Molecular analysis of anterior endoderm during Xenopus development: a funtional and genomic approach

Tese de doutoramento em Biologia (Biologia do Desenvolvimento), apresentada à Universidade de Lisboa através da Faculdade de Ciências, 2008Fundação para a Ciência e Tecnologia (FCT), (SFHR/BD/10035/2002

Microbiome-targeted interventions during gastrointestinal mucositis

Gastrointestinal mucositis (GI-M) remains a significant complication of cancer treatment that severely affects patient’s quality of life and treatment compliance. Patients frequently experience symptoms such as nausea, vomiting, abdominal pain and diarrhea. Ultimately, these symptoms lead to decreased chemotherapeutic dosage or even to a discontinuation of the treatment. Although a plethora of studies have implicated the gut microbiome in the pathobiology of GI-M, there has been relatively scarce research into the development of microbial interventions. As such, the PhD research described in this thesis aimed at describing key mechanisms involved in host-microbe interactions through in-depth longitudinal analyses in preclinical and clinical samples and at investigating the efficacy of several microbial interventions. The results show that, while vitamin C holds promise to reduce GI-M symptomology, Blautia luti and fecal microbiota transplantation (FMT) may support the gut microbiome with greater efficacy. Furthermore, B. luti was also identified as risk predictor in cancer patients undergoing chemotherapy, suggesting that the baseline microbiota is a predictor for toxicity outcomes. Additionally, work from this thesis also shows the challenges in assessing absorption of anti-infectives (e.g., ciprofloxacin and fluconazole) during GI-M, thus demonstrating the need for future studies on the exposure of different anti-infectives routinely used during chemotherapy regimens. Altogether, the results support microbial modulation in supportive care cancer as a promising approach to reduce GI-M in cancer patients. Furthermore, it also contributes to the development of new guideline for the prophylactic treatment with anti-infectives, thus optimizing supportive care in cancer patients

Public-Private Partnerships : risk of default measured by financial ratios in EP road sub-concessions

Mestrado em FinançasAs infraestruturas rodoviárias em Portugal viveram um grande desenvolvimento nos últimos anos, tornando-se um dos países com maior extensão relativa de rede de autoestradas no mundo. De facto, através dos Planos Nacionais Rodoviários elaborados em 1985 e 2000, foi construída uma vasta rede de autoestradas, inicialmente através de um modelo sem nenhum custo para o utilizador e posteriormente através do modelo de subconcessões da empresa EP -Estradas de Portugal, SA. Para a realização destes investimentos foi privilegiado o uso das Parcerias Público-Privadas (PPP), que, assim, permitiram um forte envolvimento e participação do setor privado, e uma forma de estruturação financeira conhecida como Project Finance. Este artigo analisa um dos elementos chave nos modelos de parceria público-privada - o financiamento. Qual é o comportamento da dívida durante a vida da concessão e de que forma as entidades financiadoras procuram avaliar o risco de incumprimento. A metodologia utilizada consistiu em estimar os fluxos de caixa das várias subconcessões e então calcular alguns dos rácios mais utilizados na medição do risco de incumprimento e da volatilidade dos fluxos de caixa. Os resultados permitem concluir que com maturidades elevadas e existindo estabilidade dos cash-flows, os projetos conseguem assegurar o cumprimento do serviço da dívida, reduzindo o risco de contraparte para as entidades financiadoras.The road infrastructure in Portugal experienced a great development in recent years, making it one of the countries with the highest relative extension of motorway network in the world. In fact under the National Road Plans reported to 1985 and 2000, a vast network of motorways was built initially through a model at no charge to the user and at a later stage by the sub-concessions model of Estradas de Portugal, SA. For these investments was privileged the use of Public Private Partnerships (PPPs), allowed a strong involvement and participation of the private sector and also the use of a form of financial structuring known as Project Finance. This paper analyzes one of the key aspects in public-private partnership model - the financing. What?s the behavior of debt through the life of the concession and how the financing entities seek to assess the risk of default. The methodology used consisted in estimating the cash flows of the various sub-concessions then calculate some of the ratios commonly used in the measurement of default risk and the volatility of cash flows. The results show that with high maturity and stability of existing cash flows, projects can ensure compliance with the debt service, reducing counterparty risk to lenders

Ecohydraulics of pool-type fishways for the Iberian Barbal (Luciobarbus Bocagei Steindachner, 1864)

