Invertebrate Species Richness Research Articles

Large-scale effects of green tides on macrotidal sandy beaches: Habitat-specific responses of zoobenthos

Sandy beaches are highly dynamic ecosystems mainly driven by physical variables, such as tidal regime. These ecosystems support numerous essential ecological functions and contain a distinctive biodiversity, but are threatened by increasing direct or indirect anthropogenic pressures, among which are green tides composed of free living Ulva spp. Studies that have been conducted to understand the effects of macroalgal mats on coastal sediment communities have mostly addressed responses in atidal or microtidal systems, and are often single-site assessments. Using large-scale field surveys across 13 macrotidal sandy beaches of two types (exposed and semi-exposed) distributed along 2700 km of coast for 7 years (REBENT program, Brittany, France), we analysed responses of zoobenthos to the presence of green tides in relation to tidal range, exposure, sediment characteristics, air and seawater temperature, precipitations, wind and salinity. Despite the high variability existing between two distinct categories of sandy habitats and also between macrotidal beaches within the study area, differences in macrofaunal community structure arose from the presence of green tides: mean abundance and species richness of macrozoobenthic invertebrates were higher where green tides occurred. Moreover, macrobenthic assemblages in the two beach-categories respond differently to eutrophication seen as green tides. Surprisingly, the effects of the presence of Ulva mats were stronger at exposed sandy beaches than at semi-exposed beaches. Our study also highlights species-specific responses: herbivorous marine invertebrates and suspension feeders were favoured by the presence of Ulva mats, whereas large sub-surface deposit feeders and bivalve drifters which surf up and down the shore with the tides were negatively affected by green tides.

Riqueza de especies de invertebrados en playas de arena y costas rocosas del Pacífico Norte de Costa Rica

<p>Este estudio resume información publicada sobre las especies de invertebrados reportadas para la zona intermareal de la costa rocosa y las playas de arena del Pacífico Norte de Costa Rica. Además, se presentan datos nuevos sobre la riqueza de especies de la comunidad de invertebrados de varias playas de áreas protegidas o no protegidas muestreadas durante el año 2012. Los resultados indican una amplia variación en el número de especies reportadas, siendo los principales contribuyentes a la fauna los moluscos, crustáceos y poliquetos. El número de especies dependió del grupo faunístico y el esfuerzo de muestreo de los estudios previamente realizados. Teniendo en cuenta, todos los componentes de la comunidad, se encontraron entre 29 a 175 especies en los intermareales rocosos, y de 5 a 15 especies en las playas de arena. El valor promedio de riqueza de especies fue similar entre las áreas protegidas y no protegidas, aunque en ambos casos el rango de valores fue muy amplio. Hay lugares con gran riqueza de especies, sin medidas de protección, que están actualmente expuestos a los impactos del desarrollo de las poblaciones humanas, y es ahí donde urge la gestión de dichos hábitats</p>

The Effect of Fire on the Habitat Use of the Black-Eared MinerManorina melanotis

In 2006, a widespread fire in the Bookmark Biosphere Reserve, South Australia, consumed over one-third of the old growth mallee considered to be the prime habitat of the endangered Black-eared Miner Manorina melanotis. Since 2008, the species has been observed foraging and breeding in the fire-altered area. To verify whether food resources can explain the Black-eared Miners' presence in habitat consisting of early seral stages, we examined if a link could be found between the foraging behaviour of the Black-eared Miner and its invertebrate food resources.Foraging behaviour of Black-eared Miners was sampled opportunistically using focal observations. All potential invertebrate food resources were sampled using micro-pitfalls, malaise traps, beating trays, sweep nets and active searches. Black-eared Miners devoted significantly more time to foraging in long unburned (hereafter referred to as unburned) rather than in recently burned habitat. No differences in invertebrate abundance, species richness or diversity were found between burned and unburned habitats. However, differences in community composition between habitats were found. Lerp, which is a sugary protective covering of particular insect larvae, is an important food source for the Black-eared Miners, and was found more in the unburned natural habitat.We found that Black-eared miners may be more adaptable than previously thought when it comes to utilization of burned habitat. Still, this study reaffirms the importance of unburned habitat for Black-eared Miners.

