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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.

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.

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

Restoration projects provide a valuable opportunity to experimentally establish foundational habitats in different combinations to test relative effects on community assembly. We evaluated the development of macroinvertebrate communities in response to planting of eelgrass (Zostera marina) and construction of reefs intended to support the Olympia oyster (Ostrea lurida) in the San Francisco Estuary. Plots of each type, alone or interspersed, were established in 2012 in a pilot living shorelines project, and quarterly invertebrate monitoring was conducted for one year prior to restoration, and three years post-restoration using suction sampling and eelgrass shoot collection. Suction sampling revealed that within one year, oyster reefs supported unique invertebrate assemblages as compared to pre-restoration conditions and controls (unmanipulated mudflat). The eelgrass invertebrate assemblage also shifted, becoming intermediate between reefs and controls. Interspersing both types of habitat structure led eelgrass invertebrate communities to more closely resemble those of oyster reefs alone, though the eelgrass assemblage maintained some distinction (primarily by supporting gammarid and caprellid amphipods). Eelgrass shoot collection documented some additional taxa known to benefit eelgrass growth through consumption of epiphytic algae, however, even after three years, restored eelgrass did not establish an assemblage equivalent to natural beds, as the eelgrass sea hare (Phyllaplysia taylori) and eelgrass isopod (Pentidotea resecata) remained absent or very rare. We conclude that the restoration of two structurally complex habitat types within tens of meters maximized the variety of invertebrate assemblages supported, but that close interspersion dampened the separately contributed distinctiveness. In addition, management intervention may be needed to overcome the recruitment limitation of species with important roles in maintaining eelgrass habitat.

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.

Multi-trophic conservation and management strategies may be necessary if reciprocal linkages between primary producers and their consumers are strong. While herbivory on aquatic plants is well-studied, direct top-down control of seagrass populations has received comparatively little attention, particularly in temperate regions. Herein, we used qualitative and meta-analytic approaches to assess the scope and consequences of avian (primarily waterfowl) herbivory on temperate seagrasses of the genus Zostera. Meta-analyses revealed widespread evidence of spatio-temporal correlations between Zostera and waterfowl abundances as well as strong top-down effects of grazing on Zostera. We also documented the identity and diversity of avian species reported to consume Zostera and qualitatively assessed their potential to exert top-down control. Our results demonstrate that Zostera and their avian herbivores are ecologically linked and we suggest that bird herbivory may influence the spatial structure, composition, and functioning of the seagrass ecosystem. Therefore, the consequences of avian herbivory should be considered in the management of seagrass populations. Of particular concern are instances of seagrass overgrazing by waterfowl which result in long-term reductions in seagrass biomass or coverage, with subsequent impacts on local populations of waterfowl and other seagrass-affiliated species. While our results showed that bird density and type may affect the magnitude of the top-down effects of avian herbivory, empirical research on the strength, context-dependency, and indirect effects of waterfowl–Zostera interactions remains limited. For example, increased efforts that explicitly measure the effects of different functional groups of birds on seagrass abundance and/or document how climate change-driven shifts in waterfowl migratory patterns impact seagrass phenology and population structure will advance research programs for both ecologists and managers concerned with the joint conservation of both seagrasses and their avian herbivores.

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

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.

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.

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.

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...

We conducted a 3-factor nutrient-enrichment experiment (factors: N, P, initial tissue- nutrient status) on common species of macroalgae collected from 2 sites along SW Puerto Rico. Our objective was to determine the relative importance of N- or P-limitation among species and sites and to investigate the role of tissue-nutrient status in the response to increased nutrient supply. Acan- thophora spicifera, Dictyota cervicornis, and Hypnea musciformis initially depleted in tissue nutrients responded strongly to either +N or +P alone and both nutrients together by increasing growth. In con- trast, growth of these macroalgae with enriched internal stores of nutrients was generally not as nutrient-limited. In our 3 d experiments, the calcified alga Halimeda incrassata never showed a growth response, perhaps due to the short duration or adaptation to sediment nutrient supply. Tissue N-stores in all algae with low internal nutrient concentrations increased in response to +N, whereas initially higher N-stores were diluted to support growth during the experiment. In addition, all algae depleted the added N and P from the water over the course of the experiment, regardless of tissue- nutrient status. Depleted algae also took up dissolved organic nitrogen (DON) as a secondary source of N, either directly or after mineralization, whereas enriched algae may have 'leaked' NH4. Our results demonstrated that prior storage of nutrients strongly influenced the response of a number of tropical algal species to increased nutrient supply. This variable response to nutrients within and among algae from 3 major algal divisions over small geographical scales may partially explain the mixed results in previous studies of N- and P-limitation.