Doutoramento em Engenharia Florestal - Instituto Superior de AgronomiaThis study analyses the impact of different hydraulic conditions on the Iberian barbel’s upstream movements in a pool-type fishway. Developed in an experiment pool-type fishway prototype and including fish of different sizes, this study investigates: i) the efficiency of passage through submerged orifices or notches; ii) the effect of velocity, turbulence and Reynolds shear stress on this species’ behaviour; iii) the suitability of straight and offset orifices to fish’s passage and, finally, iv) the efficiency of offset and straight orifices with a deflector bar for this specimens’ movements. The fishways was found to be efficient to the upstream passage of this species. Submerged orifices were preferentially used by specimens, mainly by small fish which, although their higher rheotatic capacity, showed strong difficulties to pass through the fishway. The behaviour of the latter was also the most affected by turbulence and Reynolds shear stress, which seemed to be the variables affecting fish’ movements the most. Straight orifices were found not be adequate to fish passage, even when added of a deflector bar. The results are discussed in terms of future research delineation

A strategy to overcome the drug resistance in epilepsy

The resistance to antiepileptic drugs (AEDs) remains a major unsolved therapeutic problem, which affects 30-40% of patients with epilepsy. The overexpression of multidrug efflux transporters, as the P-glycoprotein (P-gp), at the level of the blood-brain barrier of epileptic patients has been suggested as a key mechanism underlying the refractory epilepsy. Bearing this in mind, efforts have been made to search for therapeutically useful P-gp inhibitors. In an attempt to find potent and safer P-gp inhibitor drugs, a particular emphasis has been given to flavonoid compounds. Actually, apart from their potential value as P-gp inhibitors, these phytochemical compounds have been recognised as having a panoply of important pharmacological properties like anti-inflammatory, antioxidant, antitumoral, antimicrobial, antiviral, hormonal and even anticonvulsant effects. Taking this into account, the purpose of the present thesis was to conduct a comprehensive in vitro and in vivo evaluation of the potential of flavonoids as P-gp inhibitors, but also to explore a strategy of flavonoid/AED combined therapy as a possible approach to overcome the P-gp–mediated pharmacoresistance in epilepsy. This project involved the development and validation of appropriate and reliable bioanalytical techniques to support the accomplishment of the intended studies. Thus, high-performance liquid chromatography methods coupled with diode array detection (HPLC-DAD) were properly validated for the quantification of the target AEDs and some of their main metabolites in cell culture samples and in rat plasma and brain matrices. An additional HPLC-DAD technique was also developed to quantify several AEDs and metabolites in human plasma, which has shown to be a useful tool for the therapeutic drug monitoring in the clinical practice. According to the results of a set of in vitro assays, five out of eleven flavonoids tested, namely baicalein, (-)-epigallocatechin gallate [(-)-EPG], kaempferol, quercetin and silymarin demonstrated to have an interesting potential in inhibiting the P-gp activity. These promising flavonoids also promoted a significant increase in the intracellular accumulation of the AEDs carbamazepine (CBZ), oxcarbazepine (OXC) and phenytoin (PHT) and their active metabolites carbamazepine-10,11-epoxide (CBZ-E) and licarbazepine (LIC) in the Madin-Darby canine kidney cell line transfected with the human multidrug resistance-1 gene which encodes the human P-gp (MDCK-MRD1), showing up as important drug candidates to overcome the AED-resistance. Actually, excluding LTG, all the AEDs tested (CBZ, OXC and PHT) as well as their active metabolites (CBZ-E and LIC) were found to be P-gp substrates in the MDCK-MDR1 cells. Additionally, CBZ, CBZ-E, LIC, LTG, OXC and PHT promoted a statistically significant decrease of the intracellular concentration of rhodamine 123 (a classic P-gp probe substrate), suggesting an inducer effect on the functional activity of P-gp. An assessment of the potential synergic effects of baicalein, (-)-EPG, kaempferol, quercetin and silymarin on the P-gp inhibition was also performed, firstly in in vitro conditions and then in in vivo experiments. Indeed, when compared to their individual activity, some dual flavonoid combinations exhibited an increased potential in inhibiting the P-gp in the in vitro assays. Moreover, the dual combinations of (-)-EPG/silymarin and kaempferol/baicalein demonstrated a great potential in enhancing the intracellular accumulation of CBZ, OXC and PHT and their metabolites CBZ-E and LIC in the MDCK-MDR1 cells and such effects were comparable to those promoted by verapamil (the standard P-gp inhibitor). The effect of the combination of (-)-EPG/silymarin was also tested in transport assays of LIC (P-gp substrate) through MDCK-MDR1 cells