Food choice in Siganus fuscescens: influence of macrophyte nutrient content and availability

Using multiple-choice feeding experiments, the selection of six species of macrophytes by the herbivorous rabbitfish Siganus fuscescens was examined. The rabbitfish showed distinct food choice in the laboratory; however, selection of macrophytes by S. fuscescens was not related to their absolute nutrient content (nitrogen, carbon, energy and ash free dry mass). Nutrient assimilation estimates showed that the macrophytes which were most preferred were those that S. fuscescens assimilated best. In S. fuscescens, the macrophytes that were preferred passed through the gut significantly faster than the less preferred species. Gut transit time had a significant effect on the absolute value of a food item in terms of net nutrient gain per unit time. This study showed that food value could be inferred from the absolute nutrient content of the macrophytes. Thus both the ability to assimilate nutrients as well as the absolute nutrient content of macrophytes must be quantified when assessing food value. (C) 2004 The Fisheries society of the British Isles.

Cannibalism in juvenile blue-swimmer crabs Portunus pelagicus (Linnaeus, 1766): effects of body size, moult stage and refuge availability

Factors influencing the rate of cannibalism in juvenile blue-swimmer crabs Portunus pelagicus were investigated under controlled conditions using time-lapse video recordings. This study was undertaken to improve blue-swimmer crab culture and experimentally addressed (1) prey vulnerability (2) cannibal-victim interactions, and (3) activity patterns of juveniles in varying degrees of refuge. Crabs used in the study were aged 15 weeks and sorted into two size classes; small (less than or equal to 60 mm carapace width (CW)) and large (greater than or equal to65 mm CW) of a similar sex ratio. Vulnerability and thus survival was influenced by body size variation, moult stage and refuge availability. Crabs with carapace width less than or equal to 60 mm were more vulnerable than larger individuals, as indicated by significant differences in survival rates. As predicted, juveniles in transition stages associated with ecdysis were especially vulnerable. Premoult (redliner) crabs appeared to be in a high state of agitation as evidenced by the frequency of agonistic encounters and this may be a contributing factor to the high mortality observed at this critical premoult stag. increases in refuge density increased survival of juveniles proportionally, indicating that the quantity of shelter is important for reducing cannibalism in this species. Cannibal-victim interactions were frequently asymmetrical in terms of size and moult stage. Cannibals were significantly heavier than victims, and were predominantly at intermoult stage. Sexual biases among cannibals and victims were not found in this study. Activity patterns of juveniles were influenced by the experimental conditions. Crabs provided with high refuge showed reduced aggressive activity and increased time spent resting, but unchanged locomotion or feeding activity. Regular grading as well as the presence of suitable shelter for newly moulted crabs is recommended for improving culture of P. pelagicus. Research into inducing synchronous moulting may also yield promising results. (C) 2004 Elsevier B.V. All rights reserved.

Water and nutrient availabilities do not affect lignotuber growth and sprouting ability of three eucalypt species of south-eastern Queensland

Shoot biomass and lignotuber size of seedlings of three eucalypt species, Eucalyptus acmenoides Schauer, E. siderophloia Benth. and Corymbia variegata [syn. E. maculata (F. Muell.)K. D. Hill and L. A. S. Johnson], were measured for glasshouse-grown seedlings established under two water and nutrient regimes. Seedlings were subjected to shoot removal (clipping) at ages from 9 to 19 weeks, and transferred to the high water treatment for a further 8 weeks to assess shoot emergence from lignotubers. Seedling shoot biomass was greater in both the high than the low nutrient and water treatments, but lignotuber diameter was not affected significantly. C. variegata seedlings had the largest lignotuber diameters, followed by E. siderophloia and E. acmenoides, respectively. Although growth of shoots was influenced by nutrient availability, results suggest that species differences in the growth of lignotubers was less affected. It is suggested that lignotuber growth was strongly influenced by genotype. More than 70% of C. variegata seedlings clipped at 9 weeks sprouted, compared with only 5 and 10% of seedlings of E. siderophloia and E. acmenoides, respectively. All C. variegata seedlings sprouted after being clipped at 19 weeks, but < 80% of E. siderophloia and < 60% of E. acmenoides sprouted when clipped at the same age. It was concluded that seedlings forming part of the regeneration stratum in dry sclerophyll forests need to be protected from damage for at least 4 months (for C. variegata) or at least 6 months (for E. siderophloia and E. acmenoides) if they are to survive by sprouting from lignotubers.

