The Ecology ofPatellaLinnaeus from the Cape Peninsula, South Africa I. Zonation, Movements and Feeding

Conservation priorities in an endangered estuarine seahorse are informed by demographic history

Historical demographic events shape genetic diversity that remains evident in the genomes of contemporary populations. In the case of species that are of conservation concern, this information helps to unravel evolutionary histories that can be critical in guiding conservation efforts. The Knysna seahorse, Hippocampus capensis, is the world's most endangered seahorse species, and it presently survives in only three estuaries on the South African south coast. Factors that contributed to the species becoming endangered are unclear; additionally, the lack of information on whether the three populations should be managed separately because of potential long-term isolation hampers effective management efforts. In the present study, we reconstructed the seahorses' demographic history using a suite of microsatellite loci. We found that the largest population (Knysna Estuary) has colonised the other estuaries relatively recently (< 450 years ago), and that its population size is comparatively large and stable. Neither of the other two populations shows signs of long-term reductions in population size. The high conservation status of the species is thus a result of its limited range rather than historical population declines. Our findings indicate that the long-term survival of H. capensis depends primarily on the successful management of the Knysna population, although the other estuaries may serve as reservoirs of genetic diversity.

Trophic ecology of two co-existing Sub-Antarctic limpets of the genus Nacella: spatio-temporal variation in food availability and diet composition of Nacella magellanica and N. deaurata

Interactions between algae and herbivores can be affected by various factors, such as seasonality and habitat structure. Among herbivores inhabiting marine systems, species of the order Patellogastropoda are considered key organisms in many rocky coasts of the world. Nacella species are one of the most dominant macro-herbivores on the rocky shores of the sub-Antarctic ecoregion of Magellan. However, the importance of its key role must be associated with its trophic ecology. The objective of this work was to evaluate spatial and temporal variabilities in the dietary composition of two intertidal Nacella species, considering grazing on macro- (macroalgae) and microscopic (periphyton) food. The composition of periphyton and the availability of macroalgae in the winter and summer seasons were examined at two localities of the Magellanic province, alongside the gut contents of N.magellanica and N.deaurata. The dietary composition differed between the two Nacella species, as well as between seasons and locations. The differences observed in the diet of the two species of Nacella may be mainly due to their respective distributions in the intertidal zone. Both species presented a generalist strategy of grazing, which is relationed to the seasonality of micro- and macroalgae availability and to the variability of the assemblages between the localities. This research was the first to perform a detailed study of the diet of intertidal Nacella species.

Biological Conservation of Giant Limpets: The Implications of Large Size

Patellogastropods, also known as true limpets, are distributed throughout the world and constitute key species in coastal ecosystems. Some limpet species achieve remarkable sizes, which in the most extreme cases can surpass 35cm in shell length. In this review, we focus on giant limpets, which are defined as those with a maximum shell size surpassing 10cm. According to the scientific literature, there are a total of 14 species across five genera that reach these larger sizes. Four of these species are threatened or in danger of extinction. Inhabiting the intertidal zones, limpets are frequently affected by anthropogenic impacts, namely collection by humans, pollution and habitat fragmentation. In the case of larger species, their conspicuous size has made them especially prone to human collection since prehistoric times. Size is not phylogeny-dependent among giant limpets, but is instead related to behavioural traits instead. Larger-sized species tend to be nonmigratory and territorial compared to those that are smaller. Collection by humans has been cited as the main cause behind the decline and/or extinction of giant limpet populations. Their conspicuously large size makes them the preferred target of human collection. Because they are protandric species, selectively eliminating larger specimens of a given population seriously compromises their viability and has led to local extinction events in some cases. Additionally, sustained collection over time may lead to microevolutionary responses that result in genetic changes. The growing presence of artificial structures in coastal ecosystems may cause population fragmentation and isolation, limiting the genetic flow and dispersion capacity of many limpet species. However, when they are necessitated, artificial structures could be managed to establish marine artificial microreserves and contribute to the conservation of giant limpet species that naturally settle on them.

Quantification of radular marks as a method for estimating grazing of intertidal gastropods on rocky shores

Wax discs have been used previously on intertidal rocky shores to record the grazing activity of gastropods. This study has evaluated this methodology for recording grazing of four common intertidal microalgal grazers on intertidal shores in New South Wales, Australia. In the laboratory, the four species examined-the patellid limpet, Cellana tramoserica (Sowerby), the trochid, Austrocochlea porcata (A. Adams), the neritid, Nerita atramentosa Reeve and the littorinid, Bembicium nanum (Lamarck)-made distinctive marks in the wax. These allowed identification of each species or combinations of species grazing over the different discs. Field experiments showed that the intensity of grazing, as indicated by the mean number of scratches per disc, was positively related to the number of gastropods in the surrounding area during low tide for C. tramoserica. The number of scratches per disc in any area was correlated with the percentage of discs scratched. The relationship for C. tramoserica was found at two scales-in sites (approximately 3x3 m) and also in plots (50x50 cm) within sites. Therefore, densities that were measured when these limpets were inactive during low tide provided good estimates of grazing activity during high tide. This is largely because these limpets do not move far between where they rest and where they feed. The amount of microalgal food in the vicinity was not correlated with density, nor with grazing intensity. No relationship between density and grazing intensity was found for N. atramentosa, although experiments were only done in the field at one spatial scale (in sites, 3x3 m). Results obtained in the laboratory and in the field show that wax discs are useful to distinguish grazing by different species of gastropods on Australian rocky shores and allow tests of hypotheses about grazing activity at different spatial scales.