mounted in Ussing chambers; as expected, this combination of flavonoids increased the apparent permeability coefficient of LIC. Overall, these in vitro findings were further supported by in vivo results. In fact, after the pretreatment of male Wistar rats with silymarin an increasing in the plasma concentrations of the studied AEDs (CBZ, OXC and PHT) was observed. Nevertheless, it should be highlighted that the main effects induced by silymarin were found on the OXC pharmacokinetics, for which was found a statistically significant increase in the peak plasma concentration (50%) and in the extent of systemic exposure (41%), having a direct impact on the drug concentrations reached in the brain. On the other hand, the use of dual combinations of (-)-EPG/silymarin on the inhibition of the activity of P-gp was also evaluated in vivo in Wistar rats, being noticeable the synergic potential of (-)-EPG/silymarin combinations in enhancing the degree of systemic exposure to OXC and LIC (a pharmacologically active metabolite of OXC), and it occurred in a comparable extent to that observed for verapamil (positive control). Indeed, the pretreatment of male Wistar rats with dual silymarin/(-)-EPG combinations originated peak plasma concentrations of OXC similar to those achieved in the presence of verapamil. Moreover, the effects promoted by silymarin/(-)-EPG combinations on the magnitude of systemic drug exposure were also reflected in the corresponding drug levels attained in the brain (biophase). Hence, according to our findings, it seems that the flavonoid/AED combined therapy can be thought as a promising approach that should continue to be exploited in order to overcome the P-gp–mediated pharmacoresistance. The availability of this in vitro and in vivo information also adds support to the efflux transporter hypothesis in explaining the pharmacoresistant epilepsy. Considering all its intrinsic potential and indisputable properties, the flavonoid-type compounds may emerge as an alternative to the available P-gp inhibitors for a prospective management of patients with drug-refractory epilepsy.A epilepsia é uma das doenças neurológicas crónicas mais comuns e tem um grande impacto negativo na qualidade de vida dos doentes, sendo de extrema importância os esforços continuados para desenvolver novos fármacos antiepiléticos e novas abordagens terapêuticas. Contudo, apesar dos avanços significativos alcançados nos últimos anos, os fenómenos de farmacorresistência associados aos fármacos antiepiléticos são provavelmente um dos principais problemas no que diz respeito à terapêutica da epilepsia, afetando 30-40% dos doentes. De facto, esta situação tem proporcionado um ímpeto crescente para o desenvolvimento de abordagens terapêuticas inovadoras e mais eficazes. A sobreexpressão de transportadores de efluxo de fármacos, como a glicoproteína-P (P-gp), ao nível da barreira hematoencefálica, tem sido sugerida como um dos principais mecanismos subjacentes à epilepsia refratária. Desta forma, vários esforços têm sido realizados no sentido de descobrir e desenvolver inibidores da P-gp que sejam úteis de um ponto de vista terapêutico. No entanto, as múltiplas desvantagens apresentadas pelas primeiras gerações de inibidores da P-gp demonstraram a necessidade de encontrar agentes mais potentes e mais seguros, tendo sido dado um ênfase especial nos últimos anos a compostos flavonoides. Além do seu interesse potencial como inibidores da P-gp, uma panóplia de outras propriedades farmacológicas importantes têm sido atribuídas a estes compostos fitoquímicos, entre as quais, por exemplo, efeitos anti-inflamatórios, antioxidantes, antitumorais, antimicrobianos, antivirais, hormonais e, mesmo, anticonvulsivantes. Tendo em consideração todos estes aspetos, a presente tese teve como principal objetivo realizar uma avaliação abrangente, in vitro e in vivo, do papel potencial dos flavonoides como inibidores da P-gp, e também explorar uma estratégia de terapia combinada de flavonoides/fármacos antiepiléticos como possível abordagem para superar a farmacorresistência verificada na epilepsia. Este projeto envolveu o desenvolvimento e validação de técnicas bioanalíticas apropriadas e fiáveis para apoiar a execução dos estudos pretendidos. Neste contexto, métodos de cromatografia líquida de alta eficiência acoplados à deteção por fotodíodos (HPLC-DAD) foram devidamente desenvolvidos e validados para a quantificação dos fármacos antiepiléticos alvo de interesse e de alguns dos seus principais metabolitos em amostras de cultura celular e em matrizes de plasma e cérebro de rato. Uma técnica adicional de HPLC-DAD foi também desenvolvida para a quantificação de vários fármacos antiepiléticos e metabolitos em plasma humano, constituindo uma ferramenta útil para apoiar a monitorização terapêutica destes fármacos na prática clínica. De acordo com os resultados obtidos num conjunto de ensaios in vitro, cinco dos onze flavonoides testados, nomeadamente, a baicaleína, a (-)-epigalocatequina galato [(-)-EPG], o kaempferol, a quercetina e a silimarina demonstraram ter um potencial interessante na inibição da