Adjacent Natural Habitats Research Articles

Fish Assemblages on Estuarine Artificial Reefs: Natural Rocky-Reef Mimics or Discrete Assemblages?

If the primary goal of artificial reef construction is the creation of additional reef habitat that is comparable to adjacent natural rocky-reef, then performance should be evaluated using simultaneous comparisons with adjacent natural habitats. Using baited remote underwater video (BRUV) fish assemblages on purpose-built estuarine artificial reefs and adjacent natural rocky-reef and sand-flat were assessed 18 months post-deployment in three south-east Australian estuaries. Fish abundance, species richness and diversity were found to be greater on the artificial reefs than on either naturally occurring reef or sand-flat in all estuaries. Comparisons within each estuary identified significant differences in the species composition between the artificial and natural rocky-reefs. The artificial reef assemblage was dominated by sparid species including Acanthopagrus australis and Rhabdosargus sarba. The preference for a range of habitats by theses sparid species is evident by their detection on sand-flat, natural rocky reef and artificial reef habitats. The fish assemblage identified on the artificial reefs remained distinct from the adjacent rocky-reef, comprising a range of species drawn from naturally occurring rocky-reef and sand-flat. In addition, some mid-water schooling species including Trachurus novaezelandiae and Pseudocaranx georgianus were only identified on the artificial reef community; presumably as result of the reef's isolated location in open-water. We concluded that estuarine artificial reef assemblages are likely to differ significantly from adjacent rocky-reef, potentially as a result of physical factors such as reef isolation, coupled with species specific behavioural traits such as the ability of some species to traverse large sand flats in order to locate reef structure, and feeding preferences. Artificial reefs should not be viewed as direct surrogates for natural reef. The assemblages are likely to remain distinct from naturally occurring habitat comprised of species that reside on a range of adjacent natural habitats.

Rangeland Management for Pollinators

Pollinator conservation and rangelands don’t seem like obvious bedfellows. In this era of sustainability, the connection between pollinator conservation and row crops or pollinator conservation and orchards is obvious. But pollinator conservation and rangelands? The reality is that pollinators are a key component of a healthy rangeland ecosystem. As Kevan stated, pollination is “central to all human beings, livestock, and wildlife.”1 Pollinators are essential for rangeland food production, help with nutrient cycling, and are prey for many birds. In essence, they hold a central position in wildlife food webs. For example, many migratory songbirds require a diet of berries, fruits, and seeds from insect-pollinated plants and pollinator larvae are an important component of the diet of many young birds. Belfrage et al. demonstrated that butterfl y diversity was a good predictor of bird abundance and diversity, apparently due to a shared requirement for a complex plant community.2 Pollinators perform such a range of ecological services in natural ecosystems that they are clearly a keystone group in nearly all terrestrial ecosystems and are necessary for plant reproduction and in forming the basis of an energy-rich food web.3 The relationship between pollinators and rangeland goes both ways. Pollinators are important for rangelands but rangelands are important for pollinators because they can provide habitat. Pollinators in North America include hummingbirds and bats, but insects—mainly bees, butterfl ies, moths, wasps, fl ies, and beetles—make up the vast majority of pollinators. Of these, bees are considered the most important pollinators in temperate North America. There are approximately 4,000 species of native bees in North America, many of which will thrive in the varied conditions offered by rangelands. Shrubland and scrub habitat, in particular, can be very valuable habitat. Surveys of pollinators in different California plant communities show that the chaparral community has the largest diversity of bees per unit area of any ecosystem type. Bee habitat requires two basic components: fl owers on which to forage and nest sites. Many pollinators are adapted to forage on particular plants, so a diverse community of pollinators requires a diverse array of fl owers. This can be easily provided by native grassland comprising a variety of grasses and forbs. Most native bees are solitary-nesting. Around 70% of bee species nest in the ground, excavating shallow tunnels in patches of bare soil, with most of the remaining 30% nesting in cavities in old trees or plant stems. Bumble bees require a small cavity such as an abandoned rodent hole. Ground-nesting bees (both solitary bees and bumble bees) are likely the most important pollinators in grasslands, but fl ies, beetles, and butterfl ies will also be prevalent. Rangeland pollinators have benefi ts that go beyond the boundaries of the range. The role that adjacent natural habitat (including grassland, shrubland, and other rangeland types) plays in providing crop pollination services is increasingly well understood: The value of crop pollination by native, wild bees in the United States is estimated at $3 billion. Proximity to natural or seminatural nonagricultural land is often an important predictor of pollinator diversity in cropland. There is evidence of declines in both managed and wild pollinators. Causes of declines are diffi cult to pinpoint, but loss of habitat due to increasing urbanization, expansion of intensive agriculture, invasive plant species, and the widespread use of pesticides all negatively impact pollinator populations, as do disease and parasites affecting the pollinators themselves. Protection of habitat is one way in which rangelands can be of great signifi cance in protecting and conserving pollinators. Natural habitat is integral to maintaining a long-term population of native pollinators in agricultural landscapes. However, it is important that management of rangelands and other nonarable lands takes into account native pollinators.

