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- Pleistocene expansion, anthropogenic pressure and ocean currents: Disentangling the past and ongoing evolutionary history of Patella aspera Röding, 1798 in the archipelago of MadeiraPublication . Sousa, Ricardo; Vasconcelos, Joana; Vera-Escalona, Iván; Pinto, Ana Rita; Hawkins, S. J.; Freitas, Mafalda; Delgado, João; González, José A.; Riera, RodrigoAims: Rising sea-level following the Last Glacial Maximum lead to fragmentation of coastal limpet populations between islands of the Archipelago of Madeira. This fragmentation is reinforced by recent heavy exploitation reducing effective population size on Madeira Island. We use the limpet P. aspera to understand how the role of processes at different time scales (i.e. changes in the sea level and overexploitation) can influence the genetic composition of an extant species, relating these processes to reproductive phenology and seasonal shifts in ocean currents. Location: Madeira Island, Porto Santo and Desertas (Archipelago of Madeira, NE Atlantic Ocean). Taxon: The limpet Patella aspera. Methods: Twelve microsatellite genetic markers were used. A power analysis was used to evaluate the power of the microsatellite markers to detect a signal of population differentiation. Long-term past migrations were assessed using a Bayesian Markov Montecarlo approach in the software MIGRATE-n to estimate mutation-scaled migration rates (M = m/μ; m, probability of a lineage immigrating per generation; μ, mutation rate). Two sce narios were evaluated using an Approximate Bayesian Computation (ABC) in the software DIYABC 2.1 (i) Sce nario 1: considered a population scenario from a reduced Ne at time t3 to a higher Ne at time t2; and (ii) Scenario 2 considering a reduction of Ne from a time t3 to a time t2. Results: Colonization of the archipelago by Portuguese settlers six centuries ago probably led to an important decrease in the genetic diversity of the species (Ne). Contemporary gene flow strongly support a pattern of high asymmetric connectivity explained by the reproductive phenology of the species and spatio-temporal seasonal changes in the ocean currents. Spatio-temporal reconstructions using Bayesian methods, including coalescent and Approximate Bayesian Computation (ABC) approaches, suggest changes in the migration patterns from highly symmetric to highly asymmetric connectivity with subtle population differentiation as consequence of post-glacial maximum sea level rise during the Holocene.
- Weight–length relationships of four intertidal mollusc species from the northeastern Atlantic Ocean and their potential for conservationPublication . Sousa, Ricardo; Vasconcelos, Joana; Riera, RodrigoWeight-length relationships (WLRs) are frequently used for the development of comparative studies of life history, population dynamics, ecosystem modelling and estimation of the production and biomass of populations among regions. WLRs provide information about growth, wellbeing and fitness of a population in a marine environment. WLRs for four topshells (Phorcus atratus, Phorcus lineatus, Phorcus mariae, Phorcus sauciatus) caught in North-eastern Atlantic Ocean (Azores, Canaries, Cape Verde, Madeira and Mainland Portugal) were established and their relative growth was assessed. The results showed that almost all species exhibited a positive allometric growth. A comparative study on the effect of harvest in the relative growth of P. sauciatus in the archipelago of Madeira showed that all the populations from exploited areas exhibited a negative allometric growth in contrast to the populations from the Marine Protected Areas (MPAs) which were predominantly isometric. The present results indicate that the conservation measures established in the protected areas promoted a positive effect in the protected populations and are valuable for establishing a set of monitoring and management measures aiming at the sustainable exploitation and conservation of these species. These results are important to demonstrate the role of MPAs in the conservation of these keystone species in the north eastern Atlantic Ocean rocky shore ecosystems.
- Does harvesting affect the relative growth in Patella aspera Röding, 1798?Publication . Sousa, R.; Pinto, A. R.; Vasconcelos, J.; Riera, R.Length–weight relationships (LWRs) provide valuable information about growth and individual fitness on the population. LWRs are commonly used in studies on life history, population dynamics, ecosystem modelling and stock assessment. A comparative study on the effect of harvesting in the relative growth of Patella aspera between Marine Protected Areas (MPAs) and exploited areas was conducted in the archipelago of Madeira (NE Atlantic Ocean). The results showed that populations from the exploited areas exhibited a negative allometric growth whilst the populations from the MPAs showed predominantly isometric and positive allometric growth. The effects of protection from MPAs on the populations of P. aspera were not only restricted to an increase in mean size but also in a more balanced growth. This study highlight the importance of MPAs in the preservation of P. aspera populations in Madeira archipelago. Hence, these results should be used to corroborate the positive effects of MPAs in safeguarding the exploited resources, especially in oceanic islands were species are more prone to over-exploitation.
