Some population parameters of Ruditapes philippinarum (Bivalvia,Veneridae) on the southern coast of the Marmara Sea,Turkey

Ruditapes philippinarum, a venerid clam, is a dominant species in the sandy and muddy areas in the coastal waters of the Marmara Sea. Intensive commercial harvesting of this species is conducted in these regions. We studied the population dynamics of R. philippinarum on the southern coast of the Marmara Sea (Band?rma). Samples were collected on a monthly basis between September 2012 and August 2013. Seasonal von Bertalanffy growth parameters using the length–frequency distribution of R. philippinarum were estimated at L _∞ = 67.50 mm and K = 0.33 year^?1, and the seasonal oscillation in growth rate was 0.53. The slowest growth period was in January. The growth performance index and potential lifespan were 3.182 and 8.06 years, respectively. The growth relationship was confirmed to have a positive allometric pattern. The average total mortality rate was estimated to be 0.777 year^?1, whereas the natural and fishing mortality rates were 0.539 and 0.238 year^?1, respectively. The current exploitation rate of R. philippinarum was 0.306. The recruitment pattern peaked during June–August, and spawning occurred between May and August. The results of this study provide valuable information on the status of R. philippinarum stocks.     

Biomass dynamics in a logged forest: the role of wood density

Wood density (WD) is believed to be a key trait in driving growth strategies of tropical forest species, and as it entails the amount of mass per volume of wood, it also tends to correlate with forest carbon stocks. Yet there is relatively little information on how interspecific variation in WD correlates with biomass dynamics at the species and population level. We determined changes in biomass in permanent plots in a logged forest in Vietnam from 2004 to 2012, a period representing the last 8 years of a 30 years logging cycle. We measured diameter at breast height (DBH) and estimated aboveground biomass (AGB) growth, mortality, and net AGB increment (the difference between AGB gains and losses through growth and mortality) per species at the individual and population (i.e. corrected for species abundance) level, and correlated these with WD. At the population level, mean net AGB increment rates were 6.47 Mg ha^?1 year^?1 resulting from a mean AGB growth of 8.30 Mg ha^?1 year^?1, AGB recruitment of 0.67 Mg ha^?1 year^?1 and AGB losses through mortality of 2.50 Mg ha^?1 year^?1. Across species there was a negative relationship between WD and mortality rate, WD and DBH growth rate, and a positive relationship between WD and tree standing biomass. Standing biomass in turn was positively related to AGB growth, and net AGB increment both at the individual and population level. Our findings support the view that high wood density species contribute more to total biomass and indirectly to biomass increment than low wood density species in tropical forests. Maintaining high wood density species thus has potential to increase biomass recovery and carbon sequestration after logging.     

Bottlenecks to coral recovery in the Seychelles

Processes that affect recovery of coral assemblages require investigation because coral reefs are experiencing a diverse array of more frequent disturbances. Potential bottlenecks to coral recovery include limited larval supply, low rates of settlement, and high mortality of new recruits or juvenile corals. We investigated spatial variation in local abundance of scleractinian corals in the Seychelles at three distinct life history stages (recruits, juveniles, and adults) on reefs with differing benthic conditions. Following widespread coral loss due to the 1998 bleaching event, some reefs are recovering (i.e., relatively high scleractinian coral cover: ‘coral-dominated’), some reefs have low cover of living macrobenthos and unconsolidated rubble substrates (‘rubble-dominated’), and some reefs have high cover of macroalgae (‘macroalgal-dominated’). Rates of coral recruitment to artificial settlement tiles were similar across all reef conditions, suggesting that larval supply does not explain differential coral recovery across the three reef types. However, acroporid recruits were absent on macroalgal-dominated reefs (0.0 ± 0.0 recruits tile^?1) in comparison to coral-dominated reefs (5.2 ± 1.6 recruits tile^?1). Juvenile coral colony density was significantly lower on macroalgal-dominated reefs (2.4 ± 1.1 colonies m^?2), compared to coral-dominated reefs (16.8 ± 2.4 m^?2) and rubble-dominated reefs (33.1 ± 7.3 m^?2), suggesting that macroalgal-dominated reefs have either a bottleneck to successful settlement on the natural substrates or a high post-settlement mortality bottleneck. Rubble-dominated reefs had very low cover of adult corals (10.0 ± 1.7 %) compared to coral-dominated reefs (33.4 ± 3.6 %) despite no statistical difference in their juvenile coral densities. A bottleneck caused by low juvenile colony survivorship on unconsolidated rubble-dominated reefs is possible, or alternatively, recruitment to rubble-dominated reefs has only recently begun. This study identified bottlenecks to recovery of coral assemblages that varied depending on post-disturbance habitat condition.     