Direct seeding to restore rainforest species: Microsite effects on the early establishment and growth of rainforest tree seedlings on degraded land in the wet tropics of Australia

Reforestation in tropical areas is usually attempted by planting seedlings but, direct seeding (the artificial addition or sowing of seed) may be an alternative way of accelerating forest recovery and successional processes. This study investigated the effects of various sowing treatments (designed to create different microsite conditions for seed germination) and seed sizes on the early establishment and growth of directly sown rainforest tree species in a variety of experimental plots at three sites in the wet tropical region of north-cast Queensland, Australia. The different sowing treatments were found to have significant effects on seedling establishment. Broadcast sowing treatments were ineffective and resulted in very poor seedling establishment and high seed wastage. Higher establishment rates occurred when seeds were buried. Seed size was found to be an important factor affecting establishment in relation to micro-site condition. In general, larger seeded species had higher establishment rates at all three sites than species of small and intermediate seed size, but only in sowing treatments where seeds were buried. Overall these results suggest that direct sowing of seed can be used as a too] to accelerate recolonisation of certain rainforest tree species on degraded tropical lands, but initial success will be dependent on the choice of sowing method and its suitability for the seed types selected. The results also indicate that the recruitment of naturally dispersed tree species at degraded sites is likely to be severely limited by the availability of suitable microsites for seed germination. Consequently the natural recovery of degraded sites via seed rain can be expected to be slow and unpredictable, particularly in areas where soil compaction has occurred. (c) 2006 Elsevier B.V. All rights reserved.

Diurnal polyp expansion behavior in stony corals may enhance carbon availability for symbionts photosynthesis

Photosynthesis of zooxanthellate stony corals may be limited by inorganic carbon at high irradiances. We demonstrated that oxygen consumption of expanded corals is higher than that of contracted corals in both night-expanding and day-expanding corals. It is assumed that at the single-polyp level, the expansion of tentacles increases the surface area for solute exchange with the surrounding water, which may alleviate potential carbon limitation and excess oxygen levels in the tissue under high irradiance. We investigated this hypothesis using stable carbon isotope (613 C) analysis of coral species from the Red Sea exhibiting different morphologies. delta C-13 ratios in zooxanthellae of branched coral colonies with small polyp size that extend their tentacles during daytime (diurnal morphs) showed lower delta C-13 values in their zooxanthellae - 13.83 +/- 1.45 parts per thousand, compared to corals from the same depth with large polyps, which are usually massive and expand their tentacles only at night (nocturnal morphs). Their algae delta C-13 was significantly higher, averaging - 11.33 +/- 0.59 parts per thousand. Carbon isotope budget of the coral tissue suggests that branched corals are more autotrophic, i.e., that they depend on their symbionts for nutrition compared to massive species, which are more heterotrophic and depend on plankton predation. (c) 2005 Elsevier B.V. All rights reserved.

Fine root respiration in the mangrove Rhizophora mangle over variation in forest stature and nutrient availability

Root respiration uses a significant proportion of photosynthetically fixed carbon (C) and is a globally important source of C liberated from soils. Mangroves, which are an important and productive forest resource in many tropical and subtropical countries, sustain a high ratio of root to shoot biomass which may indicate that root respiration is a particularly important component in mangrove forest carbon budgets. Mangroves are often exposed to nutrient pollution from coastal waters. Here we assessed the magnitude of fine root respiration in mangrove forests in Belize and investigated how root respiration is influenced by nutrient additions. Respiration rates of excised fine roots of the mangrove, Rhizophora mangle L., were low (4.01 +/- 0.16 nmol CO2 g(-1) s(-1)) compared to those measured in temperate tree species at similar temperatures. In an experiment where trees where fertilized with nitrogen (N) or phosphorus (P) in low productivity dwarf forests (1-2 m height) and more productive, taller (47 m height) seaward fringing forests, respiration of fine roots did not vary consistently with fertilization treatments or with forest stature. Fine roots of taller fringe trees had higher concentrations of both N and P compared to dwarf trees. Fertilization with P enhanced fine root P concentrations in both dwarf and fringe trees, but reduced root N concentrations compared to controls. Fertilization with N had no effect on root N or P concentrations. Unlike photosynthetic C gain and growth, which is strongly limited by P availability in dwarf forests at this site, fine root respiration (expressed on a mass basis) was variable, but showed no significant enhancements with nutrient additions. Variation in fine root production and standing biomass are, therefore, likely to be more important factors determining C efflux from mangrove sediments than variations in fine root respiration per unit mass.