Non-native sea lavenders (Limonium spp.) are invasive in salt marshes of southern California and were first documented in the San Francisco Estuary (the estuary) in 2007. In this study, we mapped distributions of L. ramosissimum subsp. provinciale (LIRA) and L. duriusculum within the estuary and investigated how the invasion potential of the more common species, LIRA, varies with elevation and edaphic conditions. We contacted colleagues and conducted field searches to find and then map sea lavender populations. In addition, we measured LIRA’s elevational range at three salt marshes. Across this range we measured (1) soil properties: salinity, moisture, bulk density, and texture; and (2) indicators of invasion potential: LIRA size, seed production, percent cover, spread (over 1 year), recruitment, and competition with native halophytes (over 6 months). We found LIRA in 15,144 m2 of upper salt marsh habitat in central and south San Francisco bays and L. duriusculum in 511 m2 in Richardson and San Pablo bays. LIRA was distributed from mean high water (MHW) to 0.42 m above mean higher high water (MHHW). In both spring and summer, soil moisture and salinity were lowest at higher elevations within LIRA’s range, which corresponded with greater rosette size, inflorescence and seed production (up to 17,400 seeds per plant), percent cover, and recruitment. LIRA cover increased on average by 11% in 1 year across marshes and elevations. Cover of the native halophytes Salicornia pacifica, Jaumea carnosa, and Distichlis spicata declined significantly at all elevations if LIRA were present in plots (over a 6-month, fall–winter period). Results suggest LIRA’s invasion potential is highest above MHHW where salinity and moisture are lower, but that LIRA competes with native plants from MHW to above MHHW. We recommend removal efforts with emphasis on the salt marsh-terrestrial ecotone where LIRA seed output is highest.

Salicornia virginica (common pickleweed) is the dominant vascular plant of many saline marshes of the US west coast, yet little is known about seasonal patterns or abiotic factors controlling it. In a southern California salt marsh, quarterly sampling revealed strong seasonal trends, with 2x greater S. virginica biomass in summer than in winter. Tissue nitrogen (N) and phosphorus (P) concentrations were highest in winter and lower in spring and summer, suggesting a dilution of nutrients as plants accumulated biomass during the growing season. Despite high sediment nutrient levels in this marsh, an experiment examining N and P effects still found strong S. virginica responses to N applied biweekly for > 1 year. Increases in succulent tissue biomass after N addition were first seen in April 1998 (after fertilization for 11 months); two-fold increases in biomass and the number of branches resulted by the end of the experiment in August 1998. Addition of N increased N concentration in the woody tissues when sampled in August. The N:P ratio increased with N addition beginning in winter (7 months after fertilization began) and continuing through the remainder of the experiment. Effects of P addition were less marked, as adding P did not result in biomass responses; however, it did influence tissue nutrient levels. These amendments increased P concentrations in the woody tissue in August 1998. In contrast to N amendments, which did not affect root nutrient concentrations, P addition led to increases in P content of root tissues in the latter portion of the growing season. These data suggest that increases in nutrients (especially N, but also P) can lead to large changes in S. virginica characteristics even in estuaries with high sediment nutrient levels.

