Wheat canopies were grown at either 330 or 1200 μmol mol-1 CO2 in sealed controlled environments, where carbon fluxes and radiation interception were continuously and nondestructively measured during their life cycles. The effects of elevated CO2 on daily growth rates, canopy quantum yield, canopy and root carbon use efficiencies, and final dry mass were calculated from carbon flux measurements in an open gas exchange system. Dry biomass at harvest was predicted from the gas exchange data to within ± 8%. The greatest effect of elevated CO2 occurred in the first 15d after emergence; however, several physiological processes were enhanced throughout the life cycle. Elevated CO2 increased average net photosynthesis by 30%, average shoot respiration by 10%, and average root respiration by 40%. Crop growth rate, calculated from gas exchange data, was 30% higher during both vegetative growth and reproductive growth. Elevated CO 2 did not affect radiation interception, but increased average canopy quantum yield from 0.039 to 0.051 (31%). Average canopy carbon use efficiency was increased by 12%. Although harvest index was unaffected, these increases in the physiological determinants of yield by elevated CO2 resulted in a 14% increase in seed yield.

The resurgence of Texas' snook (Family Centropomidae) recreational fishery is coupled with an uncertainty as to what species occur in State waters, a limited understanding of life history, and habitat needs of its constituents. This study described species composition and early life history aspects of juvenile (< 100 mm SL) centropomids taken in bag seine collections in estuarine and freshwater habitats along the upper, middle, and lower coast of Texas during 2006 to 2010. Centropomus specimens (n = 548) captured from 41 locations across the Texas coast as well as congeners from Mexico (n = 24), Florida (n = 7), and Costa Rica (n = 3) were used in a genetics- and meristic-based determination of species composition, growth rates, range of hatching dates, geographic distribution, and habitat association. Genetic analyses of the mitochondrial DNA 16s ribosomal RNA gene and the mitochondrial control region (D - loop) validated the presence of smallscale fat snook (C. parallelus Poey, 1860, n = 333), common snook (C. undecimalis Bloch 1792, n = 212) and Mexican snook (C. poeyi Chavez, 1961, n = 3) in Texas, with the last of these validations representing the first known record of this species in Texas. AMOVA of 16s and D - loop sequences failed to detect genetic differentiation within Texas for C. parallelus and C. undecimalis. However, AMOVA for 16s and D - loop C. undecimalis sequences did yield significant genetic differences between Texas and Mexico against those from Florida and Costa Rica. Juvenile centropomids (< 100 mm SL) in Texas occupied backwater habitats with dissipated currents similar to those of Florida congeners (tidal sloughs, freshwater habitats, and structured shorelines). Coastal ranges of these species differed with C. parallelus taken from the Rio Grande to West Galveston Bay, whereas C. undecimalis was captured from the Rio Grande northward near Palacios. Three C. poeyi were captured at only two locations (Laguna Vista and Port Aransas). Daily growth rates varied between species and capture years, with these ranging from 0.22 to 0.97 mm d^-1. Analyses of hatch-date distribution suggest centropomids in Texas begin spawning in August and continue it through late September into mid-November.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / The aim of the study was to evaluate the influence of meteorological variables on the growth of Tungue and its implications on the growth and productivity of sugarcane in agroforestry systems. The research was conducted from 2011 to 2016, in the city of Frederico Westphalen, Rio Grande do Sul, Brazil, with geographic location 27 ° 22'S, 53 ° 25'W and 480 m altitude. The experimental design was a randomized complete block with three replications. The species Tungue (Aleurites fordii) and Sugarcane (Saccharum officinarum L.) were used to compose the agroforestry systems. The trees were distributed in two arrangements of agroforestry systems, designated I and II. In the system I, trees were distributed in rows spaced at 12m; the sugarcane was distributed in eight rows, arranged in corresponding intervals between tree rows. In the system II, trees were grown in rows spaced at 6m; the sugarcane was distributed in four rows arranged in correspondence with intervals between tree rows. For the monocrop system with sugarcane, the plants were distributed in six rows with 12 meters length. In both systems, the cultivate sugarcane was the IAC 87-3396, which was distributed in spacing 1.20m. Both lines of sugarcane as the trees