Biodiversity of settled material in a sediment trap in the Gulf of Trieste (northern Adriatic Sea)

Phytoplankton succession and sinking rates were studied from January to December 2003 at a coastal station in the Gulf of Trieste (northern Adriatic Sea), 200 m offshore, in a relatively undisturbed area. A conical sediment trap, moored at 15 m depth (water depth 17 m), was used. The hypothesis if the presence of benthic and epiphytic diatoms can lead to an overestimation of the vertical fluxes was tested. To evaluate primary and secondary sedimentation contributions, planktonic, benthic and epiphytic diatoms were distinguished. Benthic species abundance varied throughout the year and it was related to resuspension that strongly influenced sinking rates. All over the year, diatoms were the prevailing class in the trap material accounting for 75.32% of the settled cells, while flagellates represented 24.11%. Dinophyceae and resting cells constituted minor components, accounting for 0.43% and 0.14%, respectively. The gross sedimentation rates ranged from 0.006 × 10⁸ cell m⁻² d⁻¹ in the second week of May to 6.30 × 10⁸ cell m⁻² d⁻¹ in the third week of January with a mean annual value of 1.09 ± 1.43 × 10⁸ cell m⁻² d⁻¹. To the primary sedimentation rate Pseudo-nitzschia seriata of the group “Nitzschia seriata complex” contributed for 49.77% followed by Chaetoceros spp. (23.88%). The major contributor to the secondary sedimentation rate was the diatom Paralia sulcata, accounting for 24.76%. Epiphytic diatoms contributed for 11.19% and 12.27% on annual average gross abundance and biomass, respectively, reaching even 72.04% of gross abundance and 56.06% of gross biomass in the second week of August. The correlation between temperature and the logarithm of the epiphytic biomass was statistically significant, with r = 0.66 and P < 0.001. Both in the cluster analysis and in the PCA four main groups were formed, where benthic and epiphytic species were separately gathered. Planktonic, benthic and epiphytic forms accounted for 50.78%, 36.95% and 12.27%, respectively, calculated on the annual average biomass. Therefore, vertical fluxes can be overestimated of 50% or more if benthic and epiphytic species are not rejected.     

Salinity and inundation effects on productivity of brackish tidal marsh plants in the San Francisco Bay-Delta Estuary

Hydrobiologia - Plant productivity is central to numerous ecosystem functions in tidal wetlands. We examined how productivity of brackish marsh plants in northern California responded to abiotic...     

The fish assemblage of the intertidal salt marsh creeks in North Bull Island, Dublin Bay: seasonal and tidal changes in composition, distribution and abundance

An intertidal salt marsh fish assemblage inhabiting two creeks on North Bull Island, Dublin Bay was sampled monthly from June 2000 until May 2002. Water temperature and salinity were recorded in situ and samples were also taken for Suspended Particulate Matter (SPM) and Chlorophyll a. All fish caught were weighed and measured and classified into functional guilds. A total of 6,549 individuals comprising 10 fish species from 10 families were recorded within the two creeks. The community was dominated by a few species, a feature common to other estuarine fish populations. Of the 10 species found, the common goby, Pomatoschistus microps, the 3-spined stickleback, Gasterosteus aculeatus, the thick-lipped grey mullet, Chelon labrosus and the flounder, Platichthys flesus contributed 98.4% of all fish sampled. The fish population of the channels at Bull Island, Dublin, was dominated by the resident gobies (true estuarine resident species), but also hosted juveniles of species such as the bass, Dicentrarchus labrax (marine juvenile migrant species). In turn, the nekton populations were dominated by the brown shrimp, Crangon crangon and the fairy shrimp, Palaemonetes varians especially in winter when fewer fish (numbers of species and abundance) were found. Multivariate analysis of fish diversity and abundance revealed a strong seasonal pattern but there was little evidence of difference between creeks, nor of tidal (spring/neap) effects. The estuarine fish using the intertidal marsh creeks have been little studied in Europe yet they play a major role with the decapods in these habitats. This role needs to be quantified for a proper understanding of the system’s function.     

