Bacteria are ubiquitous to marine living surfaces, taking on a broad spectrum of roles from mutualistic to pathogenic. Despite their universality, much remains unknown about their basic ecology and interactions with higher organisms. To address this gap, this thesis firstly examines the bacterial communities associated with three co-occurring marine eukaryote hosts from temperate Australia: the demosponge Cymbastela concentrica, the subtidal red macroalga Delisea pulchra and the intertidal green macroalga Ulva australis. Molecular characterisation of the bacterial communities was undertaken using 16S rRNA gene library analysis to compare within-host (alpha) and between-host (beta) diversity for the three microbial communities. This study highlights the potentially substantial contribution host-associated microorganisms could have on marine microbial diversity. The remaining focus for this thesis was on the bacterial community associated with D. pulchra. This alga produces a suite of biologically active secondary metabolites (furanones) that non-toxically inhibit acyl homoserine lactone (AHL)-driven quorum sensing in bacteria, affecting a range of phenotypes including colonisation and virulence traits. The ecology of D. pulchra???s epiphytic bacteria was investigated using a mechanistic approach to explain bacterial colonisation patterns. In particular, concepts and models of ecological succession founded in eukaryote ecology were investigated. The thesis concludes with a study investigating the effect of furanones and elevated temperature on bacteria-induced disease and thallus bleaching of D. pulchra. In the presence of furanones colonisation and infection of two Roseobacter isolates from D. pulchra???s epiphytic bacterial community were inhibited. Ruegeria strain R11 was demonstrated to have temperature regulated virulence, which caused thallus bleaching in furanone-free algae. The implications of elevated sea temperatures resulting from global warming for algal health are discussed.

<p>Seagrass beds cover large intertidal and subtidal areas in coastal zones around the world and they are subjected to a wide variety of anthropogenic influences, such as nutrient enrichment due to sewage seepage. This study was undertaken to address specific questions focusing on whether near shore tropical seagrasses that receive a constant influx of groundwater nutrient inputs, would exhibit a higher productivity and to what extent epiphytic algae reflect the impacts of nutrient inputs. An additional aspect of study was to determine the prevalence of “acid zones” in tropical seagrasses. The productivity of the seagrasses <i>Cymodocea rotundata</i>,<i> Thalassia hemprichii</i> and <i>Thalassodendron ciliatum</i> was compared in two sites along the Kenyan coast; Nyali (a high nutrient site) and Vipingo (a low nutrient site). Of the three seagrasses <i>T. hemprichii</i> showed the most distinct differences with higher growth and biomass in the nutrient rich site whereas the growth of <i>C. rotundata</i> was similar in the two sites. A high epiphytic cover was found on the shoots of <i>T. ciliatum</i> found in the high nutrient site Nyali.</p><p>Morphological and genetic characterization of bacterial and cyanobacterial epiphytes showed specific associations of nitrogen fixing cyanobacteria on the seagrass <i>C. rotundata</i> in the low nutrient site (Vipingo). At this site, shoots of <i>C. rotundata</i> had a higher C:N ratio compared to shoots in the high nutrient site (Nyali) indicating that the association with nitrogen fixing cyanobacteria is a strategy, for this species, to meet its nutrient needs. Bacterial epiphytes belonging to the group Cytophaga-Flavobacteria-Bacteroides (CFB) were found on <i>T. ciliatum</i> and <i>T. hemprichii</i> from the two sites. CFB bacteria are characteristic of waste water, particularly from livestock farming areas, thereby confirming seepage of groundwater from surrounding catchment areas. These prokaryotic associations were specific for the different seagrasses and it appears that the establishment of epiphytic associations may not be a random encounter but a specific association that meets specific needs.</p><p>The seagrass <i>T. ciliatum</i> in the high nutrient site had an abundance of macroalgal epiphytes and the impact of the epiphytic coverage was assessed using Pulse Amplitude Modulated (PAM) fluorometry. The photosynthetic activity of seagrass parts that were covered by epiphytes was suppressed but the productivity of the whole shoot was not significantly reduced. In the nutrient rich site, epiphytes were found to contribute up to 45% of the total estimated gross productivity, during the SE monsoon season, while epiphytic contribution in the nutrient poor site, was 8%. Epiphytic abundance and contribution to productivity decreased during the NE monsoon. The photosynthetic activity of <i>T. ciliatum</i> shoots was similar in the two study sites with shoots in the nutrient rich site growing faster. <i>T. ciliatum</i>, in the low nutrient site, invested in the development of below ground root tissue which may indicate the development of a strategy to gain access to pore water nutrient pools.