Volatile Organic Compounds from Marine Plants: Effects on the Behaviour of Benthic Invertebrates

Table of Contents

1. Introduction

1.1 Overview

1.2 The general context of marine chemical ecology

1.3 The current knowledge on infochemicals

1.4 Volatile Organic Compounds from marine plants and their functions as infochemicals

1.5 The method: behavioural choices in the investigation of infochemicals

1.6 Behavioural traits and mechanisms of chemoreception in marine invertebrates

1.7 The seagrass Posidonia oceanica, its epiphytes and associated invertebrates

1.8 Epiphytes-herbivores interactions: the role of infochemicals within Posidonia oceanica ecosystem

1.9 Research aims and objectives

2. VOCs of epiphytes from Posidonia oceanica trigger infochemicals based communication for benthic inverterbrates

2.1 INTRODUCTION

2.2 MATERIALS AND METHODS

2.2.1 Isolation and culture of benthic epiphytes from the seagrass Posidonia oceanica

2.2.2 Extraction of algal odours: VOCs

2.2.3 Study organisms: animal sampling and biology

2.2.4 Experiment 1: choice assay in static chambers

2.2.5 Experiment 2: choice assay in straight flow-through flume

2.2.6 Baseline choice assays

2.2.7 Distribution of VOCs in static chambers

2.2.8 Distribution of VOCs in straight flow-through flume

2.3 STATISTICAL ANALYSIS

2.3.1 Standardization of behavioural data

2.3.2 Effect of time in behavioural responses of invertebrates

2.3.3 Recognition of algal odours and associative patterns

2.3.4 Distribution of odours in static chambers and in straight flow-through flumes

2.4 RESULTS

2.4.1 Kriging analysis for the diffusion in static chambers

2.4.2 Kriging analysis for the flow in straight flow-through flume

2.4.3 Behavioural responses of invertebrates to VOCs in static chambers

2.4.4 Behavioural responses of invertebrates to VOCs in flumes

2.4.5 Behavioural associative patterns to VOCs

2.5 DISCUSSION

2.6 CONCLUSION

3. Epiphyte-borne infochemicals rule the community structure of mesograzers in seagrasses

3.1 INTRODUCTION

3.2 MATERIALS AND METHODS

3.2.1 Study organisms: animal sampling and biology

3.2.2 Production of epiphytes: seaweeds and diatoms

3.2.3 VOCs extraction

3.2.4 Gel preparation and concentrations

3.2.5 Behavioural choice tests

3.2.6 Standardization of behavioural choice test: controls

3.3 STATISTICAL ANALYSIS

3.3.1 Standardization of controls

3.3.2 Behavioural choices to VOCs, effect of concentration and time of exposure

3.3.3 Multivariate analysis: taxonomy vs. environmental hypothesis

3.4 RESULTS

3.4.1 Control experiments: the need for standardization of behavioural data

3.4.2 Responses to VOCs, concentrations and time of exposure for each mesograzer

3.4.3 Responses of the community of mesograzers to infochemicals

3.5 DISCUSSION

3.5.1 The mesograzers’ standardized behaviour

3.5.2 Volatile epiphyte-borne infochemicals structure mesograzers’ microhabitat selection upon the leaves of Posidonia oceanica