The role of disturbance and resource availability in structuring plant communities

Disturbances alter competitive hierarchies by reducing populations and altering resource regimes. The interaction between disturbance and resource availability may strongly influence the structure of plant communities, as observed in the recolonization of seagrass beds in outer Florida Bay that were denuded by sea-urchin overgrazing. There is no consensus concerning the interaction between disturbance and resource availability on competition intensity (CI). On the other hand, species diversity is dependent on both factors. Peaks in species diversity have been observed to occur when both resource availability and disturbance intensity are high, thus implying that CI is low. Based on this supposition of previous models, I presented the resource-disturbance hypothesis as a graphical model to make predictions of CI as a function of both disturbance intensity and the availability of a limiting resource. The predictions of this model were tested in two experiments within a seagrass community in south Florida, in which transplants of Halodule wrightii were placed into near-monocultures of Syringodium filiforme in a full-factorial array. In the first experiment, two measures of relative CI were calculated based on the changes in the short-shoot number (SS) and of rhizome length (RHL) on the transplants. Both light and disturbance were identified as important factors, though the interaction between light * disturbance was not significant. Relative CISS ranged between 0.2 and 1.0 for the high light and high disturbance treatments and the relative CIRHL < 0 for the same treatments, though results were not significantly different due to high variability and low sample size. These results, including a contour schematic using six data points from the different treatment combinations, preliminarily suggests that the resource-disturbance hypothesis may be used may be used as a next step in developing our understanding of the mechanisms involved in structuring plant communities. Furthermore, the focus of the model is on the outcome of CI, which may be a useful predictor of changes in species diversity. Further study is needed to confirm the results of this study and validate the usefulness of this model in other systems. ^

Leaf morphology scales multi-annual trends in nutrient cycling and leaf, flower, and fruiting phenology among species in the sub-tropical hardwood forests of the northern Florida Keys

The subtropical hardwood forests of southern Florida are formed by 120 frost-sensitive, broadleaved angiosperm species that range throughout the Caribbean. Previous work on a series of small sized forest component patches of a 20 km2, forest preserve in northern Key Largo indicate that a shift in species composition was associated with a 100 year forest developmental sequence, and this shift was associated with an increasingly evergreen canopy. This document investigates the underlying differences of the biology of trees that live in this habitat, and is specifically focused on the impact of leaf morphology on changing nutrient cycling patterns. Measurements of the area, thickness, dry mass, nutrient content and longevity of several leaves from 3-4 individuals of ten species were conducted in combination with a two-year leaf litter collection and nutrient analysis to determine that species with thicker, denser leaves cycled scarce nutrients up to 2-3 times more efficiently than thin leaved tree species, and the leaf thickness/density index predicts role in forest development in a parallel direction as the index predicts nutrient cycling efficiency. A three year set of observations on the relative abundance of new leaves, flowers and fruits of the same tree species provides an opportunity to evaluate the consequences the leaf morphology/nutrient cycling/forest development relationship to forest habitat quality. Results of the three documents support a mechanistic link between forest development and nutrient cycling, and suggests that older forests are likely to be better habitats based on the availability of valuable forest products like new leaves, flowers, and fruits throughout the year.

Pattern of nutrient availability and plant community assemblage in Everglades Tree Islands, Florida, USA

We address the relative importance of nutrient availability in relation to other physical and biological factors in determining plant community assemblages around Everglades Tree Islands (Everglades National Park, Florida, USA). We carried out a one-time survey of elevation, soil, water level and vegetation structure and composition at 138 plots located along transects in three tree islands in the Park’s major drainage basin. We used an RDA variance partitioning technique to assess the relative importance of nutrient availability (soil N and P) and other factors in explaining herb and tree assemblages of tree island tail and surrounded marshes. The upland areas of the tree islands accumulate P and show low N concentration, producing a strong island-wide gradient in soil N:P ratio. While soil N:P ratio plays a significant role in determining herb layer and tree layer community assemblage in tree island tails, nevertheless part of its variance is shared with hydrology. The total species variance explained by the predictors is very low. We define a strong gradient in nutrient availability (soil N:P ratio) closely related to hydrology. Hydrology and nutrient availability are both factors influencing community assemblages around tree islands, nevertheless both seem to be acting together and in a complex mechanism. Future research should be focused on segregating these two factors in order to determine whether nutrient leaching from tree islands is a factor determining community assemblages and local landscape pattern in the Everglades, and how this process might be affected by water management.