</p><p>Carbon uptake strategies of eight tropical seagrasses were re-evaluated to determine how common the “acid zone” mechanism is among tropical seagrasses. Six of the eight species studied showed photosynthetic inorganic carbon (Ci) acquisition based on carbonic anhydrase catalysed HCO₃^- to CO₂ conversions within an acidified diffusion boundary layer (“acid zone”). <i>Cymodocea serrulat</i>a appeared to maintain its carbon uptake by extracellular carbonic anhydrase catalysed CO₂formation from HCO₃^- without the need for acidic zones, whereas, <i>Halophila ovalis</i> appeared to have a system in which H⁺ extrusion may be followed by HCO₃^--H⁺ co-transport into the cells. These findings indicate that competition for carbon, between the host seagrass species and epiphytes, could determine seagrass-epiphyte associations.</p>

Seagrass beds cover large intertidal and subtidal areas in coastal zones around the world and they are subjected to a wide variety of anthropogenic influences, such as nutrient enrichment due to sewage seepage. This study was undertaken to address specific questions focusing on whether near shore tropical seagrasses that receive a constant influx of groundwater nutrient inputs, would exhibit a higher productivity and to what extent epiphytic algae reflect the impacts of nutrient inputs. An additional aspect of study was to determine the prevalence of “acid zones” in tropical seagrasses. The productivity of the seagrasses Cymodocea rotundata, Thalassia hemprichii and Thalassodendron ciliatum was compared in two sites along the Kenyan coast; Nyali (a high nutrient site) and Vipingo (a low nutrient site). Of the three seagrasses T. hemprichii showed the most distinct differences with higher growth and biomass in the nutrient rich site whereas the growth of C. rotundata was similar in the two sites. A high epiphytic cover was found on the shoots of T. ciliatum found in the high nutrient site Nyali. Morphological and genetic characterization of bacterial and cyanobacterial epiphytes showed specific associations of nitrogen fixing cyanobacteria on the seagrass C. rotundata in the low nutrient site (Vipingo). At this site, shoots of C. rotundata had a higher C:N ratio compared to shoots in the high nutrient site (Nyali) indicating that the association with nitrogen fixing cyanobacteria is a strategy, for this species, to meet its nutrient needs. Bacterial epiphytes belonging to the group Cytophaga-Flavobacteria-Bacteroides (CFB) were found on T. ciliatum and T. hemprichii from the two sites. CFB bacteria are characteristic of waste water, particularly from livestock farming areas, thereby confirming seepage of groundwater from surrounding catchment areas. These prokaryotic associations were specific for the different seagrasses and it appears that the establishment of epiphytic associations may not be a random encounter but a specific association that meets specific needs. The seagrass T. ciliatum in the high nutrient site had an abundance of macroalgal epiphytes and the impact of the epiphytic coverage was assessed using Pulse Amplitude Modulated (PAM) fluorometry. The photosynthetic activity of seagrass parts that were covered by epiphytes was suppressed but the productivity of the whole shoot was not significantly reduced. In the nutrient rich site, epiphytes were found to contribute up to 45% of the total estimated gross productivity, during the SE monsoon season, while epiphytic contribution in the nutrient poor site, was 8%. Epiphytic abundance and contribution to productivity decreased during the NE monsoon. The photosynthetic activity of T. ciliatum shoots was similar in the two study sites with shoots in the nutrient rich site growing faster. T. ciliatum, in the low nutrient site, invested in the development of below ground root tissue which may indicate the development of a strategy to gain access to pore water nutrient pools. Carbon uptake strategies of eight tropical seagrasses were re-evaluated to determine how common the “acid zone” mechanism is among tropical seagrasses. Six of the eight species studied showed photosynthetic inorganic carbon (Ci) acquisition based on carbonic anhydrase catalysed HCO3- to CO2 conversions within an acidified diffusion boundary layer (“acid zone”). Cymodocea serrulata appeared to maintain its carbon uptake by extracellular carbonic anhydrase catalysed CO2 formation from HCO3- without the need for acidic zones, whereas, Halophila ovalis appeared to have a system in which H+ extrusion may be followed by HCO3--H+ co-transport into the cells. These findings indicate that competition for carbon, between the host seagrass species and epiphytes, could determine seagrass-epiphyte associations.

