The mussel Sernirnytilus algosus (Gould) often dominates the space on exposed rocky shores of subtropical South America. Dynamics of space occupancy was investigated in a rocky intertidal habitat in central Peru. A series of colonization expenrnents and quantitative sampling of musselassociated faunas were conducted to clarify interspec~f~c relationships anlong resident organisms. Spatial gaps created within the S. algosus zone were colonised successively by the barnacles Jehlius cirratus (Darwin) and Notochtharnalus scabrosus (Darwin), a gallery-building polychaete, Phragmatopoma moerchi Kinberg, and a mussel, S. algosus. The rate of colonisation/recruitment was highest for barnacles, intermediate for l? moerchi and lowest for S. algosus. There was no evidence that barnacles either facilitate or inhibit colonisation by later colonists l? moerchi and S. algosus. Three filter-feeding taxa showed a clear competitive hierarchy. l? moerchi was competitively superior to barnacles and S. algosus was competitively superior to both barnacles and P rnoerchi. Therefore, there are trade-offs between colonisation ability and competitive ability among these taxa. In addition to recruitment of young larvae on free rock surfaces, S. algosus individuals demonstrate continuous lateral migration at the edge of their aggregation, constantly expanding the boundaries. Gaps can be closed in this manner, with an average rate of edge advance of 1.2 cm mo-', which is comparable to the values estimated for Mytllus californianus on North American rocky shores The S. algosus bed constitutes an important habitat to a range of organisms, many of them (particularly polychaetes) being restricted to this habitat on exposed rocky shores. Comparisons were made between faunas on free rock surfaces and in the mussel bed. Proportions of taxa restricted to the mussel bed were high among all invertebrates found there, in the range of 67 to 78 % in terms of number of taxa and 80 to 94 % in terms of number of individuals. Furthermore, juveniles of many organisms find refuge in the S. algosus bed, and barnacles which are competitively inferior to S. algosus can nevertheless exist epizoically on their shells. Thus, monopolisation of space by S. algosus generally leads to an Increase in total species richness.

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Aim We evaluated whether patterns of species diversity (α, β and γ) of rocky shore assemblages followed latitudinal gradients (i.e. LDGs) along the South American coasts, and tested hypotheses related to potential processes sustaining or disrupting the expected LDG pattern at various spatial scales. Location Coasts of South America. Taxon Macroalgae and sessile/slow‐moving macrofauna on intertidal rocky shores. Methods We evaluated changes in species composition across 143 sites. The degree of replacement and loss of species at different spatial scales (i.e. coasts, regions and sites) were estimated to help distinguish among ecological, historical and evolutionary hypotheses for explaining LDGs. Furthermore, components of diversity and taxonomic distinctness were measured, and variability in these measures was decomposed using analysis of covariance. Finally, we examined relationships between diversity and a suite of environmental and anthropogenic variables to identify potential mechanisms that may be responsible for the reported spatial relationships. Results Species composition varied with latitude, and this variability was relatively consistent on both coasts. At all spatial scales, replacement of species was the dominant phenomenon (>95%), rather than loss in the total number of species (<5%). LDGs were strongly dependent on the diversity component and the spatial scale: generally, positive for regional β‐diversity, negative for α‐diversity and site β‐diversity. Sea surface temperature (SST) was the variable that best explained patterns of diversity along both coasts (14%–22%), but other regional and local environmental variables associated with river discharges, upwelling, confluence of currents, tides and anthropogenic pressures also accounted for an important portion of variation (5%–14% each). Main conclusions Species diversity of South American rocky shores followed, with interruptions, LDGs. The trend of those LDGs, however, depended on the scale and metric used to describe diversity. It is proposed that patterns of LDGs at various scales are not the result of a single overarching process but are strongly influenced by local and regional processes. Although the most evident environmental gradient was the decrease in SST towards the south, it was demonstrated that regional and local environmental variables were also important for understanding the increase in regional β‐diversity towards the tropics.

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Se reporta el hallazgo de moluscos cuya distribución conocida se encuentra dentro de los límites de la Provin cia Panameña, en diversas localidades de la Provincia Peruana entre los años 1972 y 1994, período en el que se presentaron varios eventos "El Niño". Fue posible determinar 15 especies de moluscos que ampliaron su distribu ción: Pteria sterna, Orobitella peruviana, Cryptomya californica, Cerithíum (T.) stercusmuscarum, Malea ringens, Hexaplex brassica, Thais styl/manberryí, T. (M.) triangularis, T. (T.) cal/aoensís, Acanthina brevidentata, Purpura pansa, Neorapana murícata, Anachis (C.) nigricans, Cancel/aria (C.) decussata y C. (8.) chrysostoma. Se postula una variabilidad en los límites de las provincias biogeográficas de la costa peruana, controlada por el ENSO.

