Habitat Characterisation of Infralittoral Pebble Beds in the Maltese Islands
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University of Plymouth PEARL https://pearl.plymouth.ac.uk 04 University of Plymouth Research Theses 01 Research Theses Main Collection 2014 Habitat Characterisation of Infralittoral Pebble Beds in the Maltese Islands Evans, Julian http://hdl.handle.net/10026.1/3012 Plymouth University All content in PEARL is protected by copyright law. Author manuscripts are made available in accordance with publisher policies. Please cite only the published version using the details provided on the item record or document. In the absence of an open licence (e.g. Creative Commons), permissions for further reuse of content should be sought from the publisher or author. HABITAT CHARACTERISATION OF INFRALITTORAL PEBBLE BEDS IN THE MALTESE ISLANDS by JULIAN EVANS A thesis submitted to Plymouth University in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY School of Marine Science and Engineering Marine Biology and Ecology Research Centre October 2013 Copyright statement This copy of the thesis has been supplied on condition that anyone who consults it is understood to recognise that its copyright rests with its author and that no quotation from the thesis and no information derived from it may be published without the author's prior consent. Grant Statement The research work disclosed in this thesis was partially funded by the Strategic Educational Pathways Scholarship (Malta). This scholarship is part-financed by the European Union – European Social Fund (ESF) under Operational Programme II – Cohesion Policy 2007-2013, “Empowering People for More Jobs and a Better Quality of Life”. Operational Programme II – Cohesion Policy 2007-2013 Empowering People for More Jobs and a Better Quality of Life Scholarship part-financed by the European Union European Social Fund (ESF) Co-financing rate: 85% EU Funds; 15%National Funds Investing in your future HABITAT CHARACTERISATION OF INFRALITTORAL PEBBLE BEDS IN THE MALTESE ISLANDS by JULIAN EVANS A thesis submitted to Plymouth University in partial fulfilment for the degree of DOCTOR OF PHILOSOPHY School of Marine Science and Engineering Marine Biology and Ecology Research Centre October 2013 Abstract Abstract HABITAT CHARACTERISATION OF INFRALITTORAL PEBBLE BEDS IN THE MALTESE ISLANDS Julian Evans The Mediterranean biocoenosis of infralittoral pebbles has been poorly studied and very little information is available on the physical characteristics of pebble beds, on the diversity of the associated assemblages, on the spatial and temporal variation in assemblage structure, or on interactions between the physical and biotic components. The present study was therefore carried out to characterise pebble-bed assemblages as a first step towards understanding the ecological dynamics of these habitats. Preliminary surveys were made along the low-lying coasts of the Maltese Islands to map the occurrence of pebble-bed habitats. Fifteen locations with pebble coverage >25 m2 were chosen for study and benthic sampling was undertaken between July– September 2011; water samples were also collected on a monthly basis. Five shallow sites were sampled for biota again at six-month intervals until April 2013. The pebble beds were characterised in terms of environmental parameters and biotic composition. A total of 62,742 individuals belonging to 360 macrofaunal taxa were recorded (total sampling area: 16 m2). Polychaetes, crustaceans and molluscs were the most common faunal groups. The recorded species included the endemic gastropod Gibbula nivosa, and the first central Mediterranean records of three gobiid species. Three distinct pebble-bed types were characterised based on physical and biological features: shallow beds occurring in rocky coves, beds found within creeks or seagrass meadows, and beds located in harbour environments; amendments to internationally used benthic habitat classification schemes have been proposed, since only a single category of pebble-bed habitats is currently recognised in these. A significant seasonal reduction in species richness and abundance was recorded from shallow sites, related to the higher level of disturbance occurring during winter storms. Analysis of diversity patterns in harbour sites indicated that a high richness per site and between-site variation in species composition led to the observed high diversity. Site richness was associated with fine-scale structural complexity, while environmental characteristics were correlated with variation in assemblage structure over a broad range of spatial scales. These findings suggest that pebble beds have a higher conservation value than generally thought. The biologically derived habitat classification scheme and knowledge on assemblage-environment relationships