Fish Productivity and Trophic Transfer in Created and Naturally Occurring Salt Marsh Habitat

High marsh pools are natural features in New England salt marshes that provide important subtidal refuge for the dominant resident fish, Fundulus heteroclitus (mummichog). F. heteroclitus is considered an important component in the trophic transfer pathway for its omnivorous diet and role as a prey species providing connectivity to adjacent near-shore and terrestrial habitats. Pool creation, such as ditch-plugging, is a common component of habitat restoration and enhancement projects throughout the region. Our study combined field experiments measuring fish growth and benthic invertebrates with carbon and nitrogen stable isotopes measurements to test the hypothesis that ditch plug pools have similar trophic structure and levels of productivity as naturally occurring salt marsh pools. Marked fish placed in enclosures were measured for length and weight weekly in natural pools and pools created using ditch plugs. Benthic invertebrates were sieved and sorted from soil cores to characterize invertebrate community structure, and stable isotopes were used to posit diets and trophic pathways associated with each pool type. Growth in fish length was 27 % higher and instantaneous biomass growth 17 % higher in natural pool habitat than in ditch plug habitat. Likewise, invertebrate species richness, biomass, and caloric value were all significantly greater in natural pool habitat than in ditch plugs. Stable isotope mixing models identified distinct resource utilization and trophic structure for natural and created pools. We attribute these differences to flooding and plant loss in response to ditch-plugging, which reduces habitat quality (as measured by resource availability, community structure, and trophic transfer) for fish and invertebrates. Our study increases our understanding of the ecology of salt marsh pools, and the significant results indicate that pools created using ditch plugs do not replicate the structure and function of natural pools at Moody Marsh.

Fine-scale benthic biodiversity patterns inferred from image processing

Despite potentially considerable advantages over traditional sampling techniques, image-derived indices of habitat complexity have rarely been used to predict patterns in marine biodiversity. Advantages include increased speed and coverage of sampling, avoidance of destructive sampling, and substantially reduced processing time compared to traditional taxonomic approaches, thus providing a starting point for more detailed analysis if warranted. In this study, we test the idea that the mean information gain (MIG) and mean mutual information (MMI), two indices of image heterogeneity that we derived from photographs of marine benthic assemblages, represent good preliminary predictors of biodiversity patterns for 133 benthic invertebrate and algal taxa on jetty pylons in Gulf St Vincent, South Australia. Both MIG and MMI were spatially structured, with evidence of among-site differences that were also evident in the benthic data. When combined with information on the spatial structure within the dataset (site and depth), MIG and MMI explained ∼35% of deviance in invertebrate species richness, ∼43% in Shannon's evenness and up to 50% of dissimilarity in species composition. This explanatory power is of a similar magnitude to many other, less readily available, surrogate measures of biodiversity. These results corroborate the idea that indices of image heterogeneity can provide useful and cost-effective complements to traditional methods used for describing (or predicting) marine epibiota biodiversity patterns. This approach can be applied to many case studies for which photographic data are available, and has the potential to result in substantial time and cost savings.

Changes in habitat complexity resulting from sequential invasions of a rocky shore: implications for community structure

