Abstract Laboratory experiments were undertaken to examine fertilization success in the intertidal pros- obranch limpets Patella ulyssiponensis and Patella vulgata. Alkalization of eggs (10 min in pH 9.0 sea water) prior to fertilization trials improved fertilization rates greatly. Fertilization success was found to be a function of sperm concentration, gamete age and contact time. Sperm concentration needed for opti- mum fertilization success in vivo ranged between 10 5 and 10 7 sperm ml –1 for both species although at higher concentrations the number of normally developing trochophore larvae decreased. For P. vulgata, sperm longevity (at a concentration of 10 6 sperm ml –1 ) did not exceed 6 h, whereas eggs of both species were fertilizable for up to 12 h. Maximum fertilization suc- cess occurred after 15–30 min gamete contact time. The Vogel et al. (Math Biosci 58:189–216, 1982) fertilization kinetics model is developed to allow for non-complete fertilizations under optimal sperm con- centrations, and a new parameter fitting technique is developed to improve estimates of fertilization success for short gamete contact times. Introduction In the early 20th Century the first suggestions that fertilization may be a limiting step in the reproduc- tion of broadcast spawning populations came to light. Belding (1910) suggested that fertilization success may be a limiting factor in the Massachusetts scallop fishery, and Gross and Smyth (1946) proposed reduced fertil- ization success as a reason why Ostrea edulis popula- tions did not recover around Britain following the introduction of management regulations. More recent empirical work on sessile and sedentary broadcast spawners has shown fertilization success to be affected by a number of factors including sperm concentration, gamete age, gamete ratios, contact time between gametes, distance between spawning individuals and hydrodynamic conditions (e.g. Vogel et al. 1982; Pennington 1985; Denny and Shibata 1989; Levitan et al. 1991; Denny et al. 1992; Babcock et al. 1994; Andre ´ and Lindegarth 1995; Levitan and Young 1995; Mead and Denny 1995; Serrao et al. 1996; Williams et al. 1997; Encena et al. 1998; Babcock and Keesing 1999; Mar- shall et al. 2000; Styan and Butler 2000; Baker and Tyler 2001; Powell et al. 2001; Metaxas et al. 2002). Fertil- ization success, therefore, can under some circum- stances be a limiting factor in reproduction, and hence recruitment, and several reviews discuss the implica- tions of this for natural resource managers (Quinn et al. Communicated by O. Kinne, Oldendorf/Luhe A. N. Hodgson (&) Department of Zoology and Entomology, Rhodes University, Grahamstown, South Africa e-mail: A.Hodgson@ru.ac.za Fax: +27-46-6228959 W. J. F. Le Quesne National Oceanography Centre, Waterfront Campus, University of Southampton, Southampton SO14 3HZ, UK S. J. Hawkins Æ J. D. D. Bishop Marine Biological Association, Citadel Hill, Plymouth PL1 2PB, UK Present address: W. J. F. Le Quesne School of Marine Science and Technology, Newcastle University, Newcastle, UK Mar Biol (2007) 150:415–426 DOI 10.1007/s00227-006-0354-9 123 RESEARCH ARTICLE Factors affecting fertilization success in two species of patellid limpet (Mollusca: Gastropoda) and development of fertilization kinetics models Alan N. Hodgson Æ Will J. F. Le Quesne Æ Stephen J. Hawkins Æ John D. D. Bishop Received: 25 January 2006 / Accepted: 3 May 2006 / Published online: 13 June 2006 Ó Springer-Verlag 2006