences of microclimatic variation in intertidal zone boulder habitat) A variação microclimática emergiu como um importante causador de muitos processos ecológicos e evolutivos. No entanto, dados de temperatura em escala fina ainda são raros para a maioria dos habitats, limitando nossa capacidade de compreender as conseqüências da variação microclimática sob condições atuais e futuras. Nós medimos a variação térmica numa escala fina em um habitat comum, rico em espécies, mas raramente estudado em relação à temperatura: os espaços aéreos sob as rochas nas margens dos blocos de pedra da zona entremarés. Os efeitos da variação térmica foram investigados usando respostas fisiológicas, comportamentais e demográficas do caranguejoHeiße Felsen und weniger heiße Felsen an der Küste: Muster und körpergrößenabhängige Folgen der mikroklimatischen Variation im Felsenhabitat der Gezeitenzone (Hot rocks and not-so-hot rocks on the seashore: patterns and body-size dependent consequences of microclimatic variation in intertidal zone boulder habitat) Die mikroklimatische Variation ist als wichtiger Treiber vieler ökologischer und evolutionärer Prozesse hervorgetreten. Allerdings sind detaillierte Temperaturdaten für die meisten Habitate noch selten, was unsere Fähigkeit einschränkt, die Konsequenzen mikroklimatischer Schwankungen unter gegenwärtigen und zukünftigen Bedingungen zu verstehen. Wir haben die thermische Variation hochaufgelöst in einem gewöhnlichen, artenreichen, aber in Bezug auf die Temperatur selten untersuchten Habitat gemessen: den Lufträumen unter Felsbrocken in der Gezeitenzone von Felsküsten. Die Auswirkungen der thermischen Variation wurden anhand physiologischer, verhaltensbezogener und demographischer Reaktionen der Porzellankrabbe

Both abiotic and biotic factors govern distributions of estuarine vegetation, and experiments can reveal effects of these drivers under current and future conditions. In upper San Francisco Estuary (SFE), increased salinity could result from sea level rise, levee failure, or water management. We used mesocosms to test salinity effects on, as well as competition between, the native Stuckenia pectinata (sago pondweed) and invasive Egeria densa (Brazilian waterweed), species with overlapping distributions at the freshwater transition in SFE. Grown alone at a salinity of 5, E. densa decreased fivefold in biomass relative to the freshwater treatment and decomposed within 3 weeks at higher salinities. In contrast, S. pectinata biomass accumulated greatly (~4× initial) at salinities of 0 and 5, doubled at 10, and was unchanged at 15. When grown together in freshwater, S. pectinata produced 75 % less biomass than in monoculture and significantly more nodal roots (suggesting increased nutrient foraging). At a salinity of 5, a decline in E. densa performance coincided with a doubling of S. pectinata shoot density. Additional experiments on E. densa showed elevated temperature (26 and 30 °C) suppressed growth especially at higher salinities (≥5). We conclude that salinity strongly influences distributions of both species and that competition from E. densa may impose limits on S. pectinata abundance in the fresher reaches of SFE. With a salinity increase of 5, S. pectinata is likely to maintain its current distribution while spreading up-estuary at the expense of E. densa, especially if increased temperature also reduces E. densa biomass.

Many efforts to improve science teaching in higher education focus on a few faculty members at an institution at a time, with limited published evidence on attempts to engage faculty across entire departments. We created a long-term, department-wide collaborative professional development program, Biology Faculty Explorations in Scientific Teaching (Biology FEST). Across 3 years of Biology FEST, 89% of the department’s faculty completed a weeklong scientific teaching institute, and 83% of eligible instructors participated in additional semester-long follow-up programs. A semester after institute completion, the majority of Biology FEST alumni reported adding active learning to their courses. These instructor self-reports were corroborated by audio analysis of classroom noise and surveys of students in biology courses on the frequency of active-learning techniques used in classes taught by Biology FEST alumni and nonalumni. Three years after Biology FEST launched, faculty participants overwhelmingly reported that their teaching was positively affected. Unexpectedly, most respondents also believed that they had improved relationships with departmental colleagues and felt a greater sense of belonging to the department. Overall, our results indicate that biology department–wide collaborative efforts to develop scientific teaching skills can indeed attract large numbers of faculty, spark widespread change in teaching practices, and improve departmental relations.

