Erect Growth Form Research Articles

Spatio-temporal patterns of sponge strandings in the southern Gulf of Mexico: The role of cold front events

Remnants of marine invertebrates are common in the wrack line of the coasts of many regions worldwide. However, little is known about its spatial and temporal variation. This study aimed to investigate the inter-site and intra-annual variability in species composition, abundance, and biomass of sponge strandings on the coast of a southern Gulf of Mexico tropical island. The environmental factors (oceanographic and meteorological) influencing such spatio-temporal variations on abundance and biomass of sponge strandings were also investigated. From a total of 21 demosponge species identified, three species of genus Clathria (with erect growth forms and a small basal area) were dominant in terms of abundance (93%) and biomass (89%). Both, the monthly average abundance and biomass varied significantly throughout the year, with maximum peaks during the cold fronts season. Only in the case of abundance, a combination of four predictor variables (wind speed, wave height, frequency of southeast winds, and frequency of north winds) explained 84.2% of its intra-annual variability. Results also showed that cold fronts (especially the stronger ones), aside from cyclonic events, can act as disruptive events regulating sponge populations in the coastal zone. Regarding the spatial variability, it was attributed to inter-site differences in the degree of exposure to hydrodynamic forces and the type of substrate. This study contributes to the knowledge of the biodiversity of sponge species in this coastal region of the Gulf of Mexico and demonstrates that large-scale seasonal events such as cold fronts can influence their temporal dynamics. • Sponge strandings varied spatio-temporally and erect growth forms were dominant. • Sponge strandings were more abundant during the cold fronts season. • Cold fronts act as disruptive events regulating shallow water sponge populations.

Value of Sedum species as companion plants for nectar-producing plants depends on leaf characteristics of the Sedum

Introducing nectar-producing plants to green roofs and other urban green infrastructure has been attempted to support pollinator activities. Green roofs can be drought-prone, placing limitations on the success of plant growth and nectar production in the absence of irrigation. Plant species differ greatly in water usage patterns, so companion planting with low and high water users has been proposed to increase performance of high water use species, including species important for urban pollinators. Additionally, crassulacean acid metabolism (CAM) plants such as Sedum tend to have low water usage and are reported to improve health condition of neighbors. However, Sedum species differ in morphological and physiological traits such as leaf shapes and the speed at which they switch to CAM, resulting in water usage differences during drought that could affect neighboring plants. This study quantifies the effects of companion planting with CAM plants (Sedum album, Sedum kamtschaticum) on nectar-producing plants (Fagopyrum esculentum, Trifolium repens), focusing on target plant growth form and leaf traits of neighboring Sedum. The health condition of F. esuculentum and soil water contents were improved significantly when they were planted together with S. album, which has small leaves and rapid CAM induction. Therefore, suppression of evapotranspiration of neighboring CAM plants could have positive effects on erect growth form nectar species. In contrast, the health condition of T. repens, which shows prostrate growth, was not affected by neighboring CAM plant species. Judging from these results, growth characteristics including leaf traits of neighboring Sedum and growth forms of the target plants could be important factors determining the effects of companion planting in urban green infrastructure.

A taxonomic evaluation of the Thesium confine species complex (Santalaceae)

Background: Thesium L. is the largest genus in the family Santalaceae (sandalwood family). The last taxonomic revision of the southern African species dates back to 1925. An urgent revision of the genus is required as indicated in a recent national biosystematics research strategy for South Africa.Objectives: To revise the Thesium confine species complex (Thesium durum, T. confine and Thesium spartioides) and to update the typification, nomenclature, descriptions and distribution ranges.Method: Morphological characters were studied using own field collections as well as herbarium specimens from K, NU, PRE and PRU and images on Global Plants (JSTOR). Distribution ranges of the studied species were updated.Results: An examination of morphological characters revealed great similarity between T. spartioides and T. confine. Both species have an herbaceous habit, decumbent growth form, terminal (or less frequently axillary) inflorescences and a sympatric northern distribution in South Africa. Thesium durum differs from T. spartioides and T. confine in having a shrubby habit, erect growth form and axillary inflorescences and occurs in the southern part of South Africa.Conclusion: Thesium spartioides is synonymised under T. confine, and T. durum is retained as a separate species.