- First observations of hermaphroditism in the patellid limpet Patella piperata Gould, 1846Publication . Sousa, Ricardo; Henriques, Paulo; Vasconcelos, Joana; Faria, Graça; Riera, Rodrigo; Pinto, Ana Rita; Delgado, João; Hawkins, Stephen J.Hermaphroditism is thought to be an advantageous strategy common in marine molluscs that exhibit simultaneous, sequential or alternating hermaphroditism. Several species of patellid limpets have previously been shown to be protandrous hermaphrodites. The present study aimed to confirm whether this phenomenon occurs in Patella piperata. Transitional forms of simultaneous protandrous hermaphroditism were found in intermediate size classes of P. piperata, in Madeira (North-eastern Atlantic). Sequential hermaphroditism was confirmed after histological analysis. The overall sex-ratio was biased towards females but approached similar proportions in the larger size classes. Analysis of size at sex change showed that at a shell length of 36 mm 50% of the population probably have changed sex. The results reported confirm the occurrence of sequential hermaphroditism. These findings are of utmost importance to the understanding of the reproductive biology of this species with direct effect on management and conservation of this traditionally harvested limpet.
- Stock assessment of the blue jack mackerel, Trachurus picturatus, in the North-eastern AtlanticPublication . Vasconcelos, Joana; Sousa, Ricardo; Riera, Rodrigo; Delgado, João; Faria, Graça; Serrano Gordo, LeonelA total of 49,151 blue jack mackerel, Trachurus picturatus, (Bowdich) was collected in Madeira Island (North-eastern Atlantic) between 2002 and 2016 to evaluate pos sible influence of fishing on landings and reproductive parameters. A decreasing trend in the length composition was observed over the study period and length at first maturity decreased by 2.78 cm TL. Maximum yield per recruit decreased from 2002 to 2016 but the corresponding fishing mortality was constant (Fmax = 0.4/ year). Considering the fishing mortality level in 2016, it is evident that the stock may be exploited beyond its sustainability limit. Amendments of the purse-seine fishing regulations and implementation of measures to reduce fishing effort are suggested.
- Severe shifts of Zostera marina epifauna: comparative study between 1997 and 2018 on the Swedish Skagerrak coastPublication . Riera, Rodrigo; Vasconcelos, Joana; Baden, Susanne; Gerhardt, Linda; Sousa, Ricardo; Infantes, EduardoThe interaction between bottom-up and top-down processes in coastal ecosystems has been scarcely studied so far. Temporal changes in trophic interactions of Zostera marina along the Swedish west coast are relatively well studied, with the exception of epifaunal communities. Epifauna was used as a model study to explore resource (bottom-up) or predator (top-down) regulated in a vegetated ecosystem. We conducted a 21-year comparative study (1997 and 2018) using epifauna of 19 Zostera marina meadows along the Swedish Skagerrak coast. Large changes were observed in the composition of small (0.2–1 mm) and large (> 1 mm) epifauna. In the small-sized epifauna, the nematode Southernia zosterae and harpacticoids showed an increase of 90% and a decrease of 50% of their abundances, respectively. In the large-sized epifauna, the polychaete Platynereis dumerilii and chironomid larvae were absent in 1997 but thrived in 2018 (> 2000 ind. m−2 ). Mesoherbivores (Idoteids and gammarids) were locally very abundant in 1997 but disappeared in 2018. An 83% decline of mytilids settling in Zostera marina leaves was observed. Our results showed that epifauna is predominantly top-down regulated. An in tegrative framework of the study area is outlined to shed light on the causes and consequences of the en vironmental shifts reported in Zostera meadows from the northern Skagerrak area throughout the last three decades.
- The protection effects of marine protected areas on exploited molluscs from an oceanic archipelagoPublication . Sousa, Ricardo; Henriques, Paulo; Vasconcelos, Joana; Pinto, Ana Rita; Delgado, João; Riera, Rodrigo1. Limpets are one of the most successful intertidal algal grazers in the north-eastern Atlantic. They provide valuable ecosystem services, playing a pivotal role in maintaining rocky shore ecological balance and have an important economic value, being subject to high levels of exploitation in several oceanic archipelagos. Limpets represent one of the most profitable economic activities of small-scale fisheries in the Madeira archipelago. However, limpets are extremely vulnerable to anthropogenic impacts, such as overharvesting, habitat fragmentation, and pollution. 2. The protection effects and the effectiveness of marine protected areas (MPAs) on the population dynamics of two historically highly exploited limpet species, Patella aspera and Patella candei, were analysed through a comparative study of size, reproduction, and biomass in the Madeira archipelago. 3. The effects of protection from MPAs on limpet populations resulted in a differential increase on size at first maturity, shell size, and capture per unit effort according to the degree of protection. 4. Old and enforced MPAs showed the best-preserved limpet populations in the study area, and both variables (age and enforcement) best explained the observed variability among the MPAs studied. 5. A thorough and multidisciplinary study is necessary to obtain a reliable picture of commercial stocks of the two targeted species (P. aspera and P. candei). Genetic analysis and studies on the food source of limpets may shed light to develop integrative conservation strategies.