Taxonomic composition and diversity of microphytobenthos in southern California marine wetland habitats

Sediments in coastal wetlands host communities of phylogenetically diverse primary producers such as diatoms, cyanobacteria, and anoxygenic photosynthetic bacteria, but little is understood about spatial variation in the composition of these assemblages at the highest taxonomic levels. Using High Performance Liquid Chromatography to quantify taxon-specific pigments, I investigated habitat-linked heterogeneity in microphytobenthic biomass, composition, and diversity within two natural wetland systems from southern California and tested for differences in community structure between natural and restored ecosystems. Natural vegetated habitat at Mission Bay had higher concentrations of zeaxanthin (cyanobacteria) and bacteriochlorophyll a (anoxygenic photobacteria) than unvegetated mudflat and creek banks. Organic matter was positively correlated with the concentrations of these pigments, whereas sediment pore water salinity and sand content were generally unrelated to composition. At Tijuana Estuary, community structure was generally similar between mudflat and Spartina marsh at the natural site, but concentrations of chlorophyll a and fucoxanthin (diatoms) were higher in mudflats. Restored wetland similarity with adjacent natural habitat (age 2 yr at Tijuana Estuary and 6 yr at Mission Bay) depended on habitat type and pigment measure. Restored upper intertidal succulent marsh at Mission Bay was most divergent: it had lower microalgal biomass, a lower concentration of zeaxanthin relative to fucoxanthin, and less bacteriochlorophyll a relative to chlorophyll a than natural habitat. The results suggest that patches of prokaryotic primary producers coincide with areas of high sediment organic matter and/or hypoxia superimposed on a broadly distributed flora of diatoms across various wetland landscapes.

A vessel‐deployed passive postlarval collector to assess settlement of the American lobster Homarus americanus

Passive collectors are used widely in postlarval settlement and recruitment monitoring of spiny lobsters and crabs, but they have only been used in a limited way with clawed lobsters. For nearly two decades, diver‐based suction sampling has served to monitor spatial‐temporal patterns of American lobster (Homarus americanus) postlarval settlement and early juvenile abundance in shallow near‐shore nurseries. Collectors could reveal settlement patterns in zones beyond the practical limits of diving. In 2005, we launched a fisher‐scientist collaboration to evaluate the performance of passive collectors designed to extend the reach of sampling, and to be deployable from a vessel equipped with a standard pot‐hauler. Building on previous designs, our collectors comprised wire mesh trays lined with fine screening on the floor and walls and filled with cobble to simulate natural nursery habitat. Results indicate that no newly settled lobsters were lost during the retrieval process, and densities of young‐of‐year lobsters found in the collectors were similar to those in directly adjacent natural cobble habitat sampled by divers with suction samplers. The collectors also proved to be effective samplers of juvenile fish and crabs, suggesting a possibility for wider application. This success bodes well for expanded deployment of cobble collectors to broaden our understanding of the recruitment processes of lobster and other cobble‐dwelling fauna along the coast of New England, United States and Atlantic Canada.

