Insights into the Migration Routes and Historical Dispersion of Species Surviving the Messinian Crisis: The Case of Patella ulyssiponensis and Epizoic Rhodolith Lithophyllum hibernicum

The genus Patella (Patellogastropoda, Mollusca) is represented by a group of species exclusive to the Northeast Atlantic Ocean (including Macaronesian archipelagos) and Mediterranean Sea. The species Patella ulyssiponensis and Patella aspera are common in European waters, with the first inhabiting continental coast, and the second endemic to Macaronesian archipelagos. However, the acceptance of these two lineages as separate species is still highly debated. The red coralline species algae Lithophyllum hibernicum, distributed from Northeast Atlantic to the Mediterranean, is usually found as epilithic crusts or unattached forms (named rhodolith beds), although it also forms epizoic crusts on other organisms, e.g., shell surfaces. In order to study the historic dispersal and migration routes of the Patella ulyssiponensis-aspera complex, taxonomic, genetic and biogeographic approaches were employed based on haplotype network analyses and estimations for the most common recent ancestor (TMRCA), using Cytochrome Oxydase I. A synonymy for these two species is proposed, with the presence of a shared haplotype between the continental (P. ulyssiponensis) and insular (P. aspera) lineages, and with basis of morphological and nomenclatural data. We propose an evolutionary scenario for its dispersal based on a high haplotype diversity for the Mediterranean regions, indicating its possible survival during the Messinian Salinity Crisis (6–5.3 Mya), followed by a colonization of the Proto-Macaronesian archipelagos. The epizoic association of L. hibernicum on P. ulyssiponensis shell adult surface is recorded in this study, likewise the promotion of settlement conditions provided by these coralline algae to P. ulyssiponensis larvae, may explain the reach of P. ulyssiponensis distribution through rhodolith transportation.

Recruitment of the limpet Patella ulyssiponensis and its relationship with crustose coralline algae: patterns of juvenile distribution and larval settlement

Recruitment of the limpet Patella ulyssiponensis was investigated in relation to the presence of living crustose coralline algae (CCA) in rocky-shore habitats. Juvenile limpets (≤10 mm maximum shell length) were counted in CCA-present and CCA-absent habitats, on three shores in SW Portugal during summer 2007 and winter 2009. Furthermore, the settling response of laboratory-reared larvae of P. ulyssiponensis to CCA-covered substratum, and bare-rock, was examined. Across the intertidal zone, we found a clear association between the distribution and abundance of juveniles and the presence of CCA. Although the presence of CCA was not an absolute requisite for juvenile occurrence, null juvenile densities were mostly recorded in CCA-absent areas. The highest juvenile densities (maximum of 64 individuals in 15 × 15 cm) were consistently found in CCA-dominated habitats, namely steep wave-exposed areas at low-shore and rock-pools. The hypothesis of CCA-enhanced settlement was not supported, as settlement intensities of laboratory-reared larvae were similar between chips of rock encrusted by CCA and chips of bare-rock. From the overall number of settlers onto CCA-encrusted rock chips, 51% were found in tiny pits lacking CCA. This was the first study of the settlement patterns of larvae of the genus Patella using naturally occurring rocky substrata. These results are preliminary and should be confirmed with choice-experiments and improved monitoring of the position of settlers. We suggest that CCA plays a role in the recruitment of P. ulyssiponensis, potentially promoting survivorship of early benthic stages, but possibly not enhancing settlement.

Temporal and spatial variability on rocky intertidal macrofaunal assemblages affected by an oil spill (Basque coast, northern Spain)

A large (100 km) rocky coast intertidal was sampled several times (from 2004 to 2006) to assess the affection degree of invertebrate assemblages impacted by a continuous oil spill. Twelve locations and two intertidal heights were selected along the coast representing two spatial scales (kilometres and tens of metres). Univariate and multivariate analyses of variance were used to test whether faunal assemblages exposed to different intensities of oil disturbance differ in terms of diversity, total cover, key species cover and trophic guilds. Whereas no significant differences in midshore assemblages were noted, the low intertidal zone exhibited comparatively lower abundance values of the limpet Patella ulyssiponensis at worst affected sites. Besides, a generalized increasing diversity trend was found in the low intertidal from 2004 to 2006. Natural variability of communities is also discussed as the cause of the differences we observed. With respect to spatial and temporal scales of variation, mid- intertidal communities showed a more consistent structure, while lowshore assemblages were markedly heterogeneous in practically all the variables measured.

Reproductive cycles of four species of Patella (Mollusca: Gastropoda) on the northern and central Portuguese coast

The reproductive cycles of four limpet species, Patella depressa, Patella ulyssiponensis, Patella vulgata and Patella rustica are described for several locations in northern and central Portugal. Patella depressa and P. ulyssiponensis displayed almost continual gonad activity, with two main spawning periods, September–January and March–June, and minor spawning events dispersed throughout the year. Patella vulgata and P. rustica exhibited highly synchronized reproductive cycles, with well-defined breeding and resting periods. Gonad development in P. vulgata started in September and spawning took place from November–December to March. In P. rustica development started in June and spawning occurred from September–October to December–January. Compared to the 1980s these results suggest that breeding periods are becoming longer in southern species and shorter in northern species.

Shape and growth in European Atlantic <i>Patella limpets</i> (Gastropoda, Mollusca). Ecological implications for survival

Specimens of Patella intermedia, Patella rustica, Patella ulyssiponensis, and Patella vulgata were analyzed for shell and radula characteristics. Shell growth in P. rustica and P. ulyssiponensis was basically isometric, indicating that shell shape was constant during growth. On the contrary, shell growth in P. intermedia and P. vulgata was positively allometric, indicating that as shells increased in size, the base became more circular and the cone more centred and relatively higher. Radula relative size increased in the order P. ulyssiponensis, P. vulgata, P. intermedia and P. rustica, and had negative allometric growth in all species, indicating that radula grew less as shell increased in size. Data reported in the literature estimated that the lowest risk of dislodgment for a limpet is associated with a centred apex, and a (shell height)/(shell length) or (shell height)/(shell width) ratio of ca. 0.53. However, as reported for other limpets, in all four studied Patella species, shells were more eccentric and flat than this theoretical optimum. Data reported in the literature indicated that, in limpets, decreasing the (shell base perimeter)/(shell volume) or (shell surface area)/(shell volume) ratios by increasing size results in lower soft body temperature and desiccation. In the present study, P. rustica shells displayed the lowest ratios, and P. ulyssiponensis shells, the highest. Considering that the former species lives at high shore levels, and the latter species at low levels, it appeared that shell shape in European Atlantic limpets can be directly related to resistance to desiccation and high temperature stresses. Radula relative size (in relation to shell height) also increased with increasing level in the shore, suggesting that this might be due to a decreasing abundance of algae with increasing shore level.