The last 1000 years of natural and anthropogenic low-oxygen bottom-water on the Louisiana shelf, Gulf of Mexico

The relative abundance of three species of low-oxygen tolerant benthic foraminifers, the PEB index, in foraminiferal assemblages from sediment cores is used to trace the history of low-oxygen bottom-water conditions on the Louisiana shelf. Analyses of a network of box cores indicate that the modern zone of chronic seasonal hypoxia off the Mississippi Delta began to develop around 1920 and was well established by 1960. The pattern of development over the last century is consistent with the interpretation that the formation of modern chronic hypoxia is related to anthropogenic activities resulting in increased transport of nutrients to the Louisiana shelf.The PEB index in two gravity- and box core pairs (MRD05-4 and 05-6) indicates that low-oxygen bottom-water events have occurred periodically on the Louisiana Shelf for at least the last 1000 ¹⁴C years. The pre-1900 low-oxygen bottom-water events are likely caused by intervals of increased Mississippi River discharge and widespread wetland export. The PEB record in gravity cores indicates that the pre-1900 low-oxygen bottom-water events were not as well developed or as geographically extensive as the modern hypoxia zone. We conclude that the development of low-oxygen bottom-water on the Louisiana shelf is a natural process that has been negatively modified by human activities in the last 100 years.     

Net primary productivity of two mangrove forest stands on the northwestern coast of Sri Lanka

Productivity studies were carried out from September, 1985 to August, 1987 in two mangrove stands, i.e. estuarine and island fringing, in Dutch bay, a lagoon situated on the northwestern coast of Sri Lanka. Net above-ground primary productivity was measured by monitoring litterfall and above-ground biomass increment. The average annual rate of litterfall in the estuarine and island-fringing mangrove stands are 588.14 g m^–2 (approximately 6 t ha^–1) and 407.33 g m^–2 (approximately 4 t ha^–1) respectively. The average annual rates of above ground woody growth are 614.74 g m^–2 (approximately 6 t ha^–1) in the estuarine stands and 286.8 g m^–2 (approximately 3 t ha^–1) in the island-fringing mangrove stands. Hence estuarine mangrove stands record a higher annual rate of above-ground net primary production (NPP; 1207.88 g m^–2 or approximately 12 t ha^–1) than the fringing mangrove stands (694.22 g m^–2); approximately 7 t ha^–1). The annual rate of NPP in the water front zones of the stands (1300.47 g m^–2 in the estuarine stands and 874.56 g m^–2 in the fringing stands) are greater than those in the back-mangrove zones (115.28 g m^–2 in the estuarine stands and 513.88 g m^–2 in the island-fringing stands). These variations may be attributed to the differences in tidal flushing and influence of freshwater in the two localities.     

The impact of phytoplankton on spectral water transparency in the Southern Ocean: implications for primary productivity