Suppression of root-knot nematodes in natural and agricultural soils

The potential of the invertebrate communities in agricultural and natural soils to suppress Meloidogyne incognita on coleus ( Coleus blumei) was evaluated in two greenhouse experiments. Soil from adjacent natural and agricultural habitats was collected from four locations that had very different soil types (loamy sand, muck, sand and rock). Soil of each type was placed into pots, planted with coleus seedlings, inoculated with 2000 eggs of M. incognita, and arranged in a 4 × 2 factorial design. Root-knot nematodes were suppressed in natural soil compared to agricultural soil for loamy sand, sand and rock soils, but not for muck soil. Plants grew larger and had less root galling in natural soils than in agricultural soils. Free-living nematodes (bacterivores, fungivores, omnivores and predators) were monitored but did not show population patterns consistent with the suppression of root-knot nematodes observed in natural soils. Reasons for the opposite result (higher root-knot levels in natural than in agricultural soil) on muck soil are unknown, but this soil type was very different from the other soils in its unusually high organic matter content and very low levels of omnivorous and predatory nematodes. The agricultural muck in particular was unusually low in fungivorous nematodes and extremely high in levels of sodium and macronutrients. Despite the exception on the muck soil, the relative suppression of root-knot nematodes in natural compared to agricultural soils of the other three soil types (loamy sand, sand and rock) support the idea that potential for nematode suppression may be greater in natural than in agricultural soils.

Exotic pest insects: another perspective on coffee and conservation

Research on crop systems and biodiversity conservation in the tropics has mainly been concerned with how low to mid intensity agricultural systems can benefit from adjacent natural habitats by receiving ecosystem services from natural biodiversity. One intensively studied crop in this framework is coffee. Positive effects are relatively easy to quantify by comparing coffee yield and by recording native species diversity. However, a largely overlooked issue is how agricultural areas affect native organisms in adjacent natural habitats, for example through movement of pest species that could impose a risk of degrading these habitats. We give an example from Mauritius, where an introduced coffee pest severely reduces the reproductive success of a threatened endemic plant species. We argue that such effects may be more common than suggested by the literature, especially when crop and native plants are congeneric. In the long term, such negative effects may degrade natural habitats, thereby causing ecosystem services derived from these habitats to decline.

Restoring coastal habitat using marsh terracing: The effect of cell size on nekton use

Marsh terracing is used to restore coastal wetlands by converting shallow nonvegetated bottom to intertidal marsh. Terraces are constructed from excavated bottom sediments, and are commonly arranged in a checkerboard pattern of square cells with open corners to form terrace fields. In 1999, terrace cells of three sizes (large = 122 m sides with 1.30 ha ponds; medium = 61 m sides with 0.29 ha ponds; small = 30 m sides with 0.06 ha ponds) were incorporated into a restoration project constructed at Galveston Island State Park, Texas, USA. This restoration project provided an opportunity to examine how nekton populations and the cost effectiveness of terracing projects vary with cell size. We compared nekton density and biomass (as measures of habitat value) in marsh and open water habitat types among the three cell sizes of the terrace fields. We also compared the habitat value of these terrace fields with the area before project construction, with nearby nonvegetated bottom, and with natural marsh habitat. Nekton abundance and biomass increased substantially in the project area following restoration by marsh terracing. An analysis of post-construction samples detected few statistically significant differences in animal density and biomass among cell sizes or between the terraced areas and adjacent natural habitats. Within terrace cells, density, biomass, and species richness were generally higher in marsh vegetation than over nonvegetated bottom. Using these post-construction density data, GIS, and population models for selected fishery species, we show that populations of most fishery species increase as cell size decreases. However, as cell size decreases, the cost of terrace construction increases much faster than population size. Therefore, terrace fields constructed of medium or large cells would be more cost effective in providing fishery habitat than would terraces composed of small cells.

Community homogenization and the invasiveness of commensal species in Mediterranean afforested landscapes

The ecological consequences of homogenization remain relatively unexplored. One example of landscape-homogenizing is the establishment of plantations. We studied the effect of human-made forests by contrasting plant and small-mammal community composition between planted tree stands and adjacent natural habitat in two different Mediterranean habitats in Israel: (1) inland habitat where we focused on pine (Pinus halepensis) and carob (Ceratonia siliqua) stands, and (2) coastal sand dune habitat where we focused on planted acacia (Acacia saligna) stands. We first wanted to verify whether planted trees modify plant species composition, and second, if and how the small-mammal community is affected by the different habitat conditions created in plantations with different canopy cover. We were especially interested in the abundance of the commensal house mouse (Mus musculus). All tree stands underwent biotic homogenization indicated by abundance of house mice coupled with lower diversity of indigenous vegetation and small-mammal abundances and diversities. Habitat structural diversity was positively related with small-mammals diversity and was lower in artificial tree stands in both habitats. Our results suggest that using the abundance of commensal generalist species such as the house mouse relative to other more specialist small-mammals is a good approach to determine ecosystem integrity. Pre-commercial thinning treatment is a potential management tool to maintain a proportion of native tree species within the canopy of planted tree stands. However, until sufficient data is available for making generalizations, the exact level of thinning necessary to reverse the homogenization processes in man-made plantations and keeping indigenous small-mammal communities diverse and less prone to invasion must be determined empirically.

