Magister Scientiae (Biodiversity and Conservation Biology) / 2022-01-31

Orientador: Roberto Goitein / Banca: Alberto Ferreira de Amorim / Banca: Selene Maria Coelho Loibel / Banca: Leandro Muller Gomiero / Banca: Lucy Satiko Hashimoto Soares / Resumo: Visando contribui r para o conhecimento da dieta de peixes que habitam o ambiente pelágico do Oceano Atlântico Sudoeste, e por conseqüência compreender a rede trófica na qual estas espécies estão inseridas, foi elaborado um estudo envolvendo t rês aspectos apresentados nesta tese em forma de capítulos: (1) análise do conteúdo estomacal de Thunnus albacares, T. obesus, T. alalunga, Xiphias gladius, Isurus oxyrinchus e Alopias superciliosus; (2) uso da inferência bayesiana na análise da dieta dos predadores em questão; (3) caracterização da rede t rófica pelágica considerando as assinaturas isotópicas dos consumidores e suas presas. A coleta dos peixes foi realizada em parceria com a frota atuneira de Santos - SP, cuja área de operação compreende o mar aberto frente às regiões Sudeste e Sul do Brasil . De maneira geral, os resultados indicam que: (1) A dieta de T. albacares e T. obesus é composta primariamente por peixes teleósteos (Bramidae, Gempylidae, Trichiuridae, ent re outros), e secundariamente por moluscos Teuthida (lulas em geral ); (2) Thunnus alalunga apresentou um padrão inverso aos demais atuns anal isados, alimentando-se preferencialmente de moluscos Teuthida, deixando os peixes teleósteos em segundo plano; (3) O espadarte (Xiphias gladius) alimenta-se primariamente de lulas Ommast rephidae; (4) a alimentação de I. oxyrinchus e A. superciliosus foi dominada por cefalópodes da ordem Teuthida. Ent re os peixes, destaque para as famílias Scombridae e Trichiuridae; (5) A análise da assinatura isotópica dos predadores corroborou os padrões descri tos pela análise do conteúdo estomacal; (6) as espécies de Scombridae são presas importantes para os predadores de topo, como X. gladius e A. superciliosus. Os achados remontam a importância de pesquisas que analisem a alimentação de peixes explorados comercialmente, visto que estes estudos podem... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: In order to cont ribute to the diet knowledge of fish that inhabit the pelagic environment of the southwest Atlantic Ocean, and in consequence be aware about this species insertion in the t rophic web, a study involving four distinct aspects was made up in chapters: (1) stomach content analyses of Thunnus albacares, T. obesus, T. alalunga, Xiphias gladius, Isurus oxyrinchus e Alopias superciliosus; (2) use of Bayesian inference in analyzing the diet of these predators; (3) by using the isotopic signatures of the predators, as well as their prey, to assume thei r trophic role in the system. Fish collect ions were made by collaboration of the Santos-SP tuna fishery fleet, which operates in an area comprising the open sea off the southern and southeastern Brazilian coast . In general results indicate that: (1) The T. albacares and T. obesus diet consists primarily of teleost fishes (Bramidae, Gempyl idae, Trichiuridae, among others), and secondarily of Teuthida squids; (2) Thunnus alalunga showed an opposite food composition when compared to the other tunas, feeding mainly on Teuthida squids, and teleost fish comprised a second food in importance; (3) the swordfish (Xiphias gladius) feeds mainly on the Ommast rephidae squids; (4) the food of I. oxyrinchus and A. superciliosus was dominated by cephalopods Teuthida. Among fishes, the emphasis is represented by the representatives of families Scombridae and Trichiuridae; (5) (5) The predators isotopic signature analysis corroborated the described pat terns shown by the stomach contents analyses; (6) The Scombridae species are important prey species for the top predators, such as X. gladius and A. superciliosus. The findings should help one to remember the importance of investigat ions related to fish species, which use to be important for commercial purposes, as such studies may become essential tools to be used by alternative conservation... (Complete abstract click electronic access below) / Doutor