Epiphyte loads on seagrasses and microphytobenthos abundance are not reliable indicators of nutrient availability in oligotrophic coastal ecosystems

Despite marked gradients in nutrient availability that control the abundance and species composition of seagrasses in south Florida, and the importance of nutrient availability in controlling abundance and composition of epiphytes on seagrasses in other locations, we did not find that epiphyte load on the dominant seagrass, Thalassia testudinum, or that the relative contribution of algal epiphytes to the epiphyte community, was positively correlated with nutrient availability in the water column or the sediment in oligotrophic seagrass beds. Further, the abundance of microphytobenthos, as indicated by Chlorophyll-aconcentration in the sediments, was not directly correlated with concentrations of nutrients in the sediments. Our results suggest that epiphyte and microphytobenthos abundance are not unambiguous indicators of nutrient availability in relatively pristine seagrass environments, and therefore would make poor candidates for indicators of the status and trends of seagrass ecosystems in relatively low-nutrient environments like the Florida Keys.

Responses of seagrass communities to fertilization along a gradient of relative availability of nitrogen and phosphorus in a carbonate environment

Patterns of relative nutrient availability in south Florida suggest spatial differences regarding the importance of nitrogen (N) and phosphorus (P) to benthic primary producers. We did a 14-month in situ fertilization experiment to test predictions of N and P limitation in the subtropical nearshore marine waters of the upper Florida Keys. Six sites were divided into two groups (nearshore, offshore) representing the endpoints of an N: P stoichiometric gradient. Twenty-four plots were established at each site with six replicates of each treatment (1N, 1P, 1N1P, control), for a total of 144 experimental plots. The responses of benthic communities to N and P enrichment varied appreciably between nearshore and offshore habitats. Offshore seagrass beds were strongly limited by nitrogen, and nearshore beds were affected by nitrogen and phosphorus. Nutrient addition at offshore sites increased the length and aboveground standing crop of the two seagrasses, Thalassia testudinum and Syringodium filiforme, and growth rates of T. testudinum. Nutrient addition at nearshore sites increased the relative abundance of macroalgae, epiphytes, and sediment microalgae. N limitation of seagrass in this carbonate system was clearly demonstrated. However, added phosphorus was retained in the system more effectively than N, suggesting that phosphorus might have important long-term effects on these benthic communities. The observed species-specific responses to nutrient enrichment underscores the need to monitor all primary producers when addressing questions of nutrient limitation and eutrophication in seagrass communities.

Identification of Conserved Splicing Motifs in Mutually Exclusive Exons of 15 Insect Species

Background: During alternative splicing, the inclusion of an exon in the final mRNA molecule is determined by nuclear proteins that bind cis-regulatory sequences in a target pre-mRNA molecule. A recent study suggested that the regulatory codes of individual RNA-binding proteins may be nearly immutable between very diverse species such as mammals and insects. The model system Drosophila melanogaster therefore presents an excellent opportunity for the study of alternative splicing due to the availability of quality EST annotations in FlyBase. Methods: In this paper, we describe an in silico analysis pipeline to extract putative exonic splicing regulatory sequences from a multiple alignment of 15 species of insects. Our method, ESTs-to-ESRs (E2E), uses graph analysis of EST splicing graphs to identify mutually exclusive (ME) exons and combines phylogenetic measures, a sliding window approach along the multiple alignment and the Welch’s t statistic to extract conserved ESR motifs. Results: The most frequent 100% conserved word of length 5 bp in different insect exons was “ATGGA”. We identified 799 statistically significant “spike” hexamers, 218 motifs with either a left or right FDR corrected spike magnitude p-value < 0.05 and 83 with both left and right uncorrected p < 0.01. 11 genes were identified with highly significant motifs in one ME exon but not in the other, suggesting regulation of ME exon splicing through these highly conserved hexamers. The majority of these genes have been shown to have regulated spatiotemporal expression. 10 elements were found to match three mammalian splicing regulator databases. A putative ESR motif, GATGCAG, was identified in the ME-13b but not in the ME-13a of Drosophila N-Cadherin, a gene that has been shown to have a distinct spatiotemporal expression pattern of spliced isoforms in a recent study. Conclusions: Analysis of phylogenetic relationships and variability of sequence conservation as implemented in the E2E spikes method may lead to improved identification of ESRs. We found that approximately half of the putative ESRs in common between insects and mammals have a high statistical support (p < 0.01). Several Drosophila genes with spatiotemporal expression patterns were identified to contain putative ESRs located in one exon of the ME exon pairs but not in the other.