were oriented east-west direction. The tree variables analyzed were: stem diameter (cm), diameter at breast height (cm), plant height (m) and crown diameter (m). The productive variables analyzed in sugarcane were: stalk weight (Mg ha-1), stalk length (m), stalk diameter (mm), number of nodes, number of stalks, juice volume (m3 ha-1), sucrose content (g L-1) and sucrose quantity (Mg ha-1). Sugarcane growth variables evaluated: leaf area index (m2 m-2), absolute growth rate (g day-1), net assimilation rate (g m-2 day-1), radiation use efficiency (g MJ-1), biomass partitioning (g), total dry matter (g m-2), plant height (m), number of tillers, extinction coefficient and % of intercepted global radiation. The meteorological variables occurring during the study were obtained through Climatological the National Institute of Meteorology Station, located at 200 m from the study site, with geographic location 27°39'S and 53°43'W. The dynamic interactions between Tungue trees and meteorological variables were determinant for the growth and productivity responses of sugarcane cultivated in the understory. For the sugarcane production, the use of an intercropping system with 12x12m arrangements should be prioritized, because it promotes greater sugarcane yields when compared to a 6x6m intercropping system, since the quality of the sugarcane was not affected by the cultivation systems. In the future, from the moment that Aleurites fordii trees show a productive return, a new joint analysis of the data should be made in order to verify the suggested recommendation of the present research. / O objetivo do estudo foi avaliar a influência das variáveis meteorológicas no crescimento do Tungue e suas implicações sobre o crescimento e produtividade da cana-de-açúcar em sistemas agroflorestais. A pesquisa foi conduzida no período de 2011 a 2016, no município de Frederico Westphalen, Rio Grande do Sul, Brasil, com localização geográfica de 27°22’S, 53°25’W a 480 m de altitude. O delineamento experimental utilizado foi de blocos completos casualizados, com três repetições. Foi utilizada a espécie florestal Tungue (Aleurites fordii) e a cana-de-açúcar (Saccharum officinarum L.) para compor os sistemas agroflorestais. As árvores foram distribuídas em dois arranjos de sistemas agroflorestais, denominados I e II. No sistema I, as árvores foram distribuídas em fileiras espaçadas a 12m e a cana-de-açúcar foi distribuída em oito linhas, disposta em intervalos correspondentes entre as fileiras das árvores. No sistema II, as árvores foram cultivadas em fileiras espaçadas a 6m e a cana-de-açúcar foi distribuída em quatro linhas dispostas em correspondência com intervalos entre as fileiras das árvores. Para o sistema de monocultura com cana-de-açúcar, as plantas foram distribuídas em seis linhas com 12 metros de comprimento. Em ambos os sistemas, a cultivar de cana-de-açúcar utilizada foi a IAC 87-3396, sendo distribuída em espaçamento entre linhas de 1,20m. Tanto as linhas de cana-de-açúcar quanto as das árvores foram orientadas no sentido Leste-Oeste. As variáveis de crescimento do Tungue analisadas foram: diâmetro do colo (cm), diâmetro à altura do peito (cm), altura de planta (m) e diâmetro médio da copa (m). As variáveis produtivas analisadas na cana-de-açúcar foram: massa de colmo (Mg ha-1), comprimento de colmo (m), diâmetro do colmo (mm), número de nós, número de colmos, volume de suco (m3 ha-1), conteúdo de sacarose (g L-1) e quantidade de sacarose (Mg ha-1). As variáveis de crescimento avaliadas foram: Índice de área foliar (m2 m-2), taxa de crescimento absoluto (g dia-1), taxa de assimilação líquida (g m-2 dia-1), eficiência do uso da radiação (g MJ-1), partição da matéria seca (g), matéria seca total (g m-2), altura de planta (m), número de perfilho, coeficiente de extinção de luz e % de interceptação da radiação solar. As variáveis meteorológicas ocorrentes ao longo do estudo foram obtidas por meio da Estação Climatológica do Instituto Nacional de Meteorologia, localizada à 200 m do local de estudo, nas coordenadas 27°39’S e 53°43’W. As interações dinâmicas existentes entre as árvores de Tungue e as variáveis meteorológicas foram determinantes para o crescimento e produtividade da cana-de-açúcar cultivada no sub-bosque. Para a produção de cana-de-açúcar, deve-se priorizar o uso de um sistema agroflorestal com arranjos de 12x12m, pois promove maiores rendimentos de cana-de-açúcar quando comparados com um sistema agroflorestal de 6x6m, uma vez que a qualidade da cana-de-açúcar não foi afetada pelos sistemas de cultivo. No futuro, a partir do momento em que as árvores de Tungue apresentarem retorno produtivo, uma nova análise conjunta dos dados deve ser realizada a fim de verificar a recomendação sugerida na presente pesquisa.