3.6 CONCLUSION

4. Decoding the messages beyond epiphyte-borne volatiles: food kairomones, alarm and habitat cues

4.1 INTRODUCTION

4.2 MATERIALS AND METHODS

4.2.1 Animal collection

4.2.3 Preparation of artificial foods

4.2.4 Feeding test and survival

4.2.5 Statistical analysis

4.3 RESULTS

4.3.1 Putative toxicity

4.3.2 Feeding preferences

4.4 DISCUSSION

4.5 CONCLUSION

5. Ocean acidification effects on the behaviour of mesograzers to epiphyte-borne infochemicals

5.1 INTRODUCTION

5.2 MATERIALS AND METHODS

5.2.3 Animal collection and epiphyte cultures

5.2.4 Simulated ocean acidification treatment

5.2.5 Experimental design and behavioural choice tests

5.2.6 VOCs extractions and gels preparations

5.2.7 Statistical analysis

5.3 RESULTS

5.3.1 Responses of molluscs to volatile infochemicals at different pH

5.3.2 Responses of decapods to volatile infochemicals at different pH

5.3.3 Reactions of mesograzers’ community to infochemicals at different pH

5.4 DISCUSSION

5.5 CONCLUSION

6. Discussion and Conclusion

6.1 General discussion

6.2 Conclusions and future directions

6.2.1 Epiphyte-odours are infochemicals for benthic invertebrates

6.2.2 Epiphyte-borne infochemicals structure the benthic community within the Posidonia oceanica ecosystem

6.2.3 OA disrupts behaviour to infochemicals and indirectly the structure of ecosystems

Research Objectives and Themes

This thesis explores the role of volatile organic compounds (VOCs) released by algal epiphytes as infochemicals within the seagrass ecosystem Posidonia oceanica, investigating how these chemical cues influence the behavioral choices, habitat selection, and community structure of associated benthic invertebrates, especially in the context of predicted ocean acidification.

• Standardization of behavioral choice assays for benthic invertebrates.
• Assessment of behavioral patterns of molluscs and decapods in response to epiphyte-borne VOCs.
• Evaluation of VOCs as food-finding cues or toxic triggers for associated invertebrates.
• Analysis of the influence of taxonomic relatedness versus environmental plasticity on behavioral responses.
• Investigation into the impact of ocean acidification on chemical communication and ecosystem structure.

Excerpt from the Book

Summary of Chapters

CHAPTER 1: Provides a comprehensive introduction to marine chemical ecology, defining the role of VOCs as infochemicals and setting the stage for the specific study of Posidonia oceanica interactions.

CHAPTER 2: Investigates the behavioral responses of various invertebrates to epiphyte VOC bouquets, evaluating two distinct methodologies and establishing the role of VOCs as potential infochemicals.

CHAPTER 3: Focuses on the role of epiphyte-borne infochemicals in structuring the community of mesograzers, testing the "taxonomic" versus "environmental" hypotheses through behavioral choice tests.

CHAPTER 4: Decodes the nature of the messages conveyed by VOCs, specifically analyzing whether they serve as food kairomones or indicate the presence of toxic compounds using forced feeding experiments.

CHAPTER 5: Explores the effects of ocean acidification on these chemical interactions, assessing whether lower pH levels disrupt behavioral responses and alter community chemical relationships.

CHAPTER 6: Synthesizes the findings of the thesis, providing a general discussion on the implications of chemical ecology for coastal management and outlining future research directions.

Keywords

Marine Chemical Ecology, Posidonia oceanica, Volatile Organic Compounds (VOCs), Infochemicals, Mesograzers, Benthic Invertebrates, Ocean Acidification, Behavioral Choice Assays, Kairomones, Community Structure, Microhabitat Selection, Epiphytes, Chemical Communication, Ecological Interactions.

Frequently Asked Questions

What is the central focus of this research?

The thesis examines how volatile organic compounds (VOCs) released by algal epiphytes on the seagrass Posidonia oceanica function as infochemicals to influence the behavior and community organization of associated benthic invertebrates.

Which organisms are specifically studied?

The research focuses on a range of benthic mesograzers, including gastropods (e.g., Alvania lineata, Rissoa italiensis), decapods (e.g., Hippolyte inermis, Cestopagurus timidus), and various polychaete species.

What is the primary scientific method used?

The work employs standardized behavioral choice assays, specifically using static chambers and flow-through flumes, combined with multivariate statistical analyses and separate-offer feeding experiments to quantify responses.

How do VOCs affect the community structure?

VOCs act as specific chemical cues that allow mesograzers to fine-tune their distribution based on their specific ecological niches and microhabitats on the Posidonia oceanica leaf axis.

Does ocean acidification disrupt these interactions?

Yes, the study indicates that ocean acidification can act as an 'info-disruptor,' causing invertebrates to switch their behavioral patterns and potentially leading to a simplification of chemical relationships within the ecosystem.

What do the findings suggest for environmental management?

The findings emphasize that chemical communication is a critical factor in maintaining biodiversity, and suggest that management strategies for coastal ecosystems should account for the indirect impacts of global climate change on these chemical networks.

What is the "Environmental hypothesis" tested in Chapter 3?

This hypothesis posits that mesograzers respond to VOCs based on their familiarity with the infochemicals of their own preferential microhabitat, rather than purely due to their taxonomic relatedness.

Are the VOCs from all epiphytes equally recognized?

No, the study reveals that responses are species-specific; for instance, some invertebrates showed strong attraction to cyanobacterial VOCs, while others were repelled or indifferent to those from macroalgae.