Spectral water transparency in the Northern Weddell Sea was studied during Austral spring. The depth of the 1-% surface irradiance level (euphotic depth) varied between 35 and 109 m and was strongly influenced by phytoplankton biomass. Secchi depths were non-linearly related to euphotic depth. In phytoplankton-poor water, the most penetrating spectral region was restricted to a relatively narrow waveband in the blue (488 nm), but the range was broader, between 488 and 525 nm when phytoplankton were abundant. Water transparency in the red spectral range was always low and only to a small extent affected by phytoplankton. Two independent procedures were used to quantify the impact of phytoplankton on spectral water transparency: (1) Regression analysis of spectral in situ vertical light attenuation coefficients in the sea, against coincident chlorophyll concentrations. This method gave chlorophyll-specific light attenuation coefficients; the y-intercept could be interpreted as a measure of light attenuation by pure water plus non-algal material. (2) Spectra of in vivo light absorption derived by spectroscopy, using phytoplankton enriched to varying degrees onto filters. Thus chlorophyll-specific absorption cross-sections were determined. Estimates obtained by both procedures were in close agreement. By integrating over the spectrum of underwater irradiance, in situ chlorophyll-specific absorption cross sections of phytoplankton suspensions, related to all photosynthetically active radiation, were calculated. Light absorption by phytoplankton for photosynthesis is accomplished mainly in the blue spectral range. Also dissolved and particulate organic matter contributed to the attenuation of blue light. Because in water poor in phytoplankton, underwater irradiance was progressively restricted to blue light, chlorophyll-specific absorption cross-sections of phytoplankton, averaged over the spectrum of photosynthetically active irradiance, increased with water depth. In water with elevated phytoplankton biomass, overall light attenuation was generally enhanced. However, because the spectral composition of underwater light changed relatively little with depth, except immediately below the water surface, light absorption cross-sections of phytoplankton changed little below 10 m depth. Vertical differences in the proportions of underwater light absorbed by the phytoplankton community here were mainly dependent on biomass variations. Because of the comparatively small attenuation of blue light by non-algal matter, the efficiency of light harvesting by phytoplankton at any given concentration of chlorophyll in Antractic waters is greater than in other marine regions. At the highest phytoplankton biomass observed by us, as much as 70% of underwater light was available for phytoplankton photosynthesis. When phytoplankton were scarce, <10% of underwater light was harvested by phytoplankton.Contribution within the European Polarstern Study (EPOS), supported by the Deutsche Forschungsgemeinschaft, Grant Ti 115/16-1 to MMT, the European Science Foundation, and by the Alfred Wegener Institut für Polar-und Meeresforschung, Bremerhaven     

Use of coastal waters as condenser coolant in electric power plants: Impact on phytoplankton and primary productivity

(1) Studies on phytoplankton entrained in cooling system of a power plant revealed a reduction in biomass and gross primary productivity (GPP) at outfall, compared to intake.     

The chemical character and burial of phosphorus in shallow coastal sediments in the northeastern Baltic Sea

The chemical composition and vertical distribution of sediment phosphorus (P) in shallow coastal sediments of the northeastern Baltic Sea (BS) were characterized by sequential extraction. Different P forms were related to chemical and physical properties of the sediments and the chemistry of pore water and near-bottom water. Sediment P composition varied among the sampling sites located in the Archipelago Sea (AS) and along the northern coast of the Gulf of Finland (GoF): the organic rich sites were high in organic P (OP), while apatite-P dominated in the area affected by sediment transportation. Although the near-bottom water was oxic, the sediments released P. Release of P was most pronounced at the site with high sediment OP and reduced conditions in the sediment-water interface, indicating that P had its origins in organic sources as well as in reducible iron (Fe) oxyhydroxides. The results suggest that even though these coastal areas are shallow enough to lack salinity stratification typical for the brackish BS, they are vulnerable to seasonal oxygen (O₂) depletion and P release because of their patchy bottom topography, which restricts mixing of water. Furthermore, coastal basins accumulate organic matter (OM) and OP, degradation of which further diminishes O₂ and creates the potential for P release from the sediment. In these conditions, an abundance of labile OP may cause marked efflux of P from sediment reserves in the long-term.     

Long-term persistence of low coral cover and abundance on a disturbed coral reef flat in the northern Red Sea

Levels of coral cover and abundance on a coral reef flat in Eilat (Israeli Red Sea) were estimated in 2001 by surveying nineteen 10-m transects, and compared to the levels reported in the same area between 1966 and 1973. Lower values compared to 1966 levels are evident, and there has been only a modest recovery following a catastrophic low tide that killed a large proportion of the corals in 1970. Percent cover of soft and stony corals (16.1%) was less than half of that reported for 1969 (35%), when a sharp decrease in coral abundance had already been observed. The total number of soft and stony coral colonies observed was 300, compared to 541 in 1966. In contrast to 1966, when half of the transects surveyed contained more than 30 coral colonies, no transects with this number of corals were observed. The cover of seven of the most common stony coral species was 841 cm, which is twice the coral cover of that in 1973, but only 22% of the 1969 level. Millepora dichotoma, an abundant species before 1970, has almost disappeared, and the soft coral Litophyton, abundant in 1972, was not observed. Anthropogenic nutrient enrichment is apparently among the causes for the lack of coral recovery in the studied reef flat. Reefs located further away from sources of pollution have recovered quickly after natural and anthropogenic disturbances and have retained their coral abundance and diversity.     