derived from the present work will be useful to inform and guide management decisions concerning these pebble-bed habitats. - i - - ii - Contents Contents Abstract i Contents iii List of Figures v List of Tables ix Acknowledgements xi Author’s Declaration xiii Chapter 1. Introduction 1 1.1 Rationale for characterisation of benthic assemblages 3 1.2 Ecological aspects of sublittoral pebble-bed assemblages 9 1.3 The Maltese Islands 13 1.4 The present study 18 Chapter 2. Physical characterisation of infralittoral pebble beds in the Maltese Islands 21 Abstract 23 2.1 Introduction 24 2.2 Material and methods 28 2.3 Results 36 2.4 Discussion 44 Chapter 3. Biological characterisation of infralittoral pebble beds in the Maltese Islands 51 Abstract 53 3.1 Introduction 54 3.2 Material and methods 58 3.3 Results 64 3.4 Discussion 74 Chapter 4. Seasonal variation in the motile macrofaunal assemblage associated with infralittoral pebble beds in the Maltese Islands 81 Abstract 83 4.1 Introduction 84 4.2 Material and methods 88 4.3 Results 92 4.4 Discussion 100 - iii - Contents Chapter 5. Spatial patterns of species diversity within infralittoral pebble beds in the Maltese Islands 105 Abstract 107 5.1 Introduction 108 5.2 Material and methods 112 5.3 Results 118 5.4 Discussion 124 Chapter 6. Discussion 129 6.1 Introduction 131 6.2 Characterisation of infralittoral pebble-bed assemblages 132 6.3 Other noteworthy outcomes of this study 136 6.4 Implications of the present work 139 6.5 Conclusions 146 Appendices 149 Appendix A. Classified list of taxa recorded during the present study, indicating the respective pebble-bed types from which each taxon was recorded 151 Appendix B. Mean (± SD) values of the physical parameters measured in the present study for each of the nineteen sites 161 References 165 Publications 185 - iv - List of Figures List of Figures 1.1 Map of the Mediterranean Sea indicating the boundaries of the main biogeographic sectors (A – J) according to Bianchi and Morri (2000) [solid black lines] and the position of the boundary between the western and eastern bioregions according to (i) Giaccone and Sortino (1974) and (ii) Pérès and Picard (1964) [dotted blue lines]. 17 2.1 Map of the Maltese Islands indicating the position of the nineteen sampling sites used in the present study. Inset shows enlarged view of Marsamxett Harbour. Site numbers correspond to those listed in Table 2.1. 29 2.2 Pebble-bed profile showing vertical stratification, with an upper layer of pebbles and a lower layer of granules and sand; a basal layer of silty sand was typically present in harbour environments. 36 2.3 Dendrogram obtained by CLUSTER analysis utilising group-average hierarchical clustering, based on a Euclidean distance resemblance matrix calculated on standardised environmental variables; sites which were not considered to be statistically different by the SIMPROF routine are shown connected by dotted red lines. 39 2.4 PCA ordination plot of the nineteen sites in terms of their (standardised) environmental variables. Dashed blue lines indicate the site groupings as identified by CLUSTER analysis (Figure 2.3). 40 2.5 Distance-based RDA ordination relating environmental variables to the biotic data, performed using Bray-Curtis similarity of square-root transformed species counts, with vector projections of the physical factors selected by the DistLM routine (Table 2.3(b)). Length and direction of the vectors represent the strength and direction of the relationship. 43 2.6 Distance-based RDA ordination relating environmental variables to the biotic data, performed using χ2 distance of square-root transformed species counts, with vector projections of the physical factors selected by the DistLM routine (Table 2.3(c)). Length and direction of the vectors represent the strength and direction of the relationship. 44 - v - List of Figures 3.1 Map of the Maltese Islands indicating the position of the nineteen sampling sites used in the present study. Inset shows enlarged view of Marsamxett Harbour. Site numbers correspond to those listed in Table 3.1. 59 3.2 Percentage abundance of major faunal groups recorded from infralittoral pebble beds at 19 sites in the Maltese Islands. 65 3.3 Dendrogram resulting from group-average hierarchical cluster analysis, based on Bray-Curtis resemblances produced using square-root transformed abundance data; sites which were not considered to be statistically different by the SIMPROF routine are shown connected by dotted red lines. 66 3.4 Non-metric multi-dimensional scaling ordination plot of the 19 sites, based on Bray-Curtis resemblances produced using square-root transformed abundance data. Dashed blue lines indicate the site groupings as identified by CLUSTER analysis (Figure 3.3). 67 3.5 Mean diversity profiles for each of the three clusters shown in Figure