Latitudinal gradients in species interactions are widely cited as potential causes or consequences of global patterns of biodiversity. However, mechanistic studies documenting changes in interactions across broad geographic ranges are limited. We surveyed predation intensity on common prey (live amphipods and gastropods) in communities of eelgrass (Zostera marina) at 48 sites across its Northern Hemisphere range, encompassing over 37 degrees of latitude and four continental coastlines. Predation on amphipods declined with latitude on all coasts but declined more strongly along western ocean margins where temperature gradients are steeper. Whereas insitu water temperature at the time of the experiments was uncorrelated with predation, mean annual temperature strongly positively predicted predation, suggesting a more complex mechanism than simply increased metabolic activity at the time of predation. This large-scale biogeographic pattern was modified by local habitat characteristics; predation declined with higher shoot density both among and within sites. Predation rates on gastropods, by contrast, were uniformly low and varied little among sites. The high replication and geographic extent of our study not only provides additional evidence to support biogeographic variation in predation intensity, but also insight into the mechanisms that relate temperature and biogeographic gradients in species interactions. NSF BIO-OCE [1336206, 1336741, 1336905] info:eu-repo/semantics/publishedVersion

Active-learning pedagogies have been repeatedly demonstrated to produce superior learning gains with large effect sizes compared with lecture-based pedagogies. Shifting large numbers of college science, technology, engineering, and mathematics (STEM) faculty to include any active learning in their teaching may retain and more effectively educate far more students than having a few faculty completely transform their teaching, but the extent to which STEM faculty are changing their teaching methods is unclear. Here, we describe the development and application of the machine-learning-derived algorithm Decibel Analysis for Research in Teaching (DART), which can analyze thousands of hours of STEM course audio recordings quickly, with minimal costs, and without need for human observers. DART analyzes the volume and variance of classroom recordings to predict the quantity of time spent on single voice (e.g., lecture), multiple voice (e.g., pair discussion), and no voice (e.g., clicker question thinking) activities. Applying DART to 1,486 recordings of class sessions from 67 courses, a total of 1,720 h of audio, revealed varied patterns of lecture (single voice) and nonlecture activity (multiple and no voice) use. We also found that there was significantly more use of multiple and no voice strategies in courses for STEM majors compared with courses for non-STEM majors, indicating that DART can be used to compare teaching strategies in different types of courses. Therefore, DART has the potential to systematically inventory the presence of active learning with ∼90% accuracy across thousands of courses in diverse settings with minimal effort.

Understanding the individual and interactive roles of consumer species is more than academic when the host plant is a subject of intense conservation interest. In a mesocosm experiment, we compared effects of common invertebrate grazers in San Francisco Bay seagrass (Zostera marina, eelgrass) beds, finding that some species (a native opisthobranch, Phyllaplysia taylori, a native isopod, Idotea resecata, and an introduced gastropod, Ilyanassa obsoleta) enhanced eelgrass growth through removal of epiphytic algae, as is often predicted for small invertebrate grazers on seagrasses, while one (an introduced caprellid amphipod, Caprella cf. drepanochir) had neutral effects. In contrast, the putatively-introduced gammaridean amphipod, Ampithoe valida, had strong negative effects on eelgrass (in addition to epiphytes) through consumption, as we had previously observed in the field during restoration programs. We tested whether other common grazer species could influence the effects of the eelgrass-grazing Ampithoe, and found that Idotea induced production of phenolic compounds and limited eelgrass damage by Ampithoe, without affecting Ampithoe abundance. These results have implications for restoration strategies, and contribute to a growing awareness of the importance of trait-mediated indirect grazer interactions through grazer-induced changes in plant traits, providing the first example in a seagrass system.