Feeding habits of young predatory fishes in marsh creeks situated along the salinity gradient of the Schelde estuary, Belgium and The Netherlands

Fish and macrobenthos were sampled in four different marshes along the salinity gradient of the Schelde estuary, Belgium/Netherlands, to investigate the importance of marsh creeks as foraging grounds for the dominant, larger fish species. The total density and biomass of all the main macrobenthic taxa (Corophium volutator, Nereis diversicolor, Oligochaeta, Macoma baltica and Heteromastus fliliformis) were measured. The feeding habits of the larger predatory fishes (Platichthys flesus, Dicentrarchus labrax) were investigated. Qualitative and quantitative stomach analyses included the calculation of different indices, showing the niche breadth (as diet diversity) and the niche overlap (as similarity between the predators diet) for this habitat. These analyses showed that the two most important benthic prey species for P. flesus were C. volutator and N. diversicolor. D. labrax preyed upon a wider range of species, including C. volutator, N. diversicolor, Crangon crangon, Carcinus maenas and Orchestia spp. The stomach diversity of D. labrax and P. flesus showed differences between the marshes although there was no consistent pattern in diet composition, reflecting the opportunistic nature of feeding by these large predators. The fullness indices of both flounder and sea bass did not differ significantly along the salinity gradient and the estimated minimum consumption by these predators did not indicate a top-down control of the macrobenthic community. The salt marsh creeks seem to provide excess food for the visiting fish species. The benthic prey was present in very high abundances, which may suggest that the typical nursery species such as C. crangon and C. maenas, and early juveniles of P. flesus, D. labrax and Pomatoschistus microps were not preyed upon significantly. This supports the hypothesis that salt marsh creeks provide good refuge areas for nursery species against predation by larger fish.     

The impact of cell wall carbohydrate composition on the chitosan flocculation of Chlorella

The carbohydrate composition of the algal cell wall was investigated for its role in cell flocculation. Cultures of Chlorella variabilis NC64A, which were found to have different levels of neutral sugar, uronic acid and amino sugar in the cell wall when cultured in different nitrogen sources and concentrations, were subjected to flocculation with chitosan at dosages of 0–69.6 mg/l and pH values of 5.5, 7 and 8.5. In addition, flocculations of another three strains of Chlorella, which have different levels of cell wall components, were tested. Flocculation improved for all strains at pH 8.5 suggesting that inter molecular forces such as hydrogen bonding might be more important than charge neutralization in the flocculation of Chlorella. Total carbohydrate content in the cell wall was the most significant factor positively affecting the flocculation efficiency of C. variabilis NC64A cells with different cell wall compositions and the other Chlorella strains. The results presented in this study suggest that chitosan flocculation can be improved by optimizing the cell culture conditions to achieve higher cell wall polysaccharide content or selecting an algal strain with higher cell wall polysaccharide content.     

