Going with the flow: ecomorphological variation across aquatic flow regimes: an introduction to the symposium.

Understanding the relationships between the morphology of organisms and the environments in which they live is a broad and unifying goal in fields ranging from organismal biology to ecology to evolutionary biology. Life in aquatic systems is particularly interesting because of the physical challenges presented by water and the broad array of flow regimes to which organisms have adapted, ranging from the open ocean and wave-swept shores to still lakes and fast-flowing streams. The publication of three volumes in the early 1990s helped to synthesize work on this topic: Denny’s (1993) Air and Water, Vogel’s (1994) expanded second edition of Life in Moving Fluids with regard to life in fluids in particular, and Wainwright’s and Reilly’s (1994) Ecological Morphology with regard to the general theme of matches between form, function, and environment in organisms. In the years since the publication of those volumes, a wide range of novel systems have been examined and numerous technological and methodological advances have been made. Our goal in organizing this symposium was to bring together a diverse group of biologists who study the relationship between morphology and aquatic habitat in a variety of marine and freshwater vertebrates, invertebrates and algae, with the hope that through such a diversity of systems and perspectives we could identify general functional strategies observed in organisms subjected to different conditions of flow. This symposium thus provided an opportunity to synthesize work in this area since the 1990s, to present new case studies of established systems at a variety of scales (e.g., seasonal, ontogenetic, size, geographic), and to showcase systems that have only recently been explored in detail. A second goal of this symposium was to highlight the use of several relatively new techniques for examining such systems, such as digital particle image velocimetry (DPIV) and 2D/3D geometric morphometrics. By addressing this breadth of topics, we hoped this symposium would promote new, interdisciplinary approaches to advancing understanding of the relationship between the physical characteristics of aquatic environments and the morphology of organisms that inhabit them. Several topics ran as common threads through many of the studies presented, with a number of issues emerging as directions for future research on ecomorphological variation across aquatic flow regimes. First, it is clear that accommodating environmental flow is critical for the performance of a wide range of functions in organisms. A major focus of work has been the relationship between flow and locomotor function (Bartol et al. 2008; Blob et al. 2008; Fish et al. 2008; Langerhans 2008; Rivera 2008; Vogel 2008), which could be somewhat more broadly considered as including other functions related to organismal movement such as dispersal and resistance to dislodgement (Carrington et al. 2008; Koehl et al. 2008; Stewart 2008). However, other vital functions are also substantially affected by flow and remain important areas of examination, highlighted by Pratt’s (2008) study of feeding efficiency in bryozoans and Mead’s (2008) study of the effects of flow on olfactory function in crayfish. A major factor repeatedly identified as critical to the accommodation of the demands of flow, particularly in studies of locomotor function, is the pervasive effects of body size on organismal performance. Although commonly highlighted in interspecific comparisons (Vogel 2008), the effects of body size are also important factors in performance within species as individuals change size through ontogeny. In some cases, as shown by Bartol et al. (2008) for squid, larger individuals may be capable of a broader range of functions and be able to make successful use of a wider range of morphology than can smaller individuals. In other cases, illustrated by the waterfallclimbing fish examined by Blob et al. (2008), certain means of performing in flow may only be possible for