Morphology and Typification of Mastogloia Smithii and M. Lacustris, with Descriptions of Two New Species from the Florida Everglades and the Caribbean Region

The names Mastogloia smithii Thwaites ex Smith and M. smithii var. lacustris Grunow have been attributed to a variety of related diatom morphologies, partly due to the poor availability of type material and complicated nomenclatural history. The history is detailed, clarifying the type morphologies of M. smithii and reconfirming a neglected elevation of M. smithii var. lacustris to M. lacustris (Grunow) Grunow. Populations reported as M. smithii and M. lacustris from the temperate zone (Ontario, Canada and Iowa and Michigan, USA), karstic wetlands of the subtropical Everglades (Florida, USA) and the tropics (Jamaica, Mexico and Belize) are compared with each other. Based on morphological differences including density of partecta, striae and areolae, M. calcarea sp. nov. and M. pseudosmithii sp. nov. are described from the Everglades and the Caribbean region, and a lectotype of M. smithii and a neotype of M. lacustris are designated.

Projected responses of North American grassland songbirds to climate change and habitat availability at their northern range limits in Alberta, Canada

Across North America, grassland songbirds have undergone steep population declines over recent decades, commonly attributed to agricultural intensification. Understanding the potential interactions between the impacts of climate change on the future distributions of these species and the availability of suitable vegetation for nesting can support improved risk assessments and conservation planning for this group of species. We used North American bioclimatic niche models to examine future changes in suitable breeding climate for 15 grassland songbird species at their current northern range limits along the boreal forest–prairie ecotone in Alberta, Canada. Our climate suitability projections, combined with the current distribution of native and tame pasture and cropland in Alberta, suggest that some climate-mediated range expansion of grassland songbirds in Alberta is possible. For six of the eight species projected to experience expansions of suitable climate area in Alberta, this suitable climate partly overlaps the current distribution of suitable land cover. Additionally, for more than half of the species examined, most of the area of currently suitable climate was projected to remain suitable to the end of the century, highlighting the importance of Alberta for the long-term persistence of these species. Some northern prairie-endemic species exhibited substantial projected northward shifts of both the northern and southern edges of the area of suitable climate. Baird’s Sparrow (Ammodramus bairdii) and Sprague’s Pipit (Anthus spragueii), both at-risk grassland specialists, are predicted to have limited climate stability within their current ranges, and their expansion into new areas of suitable climate may be limited by the availability of suitable land cover. Our results highlight the importance of the preservation and restoration of remaining suitable grassland habitat within areas of projected climate stability and beyond current northern range limits for the long-term persistence of many grassland songbird species in the face of climate change.

The impact of fluctuating light on the dinoflagellate Prorocentrum micans depends on NO3- and CO2 availability

Increasing atmospheric pCO2 and its dissolution into oceans leads to ocean acidification and warming, which reduces the thickness of upper mixing layer (UML) and upward nutrient supply from deeper layers. These events may alter the nutritional conditions and the light regime to which primary producers are exposed in the UML. In order to better understand the physiology behind the responses to the concomitant climate changes factors, we examined the impact of light fluctuation on the dinoflagellate Prorocentrum micans grown at low (1 µmol/L) or high (800 µmol/L) [NO3(-)] and at high (1000 µatm) or low (390 µatm, ambient) pCO2. The light regimes to which the algal cells were subjected were (1) constant light at a photon flux density (PFD) of either 100 (C100) or 500 (C500) µmol/m**2/s or (2) fluctuating light between 100 or 500 µmol photons/m**2/s with a frequency of either 15 (F15) or 60 (F60) min. Under continuous light, the initial portion of the light phase required the concomitant presence of high CO2 and NO3(-) concentrations for maximum growth. After exposure to light for 3h, high CO2 exerted a negative effect on growth and effective quantum yield of photosystem II (F'(v)/F'(m)). Fluctuating light ameliorated growth in the first period of illumination. In the second 3h of treatment, higher frequency (F15) of fluctuations afforded high growth rates, whereas the F60 treatment had detrimental consequences, especially when NO3(-) concentration was lower. F'(v)/F'(m) respondent differently from growth to fluctuating light: the fluorescence yield was always lower than at continuous light at 100 µmol/m**2/s, and always higher at 500 µmol/m**2/s. Our data show that the impact of atmospheric pCO2 increase on primary production of dinoflagellate depends on the availability of nitrate and the irradiance (intensity and the frequency of irradiance fluctuations) to which the cells are exposed. The impact of global change on oceanic primary producers would therefore be different in waters with different chemical and physical (mixing) properties.