Tree dynamics of a fire-protected <Emphasis Type="Italic">cerrado sensu stricto</Emphasis> surrounded by forest plantations,over a 13-year period (1991–2004) in Bahia,Brazil

Structural and floristic changes of a fire-protected cerrado sensu stricto are described over a 13-year period. The study site is located in a biological reserve (2,800 ha) surrounded by large Pinus spp. and Eucalyptus spp. plantations (36,000 ha), in southwestern Bahia, Brazil. The region occurs in the outer-core of the Cerrado domain, near the Cerrado-Caatinga ecotone, and is mainly occupied by pasture and cropland. Surveys were carried out in 1991 and 2004 in 13 permanent plots (20 × 50 m). Stems with diameter ≥5 cm at 0.30 m above ground level were identified and measured. Floristic changes were significant (Sørensen´s index = 0.45). Species number rose from 62 to 84 (35.48%). Alpha diversity increased significantly (P > 0.001). New species migrated to the area, and there was an expansion of many fire-sensitive species. Woody layer expanded, increasing 19.09% in density and 14.93% in basal area. Diameter distributions followed a “reversed-j” pattern on both occasions, but differed (P > 0.05) due to a significant increase in the first two size-classes, indicating a high recruitment. Community dynamics was high and had a positive balance between recruitment (3.72% yr^?1) and mortality (1.93% yr^?1). Conversely, mean annual increment was very small, 0.096 cm yr^?1 (SD = 0.14; N = 808). Most species, including many dominant ones, had a positive balance in favor of recruitment and low turnover, indicating that although species immigration rate is high (1.42 spp ha^?1), structural changes in species composition happens at a much slower pace. The surrounding forest plantations are permeable and do not limit species immigration; and may be connecting the reserve with the larger neighboring natural fragments, providing an abundant source for diaspores, and possibly neutralizing any fragmentation effects. Succession is also influenced by the ecotonal condition. The structure and floristics of the cerrado sensu stricto at this site (under present climatic conditions) is fire-dependent.     

Nitrogen budgets of urban lawns under three different management regimes in southern California

We constructed nitrogen (N) budgets for the lawns of three simulated residences built to test the environmental impacts of three different residential landscape designs in southern California. The three designs included: a “Typical” lawn planted with cool season tall fescue (Schedonorus phoenix), fertilized at the recommended rate for this species (192 kg^?1 ha^?1 year^?1) and irrigated with an automatic timer; a design intended to lower N and water requirements (“Low Input”) with the warm season seashore paspalum (Paspalum vaginatum) fertilized at 123 kg^?1 ha^?1 year^?1 and irrigated with a soil moisture-based system; and a design incorporating local best practices (“Low Impact” lawn) that included the native sedge species Carex, fertilized at 48 kg^?1 ha^?1 year^?1 and irrigated by a weather station-based system. Plant N uptake accounted for 33.2 ± 0.5 (tall fescue), 53.7 ± 0.7 (seashore paspalum), and 12.2 ± 1.3 % (Carex) of annual N inputs, while estimated N retention in soil was relatively large and similar in the three lawns (41–46 %). At lower N and water inputs than Typical, Low Input showed the highest annual clipping yield and N uptake, although it also had higher denitrification rates. Leaching inorganic N losses remained low even from the Typical lawn (2 %), while gaseous N losses were highly variable. The Low Input lawn was most efficient in retaining N with relatively low water and N costs, although its fertilization rates could be further reduced to lower gaseous N losses. Our results suggest that the choice of a warm-season, C₄ turf species with reduced rates of irrigation and fertilization is effective in this semi-arid region to maintain high productivity and N retention in plants and soils at low N and water inputs.     

