Description: Epibiosis in the marine environment is a stressor that may determine invasion success in introduced species. Previous comparisons showed resistance to epibionts can be higher in non-native than in resident seaweed species, but we do not know whether it is an intrinsic trait of the non-natives or it has been acquired during the invasion process. To elucidate this question, a comparison between native and non-native populations of the same species is needed. Resistance against two groups of epiphytes was assessed in living thalli and in artificial substrata coated with surface extracts, both gained from four Asian (native) and four European (non-native) populations of the red alga Gracilaria vermiculophylla. Two diatom species and two filamentous macroalgae were used as micro- and macro-epiphytes, and one of each type was collected in Asia, while the other came from Europe. Laboratory assays were done in both distributional ranges of G. vermiculophylla and in different seasons. We used G. vermiculophylla from four populations in each range and used a fully crossed design with the factors (i) ‘Origin of Gracilaria’, (ii) ‘Origin of epiphytes’, (iii) ‘Season’ and (iv) ‘Solvent used for extraction’. Both groups of epiphytes, regardless of their origin, attached less to living thalli and to surface extracts from non-native G. vermiculophylla. Fewer diatoms attached to hexane-based extracts, while fewer Ceramium filaments settled on extracts gained with dichloromethane. Synthesis. Our results show for the first time that non-native individuals of a marine organism are better defended against epiphytes than native conspecifics. Furthermore, we found evidence that at least a part of the defence is based on extractable secondary metabolites. We discuss several mechanisms that could explain the increased resistance to epiphytes in non-native individuals, including the release from enemies in the non-native range, which could lead to an increase in algal performance during the invasion process. We suggest that an enhanced defence against epiphytes after introduction is one reason for G. vermiculophylla's invasion success. Our observation may also apply to other basibiont–epibiont and host–enemy systems, including plant–plant, plant–animal and animal–animal interactions, in aquatic environments and could be a key feature of bioinvasions.

Description: In this chapter a variety of field and laboratory techniques to assess biofouling assemblages are described. The first part, focusing on traditional methods, also includes methods of using image analysis, functional groups and several mathematical and theoretical models to estimate species diversity. The second part is applied and deals with the assessment of biofouling on in-service vessels in order to determine their biosecurity risk. The third part gives an overview of the methods required to undertake field experiments with biofouling assemblages on a global scale. Assessing fouling assemblages: This chapter focuses on traditional methods, also includes methods of using image analysis, functional groups and several mathematical and theoretical models to estimate species diversity. In ecology, manipulative experiments of living organisms are often carried out in the field, providing a real assessment of the community in question. As a precursor to these experiments a baseline survey of the natural community is essential to provide the wider context for change. The chapter gives some of the more popular methods used to assess fouling communities. The protocols necessary for carrying out these methods along with appropriate statistical techniques are discussed. Finally, a critique of the problems associated with each method is provided, and suggestions made for how to address these problems. Both field methods and digital methods are discussed in the chapter. Assessment of in-service vessels for biosecurity risk: Biofouling organisms, including sessile and mobile species, are encountered on all vessel types, including commercial vessels of all categories, naval ships, and recreational vessels. Criteria used to determine the biosecurity risk posed by hull fouling of in-service vessels are often specific to the requirements of environmental management agencies and result in the use of different sampling approaches. The biosecurity risk of vessels can also be estimated using abundance, biomass or richness of biofouling as the metrics of interest. This chapter provides guidance on approaches to determining the biosecurity risk of in-service vessels in situ or in dry-dock. It focuses on surveys designed to create biological inventories of vessel hulls and associated estimates of biofouling abundance. An absence of biofouling can only be guaranteed for inspections that have been designed using a statistical framework that provides a level of confidence of "freedom of infestation". Experiments on a global scale: The international research and student training program-Global Approach by Modular Experiments (GAME)-is one of a few initiatives worldwide that implements the scaling up of ecological studies from the regional to the global scale. Moreover, the innovative coupling of teaching and research and the propagation of a modular approach in experimental research makes it unique in marine sciences. Modularity means the simultaneous execution of identical experiments at multiple study sites that cover several biogeographic regions and climate zones. Marine epibiotic communities have repeatedly been recognized as suitable model systems for studies in community ecology and biodiversity research and such consortia of sessile metazoans and macroalgae have properties that make them for experimental studies. The chapter also presents chronology of a GAME project in seven major steps.

Description: 1 Several theoretical models predict under what conditions maximum species diversity can be maintained, and they are often used to develop effective ecosystem management plans. 2 Two models that are currently used to predict patterns of species diversity were empirically tested in marine subtidal benthic communities of different successional stages. 3 The two models were: the interactive effects of nutrient availability and disturbance frequency proposed by Kondoh (2001; Proceedings of the Royal Society London B, 268, 269–271), and the intermediate disturbance hypothesis (IDH) proposed by Connell (1978; Science, 199, 1302–1310). 4 Interactive effects were found to be transient and only occurred in the older communities, while the unimodal pattern suggested by the IDH was not supported in either successional stage. 5 It is concluded that these models are very general and thus lack sufficient explanatory power. Both models require a number of specific prerequisites for maximum diversity to be found, and though applicable in many different ecosystems they need to be refined as tools in order that they can be effectively used in habitat management plans.

Description: Development of a mechanistic understanding and predictions of patterns of biodiversity is a central theme in ecology. One of the most influential theories, the intermediate disturbance hypothesis (IDH), predicts maximum diversity at intermediate levels of disturbance frequency. The dynamic equilibrium model (DEM), an extension of the IDH, predicts that the level of productivity determines at what frequency of disturbance maximum diversity occurs. To test, and contrast, the predictions of these two models, a field experiment on marine hard-substratum assemblages was conducted with seven levels of disturbance frequency and three levels of nutrient availability. Consistent with the IDH, maximum diversity, measured as species richness, was observed at an intermediate frequency of disturbance. Despite documented effects on productivity, the relationship between disturbance and diversity was not altered by the nutrient treatments. Thus, in this system the DEM did not improve the understanding of patterns of diversity compared to the IDH. Furthermore, it is suggested that careful consideration of measurements and practical definitions of productivity in natural assemblages is necessary for a rigorous test of the DEM.

Description: Disturbance and productivity are often cited as the main factors determining temporal and spatial patterns in species distribution and the diversity of communities. A field experiment was conducted to test the role of these factors in the structuring of early successional fouling communities in a nutrient limited system at the south coast of Madeira Island. Macro-benthic sessile communities, established on artificial settlement substrata, were manipulated and surveyed over a 9-week period. We applied mechanical disturbances of four different frequencies crossed with three levels of inorganic nutrient enrichment. Fertilization enhanced community diversity by favouring the establishment and growth of macroalgae. Disturbance reduced diversity by eliminating species – but only at the highest nutrient level. This is explained by a multiple-stressor model; species most sensitive to nutrient deficiency (only present in the highest enrichment treatment) were simultaneously the most sensitive to disturbance