Seagrass meadows are highly productive, ecologically and economically valuable ecosystems. However, increased human activities along the coastal areas leading to processes such as eutrophication have resulted in the rapid loss and deterioration of seagrass ecosystems worldwide. This thesis focuses on the responses of seagrasses to increases in nutrients, subsequent increases in ephemeral algae, and changes in the physical-chemical properties of seawater induced by interaction with other marine biota. Both in situ and laboratory experiments conducted on the tropical seagrasses Cymodocea serrulata and Thalassia hemprichii revealed that increased concentrations of water column nutrients negatively affected seagrass photosynthesis by stimulating the growth of the epiphytic biomass on the seagrass leaves. Interaction between seagrasses and other marine organisms induced different responses in seagrass photosynthesis. Ulva intestinalis negatively affected the photosynthetic performance of the temperate seagrass Zostera marina both by reducing the light and by increasing the pH of the surrounding water. On the other hand, the coexistence of mussels Pinna muricata and seagrass Thalassia hemprichii enhanced the photosynthetic activity of the seagrass, but no effect on the mussels' calcification was recorded. This study demonstrates that seagrass productivity is affected by a multitude of indirect effects induced by nutrient over-enrichment, which act singly or in concert with each other. Understanding the responsive mechanisms involved is imperative to safeguard the ecosystem by providing knowledge and proposing measures to halt nutrient loading and to predict the future performance of seagrasses in response to increasing natural and human perturbations. / At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Papers 1, 3 and 4: Submitted. Paper 2: Manuscript. / Swedish Agency for Research Cooperation (Sida/SAREC) marine bilateral programme

Bacteria are ubiquitous to marine living surfaces, taking on a broad spectrum of roles from mutualistic to pathogenic. Despite their universality, much remains unknown about their basic ecology and interactions with higher organisms. To address this gap, this thesis firstly examines the bacterial communities associated with three co-occurring marine eukaryote hosts from temperate Australia: the demosponge Cymbastela concentrica, the subtidal red macroalga Delisea pulchra and the intertidal green macroalga Ulva australis. Molecular characterisation of the bacterial communities was undertaken using 16S rRNA gene library analysis to compare within-host (alpha) and between-host (beta) diversity for the three microbial communities. This study highlights the potentially substantial contribution host-associated microorganisms could have on marine microbial diversity. The remaining focus for this thesis was on the bacterial community associated with D. pulchra. This alga produces a suite of biologically active secondary metabolites (furanones) that non-toxically inhibit acyl homoserine lactone (AHL)-driven quorum sensing in bacteria, affecting a range of phenotypes including colonisation and virulence traits. The ecology of D. pulchra???s epiphytic bacteria was investigated using a mechanistic approach to explain bacterial colonisation patterns. In particular, concepts and models of ecological succession founded in eukaryote ecology were investigated. The thesis concludes with a study investigating the effect of furanones and elevated temperature on bacteria-induced disease and thallus bleaching of D. pulchra. In the presence of furanones colonisation and infection of two Roseobacter isolates from D. pulchra???s epiphytic bacterial community were inhibited. Ruegeria strain R11 was demonstrated to have temperature regulated virulence, which caused thallus bleaching in furanone-free algae. The implications of elevated sea temperatures resulting from global warming for algal health are discussed.