Worldwide, marine rocky shores are being modified by alien species, but their successive impacts are rarely recorded. We documented sequential invasions of Marcus Island on the west coast of South Africa by comparing communities from 1980 (pre-invasion), 2001 (after invasion by the mussel Mytilus galloprovincialis) and 2012 (following invasions by another mussel, Semimytilus algosus, and the barnacle Balanus glandula). Their influence on habitat complexity was measured with a novel technique enabling retrospective calculation of historical complexity. In 1980, habitat complexity, invertebrate abundance and species richness decreased from the low-shore to the high-shore, but homogenised in 2001 after M. galloprovincialis elevated habitat complexity across most of the shore. In 2012, these variables returned to pre-invasion patterns, after M. galloprovincialis declined in the high-shore and was replaced there by B. glandula. With the first mussel invasion, several indigenous species extended up the intertidal, but retreated once M. galloprovincialis receded. Community composition differed significantly among nearly all years and zones, irrespective of whether the alien species were included in the analyses or not. Some once-dominant native species were negatively affected by the invasions: one indigenous mussel, Choromytilus meridionalis, disappeared by 2012, and another, Aulacomya atra, declined. The abundance of recruits of the limpet Scutellastra granularis rose and fell with the arrival and recession of M. galloprovincialis, but adults were adversely affected. Changes to habitat complexity induced by sequential invasions supported hypothesised changes in invertebrate abundance and species richness, but could not alone predict changes in community composition, which were also influenced by zonation.

Adopting Workable Methods for Stream Water Quality Monitoring in Zambia

Invertebrates are among the most ubiquitous and diverse organisms that play a central ecological role in many freshwater ecosystems. However, the diversity and community composition of these organisms are affected by many physical, chemical and biological factors which are introduced naturally or by human (anthropogenic) activities into the stream systems. A study was conducted to assess the impact of water quality on invertebrate species abundance, diversity and richness in the Mwekera stream in Kitwe district on the Copperbelt Province in Zambia. The study also examined the potential use of invertebrates as indicators of water quality using the South African scoring system version 5 (SASS 5) as a standard. The invertebrate community of the stream was studied to Order level of taxonomy in the dry season from July to August 2014. Across the sampling sites, a total of 106 invertebrate individuals belonging to 12 Orders were collected. The Shannon-Wiener diversity Index was calculated in relation to four water quality parameters namely, pH, conductivity, redox and temperature. The study revealed that species diversity along the stream was significantly different ( p 0.05) was found between diversity and redox. Overall, water quality seemed to have had effect on species diversity, abundance and richness of the invertebrate community which therefore can be used as bio-indicators to aquatic health.

Ecosystem engineering effects on species diversity across ecosystems: a meta-analysis.

Ecosystem engineering is increasingly recognized as a relevant ecological driver of diversity and community composition. Although engineering impacts on the biota can vary from negative to positive, and from trivial to enormous, patterns and causes of variation in the magnitude of engineering effects across ecosystems and engineer types remain largely unknown. To elucidate the above patterns, we conducted a meta-analysis of 122 studies which explored effects of animal ecosystem engineers on species richness of other organisms in the community. The analysis revealed that the overall effect of ecosystem engineers on diversity is positive and corresponds to a 25% increase in species richness, indicating that ecosystem engineering is a facilitative process globally. Engineering effects were stronger in the tropics than at higher latitudes, likely because new or modified habitats provided by engineers in the tropics may help minimize competition and predation pressures on resident species. Within aquatic environments, engineering impacts were stronger in marine ecosystems (rocky shores) than in streams. In terrestrial ecosystems, engineers displayed stronger positive effects in arid environments (e.g. deserts). Ecosystem engineers that create new habitats or microhabitats had stronger effects than those that modify habitats or cause bioturbation. Invertebrate engineers and those with lower engineering persistence (<1 year) affected species richness more than vertebrate engineers which persisted for >1 year. Invertebrate species richness was particularly responsive to engineering impacts. This study is the first attempt to build an integrative framework of engineering effects on species diversity; it highlights the importance of considering latitude, habitat, engineering functional group, taxon and persistence of their effects in future theoretical and empirical studies.