The impact of harbour sludge disposal on benthic macrofauna communities in the Weser estuary

During an open-water disposal of about 710,000 m³ of harbour sludge in the polyhaline zone of the Weser estuary, Germany, a monitoring programme was carried out to investigate the impact on benthic invertebrates. The macrofaunal communities of four sites within the disposal area and five sites in a reference area were compared after discharge. The location and extent of the potentially affected area were inferred from a morphodynamic computer model (TIMOR 3; Zanke 1998). Disposal effects were analysed by comparing species numbers, densities, diversity and faunal similarity using multivariate methods. A loss of diversity and a decline in the abundance of several species in the disposal area were measured. The species number was reduced up to 50% and important habitat structures were absent from the disposal area. Several benthic species were affected by the disposal. The importance of species such as Mytilus edulis (Mollusca) and Lanice conchilega (Polychaeta) for the diversity of the community, and the sensitivity of these species to sediment discharge are analysed. The difficulties of separating dumping effects from natural variation in a dynamic estuarine channel system are discussed.Communicated by H.-D. Franke     

Variability in seed germination at the interpopulation,intrapopulation and intraindividual levels of the shrub Erica australis in response to fire-related cues

In Mediterranean ecosystems, as well as in other fire prone ones, seedling establishment by some species is particularly favorable right after fire. It has been well established that many plants from these ecosystems have enhanced germination after exposing their seeds to heat or to chemicals related to the passage of fire. Less known it is how variable is this germination response among seeds from different sources (populations, individuals within a population, or parts of the plant within an individual) and whether such differences persist after exposing the seeds to germination-triggering, fire-related cues. In this work we studied the germination response to several fire-related factors of the Mediterranean, lignotuberous shrub Erica australis. This species produces a very combustible fuel, and resprouts vigorously after fire, but conditions for seedling establishment are poorly known. The objective of this study was to evaluate how variable was the germination response of this species among seeds from different sources, and whether this variability changed after exposing the seeds to fire-related factors. Seeds from three different sites, from different individuals at each site, and from different branches within each individual were set to germinate under control conditions or after exposing them to heat or to additions of nitrogenous compounds. Germination was highly variable among populations, individuals within populations or branches within individuals. Exposure to moderate heat promoted germination, but high temperatures were lethal. Differences at the various provenance levels were, however, also observed after heat exposure. Germination of seeds exposed to nitrogenous compounds increased, but differences among populations were always significant. These results indicate that the germination of Erica australis may be linked to disturbances, but it does not seem to be particularly related to passage of fire. On the contrary, this type of response appears more common in plants from heterogeneously disturbed environments. This revised version was published online in August 2006 with corrections to the Cover Date.     

The Influence of Habitat Complexity on Reef Fish Communities in the Northeastern Gulf of Mexico

Several previous studies have attempted to correlate habitat complexity and reef fish species diversity. These studies have mostly examined natural reef systems, but results differed. To examine this relation, we built 1 m² habitats with 20 replicates of five complexity levels from July to August 2001 in the northeastern Gulf of Mexico (n=100). In June and July 2002, we built new habitats using the 2001 design, but also added a sixth complexity level (n=120). In order of increasing complexity these included: cage, shell, cage-shell, block-shell, cage-block-shell, and shell-block-pyramid habitats. Most fish in both years were juveniles and included species common to reef structures in the northeastern Gulf of Mexico. In 2001, we identified 26 fish species, and the dominant species was red snapper, Lutjanus campechanus (41%), followed by rock sea bass, Centropristis philadelphica (23%), and sand perch, Diplectrum spp. (14%). In 2002 we identified 36 species, and the dominant species was tomtate, Haemulon aurolineatum (36%), followed by Diplectrum spp. (19%), and L. campechanus (13%). In 2001, species diversity and richness were significantly (P<0.05) higher on more complex habitats (H′=1.7, S=11–12) compared to less complex habitats (H′=0.8–1.0, S=4–9). In 2002, patterns among diversity, richness and reef complexity were less apparent with only the least complex habitats shell and cage showing significantly lower values. In both years, multidimensional scaling grouped by complexity levels with cage and shell habitats showing the clearest separation from other habitat types. Also, with few exceptions (only 8%) analysis of similarities showed significant (P<0.05) differences in fish communities across complexity levels. Although community composition varied between years, this study provided evidence to support the hypothesis that habitat complexity increased reef fish species diversity.     