To investigate whether tissue N and P content of morphologically distinct macroalgae reflect different processes controlling nutrient availability, we measured water column nutrients and collected 5 species of algae for tissue N and P analysis from 18 stations along the southwestern coast of Puerto Rico. Nutrient content of sediments was also determined for a subset of stations. South- western Puerto Rico was chosen because the literature suggests that gradients in sediment type and organic matter content, advection, and terrestrial influence occur in this region. Stations were either inshore or offshore areas with 3 stations per area chosen a priori as High Nutrient Stations (HNS). Water column and sediment nutrient concentrations were elevated inshore and in HNS. Species were of 3 morphological forms: upright thalli with open branches, densely packed mats, and rhizophytic thalli. In the first category, Acanthophora spicifera had higher N content inshore compared to off- shore while both A. spicifera and Hypnea musciformis had higher tissue N and P contents in HNS. In contrast, mat-forming algae (Dictyota dichotoma and D. cervicornis) had higher tissue N and P con- tents offshore compared to inshore. Although these species had high nutrients in many of the HNS, samples from some offshore reefs were equally high. Halimeda incrassata, a rhizophytic form, had greater tissue N content inshore than offshore. H. incrassata tissue nutrients were also elevated in some HNS, but not others. There were significant correlations between water column and sediment nutrients and the tissue N and P content of A. spicifera and H. incrassata, but not for either Dictyota. These results suggest algae with upright thalli and open-branching patterns may have a more direct relationship between tissue nutrient content and water column nutrient concentration than other forms. In contrast, mat-forming species may deplete nutrients within the mat, relying on strong cur- rents found offshore to penetrate dense mats and replenish nutrients. Rhizophytic algae have access to both water column and sediment nutrients, and higher inshore tissue contents and at some HNS may reflect enhanced nutrient supplies from these sources. Our findings suggest that if other envi- ronmental factors are carefully taken into consideration, the tissue N and P content of macroalgae may prove to be an effective indicator of different nutrient sources in tropical systems.

At a salt marsh restoration site, fertilizer trials to improve height growth of Spartina foliosa (a C 4 perennial grass that can reach 140 cm) appeared to favor Salicornia bigelovii (an annual C 3 succulent under 40 cm tall) where the two species co-occurred on the marsh plain. This observation prompted a field experiment to examine the potential for nitrogen (N) addition to shift community composition. Without N addition, total stem length and stem density of S. foliosa did not respond to the presence or absence of S. bigelovii. But where N was added, S. foliosa growth increased only where S. bigelovii was removed from plots. S. bigelovii responded strongly to fertilizer, with mean heights matching those of S. foliosa and 600% increases in biomass, branching, and seed production (to more than 1 million seeds/m 2 ). Soil N also increased seasonally where S. bigelovii was present, suggesting that this species may aid accumulation of N at restoration sites with poor soils. S. foliosa growth is greatest at lower elevations along tidal creeks where it occurs alone. Beyond creek edges, where S. bigelovii and other potential competitors occur, S. foliosa is unlikely to grow tall even with N addition. Thus, there is little point in trying to force mixed-species stands to provide tall S. foliosa for nesting by an endangered bird, Rallus longirostris levipes (the Light-footed Clapper Rail). A marsh construction design that maximizes tidal creek edges is thus recommended when restoration goals include providing habitat for clapper rails.

We explored the use of an opportunistic green alga, Enteromorpha intestinalis (L. Link), as an indicator of N enrichment in a southern California salt marsh. In conjunction with N additions to cordgrass ( Spartina foliosa , Trin) in April, June and August 1995, mesh bags containing N-starved algal tissue were placed within cordgrass patches, at their edges along islands, and in adjacent channels. After 1 week in the field, recovered algal tissue was used to test detection of two levels of total N supply (one twice as high as the other), as well as no added N (control). Tissue N concentration, calculated as the percentage change in N, was the best of several algal measures at discerning differences in N availability in any month. In both April and June, tissue N declined from the marsh plain to the channels, reflecting declining N supply. Tissue N concentration also reflected differences in the total quantity of N added. Within the channels adjacent to fertilized areas, algal tissue N was similar to control areas, suggesting that N additions to cordgrass are not resulting in eutrophication of open waters. In August, the algae detected N additions on the marsh plain, but survivorship was poor; other algal species may be better indicators of enrichment in late-summer. With further investigation, the technique presented in this paper has the potential to be developed into a useful bioassay for detecting eutrophication of coastal salt marshes and lagoons.