Thresholds of Logging Intensity to Maintain Tropical Forest Biodiversity

Primary tropical forests are lost at an alarming rate, and much of the remaining forest is being degraded by selective logging. Yet, the impacts of logging on biodiversity remain poorly understood, in part due to the seemingly conflicting findings of case studies: about as many studies have reported increases in biodiversity after selective logging as have reported decreases. Consequently, meta-analytical studies that treat selective logging as a uniform land use tend to conclude that logging has negligible effects on biodiversity. However, selectively logged forests might not all be the same. Through a pantropical meta-analysis and using an information-theoretic approach, we compared and tested alternative hypotheses for key predictors of the richness of tropical forest fauna in logged forest. We found that the species richness of invertebrates, amphibians, and mammals decreases as logging intensity increases and that this effect varies with taxonomic group and continental location. In particular, mammals and amphibians would suffer a halving of species richness at logging intensities of 38 m(3) ha(-1) and 63 m(3) ha(-1), respectively. Birds exhibit an opposing trend as their total species richness increases with logging intensity. An analysis of forest bird species, however, suggests that this pattern is largely due to an influx of habitat generalists into heavily logged areas while forest specialist species decline. Our study provides a quantitative analysis of the nuanced responses of species along a gradient of logging intensity, which could help inform evidence-based sustainable logging practices from the perspective of biodiversity conservation.

Invasive plant ecosystem engineer facilitates community and trophic level alteration for brackish marsh invertebrates

Wetland habitats are becoming increasingly scarce worldwide while experiencing exceptionally high levels of plant invasion. Invasive plant species affect ecosystems through numerous avenues, including acting as ecosystem engineers, contributing unique plant functional traits, and altering trophic dynamics. We examined the impacts of the invasive weed Lepidium latifolium on soil‐dwelling and canopy‐dwelling invertebrate communities in a brackish marsh of northern California. Invertebrate abundance, species richness, diversity, and community composition were measured in both invaded and non‐invaded areas of the marsh in four time periods that correspond with different L. latifolium phenologic phases. We observed these different stages of L. latifolium, and we recorded alterations in the habitat structure provided by L. latifolium as the plant entered senescence. L. latifolium had differential impacts on the two invertebrate communities studied. The presence of L. latifolium increased abundance of soil‐dwelling invertebrates and decreased the species richness of canopy‐dwelling invertebrates in the tidal marsh‐terrestrial ecotone where L. latifolium ameliorates harsh physical conditions. No changes occurred in the tidal marsh plain and fringing tidal marsh where L. latifolium's physical structure is more similar to existing non‐L. latifolium structure. During full senescence, L. latifolium reduced canopy‐dwelling invertebrate abundance and altered trophic dynamics, shifting composition to a predator‐dominated community. Our results demonstrate that L. latifolium can impact brackish marsh ecosystems, and we hypothesize L. latifolium's unique functional traits (large inflorescence and seasonal senescence) enable it to act as an ecosystem engineer that alters community and trophic dynamics. Mechanisms through which plant invaders alter ecosystem processes are dynamic in space and time, thus, future research will require the use of manipulative experiments to inform site‐specific management strategies.

Invertebrate herbivory decreases along a gradient of increasing land-use intensity in German grasslands

Land use is a major driver of biodiversity loss in many taxa including species-rich invertebrate assemblages, but consequences for invertebrate-mediated processes are still little studied. We assessed invertebrate herbivory in 146 managed temperate grasslands across a broad range of land-use intensities in three regions of Germany. Average herbivory decreased with increasing land-use intensity independent of region from 1.3 to 0.4% leaf area assessed. Among grassland land-use practices, the frequency of mowing and the degree of fertilization decreased herbivory while the intensity of vertebrate grazing had no significant effect on invertebrate herbivory. Thus, grassland management not only affects the diversity and abundance of invertebrate assemblages but also the amount of leaf tissue consumed.

Aquatic invertebrate communities in tank bromeliads: how well do classic ecological patterns apply?