Both temperature and terrestrial dissolved organic carbon (TDOC) have strong impacts on aquatic food web dynamics and production. Temperature affects vital rates of all organisms and terrestrial carbon has been shown to alter the dynamics of phytoplankton and bacterial production and affect the trophic structure of planktonic food webs. As climate change predictions for the Baltic Sea suggests future increases in both terrestrial carbon run-off and increases in temperature, the aim of thesis was to adopt a system-ecological approach and study effects of these abiotic variables, not only on interactions within planktonic food webs, but also on the growth and consumption rates of one of the most common zooplanktivorous fish in the Baltic Sea, the three-spined stickleback Gasterosteus aculeatus. Results showed that three-spined sticklebacks display a high degree of resilience against increasing temperatures, as both growth rates as well as consumption rates on zooplankton were high at temperatures well over 20 °C. Furthermore, it was shown that the minimal resource densities required to sustain individual and population growth, actually decreased with increasing temperatures, implying that sticklebacks around their optimum temperature for growth at 21 °C will actually have an increased scope for growth. As stickleback population densities have increased over the last decade in the Baltic Sea and are now suggested to out-compete other coastal fish species for shared zooplankton resources, the results presented in this thesis suggest that increased water temperatures would only serve to increase sticklebacks competitive advantage. As the structuring role of this small zooplanktivore on pelagic communities might be considerable, further studies investigating competitive interactions as well as patterns of population abundances are definitely warranted. TDOC was overall shown to stimulate bacterial production and the microbial food web. Because of the longer trophic pathways required to transport carbon from bacterial production to higher trophic levels, the addition of TDOC always reduced food web transfer efficiency. However, it became apparent that the full effect of TDOC additions on pelagic food webs was complex and depended heavily not only on the existing trophic structure to which the carbon was introduced, but also on ambient temperature levels. When three-spined sticklebacks were part of food webs with significant TDOC inputs, the presence of fish, indirectly, through predator release of lower trophic levels, amplified the magnitude of the effects of carbon addition on bacterial production, turning the base of the system significantly more heterotrophic, which ultimately, impacted negatively on their own production. However, when a pelagic food web containing sticklebacks was simultaneously subjected to realistic increases in temperature and TDOC concentrations, food web efficiency and fish production increased compared to present day conditions. These results were explained by a temperature dependent increased production potential of zooplankton, sustained by an increased production of heterotropic microzooplankton via TDOC additions, which lead to higher fish production. Although the increased number of trophic linkages in heterotrophic food webs should have reduced energy transfer efficiency, these negative effects seem here to have been overridden by the positive increases in zooplankton production as a result of increased temperature. These results show that heterotrophic carbon transfer can be a viable pathway to top-consumers, but also indicates that in order to understand the full effects of climate change on trophic dynamics and fish production, abiotic variables cannot be studied in isolation.