Climate change and fisheries have affected marine environments worldwide leading to impacts on ecosystem structure and functioning. However there is clear evidence of spatial variability in the response of these impacts both within and among marine ecosystems. Although several studies have tried to explain the effect of these impacts on marine food webs, it is unclear how they interact, and how they may affect marine ecosystems remains an important unanswered question. This suggests the urgent need for multiple-trophic level and ecosystem-based management approaches to account for both fisheries and climate change impacts at ocean basins across the globe. Marine apex predators, such as seabirds, are vulnerable to the effects of both climate and fishing impacts, and can be used as reliable and sensitive bio-indicators of the status of the marine ecosystem. The Celtic Sea ecosystem is a productive shelf region in the Northeast Atlantic. It is characterized by high fish and invertebrate biodiversity. In addition, internationally important numbers of seabirds, such as Northern gannet Morus bassanus (L.), Manx shearwater Puffinus puffinus (B.), Common guillemot Uria aalge (P.) and Black-legged kittiwake Rissa tridactyla (L.), breed along the Celtic Sea coasts. In recent years, fisheries from across Europe have intensively exploited the Celtic Sea, leading to changes in stock structure. Moreover, the increase in annual average Sea Surface Temperature by 0.67 oC over the past two decades has altered the composition of plankton communities. These impacts, independently and in tandem, are likely to have had dramatic effects upon the Celtic Sea food web emphasizing the need to enhance our understanding of this important marine ecosystem. In this thesis the effects of climate change and fisheries on the Celtic Sea pelagic food web are evaluated, in particular focussing on the response of seabird populations. This is in part because of recent declines in the breeding success of many seabird colonies in the northeast Atlantic, particularly around the North Sea. Long-term data across four trophic levels (phytoplankton, zooplankton, mid-trophic level fish and seabirds) and different modelling approaches are used to determine factors influencing seabird productivity at different geographical scales. First, I review the direct and indirect effects of climate change and fisheries upon marine ecosystems, as well as their impacts upon marine birds. Second, I use data collected during 1986-2007 from a single seabird colony, across four trophic levels, to investigate long-term direct and indirect climate effects. The results suggest only a weak climate signal in the Celtic Sea, and this is only evident between mid-trophic level fish and certain species of seabird. Third, a similar multi-trophic level approach across three nearby regions in the southwest UK (Irish Sea, Celtic Sea, and English Channel) reveal no evidence of a bottom-up signal during the period 1991-2007. These findings are in contrast with the nearby North Sea region, where a strong bottom-up effect was found to affect seabird populations, highlighting the importance of regional-based studies across multiple trophic levels. Finally, to provide a more complete picture of the Celtic Sea, and how it might respond to changes in fisheries management and climatic variation, I use the complex tropho-dynamic ecosystem model Ecopath with Ecosim. The main focus is on how seabird biomass changes in response to the application of different fisheries regimes likely to be implemented under forthcoming reforms to the Common Fisheries Policy (e.g. the application of quotas and discard bans), as well as future climate change scenarios, in order to provide guideline support for resource management and seabird conservation in the Celtic Sea. The results suggest that some seabird guilds (gulls and some other scavengers) may be negatively affected by a reduction in discards, while other species (offshore divers) will benefit from a decrease in the fishing of pelagic fish species. Climate change is likely to have a negative impact across all trophic levels with a strong negative impact upon seabird populations. Therefore seabirds are likely to show species-specific responses to both climate variation (bottom-up effect) and changes in fishing practices, in particular our findings suggest that for some species climate may outweigh the fisheries impacts even when fisheries pressure is reduced by 50%. In summary, this study suggests that despite the generally negative impact of climate described for some regions in the Northeast Atlantic, the Celtic Sea ecosystem seems to be more resilient. However, both climate and fisheries and the interactions between these factors should be taken into account in the formulation of future management plans for the Celtic Sea ecosystem. The use of multiple-trophic level and ecosystem-based approaches over multiple spatial and temporal scales has helped to elucidate possible trophic mechanisms that are the response to future fishing and climate impacts in the Celtic Sea. The results of this study could have implications for both management plans and conservation policy.