Nine years of climber community dynamics in a Nigerian lowland rain forest 31 years after a ground fire

Successional studies in tropical forests have generally emphasized the tree component, ignoring the community dynamics of non-tree life-forms, and so there is a limited understanding of how the plant community as a whole is changing during succession within forests. Thus, this study examined the changes in climber community composition and structure in a regenerating secondary lowland rain forest at Ile-Ife that was ravaged by a ground fire 31 years ago using six sample plots. All individual climbers in each sample plot were identified, enumerated and their girths at breast height were measured. The girths were measured at 1.3 m height or just before the point of branching. Our data were compared with those of previous studies in the forest to determine the changes in floristics and structure of climber community over the years using Sorenson’s similarity index. The mortality and recruitment rates in the forest during the course of succession were determined. Climber species increased from 49 (2005) to 61 (2014). Climber density increased astronomically from 448–1152 ha^?1 (2005) to 1712–4492 ha^?1 but basal area only increased slightly from 0.37–1.10 m² ha^?1 (2005) to 0.40–1.14 m² ha^?1. The recruitment rate (8%) was higher than the mortality rate (5.8%). The similarity of the climber species composition calculated using the Sorenson similarity index showed that the similarity between the two periods of study was 0.53 (53%). This study concluded that during the study period, the climber community changed, and climber species abundance and structure increased.     

Carbon sequestration in freshwater wetlands in Costa Rica and Botswana

Tropical wetlands are typically productive ecosystems that can introduce large amounts of carbon into the soil. However, high temperatures and seasonal water availability can hinder the ability of wetland soils to sequester carbon efficiently. We determined the carbon sequestration rate of 12 wetland communities in four different tropical wetlands—an isolated depressional wetland in a rainforest, and a slow flowing rainforest swamp, a riverine flow-through wetland with a marked wet and dry season, a seasonal floodplain of an inland delta—with the intention of finding conditions that favor soil carbon accumulation in tropical wetlands. Triplicate soil cores were extracted in these communities and analyzed for total carbon content to determine the wetland soil carbon pool. We found that the humid tropic wetlands had greater carbon content (P ≤ 0.05) than the tropical dry ones (96.5 and 34.8 g C kg^?1, respectively). While the dry tropic wetlands had similar sequestration rates (63 ± 10 g Cm^?2 y^?1 on average), the humid tropic ones differed significantly (P < 0.001), with high rates in a slow-flowing slough (306 ± 77 g Cm^?2 y^?1) and low rates in a tropical rain forest depressional wetland (84 ± 23 g Cm^?2 y^?1). The carbon accumulating in all of these wetlands was mostly organic (92–100%). These results suggest the importance of differentiating between types of wetland communities and their hydrology when estimating overall rates at which tropical wetlands sequester carbon, and the need to include tropical wetland carbon sequestration in global carbon budgets.     