We investigated the potential for an invasive sea lavender, Limonium ramosissimum subsp. provinciale (Algerian sea lavender; LIRA) to spread in San Francisco Estuary (SFE) tidal marshes by testing how two determinants of tidal marsh plant distribution, salinity and inundation, affect LIRA dispersal, germination, growth, and reproduction. Simulating dispersal in 0, 15, and 30 parts per thousand (ppt) salinity water, we found seeds remained afloat similarly regardless of salinity, and seed viability after floatation was high (88%); however, seeds in 0 ppt aquaria germinated after just 4 d, suggesting shorter dispersal distances in fresh than in brackish or saline water. Next, we compared LIRA and native halophyte seed germination in 0, 15, 30, and 45 ppt water. Percentage of germination was similar between species after 3 wk, but LIRA germinated faster in fresh water than all native species (90% vs. 5% germination after 4 d), suggesting a possible establishment advantage for LIRA at low salinities. Finally, we grew LIRA under crossed salinity and inundation levels in a tidal simulator for a growing season. LIRA growth and seed production increased when either salinity or inundation was reduced. We conclude that spread could be greatest among salt marshes due to high potential for seed dispersal in saline water, yet spread within marshes may be greatest in relatively lower salinity conditions where growth and reproduction are maximized.

Herbivores can have highly variable effects across their ranges, sometimes with unanticipated effects on trophic dynamics that in turn affect management and conservation programs. In seagrass beds, small invertebrate grazers (mesograzers) are expected to benefit the habitat-forming plants by removing competing algae; however, harm by mesograzers has been documented increasingly in a number of regions. In San Francisco Bay, California, USA, a gammaridean amphipod (Ampithoe valida), native to the US East Coast and putatively introduced to Pacific coastlines, reaches outbreak densities and consumes large quantities of eelgrass Zostera marina, while it is not known to do so elsewhere in its range. Using a series of mesocosm experiments, we manipulated predator (fish) identity and density, herbivore assemblage, and habitat complexity to test how variation at multiple trophic levels influences the abundance and role of A. valida. Reductions in A. valida abundance by native San Francisco Bay shiner surfperch and bay pipefish were less pronounced than by a pinfish brought in from North Carolina, USA; however, the former 2 predators enhanced eelgrass biomass, while consumption of both amphipods and eelgrass by pinfish netted limited benefits to eelgrass. Increasing density of the surfperch in a separate experiment did not further reduce A. valida abundance but nonetheless strengthened positive effects on eelgrass, presumably through behavioral response to increased threat. The presence of a second (introduced) grazer reduced predation pressure on A. valida, weakening the trophic cascade to the detriment of eelgrass. Increasing habitat complexity by substituting flowering shoots reduced predation success, leading to higher A. valida abundances. Our results point to the importance of predator control of A. valida to reduce eelgrass damage; however, the strength of the trophic cascade across this grazer’s range is likely to be modulated by composition of predator and grazer assemblages as well as flowering rates and phenology.

Submerged macrophyte vegetation provides valuable ecosystem services, but climate- and management-driven changes may alter plant traits in unexpected and interactive ways. Further, such changes in plant traits may influence herbivore response, with feedback to bed characteristics. We manipulated temperature (20, 25, 30 °C) and salinity (0, 6, 12) in mesocosms to simulate current and predicted scenarios for the San Francisco Bay area. We measured traits of Stuckenia pectinata (sago pondweed) and subsequent effects on invertebrate (amphipod, Ampithoe valida) grazing. Counter to predictions, higher temperatures tended to have positive effects on plant traits (leaf area, aboveground biomass, nitrogen [N], phosphorus [P], protein, and total phenolic content). Also, unexpectedly, the highest salinity treatment had few negative effects except when temperature was coolest; i.e., 20 °C and a salinity of 12 led to decreased carbon [C], N, P, protein, phenolic concentrations, and aboveground biomass. Conversely, the highest salinity (12) at the highest temperature (30 °C) produced the highest leaf N and P, and plants from this treatment suffered most from herbivory. Consumption rates significantly increased with lower leaf fiber and higher total leaf N and protein content; i.e., plants with more nutritious leaves and less structural defense were consumed most. Climate change is expected to increase both salinity and temperature, but manipulation of freshwater supply could lead to decreased salinity. The range of responses in S. pectinata traits and invertebrate grazing shown by our results imply that the specific combination and magnitude of human influences will differentially shape these submerged macrophyte beds and their functions.