atividade da P-gp. Estes flavonoides promoveram também um aumento significativo da acumulação intracelular dos fármacos antiepiléticos carbamazepina (CBZ), oxcarbazepina (OXC) e fenitoína (PHT), e dos seus metabolitos ativos carbamazepina-10,11-epóxido (CBZ-E) e licarbazepina (LIC), na linha celular Madin-Darby canine kidney, transfetada com o gene de resistência a múltiplos fármacos 1 (MDR1) que codifica para a P-gp humana (MDCK-MRD1), evidenciando-se como candidatos promissores para reverter a resistência associada aos fármacos antiepiléticos. Além disso, com exceção da lamotrigina (LTG), todos os fármacos antiepiléticos testados (CBZ, PHT e OXC), assim como os seus respetivos metabolitos ativos (CBZ-E e LIC), demonstraram ser substratos da P-gp neste modelo celular. Adicionalmente, a CBZ, CBZ-E, LIC, LTG, OXC e PHT promoveram uma diminuição significativa nas concentrações intracelulares de rodamina 123 (um substrato “sonda” clássico da P-gp), o que sugere um efeito indutor, mediado pelos próprios fármacos e metabolitos, da atividade funcional da P-gp. Reconhecendo-se as várias propriedades biológicas atribuídas aos flavonoides e tendo-se em consideração que misturas complexas de flavonoides são consumidas diariamente na nossa dieta, não se poderá ignorar o seu potencial farmacológico sinérgico. Neste sentido, foi concretizada uma avaliação dos potenciais efeitos sinérgicos da baicaleína, (-)-EPG, kaempferol, quercetina e silimarina relativamente à inibição da P-gp, primeiro in vitro e depois in vivo. Na verdade, comparativamente aos resultados individuais obtidos, algumas combinações duais de flavonoides apresentaram um potencial acrescido para inibição da P-gp in vitro. Além disso, algumas dessas combinações, nomeadamente (-)-EPG/silimarina e kaempferol/baicaleína, proporcionaram um aumento substancial da acumulação intracelular de CBZ, OXC e PHT, bem como dos seus metabolitos CBZ-E e LIC, na linha celular MDCK-MDR1, sendo estes efeitos comparáveis aos obtidos com o verapamilo, inibidor de referência da P-gp. Assim, enquanto os flavonoides baicaleína, (-)-EPG, kaempferol, quercetina e silimarina testados individualmente aumentaram em 1,2 a 31 vezes a acumulação intracelular dos fármacos antiepiléticos e metabolitos ativos considerados nas células MDCK-MDR1, as combinações duais desses flavonoides permitiram alcançar aumentos de cerca de 1,5 a 76 vezes. Adicionalmente, o efeito da combinação da (-)-EPG com a silimarina foi também avaliado em ensaios de transporte com a LIC (substrato da P-gp) através de uma monocamada de células MDCK-MDR1 montadas em câmaras de Ussing; como esperado, esta combinação aumentou o coeficiente de permeabilidade aparente da LIC. Em geral, os resultados dos estudos in vitro foram suportados pelos resultados dos estudos in vivo. De facto, após pré-tratamento de ratos Wistar machos com silimarina observou-se um aumento nas concentrações plasmáticas dos fármacos antiepiléticos alvo (CBZ, OXC e PHT). No entanto, é de ressaltar que os principais efeitos induzidos pela silimarina foram notados na farmacocinética da OXC, para a qual foi observado um aumento estatisticamente significativo na sua concentração plasmática máxima (50%) e na sua extensão de exposição sistémica (41%), tendo tais efeitos um impacto direto nas concentrações farmacológicas alcançadas no cérebro. Por outro lado, o uso de combinações duais de (-)-EPG/silimarina na inibição da atividade da P-gp foi também avaliado in vivo em ratos Wistar, sendo evidente o potencial sinérgico destesdois flavonoides no aumento do grau de exposição sistémica à OXC e LIC (metabolito farmacologicamente ativo da OXC), o que ocorreu numa extensão comparável à observada para o verapamilo (controlo positivo). De facto, o pré-tratamento de ratos Wistar com combinações de silimarina/(-)-EPG originou concentrações plasmáticas máximas de OXC semelhantes àquelas obtidas na presença do verapamilo. Além disso, os efeitos promovidos pelas combinações de silimarina/(-)-EPG no que diz respeito à magnitude da exposição sistémica ao fármaco foram também refletidos nos níveis de OXC e LIC alcançados no cérebro (biofase). Assim, de acordo com os nossos resultados, a terapia combinada de flavonoides/fármacos antiepiléticos pode ser considerada como uma abordagem promissora que deve continuar a ser explorada no sentido de superar a farmacorresistência mediada pela P-gp. A disponibilidade desta informação resultante de ensaios in vitro e in vivo contribui também para apoiar a hipótese do envolvimento de transportadores de efluxo, em particular da P-gp, na condição de epilepsia farmacorresistente. Considerando todo o seu potencial intrínseco e propriedades biológicas indiscutíveis, os compostos de tipo flavonoide podem então emergir como uma alternativa aos inibidores da P-gp disponíveis para um tratamento prospetivo dos doentes com epilepsia refratária.The experimental work presented in this thesis was carried out at the Health Sciences Research Centre, Faculty of Health Sciences, University of Beira Interior (CICS-UBI) and at the Center for Neuroscience and Cell Biology (CNC), University of Coimbr