The evaluation of the role of pelagic invertebrate versus vertebrate predators on the seasonal dynamics of filtering Cladocera in a shallow, eutrophic reservoir

An evaluation of the role of invertebrate (Leptodora kindtii) versus vertebrate (juvenile fish) predators in the dynamics of filtering zooplankton (Daphnia sp.) in the pelagic zone of the Sulejow Reservoir was conducted during summer from 1994 to 1996. Leptodora kindtii appeared in high densities (mid-July: 2–6 ind. l^?1) in the pelagic zone. Its predation impact on the dominant filtering zooplankter population Daphnia cucullata, expressed by consumption, was significant and accounted for a reduction of 10 to 51% of Daphnia biomass. Although D. cucullata was a preferred food of juvenile pikeperch in June, due to low biomass, these fish were able to eliminate daily only 0.1–5.4% of Daphnia biomass in the pelagic zone. Thus, the role of juvenile fish in the midsummer decline of D. cucullata density in the pelagic zone seems to be much smaller than that of Leptodora kindtii.     

Population dynamics and production of the small copepod Oithona spp. in a subarctic fjord of West Greenland

The small cyclopoid copepod Oithona is widely occurring in polar areas; however, knowledge of its biology and ecology is very limited. Here, we investigate the population dynamics, vertical distribution, and reproductive characteristics of Oithona spp. from late winter to summer, in a subarctic fjord of West Greenland. During winter–early spring, the abundance of Oithona spp. was low (1.8 × 10³ ind. m^?2) and the population was mainly composed of late copepodites and adults, whereas in summer, abundance peaked and younger stages dominated (1.1 × 10⁶ ind. m^?2). In general, all stages of Oithona spp. remained in the upper 100 m, with nauplii exhibiting a shallower distribution. Although no general seasonal migration was found, a deeper distribution of the adult females in winter was observed. The mean clutch size of Oithona spp. varied from 16 to 30 eggs per female, peaking in summer. Egg production rates (EPR) were low in winter–early spring (0.13 ± 0.03 eggs female^?1 day^?1) and reached maximum values in summer (1.6 ± 0.45 eggs female^?1 day^?1). EPR of Oithona spp. showed a significantly positive relationship with both temperature and protozooplankton biomass, and the development of the population seemed to be appreciably affected by temperature. Oithona spp. remained active throughout the study, stressing the key importance of these small copepods in high-latitude ecosystems, especially in periods when larger copepods are not present in the surface layer.     

Recruitment bottlenecks in the rare Australian conifer Wollemia nobilis

Seedling survival plays a critical role in maintaining a supply of potential recruits. We examined seedling recruitment, survival and growth in Wollemia nobilis, a rare, long-lived Australian conifer. Wollemia nobilis seedlings and juveniles were monitored for 16 years (1996–2011). While W. nobilis can recruit from seed and, unlike most conifers, persist through resprouting, seed-based recruitment was the primary focus of this study. Sixty-five per cent of new seedlings died within their first year and only 7 % persisted for the 16-year monitoring period. However, 44 % of established juvenile plants (of unknown age at the beginning of the study) persisted throughout the 16-year monitoring period. Growth of seedlings and juveniles was very slow; growth estimates for most individuals had 95 % confidence intervals that included zero. The recruitment strategy of W. nobilis may be to maintain a slow-growing juvenile bank—a strategy typical of other shade-tolerant rainforest trees, including other Araucariaceae. Seedling recruitment in W. nobilis may act together with resprouting to maintain the population.     

Demography of the long‐lived conifer Agathis ovata in maquis and rainforest,New Caledonia