The quest to discover simple, sensitive and global bioindicators of nutrient enrichment and ecological health continues. The present study is the first to address this quest in Hervey Bay by investigating links between key physico-chemical water quality parameters and two diatom forms. Free floating in the water column as phytoplankton, and attached to seagrass leaves and artificial substrates as microalgal epiphytes, diatoms are assessed for their abundance and diversity along an environmental gradient. Relationships between Secchi depth (Zsd), light attenuation coefficient (Kz) and minimum seagrass compensation depth (Zc) are established for the recovery, growth and survival of aquatic plants following disturbance, with equations derived specifically for this region to allow conversions from Zsd to Kz. These relationships allow predictions to be made and provide a management tool to meet water quality targets and combat elevated nutrient and sediment loads that result from anthropogenic activity and affect all marine life, from microalgae to marine mammals. Environmental links, identified as drivers of change to biodiversity, focus research effort and provide predictive management tools. Consequently, catchment and coastal activities such as dredging, construction and canal development, with the potential to increase nutrient and sediment loads, can be managed and scheduled at times least likely to adversely impact near shore ecosystems and therefore improve the balance between growth and sustainability. Seasonal and zone differences were significant for many of the water quality parameters monitored in Hervey Bay during 1994. Water clarity measures consistently showed significant differences between near and offshore zones (Secchi depth; P<0.01, turbidity; P<0.05 and TSS; P<0.01) as well as oxygen (P<0.01), soluble reactive phosphate (SRP, P<0.05), oxides of nitrogen (NOx, P<0.01), chlorophyll a (Chl a, P<0.01) and pH (P<0.01). Some default trigger values for water quality targets listed by ANZECC/ARMCANZ (2000) for concentrations of key indicators, a threshold for risk of adverse biological effects, were exceeded in dry and flood periods during the 1993 to 1995 survey. The community structure of phytoplankton and seagrass epiphytes were examined by monitoring changes to and 35 seagrass epiphyte species coincident with changes in some key water quality parameters along a water quality gradient. Chl a, Secchi depth (Zsd), soluble reactive phosphate (SRP) and pH were found to be the best subset of water quality parameters to maximise the rank correlation with phytoplankton communities whereas NOx and temperature maximised the rank correlation with the Halophila ovalis seagrass epiphyte communities. These parameters statistically link key water quality parameters to changes in phytoplankton and seagrass epiphyte density and assemblage structure and are supported as significant drivers of change in biodiversity research. Evidence for nitrogen limitation was found in the post flood surveys for phytoplankton and the growth and assemblage structure for seagrass systems and their epiphytes. Seasonal and zone differences in phytoplankton assemblage structure were most apparent with some site influence detected. Cylindrotheca closterium dominated the phytoplankton assemblage structure at the near shore zone while Thalassionema nitzschioides and Chaetoceros sp. differentiated the river from the Waste Water Treatment Plant (WWTP) creek site. Rhizolsolenia and Guinardia sp. were found in significantly higher concentrations at offshore sites (P < 0.01) and Thalassionema nitzschioides (P < 0.01), Thalassiosira sp. (P < 0.01) and Pseudonitzschia sp. (P < 0.05) were found in significantly higher abundance in the near shore zone A Trichodesmium bloom was examined and post flood changes to the phytoplankton assemblage structure associated with increased nutrient loads, reduced water clarity (Secchi depth, TSS and turbidity) and changes to pH and salinity were assessed. The results of analyses of variance provided support to multivariate statistical analyses to identify phytoplankton as a useful and sensitive bioindicator of environmental change. Post flood phytoplankton cell density increased and species diversity rose from 10 to 38 species at the Mary River mouth however, the changes to cell density and assemblage structure were not reflected in Chl a concentrations. The Mary River mouth experienced growth of mainly small phytoplankton species (< 20 µm) while Pulgul Creek, a source of WWTP effluent, experienced a disproportional increase in the larger phytoplankton species (>20µm). The increase in phytoplankton cell density at offshore sites occurred for both large and small species. Phytoplankton species dominance changed at each site during the postflood period. C. closterium remained the dominant species but increased from 34 to 648 cells/mL at Pulgul Creek however, C. similis, the second most dominant species was replaced by Pseudonitszchia sp., whose cell density rose from 2.0 to 320 cells/mL. A