Rev Fish Biol Fisheries (2011) 21:205–223 DOI 10.1007/s11160-010-9167-5 REVIEWS The importance of seahorses and pipefishes in the diet of marine animals D. Kleiber • L. K. Blight • I. R. Caldwell • A. C. J. Vincent Received: 29 September 2009 / Accepted: 12 May 2010 / Published online: 1 June 2010 Ó Springer Science+Business Media B.V. 2010 Abstract A review of 135 accounts of predation on predators: these included taxa that do not frequent the seahorses and pipefishes identified 82 predator spe- demersal habitat generally occupied by seahorses and cies, with nine species of seahorses and 25 of pipefishes. Thus, seahorses and pipefishes may be pipefishes recorded as prey. These cryptic fishes moving in the open ocean more than suspected, were generally depredated in low numbers. Where perhaps using floating mats of marine vegetation. If syngnathids formed a high proportion of predator so, this behaviour could act as a hitherto unknown diets, predation occurred on (1) a single abundant vector for syngnathid movement and dispersal. species during a population boom or large die-off, (2) Information on syngnathid abundance in predator concentrations of individuals utilising floating marine diet (measured as percent number, volume, or mass) vegetation, or (3) juveniles when abundant during the was available in 45 reviewed accounts; in 27% breeding season. Predation coinciding with high (n = 12) of these studies seahorses or pipefishes syngnathid densities suggests their predators are comprised C20% of predator diet (range 0.005– foraging opportunistically rather than targeting syng- 100%). Frequency of occurrence (percent stomachs, nathids as prey. Invertebrates, fishes, sea turtles, seabird bill-loads, or regurgitations in which a prey waterbirds and marine mammals were all syngnathid item occurred) was provided in 39 accounts, with 15% (n = 6) of these recording a frequency of C20% (range 0.003–65%). D. Kleiber and L. K. Blight contributed equally to this work. Keywords Marine food webs Á Electronic supplementary material The online version of Predator–prey interactions Á Syngnathidae Á this article (doi:10.1007/s11160-010-9167-5) contains Hippocampus Á Crypsis Á Dispersal supplementary material, which is available to authorized users. D. Kleiber Á L. K. Blight Á I. R. Caldwell Á A. C. J. Vincent Introduction Project Seahorse, Fisheries Centre, The University of British Columbia, 2202 Main Mall, Vancouver, BC V6T 1Z4, Canada Predation risk can shape individual behaviour and ecology as well as population level processes. L. K. Blight (&) According to the ‘‘life-dinner’’ principle (Dawkins Centre for Applied Conservation Research, and Krebs 1979), in the arms race between predator The University of British Columbia, 2424 Main Mall, Vancouver, BC V6T 1Z4, Canada and prey, adaptive pressure should be greater on the e-mail: [email protected] prey than on the predator. In marine ecosystems, 123 206 Rev Fish Biol Fisheries (2011) 21:205–223 predation pressure can affect: where individuals are corals, or mangroves) and can change their colour to found (Walters and Martell 2004); select for predator adapt to changes in their environment. Species of avoidance behaviours such as schooling (Seghers seahorses, pipehorses, and seadragons that live 1974; Magurran 1990; Pitcher and Parrish 1993)or among seagrass or other flora often have filaments refuge use (Sih 1997; Krause et al. 2000); create that increase their resemblance to their habitat, while trade-offs with other behaviours such as mating those living amongst coral often have a textured body (Berglund 1993; Sih 1994) or feeding (Krause et al. surface. Although some species of pipefishes lack 2000; Plath and Schlupp 2008); and select for filaments, these nonetheless have an elongated body attributes to either evade detection (e.g., crypsis) or that allows them to mimic vertical features of the make prey less palatable or otherwise less attractive environments in which they live such as blades of (Endler 1986; Smith 1997). Knowing the predation seagrass, loose weeds, or sticks (Kuiter 2000, 2009). risk faced by a given species can help to elucidate the Overall, predator avoidance through crypsis is highly pressures that have shaped its behaviour, morphol- evolved in this family of fishes. ogy, and general biology. Although effective, crypsis is an imperfect defence The Syngnathidae (seahorses, pipefishes, pipehors- strategy and predation of cryptic species does occur. es and seadragons) are a cosmopolitan family of In the predator–prey arms race, predators may charismatic fishes that serve as flagship species for develop more effective search images (Gendron marine conservation, yet little is known about their 1986) or search rates (Guilford and Dawkins 1987) basic biology. Syngnathids