Abstract. The endemic New Caledonian conifer Agathis ovata occurs as an emergent tree in fire‐prone shrublands (maquis), and fire‐sensitive rainforest. Growth, survivorship and recruitment over 5 yr were compared for populations from forest and maquis on ultramafic substrates in New Caledonia to investigate whether demographic behaviour varied in response to the strongly contrasting forest and shrubland environments. Growth of seedlings and of small (30–100 cm height) and large (100 cm height; 5 cm DBH) saplings was slow, but varied significantly among stages, site types and years. The greatest difference in growth rates was among stages, seedlings growing 0.34 cm.yr^?1, small saplings 1.06 cm.yr^?1 and large saplings 2.13 cm.yr^?1. Tree DBH increased by only 0.05 cm.yr^?1 and, based on these rates, individuals with DBH of 30 cm are estimated to be more than 700 yr old. Few trees (3.5%) produced cones in any year and seedling recruitment was low, but some recruitment was recorded each year in both maquis and forest. Rates of recruitment per parent were highest in forest (1.28.yr^?1, cf 0.78.yr^?1), but the higher density of trees in maquis meant that overall recruitment was greater there (92 ha^?1.yr^?1, cf 56 ha^?1.yr^?1). Seedling mortality ranged from 0.9 to 2.9% among years with no significant difference between maquis and forest. No sapling mortality was recorded, but annual tree mortality ranged from 0 to 1.4%. Evidence from a recently burned site indicated that while trees may survive fire, seedlings and saplings do not. Post‐fire seedling recruitment per ha from surviving trees was four times lower than in unburned sites, but growth rates were four times higher. Similar demographic attributes, including high survivorship, low growth rate and low rates of recruitment over a long reproductive life, characterize Agathis ovata populations in both maquis and rainforest in New Caledonia and are indicative of a broad tolerance of light environments that is unusual among tree species. These demographic attributes help to explain the long‐term persistence of the species in these strongly contrasting habitats.     

Dynamics of a <Emphasis Type="Italic">Limecola</Emphasis> (<Emphasis Type="Italic">Macoma</Emphasis>) <Emphasis Type="Italic">balthica</Emphasis> population in a tidal flat area in the western Wadden Sea: effects of declining survival and recruitment

We followed the dynamics of the population of the bivalve Limecola (Macoma) balthica in the westernmost part of the Wadden Sea by monitoring for 44 years (1973–2016) its numbers and age composition at 15 sites in a 50-km² tidal-flat area. During the first half of this period, the annual recruitment and adult survival were at a relatively constant level, resulting in rather constant numbers. During the second half of the observation period, annual recruitment and adult survival showed declining trends, resulting in seriously reduced adult abundance. Sudden substantial reductions in adult survival started around 1996 at a few sites to spread over the entire area within 5 years, like an infectious disease. The resulting small adult stocks produced small numbers of recruits. The stock–recruitment curve showed an increasing part up to about 30 adults m^?2, followed by invariably successful recruitments at > 40 adults m^?2. Both recruitment and adult survival were negatively related to water temperatures. However, elevated temperatures after 1997 could not explain the very low survival rates observed after 1996 and the very low recruitment success after 2003. So far, recovery of the population has hardly taken place, with both recruitment and adult survival at lower levels than observed for the initial stable period.     

Demographic Drivers of Aboveground Biomass Dynamics During Secondary Succession in Neotropical Dry and Wet Forests

The magnitude of the carbon sink in second-growth forests is expected to vary with successional biomass dynamics resulting from tree growth, recruitment, and mortality, and with the effects of climate on these dynamics. We compare aboveground biomass dynamics of dry and wet Neotropical forests, based on monitoring data gathered over 3–16 years in forests covering the first 25 years of succession. We estimated standing biomass, annual biomass change, and contributions of tree growth, recruitment, and mortality. We also evaluated tree species’ contributions to biomass dynamics. Absolute rates of biomass change were lower in dry forests, 2.3 and 1.9 Mg ha^?1 y^?1, after 5–15 and 15–25 years after abandonment, respectively, than in wet forests, with 4.7 and 6.1 Mg ha^?1 y^?1, in the same age classes. Biomass change was largely driven by tree growth, accounting for at least 48% of biomass change across forest types and age classes. Mortality also contributed strongly to biomass change in wet forests of 5–15 years, whereas its contribution became important later in succession in dry forests. Biomass dynamics tended to be dominated by fewer species in early-successional dry than wet forests, but dominance was strong in both forest types. Overall, our results indicate that biomass dynamics during succession are faster in Neotropical wet than dry forests, with high tree mortality earlier in succession in the wet forests. Long-term monitoring of second-growth tropical forest plots is crucial for improving estimates of annual biomass change, and for enhancing understanding of the underlying mechanisms and demographic drivers.     