Experimento I: Foram utilizadas 60 borregas da raça Santa Inês com o objetivo de avaliar os efeitos de três taxas de crescimento até os 7 meses de idade. Os tratamentos foram delineados visando obter alta taxa de crescimento (ATC), moderada taxa de crescimento (MTC) e baixa taxa de crescimento (BTC). Foram avaliados o consumo de matéria seca, o ganho de peso corporal e as concentrações séricas de progesterona para a detecção da idade à puberdade. Foram verificados efeitos lineares (p<0,01) para o peso corporal e metabólico, sendo os maiores valores encontrados para os animais do tratamento ATC. Efeito linear (p<0,01) foi verificado para o ganho médio diário (GMD) sendo de 0,182; 0,156 e 0,136 kg/dia para os tratamentos ATC, MTC e BTC respectivamente. Borregas pertencentes ao tratamento ATC apresentaram maior conversão alimentar sendo os valores para o tratamento ATC de 6,1; MTC de 7,1 e BTC de 9,2 kg MS/ kg de ganho de peso. Verificou-se diferença (p<0,01) quanto a porcentagem de animais que atingiram a puberdade sendo o tratamento MTC com o maior número de borregas púberes até os 7 meses de idade (60%), seguida dos tratamentos ATC (45%) e BTC (15%)com peso médio de 39,3 kg de peso corporal, sendo 70% do peso adulto. Experimento II: As borregas utilizadas no experimento 1 com 37 Kg de PC entraram em estação de monta e após o parto receberam uma única dieta, sendo blocadas de acordo com o peso e dias de lactação. Observou-se efeito quadrático (p<0,01) na produção de leite em 3h (137,9; 150,1 e 104,4 g), efeito quadrático (p<0,05) para LCG (167,2; 178,9 e 129,4) e efeito quadrático (p<0,03) LCGP (216,5; 140,5 e 162,7). Os teores de gordura (9,8; 8,9 e 8,3%) e de proteína (4,2; 4,2 e 4,6 apresentaram efeitos lineares sendo (p=0,01) para gordura e (p<0,01) para proteína. Experimento III: Os objetivos deste experimento foram avaliar o efeito da inclusão de bagaço de cana-de-açúcar in natura (BIN) sobre o consumo e a digestibilidade aparente dos nutrientes, balanço de nitrogênio e os parâmetros ruminais de cordeiros Santa Inês. Quatro cordeiros providos de cânula ruminal com peso corporal (PC) médio inicial de 30kg foram alojados individualmente em gaiolas para ensaios de metabolismo. O tratamento controle positivo (CONT) consistia de uma ração de alto concentrado contendo de 10% de feno de coastcross (Cynodon sp.) na MS, sendo os demais tratamentos níveis crescentes de BIN em 10, 20 e 30% da MS, constituindo os tratamentos 10BC, 20BC e 30BC. As rações experimentais foram isonitrogenadas (13,75±0,25% PB). Não verificou-se efeito de tratamento (p>0,05) sobre o consumo de MS, MO, e PB em kg/dia e g/kg de PC 0,75; apenas sobre consumo de FDN com efeito linear (p< 0,01). O balanço de nitrogênio, assim como a concentração de acetato, propionato, butirato, concentração total de AGCC, amônia no fluido ruminal e a de digestibilidade aparente da MS, MO, PB e FDN não foram afetados pelos tratamentos. / Trial I: Sixty Santa Ines ewe lambs were used to evaluate the effects of three growing rates until 7 months of age. Treatments were defined to achieve high (HGR), moderate (MGR) and low (LGR) growing rates. The dry matter intake and average daily gain (ADG) were evaluated, well as serum levels of progesterone in order to detect the age of puberty. Linear effects (P<0.01) to body weight (BW) with values being 59.5, 61.4, and 58.0 to HGR, MGR and LGR, respectively. Linear effects (P<0.01) was also observed for average daily gain with values being 0.182, 0.156, and 0.136 kg/day, for HGR, MGR and LGR, respectively. The feed:gain ratio showed a linear effects (p<0.02) according to raw sugarcane bagasse inclusion in diet with values being 6.1, 7.1 (M) and 9.2 kgDM/kg BW for HGR, MGR and LGR, respectively. Linear effects (p<0.01) was observed for the percentage of animals of ewe lambs the reached puberty at 7 months of age, showing highest values for MGR (60%), followed by HGR (45%) and LGR (15%) treatment. Trial II: The same ewe lambs of Experiment 1 were bred at 37 kg of BW and after lambing they received a unique diet. The ewe lambs were blocked according to body weight and days in milking. According to the energy density increase in the diet, quadratic effects (p<0.01) was observed on milk production recorded in a 3-hour interval (137.9; 150.1 and 104.4 g), fat corrected milk (167.2, 178.9 and 129.4 g) and fat and protein corrected milk (216.5, 140.5, 162.7g). Fat (9.77, 8.92 and 8.35%) and protein (4.2, 4.2, and 4.6%) showed linear effects (P=0.01) for