<p>Fisheries agencies around the Baltic Sea use hydroacoustics to assess stock sizes of herring and sprat. These assessments rely on the assumption that the acoustic properties of Baltic clupeids are the same as North Sea herring. This may lead to biased results, as system-specific differences in salinity and fish fat content may influence acoustic target strength. The acoustic properties of the Baltic clupeids were explored and a new relationship between target strength and fish length was developed (paper I). The intercept of this new relationship is 3.4 dB higher than normally used by the agencies. Applying this new relationship would reduce the acoustic stock biomass estimates by approximately 50%.</p><p>Diel variation in the vertical distribution of fish may influence acoustic abundance estimates. Fish body posture may influence target strength and if fish concentrate near the surface or bottom this may affect detectability by an echo sounder. A seabed-mounted, upward pinging echo sounder was used to study diel variation in vertical distribution, acoustic size distribution and abundance of fish (Paper II). Differences between day and night were substantial and it was concluded that night time acoustics are to be preferred, at least in our study area. The seabed-mounted echo sounder was also used to study fish swimming activity and vertical distribution in relation to light intensity and water temperature (paper III). Four phases of fish distribution were distinguished over the diel cycle (day, night, dawn and dusk). Acoustic tracking was used to estimate the swimming speed of individual fish. The speed varied among the diel periods and the greatest difference was observed between day and night with twice as high swimming speed during the day. Regression models were developed to investigate the effects of fish size and environmental factors (water temperature, light intensity at the sea surface and<i> in situ</i>, measured at the depth of the fish) on swimming speed. Fish size, light intensities and temperature were all significant variables in the models, with fish size being generally most important. These results have clear implications for fish bioenergetics models. Such models should account for seasonal, light-driven cycles in the activity-induced respiration estimates, in particular when modelling populations at high latitudes.</p><p>Vertical and horizontal fish distributions were studied from spring through autumn during two consecutive years (paper IV). The seasonal dynamics in vertical distribution patterns were consistent between years. Prior to thermocline formation, fish of all sizes concentrated near surface where water temperatures were higher than in the underlying water mass. During the summer period of pronounced thermal stratification, larger fish were found deeper than small individuals (including young-of-the-year fish), which remained close to the surface. In the autumn, when the thermal stratification diminished, the small fish moved somewhat deeper while larger individuals dispersed throughout the water column. Fish showed clear horizontal patchiness, but horizontal distributions were not significantly related to wind directions.</p>

Fisheries agencies around the Baltic Sea use hydroacoustics to assess stock sizes of herring and sprat. These assessments rely on the assumption that the acoustic properties of Baltic clupeids are the same as North Sea herring. This may lead to biased results, as system-specific differences in salinity and fish fat content may influence acoustic target strength. The acoustic properties of the Baltic clupeids were explored and a new relationship between target strength and fish length was developed (paper I). The intercept of this new relationship is 3.4 dB higher than normally used by the agencies. Applying this new relationship would reduce the acoustic stock biomass estimates by approximately 50%. Diel variation in the vertical distribution of fish may influence acoustic abundance estimates. Fish body posture may influence target strength and if fish concentrate near the surface or bottom this may affect detectability by an echo sounder. A seabed-mounted, upward pinging echo sounder was used to study diel variation in vertical distribution, acoustic size distribution and abundance of fish (Paper II). Differences between day and night were substantial and it was concluded that night time acoustics are to be preferred, at least in our study area. The seabed-mounted echo sounder was also used to study fish swimming activity and vertical distribution in relation to light intensity and water temperature (paper III). Four phases of fish distribution were distinguished over the diel cycle (day, night, dawn and dusk). Acoustic tracking was used to estimate the swimming speed of individual fish. The speed varied among the diel periods and the greatest difference was observed between day and night with twice as high swimming speed during the day. Regression models were developed to investigate the effects of fish size and environmental factors (water temperature, light intensity at the sea surface and in situ, measured at the depth of the fish) on swimming speed. Fish size, light intensities and temperature were all significant variables in the models, with fish size being generally most important. These results have clear implications for fish bioenergetics models. Such models should account for seasonal, light-driven cycles in the activity-induced respiration estimates, in particular when modelling populations at high latitudes. Vertical and horizontal fish distributions were studied from spring through autumn during two consecutive years (paper IV). The seasonal dynamics in vertical distribution patterns were consistent between years. Prior to thermocline formation, fish of all sizes concentrated near surface where water temperatures were higher than in the underlying water mass. During the summer period of pronounced thermal stratification, larger fish were found deeper than small individuals (including young-of-the-year fish), which remained close to the surface. In the autumn, when the thermal stratification diminished, the small fish moved somewhat deeper while larger individuals dispersed throughout the water column. Fish showed clear horizontal patchiness, but horizontal distributions were not significantly related to wind directions.