Do invasive species live faster? Mass‐specific metabolic rate depends on growth form and invasion status

AbstractInvasive organisms often share characteristics that make them successful. Traits such as rapid growth and short generation times are classic “weed” phenotypes, such that invasive species often have r‐selected rather than k‐selected life histories. Given that invasive species often display “fast” life histories, invasive species may have relatively higher metabolic rates but systematic tests across taxa are lacking.We compared metabolic rate across 14 sessile invasive and native marine invertebrates. We also investigated the influence of growth form (erect vs. flat species) on the metabolic rate of these species, since growth form can also affect metabolic rate.For species with an erect growth form, we found an effect of invasive status on mass‐specific metabolic rate. Invasive species had much higher mass‐specific metabolic rates than native species and this was particularly pronounced for organisms with smaller body masses.Given that smaller‐bodied invasive organisms are typically early‐successional, “fugitive” species, a higher metabolic rate may allow a faster pace of life, enhancing their capacity to invade and reproduce in newly created disturbed habitats.Aplain language summaryis available for this article.

Diatom communities on commercial biocidal fouling control coatings after one year of immersion in the marine environment

Little is known about the effect of commercial biocidal fouling control coatings on fouling diatom communities and their growth forms after long periods of exposure in the marine tropical environment. The current study investigated the abundance and composition of fouling diatom communities developed on 11 commercially available biocidal antifouling coatings, covering the three main technology types in recent historic use (Self-Polishing Copolymers, Self-Polishing Hybrid and Controlled Depletion Polymers) after one year of static immersion at two locations in Muscat, Oman (Marina Shangri La and Marina Bandar Rowdha). Light microscopy demonstrated that the total abundance of diatoms and the relative abundance of growth forms were significantly affected by the choice of biocidal antifouling coating and experimental location. Using scanning electron microscopy, a total of 21 diatom genera were identified which were grouped into adnate, motile, plocon and erect growth forms. The adnate growth forms, mainly the genera Amphora, Cocconeis and Mastogloia, dominated the other growth forms in terms of their relative abundance. Current results revealed the importance of exposure location and choice of biocidal antifouling coating on the relative abundance of diatom growth forms.

Do low oxygen environments facilitate marine invasions? Relative tolerance of native and invasive species to low oxygen conditions.

Biological invasions are one of the biggest threats to global biodiversity. Marine artificial structures are proliferating worldwide and provide a haven for marine invasive species. Such structures disrupt local hydrodynamics, which can lead to the formation of oxygen-depleted microsites. The extent to which native fauna can cope with such low oxygen conditions, and whether invasive species, long associated with artificial structures in flow-restricted habitats, have adapted to these conditions remains unclear. We measured water flow and oxygen availability in marinas and piers at the scales relevant to sessile marine invertebrates (mm). We then measured the capacity of invasive and native marine invertebrates to maintain metabolic rates under decreasing levels of oxygen using standard laboratory assays. We found that marinas reduce water flow relative to piers, and that local oxygen levels can be zero in low flow conditions. We also found that for species with erect growth forms, invasive species can tolerate much lower levels of oxygen relative to native species. Integrating the field and laboratory data showed that up to 30% of available microhabitats within low flow environments are physiologically stressful for native species, while only 18% of the same habitat is physiologically stressful for invasive species. These results suggest that invasive species have adapted to low oxygen habitats associated with manmade habitats, and artificial structures may be creating niche opportunities for invasive species.

Impact of a harbour construction on the benthic community of two shallow marine caves

Marine caves are unique and vulnerable habitats, threatened by multiple global and local disturbances. Whilst the effects of climate change on marine caves have already been investigated, no information exists about the effects of local human impacts, such as coastal development, on these habitats. This study investigated the impact of the construction of a touristic harbour on two shallow underwater marine caves in the Ligurian Sea (NW Mediterranean). As a standard methodology for monitoring marine caves does not exist yet, changes over time on the benthic community were assessed adopting two different non-taxonomic descriptors: trophic guilds and growth forms. Harbour construction caused an increase of sediment load within the caves, with a consequent decline of filter feeder organisms. Abundance of small organisms, such as encrusting and flattened sponges, was greatly reduced in comparison to organisms with larger and erect growth forms, such as domed mounds and pedunculated sponges. Our study indicated that growth forms and trophic guilds are effective descriptors for evaluating changes over time in marine caves, and could be easily standardised and applied in monitoring plans. In addition, as the harbour construction impacted differently according to the cave topography, the use of a systematic sampling in different zones of an underwater cave is recommended.