fat and (P<0.01) for protein. Trial III: The aim of this study was to evaluate the inclusion of raw sugarcane bagasse (RSB) on dry matter intake and apparent digestibility of nutrients, nitrogen balance and ruminal parameters of Santa Ines ram lambs. Four ruminally fistulated ram lambs averaging 30 kg of BW were placed in metabolism crates. The control treatment (CONT) consisted of a high concentrate diet with 10% of coastcross (Cynodon sp.) hay in the dietary DM and the others treatments consisted of 10, 20 and, 30% of RBS in the dietary DM. The diets were formulated to provide similar concentration of crude protein (13.75±0.25%). No effects were observed for DMI, OM, and CP in kg/day and g/kg of BW0.75. Linear effects (p<0.02) was observed for NDF intake according RBS inclusion. Variables, as well as total SCFA, acetate, propionate, and butyrate concentrations. Ruminal ammonia and apparent nutrient digestibility also did not differ among treatments.

Differences in physiology between r and K-bacterial strategists. The definition of bacterial r/K-strategists is currently based on the time interval they need to form a colony on agar plate. Also, their growth rate which is often used to identify r/K-position within a pair of bacterial strains. To date it was evidenced that also other physiological characteristics relate to bacterial r/K-status, for example their different ability to 1) adapt for changing conditions 2) utilize complex or very diluted substrates, 3) use secondary metabolites to cope with other strains and possibly also others. The intersection of macro- and microbiological r/K-conceptions lies in time distribution of r/K-strategists during succession. The aim of this study was to verify the basic r/K-characteristics on nine chosen strains and to correlate them with their physiological differences that are implicitly regarded as characteristic for r/K-groups. The study deals with growth rates measurements on both liquid and solid media, identification of fatty acid composition and membrane fluidity of strains cultivated at near-optimum and cold temperature in order to track the differences in cold adaptation. The study also deals with the description of possible new K-strategist characteristic: the lack of correlation between the colony...

Seston is the complex of organic and inorganic particles suspended in the water column in stream ecosystems. This detrital pool is a significant vector of energy and nutrients from headwaters to the ocean. Many of the processes involved in seston generation in streams involve the terrestrial ecosystems they drain. My objective was to determine how land use influences seston quality. Seston was collected from 9 streams along a gradient of catchment forest cover, draining 3 land-use categories: forested, agricultural, and residential. Quality variations were determined through the physical composition (size classes and concentration), chemical composition (carbon, nitrogen, and phosphorous) and organic content of seston, as well as microbial respiration of associated assemblages and growth rates of Chironomus tentans fed seston. There was more seston in streams draining less forested catchments but proportionally that material was less organic. Ultrafine particles dominated seston size classes at all sites and was higher in streams with less catchment forest cover. Phosphorous content of seston, as a % of ash free dry mass, and dissolved P in the water were higher in more disturbed streams, and C:N and N:P ratios of seston were higher in forested streams. Microbial respiration and instantaneous growth rates of C. tentans were highest on residential seston, indicating seston from those streams was more bioavailable. These results indicate that the quality of seston in stream ecosystems is linked to terrestrial processes and influenced by land use. / Master of Science

