Reproductive biology and distribution of Syngnathus temminckii and S. watermeyeri (Pisces: Syngnathidae) in southern Africa

Abstract

The reproductive biology and distribution of two species of Syngnathus (S. temminckii and S. watermeyeri) were investigated using information from museum specimens, published data, survey data and samples collected during mouth-breaching events of temporarily open/closed estuaries over the period 1950–2011. Distribution records indicate that the two species are restricted to specific habitats and bioregions in southern Africa. Although S. temminckii has marine and estuarine populations, the species is most prevalent in warm and cool temperate estuarine systems. Syngnathus watermeyeri has limited dispersal capabilities owing to life-history characteristics and is completely dependent on shallow vegetated habitat in mesosaline estuarine systems in the warm temperate region, where it co-occurs with S. temminckii. The presence of breeding individuals and juveniles indicated that the spawning period of both species occurs in spring and summer, coinciding with warmer water temperatures and enhanced food resources, with reproductive activity of S. temminckii peaking in November. The estimated lengths (standard length) at 50% maturity of males and females of S. temminckii (129 and 120 mm respectively), were larger than those of S. watermeyeri (118 and 102 mm) and similar to those for other syngnathids. Although the observed sex ratios for S. temminckii (0.5:1.0, M:F) and S. watermeyeri (0.7:1.0), were biased towards females and similar to those observed among congeners, only S. temminckii was significantly different from the expected 1:1 ratio. The mean number of mature oocytes in the females (n = 379; 95% CI = 244–658) of S. temminckii was not significantly different from the mean number of eggs/embryos in the male brood pouch (n = 451; 95% CI = 270–486). The relationship between carrying capacity and size was linear and positively correlated, implying that fecundity, and hence reproductive efficiency, increases with the size of the individual. Comparative analyses indicated that these species have different life-history strategies and dispersal capabilities. However, they are both highly vulnerable as a result of anthropogenic threats to the unstable estuarine environment.