recent study also found that Cylindrotheca closterium, Skeletonema costatum, and Cyclotella choctawhatcheeana had strong positive relationships with coastal nutrients and suggested these species be used as potential reliable indicators of eutrophication (Toming and Jaanus, 2007). Some Pseudonitszchia sp. and dinoflagellate species have previously been noted as toxic and Chaetoceros sp. are associated with gill damage and fish kills. Rhizosolenia sp. and the Guinardia species G. flaccida and G. striatula, were indicators for the offshore relatively pristine sites, which may conversely, determine these species as indicators of environmental health in this waterway. Specificity of epiphyte attachment to particular seagrass species were detected and microalgal epiphyte assemblages on Halophila ovalis were identified as useful bioindicators of environmental gradients as this seagrass species is located at intertidal, shallow and deep water sites for a substantial part of the year. H. ovalis also recorded the highest average annual epiphyte loads (3873 ± 1882 cells/mm2) with the diatoms Diatoma vulgare and Cocconeis scutellum representing 19.6% and 17.2% of the total epiphyte cover. Highest cell density was recorded in autumn, followed by summer and winter: spring recorded the lowest epiphyte cover. Micro-algal epiphyte load was assessed as dry weight (g/m2), Chl a (µg/L) and cell density (cells/mm2) on artificial seagrass deployed along a water quality gradient. Equations were derived to describe percentage light transmission as a function of each measure of epiphyte load which allows transformation of data from one unit of expression to another and hence, allow comparison of past, current and future studies. Water column light attenuation was evaluated along a water quality gradient and linked to Secchi depths (Zsd) to derive equations that describe this relationship where for Hervey Bay, when Zsd < 4.26m, Kz = -1.2 ln Zsd + 1.74 and when Zsd ≥ 4.26m, Kz=1.37/Zsd. Species succession, diversity and seagrass growth were monitored for the first time during a recovery phase and limits for the seagrass compensation depth (Zc), were established on a seasonal basis for five seagrass species at four locations within intertidal, shallow and deep water zones in Hervey Bay and the Great Sandy Straits. Conceptual models for each site were constructed to describe habitat characteristics and include nutrient concentrations for SRP, NOx and ammonia (NH4+), Chl a, phytoplankton density, epiphyte density and light requirements measured as light attenuation, total suspended sediment, turbidity and Secchi depth at each location. The study provides a descriptive model for light attenuation and establishes (1) an annual and seasonal baseline water quality data set that characterises the waterways of Hervey Bay and the Great Sandy Straits (2) identification of phytoplankton species in Hervey Bay and their response to post flood changes in water quality (3) phytoplankton density and diversity along an environmental gradient with links established to Chl a, Secchi depth, SRP and pH (4) seagrass epiphyte assemblage structure along an environmental gradient with links established to NOx and temperature (5) conversion factors for epiphyte load expressed as dry weight, Chl a and cell density (6) functions to convert Secchi depth to light attenuation coeffiecients (Kz) (7) seagrass species succession at intertidal, shallow and deep water sites during a recovery growth phase in Hervey Bay (8) seagrass compensation depths (Zc) for five seagrass species at four locations and (9) habitat characterisation for seagrass recovery in Hervey Bay. Identification catalogues for phytoplankton and seagrass epiphytes were prepared with light and electron micrographs to assist future identification studies of diatoms in this region and for other similar biogeographical areas. The management of water quality to reach specific targets requires the capacity to predict seagrass compensation depth (Zc) as a function of water quality. Seasonal and annual light attenuation measurements are derived as a function of water quality at intertidal, shallow and deep water habitats during the colonisation of Zostera Capricornii, Halodule uninervis, Halophila ovalis, Halophila spinulosa and Halophila decipiens.

Thesis (M.S.)--State University of New York at Binghamton, Department of Biological Sciences, 2007. / Includes bibliographical references.