Photosynthetic and respiratory responses of Gracilaria parvispora from the southeastern Gulf of California

Photosynthetic and respiratory responses (P–E curves) of Gracilaria parvispora from the southeast Gulf of California were studied at four temperatures (20, 25, 30, 35 °C) and salinity (25, 30, 35, 40 psu) combinations. The alga showed acclimation in its photosynthetic and respiratory responses to tropical temperature as well as to oceanic salinity. A positive effect of temperature on photosynthetic rate (P _max) was observed for all salinities. Photosynthetic rates for treatments at 20 and 25 °C were lower (<9.2 mg O₂?g dry weight (dw)^?1?h^?1) than for treatments at 30 and 35 °C (>12 mg O₂ g dw^?1?h^?1). G. parvispora showed limited tolerance to low salinities (25 psu) and low temperatures (20 °C) and the interaction between temperature and salinity was significant (analysis of variance, P?<?0.05). Responses to salinity indicated adaptation to oceanic salinity. Photosynthetic responses were lower at 25 psu than at higher salinities. The lowest P _max values (6.2–8.2 mg O₂?g dw^?1?h^?1) were observed at the lowest salinity (25 psu) regardless of temperature. Compensation and saturation irradiances (26–170 and 57–149 μmol photons m^?2?s^?1, respectively) indicate adaptation to lower irradiances in shallow (1–2 m depth) habitats, where turbidity can be high, and the capacity of shade adaptation has been developed. Results suggest distribution of this species is mainly related to salinity or temperature. The potential mariculture efforts of G. parvispora would be limited by low temperatures in winter, and indicate that this species will probably not be able to spread further due to low temperatures (<15 °C) in the upper part of the Gulf of California.     

A stable isotope (δ 2H) approach to deriving origins of harvested woodcock (Scolopax rusticola) taken in France

A crucial but elusive aspect of the effective conservation and management of migratory birds is the determination of which regions or habitats contribute to the recruitment of juvenile birds into the adult breeding population or, in the case of hunted species, the annual harvest. Although ring recoveries have provided important information for several game species, limitations of this approach include the bias to only marked populations and the tremendous scale of effort required to recover enough individuals. Here, we explored the use of an intrinsic marker, the stable hydrogen isotope composition of feathers (δ ²H_f) of juvenile woodcock (Scolopax rusticola), as a means of assigning birds to natal origin using a woodcock-specific δ ²H_f isoscape. We applied this approach to 987 juvenile woodcock during the winters of 2005–2006 and 2006–2007, and 1875 juvenile woodcock sampled during autumn migration of 2005 and 2006. We used a likelihood-based assignment approach to determine origins from four regions. Considering only the feather isotope data, the majority (50 %) were assigned to origins in the Baltic—Western European Russia region (including western Russia) and 44 % assigned to central European origins. Few (6 %) were considered residents in France and <1 % were assigned to northern Fennoscandia and northern European Russia. Using the amount of forest cover available within zones as a prior resulted in greater emphasis on origins in the Baltic and western European Russia (62 %) and less emphasis (29 %) on central Europe as a potential origin. We also depicted origins of birds on a continuous isoscape surface which emphasised more extant forests of central and eastern Europe and western Russia. Results were relatively similar regardless of whether we considered samples collected during migration versus those collected during the wintering period. Spatial assignment of 51 woodcock sampled in Switzerland was consistent with the Baltic and central Europe. Our results are in general agreement with ring-recovery data and emphasise the utility of an isotope approach to assignment of gamebirds to origin.     