Tank bromeliads (Bromeliaceae) often occur in high densities in the Neotropics and represent a key freshwater habitat in montane forests, housing quite complex invertebrate communities. We tested the extent to which there are species richness–altitude, richness–environment, richness–size, richness–habitat complexity and richness–isolation relationships for the aquatic invertebrate communities from 157 bromeliads in Cusuco National Park, Honduras. We found that invertebrate species richness and abundance correlated most strongly, and positively, with habitat size, which accounted for about a third of the variance in both. Apart from bromeliad size (equivalent of the species–area relationship), we found remarkably little evidence of classic biogeographic and ecological relationships with species richness in this system. Community composition correlated with altitude, bromeliad size and position, though less than 20% of the variation was accounted for by the tested variables. The turnover component of dissimilarity between the communities correlated with altitude, while the nestedness-resultant component was related to bromeliad size. The unexplained variance could reflect a large stochastic component in the system, associated with the ephemerality of the habitat patches (both the plants themselves and the fluctuations in their water content) and stochasticity due to the dispersal dynamics in the system. We conclude that there is a small contribution of classic biogeographic factors to the diversity and community composition of aquatic invertebrates communities in bromeliads. This may be due to the highly dynamic nature of this system, with small patch sizes and high emigration rates. The patterns may mostly be driven by factors affecting colonisation success.

Using GIS Methods to Evaluate Rhodolith andSargassumBeds as Critical Habitats for Commercially Important Marine Species in Bahía Concepción, B.C.S., México

Bahía Concepción was once recognized as a very productive coastal lagoon not only for the Peninsula of Baja California but also for all Mexico. However, lack of proper management has resulted in the closure of various fisheries, such as the Calico scallop, Argopecten ventricosus, in 1994. One of the main challenges for the management of coastal resources is the selection of critical habitats for conservation considering the economic activities of the communities associated with them. This study used Geographic Information Systems (GIS) and remote sensing to assess the roll of rhodoliths and Sargassum spp. as critical habitats in Bahía Concepción for endangered and commercial species. Underwater surveys, on 72 randomly selected sites within the bay, were conducted to characterize the shallow benthic habitats, fish and invertebrate species abundance and richness during the spring of 2011. Analyses show that rhodoliths are important for the invertebrate assemblages and for at least 4 species protected under the Mexican law, NOM-059, for threatened species. Sargassum spp. and seagrass beds are also relevant for diversity but their annual life cycle limits the time when these are available as habitat for other species. GIS tools proved an innovative and effective method to provide essential information to protect critical habitats such as rhodoliths, Sargassum spp. and seagrasses, for the recovery and conservation of diversity.

Spatial Distribution of Plant-Associated Invertebrates and Environmental Bioassessment in a Natural Riverine Lake (Lake Fibreno, Central Italy)

Lake Fibreno is a Mediterranean riverine lake located in Central Italy and fed by large flows of groundwater and characterized by the presence of a wide reed stand area and of the only floating island of the South Europe. It is enclosed in a Natural Reserve recognized as Special Area of Conservation (SAC-IT6050015) for the presence of habitats and species (92/43/EEC) of relevant scientific interest. In this paper, we compare the plant-associated meio-macrobenthic invertebrates among sites with different environmental characteristics. Both vegetation and invertebrates of Lake Fibreno were well diversified and abundant and were composed of a mixing of species typical of lentic and lotic waters. Our results show that a gradient of orthophosphate and nitrite contents and current velocity appeared to be the driver factors affecting the flora and fauna spatial distribution at the sampling sites. To obtain a bioassessment of the ecological quality of the vegetation zone, we compared the riverine Lake Fibreno with typical lentic lakes previously studied in Central Italy. We selected metrics, such as macrophyte belt extent and taxa richness, invertebrate species richness and Shannon diversity, ETOM (Ephemeropta + Trichoptera + Odonata + Mollusca), ETOC (Ephemeropta + Trichoptera + Odonata + Coleoptera) and LCrM (Large Crustacea + Mollusca). The comparison indicated a good ecological status of the vegetation zone of Lake Fibreno mainly due to the continuous washout effects (dilution and fast water removal) which reduce the nutrient content available for phytoplankton and maintain the high transparency and good oxygenation of the lake waters.