Because tall vegetation can enhance habitat quality in intertidal wetlands, we examined the effects of N fertilization on the height growth of a constructed cordgrass (Spartina foliosa) marsh in San Diego Bay, where plants are short and soil N low. We varied the duration (therefore also the quantity; 30 g N/M2 every month for 1, 2, 4, or 6 mo) and timing (30 g N/M2 in March, April, June, or August) of N additions during 1993. By fertilizing a second set of replicates for the 6-mo treatment during 1994, we were able to examine the persistence of effects from 1993 vs. the effects of amendments in both years. Traditional canopy response measures (total stem length, maximum height, foliar N) increased most with the greatest duration/quantity of additions in 1993. All duration and timing treatments produced canopies with >100 stems/M2 and ?30 stems/M2 taller than 90 cm, considered suitable for nesting by the endangered Light-footed Clapper Rail (Rallus longirostris levipes). However, without additional fertilizer in 1994, the previous year's canopy responses were not retained, suggesting insufficient storage of N in belowground tissues. Only plots fertilized in both years continued to produce ?30 tall stems/M2. The coarse dredge-spoil sediments of the constructed marsh had only 1/4 to 1/3 the total N found in the fine-textured soils of a nearby natural marsh, where cordgrass grows tall and clapper rails nest. We recommend that future marsh restoration projects begin with fine soils that promote N retention and accumulation to sustain tall canopies, rather than sug- gesting long-term fertilization.

Eelgrass (Zostera marina) forms the foundation of an important shallow coastal community in protected estuaries and bays. Widespread population declines have stimulated restoration efforts, but these have often overlooked the importance of maintaining the evolutionary potential of restored populations by minimizing the reduction in genetic diversity that typically accompanies restoration. In an experiment simulating a small-scale restoration, we tested the effectiveness of a buoy-deployed seeding technique to maintain genetic diversity comparable to the seed source populations. Seeds from three extant source populations in San Francisco Bay were introduced into eighteen flow-through baywater mesocosms. Following seedling establishment, we used seven polymorphic microsatellite loci to compare genetic diversity indices from 128 shoots to those found in the source populations. Importantly, allelic richness and expected heterozygosity were not significantly reduced in the mesocosms, which also preserved the strong population differentiation present among source populations. However, the inbreeding coefficient F IS was elevated in two of the three sets of mesocosms when they were grouped according to their source population. This is probably a Wahlund effect from confining all half-siblings within each spathe to a single mesocosm, elevating F IS when the mesocosms were considered together. The conservation of most alleles and preservation of expected heterozygosity suggests that this seeding technique is an improvement over whole-shoot transplantation in the conservation of genetic diversity in eelgrass restoration efforts.

Differential tolerance of low salinity, competition for nitrogen (N), and facilitation by altering N supply all may act to determine the pattern of seasonal succession of Enteromorpha intestinalis (L.) Link and Ulva expansa (Setch) S. and G. in estuaries and lagoons of southern California. Low salinity negatively affected both of these algae. However, when N was in sufficient supply, salinities of 15 ppt favored E. intestinalis while oceanic salinity (35 ppt) favored U. expansa; neither alga had a clear advantage at 25 ppt. When starved of N, E. intestinalis and U. expansa competed directly for nutrients. When grown alone, they had similar N uptake and growth rates; when grown together, E. intestinalis was the superior competitor, negatively affecting growth of U. expansa. In addition, U. expansa facilitated the growth of E. intestinalis when N was in short supply; when grown together, there was a positive effect of U. expansa on E. intestinalis. The mechanism of this effect may have been the release or ‘leaking’ of DON when U. expansa no longer had sufficient tissue N to grow. Thus, E. intestinalis would be favored immediately after a rain, but would be replaced by U. expansa when N is available and tidal action reestablishes oceanic salinity. However, at the end of the rainy season when N becomes scarce, E. intestinalis would outcompete U. expansa. We hypothesize that U. expansa may facilitate the dominance of E. intestinalis by leaking N that can be assimilated by E. intestinalis.