Community structure of epiphytic diatoms on seaweeds in Northeastern Brazil

Abstract Epiphytic diatoms associated with three species of seaweeds, the phaeophyte Bachelotia antillarum, the ulvophyte Caulerpa verticillata, and the rhodophyte Haloplegma duperreyi, were investigated in the subtidal zone of Northeastern Brazil. A total of 54 diatom species were recorded, distributed among motile (24 species), erect (20 species), and adnate growth forms (five species), in addition to accidental occurrences (five species). Although motile diatoms showed the highest number of species, erect growth forms were the most abundant, accounting for 69% of the entire epiphytic diatom cell abundance. The total abundance ranged from 29,783 to 45,842 cells g-1 wet weight (ww), with Melosira moniliformis (erect), Rhabdonema adriaticum (erect), Cocconeis scutellum (adnate), and Surirella fastuosa (motile) as the most abundant species. The results confirmed qualitative and quantitative differences between the hosts with a greater shape diversity in B. antillarum whose thalli (filamentous-like tufts) offered an increased surface area for colonization mainly by epiphytic erect growth forms.

Vertical concentration gradients of heavy metals in Cladonia lichens across different parts of thalli

Certain lichens of the genus Cladonia are effective heavy-metal-tolerant colonisers of strongly contaminated and disturbed sites. Among them, Cladonia cariosa, Cladonia pyxidata and Cladonia rei are the major components of specific cryptogamic assemblages proven to be bioindicators of soil pollution. This study examines the bioaccumulation capacity and heavy metal accumulation pattern of these species in the context of element concentration levels in various parts of their thalli at various vertical distances from the ground. The content of Zn, Pb, Cd, As and Cu in primary squamules, lower and upper parts of secondary thalli (podetia), and fruiting bodies (apothecia), as well as the corresponding substrate, was analysed using the AAS method. The substrate turned out to be the main source of heavy metals in the examined Cladonia lichens. Element accumulation in particular parts of thalli greatly depends on metal enrichment in the immediate vicinity while Cu/Zn ratios for both substrate and lichen samples were very low and comparable within the species. Concentration levels in thalli usually decrease significantly with distance from the substrate. The exception is copper, which content was frequently higher in apothecia than in the upper parts of podetia. Low bioaccumulation factors calculated for the examined Cladonia specimens classified these lichens as weak accumulators of heavy metals. Even given an extremely high level of contaminants in the substrate, the upper parts of thalli are not greatly affected. Consequently, fruticose and erect growth form, in combination with low accumulation capacity and a remarkable decrease in metal content along a vertical gradient, may be an important attribute of Cladonia lichens in the colonisation of a highly contaminated substrate. The content of elements differs significantly between particular parts of Cladonia thalli; this should be taken into account whenever burdens of heavy metals are used as indicators in biomonitoring studies.

Benthic algal resilience to frequent wet-season storm flows in low-order streams in the Australian tropical savanna

AbstractStorm-flow disturbances are frequent during the wet season of Australian tropical savannas. We examined benthic algal resistance and resilience in open-canopy streams in the Daly River watershed. Storm flows occurred every 2 to 3 d at 1st- to 4th-order sites, with sharp rises and falls and relatively long periods of shallow, low-turbidity base flow. At a 5th-order site, storm-flow duration was longer and base flows were deeper and more turbid. We hypothesized that: 1) storm flow would dislodge benthic algal biomass, 2) baseflow biomass would be low, 3) taxon richness would be low, and 4) algal composition would be dominated by resistant algae with prostrate or erect growth forms or by fast growing colonizing algae. Hypothesis 1 was supported. Storm flows dislodged ∼93% of epilithic biomass. Support for hypothesis 2 was equivocal. At the 5th-order site, sand mobility prevented establishment of benthic algae until seasonal flows receded. At the other sites, epilithon net growth rates were much great...