Orientador: Reinaldo Monteiro / Banca: Marco Antonio de Assis / Banca: Fábio de Barros / Resumo: O epifitismo é responsável por parte significativa da diversidade que faz das florestas tropicais úmidas um dos mais ricos e complexos ecossistemas da Biosfera. Assim, a comunidade de plantas epífitas vasculares teve suas espécies levantadas neste estudo em floresta alta de restinga da planície litorânea da Praia da Fazenda, Núcleo Picinguaba, situada no extremo norte do município de Ubatuba, SP (23°20'-23°22'S / 44°48'-44º52'W). Além disso, foram analisadas a distribuição dessas plantas e as relações com seus respectivos forófitos. Foram consideradas todas as epífitas vasculares fixadas nas dez espécies arbóreas dos dez maiores VI (Valor de Importância) identificadas na região do estudo. As coletas foram realizadas mensalmente, durante o período de um ano, com o uso do método de escalada nas árvores e outras técnicas de coleta e observação. Para a identificação, foram utilizadas monografias, levantamentos florísticos na área de estudo, revisões taxonômicas e consultas a especialistas diversos e a Herbários. Todo material coletado foi preparado e herborizado, sob autorização da Secretaria do Meio Ambiente - Instituto Florestal (COTEC) (processo nº 41.773/2006), e as exsicatas depositadas no Herbário Rioclarense (HRCB), pertencente à UNESP/Rio Claro. Foram identificadas 65 espécies de epífitas vasculares, em 446 árvores, sendo Orchidaceae, Bromeliaceae, Polypodiaceae e Araceae as famílias com maior número de espécies. A anemocoria esteve presente na maioria das epífitas (61%), enquanto que as demais espécies apresentaram a zoocoria como método de dispersão. A forma de vida mais freqüente nas espécies encontradas foi a holoepífita obrigatória (75%), seguida das holoepífitas facultativas (12%), estas exclusivamente da família Bromeliaceae. / Abstract: The epiphytism is responsible for a significant part of the diversity that makes humid tropical forests one of the most rich and complex ecosystems of the Biosphere. Thus, this study surveied the community of vascular epiphytes of the high forest of "restinga" in the coastal plain of Praia da Fazenda, Núcleo Picinguaba, located in the far north of Ubatuba municipality, SP (23°20'-23°22'S and 44°48'-44°52'W). Moreover, the distribution of these plants and relations with their phorophytes were analyzed: all vascular epiphytes growing on the ten tree species of largest VIs (Value of Importance) identified in the present study, were considered. The observations were carried out were monthly for a period of one year with the use of several methods of collection and marking. For the identification all available literature was used: books, floristics surveys done in the study area, taxonomic revisions and consultations with diverse experts and Herbaria. All collected material was prepared, under authorization of the Secretaria do Meio Ambiente - Instituto Florestal (COTEC) (case nº 41.773/2006), and the exsiccatae deposited in the Herbário Rioclarense (HRCB), belonging to UNESP / Rio Claro. Sixty-five species of vascular epiphytes, in 446 trees, were identified, with the Orchidaceae, Bromeliaceae, Polypodiaceae and Araceae grouping the greatest number of species. The anemocory was verified in the largest amount of epiphytic species (61%), whereas the remaining species had zoocory as the dispersal method. The life form true epiphytes was the frequentest in species number (75%), while the facultative species constituted the second contingent (12%), which belongs exclusively to the Bromeliaceae. The assumption was to find larger quantities of epiphytes in large phorophytes, with rugous texture of bark and favourable crown architecture. / Mestre

Entre os vegetais existem duas estratégias distintas para superar as condições de estresse hídrico que condicionam a sensibilidade a dessecação (SD) que está associada a mecanismos de evitação e a tolerância a dessecação (TD) que envolve suportar o estresse hídrico diretamente no nível dos tecidos e no nível subcelular. Sabe-se que os custos acoplados aos mecanismos de dessecação e reidratação em espécies TD são elevados, e provavelmente superiores aos de espécies SD. Desta forma, a coexistência de espécies com estas estratégias, como ocorre no ambiente epifítico da Cidade Universitária Armando Sales de Oliveira (CUASO), induzem questões quanto a as vantagens relativas de espécies TD sobre SD. Devido aos altos custos da estratégia TD é possível propor que estas deveriam apresentar um ganho médio de carbono superior a de espécies SD durante o período favorável (com disponibilidade hídrica). Além disso, também é razoável esperar que as distintas formas de uso da água, vinculadas às estratégias, poderiam facilitar o convívio de espécies TD e SD através da segregação de nichos. Com intuito de verificar essas hipóteses, foram realizadas análises relacionadas a estrutura de comunidade de epífitas da CUASO e, a partir destas, a detecção da associação espacial mais freqüente, que resultou composta por Pleopeltis hirsutissima (TD) e Microgramma squamulosa (SD). Estas espécies foram então selecionadas para avaliar parâmetros associados à dinâmica do uso da água, assimilação líquida de carbono, dinâmica da capacidade de uso da luz, estado de hidratação foliar e pigmentos fotossintéticos. Os resultados apontaram que espécies de ambas as estratégias não apresentam sinais de estresse crônico no ambiente estudado. Os dados reforçaram as respostas contrastantes de TD e SD, refletindo as formas distintas de lidar com os recursos e condições do ambiente. Ao contrário do esperado, P. hirsutissima não apresentou uma assimilação de