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ResumenEl presente trabajo analiza información de las mudas y observaciones del comportamiento reproductivo de G. grapsus, relacionando las frecuencias de mutilaciones y el comportamiento caní-bal observado en las cópulas. Las colectas de mudas y observaciones sobre las cópulas se llevaron a cabo entre diciembre de 1990 y diciembre de 2001, en 200 m de una orilla rocosa al sur de la Bahía de Ancón, Lima, Perú. G. grapsus vive en grupos de número variable y asociados a grietas donde los individuos buscan refugio. El comportamiento de cortejo observado fue el de "búsqueda-intercepción" he incluyó diferencias como la defensa de territorios no temporales, largas persecusiones e intercepción por varios machos. Un total de 312 cópulas fueron observadas siendo más frecuentes durante el verano. Un total de once intentos de cópula produjeron la muerte de los individuos, siete fueron machos. En todo el periodo de estudio se colectaron un total de 8421 mudas de las cuales 418 presentaban mutilaciones o heridas en el cefalotórax o abdomen. No se observan diferencias significativas entre las tallas de mutilados de ambos sexos. El 73% de las mudas mutiladas presentan una sola mutilación, el 20% presentan dos mutilaciones y el 6% tres; se encontraron mudas hasta con siete apéndices mutilados. Las frecuencias de mutilaciones son significativamente mayores en machos. Las mutilaciones de las quelas y la segunda pata caminadora son más frecuentes en machos, mientras que en las hembras las mutilaciones de la cuarta y tercera pata caminadora son más frecuentes. Se propone que las mutilaciones se producen durante los intentos de cópula, principalmente por diferencias entre el tamaño de los individuos. Palabras clave:Grapsus grapsus, comportamiento reproductivo, canibalismo, mudas, mutilaciones. AbstractWe have analysed molt frequency and reproductive behaviour of G. grapsus in relation to mutilation frequency and cannibalism observed during mating. Observations and surveys were carried out between December 1990 and December 2001, on a 200 m stretch rocky shore in the south of Ancon Bay, Lima, Peru. Population of G. grapsus was organized in groups of variable numbers around crevices. The courtships behaviour of G. grapsus was based on the «search-interception» process including the defence of semi-permanent territory, along mate-tracking behaviour and interception by several males. A total of 312 copulation events were observed with the highest in summer. Eleven matings ended in death, seven victims of those being males. In this study 8421 molts were collected, 418 had mutilations or injuries in the cephalothorax or abdomen. There was no significant difference in the sizes of mutilated individuals between the two sexes. 73% of mutilated molts had one mutilation (injury), 20% two mutilation and 6% three mutilations and up to seven mutilations were recorded. Frequency of mutilation was significantly higher in males than in females. Mutilated appendices were different between sexes. Chela and second legs were more frequently mutilated in...

Abstract. Mussel beds in the intertidal of subtropical South America are known to harbour a large number of invertebrates, particularly polychaetes. This paper presents a quantitative analysis of the patterns of spatial overlap and coexistence in an assemblage of polychaetes associated with mussel beds in a rocky intertidal habitat on the Pacific coast of Peru. Mussel beds are made up of two zones in the intertidal: the lower, more extensive zone formed by Semimytilus algosus and the upper zone formed by Perumytilus purpuratus. Null models were employed to assess the magnitude of spatial overlap between pairs of taxa encompassing a total of seven taxonomic groups. Two taxa belonging to the same functional group tended to be spatially segregated in the Semimytilus bed: Pseudonereis vs. Halosydna (large free‐ranging predators) and Scoloplos vs. Mediomastus (deposit feeders), with further segregating tendencies between Pseudonereis and Mediomastus, and between Halosydna and Scoloplos. Small‐sized, free‐ranging ‘Typosyllis’ and the bottom‐dwelling scavenging predator Lumbrineris were also spatially associated. Thus, this polychaete assemblage appears to be loosely organised around groupings of taxa which are somewhat different in ecological traits and form mosaic patterns of distribution with reduced overlap within the Semimytilus bed. These relationships were weak to non‐existent in the upper, drier Perumytilus habitat where polychaete density was low.