ALMA MATER STUDIORUM UNIVERSITA’ DI BOLOGNA FACOLTA’ DI SCIENZE MATEMATICHE FISICHE E NATURALI Corso di laurea magistrale in BIOLOGIA MARINA Effects of Paramuricea clavata (Risso, 1826) (Anthozoa: Plexauridae) forests on settlement of benthic species: an experimental approach. Relatore Presentata da Prof. Marco Abbiati Rossella Perlini Correlatori Dr. Massimo Ponti Dr. Carlo Cerrano III sessione Anno Accademico 2009/2010 2 “Alla mia cara amica Rossella, i cui capelli biondi, sul fondo del mare, si muovono armoniosi, morbidi, come le tenere gorgonie in corrente. Conserva il gusto dell’andare per mare Rossella. Che il mare è tenerezza; e silenzio, cose delle quali le persone sensibili hanno un assoluto bisogno!” Armando Lombardi La Maddalena, Agosto 2003 Al Mare perché il tempo passa, ma Tu non passi mai 3 4 Index CHAPTER 1: INTRODUCTION .................................................................... 7 1.1 Overview on coralligenous assemblages .............................................. 7 1.2 Variables affecting coralligenous assemblages ................................... 8 1.2.1 Light ............................................................................................................. 8 1.2.2 Inclination of substrata ................................................................................. 9 1.2.3 Hydrodynamism and nutrients ................................................................... 10 1.2.4 Temperature ................................................................................................ 10 1.2.5 Biologic interactions ................................................................................... 11 1.3 Paramuricea clavata (Risso, 1826) as a key species ........................... 14 1.3.1 Paramuricea clavata’s facies ..................................................................... 18 1.4 Disturbances factors affecting coralligenous habitats ..................... 19 1.4.1 Human activities ......................................................................................... 19 1.4.2 Pollution ..................................................................................................... 21 1.4.3 Invasive species .......................................................................................... 22 1.4.4 Climatic anomalies ..................................................................................... 23 1.5 Paramuricea clavata and mass mortality events ............................... 24 1.5.1 Thermal stress ............................................................................................. 24 1.5.2 Mucilage events .......................................................................................... 26 1.5.3 Pathogens.................................................................................................... 27 1.6 Recovery after mass mortality events ................................................ 28 1.7 Our goal ................................................................................................ 30 CHAPTER 2: MATERIALS AND METHODS ........................................... 33 2.1 Sampling design ................................................................................... 33 2.2 Risk assessment .................................................................................... 34 5 2.3 Experiment setup ................................................................................ 34 Study area ........................................................................................................ 37 2.3.1 MPA Tavolara Punta Coda Cavallo, Sardinia ............................................ 37 2.3.2 MPA Portofino, Liguria .............................................................................. 40 2.4 Data collection ..................................................................................... 42 2.5 Laboratory Analysis ........................................................................... 43 2.6 Data Analysis ...................................................................................... 44 2.6.1 Analysis on assemblages structure ............................................................. 44 2.6.2 Analysis on single taxon abundance ........................................................... 45 2.6.3 Analysis on ecologic structure .................................................................... 45 2.6.4 Analysis on higher Taxa group patterns ..................................................... 46 2.6.5 Analysis on species diversity ...................................................................... 47 2.7 Practical considerations at underwater work .................................. 48 CHAPTER 3: RESULTS ............................................................................... 53 3.1.1 Results on assemblages structure patterns .................................................. 54 3.1.2 Possible effects of gorgonian forest on single taxon abundances ............... 57 3.1.3 Effects of gorgonian forest on ecological structure patterns ....................... 77 3.1.4 Effects of gorgonian forest on single ecological groups ............................. 78 3.1.5 Effects of gorgonian forest at Phylum taxonomic level .............................. 85 3.1.6 Effects on gorgonian forest on species diversity ........................................ 89 CHAPTER 4: DISCUSSION ......................................................................... 95 ACKNOWLEDGEMENTS ......................................................................... 101 REFERENCES ............................................................................................. 105 6 Chapter 1: Introduction 1.1 Overview on coralligenous assemblages Coralligenous habitat is considered the second most important subtidal “hot spot” of species diversity in the Mediterranean Sea after the Posidonia oceanica meadows (Boudouresque 2004). Despite the wide use of this term, there is no real consensus among scientists studying Mediterranean benthic communities about what a coralligenous habitat is (Ballesteros 2006). The word “coralligenous” (coralligène in French), for the first time used by Marion 1883 to describe Marseilles hard bottoms, stems from a misunderstanding: during XVIII sec. it was easy to find in the bottom trawls, that fished between 30 and 70 m deep, red coral branches (Corallium rubrum) whence derives the name. Today we know that this species does not characterise this particular habitat, but it is only occasionally part of it. Pérès and Picard (1964) defined coralligenous as the hard bottom “biocenose”, developed in the circalittoral zone, characterised by encrusting red calcareous algae associated with a rich fauna in way to forming a high micro-spatial variability habitat (Fig. 1). They also make a distinction introducing the word pre-coralligenous: a zone that comprises sciaphilic erect algae with thallus weakly calcified therefore unable to produce a significant concretion, sometimes considered as an impoverished facies of the proper coralligenous. In the opinion of these two authors it is apparent that the coralligenous habitat is bound to two different phenomena: the first concerns light intensity, low enough to permit the colonization of sciaphilic algae and animals, the second refers to the ability of these organisms to form conspicuous limestone substrates. Many authors in subsequent publications (Laubier 1966; Sarà & Pulitzer-Finali 1970; Ros et al. 1985; Gili & Ros 1985), claimed that defining coralligenous as a single biocenose is ambiguous and restrictive to describe this multidimensional environment. Therefore this habitat should be considered as a set of biocenose or a community puzzle (Cinelli & Colantoni 1993; Ballesteros 2006). 7 Thus, considering all the progress acquired in the knowledge of this field, we can define coralligenous habitat as a typical Mediterranean hard bottom of biogenic origin, mainly produced by the accumulation of calcareous encrusting algae, that can be colonized by other sciaphilic organisms, forming an intricate assemblage of species able to transform it in a multidimensional habitat with a high micro-spatial variability (Ballesteros 2006). Fig. 1 - An example of the coralligenous system showing an explosion of colours and life represented by a high species variability on a small spatial scale (picture by Guido Villani). 1.2 Variables affecting coralligenous assemblages Light seems to be the main environmental factor that determines the distribution of coralligenous assemblages (Ballesteros 1992; Marti et al. 2005) but inclination of substrata, hydrodynamism, nutrients, temperature and biologic interactions can also play a relevant role in structuring these benthic assemblages. 1.2.1 Light Encrusting algae cannot withstand high levels of irradiance, but they need light as well to carry out photosynthesis process. Accordingly to Ballesteros (1992) 8 the optimal amount of light for the development of these environments must range between 0.05% and 3% of the surface irradiance. In addition he find out that also quality of light should be taken into account: red algae in coralligenous system reach their deepest distribution linked with the ability of phycobilines to capture light in green window, the most abundant wavelength range in these habitats. We can find these ecological requirements at different depths in the Mediterranean Sea, in relation to local environmental conditions. The minimal depths recorded are around 10 - 15 m but on the other hand coralligenous