Instructor Talk—noncontent language used by instructors in classrooms—is a recently defined and promising variable for better understanding classroom dynamics. Having previously characterized the Instructor Talk framework within the context of a single course, we present here our results surrounding the applicability of the Instructor Talk framework to noncontent language used by instructors in novel course contexts. We analyzed Instructor Talk in eight additional biology courses in their entirety and in 61 biology courses using an emergent sampling strategy. We observed widespread use of Instructor Talk with variation in the amount and category type used. The vast majority of Instructor Talk could be characterized using the originally published Instructor Talk framework, suggesting the robustness of this framework. Additionally, a new form of Instructor Talk—Negatively Phrased Instructor Talk, language that may discourage students or distract from the learning process—was detected in these novel course contexts. Finally, the emergent sampling strategy described here may allow investigation of Instructor Talk in even larger numbers of courses across institutions and disciplines. Given its widespread use, potential influence on students in learning environments, and ability to be sampled, Instructor Talk may be a key variable to consider in future research on teaching and learning in higher education.

Author(s): Cloern, James E.; Robinson, April; Richey, Amy; Grenier, Letitia; Grossinger, Robin; Boyer, Katharyn E.; Burau, Jon; Canuel, Elizabeth A.; DeGeorge, John F.; Drexler, Judith Z.; Enright, Chris; Howe, Emily R.; Kneib, Ronald; Mueller–Solger, Anke; Naiman, Robert J.; Pinckney, James L.; Safran, Samuel M.; Schoellhamer, David; Simenstad, Charles | Abstract: To evaluate the role of restoration in the recovery of the Delta ecosystem, we need to have clear targets and performance measures that directly assess ecosystem function. Primary production is a crucial ecosystem process, which directly limits the quality and quantity of food available for secondary consumers such as invertebrates and fish. The Delta has a low rate of primary production, but it is unclear whether this was always the case. Recent analyses from the Historical Ecology Team and Delta Landscapes Project provide quantitative comparisons of the areal extent of 14 habitat types in the modern Delta versus the historical Delta (pre-1850). Here we describe an approach for using these metrics of land use change to: (1) produce the first quantitative estimates of how Delta primary production and the relative contributions from five different producer groups have been altered by large-scale drainage and conversion to agriculture; (2) convert these production estimates into a common currency so the contributions of each producer group reflect their food quality and efficiency of transfer to consumers; and (3) use simple models to discover how tidal exchange between marshes and open water influences primary production and its consumption. Application of this approach could inform Delta management in two ways. First, it would provide a quantitative estimate of how large-scale conversion to agriculture has altered the Delta's capacity to produce food for native biota. Second, it would provide restoration practitioners with a new approach—based on ecosystem function—to evaluate the success of restoration projects and gauge the trajectory of ecological recovery in the Delta region.

The seagrass Zostera marina is widely distributed in coastal regions throughout much of the northern hemisphere, forms the foundation of an important ecological habitat, and is suffering population declines. Studies in the Atlantic and Pacific oceans indicate that the degree of population genetic differentiation is location dependent. San Francisco Bay, California, USA, is a high-current, high-wind environment where rafting of seed-bearing shoots has the potential to enhance genetic connectivity among Z. marina populations. We tested Z. marina from six locations, including one annual population, within the bay to assess population differentiation and to compare levels of within-population genetic diversity. Using 7 microsatellite loci, we found significant differentiation among all populations. The annual population had significantly higher clonal diversity than the others but showed no detectible differences in heterozygosity or allelic richness. There appears to be sufficient input of genetic variation through sexual reproduction or immigration into the perennial populations to prevent significant declines in the number and frequency of alleles. In additional depth comparisons, we found differentiation among deep and shallow portions in 1 of 3 beds evaluated. Genetic drift, sweepstakes recruitment, dispersal limitation, and possibly natural selection may have combined to produce genetic differentiation over a spatial scale of 3-30 km in Z. marina. This implies that the scale of genetic differentiation may be smaller than expected for seagrasses in other locations too. We suggest that populations in close proximity may not be interchangeable for use as restoration material.