The urban fire ant paradox: native fire ants persist in an urban refuge while invasive fire ants dominate natural habitats

In contrast to the widespread extirpation of native fire ants (Solenopsis geminata) across southern US following the invasion by imported red fire ants (S. invicta), some residential areas of Austin form unexpected refuges for native fire ants. Ironically, these urban environments provide refuges for the native fire ants while adjacent natural habitats have been overrun by invasive fire ants. Resistance to invasive fire ants in these urban areas occurs mainly in older residential properties constructed prior to the S. invicta invasion, while more recent construction has allowed establishment by S. invicta. The invasive ability of S. invicta is often attributed to escape from parasitoids and efficient dispersal of polygyne multiple queen colonies. Here we also show the importance of landscape parameters in the invasion process, where low levels of disturbance and continuous plant cover in older residential areas form possible barriers to colonization. Dense leaf cover (high NDVI) was also found to be associated with native ant refuges. Long term residential land ownership may have resulted in lower recent disturbance levels and increased plant cover that support refuges of native fire ants.

Differential recruitment of benthic communities on neighboring artificial and natural reefs

Shedding light on the ability of benthic artificial reef (AR) communities to resemble those of a natural reef (NR) is of great importance if we are to harness ARs as tools for rehabilitation and restoration of degraded marine habitats. Studying recruitment processes to experimental settlement plates attached to ARs and NRs reveal the factors that shape community structure at the two reef types, and determine the ability of an AR to support communities similar to those found in adjacent natural habitats. In this study, conducted in Eilat (Red Sea), we used settlement plates to test the hypothesis that differences in benthic communities between ARs and NRs are derived from differential recruitment processes. A monitoring period of 18 months revealed great differences in the recruitment of corals and other benthic communities between the studied ARs and adjacent NRs. The ARs were either made of PVC or metal and 10–17 years old when the study commenced. The recruitment of soft corals reflected the species assemblage found in the area, consisting mainly of the family Nephtheidae and Xeniidae, species, while that of stony corals was mostly determined by the life history traits of the recruited taxa, e.g., the opportunistic nature of the family Pocilloporidae. Benthic organisms, mainly filter feeders like bryozoans, bivalves, sponges and tunicates, were more abundant at the ARs than at the NRs, mainly on the underside of the plates. We suggest that this differential recruitment resulted from a synergistic effect of abiotic and biotic factors, including current regime, sedimentation load and larval settlement preferences, which subsequently differentiated the composition of the benthic communities at the ARs and NRs. Thus, in order to construct an AR for restoration purposes, it must offer similar structural features to those found in the natural surrounding, leading to recruitment of local taxa. However, if the AR and NR will differ structurally, the composition of recruits will also differ and eventually the communities at the two reef types will become distinct, hereby increasing the species diversity in the area.

Spillover edge effects: the dispersal of agriculturally subsidized insect natural enemies into adjacent natural habitats

The cross-edge spillover of subsidized predators from anthropogenic to natural habitats is an important process affecting wildlife, especially bird, populations in fragmented landscapes. However, the importance of the spillover of insect natural enemies from agricultural to natural habitats is unknown, despite the abundance of studies examining movement in the opposite direction. Here, we synthesize studies from various ecological sub-disciplines to suggest that spillover of agriculturally subsidized insect natural enemies may be an important process affecting prey populations in natural habitat fragments. This contention is based on (1) the ubiquity of agricultural-natural edges in human dominated landscapes; (2) the substantial literature illustrating that crop and natural habitats share important insect predators; and (3) the clear importance of the landscape matrix, specifically distance to ecological edges, in influencing predator impacts in agroecosystems. Further support emerges from theory on the importance of cross-boundary subsidies for within site consumer-resource dynamics. In particular, high productivity and temporally variable resource abundance in agricultural systems are predicted to result in strong spillover effects. More empirical work examining the prevalence and significance of such natural enemy spillover will be critical to a broader understanding of fragmentation impacts on insect predator-prey interactions.

