# Chapter 21 - Perspectives on marine fish ecology research

Henrique Cabral, Jérémy Lobry, Mario Lepage, Olivier Le Pape

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Henrique Cabral, Jérémy Lobry, Mario Lepage, Olivier Le Pape. Chapter 21 - Perspectives on marine fish ecology research. Academic Press. Ecology of Marine Fish, Elsevier, pp.413-415, 2025, 978-0-323-99036-3. 10.1016/B978-0-323-99036-3.00001-5. hal-05070861

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# Chapter 21 - Perspectives on marine fish ecology research

Henrique Cabral (1) , Jérémy Lobry (2, 1) , Mario Lepage (1) , Olivier Le Pape (3, 4)

1 UR EABX - Ecosystèmes aquatiques et changements globaux

2 INRAE - Institut National de Recherche pour l'Agriculture, l'Alimentation et l'Environnement

3 DECOD - Dynamique et durabilité des écosystèmes : de la source à l'océan

4 Institut Agro Rennes Angers

This book aims to bridge a gap in the literature on marine fish ecology by providing a comprehensive and up-to-date overview of the field. It brings together contributions from nearly a hundred leading experts worldwide, offering a state-of-the-art summary of current knowledge and research. While many significant works have preceded this book, some are relatively dated and require updating to reflect the latest advancements. Others have primarily focused on ichthyology, emphasizing fish biology, or have covered fish from various aquatic systems, including freshwater and marine environments, without a specific emphasis on marine ecosystems. This volume sets itself apart by offering a dedicated and contemporary exploration of marine fish ecology, synthesizing the latest findings and insights from leading authorities in the field. It serves as an invaluable resource for researchers, students, and professionals seeking a comprehensive and authoritative reference on this crucial area of study.

The study of fish ecology has greatly benefited from the countless advances in ecological theory and methods while simultaneously making significant contributions to the advancement of this scientific field. Fish serves as an extremely interesting biological model for exploring certain ecological aspects, making them a valuable subject of study. Research on fish ecology has followed the general pattern of scientific evolution globally, characterized by a significant increase in the number of articles published annually, a broadening of the geographical scope of these publications, and, in some cases, a shift in the leadership of countries in terms of scientific production. Moreover, the evolution of science funding has also influenced scientific production in this area. Notably, there has been a generalization of priority themes for research (often presented as "hot topics") to which funding is primarily channeled. Additionally, studies with a broad geographic scope resulting from large teams of researchers involving numerous institutions have become more attractive for successful publication. One of the pernicious consequences of this funding direction has been the difficulty in developing more conventional basic studies (such as studies of growth, reproduction, trophic ecology, taxonomy, and systematics), which are often essential prerequisites before undertaking more elaborate research, especially in geographical areas that are still poorly investigated

More than 15,000 species of marine fish are currently known to science, but this number is certainly underestimated due to biases in our knowledge. Many geographic areas, such as various regions of the Southern Hemisphere and polar zones, or marine ecosystems like the deep sea, remain poorly studied. This fact is evidenced by the continuous discovery of new species or new occurrences in these understudied areas. Fish are inherently challenging organisms to observe directly, either because they reside in environments that are difficult for humans to access, or due to the immensity
of their habitats, or their mobility and avoidance of observation or capture devices. Various technical and methodological advances have facilitated our ability to observe and capture fish, and it is hoped that these advancements will enable the generation of valuable, sometimes disruptive, knowledge beyond our current understanding. As with all biological communities, the abundance of various fish species is highly uneven, with a large number of relatively rare species for which scientific knowledge is scarce. Other species have become rare due to human actions on marine ecosystems, such as overfishing and habitat destruction. In these cases, there is often a considerable research effort, but their conservation status can create limitations for their study. For example, some species may have restrictions or prohibitions on capture or experimentation, even for scientific purposes. It is also important to emphasize the profound heterogeneity of scientific knowledge that often exists for many species regarding ontogenetic states. For the vast majority of fish, their spatiotemporal abundance patterns vary according to life cycle stage. This reality implies different areas, periods, and sampling techniques for each of these stages, with varying levels of difficulty and success in the sampling process. For instance, sampling pelagic larval stages, juveniles in coastal areas, and adults in deeper ocean areas presents distinct challenges. Consequently, a lack of knowledge about the ecology of some species' life stages persists, even for abundant and commercially exploited species.