Linking nutrient loading, local abiotic variables, richness and biomasses of macrophytes, and associated invertebrate species in the north-eastern Baltic Sea

Abstract. We studied relationships between nutrient loading, local abiotic variables, richness and biomasses of macrophytes, and associated invertebrate species in the north-eastern Baltic Sea. The study showed that nutrient load strongly correlated to the richness and biomass of macroalgal and invertebrate species and functions and often interacted with local abiotic variables such as salinity and depth. Generally elevated nutrient loads increased the species richness of macrophytes and benthic invertebrates and the biomass of annual macroalgae and of the majority of invertebrate feeding groups, but reduced the biomass of perennial macroalgae. The study also showed that the effect of nutrient loading was scale-specific, i.e. different responses to nutrients were observed at water-body and gulf scales. The biomass of the majority of species and functions was a function of the gulf-scale nutrient loading whereas the variability of annual algae and chironomidae reflected changes in the water-body level nutrient loading.

Biodiversity loss in seagrass meadows due to local invertebrate fisheries and harbour activities

Seagrass meadows provide a wide variety of ecosystem services, but their distribution and health are adversely affected by man. In the present study, we examined the influence of coastal exploitation in terms of invertebrate harvesting and harbour activity on invertebrate community composition in subtropical seagrass meadows at Inhaca Island, Mozambique, in the Western Indian Ocean. There was a fivefold higher invertebrate density and biomass, and clearly higher invertebrate species richness, in the protected (control) site compared to the two exploited sites. The causes for the clear differences between protected and exploited sites were probably a result of (1) the directional outtake of large edible or saleable invertebrates (mostly molluscs) and the absence of boat traffic in the harvested site, and (2) harbour activities. Invertebrate community composition in the two exploited sites also differed (although less clear), which was likely due to inherent distinction in type of disturbance. Our findings revealed that protection of seagrass habitat is necessary and that disturbances of different origin might require different forms of management and conservation. Designing protected areas is however a complex process due to competition for use and space with activities such as invertebrate harvesting and harbours.

Macrophyte loss drives decadal change in benthic invertebrates in peatland drainage ditches

Summary Agricultural peatlands and their associated drainage systems are often highly managed and exposed to anthropogenic pressures, such as eutrophication and stable water tables, maintained via drainage during periods of high rainfall and inlet of, alkaline‐rich, waters during dry periods. These pressures promote peat degradation, resulting in the accumulation of fine‐degraded peat particles that dramatically alter aquatic habitats by smothering surfaces and decreasing water quality. Consequential effects on benthic communities are expected but have not been investigated so far. We hypothesised that peat degradation can lead to the decline in submerged macrophytes, which are of critical importance to sustaining biodiversity of benthic invertebrate communities. To investigate this, we analysed decadal (1985–2007) changes in benthic species richness in 29 peat ditches in the Netherlands and, to determine patterns of macroinvertebrate habitat occupancy, carried out a complementary field experiment with submerged artificial macrophytes, natural sediments and emergent bank vegetation. Results from long‐term monitoring indicate that chemical conditions in agricultural peat ditches have improved slightly over the last decades; however, there has been a simultaneous decline in benthic invertebrate species richness and densities corresponding to a decline in the numbers of submerged macrophytes. The apparent dependence of macroinvertebrates on macrophytes was reinforced by our field experiment which revealed that invertebrate density was highest in submerged artificial plants, while invertebrate species richness was highest in natural emergent vegetation. Conversely, degraded peat sediments supported extremely few invertebrates. Our results clearly illustrate the strong influence of submerged macrophyte loss on macroinvertebrate assemblages in peatland waters. Furthermore, this suggests that improvements in water quality alone will not benefit invertebrates in the absence of suitable vegetative habitats.