Total mercury (Hg) levels were determined in the tissues of ten taxa of pelagic fishes, with a special emphasis on apex predators (large vertebrates). Highest Hg levels were observed in blue marlin (Makaira nigricans), carcharhinid sharks (Genus Carcharhinus) and little tunny (Euthynnus alletteratus), ranging from 1.08 to 10.52 ppm. Moderate to low concentrations (<1.0 ppm) were observed in blackfin tuna (Thunnus atlanticus), cobia (Rachycentron canadum), dolphinfish (Coryphaena hippurus), greater amberjack (Seriola dumerili), king mackerel (Scomberomorus cavalla), wahoo (Acanthocybium solandri) and yellowfin tuna (Thunnus albacares). For the majority of species examined, Hg level did not vary significantly between locations (Texas and Louisiana) and years (2002 and 2003). The relationship between Hg level and fish size/weight was also explored and six taxa (blackfin tuna, carcharhinid sharks, dolphinfish, king mackerel, wahoo, yellowfin tuna) showed significant positive relationships between Hg level and body size and/or weight. Natural dietary tracers, stable isotopes (15N, 13C) and fatty acids were used to evaluate the relationship between Hg and trophic position and the relationship between Hg and dietary history. Stable nitrogen isotope analysis showed that Hg levels in fish tissues were positively associated with trophic position. Based on the 13C and 15N values of pelagic consumers examined in this study, three natural groups were identified with cluster analysis, and the same groupings were detected based on fatty acid profiles. This not only confirmed the existence of these natural groupings, but also indicated that the distinguishing factors for the grouping was likely connected with the dietary history of these fishes. The classification tree based on the fatty acid profiles of pelagic fishes readily separated fishes from different regions, suggesting that diets of pelagic taxa within the same region are similar or these consumers share a common source of organic matter in their food web. Findings from this study complement other Hg investigations conducted in the Gulf and also furthered our understanding of the link between feeding ecology and Hg accumulation. Moreover, the combined use of stable isotope and fatty acid techniques provided new insights on the dietary history of pelagic fishes in the Gulf of Mexico.

Annotation Long-term fixed-location hydroacoustic study with uplooking transducer was performed during 2005 in Římov reservoir, Czech Republic. It dealt mainly with fish behaviour in the open water of reservoir, especially with sinusoidal swimming behaviour. The dependence of pelagic fish behaviour on environmental conditions was also studied.

With the sampling limitations for the study of the hadopelagic environment, an alternative in the use of sediment eDNA is utilized in one of the world’s most productive ecosystems: The Atacama Trench. Having a history of overfishing events and effects of ENSO of differing intensities, five sites were sampled through sediment cores at depths going from 2400 to nearly 8000m. As layers of sediment are formed over time, within each layer are fragments of eDNA deposited by the pelagic fauna that inhabited at that time. For this study, the sediment layers were dated and the community composition for the years in which they inhabited was determined utilizing metabarcoding with the Euka02 and 18SMini primers. The communities identified for both primers are mainly composed of chordates and members of the recently established Chromista kingdom, and through further beta-diversity analyses, are shown to not be too distinct from one another. Alphadiversity was calculated for all sites in intervals of 15 years, and it became clear that there was a drop in biodiversity from 1977 to 2002. This is attributed to human influence, as the extensive fishing efforts in this period of time combined with the escape of salmonids from farms and adverse ENSO events contributed to the reduction of diversity, warning that although diversity is currently back at previous levels, anthropogenic impacts must be limited for conservation purposes. Overall, it is shown that sediment eDNA is a valuable emerging tool not only for research on the current state of communities in pelagic environments, but also as a snap-shot of the past that allows for comparisons within an ecosystem.