We explored the role of food quality in herbivore preference for macroalgae by comparing consumption of Acanthophora spicifera with and without elevated tissue nitrogen and phosphorus concentrations. Algal enrichment effects on herbivory were examined in coral, seagrass, and mangrove habitats along a sparsely populated Honduran island protected from fishing. Nutrient enrichment led to significantly increased grazing by herbivores across habitats. Consumption of enriched algae increased by 91% compared to controls among the mangrove roots, where herbivory rates were generally lowest. In the heavily grazed seagrass and coral habitats, nutrient enrichment increased consumption by 30 and 20%, respectively, with the effect more spatially variable than among the mangrove roots. We suggest that, at least on the local scale, intact herbivore populations may be able to compensate for effects of increased nutrient supply by locating and consuming nutrient-enriched algae, but that the importance of this mechanism varies both among and within habitats.

We report the first data on belowground tissue mass and nitrogen (N) concentration forSpartina foliosa in southern California, assessing one natural and two constructed marshes on San Diego Bay. Biomass at the natural marsh was low compared to that of otherSpartina spp., but higher than values reported forS. foliosa in northern California. In sandy constructed marshes planted 5 and 10 years before this study,S. foliosa had lower belowground tissue N, lower N crop (%N×biomass), and shallower roots than in the adjacent natural marsh. We took advantage of a 2-yr, large-scale fertilization project being performed in the older constructed marsh and examined biomass and N storage after N additions. Although there was a trend toward N accumulation with fertilization, N crop remained at approximately 50% of natural marsh levels, unlike the large aboveground responses to N addition in our previous studies. Lower belowground reserves help to explain poor aerial growth in the created marshes and suggest the need for finer sediments (with greater potential for holding and supplying nutrients) to sustain (S. foliosa. While fine sediments are beginning to accumulate on the surface of the created marshes, vertical accretion is more likely to shift the plant community toward other species than to enhanceS. foliosa growth. We suggest salvaging and importing fine, organic marsh sediments or providing organic amendments to establish proper substrate conditions. Overexcavating and allowing fine sediments to accumulate remains an option, although the time scale is unpredictable due to the stochasticity of accretion events.

Because tall cordgrass (Spartina foliosa) is needed for nesting by the endangered light-footed, clapper rail, managers of constructed salt marshes in southern California are proposing large-scale nitrogen fertilization to improve cordgrass growth. How this might affect an existing infestation of scale insects (Haliaspis spartina) and the degree of damage these insects cause to their cordgrass hosts was unknown. We explored the effects of timing and duration of fertilization onHaliaspis damage to cordgrass, as well as the timing ofHaliaspis dispersal, in a constructed marsh at Sweetwater Marsh National Wildlife Refuge in San Diego Bay, California. Fertilization did not result in increasedHaliaspis abundance. After a large dispersal pulse in late May,Haliaspis establishment in the long-term fertilized plots was greater than in the controls; however, this trend reversed in August, when many more stems in the control plots were infested with large numbers ofHaliaspis. Since adultHaliaspis cannot leave a feeding site, losses of individuals in the fertilized plots were apparently due to mortality, perhaps resulting from mechanical or chemical changes in the fertilized plants or increased predation. Late in the growing season, plots fertilized with 10 applications of urea over 20 wk had the lowest meanHaliaspis abundance. Plots fertilized only in March, April, June, or August did not differ from controls in meanHaliaspis abundance.Haliaspis was never abundant in the fertilized or control plots in the adjacent natural marsh. This study suggests that fertilization, of constructed salt marshes in San Diego Bay may proceed without concern that furtherHaliaspis outbreaks will be facilitated.