Abiotic surrogates for temperate rocky reef biodiversity: implications for marine protected areas

AbstractAimTo examine the potential of remotely sensed abiotic measures as surrogates for the abundance, diversity and community composition of temperate rocky reef fishes and sessile invertebrates.LocationBatemans Marine Park, south‐eastern Australia.MethodsWe used high‐resolution bathymetric side‐scan sonar imagery to quantify abiotic measures of rocky reef habitat, within a marine protected area (MPA), and examine the relationship between abiotic measures and (1) sessile invertebrate abundance, (2) sessile invertebrate species richness, (3) total fish abundance, (4) fish species richness, and (5) Monacanthidae abundance using generalized additive mixed models (GAMMs). We chose GAMMs as the preferred statistical analysis to account for the spatial autocorrelation present in our data.ResultsWe found a strong positive relationship between abiotic measures and sessile invertebrate abundance and diversity (r2 &gt; 0.64). By far the most important predictor was vertical relief within a 75 m radii seascape surrounding the faunal survey. Overall, abiotic measures were poor predictors of total fish abundance (r2 = 0.175) and fish species richness (r2 = 0.276), with minimum adequate models producing low explanatory power. In contrast, Monacanthids exhibited a strong positive relationship with abiotic variables (r2 = 0.385), with increased abundance associated with greater depth and distance from soft sediment.Main conclusionsRemotely sensed abiotic measures are important predictors in describing the spatial patterns of sessile invertebrate abundance and diversity and Monacanthid abundance. In contrast, abiotic variables were poor predictors of total fish abundance and diversity. Habitat could be a useful cost‐effective surrogate to determine areas of conservation value for certain temperate rocky reef assemblages. This information is valuable for future MPA development and design.

New metric of microhabitat complexity predicts species richness on a rocky shore

AbstractMost habitat complexity–species diversity relationships are specific to the habitat type, taxonomic group and spatial scale investigated. There is a need for a biologically relevant metric of habitat complexity that is transferable across systems and scales. Here, we introduce a novel metric of landscape microhabitat complexity that may overcome such constraints. It is scaled to the size of individual organisms and it numerically captures structural elements of the habitat that are biologically relevant to individuals. Our model ecosystem to develop this metric was a rocky shore in Eastern Australia. Here species richness of invertebrates was linked to habitat complexity quantified by the new metric. Importantly, measurements made at the scale of the organism predicted species richness at the landscape scale. Testing the generality of this approach across different systems may prove useful in a broader conservation biology context.

Taxon‐ and vector‐specific variation in species richness and abundance during the transport stage of biological invasions

Recent empirical and statistical evidence suggest that propagule pressure (i.e., number of individuals introduced per event, and the number and frequency of events) and colonization pressure (i.e., number of species released per event, and the number and frequency of events) are of vital importance to invasion success. To explore possible changes in propagule and colonization pressure during the transport stage of the invasion process, we examine abundance and species richness of virus‐like particles, bacteria, diatoms, dinoflagellates, and invertebrates transported in commercial ships—a leading vector for global spread of aquatic nonindigenous species. We collected 154 ballast water samples from ships that had performed or were exempt from ballast water exchange (BWE) prior to arrival at Pacific and Atlantic ports in Canada and Laurentian Great Lakes ports. We found that abundance and species richness varied across taxa and regions, with ships arriving to the Atlantic region carrying the highest abundance of taxa. The highest species richness of invertebrates and diatoms was recorded from ships arriving to the Pacific, whereas the richest communities of dinoflagellates occurred in the Atlantic region. We also found that BWE had no effect on abundance or species richness of most taxa (dinoflagellates, diatoms, bacteria, and virus‐like particles), whereas the effect on abundance of invertebrates was not clear. Finally, longer voyages resulted in lower abundance of all taxa except dinoflagellates, and lower species richness of diatoms. Paradoxically, the elevated abundance and species richness of dinoflagellates following BWE suggest that this group could have enhanced invasion potential when ships manage ballast water by exchange.