Intense herbivory can alter habitat characteristics, and grazing on reproductivestructures can reduce plant fitness and long-term population stability. Herbivory on seagrasses isoften limited to epiphytes; however, direct grazing has been observed recently in several systems.In San Francisco Bay, California, we documented extensive damage to leaves and especially inflo-rescences of eelgrass Zostera marina concurrent with blooms of the non-native amphipod Ampi -thoe valida. Field surveys found peaks of A. valida abundance when eelgrass was flowering, andgreater abundance on flowering than vegetative shoots, with particularly high abundances onreproductive structures (spathes) in late developmental stages (with ripe fruits or post seedrelease). Laboratory experiments showed that A. valida consumed leaf and spathe tissue (as wellas whole fruits), but usually preferred spathes to leaves. Spathes are structurally complex andlikely provide better habitat, increasing opportunity for consumption. Low field algal abundancesdo not fully explain eelgrass herbivory, as amphipods grazed eelgrass substantially even whenoffered algae. When presented with eelgrass from both the amphipod’s native (Virginia) andinvaded range (California), the latter was consumed at significantly higher rates. Neither nutrientnor phenolic content adequately explain the tissue preference. Greater size of California eelgrassmay have promoted incidental feeding on spathes used as habitat, but does not explain a Califor-nia bias during consumption of structurally simple leaves. Field densities and laboratory consump-tion rates suggest that this non-native amphipod could remove all seeds in a California eelgrassmeadow in 1−3 wk, thus challenging maintenance of genetic diversity and long-term meadowpersistence.KEY WORDS: Seagrass · Zostera marina · Ampithoe valida · Herbivory · Seed predation

Aims Human alterations of the environment are combining in unprecedented ways, making predictions of alterations to natural communities a difficult and pressing challenge. Estuarine systems have been subject to a high degree of modification, including increased nitrogen (N) inputs and altered salinity, factors important in shaping estuarine plant communities. As human populations increase and the climate changes, both N and salinity levels are likely to increase in these coastal marshes. Our objective was to evaluate the interactive effects of N and salinity on US West Coast salt marsh species; in particular, the performance of the dominant species Sarcocornia pacifica (pickleweed) alone and in mixed species assemblages. We expected increased salinity to favor S. pacifica but that N enrichment could help maintain greater species richness through use of N in salinity tolerance mechanisms. Methods We crossed treatments of N (added or not) and salinity (salt added or not) in a field experiment at a salt marsh in the San Francisco Estuary, California, USA, in each of three habitats: (i) monotypic pickleweed on the marsh plain, (ii) monotypic pickleweed along channels and (iii) mixed assemblages along channels. In a greenhouse experiment, we crossed treatments of N (added or not) and salinity (at three levels to simulate brackish to saline conditions) in (i) pots of pickleweed only and (ii) the same species mix as in the field. Important Findings NadditiondoubledS.pacificabiomassandbranchinginbothchannel and marsh plain habitats regardless of salinityand greatly increased its dominance over Distichlis spicata and Jaumea carnosa in mixed assemblages along channels. In the greenhouse, S. pacifica biomass increased 6- to 10-fold with N addition over the range of salinities, while D. spicata and J. carnosa biomass increased with N addition onlyat lower salinity levels. Thus, while localized management could influence outcomes, expected overall increases in both N and salinity with human population growth and climate change are likely to enhance the productionofS.pacificain USWest Coast marshes while reducing the diversity of mixed species assemblages. This decline in diversity may have implications for the resilience of marshes already subject to multiple stressors as the climate changes.

Epifaunal invertebrate species, such as amphipods and isopods, have been shown to play key but varying roles in the functioning of seagrass habitats. In this study, we characterized patterns in the poorly known epifaunal communities in eelgrass (Zostera marina) beds in San Francisco Bay as a first step in understanding the individual and collective importance of these species, while testing predictions on spatial patterns derived from previous studies in other regions. Surveys conducted at five beds across multiple time periods (April, June, August and October 2007) showed that San Francisco Bay eelgrass beds varied strongly in epifaunal community composition, total, and relative abundance, and that abundance differed markedly among time periods. In contrast to findings by others, morphologically complex flowering shoots frequently harbored greater numbers of epifauna (>2· and up to 10· more individuals) than vegetative shoots, but not different species assemblages. Similar to previous studies, several abiotic factors did not explain patterns in distribution and abundance among beds. The proportion of introduced species was very high (>90% of all individuals), a finding unique among seagrass epifaunal studies to date. Defining numerical patterns in epifaunal communities will inform related efforts to understand effects of epifaunal species and assemblages on eelgrass growth dynamics, seed production, and higher order trophic interactions over space and time.