Globally, riparian ecosystems are in decline due to anthropogenic modifications including damming, channelization and the conversion of the floodplain for human use. These changes can profoundly affect riparian species as many have adapted to the historical dynamism of these ecosystems. On the managed Missouri River, an imperiled shorebird, the piping plover (Charadrius melodus) uses riverine sandbars to breed. From 2004 to 2009, due to limited breeding habitat and low population numbers, the U.S. Army Corps of Engineers constructed 255 ha of sandbar habitat to benefit piping plovers and least terns (Sternula antillarum). During the breeding seasons of 2010 and 2011, historically high flows resulted in the creation of 1,887 ha of suitable sandbar habitat. Our study compared the demographic response and the condition of piping plovers to these anthropogenic and natural habitat creation events. From 2005–2014 we monitored 1,071 nests, and from those nests we uniquely banded 968 adults and 2,021 piping plover chicks. We obtained 405 egg (clutch) mass measurements, 1,285 mass measurements from 633 adults, and 7,093 mass measurements from 1,996 plover chicks resulting in 3,175 mass measurements from 654 broods of chicks. We also collected 3,347 invertebrate prey samples. We used a random effects logistic exposure model to estimate nest success, a random effects Cormack-Jolly-Seber model in RMARK to estimate pre-fledge chick survival and the Barker model in RMARK to estimate hatch-year (HY) and after hatch-year (AHY) survival and fidelity to our study area. We then used estimates from these analyses to calculate reproductive output, reproductive output necessary for a stationary population, and population growth (λ). For adult condition and egg (clutch) mass we used generalized linear mixed regression, and for pre-fledge chick growth rates we used a modified Richard's model to estimate the effects of habitat type (pre- vs. post-flood). We also tested for differences in invertebrate prey abundance between habitat types using negative binomial regression. Our results indicated that AHY survival varied throughout our study and was lowest during the flood (2010 and 2011). We found that nest success, pre-fledge chick survival, reproductive output, and HY survival and fidelity were consistently higher on the flood-created habitat than engineered habitat, leading to sustained population growth after the flooding, as compared to just one year of population growth prior to the flood. Unlike pre-flood engineered habitat, the demographic parameters we measured did not decrease as the post-flood habitat aged. These differences were related to increased sandbar habitat, low nesting densities, and decreased nest and chick predation on the post-flood habitat. Although we hypothesized that increased demographic rates would be reflected by increased piping plover condition following the flood, we found that our measured condition variables (adult mass, clutch mass, and pre-fledge chick growth rates) remained unchanged following the flood. We also found evidence that clutch mass, chick growth rates and invertebrate prey abundance decreased as the post-flood sandbar habitat aged. As the condition of individuals did not appear to contribute directly to the increased demographic rates following the flood, we suggest that the change in density-dependent predation pressure may explain the discrepancy. As many ecosystems have previously been altered, it's rare that ecologists have the opportunity to compare management practices with natural ecosystem processes. Results from this study suggest that management intervention may not be an equivalent substitute for natural ecosystem processes and provide insight on future management of riparian ecosystem. / Master of Science

Synura petersenii represents a complex of pseudo-cryptic species. These are planktonic colonial organisms belonging to the class Chrysophyceae. The species are abundant in spring and autumn, when they produce golden-brown blooms in oligo-mesotrophic waters. In this thesis, I focused on investigating the effect of temperature to growth parameters of four selected species: S. petersenii, S. americana, S. glabra and S. conopea. Several temperature experiments were performed and statistically analyzed. According to growth curves the temperature 25 žC was mostly stressful for these organisms. Only S. petersenii sensu stricto was sometimes able to growth at this temperature. In general, the significant differences in growth rates were detected between S. petersenii and S. americana. In all experiments, S. petersenii had the lowest growth rate. This ubiquitous species probably acts as a K-strategist. S. americana grew generally very quickly, especially at temperature 13 žC that is obviously optimal for it. Further, I observed a significant strain specificity, which is largely a well-known phenomenon in the ecophysiology. Significant differences in growth rates were noted between temperatures 13 žC and 16 žC, where all tested species grew best, as well. This is in accordance with a general recognition of...