- Long-term population status of two harvested intertidal grazers (Patella aspera and Patella candei), before (1996–2006) and after (2007–2017) the implementation of management measuresPublication . Sousa, Ricardo; Vasconcelos, Joana; Henriques, Paulo; Pinto, Ana Rita; Delgado, João; Riera, RodrigoIntertidal limpets are subject to harvesting pressure in regions, e.g. oceanic islands, where marine organisms are a more accessible source of protein. These molluscs are very sensitive to human exploitation which often results on a decrease of their densities and an over-representation of immature individuals, because of the loss of large sized reproductive specimens. Two species of exploited limpets (Patella aspera and Patella candei) were assessed throughout 21 years, before (1996–2006) and after (2007–2017) the implementation of conservation measures for their sustainable management in Madeira (North-eastern Atlantic Ocean). Different levels of anthropogenic pressure were also taken in account in this comparative study: (i) proximity to coastal settlements (“Near” vs. “Far”) and (ii) accessibility to the coast (North vs. South), that may be considered surrogates of harvesting pressure on the intertidal of Madeira. The present results showed that the stocks of P. aspera and P. candei are slightly recovered after regulatory measures entered into force, with an increase of mean shell length and dominance of reproductive individuals (> 40 mm). P. aspera populations showed a clearer effect mainly due to the higher exploitation rate relative to P. candei. Conservation measures prompted a positive effect on both exploited limpet species, but further assessment studies are necessary to address the evolution of stocks over time.
- Potential impact of harvesting management measures on the reproductive parameters of the limpets Patella aspera and Patella candei from Madeira IslandPublication . Sousa, Ricardo; Vasconcelos, Joana; Riera, Rodrigo; Pinto, Ana Rita; Delgado, João; Henriques, PauloIntertidal and shallow subtidal molluscs are highly sensitive to overharvesting because of their restricted habitat, limited mobility and easy access to humans. Several parameters have been previously used to determine their exploitation status, e.g. sizes, abundances and reproductive stages. Herein the reproductive parameters of two exploited limpets, Patella candei and the protandrous hermaphrodite Patella aspera were examined. Limpets were collected “before” (1996–2006) and “after” (2007–2017) the implementation of management measures aiming to preserve limpet populations in Madeira Island (NE Atlantic Ocean). The proportion of reproductive in dividuals increased approximately 14% after the implementation of management measures for both species. An increase in the size and age at first maturity of both species (from 34.6 to 37.5 mm in P. aspera and from 33.4 to 37.4 mm in P. candei) also occurred after such implementation. “Before” samples of P. aspera showed male biased populations (1.7:1) shifting towards a balanced sex ratio (1:1) after the regulations. No “before” nor “after” sex ratio variations were observed in P. candei populations. Reproductive parameters revealed feasible to determine the efficiency of the implementation of management measures and to detect a slight improvement in reproductive potential of both limpet species.
- Major ocean currents may shape the microbiome of the topshell Phorcus sauciatus in the NE Atlantic OceanPublication . Sousa, Ricardo; Vasconcelos, Joana; Vera-Escalona, Iván; Delgado, João; Freitas, Mafalda; González, José A.; Riera, RodrigoStudies on microbial communities are pivotal to understand the role and the evolutionary paths of the host and their associated microorganisms in the ecosystems. Meta-genomics techniques have proven to be one of the most efective tools in the identifcation of endosymbiotic communities of host species. The microbiome of the highly exploited topshell Phorcus sauciatus was characterized in the Northeastern Atlantic (Portugal, Madeira, Selvagens, Canaries and Azores). Alpha diversity analysis based on observed OTUs showed signifcant diferences among regions. The Principal Coordinates Analysis of beta-diversity based on presence/absence showed three well diferentiated groups, one from Azores, a second from Madeira and the third one for mainland Portugal, Selvagens and the Canaries. The microbiome results may be mainly explained by large-scale oceanographic processes of the study region, i.e., the North Atlantic Subtropical Gyre, and specifcally by the Canary Current. Our results suggest the feasibility of microbiome as a model study to unravel biogeographic and evolutionary processes in marine species with high dispersive potential.