Contents lists available at ScienceDirect Biological Conservation journal homepage: www.elsevier.com/locate/biocon Life-histories explain the conservation status of two estuary-associated pipefishes Alan K. Whitfield a,⁎ , Thomas K. Mkare b,1 , Peter R. Teske b , Nicola C. James a , Paul D. Cowley a a South African Institute for Aquatic Biodiversity (SAIAB), Private Bag 1015, Grahamstown 6140, South Africa b Molecular Zoology Laboratory, Department of Zoology, University of Johannesburg, Aukland Park 2006, South Africa ABSTRACT Two endemic southern African pipefish species (Teleostei: Syngnathidae) co-occur in estuaries on the southeast coast of South Africa. The larger longsnout pipefish, Syngnathus temminckii, is abundant and has a wide range that comprises coastal and estuarine habitats in all three of the region's marine biogeographic provinces. In contrast, the smaller estuarine pipefish S. watermeyeri is critically endangered, and confined to a few warm- temperate estuaries. Here, we explore reasons for these considerable differences in conservation status. Fecundity is related to fish size, with large live-bearing S. temminckii males carrying up to 486 developing eggs/ embryos, compared to a maximum of only 44 recorded for S. watermeyeri. Loss of submerged seagrass habitats due to episodic river flooding appears to be correlated with the temporary absence of both species from such systems. Prolonged cessation in river flow to estuaries can cause a collapse in estuarine zooplankton stocks, a food resource that is important to pipefish species. The greater success of S. temminckii when compared to S. watermeyeri can be attributed to the former species' wider geographic distribution, fecundity, habitat selection and ability to use both estuaries and the marine environment as nursery areas. Genetic data indicate that this has resulted in a much smaller long-term effective population size of S. watermeyeri, a situation that has persisted since the beginning of the present interglacial period. Syngnathus watermeyeri is thus naturally more susceptible to anthropogenic disturbances, which have resulted in an alarming reduction in its contemporary population size. Possible measures to promote the conservation of S. watermeyeri are presented. 1. Introduction Fishes have over 30 reproductive guilds that can essentially be di- vided into three main categories, namely non-guarders, guarders and bearers (Balon, 1975). Pipefishes belong to the bearer category and more specifically the external bearers. Typically they exhibit parental care, have a low fecundity but invest a large amount of energy in each of a small number of well-developed precocial young. The adults of such species are often specialists, have a narrow trophic niche and usually live in a stable and predictable environment (Bruton, 1989). Although the longsnout pipefish Syngnathus temminckii Kaup, 1856 and the estuarine pipefish S. watermeyeri Smith, 1963 fulfil many of the criteria outlined above, both species occur in estuaries that are gen- erally unstable and unpredictable environments (Whitfield, 1990). Fortunately for S. temminckii, it also occurs in the marine environment that is much more stable and predictable, thus conferring this species with a distinct advantage over S. watermeyeri. This study will show that this is but one of the many life-history traits that places the former species at an advantage over the latter. Syngnathus temminckii and S. watermeyeri have a conservation status that also differs considerably between the two species. The former is common within its South African distributional range, from the cool temperate west coast, through the estuaries and marine environment of the warm temperate southern and south-eastern coasts, reaching into the subtropical zone on the east coast (Mwale et al., 2014). In contrast, S. watermeyeri has been recorded in only a limited number of estuaries on the warm temperate south-east coast and, even in those estuaries, the numbers are generally very low (Whitfield, 1995). More recently, S. watermeyeri has been listed as Critically Endangered (CR) in the IUCN Red List (www.iucnredlist.org). The main threats to its existence are habitat loss, river degradation and loss of freshwater inputs to estuaries (Vorwerk et al., 2007). River inflow provides the nutrients required to stimulate planktonic productivity in estuaries (Grange et al., 2000), the food chain upon which this species depends for its survival (Whitfield, 1995). Loss of river pulses due to excessive freshwater abstraction in the catchments leads to a reduction http://dx.doi.org/10.1016/j.biocon.2017.06.024 Received 3 October 2016; Received in revised form 2 June 2017; Accepted 15 June 2017 ⁎ Corresponding author. 1 Present address: Kenya Marine and Fisheries Research Institute, P.O. Box 81651, Mombasa 80100, Kenya. E-mail address: a.whitfield@saiab.ac.za (A.K. Whitfield). Biological Conservation 212 (2017) 256–264 0006-3207/ © 2017 Elsevier Ltd. All rights reserved. MARK