carbono superior a M. squamulosa, indicando que o ganho de carbono não é um dos fatores possíveis na compensação dos custos acoplados a sua estratégia (TD). Porém, os resultados apresentados quanto a dinâmica da capacidade de uso da luz sugerem que a coexistência é facilitada pela segregação de nichos de luz, sendo a espécie TD mais heliófila do que a espécie SD / In land plants the resistance to drought can be accomplished by two main strategies. One involves mainly dehydration avoidance mechanisms and the other is based on the ability to withstand drought at the tissues and down to subcellular levels. The former is found on the desiccation sensitive plants (DS) and the last describes the desiccation tolerant plants (DT). The metabolic costs of the desiccation tolerance mechanisms are probably high, at least when considering the cessation of photosynthesis during anabiosis - a condition that is absent in drought avoidance strategies. The coexistence of drought avoiders and desiccation tolerant plants in the same substrate and condition can rise some questions about the relative advantages of each strategy when submitted to similar water regime. We ask whether desiccation tolerant plants have a compensatory carbon gain under a watering regime that induces frequent anabiosis or cumulative damage in drought avoidance have a detrimental effect comparable to the costs of the desiccation tolerance. An analysis of the epiphytic plant community associated to the trees of the CUASO urban landscape showed a very frequent co-occurring species pair including the desiccation sensitive Microgramma squamulosa and a desiccation tolerant Pleopeltis hirsutissima, both cryptogams of the same plant family. These species were thoroughly examined regarding the patterns of light, water and carbon dynamics together with pigments concentration during cycles of natural drought and wet climate field conditions. These observations were complemented with experimental induction of different water and light regimes. The results showed no sign of chronic stress in both plants living at the same condition but allowed us to identify large distinctions in resource use patterns. A compensatory carbon assimilation was not found in P.hirsutissima. Both species have similar CO2 assimilation values. Experimental induction of drought in different light regimes allowed to verify a relative advantage in desiccation tolerant P.hirsutissima in comparison to the desiccation sensitive M.squamulosa under high irradiance values. Furthermore, light curve analysis suggest that they share the same tree but their niches differ in light intensity regime allowing the high frequency of co-occurrence observed in the field

Neste trabalho são estudadas epífitas, aqui consideradas como plantas vasculares usualmente encontradas sobre outras, sem parasitá-las, durante alguma fase do ciclo de vida. O local de estudos, a reserva da Cidade Universitária "Armando de Salles Oliveira" (aproximadamente 46o43’W, 23o33’S), em São Paulo-SP, é uma ilha de mata secundária em ambiente urbano e representa uma das poucas áreas cobertas por floresta na região. O clima em São Paulo é Cwa, com temperatura média anual de 19,2oC e precipitação de 1207 mm. As famílias de epífitas representadas são Polypodiaceae (9 espécies), Bromeliaceae (8), Orchidaceae (6), Moraceae (5), Araceae (4), Cactaceae (3), Piperaceae (1), Blechnaceae (1) e Araliaceae (1), totalizando 38 espécies, 3 delas exóticas. As epífitas representam 12% do total de espécies vasculares citadas para a reserva. Esta riqueza em espécies é maior do que seria esperada, dada a pequena pluviosidade local. Estão representadas todas as principais formas de vida epifíticas conhecidas. A estrutura do componente epifítico foi estudada em uma área contígua de 2000 m2 no interior da reserva, sobre todas as árvores de perímetro do caule a 1,30 m de altura (PAP) > 40 cm. As árvores foram mapeadas e espécie, altura, PAP e presença ou ausência de lianas foram registradas para cada uma delas. Dos 86 indivíduos arbóreos, 29 são de Alchornea sidifolia, 10 de Croton floribundus e 8 de Piptadenia gonoacantha, as espécies mais abundantes. Pterocarpus rohrii, Rollinia sylvatica e Myrcia tenuivenosa são citações novas para a reserva. Foram reconhecidas 2 subáreas na área amostrada, com base no estádio sucessional das árvores, evidenciando o caráter de mosaico da vegetação. Análises de distribuição de freqüências de DAP indicam o declínio das espécies mais abundantes e prevêem profundas alterações na estrutura da floresta. Foi feito um censo total dos indivíduos epifíticos com mais de 15 cm de comprimento presentes sobre todas as árvores amostradas. Foi considerado como indivíduo cada colônia, ou grupo compacto de plantas distintamente separado de outros da mesma espécie. Foram encontrados 380 indivíduos, sobre 58 árvores (67% do total). Para cada um deles foram registrados altura de fixação, diâmetro do substrato, inclinação, região da árvore (fuste; alta, média e baixa copa), tipo de substrato (bifurcação, cavidade e casca) e