Invasion of Pinus halepensis from plantations into adjacent natural habitats

Questions: Do invasions of P. halepensis (Aleppo pine) from plantations into adjacent natural communities occur in the Mediterranean region, where the species is native? What are the spatio-temporal processes involved in pine invasions in contrasting Mediterranean and semi-arid climatic regions? Location: Mediterranean and semi-arid regions of Israel. Methods: The density of invading Pinus was measured in relation to the distance from the plantation edge. Plants were categorized by age, height, basal stem girth and developmental stage, their spatial distribution was also recorded. Results: Analysis of plant age distribution indicates that the invasion process started when the plantations were 20-25 years old. Most invading plants were found within 20 m from the plantation edge, but a few individuals reached distances up to 100 m and became new invasion foci. Plant density declined sharply with distance from adult trees, data showing a better fit to a power model than to a negative exponential model. Invading Pinus began to produce cones earlier in the semi-arid than in the Mediterranean region (9 vs 12 years to 50% reproductive plants). In both regions, higher densities of invading plants were found on the west side of the plantation, the opposite direction to the hot winds that prevail during seed release. Conclusion: The frontal advance of P. halepensis from plantations is relatively slow, but the populations also expand by a saltation process, creating spreading ‘islands’ of pine trees in the natural vegetation. Spatial pattern of recruits with distance from the source population was remarkably similar to the pattern of seed dispersal in the same region (Nathan et al. 1999). This implies that the probability of a dispersed seed developing into a plant is independent of the distance from the forest edge.

Revirstruktur och häckningsframgång hos ett unikt bestånd av skärpiplärka Anthus petrosus littoralis i hamnmiljö

A unique Rock Pipit Anthus petrosus littoralis population was established in an industrial environment in the harbour of Varberg in the late 1980s. It rose to 17 territories in 1994, then declined to extinction in 2004. In a detailed study (1993—1996), 57 territories were found (41 breeding pairs, 8 non-breeding pairs, and 8 unpaired males). Most nests lay on the ground but several up to 5.5 m above ground. 52 clutches were found: 38 first clutches, 19 failed; 9 replacement clutches, 6 failed; 5 true second clutches, 4 failed. 65% of the failures were caused by predators. Fledging success was 1.6 young per breeding attempt and 2.2 per breeding pair. 61% of males, 40% of females, but only 1% of fledglings returned to the study area in the following spring, adults always to the same territory. The establishment of this unique harbour population may be explained by habitat deterioration (higher vegetation, bushes), possibly enhanced by increasing predation, in adjacent natural coastal habitats. Later, harbour development and pavement of former weedy feeding grounds, and the high depredation of nests, explains the decline and extinction of the harbour population.