Modeling the effects of Hurricane Hugo on spatial and temporal variation in primary productivity and soil carbon and nitrogen in the Luquillo Experimental Forest, Puerto Rico

Hurricanes account for much of the spatial and temporal variation in forest productivity and soil organic matter pools in many forest ecosystems. In this study, we used an ecosystem level model, TOPOECO, to simulate the effects of Hurricane Hugo (18 September 1989) on spatial and temporal patterns of gross primary productivity (GPP), net primary productivity (NPP), soil organic carbon (SOC) and nitrogen over the entire Luquillo Experimental Forest (LEF), Puerto Rico, a tropical rainforest. Our simulation results indicated that simulated annual GPP increased by an average of 30% five years after Hugo in the Tabonuco forest at low elevations where there was a fast recovery of the canopy, whereas simulated GPP decreased by an average of 20% in the Palm and Dwarf forests at high elevations as a result of the slow recovery of the canopy. Simulated annual NPP in the Palm and Dwarf forests also did not recover to pre-Hugo levels within 5 years. Simulated storages of SOC, CO₂ emission from decomposition of SOC and total soil nitrogen increased slightly but N mineralization rate increased significantly in all four vegetation types due to the massive input of plant materials from Hugo at low elevations and the slow decomposition at high elevations.     

The impact of trampling by tourists on a high altitudinal grassland in the Tyrolean Alps,Austria

The long term effect of tourist trampling on a high altitudinal grassland (Caricion curvulae) in the Tyrolean Alps was investigated.Even under slight trampling the frequency of sensitive species decreases. The most sensitive species were found to be fruticose lichens, followed by mosses, some forbs and broadleaved grasses. Tolerant to trampling are the dominant species Carex curvula, and Ligusticum mutellina, which do not disappear completely even at a tourist frequency of 150 tourists per metre per day. Trampling increases soil bulk density moderately but has no marked effect on the soil water content.Comparison with high alpine sedge heath vegetation in North America shows a surprising uniformity of this vegetation type in response to trampling and also indicates that the common generalisation that alpine ecosystems are fragile and sensitive to disturbance does not hold true in this context. Furthermore these results represent evidence against the theory that ecosystems with low diversity are much more sensitive to arteficial impact than ecosystems with high diversity. However, if even the most resistant plants which are the dominant sedges are destroyed completely the rate of recovery is very low and may last for a long time. In the case of Carex curvula this is supported by the fact that it has very low seed production and grows mainly vegetatively. The rate of spread of the rhizome system of this species is 8 mm in 10 years. Similar figures may apply for the sedge species dominating in the alpine vegetation of North America. Thus fragility of this vegetation in regard to trampling does not mean low tolerance but low regeneration.Nomenclature of species follows Ehrendorfer (1973) for vascular plants and Poelt (1974) for lichens.The PCA calculations were done at the Computer laboratory of the University of Wales during a post doctoral stay at the School of Plant Biology in Bangor, U.K. I would like to record my thanks to Prof. Dr. P. Greig-Smith for fruitful discussions and reading the draft.     

Synergistic impact of water level fluctuation and invasion of Glyceria on Typha in a freshwater marsh of Lake Ontario

The effects of multiple stressors on the native Typha marsh community (mainly Typha latifolia) were examined using historical records of water levels, human census population, and field vegetation maps. Percent cover of the major plant species was estimated in a GIS, and the percent cover of Typha was related to changes in water level, human population growth, and percent cover of exotic Glyceria maxima and invasive Phragmites australis. Water level fluctuation was the major natural disturbance and it alone accounted for 88% of the variation in Typha. After partitioning out the effect of water level, both human population growth and the presence of exotic species were still significantly related to the decline of native Typha. We suggest that multiple stressors interact with each other to influence changes in native Typha community and cause greater detrimental impact. An important implication of our results is that projected water level decline due to climate change may not necessarily favor the restoration of a desirable native marsh because of the presence of other disturbances such as exotic and invasive species and altered nutrient regime.     