espécie. Análises detalhadas de distribuição ao longo das variáveis foram feitas para as 5 espécies mais abundantes: Microgramma squamulosa(75 indivíduos), Rhipsalis baccifera (67), Pleopeltis astrolepis (57), Aechmea bromeliifolia (52) e Polypodium hirsutissimum (45). O tamanho da árvore é positivamente correlacionado com a quantidade de epífitas que suporta. Há grandes variações entre as espécies arbóreas neste sentido. P. rohrii e Casearia sylvestris são as que suportam maiores quantidades de epífitas por indivíduo. As variáveis ligadas à árvore (espécie, DAP, estádio sucessional,subárea, presença ou ausência de lianas) parecem não influir na composição epifítica sobre ela. As epífitas apresentam ampla distribuição vertical e ao longo de diâmetros de substrato, com grande sobreposição entre as espécies e conseqüente ausência de estratificação. A. bromeliifolia apresentou preferência de estabelecimento em cavidades. A baixa copa e o fuste são as regiões das árvores com maior quantidade de epífitas. De forma geral, as epífitas têm preferência por alturas médias dentro da floresta (ca. 8 m), diâmetros grandes (10-30 cm), inclinações horizontais a médias e positivas. R. baccifera demonstrou preferência por P. rohrii como suporte; P. hirsutissimum e P. astrolepis, por A. sidifolia. M. squamulosa é a espécie de maior dispersão considerando-se todas as variáveis. / This work assesses floristics and structure of epiphytes, here defined as vascular plants usually found living on others, without parasitizing them, during at least a part of their life cycles. The study site, the reserve of the Cidade Universitária "Armando de Salles Oliveira" (nearly 46o43’W, 23o33’S), in São Paulo-SP (Brazil), is a secondary forested area isolated in urban environment and represents one of the few forested areas in this city. The climate type is Köppen’s Cwa, the mean annual temperature is 19,2 oC and the mean annual precipitation is 1207 mm. Polypodiaceae (9 species), Bromeliaceae (8), Orchidaceae (6), Moraceae (5), Araceae (4), Cactaceae (3), Piperaceae (1), Blechnaceae(1) and Araliaceae (1) are the families of epiphytes found at the study site, making up 38 species, 3 of them being exotic. Epiphytes are 12% of the vascular plant species cited for the reserve. This species richness is larger than expected in face of the little mean annual precipitation. All main epiphytic life forms are represented. The structure of the epiphyte community upon all the trees with girth of trunk at the height of 1,30 m (GBH) with more than 40 cm was studied in a 2000 m2 plot inside the reserve. The trees’ location inside the plot was mapped and species, height, GBH and presence/absence of lianas were recorded for each of them. From 86 trees, 29 were of Alchornea sidifolia, 10 of Croton floribundus and 8 of Piptadenia gonoacantha, the most abundant species. Pterocarpus rohrii, Rollinia sylvatica and Myrcia tenuivenosa are cited for the first time for the reserve. Two different subareas could be distinguished inside the plot as to the successional stage of the trees, an evidence for the mosaic character of the vegetation. DBH frequency distributions predict the decline of the most abundant species populations and consequent deep changes in the structure of the forest. A total census of the epiphytic stands more than 15 cm long was made upon all sampled trees. A stand was defined as a compact group of plants well separated from conspecifics. 380 stands were found, on 58 trees(67% of total). For each stand, height of attachment, branch or trunk diameter, inclination, height zone (trunk, lower, middle or upper crown), type of substrate (hole, fork or bark) and epiphyte species were recorded. The five more abundant species were analysed as to the distribution along the variables. They were: Microgramma squamulosa (75 stands), Rhipsalis baccifera (67), Pleopeltis astrolepis (57), Aechmea bromeliifolia (52) and Polypodium hirsutissimum (45). Tree height and DBH were positively correlated with number of stands and number of epiphyte species. There is great variability between tree species in these aspects. P. rohrii and Casearia sylvestris are the species with highest numbers of stands per tree. Tree characteristics such as species, DBH, successional stage, successional vegetation stage and presence/absence of lianas don’t seem to have influence on epiphyte composition on them. Epiphytes show broad vertical and diameter distributions. Species’ vertical and diameter distributions overlap largely and, as a consequence, there is no distinct stratification. A. bromeliifolia showed preference for establishment in holes. Lower crown and trunk were the zones with the largest number of stands. Epiphytes as a whole show preference for middle heights in the forest (ca. 8 m), large diameters (10-30 cm), horizontal to middle and positive inclinations. R. baccifera showed preference for P. rohrii as support tree; P. hirsutissimum and P. astrolepis showed preference for A. sidifolia. M. squamulosa is the most ubiquituous epiphytic analyzed species.