are harvested in a global to find cryptic prey. Crypsis can also become less trade for use in traditional medicines and curios effective when shifts in habitat no longer favour a (Foster and Vincent 2004). The extent of syngnathid certain phenotype (e.g., changed frequency of dark vs. exploitation by humans is well documented, but little light substrates; Mallet 2004), or when there is a trade- is known about their ecological role and the forces off between predator avoidance and other life history that structure their populations (Martin-Smith and requirements (e.g., mating, feeding; Sih 1994; Walters Vincent 2005). Two syngnathid species are listed on and Martell 2004). For example, work by Berglund the International Union for the Conservation of (1993) on the mating behaviour of the pipefish Nature (IUCN) Red List as ‘‘Endangered’’, seven as Syngnathus typhle during the presence of a predator ‘‘Vulnerable’’, and two as ‘‘Near Threatened’’. How- suggests that adults may be at high risk of predation ever, the vast majority are assessed as ‘‘Data Defi- during mating. Conversely, remaining cryptic may cient’’, indicating the practical need for further restrict an animal’s access to other resources. Sea- information about these species. The purposes of this horses and pipefishes use rapid (from dark to light review were to find out which predators eat this within seconds, and vice versa) colour change to cryptic group of fishes, and under which circum- attract mates yet at least some species limit such stances; to identify in more detail the role of displays when exposed to predation risk (Fuller and syngnathids in marine food webs; and to attempt to Berglund 1996). Seahorses have a prehensile tail, elucidate poorly known syngnathid life history traits allowing them to grasp vegetation and remain related to movement and behaviour. stationary; by limiting their movement and staying All Syngnathidae have physical characteristics that within small home ranges (Foster and Vincent 2004; allow them to hide from predators. Avoiding preda- Vincent et al. 2005), seahorses can ensure they remain tion by blending with surroundings is a well-studied camouflaged. However, with a simple grasping tail or strategy used by a wide range of organisms (e.g., an otherwise reduced caudal fin, seahorses, pipehors- Endler 1986). Such crypsis comes in two main forms: es, and seadragons primarily use their dorsal fin for (1) disguise (blending with the background) and (2) thrust and may be weaker swimmers than other fish. masquerade (the imitation of another object; Ruxton Thus, if they are caught outside their normal habitat or et al. 2004). Syngnathids are notable marine exam- their camouflage fails they are presumably vulnerable ples of cryptic fauna that rely on both colouration and to more rapidly-swimming predators. Developing an form to blend with their habitat (Foster and Vincent understanding of the circumstances under which 2004; Kuiter 2000, 2009). Most syngnathids are crypsis fails, then, may provide an indirect window coloured to blend into their marine habitats (seagrass, on little-studied aspects of syngnathid life history. 123 Rev Fish Biol Fisheries (2011) 21:205–223 207 The role of syngnathids as potential prey has been Emphasis was placed on identifying measures of highlighted by a recent and dramatic population relative abundance of syngnathids in the diet. We increase in snake pipefish Entelurus aequoreus that made several ‘‘rationalized’’ assumptions to convert has occurred in the northeast Atlantic and North Sea qualitative terms where possible into quantitative since 2003 (Kirby et al. 2006; Harris et al. 2007a; metrics for comparative purposes. Specifically, Kloppmann and Ulleweit 2007). For example, Con- descriptions of stomachs being ‘‘full’’ and tinuous Plankton Recorder data from the NE Atlantic ‘‘crammed’’ with syngnathids were considered to showed more juvenile and larval E. aequoreus in the represent 100% occurrence by stomach volume, first half of 2005 than in the entire period from 1958 while terms such as ‘‘numerous’’ and ‘‘on many to 1972 (Kirby et al. 2006). Though the E. aequoreus occasions’’ were taken to be 30% occurrence. This population increases have been linked to anomalous deliberately conservative latter estimation was used sea surface temperatures (Kirby et al. 2006), eruptive so as not to overinflate subjective descriptions. In two population events may be a general feature of instances, percent volume was estimated from pho- syngnathid population biology. There have been tographs of stomach contents included in these similar observations of dramatically increased inci- papers. As frequency of occurrence (FOO; percent dence of pipefishes as prey off the California coast of total stomachs—or, for marine