Present population and habitat status of potentially threatened Asian horseshoe crabs <Emphasis Type="Italic">Tachypleus tridentatus</Emphasis> and <Emphasis Type="Italic">Carcinoscorpius rotundicauda</Emphasis> in Hong Kong: a proposal for marine protected areas

While there are persistent calls for developing more marine protected areas (MPAs) for Asian horseshoe crab conservation in response to population declines in Asia–Pacific region, most existing horseshoe crab MPAs were designated without prior comprehensive population assessment and habitat characterization. This study collected biological and habitat information in Hong Kong, in order to identify priority sites for conservation and management of Asian horseshoe crab populations. The territory-wide surveys at 18 spawning/nursery beaches displayed a persistently low mean juvenile density from 0.16 to 2.19 ind/100 m² in 2012 and 0.08 to 1.41 ind/100 m² in 2014. These density data were within the same range of that in 2002 and 2007 (0.10–1.97 ind/100 m²), apart from a low survey return of 0.08–0.31 ind/100 m² in 2004. The current population of juvenile T. tridentatus and C. rotundicauda in Hong Kong is estimated about 2100–4300 and 2400–3000 individuals, respectively. From the 2012–2014 data, no new recruitments of 1st–3rd instar juveniles were found, as the shores were occupied mostly by 6th–9th instar juveniles of prosomal width between 23 and 45 mm, in which considerably high mortality rates were noted. The present findings of existing small and discrete juvenile populations, coupled with relatively few recruits, suggest that the status of juvenile horseshoe crabs in Hong Kong is fragile and vulnerable to local extirpation, especially if no urgent protection measures are implemented. Based on available population data and habitat characteristics, three MPAs, ranging from 5 to 7 km², are proposed, so as to conserve over 60 and 70 % of the existing juvenile populations of T. tridentatus and C. rotundicauda, respectively. The approach adopted in this study may serve as a case study for proposing other horseshoe crab MPAs in Asia, where increasing human disturbances and over-harvest are imminent.     

Migration and habitat use of the tropical eels Anguilla marmorata and A. bicolor pacifica in Vietnam

The patterns of use of marine and freshwater habitats by the tropical anguillid eels Anguilla marmorata and A. bicolor pacifica were examined by analysing the otolith strontium (Sr) and calcium (Ca) concentrations of yellow (immature) and silver (mature) stage eels collected in Vietnamese waters. In A. marmorata, the change in the Sr:Ca ratios outside the high Sr:Ca core was generally divided into three patterns: (1) typical catadromous life history pattern; (2) constant residence in brackish water; and (3) habitat shifting between sea and brackish waters with no freshwater life. In A. bicolor pacifica, no eels had a general life history as freshwater residents. The eels were also divided into three patterns: (1) constant residence in sea water; (2) constantly living in brackish water; and (3) habitat shifting from brackish to sea water with no freshwater residence. The mean Sr:Ca ratio value after recruitment to coastal waters ranged from 1.73 to 5.67 × 10^?3 (mean 3.2 × 10^?3) in A. marmorata and from 2.53 to 6.32 × 10^?3 (mean 4.3 × 10^?3) in A. bicolor pacifica. The wide range of otolith Sr:Ca ratios in both species indicated that the habitat use of these tropical eels was facultative among fresh, brackish, and marine waters during their growth phases after recruitment to coastal areas. Tropical eel species may have the same behavioural plasticity as temperate anguillid species regarding whether to enter freshwater or to remain in estuarine and marine environments.     

Arbuscular mycorrhizal fungi affect seedling recruitment: a potential mechanism by which N deposition favors the dominance of grasses over forbs

Background and aims

Nitrogen (N) deposition usually alters plant community structure and reduces plant biodiversity in grasslands. Seedling recruitment is essential for maintaining species richness and determines plant community composition. Arbuscular mycorrhizal fungi (AMF) are widespread symbiotic fungi and could facilitate seedling establishment. Here we conducted an experiment to address whether the influence of AMF on seedling recruitment depends on N addition and plant species.