In a broad sense, our knowledge about fish ecology stems from three distinct types of studies: observational studies in marine ecosystems, experimentation (primarily in laboratories but also potentially involving field studies), and modeling. Although relatively uncommon, some studies combine various components of these approaches, potentially offering a more comprehensive perspective. Each of these approaches has its own unique characteristics, requiring specific assumptions and allowing for vastly different considerations and insights. For instance, an observational study may indicate that a particular species is more abundant in a specific location, but determining the underlying cause can be challenging due to the multitude of variables that can influence its occurrence and the inherent limitations in measuring environmental variables. In most observational studies, fewer than 10 variables are typically measured, with biotic factors often absent. In contrast, an experimental approach enables researchers to test for instance the preference or mortality of individuals of a species in relation to one or a few environmental factors (e.g., temperature and oxygen) that are controlled and (usually) fixed at certain levels. However, extrapolating these findings to natural environments is not straightforward, as there may be synergistic, additive, or antagonistic interactions with other unmeasured variables. Modeling, on the other hand, involves an extreme simplification of natural systems, requiring an enormous amount of high-quality data, which is often difficult to obtain or nonexistent. Additionally, validating the estimates derived from models may also be extremely difficult or constrained. Integrative studies that combine various components of these approaches are clearly scarce, as is interdisciplinary research that bridges different fields of study. Such holistic approaches are crucial for gaining a comprehensive understanding of fish ecology, as they can compensate for the limitations of individual methods and provide a more nuanced and accurate representation of these complex systems.

In a broad sense, our knowledge about fish ecology stems from three distinct types of studies: observational studies in marine ecosystems, experimentation (primarily in laboratories but also potentially involving field studies), and modeling. Although relatively uncommon, some studies combine various components of these approaches, potentially offering a more comprehensive perspective. Each of these approaches has its own unique characteristics, requiring specific assumptions and allowing for vastly different considerations and insights. For instance, an observational study may indicate that a particular species is more abundant in a specific location, but determining the underlying cause can be challenging due to the multitude of variables that can
influence its occurrence and the inherent limitations in measuring environmental variables. In most observational studies, fewer than 10 variables are typically measured, with biotic factors often absent. In contrast, an experimental approach enables researchers to test for instance the preference or mortality of individuals of a species in relation to one or a few environmental factors (e.g., temperature and oxygen) that are controlled and (usually) fixed at certain levels. However, extrapolating these findings to natural environments is not straightforward, as there may be synergistic, additive, or antagonistic interactions with other unmeasured variables. Modeling, on the other hand, involves an extreme simplification of natural systems, requiring an enormous amount of high-quality data, which is often difficult to obtain or nonexistent. Additionally, validating the estimates derived from models may also be extremely difficult or constrained. Integrative studies that combine various components of these approaches are clearly scarce, as is interdisciplinary research that bridges different fields of study. Such holistic approaches are crucial for gaining a comprehensive understanding of fish ecology, as they can compensate for the limitations of individual methods and provide a more nuanced and accurate representation of these complex systems.

A final note on the opportunities and challenges associated with the study of fish ecology during a period of profound environmental changes, which, due to its multitude of factors and spatial extent, is commonly referred to as the era of global change. Environmental conditions have been constantly changing throughout the planet's history. Although disruptive episodes are recognized, during which environmental conditions were altered over a relatively short period, there is a relatively broad consensus that the current period is unprecedented in terms of the magnitude and pace of these changes. Numerous contributions published over the past two decades have documented these alterations in fish populations, communities, and marine ecosystems in general. Despite the overwhelmingly negative impacts of human actions, there is an opportunity to study and document their consequences through scientific research, in this case, using fish as model organisms. Although there are relatively reliable predictions at the climatic level, other components of the global change scenario are more unpredictable, reinforcing the need for interdisciplinary and integrative studies in terms of the approaches used. While the challenges posed by global change are daunting, the study of fish ecology during this period holds immense importance for understanding and mitigating the impacts on marine ecosystems. By embracing interdisciplinary collaborations, leveraging cutting-edge technologies, and fostering a deep understanding of the complex interactions between fish and their changing environments, researchers can contribute to the development of effective conservation strategies and promote the resilience of these vital components of marine ecosystems.