The effects of a mountain lake on nitrogen dynamics in a sub-alpine watershed were examined via watershed monitoring, mesocosm experiments, microcosm experiments, and enzymatic assays during spring and summer of a single year. Our study addressed the questions: (1) How does hydrologic transport through the lake affect the net fluxes of dissolved nitrogen (N) species? (2) What are the net effects of the littoral zone biota on dissolved N fluxes? (3) What are the seston and benthic uptake rates of nitrate? (4) What is the magnitude of N retention in littoral zone sediments? (5) What role does microbial hydrolysis of amino-groups from organic matter play in the uptake of dissolved nitrogen, relative to rates of nitrate uptake? Our study found a net positive flux of total dissolved N and dissolved organic N (DON), and a net negative flux of nitrate through the lake. During snowmelt, when the majority of nutrients are transported in this watershed, DON was retained in the lake. Several experiments were run to more closely examine the mechanisms behind these observations. Experiments in 2.1 m3 mesocosms in June and July measured rates of DON flux from the littoral zone sediments into the water column that were similar to increments measured in the lake. 15N-nitrate mesocosm and microcosm tracer experiments quantified benthic and pelagic nitrate uptake and retention of that nitrate in the benthic sediments. Areal nitrate uptake was 65-times greater in the sediments than in the water column seston and the turnover rate (half life) of the newly input nitrate pool in the sediments was 33-64 days. Finally, the prevalence of DON relative to dissolved inorganic N (DIN) and high measured rates of enzymatic amino acid hydrolysis suggest the importance of DON as a source of N for this aquatic system.

Coastal environments are among the most threatened ecosystems globally, with water quality degradation constituting a major scientific and management issue that requires addressing. Burrowing sandprawns (Kraussillichirus kraussi) have been shown in past research to improve water quality by removing microalgae from the water column. Their burrows are thought to act as biofiltration systems, with water-borne phytoplankton particles being adsorbed onto burrow walls during bi-directional water pumping. However, not much is known about ecological repercussions of this hypothesised mechanism and whether it indiscriminately impacts all microorganisms in the water column. This issue forms the foundation of my research, which aimed to experimentally determine whether potential filtration effects of sandprawns are consistent across pelagic bacterial and phytoplankton assemblages or whether there are any discriminatory responses. Findings demonstrated that increasing sandprawn density did not significantly reduce the abundance of bacterial water quality indicators (Escherichia coli and total heterotrophic bacteria). However, sandprawns were found to reduce the abundance of phytoplankton cells. At the end of the experiment, the relative abundance of phytoplankton in the controls were 1.9 times higher relative to the 100% treatment. Similarly, the concentrations of nitrite were 17.7 times higher in controls relative to 100% treatment at the end of the experiment. Furthermore, increasing sandprawn abundance induced a phytoplankton sizebased shift from pico- to nano dominance, with nanophytoplankton contributing 17.76% at the beginning of the experiment, but shifting to 58.07% at the end of the experiment in the maximum sandprawn density treatment. Additionally, sandprawn presence had no significant impact on cryptophytes or Prochlorococcus-like algal abundance. These results demonstrate that sandprawns disproportionately impact certain groups and influence phytoplankton assemblages beyond biomass decline. These findings are novel as such discriminatory effects on pelagic assemblages have previously not been attributed to endobenthic deposit-feeding ecosystem engineers. This study therefore provides novel insights into mechanisms by which these organisms may alter coastal ecosystems and influence bentho-pelagic coupling processes. This is especially significant when viewed in the context of global change, where understanding the factors that influence phytoplankton dynamics are important for predicting ecosystem functioning under projected climatic conditions. Given the overall top-down impact of sandprawns on phytoplankton, this study supports the idea of sandprawns being effective nature-based tools that can mitigate the global challenge of eutrophication in coastal ecosystems. The results of this study ultimately emphasises the need for protection and conservation of sandprawns (and functionally similar endobenthic engineers) and their habitats from threats such as habitat loss.