Tracing the wild genetic stocks of crop plants

A number of attempts have recently been made to identify the wild populations that form the founder germplasm stock of our crop plants (Huen et al. 1997; Molina-Cano et al. 1999; Ladizinsky 1999; Zhou et al. 1999; Badr et al. 2000). Some of these works were based mainly on comparative analyses and statistical treatments of genomic DNA polymorphism data (Huen et al. 1997; Molina-Cano et al. 1999; Zhou et al. 1999). This approach can lead to biased or, at times, conflicting conclusions because the criteria for comparisons are traits that are polymorphic both in the wild and among the cultivated material. Therefore, the end result of these comparisons is a set of values expressing relative difference (or similarity) between the accessions studied, presented in most cases as a dendrogram or set of dendrograms. Therefore, any relative approach analyses using isozyme, random amplified polymorphic DNA (RAPD), restriction fragment length polymorphism (RFLP), amplified fragment length polymorphism (AFLP), simple sequence repeats (SSR), or single nucleotide polymorphisms might yield different results when carried out under similar conditions. The inconclusiveness of the genetic distance approach has been demonstrated in several crops, of which lentil is one example. Ranges of genetic similarity among accessions of cultivated lentil (Lens culinaris Medikus), its wild progenitor subsp. orientalis (Boiss.) Hand.-Mazz., and a more distantly related L. odemensis Ladiz. are 0.71–1.00, 0.76–1.00, and 0.75–0.95, respectively, with 0.76–1.00 between the cultivated lentil and its wild progenitor and 0.75–0.95 between the cultivated lentil and L. odemensis (Hoffman et al. 1986). Another difficulty in using relative genetic distance to identify the wild genetic stock of a crop plant is the genetic bottleneck typical of most domestication events (Ladizinsky 1985). Usually, domesticated crops are thought to have originated as a result of mutations in the seed dispersal loci of a few individuals. In a wild population encompassing high DNA polymorphism, such mutations did not necessarily occur in the most frequent DNA morph at any one locus. Genetic distance analysis was recently utilized to suggest Morocco as a centre of origin of domesticated barley (Hordeum vulgare L.) (Molina-Cano et al. 1999). The main problem with this contention has to do with the identification of the so-called wild barley (Hordeum spontaneum C. Koch) from Morocco. These populations were collected in a restricted area in the Djebel Siroua range, where they grow exclusively in cultivated fields and never spread into the adjacent natural habitats dominated by the wild desert plant Artemisia herba-alba Asso. (Molina-Cano et al. 1982). Moreover, in their analysis these authors included a tough rachis type, indicating their failure to take into account the differences between wild and domesticated plant forms. Yet another disturbing point (in addition to the title), is the conclusion suggesting Morocco as a possible centre of origin of cultivated barley. It is hard to understand how the high level of internal similarity of the Moroccan barley, which is likely to be a mere result of a founder effect (Ladizinsky 1985), supports such a conclusion. In our view, the spontaneous barley types from Morocco originated from back mutations in one or two of the brittlerachis genes (bt1, bt2) of cultivated barley grown in that area. This would provide a plausible explanation for the high degree of internal similarity of the Moroccan barley, its adaptation to cultivated fields, and its inability to survive in the surrounding natural habitats (Molina-Cano et al. 1982). Recently, AFLP markers were used to estimate genetic distance between wild and cultivated barley (Badr et al. 2000). In this study, accessions from Israel, Jordan, Lebanon, Syria, Turkey, Iraq, Iran, northern Africa, central Asia, and the Himalayas were compared. Interestingly, the hypothesis of Molina-Cano et al. (1999) regarding Morocco as a center of origin of cultivated barley was not confirmed by Badr et al. (2000). Based on their DNA marker analyses, Badr et al. (2000) suggest that certain populations in the central and northern parts of Israel along with several Jordanian populations are the possible origin of cultivated barley. Inspection of the number of Israeli and Jordanian accessions versus the numbers of lines from the rest of the geographic regions relative to the actual area of the respective territories reveals the following: Israel and Jordan, while holding less than one thirtieth of the area of the other regions, are represented by 132 wild accessions. The remainder of the wild barley distribution range (including northern Africa, central Asia, the Himalayas, Turkey, Iran, Iraq, Syria, and Lebanon) are represented by 185 accessions. Had the Israeli–Jordanian wild barley genepool been represented by merely 6 lines in accordance with its relative area, what might have been the

Migratory Aphid (Hemiptera: Aphididae) Habitat Selection in Agricultural and Adjacent Natural Habitats

Paired suction traps were used to study the habitat choice of migrating aphids in adjacent crop and natural habitats in east central Illinois. Traps were placed in a row-crop field and a restored prairie for 4 yr at one site, and a row-crop field and a wooded plot for 3 yr at another. Row crops were corn or soybean, rotated annually. We did not wish to sample aphids that were native to the local habitats because they would be in a habitat by circumstance of birth, and not necessarily by choice. We therefore removed from the habitat choice analysis any aphid species that colonize plants in either the agricultural or natural habitat. Numbers of aphids from outside sources in the two adjacent habitats were compared. In 2 of 4 yr, outside-source aphids were more abundant in the row-crop than the restored prairie, despite the absence of potential host plants in both habitats. In all 3 yr, outside-source aphids were trapped in greater numbers in the crop than in the woods. Selection of the crop over the natural habitat occurred during almost all sampling periods throughout the summers. We present possible explanations for the aphids’ apparent preference for crop habitats and provide brief discussions of abundant aphids, local—as well as outside—source species, trapped in our study. We also discuss the relevance of our study to the understanding of long- and short-distance aphid migration and aphid vectoring of plant pathogens.