Gracilaria caudata J. Agardh is one of the naturally occurring species in Brazil that produce good quality agar. In Rio do Fogo (RN), Brazil, a green variant was discovered in a G. caudata population of predominantly red (wild phenotype) tetrasporophytes. Epiphytes gametophytes on tetrasporophytes have been observed for both strains. Considering the wild and green variant strains in laboratory control conditions, this study: (i) assessed the impacts of epiphyte gametophytes on tetrasporophytes by evaluating the growth rates, the pigment content, and the photosynthetic potential of the tetrasporophytes; (ii) evaluated the amount of time required for the differentiation of cystocarps in free-living gametophytes and epiphyte gametophytes on tetrasporophytes; (iii) evaluated the number of epiphyte gametophytes produced by tetrasporophyte; and (iv) analyzed anatomical aspects of the intersection between the tetrasporophytes and the tetraspores that germinated on the tetrasporophytes. Samples were cultivated for 12 weeks on laboratory conditions. Control samples had epiphyte gametophytes growing on them, while treatment samples had their epiphyte gametophytes removed weekly. Physiological analyses compared control and treatment samples, while anatomical analysis used the control samples only. Considering the tetrasporophyte growth rates before fertility (2nd week), wild strain showed higher values than green variant; however, after 12 weeks, no differences were found between strains or between samples without epiphyte gametophytes. The wild strain produced tetraspores more frequently than the green variant and showed deficiency in phycoerythrin and allophycocyanin. Green variant treatment samples had higher content of allophycocyanin, phycocyanin and phycoerythrin than the control samples. Chlorophyll a was higher in the wild strain, and treatment samples had lower values in comparison to control samples. Epiphyte gametophytes possibly promoted reduction in pigment content of the tetrasporophytes on both strains. Wild strain samples without epiphyte gametophytes had higher photosynthetic efficiency. Epiphyte gametophytes produced cystocarps one week before free-living gametophytes. The amount of epiphyte gametophytes on tetrasporophytes is not different between strains. Epiphyte gametophytes were visible one week before on the wild strain than in the green variant strain. It was found that tetraspores give rise to epiphyte gametophytes through two distinct germination methods: outside or inside the thallus of the tetrasporophyte. Germination outside the tetrasporophyte thallus was more common, produced visible holdfasts and promoted cortex thickening in the cortical region of the tetrasporophyte. Germination inside the tetrasporophyte thallus did not show evidences of holdfasts nor cortex thickening on the tetrasporophytes. Epiphyte gametophytes holdfasts had adjacent cells to the cortex of the tetrasporophytes when they germinate outside the thallus; however, when germination occurred inside the thallus, the connection interface was closer to the medulla of the tetrasporophyte. Epiphyte gametophytes might represent a new life strategy that promotes sexual variability in a population mostly composed of tetrasporophytes. For cultivation purposes, wild tetrasporophytes with epiphyte gametophytes yielded more mass than the variant tetrasporophytes, being the best option for production. However, the green variant without epiphyte gametophytes produced more phycobiliproteins, making it a better option to harvest those substances / Gracilaria caudata J. Agardh é uma das espécies encontradas na costa brasileira que produzem ágar de boa qualidade. Em Rio do Fogo (RN), Brasil, uma linhagem variante verde de G. caudata foi descoberta em uma população composta principalmente por indivíduos de coloração vermelha (fenótipo selvagem). Gametófitos epífitos em tetrasporófitos foram observados para as duas linhagens. Considerando-se as linhagens selvagem e verde em condições controladas de laboratório, este estudo analisou: (i) os impactos dos gametófitos epífitos nos tetrasporófitos por meio de taxas de crescimento, conteúdo pigmentar e potencial fotossintetizante dos tetrasporófitos; (ii) o tempo necessário para a diferenciação de cistocarpos em gametófitos de vida livre e gametófitos epífitos; (iii) o número de gametófitos epífitos produzidos por tetrasporófito; e (iv) aspectos anatômicos da interseção entre tetrasporófitos e gametófitos epífitos. O experimento teve duração de 12 semanas. Amostras controle foram mantidas com seus gametófitos epífitos durante o experimento, enquanto as amostras tratamento tiveram seus gametófitos epífitos