Production of catalysts for the valorization of plastic waste, and for the wet peroxide oxidation of paracetamol

Mestrado de dupla diplomação com a UTFPR - Universidade Tecnológica Federal do ParanáThe efficient treatment of waste plastics and pharmaceutical pollutants is of conspicuous environmental, social and economic benefits. Therefore, here it is approached the application of catalysts that can be efficient in mitigating both environmental problems. In this work, four different catalysts were prepared. Three of them were synthesized by co-precipitation of Ni, Al and Fe nitrates with different mass ratios (5%Ni:95%Al, 20%Ni:80%Al and 10%Ni10%Fe80%Al). The fourth catalyst was prepared by wet impregnation of nickel on alumina. Then fresh catalysts were characterized by Fourier Transformed Infrared Spectroscopy and X-ray diffraction to observe crystalline phases. Carbon structures were prepared from low-density polyethylene, used as representative compound of plastic solid waste by Chemical Vapor Deposition over 20% Ni/Al catalyst in a tubular furnace. Scanning Electron Microscopy analyses were performed, identifying the carbon nanostructures with size variation (1 μm to 4 μm). For paracetamol (PCM) removal Catalytic Wet Peroxide Oxidation was assessed with 20%Ni:80%Al, 10%Fe:10%Ni:80% and commercial Al2O3 catalysts. The conversion of paracetamol, hydrogen peroxide and Total Organic Carbon (TOC) were monitorized by High-Performance Liquid Chromatography, UV-Vis spectrophotometer and TOC analyzer, respectively. The iron-containing catalyst showed the highest catalytic activity in the CWPO of PCM satisfactory conversions (complete removal of PCM after 4 h of reaction time under the following operating conditions: Ccat = 2.5 g/L, CPCM,0 = 100 mg/L, pH0 = 3.5, and CH2O2 = 472.4 mg/L).Um tratamento eficiente de resíduos plásticos e poluentes farmacêuticos traz benefícios ambientais, sociais e econômicos notáveis. Portanto, neste trabalho é proposta a aplicação de catalisadores que possam ser eficientes na mitigação de ambos os problemas ambientais. Neste trabalho preparou-se quatro tipos diferentes de catalisadores. Três deles foram sintetizados por co-precipitação dos nitratos de Ni, Al e Fe, como diferentes proporções de massa (5%Ni:95%Al, 20%Ni:80%Al and 10%Ni10%Fe80%Al). O quarto catalisador foi preparado por impregnação úmida de níquel em alumina. Em seguida, os catalisadores frescos foram caracterizados por Espectroscopia no Infravermelho Transformado por Fourier e difração de raios X, para observar as fases cristalinas. As estruturas de carbono foram preparadas a partir, do polietileno de baixa densidade, usado como composto representativo de resíduos sólidos de plástico, e pelo método de Deposição Química por Vapor realizada em um forno tubular e aplicação do catalisador de 20% Ni/Al. Realizou-se análises de microscopia eletrônica de varredura, para identificar as nanoestruturas de carbono com variação de tamanho (1 μm a 4 μm). Para a remoção do paracetamol (PCM), o método utilizado foi a Oxidação Húmida Catalítica com Peróxido de Hidrogênio, realizado com os catalisadores 20%Ni:80%Al, 10%Fe:10%Ni:80% e alumina comercial. A conversão do paracetamol, peroxido de hidrogênio e carbono orgânico total, foram monitoradas por cromatografia líquida de alta eficiência, espectrofotômetro UV-VIS, e TOC respectivamente. O catalisador contendo ferro mostrou a maior atividade catalítica no processo de CWPO, obtendo conversões satisfatórias de PCM (remoção completa do paracetamol após 4 horas, nas seguintes condições de operação: Ccat = 2.5 g/L, CPCM,0 = 100 mg/L, pH0 = 3.5, and CH2O2 = 472.4 mg/L).This experience made me grow professionally. This work is a result of Project “PLASTIC_TO_FUEL&MATs - Upcycling Waste Plastics into Fuel and Carbon Nanomaterials”, with the reference POCI-01-0145-FEDER-031439, through the Competitiveness and Internationalization Operational Program, supported by the European Regional Development Fund (ERDF); Associate Laboratory LSRE-LCM - UID/EQU/50020/2019 - funded by national funds through FCT/MCTES (PIDDAC) and CIMO (UID/AGR/00690/2019) through FEDER under Program PT2020

