The Response of a protandrous species to exploitation, and the implications for management: a case study with patellid limpets

A zygote production model for the patellid limpet Patella vulgata has been developed to examine the effect of exploitation on the reproductive output of a protandrous (male to female sequential) hermaphrodite. Patellid limpets are broadcast spawners which can have specific implications for the effect of exploitation on reproductive output, due to sperm limitation. The combined zygote production model was made of three component sub-models; a population fecundity model, a gamete dispersal model, and a fertilisation model. The model makes explicit account of sperm limitation, and is based upon data collected through field and laboratory investigations conducted as part of this thesis.The model was used to examine the relationship between egg and zygote production, and spawning stock biomass (SSB) and fishery yield for a range of P. vulgata populations across a wave exposure gradient. The effect of different management strategies, minimum landing size or marine protected areas, on the relationship between reproductive output and yield was also examined.Protandry lead to a decoupling between SSB and zygote production as the populations were exposed to the simulated fishery. There was a five-fold variation in zygote production per unit area across a wave exposure gradient. Comparison of different management strategies indicates that the fishery yield could vary by up to three-fold depending on the management strategy used, whilst still protecting the same level of population reproductive output. The genetic population structure of the Azorean Patella candei population was also examined to determine the scale of larval dispersal to allow the management recommendations of the zygote production model to be examined in a wider ecological context. Due to evidence of a recent population bottleneck in the Azorean P. candei population no firm conclusions could be drawn from this study as to the scale of larval dispersal

Direct observations of protandrous sex change in the patellid limpet Patella vulgata

Direct observations of sex change were made on Patella vulgata, which has long been considered a protandrous hermaphrodite based on indirect methods. Thirty per cent of the male limpets that were marked during the spawning season in 2003 here female when they were re-examined during the spawning season in 2004. This confirms that protandry does occur within the superfamily Patellida

Factors affecting fertilization success in two species of patellid limpet (Mollusca: Gastropoda) and development of fertilization kinetics models

Laboratory experiments were undertaken to examine fertilization success in the intertidal prosobranch 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 optimum fertilization success in vivo ranged between 105 and 107 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 106 sperm ml–1) did not exceed 6 h, whereas eggs of both species were fertilizable for up to 12 h. Maximum fertilization success 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 concentrations, and a new parameter fitting technique is developed to improve estimates of fertilization success for short gamete contact times

Identifying potentially invasive non-native marine and brackish water species for the Arabian Gulf and Sea of Oman

Invasive non‐native species (NNS) are internationally recognized as posing a serious threat to global biodiversity, economies and human health. The identification of invasive NNS is already established, those that may arrive in the future, their vectors and pathways of introduction and spread, and hotspots of invasion are important for a targeted approach to managing introductions and impacts at local, regional and global scales. The aim of this study was to identify which marine and brackish NNS are already present in marine systems of the northeastern Arabia area (Arabian Gulf and Sea of Oman) and of these which ones are potentially invasive, and which species have a high likelihood of being introduced in the future and negatively affect biodiversity. Overall, 136 NNS were identified, of which 56 are already present in the region and a further 80 were identified as likely to arrive in the future, including fish, tunicates, invertebrates, plants and protists. The Aquatic Species Invasiveness Screening Kit (AS‐ISK) was used to identify the risk of NNS being (or becoming) invasive within the region. Based on the AS‐ISK basic risk assessment (BRA) thresholds, 36 extant and 37 horizon species (53.7% of all species) were identified as high risk. When the impact of climate change on the overall assessment was considered, the combined risk score (BRA+CCA) increased for 38.2% of all species, suggesting higher risk under warmer conditions, including the highest‐risk horizon NNS the green crab Carcinus maenas, and the extant macro‐alga Hypnea musciformis. This is the first horizon‐scanning exercise for NNS in the region, thus providing a vital baseline for future management. The outcome of this study is the prioritization of NNS to inform decision‐making for the targeted monitoring and management in the region to prevent new bio‐invasions and to control existing species, including their potential for spread