The influence of simulated exploitation onPatella vulgatapopulations: protandric sex change is size-dependent

Grazing mollusks are used as a food resource worldwide, and limpets are harvested commercially for both local consumption and export in several countries. This study describes a field experiment to assess the effects of simulated human exploitation of limpets Patella vulgata on their population ecology in terms of protandry (age-related sex change from male to female), growth, recruitment, migration, and density regulation. Limpet populations at two locations in southwest England were artificially exploited by systematic removal of the largest individuals for 18 months in plots assigned to three treatments at each site: no (control), low, and high exploitation. The shell size at sex change (L50: the size at which there is a 50:50 sex ratio) decreased in response to the exploitation treatments, as did the mean shell size of sexual stages. Size-dependent sex change was indicated by L50 occurring at smaller sizes in treatments than controls, suggesting an earlier switch to females. Mean shell size of P. vulgata neuters changed little under different levels of exploitation, while males and females both decreased markedly in size with exploitation. No differences were detected in the relative abundances of sexual stages, indicating some compensation for the removal of the bigger individuals via recruitment and sex change as no migratory patterns were detected between treatments. At the end of the experiment, 0–15 mm recruits were more abundant at one of the locations but no differences were detected between treatments. We conclude that sex change in P. vulgata can be induced at smaller sizes by reductions in density of the largest individuals reducing interage class competition. Knowledge of sex-change adaptation in exploited limpet populations should underpin strategies to counteract population decline and improve rocky shore conservation and resource management

Exploitation promotes earlier sex change in a protandrous patellid limpet, Patella aspera Röding, 1798

Exploitation of organisms can prompt the reduction in the number and size of target populations consequently affecting reproductive output and replenishment. Here, we investigated the effects of exploitation on the population structure of a protandrous patellid limpet, Patella aspera, an overexploited Macaronesian endemic. Timed dives were used to collect animals across eleven islands of Macaronesia. Individuals were inspected for sex, size, and gonad stage. Using catch effort (time per person) per island coastal perimeter as a surrogate for exploitation intensity, we found that limpet abundance (CPUE) and mean size tended to decrease with exploitation intensity. When considering the sex of animals separately, the size of the largest male, but not females, decreased with exploitation. In contrast, the size of the smallest male remained relatively consistent, whereas the size of the smallest female decreased significantly with exploitation. As exploitation is mostly targeting larger individuals, results suggest that males are compensating the removal of larger females, by undergoing sex change at smaller and presumably earlier sizes. These results have wider implications for the conservation of P. aspera, as a reduction in female size will likely affect the numbers of oocytes produced, hence fecundity. Regulations promoting the protection of the larger-sized animals should be enforced to safeguard the replenishment of the population

Broad-scale patterns of sex ratios in Patella spp.: a comparison of range edge and central range populations in the British Isles and Portugal

Sex change, or sequential hermaphroditism, occurs in the plant and animal kingdoms and often determines a predominance of the first sex. Our aim was to explore changes in sex ratios within the range of the species studied: Patella vulgata and Patella depressa. The broad-scale survey of sex with size of limpets covered a range of latitudes from Zambujeira do Mar (southern Portugal) to the English Channel. Indirect evidence was found for the occurrence of protandry in P. vulgata populations from the south of England, with females predominating in larger size-classes; cumulative frequency distributions of males and females were different; sex ratios were biased towards males and smallest sizes of males were smaller than the smallest sizes of females. In contrast in Portugal females were found in most size-classes of P. vulgata. In P. depressa populations from the south coast of England and Portugal females were interspersed across most size-classes; size distributions of males and females and size at first maturity of males and females did not differ. P. depressa did, however, show some indications of the possibility of slight protandry occurring in Portugal. The test of sex ratio variation with latitude indicated that P. vulgata sex ratios might be involved in determining the species range limit, particularly at the equatorward limit since the likelihood of being male decreased from the south coast of England to southern Portugal. Thus at the southern range limit, sperm could be in short supply due to scarcity of males contributing to an Allee effect

The intertidal zone of the North-East Atlantic region: pattern and process.