A Synopsis of Research on Meandering: State-of-the-Art and Future Challenges

Source: ICHE Conference Archive - https://mdi-de.baw.de/icheArchiv

PREDATION BY CRABS ON ROCKY SHORES IN NORTH-EAST ATLANTIC

Highly mobile predators are known to have an important influence on shallow-water habitats. There is, however, little information about the role of crabs on the ecology of rocky shores. Here I examine the extent and consequences of predation by crabs on shores in the North-East Atlantic. The specific aims of this thesis are to: investigate spatial variation in use of the intertidal by crabs along a horizontal gradient of exposure to wave action and a vertical gradient of tidal elevation; assess their use of the intertidal as a feeding area by examining stomach content composition; examine the extent of connectivity between the subtidal and intertidal habitats as a consequence of predation by crabs, investigate the ecological role of crabs as predators in the intertidal, and to assess the importance of behavioral and morphological factors in determining the outcomes of these predator-prey interactions. Field sampling showed that on shores in southwest Britain, the abundance of Carcinus maenas, Necora puber and Cancer pagurus varied between high and low-tide, with the vertical gradient of tidal height and horizontal gradient of exposure to wave action. Crabs were typically more abundant on the lower shore than on the upper shore. C. maenas and N. puber were more abundant on sheltered shores than on exposed shores, while C. pagurus showed the opposite pattern. Individuals captured at high-tide were on average larger than those captured at low-tide. Stomach content analysis of individuals captured with traps at high-tide showed that all three crabs feed on intertidal prey including limpets, chitons and algae. In a mark-recapture field experiment, I demonstrate the migration of sublittoral crabs into the intertidal during high-tide. Subsequent manipulative field experiments showed that predation by crabs can have a considerable effect on abundance of limpets. Laboratory experiments showed that Necora puber has a preference for smaller limpets, indicating that the population structure of these grazers may also be modulated by predation. On shores of differing exposure in Portugal I examine cheliped morphological variation of Eriphia verrucosa in response to variation in prey abundance. Chelipeds were typically larger on exposed shores, where hard shelled prey such as mussels were more abundant than they were on sheltered shores, which were dominated by chitons and algae. Predation by crabs therefore appears to have an important ecological role in shallow-water habitats by influencing intertidal prey populations and establishing an important trophic link between intertidal and subtidal habitats. The implication of predation by crabs on the ecology of rocky shores is discussed