Lepidium latifolium (perennial pepperweed) is recognized as a threat to wetland habitats throughout much of the western United States, but its role in tidal marshes has not been explored. Over three seasons in three regions of San Francisco Estuary (Suisun, San Pablo, and South San Francisco bays), we characterized locations in tidal marshes where monotypic stands of L. latifolium are replacing the native Sarcocornia pacifica (pickleweed). Soils within L. latifolium stands had significantly lower moisture, salinity, organic matter, and carbon : nitrogen (C : N) and higher pH than in adjacent S. pacifica stands at similar elevation and distance from channels. In addition, L. latifolium canopies were 2 to 3 times taller, thus increasing light reaching soils, and tended to support different insect/spider assemblages (sampled only at the Suisun site). Patterns were generally consistent across the three sites, although less pronounced for some measures at the South Bay site. Overall, these data suggest that L. latifolium invasion of tidal marshes is leading to modification of both structural and functional properties, several of which might further facilitate spread of the invader; however, additional study is needed to determine cause vs. effect for several soil characteristics.

Several management techniques are effective in controlling Lepidium latifolium (perennial pepperweed) in rangelands and hay meadows; however, this invader’s rapid spread into sensitive aquatic habitats throughout the western US calls for alternative control strategies. To evaluate control methods for use in tidal marshes of San Francisco Estuary, we tested chemical, mechanical, and biological methods in field and greenhouse experiments. In a field experiment in three brackish marshes spanning the estuary, application of the herbicide glyphosate to re-growth of L. latifolium following hand-removal reduced L. latifolium cover by an average of 80% after 2 years and led to a 60% increase in native vegetation cover. Glyphosate alone was less effective at reducing L. latifolium cover (20% decrease) and increasing native cover (34% increase). Preliminary tests of a potential biological control, a native parasitic plant, were not successful, thus plots intended for field trials were instead used to test the newly approved herbicide imazapyr, which showed promise in controlling L. latifolium. An additional greenhouse experiment found large reductions in stem lengths with either glyphosate following clipping or imazapyr with or without clipping, all significantly more so than glyphosate alone. We conclude that an integrated management approach of applying glyphosate following mechanical removal can be effective at reducing L. latifolium cover and allowing recovery of native tidal marsh plants, providing a useful solution for controlling smaller, accessible infestations of the invader. Our preliminary tests of imazapyr suggest that it may be very effective at controlling L. latifolium in tidal marshes, although further assessment of non-target effects and native plant recovery are needed to evaluate its relative merit.

The influence of biodiversity on ecosystem functioning has been the focus of much recent research, but the role of environmental context and the mechanisms by which it may influence diversity effects on production and stability remain poorly understood. We assembled marine macroalgal communities in two mesocosm experiments that varied nutrient supply, and at four field sites that differed naturally in environmental conditions. Concordant with theory, nutrient addition promoted positive species richness effects on algal growth in the first mesocosm experiment; however, it tended to weaken the positive diversity relationship found under ambient conditions in a second experiment the next year. In the field experiments, species richness increased algal biomass production at two of four sites. Together, these experiments indicate that diversity effects on algal biomass production are strongly influenced by environmental conditions that vary over space and time. In decomposing the net biodiversity effect into its component mechanisms, seven of the eight experimental settings showed positive complementarity effects (suggesting facilitation or complementary resource use) countered by negative selection effects (i.e. enhanced growth in mixture of otherwise slow growing species) to varying degrees. Under no conditions, including nutrient enrichment, did we find evidence of positive selection effects commonly thought to drive positive diversity effects. Species richness enhanced stability of algal community biomass across a range of environmental settings in our field experiments. Hence, while species richness can increase production, enhanced stability is also an important functional outcome of maintaining diverse marine macroalgal communities.