The growth form of dominant grasses regulates the invasibility of Uruguayan grasslands

In this paper we report the results of a small‐scale experiment on patches of natural grasslands in Uruguay. We analyzed whether growth form of C4 grasses affects invasion success. The experimental plots represented three patch‐types arising from short‐term grazing effects and were dominated by prostrate C4 grasses, erect C4 grasses and codominated by prostrate C4 grasses and forbs. We seeded the plots with four exotic species: one perennial C4 grass, one annual C3 grass, one perennial forb and one annual legume. Contrary to many studies conducted at small spatial scales, our results suggest that in our system, the processes that control invasibility are not directly linked with resident species richness or biomass, but rather are driven by growth form. Emergence of invaders did not differ among patch‐types, but seedlings survived less in plots dominated by erect grasses. We suggest that the erect growth form of C4 grass species is more successful in preventing invasion by mediating seedling competition for light under the canopy for a longer period of time. Grazing management, through its ability to regulate canopy architecture, is a potentially important tool in controlling invasion.

Experimental test of plant defence evolution in four species using long‐term rabbit exclosures

Summary Plant defence traits have evolved over macro‐ and microevolutionary time‐scales in response to herbivores. Although a number of studies have investigated the evolutionary impacts of herbivores over short time‐scales, few studies have experimentally examined what defence traits most commonly evolve and whether multiple coexisting species exhibit similar evolutionary responses to herbivores. We addressed these questions using a long‐term experiment at Silwood Park, England, United Kingdom, where we excluded rabbits from 38 grassland plots for <1–34 years. To assess the evolutionary impacts of rabbits on plant defence traits, we collected seeds from plots containing the following perennial species: Anthoxanthum odoratum (Poaceae), Festuca rubra ssp. rubra (Poaceae), Holcus lanatus (Poaceae) and Stellaria graminea (Caryophyllaceae). We then grew these plants in a common garden and measured defensive and morphological traits. We found some evidence for evolutionary change of defence traits in three of the four species following the exclusion of rabbits. We observed the clearest changes in F. rubra, which showed a 9% decline in tolerance to herbivory and a 26% decline in leaf number. We also observed weak evidence for a change in all grass species towards a more erect growth form suggesting that grazing selects for plants that grow close to the ground. Although our results are most consistent with evolution due to changes in the frequency of alleles and genotypes, we cannot rule out that epigenetic changes (e.g. methylation) or maternal environmental effects also contributed to or caused the observed long‐term phenotypic responses. Synthesis. Our study provides an experimental test of the evolutionary effects of an ecologically important herbivore. We found evidence for plant defence evolution following >20 years of rabbit exclusion. However, the evidence was only strong in one species for multiple traits, weak in all three grass species for avoidance and absent in an herb species. This suggests that the evolutionary effects of an ecologically important herbivore on plants will be variable and difficult to predict in nature.

Bucklandiella seppeltii, a new species of Grimmiaceae from Australasia, and its phylogenetic position based on molecular data

A new species, Bucklandiella seppeltii Bednarek-Ochyra, Ochyra, Sawicki & Szczecinska, is delimited by its distinct morphology and biogeography. The geographical range of the new species is restricted to the southern-temperate and southern-cool-temperate zones of Tasmania and New Zealand, with maximum occurrence on the South Island of the latter insular country. The species is described and illustrated and its distribution is mapped. The systematic position of B. seppeltii is revealed to be a sister to New Zealand B. allanfifei Bednarek-Ochyra & Ochyra by molecular evidence based on parsimony analysis of nuclear sequences. In some morphological and anatomical traits, B. seppeltii is similar to southern South American cool-temperate B. heterostichoides (Cardot) Bednarek-Ochyra & Ochyra but is distinct by its smooth laminal cells, strict hyaline leaf hair points, erect growth form, and very broadly recurved leaf margin in the distal portion.

Upper Ordovician (Sandbian) bryozoan fauna from Argentine Precordillera

A stenolaemate bryozoan fauna containing 20 species belonging to 18 genera is described from the Las Plantas and Las Aguaditas formations (Upper Ordovician, Sandbian) in San Juan Province, Precordillera of Western Argentina. One genus with one species is new:Argentinodictya lenticulatan. gen. n. sp. (Cryptostomata, Ptilodictyina). Four species are new: one trepostomeParvohallopora parvulan. sp., two cryptostomesTrigonodictya parvulan. sp. andPtilodictya intermedian. sp., and phyloporinineChasmatopora rossaen. sp. The bryozoan assemblage of the Las Plantas Formation is more diverse than that of the Las Aguaditas Formation. Fourteen species are restricted to the Las Plantas Formation, five species occur in both formations, and one species is restricted to the Las Aguaditas Formation. Erect growth forms are dominant in the studied fauna. The majority of bryozoan taxa display palaeobiogeographic relations to Sandbian–Katian deposits of North America, with two species also known from the Katian of Europe.