The influence of tidal channels on the distribution of salt marsh plant species in Petaluma Marsh,CA, USA

Tidal channels influence the distribution and composition of salt marsh vegetation in a San Francisco Bay salt marsh. Two channel networks in the Petaluma Marsh, Sonoma County, CA, were mapped and characterized using global positioning and geographic information systems. Plant species abundance was sampled on transects placed perpendicular to and extending away from the channel banks. The vegetation showed significant increases in species richness along channel banks and larger areas of effect which increased approximately linearly with channel size. Composition of species assemblages varies with distance from the channel bank and channel size. These results demonstrate that salt marsh plant assemblages, composed of both major and minor species, are distributed with respect to the channel network in Petaluma Marsh.     

On the edge: The use of infrared thermography in monitoring responses of intertidal organisms to heat stress

Monitoring changes in the environment and the corresponding effects on biological systems still represents a major challenge in many marine and terrestrial ecological studies. Infrared thermography (IRT), and its application within the marine environment, represents an effective non-invasive tool for measuring the temperatures of organisms and their surrounding environment in situ. The use of IRT within the intertidal zone is particularly useful since habitat and organismal temperatures are highly variable across both fine spatial and temporal scales. We review the growing number of intertidal studies that utilise IRT to investigate the role of small-scale temperature variability in contributing to various demographic and ecological processes. In particular, we introduce two indicators of the thermal quality of intertidal habitats that can be readily used by ecologists but also management and conservation policy makers to assess the suitability of a given habitat for a range of species under actual and predicted climatic conditions. We also outline a range of potential applications involving IRT that have yet to be explored for monitoring coastal environments. These include combining photogrammetry, unmanned aerial vehicles and IRT to large-scale three-dimensional thermal maps of intertidal habitats. We also suggest ways in which this technology could facilitate environmental management objectives in a warming world, such as the identification and quantification of thermal refugia across various spatial and temporal scales. We affirm with previous studies that such thermal refugia are vital for the adaptation of intertidal communities to climate change and that IRT could facilitate more effective management and conservation of these areas. The IRT applications outlined in this review are by no means exhaustive or limited to rocky intertidal environments. We envision that IRT will become increasingly popular as environmental management agencies become increasingly concerned about global climate change and how to combat its negative consequences on ecosystems.     

The impact of the invasive alien grass Cortaderia jubata (Lemoine) Stapf on an endangered mediterranean-type shrubland in California

Abstract. Since its introduction in the late 1800s, the perennial tussock grass Cortaderia jubata (Lemoine) Stapf has become an increasingly frequent member of coastal plant communities in California and Oregon. In this study, the community changes associated with C. jubata invasion into the mediterranean-type vegetation of Vandenberg Air Force Base, California were examined. Pristine plots of maritime chaparral were compared with spatially and topographically matched plots dominated by C. jubata . Aerial photographs indicated that the invaded plots had previously been shrubland. C. jubata invasion created a structurally less complex perennial grassland that was markedly depauperate in native shrub species. The absence of native shrubs depressed native richness in jubata grassland, but the greater richness of both native and alien herbaceous species made overall richness in jubata grassland indistinguishable from maritime chaparral. Vegetational differences were associated with differences in arthropod and small mammal populations between vegetation types. Arthropod abundance and order diversity were lower in plots dominated by C. jubata than in adjacent chaparral. Insect traps in C. jubata plots contained a significantly smaller proportion of Hymenoptera and Homoptera and a significantly greater proportion of Aràneae than traps in maritime chaparral. Rodent activity was significantly lower while rabbit activity was significantly greater in jubata grassland compared to maritime chaparral. This study indicates that the presence of C. jubata can dramatically alter the mediterranean-type landscape of central California. While it is likely that the initial establishment of C. jubata is associated with disturbances that are common in this ecosystem, the ability of C. jubata to expand from founding populations and to persist for long periods of time pose a serious threat to the native diversity of these unique systems.