The north-east Atlantic region is an area where clades originating in the north Pacific (fucoids, balanoids, littorinids, thaids, laminarians) collide with clades from further south in the Atlantic (e.g., patellids, trochids, chthamalids). At high latitudes in the north, seaweeds dominate the midshore zone of all but the most exposed shores. Further south, midshore space-occupying invertebrates (mussels and barnacles) win, facilitated by grazing by patellid limpets that controls algal recruitment; propagule pressure is much less as fucoids become rarer, and juvenile growth is slower due to environmental stress, thereby reducing the probability of escapes from grazing (Figure 2.4) (Ferreira et al., 2014, 2015a, 2015b). Low on the shore seaweeds dominate space by forming algal turfs or kelp or fucoid canopies. These algae outpace the ability of grazing limpets to control them in the low-intertidal zone. L. digitata canopies can lead to rock covered by encrusting algae and sponges, facilitating limpets. If canopy is removed, then colonising ephemeral algae and turf-forming algae swamp the limpets. There is usually too much water movement immediately either side of low water for effective foraging by sea urchins. Psammechinus miliaris and Echinus esculentus only appear in the subtidal, and Paracentrotus lividus is confined to refuges in burrows relying mainly on the drift of food (Benedetti-Cecchi and Cinelli, 1995;Boudouresque and Verlaque, 2007; Jacinto and Cruz, 2012). High on the shore, physical factors dominate. At high latitudes in the north of the Atlantic, ephemeral algae are present all year round. Further south they are only present in the winter, dying-off in the summer. Grazing has limited effects, only occurring around refuges that littorinids maintain (Stafford and Davies, 2005; Skov et al., 2010, 2011). Patterns are also strongly modified by mesoscale processes driven by upwelling that influences nutrient and larval supply (North Africa, Iberia) and coastal configuration, where embayed versus headlands also strongly influence larval supply (France northwards). In high-recruitment areas, interactions can be intense between spaceoccupying species, also driving predator abundance (e.g., dog whelks). Connell’s (1961a) classic paper on competition was possible on the Isle of Cumbrae because space was almost saturated; elsewhere lower larval supply would have created less intense interactions, as shown by Gordon and Knights (2017) in Plymouth. The north-east Atlantic has faster rates of warming than any other ocean, although the region south of Greenland and Iceland is undergoing cooling due to a climate-driven slowdown in the Atlantic meridional overturning circulation, causing a weakening in the Gulf Stream (Rahmstorf et al., 2015). Species are responding to rapid alterations in the marine climate by adapting or exhibiting range shifts, or by becoming locally extinct. There is a high degree of spatial and temporal heterogeneity in the resultant impacts on marine communities due to the idiosyncratic responses of individual species. Warming seas have resulted in biogeographic range shifts of intertidal and subtidal species in coastal waters of the northeast Atlantic. The leading range edges of Lusitanian species are expanding, while the trailing edges of boreal species are retracting to higher latitudes, but with some cold-water species showing surprising resilience (Southward et al., 1995; Mieszkowska et al., 2006, 2014b; Lima et al., 2007; Hawkins et al., 2008, 2009; Wethey and Woodin, 2008; Mieszkowska and Sugden, 2016). In addition to changes in the distribution ofspecies, community structure is also altering as species dominance and interactions change (Poloczanska et al., 2008; Hawkins et al., 2008, 2009; Mieszkowska et al., 2014b). In a warming world the midshore of France and the British Isles are likely to show much less cover by large canopy-forming fucoids as harsher warmer, drier and stormier conditions coupled with increased grazing pressure from more grazing species reduces the probability of fucoids recruiting to form adult populations. Lowshore kelp forests will likely change with less L. digitata and A. esculenta and more S. polyschides. The late autumn to early spring window of dense ephemeral algal growth high on the shore (Hawkins and Hartnoll, 1983a) will also constrict, except in the north and in extreme exposure. These changes will have consequences for biodiversity (Thompson et al., 1996; Smale et al., 2013; Teagle et al., 2017) and productivity (Hawkins et al., 1992) – particularly the decrease in export of algal detritus (Notman et al., 2016). More shores will become dominated by suspension-feeding barnacles and mussels. Thus, there will be switches on many mid-latitude shores as many become net importers rather than exporters of energy (Hawkins et al., 2008, 2009)

Influence of environmental variables and fishing pressure on bivalve fisheries in an inshore lagoon and adjacent nearshore coastal area

Climate changes affect marine ecosystems and the survival, growth, reproduction and distribution of species, including those targeted by commercial fisheries. The impact of climate change has been reported for many fish species, but studies focusing on the effects of climate on bivalve resources are lacking. In Portugal, the harvesting of bivalves is an old and artisanal activity, of special importance along the Algarve coast (South of Portugal). This study aims to evaluate the influence of climatic, environmental and fisheries factors on the landings of intertidal coastal lagoon and coastal bivalve species (subtidal nearshore species). The environmental and fisheries parameters considered to affect the landings of bivalves in the eastern Algarve were: fishing effort (number of fishing events), sea surface temperature, North Atlantic Oscillation (NAO) index, upwelling index, wind magnitude and direction and river discharges. Analysis of time series data using min/max autocorrelation factor analysis and dynamic factor analysis showed that, for most species, fishing effort was positively related with landings per unit effort trends in the following year. Lagoon bivalve species (Cerastoderma edule and Ruditapes decussatus) responded to different environmental variables than the coastal bivalve species (Chamelea gallina, Pharus legumen, Donax spp. and Spisula solida). Upwelling index had a significant effect on the lagoon bivalves while the NAO index, wind magnitude and direction, and river discharges only affected the coastal species. This study highlighted the need to adapt fishing effort regimes, while considering the background effects of environmental variability, in order to improve fisheries management