Increasing heterogeneity of sensitive assemblages as a consequence of human impact in submarine caves

Submarine caves are considered as a top priority for conservation, but the effects of common pressures are poorly known for these habitats. Here, we examined the effect of recreational human visitation on a selection of submarine caves in a Mediterranean Marine Protected Area (40°35′40″N; 8°11′39″E) where diving activities are regulated. Sampling was conducted in visited and not visited caves to assess whether diving activities have a significant effect on cave habitats, what are the components of biodiversity most affected by this disturbance, and its potential effects on spatial heterogeneity of benthic assemblages. Results clearly showed that human visitation could significantly affect spatial patterns of benthic assemblages. Organisms with erect growth forms were significantly more abundant and homogeneously distributed where diving activities are forbidden. An increase in the small-scale heterogeneity of assemblages and a decrease in their three-dimensional structure could be the ultimate consequences of human visitation. The interaction between specific stressors and the patterns of distribution of species and assemblages can drive their spatial heterogeneity also in unique habitats like marine caves, representing an early warning for the development of appropriate management measures.

Phylogeny of the genusBryoria

AbstractThe phylogenetic relationships of the genusBryoriawere examined using ITS, partial glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and mitochondrial SSU rDNA sequence data in addition to 20 chemical and morphological characters. This first comprehensive molecular study to assessBryoriaphylogeny includes representatives from all the traditionally recognized four sections. Combined cladistic analyses of 88Bryoriaspecimens representing at least 25 species resulted in highly resolved phylogenies. Based on the results, a new infrageneric classification for the genus is proposed. Five sections are recognized, largely corresponding to the existing classification, with the addition of sectionAmericanae. The study shows that while most species with an erect growth-form are clearly monophyletic, current species status of many pendent taxa can be questioned.

Epiphytic diatom communities on intertidal seaweeds from Iceland

Epiphytic diatom communities on macroalgae from Iceland coastal waters were investigated during July 2005. Ten species of seaweeds have been collected belonging to brown, red and green algae. The analysis of epiphytic diatom community was carried out under scanning electron microscopy. The epiphytic diatom abundances varied from 7 ± 5 to 7524 ± 3491 cells mm−2. Erect growth forms were the most abundant, representing on average 50% of the total diatoms (Achnanthes cf. brevipes var. parvula, Tabularia investiens, T. fasciculata, Hyalosira cf. delicatula, Gomphoseptatum aestuarii, Pseudogomphonema plinskii), followed by adnate (29%) (Cocconeis stauroneiformis, C. scutellum) and motile forms (21%) (Nitzschia cf. amphibia and Navicula perminuta). Highly branched seaweeds with articulated thallus surface, offering a number of microenvironments to be occupied by the epiphytes, showed a high level of colonization, mainly due to erect and motile diatoms. Flat thalli with smooth surface allowed for the growth of mainly erect diatoms.

Photosynthesis in Codium fragile (Chlorophyta) from a Nova Scotia estuary: responses to desiccation and hyposalinity

Codium fragile ssp. tomentosoides from Caribou Harbour, an estuarine site in the southern Gulf of St. Lawrence, was extremely tolerant to stresses from desiccation and reduced salinity. Photosynthetic responses of both rhizomatous and erect growth forms were measured using pulse amplitude modulation (PAM) fluorometry of chlorophyll a fluorescence to determine effective quantum yield (ΦPSII) and relative electron transport rate (rETR). After 5 h of desiccation, thalli lost 20% of their mass, but still showed high levels of ΦPSII. Thalli survived for at least 6 h in freshwater, and showed virtually complete recovery of photosynthetic capacity within a few hours of return to full seawater. Immersion in 8 psu showed virtually complete recovery until the 24 h treatment period. Combining desiccation and salinity stresses produced a synergistic effect, but plants still showed strong recovery even after 86% dehydration and reimmersion in 16 psu. These results suggest that the photosynthetic physiology of Codium fragile is highly adapted to growth in estuarine conditions.