Poor design of behavioural experiments gets poor results: examples from intertidal habitats

Many patterns of distribution and abundance of intertidal animals are explained by processes of movements of animals, selecting particular habitats or levels on the shore, or interacting with other species. Movements of intertidal animals have therefore been studied over many years. During this long history, much intertidal ecology has changed in focus from broad-scale to small-scale patterns and processes, although there has been recent refocus on a combination of many scales. Simultaneously, there has been an increase in the incidence of field experiments and growing recognition that behaviour is more flexible than originally thought. This review examines changes in the ways that experiments on movements on intertidal animals have been and are being done, taking into account these changes in emphasis. Although some progress has been made, there is still a long way to go. The idea is still prevalent that behaviour is simple, rather invariant and that the animals respond to broad-scale cues that have traditionally been of interest to many investigators. This means that many experiments are still designed to minimise (or ignore) natural variation in behaviour rather than to measure it and that any associated disturbances are considered irrelevant and therefore not evaluated. Understanding the role that behaviour has in establishing and maintaining many of the patterns observed on intertidal shores is crucial to our understanding of the ecology of these habitats. Better experiments, designed logically with appropriate controls to evaluate realistic processes and to measure how behaviour varies among places and from time to time can only improve this understanding.

A molecular phylogeny of the patellid limpets (Gastropoda: Patellidae) and its implications for the origins of their antitropical distribution

The geographical distribution of the limpet family Patellidae is essentially antitropical, with 18 species in southern Africa, 10 in the northeastern Atlantic, and only 11 species elsewhere (although 4 of these do occur in the tropics). One possible explanation for this distribution is the suggestion of a recent, perhaps Early Pliocene, migration from southern Africa northward. We tested this hypothesis by constructing a molecular phylogeny, derived from partial sequences of the 12S and 16S mitochondrial genes, obtained from 34 of the 38 patellid species. Five species of Nacellidae and 3 of Lottiidae were included as potential outgroups. Analysis revealed that two patellid clades are represented in the northeastern Atlantic. The typical European patellids (Patella sensu stricto) form a single clade within which there is little molecular divergence, but are distant from all other patellids, thus refuting the idea of recent southern ancestry. From the limited fossil record and estimated rates of molecular divergence, we suggest that Patella s.s. may have originated at least as early as the Upper Cretaceous and that its northern distribution may have been achieved at the same time. The second patellid clade present in the northeastern Atlantic is the genus Cymbula, of which the single species Cymbula safiana extends from West Africa to the Mediterranean. In contrast to Patella s.s., C. safiana is indeed a member of an otherwise southern African clade and may have attained its present distribution more recently, during the Miocene. The geographical origin of the family remains unclear, but a Mesozoic radiation in southern Gondwana is possible. By optimizing morphological characters on our molecular tree, we consider the evolution of shell mineralogy and sperm ultrastructure. We also discuss the phylogenetic classification of the patellids and present some evidence that the family may not be monophyletic.

A cladistic phylogeny of the family Patellidae (Mollusca: Gastropoda)

A phylogenetic hypothesis for the patellid limpets is reconstructed by cladistic analysis of morphological characters from 37 species, representing all but one of the living members of the family. Characters included in the analysis are derived from shell shape and microstructure, headfoot and pallial complex, radula and sperm. The species fall into four clades, providing the basis for a new phylogenetic classification into four monophyletic genera: Helcion (four species; southern Africa), Cymbula (eight species; southern Africa, eastern Atlantic, southern Indian Ocean), Scutellastra (17 species; southern and southwestern Africa, Australia, Indo–West Pacific, Eastern Pacific) and Patella (nine species; northeastern Atlantic and Mediterranean). The analysis suggests sister–group relationships between Helcion and Cymbula , and between Scutellastra and Patella . In combination with present–day patterns of geographical distribution, this phylogenetic hypothesis is used to discuss the historical biogeography of the Patellidae. Scutellastra may have originated in southern Africa and dispersed across the Pacific, or alternatively may be a primitively Tethyan group. Both Helcion and Cymbula appear to have originated in southern Africa, but three Cymbula species have dispersed respectively to northwest Africa, St Helena and the southern Indian Ocean. The patellids of the northeastern Atlantic form a single clade, Patella (including P. pellucida ), which may have arrived by northward dispersal of an ancestor from southern Africa, or possibly by vicariance of a widespread ancestral Tethyan distribution. The known fossil record of patellids is too fragmentary to permit choice between these alternatives.