Through bioassay techniques and field collections of red macroalgae (Gracilariopsis sp.) and eelgrass (Zostera marina), we evaluated growth, tissue %Nitrogen (N) and N stable isotopic signatures as bioindicators of potential changes in N supply to Tomales Bay, CA (USA). Gracilariopsis sp. collected, cultured, and outplanted across a spatial gradient in Tomales Bay showed pronounced changes in N patterns from past studies in this system, and was superior to field collections in detecting spatial N signals. Rather than a single peak in N concentration near the oceanic source found in previous work, we detected two N peaks, one near the bay head and one near the bay mouth. This spatial pattern suggests two sources account for these discrete regions of increased N supply. The temporal N patterns showed marked seasonality, with greater tissue N concentration during the wet season and reduced N concentrations during the dry season. The spatial patterns presented here suggest shifting nutrient dynamics within To...

Observations of increasing red macroalgal (Gracilariopsis sp.) abundance in Tomales Bay, California (USA) prompted a field survey and an in situ experiment testing algal mat effects on eelgrass (Zostera marina) growth. At the conclusion of a 3 mo macroalgal enclosure/exclosure study, experimental plots containing high macroalgal loads (1700 g m -2 wet weight = mean maximum in a field survey) had significantly lower Z. marina shoot densities and growth rates than plots with no algae or with mean algal field abundance (325 g m -2 ). Eelgrass aboveground biomass followed a sim- ilar trend, decreasing under high macroalgal loads. We explored possible mechanisms of algal impacts on eelgrass, including changes to redox potential, sediment nitrogen, and light. Of these, light limitation is the most likely explanation for decreases in eelgrass shoot density. Light reaching the benthos where new shoots establish was only 2% of surface irradiance under high algal loads, while the canopy of adult eelgrass shoots received nearly 40% of surface irradiance regardless of macroalgal abundance. Reduced Z. marina growth rates may also be attributable to light limitation, as light levels neared the compensation irradiance for eelgrass under high macroalgal loads. Phase shifts from seagrass to macroalgae have been well documented in other estuaries, although studies are generally conducted well after the shift to macroalgal dominance has occurred. Our results indi- cate a similar transition is possible in Tomales Bay and suggest the need to monitor and manage this system prior to a future shift.

Establishing species-rich plant communities is a common goal of habitat restoration efforts, but not all species within a target assemblage have the same capacity for recruitment and survival in created habitats. We investigated the development of a tidal salt marsh plant community in the presence of a rapidly colonizing dominant species, Salicornia virginica, in a newly created habitat in Mugu Lagoon, California, USA. We planted rooted cuttings of S. virginica, Distichlis spicata, Jaumea carnosa, and Frankenia salina in single- and mixed-species stands, where each species was planted alone or in combination with S. virginica in 4 m 2 plots. We measured species percent cover, recruit density, canopy structure, and aboveground biomass after three growing seasons. When planted alone, S. virginica achieved the greatest cover, up to 70%, followed by J. carnosa (55%), F. salina (35%), and D. spicata (12%). Total percent cover was about 30% lower than in a reference site. For each species, average percent cover and aboveground biomass per plant were generally similar between single-species and mixed planting treatments, suggesting that on the time scale of this study, competition between species was weak. Canopy structure (height, number of layers) and total aboveground biomass of all species were largely unaffected by planting treatments, although S. virginica was shorter when planted with J. carnosa. Salicornia virginica recruits constituted approximately 98% of the cover of seedling recruits into the created site. Despite intense S. virginica recruitment, our intervention in the successional process by planting species with poorer colonization abilities, particularly J. carnosa and F. salina, prevented S. virginica from completely dominating the canopy, thus increasing vascular plant richness in the created site. Artificially increased richness may enhance some ecosystem functions and create a seed source to facilitate the persistence of a diverse plant assemblage in restored sites.