Methods

Leymus chinensis were cultivated for 5 months in the microcosms that were inoculated with or without AMF at five N addition rates. Seeds of three main species (two C₃ grasses and one non-N₂-fixing forb) of the Eurasian steppe were sown to the 5-month-old microcosms. Seedling establishment was estimated by shoot biomass, N and P contents 7 weeks after seedling germination.

Results

AMF promoted seedlings recruitment of two C₃ grasses at addition rates above 0.5 g N m^?2. In contrast, seedling recruitment of the non-N₂-fixing forb was increased by AMF at addition rates below 0.5 g N m^?2 but was decreased above 2.5 g N m^?2.

Conclusions

These results partly explain why N addition favored the dominance of grasses over forbs in perennial grassland communities. Our study indicates that AMF have the potential to influence plant community composition by mediating revegetation in the face of N deposition.     

Post-biological control invasion trajectory for Melaleuca quinquenervia in a seasonally inundated wetland

The recruitment and mortality of Melaleuca quinquenervia seedlings were evaluated over a 3-year period in a seasonally inundated wetland in the western Everglades region. The mean (±SE) density of seedlings/saplings m^?1 declined from 64.8 (±4.5) to 0.5 (±0.2) over the 3 years, a population reduction of 99.2%. Four distinct water regimes characterized this site: dry, dry to wet transition, flooded, and wet to dry transition. Seedling recruitment was highest in the dry to wet transition and lowest in the flooded water regime, while mortality was highest under flooded and dry water regimes. The mean estimate of population growth (λ) across water regimes was 0.64 ± 0.05 indicating negative population growth. Elimination of introduced insect herbivores using insecticides did not reduce mortality of recruited M. quinquenervia seedlings/saplings indicating that direct herbivory was not responsible for the decline in seedling density. On the other hand, a mean of only 0.2 (±0.03) viable seeds m^?2 d^?1 fell into the plots, an amount considerably lower than in previous studies. We submit that change in the invasion trajectory M. quinquenervia was most likely caused by reduced seed inputs from aerial seed banks depleted by insect herbivory rather than direct herbivory on seedlings. This may indicate a fundamental alteration of M. quinquenervia population dynamics ultimately resulting in a less invasive and, therefore, less ecologically damaging species.     

Therapeutic efficacy in BALB/C mice of extract from marine alga <Emphasis Type="Italic">Canistrocarpus cervicornis</Emphasis> (Phaeophyceae) against herpes simplex virus type 1

Studies with diterpenes from marine brown alga Canistrocarpus cervicornis showed the antiviral potential of the products from this alga in controlling the replication of HSV-1 and maintaining low cytotoxicity. Hence, the aim of this work was to evaluate the anti-herpetic efficacy of C. cervicornis extract ointment in BALB/c mice. To test the anti-herpetic efficacy in vivo, four groups of BALB/c mice (n?=?5) were used: 1—untreated, 2—extract ointment (2 % or 0.4 mg cm^?2 dose^?1), 3—Acyclovir cream (5 % or 1.0 mg cm^?2 dose^?1), and 4—ointment base. The right midflank of each mouse was clipped and depilated with a chemical depilatory. After 2 days, the skin area was scratched and inoculated with HSV-1. The ointments and cream were applied three times a day over a 16-day period, beginning 1 h after virus inoculation. The development of skin lesions was continuously monitored and scored. To evaluate the effect of C. cervicornis topical treatment on biochemical parameters and on body weight, two uninfected groups were formed: an untreated group and a group treated with ointment C. cervicornis extract (2 %). The signs of infection appeared from the second day after infection, while on the 10th day of the experiment, the ointment base and untreated groups had significantly more severe lesions than did the groups that were treated with extract (p?<?0.05) or acyclovir (p?<?0,01). The topical application of extract ointment did not change body weight, hepatic, or renal function suggesting that the extract has a low toxicity in this route of administration. These results suggest that the extract may be useful in reducing the severity of HSV-1 cutaneous lesions.