Fish assemblage on natural versus vertical artificial reefs: the rehabilitation perspective

Artificial reefs have been suggested as a potential tool for the restoration of marine habitats. In the present study, the fish assemblage established around the oil jetties of Eilat (northern Red Sea, Israel) was compared to those found in three adjacent natural reef habitats: two in a nature reserve (one shallow and one deep) and a third deep site located near the city. Both species richness and fish abundance were found to be significantly higher around the vertical structures of the jetty's pillars than at all three natural sites, with the lowest values at the site closest to the city. The higher species richness at the jetties may be explained by (1) the vertical relief and high complexity of the jetty which offers a variety of niches for both shallow and deep coral reef species, and (2) by the reduction in available niches at the natural sites as a result of coral destruction due to anthropogenic activity. The pronounced difference in fish abundance is attributed mainly to the high seasonal recruitment at the jetty which was much lower at the natural sites. We therefore suggest that vertical structures are more attractive to fish settlement and recruitment than moderately sloped bottoms such as those found at the fringing reefs of Eilat. High similarity (51 to 56%) was found between fish assemblages at the natural sites while relatively low similarity (27 to 37%) was found between the jetty and the natural reefs. The jetty's complex vertical artificial structures can serve as a model for future construction of artificial reefs designed to restore the fish community in areas where the natural reefs have been damaged. It should be taken into account, however, that these do not necessarily mimic the natural environment but may rather establish a community of their own, which is influenced by the spatial orientation and complexity of the structure.

Wildlife conservation in urban greenways of the mid-southeastern United States

Goals related to wildlife conservation are stated or implied in many urban greenway plans, but the actual wildlife conservation value of urban greenways is unclear. We surveyed 72 km. of greenway consisting of 38 different greenway segments in six cities in the mid-southeastern United States to determine the presence or absence of red fox (Vulpes vulpes), grey fox (Urocyon cinereoargenteus), and white-tailed deer (Odocoileus virginianus), and to assess characteristics of the greenways and adjacent lands that might promote or limit the presence of these species in each greenway. We focused on fox and deer because these mammals, while habitat generalists, require diverse habitats within close proximity, and are more sensitive to human disturbance and have larger territories than the majority of urban wildlife in this region. Thus, they can serve as indicator species for these habitat values in urban greenways in the southeastern United States. Field observations and scent station inventories revealed that only 18 of the 38 greenway segments had either fox or deer, 12 had only fox, 6 had fox and deer, and none had deer alone. Greenway segments with more forest cover, wider corridors, greater amounts of adjacent natural or seminatural habitat, and forest connectivity between greenways and nonadjacent natural areas were more likely to have fox or deer present. Characteristics associated with fox and deer presence were not independent of each other. Because greenways with such characteristics tend to be surrounded by less urban areas, adjacent land use is a good predictor of fox and deer presence in the surveyed greenways. Whether greenways that are beneficial to fox and deer can be developed in urban settings is strongly site specific, because the greenway variables that appear most essential to these species are often dictated by the preexisting urban form and the vegetation in the vicinity of the greenway. Because the wildlife conservation value of urban greenways depends greatly on factors external to the greenway, greenways that have fox and deer present today may be particularly vulnerable to future changes in surrounding land use.

Mycorrhizas in the Kakadu region of tropical Australia

Bioassays were used to provide estimates of both the distribution and abundance of mycorrhizal fungus propagules in soils from mine sites and natural habitats in tropical Australia. These bioassays measured mycorrhizal formation by bait plants that were grown in intact cores of soil collected along a transect at each site. The mine sites included, had sparse, patchy or dense vegetation cover on waste-rock materials that would initially have been devoid of mycorrhizal fungus propagules. The natural habitats included eucalypt savanna sites which had been subjected to hot annual fires for 4 years or remained unburnt. Propagules of vesicular-arbuscular mycorrhizal (VAM) and ectomycorrhizal (ECM) fungi occurred in all sites, but were sporadically distributed in highly disturbed areas, where they were associated with patches of vegetation. Both the relative abundance and frequency of occurrence of inoculum of VAM and ECM fungi increased with vegetation cover in older disturbed sites. Propagules of VAM fungi were substantially more numerous in some mine site habitats with dense vegetation cover, than in adjacent natural habitats. The presence of substantial amounts of phosphorus, released from weathering rock, in mine waste rock materials may have reduced the requirement of plants for mycorrhizal associations during vegetation establishment in mine sites. In woodland sites, hot annual fires appeared to restrict ECM fungi to infrequent patches in the surface horizon, while ECM fungus inoculum was much more frequently detected in soil from the unburnt site. These fire regimes apparently had less effect on the distribution or quantity of VAM fungus inoculum.

Polychaete larval settlement: Correspondence of patterns in suspended jar collectors and in the adjacent natural habitat in Monterey Bay, California1

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