Social structure and space use in a wild population of the Australian short-headed seahorse Hippocampus breviceps Peters, 1869

Abstract

This paper presents the first information available from repeated field observations of a wild Hippocampus breviceps population, and an uncommon example of mixed-sex social grouping in seahorses. At two study sites in Port Phillip Bay, Victoria, Australia, adult seahorses were found at a mean density of 0.21seahorses per m2 over rocky reef–algal habitat. Each site had a sex ratio of 1 : 1. Seahorses showed varying degrees of site fidelity, with 12 of 38 adults present in the study area throughout the 5-week study period. Adults at the sites moved within small (1–12m2) and overlapping (with 2–10 others) spatial areas, with most seahorses restricting their movements in the early morning to a smaller core area. Females used significantly larger spatial areas and core areas than did males. Core areas generally coincided with particular seaweeds at which stable groups of two to five seahorses would be found each morning. These core areas were commonly the site of social encounters. Adult seahorses engaged in displays and interactions with opposite-sex partners, although not every day, and not necessarily with the same partner at each encounter. Longer-term observations over a larger study area are necessary to characterise H.breviceps’ movement patterns and mating system more precisely.

Extreme habitat specialisation and population structure of two gorgonian-associated pygmy seahorses

“…In this study, neither species exhibited a sex ratio bias, which is consistent with in situ population estimates of the seahorses Hippocampus whitei, H. comes and H. breviceps (Vincent & Sadler 1995, Perante et al 2002, Moreau & Vincent 2004. Whilst the overall sex ratio for the population was not skewed, perhaps more important in gorgonian-associated pygmy seahorse ecology is the sex ratio of distinct groups, particularly since animals appear isolated on their gorgonian host following settlement (Smith 2011).…”

“…Polygamy is predicted where one sex is able to monopolise partners, which is possible in pygmy seahorses given that groups are isolated together on a host gorgonian and at a comparatively high density (Emlen & Oring 1977, Ihara 2002, Kokko & Rankin 2006, Hernaman & Munday 2007. Other recent studies of seahorses have shown that the strict social and genetic monogamy observed in early research of seahorse reproductive biology is subject to variation (Kvarnemo et al 2000, Moreau & Vincent 2004, thus the mating systems of pygmy seahorses would be an interesting direction for future research.…”

“…Polygamy is predicted where one sex is able to monopolise partners, which is possible in pygmy seahorses given that groups are isolated together on a host gorgonian and at a comparatively high density (Emlen & Oring 1977, Ihara 2002, Kokko & Rankin 2006, Hernaman & Munday 2007. Other recent studies of seahorses have shown that the strict social and genetic monogamy observed in early research of seahorse reproductive biology is subject to variation (Kvarnemo et al 2000, Moreau & Vincent 2004, thus the mating systems of pygmy seahorses would be an interesting direction for future research.The link between group size and host size has been studied in various species of reef fishes where a correlation between these factors has been attributed to resource limitation or as an indirect consequence of patch size effects, such as through dominance of 1 group member (Elliott & Mariscal 2001, Mitchell & Dill 2005. We found no significant effect of gorgonian host area on the number of resident Hippocampus bargibanti or H. denise.…”

Population characteristics, space use and habitat associations of the seahorse Hippocampus reidi (Teleostei: Syngnathidae)

“…Perante et al, 1998;Teixeira & Musick, 2001;Bell et al, 2003;Martin-Smith & Vincent, 2005). The equivalent total number of males and females observed in our study agrees with the results obtained by Dauwe (1992) for H. reidi, as well as with studies on some other seahorse species (Vincent & Sadler, 1995;Bell et al, 2003;Moreau & Vincent, 2004;Curtis & Vincent, 2006). The discrepancies found at the Camurupim site may be related to the seahorse harvesting which took place until 2003, whereas at the Mal Cozinhado it reflects the few records of adult males (which were used to estimate the sex ratio).…”

The life history of weedy seadragons, Phyllopteryx taeniolatus (Teleostei:Syngnathidae)

“…Berglund et al (1986) noted that S. typhle female-female interactions were less important in breeding behaviours and this appeared to be the case with weedy seadragons. Weedy seadragon mating behaviour is also similar to that of S. typhle and Hippocampus breviceps, which involves the mating pairs rising to the surface during mating (Berglund et al 1986;Moreau and Vincent 2004).…”