Plant biodiversity can enhance primary production in terrestrial ecosystems, but biodiversity effects are largely unstudied in the ocean. We conducted a series of field and mesocosm experiments to measure the relative effects of macroalgal identity and richness on primary productivity (net photosynthetic rate) and biomass accumulation in hard substratum subtidal communities in North Carolina, USA. Algal identity consistently and strongly affected production; species richness effects, although often significent, were subtle. Partitioning of the net biodiversity effect indicated that complementarity effects were always positive and species were usually more productive in mixtures than in monoculture. Surprisingly, slow growing species performed relatively better in the most diverse treatments than the most productive species, thus selection effects were consistently negative. Our results suggest that several basic mechanisms underlying terrestrial plant biodiversity effects also operate in algal-based marine ecosystems, and thus may be general.

In many temperate estuaries, mats of opportunistic macroalgae accumulate on intertidal flats and in lower elevations of salt marshes, perhaps playing a role in linking water column nitrogen (N) supply to these benthic habitats. Using a flow-through seawater system and tidal simulator, we varied densities (equivalent to 0, 1, 2, or 3 kg m 2 wet mass) of 15 N-labelled macroalgae (Enteromorpha intestinalis) on estuarine sediments in microcosms with/without pickleweed (Salicornia virginica) to assess N transfers from algae. In the 6-week experiment, macroalgal biomass increased from initial levels in the lower density treatments but all algae lost N mass, probably through both leakage and decomposition. With all densities of algae added, sediments and pickleweed became enriched in 15 N. With increasing mat density, losses of algal N mass increased, resulting in stepwise increases in 15 N labeling of the deeper sediments and pickleweed. While we did not detect a growth response in pickleweed with macroalgal addition during the experiment, N losses from algal mats that persist over many months and/or recur each year could be important to the mineral nutrition of N-limited marsh plants. We conclude that N dynamics of intertidal sediments and lower salt marsh vegetation are linked to the N pools of co-occurring macroalgae and that further study is needed to assess the magnitude and importance of N transfers. D 2005 Elsevier B.V. All rights reserved.

The roles of co-occurring herbivores that modify habitat structure and ecosystem processes have seldom been examined in manipulative experiments or explored in early successional communities. In a created marsh in southern California (USA), we tested the individual and combined effects of two epibenthic invertebrates on nutrient and biomass pools, community structure, and physical habitat features. We manipulated snail (Cerithidea californica) and crab (Pachygrapsus crassipes) presence in field enclosures planted with pickleweed (Salicornia virginica) at elevations matching the plant's lower extent in an adjacent natural marsh. In the 4-month experiment, C. californica altered habitat structure by reducing sediment surface heterogeneity and shear strength (a measure of sediment stability) markedly throughout the enclosures. Both invertebrates had strong negative effects on a group of correlated sediment physicochemical characteristics, including nitrogen and organic matter concentrations and soil moisture. In addition, both invertebrates greatly reduced benthic chlorophyll a, a proxy for biomass of microphytobenthos. Compared to controls, macroalgal cover was up to sixfold lower with crabs present, while snails increased cover at low elevations of enclosures. Unexpectedly, macroalgal cover was eliminated with both species present, perhaps through P. crassipes consumption of larger thalli and C. californica reduction in cover of recruits. Neither species influenced the S. virginica canopy (quantified with an index of branch length and number); however, at the lower elevation of enclosures, the two species together negatively impacted the plant canopy. The two invertebrates' modifications to our experimental marshes led to distinct suites of biotic and physicochemical features depending on their presence or co-occurrence, with the latter producing several unexpected results. We propose that the roles and interactions of habitat-modifying fauna deserve further attention, particularly in the context of efforts to conserve and restore the processes found in natural systems.

Previous attempts to reverse the degradation of a coastal wetland and restore nesting habitat for an endangered bird showed that adding nitrogen could temporarily increase the height of Spartina foliosa, but not produce self-sustaining tall canopies. We asked if increased effort (up to five years of N fertilization) would shift canopy attributes across the hypothesized threshold. Thirty plots were treated with 0–5 yr of urea addition, and all were followed for 5 yr. Canopies were robust while urea was being added, but Spartina reverted to short stature soon after fertilization ended, supporting R. J. Hobbs and D. A. Norton's concept of an irreversible transition. However, specific outcomes depended on the choice of response variable (six comparisons), the choice of reference data (initial conditions, same-year data, and pooled data), and the choice of statistical design (repeated measures vs. complete design), indicating the need to assess experiments thoroughly before making strong recommendations for ma...