Height growth response of tree line black spruce to recent climate warming across the forest‐tundra of eastern Canada

Summary The northward expansion of the boreal forest vegetation zone is generally predicted under a warmer doubled CO2, but the delay associated with vegetation development processes often has been overlooked. In the subarctic forest‐tundra of northern Québec, reforestation of tundra uplands appears currently limited by the poor reproductive capacity of shrubby black spruce (Picea mariana), and the development of erect stems through accelerated height growth should be the first registered response to 20th century climate warming. The subarctic forest‐tundra is characterized by small‐ and large‐scale heterogeneity in topography, vegetation structure and climate. This spatial heterogeneity, added to the complexity of tree growth–climate relationships, can cause various growth responses of subarctic tree line black spruce to 20th century climate change. Twenty spruce populations at subarctic tree lines and seven isolated clones at the species limit were sampled along a > 300‐km latitudinal transect from the southern forest‐tundra to the shrub tundra. Height growth patterns of black spruce at tree line and above tree line were examined (i) over their life span, using dendrochronological dating of stem cross‐sections, and (ii) for the recent decades, using leader shoot elongation measurements. Indexed elongation chronologies were compared with regional climate data. Height growth of tree line trees generally decreased with increasing latitude. However, tree line trees in the northern forest‐tundra have experienced an acceleration of height growth since the 1970s, with their growth comparable to that of trees in the southern forest‐tundra. Height growth response of spruce trees appeared increasingly delayed from the northern forest‐tundra to the species limit. Above the subarctic tree line, wind‐exposed conditions obscured the decrease in height growth with latitude observed for tree line trees. Leader shoot elongation of spruce trees established on tundra hilltops appeared more controlled by summer heat sums than those at tree line all over the forest‐tundra, except at the arctic tree line. Winter precipitation also was linked to leader shoot elongation in some forest‐tundra sites. The increasing snow cover associated with recent warming appeared to have reduced the shoot elongation of spruce at forest margins showing the steepest slopes, hence subjected to snow overloading. In the northern forest‐tundra sites, the recent increase in height growth and positive trend in leader shoot elongation, consistent with a 1990s’ increase in heat sums, point to the development of spruce krummholz into erect growth forms. In the southern forest‐tundra, reforestation of tundra hilltops and northward expansion of the boreal forest predicted under doubled CO2 conditions could be delayed, as suggested by suppressed height growth of spruce above tree line.

Facilitated invasion by hybridization of Sarcocornia species in a salt‐marsh succession

Summary We examined salt marsh development over 17 years (1984–2001) in a rapidly accreting, well‐drained lagoon of a macrotidal marsh in south‐west Spain. Scattered, elevated tussocks of colonizing Spartina maritima expanded radially until they either coalesced or were separated only by narrow drainage channels. We recorded changes in elevation of the tussocks and investigated the cover and biomass of successive species invading them. Sediment accretion produced a mean annual increase in tussock elevation of 3.5 cm. Sarcocornia perennis had begun to invade the raised centres of the tussocks by 1984, subsequently displacing Spartina maritima radially to become dominant by 1990. A hybrid form of Sarcocornia, which appeared on some of the tussocks occupied by S. perennis in 1997, also expanded radially and had achieved dominance on many of the invaded tussocks by 2001, by virtue of its more erect growth form and rapid accumulation of high above‐ and below‐ground biomass. Tussocks not yet invaded by the hybrid remain dominated by S. perennis and have maintained sediment accretion rates and redox potentials similar to those that have been invaded. Genetic analysis, using random amplified DNA (RAPD) markers, indicated that the hybrid was a cross between the diploid Sarcocornia perennis (2n = 18) and the octaploid S. fruticosa (2n = 72), a high‐marsh species, and suggested that each hybrid individual may have resulted from a separate pollination of an indigenous S. perennis plant. Invasion by the new hybrid thus probably occurred as a result of pollen flow from high‐marsh S. fruticosa, some 1 km distant, to the stigmas of the established dominant S. perennis. Succession might therefore be facilitated genetically rather than simply by the enhanced sediment accretion, which ameliorated the effects of submersion and low sediment redox potentials that presumably exclude S. fruticosa from lower parts of the marsh.