removidos semanalmente. Análises fisiológicas compararam amostras controle e tratamento, enquanto que para os estudos anatômicos utilizou-se apenas as amostras controle. A linhagem selvagem apresentou maiores taxas de crescimento que a linhagem verde nas duas primeiras semanas do experimento, quando ainda não estavam férteis; entretanto, após as doze semanas de cultivo, não foram observadas diferenças entre as linhagens tetrasporofíticas. A linhagem vermelha produziu tetrásporos com mais frequência do que a linhagem verde e apresentou deficiência em ficoeritrina e aloficocianina. As amostras tratamento da linhagem verde apresentaram valores maiores de aloficocianina e ficoeritrina do que às do controle. A linhagem selvagem apresentou menores teores de ficoeritrina e aloficocianina quando comparada à linhagem verde. As amostras tratamento da linhagem verde apresentaram maiores valores de aloficocianina, ficocianina e ficoeritrina que as amostras controle da mesma linhagem. A quantidade de clorofila a foi maior na linhagem selvagem, e as amostras tratamento desta linhagem apresentaram valores maiores que às do controle. A presença de gametófitos epífitos promoveu a redução no conteúdo pigmentar nas duas linhagens. Amostras tratamento da linhagem selvagem apresentaram potencial fotossintetizante maior do que amostras controle. A quantidade de gametófitos epífitos não foi diferente entre as linhagens. Gametófitos epífitos produziram cistocarpos uma semana antes do que gametófitos de vida livre. A linhagem selvagem produziu gametófitos epífitas uma semana antes da linhagem verde. A germinação de tetrásporos em tetrasporófitos ocorreu de duas maneiras: antes e após a liberação de tetrásporos. A liberação de tetrásporos seguida da germinação sobre o tetrasporófito foi mais frequente, produziu apressórios e promoveu aumento do número de células no córtex do tetrasporófito. A germinação de tetrásporos dentro do talo do tetrasporófito não apresentou evidências de apressórios ou espessamento da região cortical do tetrasporófito. A porção basal de apressórios de gametófitos epífitos permaneceu adjacente ao córtex do tetrasporófito. Quando a germinação do tetrásporo ocorreu ainda dentro do talo, a interface de conexão das células foi mais próxima da medula do tetrasporófito. Gametófitos epífitos podem representar uma nova estratégia de vida para a espécie por possibilitar a variabilidade por reprodução sexual em uma população predominantemente composta por tetrasporófitos. Para um possível cultivo em larga escala, tetrasporófitos com gametófitos epífitos da linhagem selvagem seriam mais adequados por produzirem mais massa que os da variante verde. Entretanto, se o objetivo for a produção de ficobiliproteínas, a linhagem verde seria a mais indicadaphycoerythrin and allophycocyanin. Green variant treatment samples had higher content of allophycocyanin, phycocyanin and phycoerythrin than the control samples. Chlorophyll a was higher in the wild strain, and treatment samples had lower values in comparison to control samples. Epiphyte gametophytes possibly promoted reduction in pigment content of the tetrasporophytes on both strains. Wild strain samples without epiphyte gametophytes had higher photosynthetic efficiency. Epiphyte gametophytes produced cystocarps one week before free-living gametophytes. The amount of epiphyte gametophytes on tetrasporophytes is not different between strains. Epiphyte gametophytes were visible one week before on the wild strain than in the green variant strain. It was found that tetraspores give rise to epiphyte gametophytes through two distinct germination methods: outside or inside the thallus of the tetrasporophyte. Germination outside the tetrasporophyte thallus was more common, produced visible holdfasts and promoted cortex thickening in the cortical region of the tetrasporophyte. Germination inside the tetrasporophyte thallus did not show evidences of holdfasts nor cortex thickening on the tetrasporophytes. Epiphyte gametophytes holdfasts had adjacent cells to the cortex of the tetrasporophytes when they germinate outside the thallus; however, when germination occurred inside the thallus, the connection interface was closer to the medulla of the tetrasporophyte. Epiphyte gametophytes might represent a new life strategy that promotes sexual variability in a population mostly composed of tetrasporophytes. For cultivation purposes, wild tetrasporophytes with epiphyte gametophytes yielded more mass than the variant tetrasporophytes, being the best option for production. However, the green variant without epiphyte gametophytes produced more phycobiliproteins, making it a better option to harvest those substances