Histopathological survey of parasites harboured by the clam Tawera elliptica (Lamarck, 1818) from Chiloé Archipelago, southeastern Pacific.

Tawera elliptica (commonly known as "Almeja Juliana", is a venerid clam that inhabits sandy bottoms and is distributed from Valparaíso on the Pacific coast up to the Mar del Plata area along the Atlantic coast. Harvests of this clam have declined substantially over the last decade. Therefore, an analysis of common parasites and pathological conditions of this clam was undertaken along with histopathology. Monthly samples were prepared for routine histology for examination under light and electron microscopy. T. elliptica has a sex ratio of 1:1 and the relationship between the shell length and the wet tissue weight is not significantly different between females and males. The maximum values for de condition index and meat yield were found during the austral winter. The following parasites (and their overall prevalence) were detected: intracellular microcolonies of bacteria in digestive gland (22.9%), intestinal epithelium (9.3%) and gills (3.17%), an unidentified cyst in gills (59,3%), a Steinhausia-like intraoocytic microsporidian (5.2%), Gregarine spores (41.3%), ciliated protozoa (16.7%), two metazoa, a Paravortex like flatworm (4.3%), and a digenean trematode (8%). The monthly mean intensity of the most relevant parasites was between 2.3 and 35.6 for digestive gland intracellular microcolonies of bacteria (IMC), 0-5.1 for intestinal epithelium IMC, 0-2 for branchial IMC and 0 - 48 for intraoocytic microsporidium. The prevalence and the infection intensity were low-to very low, and no World Organisation for Animal Health OIE listed parasite was detected. It is concluded that this is a healthy clam, and no disease risks for the cultivation are visualized at present. However, IMC at high prevalence and intensities of infection could be potentially impactful, and the intraoocytic microsporidian could jeopardize reproduction if present in high intensities of infection.

Testing Bergmann's rule and the Rosenzweig hypothesis with craniometric studies of the South American sea lion.

We tested the validity of Bergmann's rule and Rosenzweig's hypothesis through an analysis of the geographical variation of the skull size of Otaria flavescens along the entire distribution range of the species (except Brazil). We quantified the sizes of 606 adult South American sea lion skulls measured in seven localities of Peru, Chile, Uruguay, Argentina, and the Falkland/Malvinas Islands. Geographical and environmental variables included latitude, longitude, and monthly minimum, maximum, and mean air and ocean temperatures. We also included information on fish landings as a proxy for productivity. Males showed a positive relationship between condylobasal length (CBL) and latitude, and between CBL and the six temperature variables. By contrast, females showed a negative relationship between CBL and the same variables. Finally, female skull size showed a significant and positive correlation with fish landings, while males did not show any relationship with this variable. The body size of males conformed to Bergmann's rule, with larger individuals found in southern localities of South America. Females followed the converse of Bergmann's rule at the intraspecific level, but showed a positive relationship with the proxy for productivity, thus supporting Rosenzweig's hypothesis. Differences in the factors that drive body size in females and males may be explained by their different life-history strategies. Our analyses demonstrate that latitude and temperature are not the only factors that explain spatial variation in body size: others such as food availability are also important for explaining the ecogeographical patterns found in O. flavescens.

Effect of Sperm Ratio and Temperature on Fertilization and Early Larval Development of the Surf Clam Mesodesma donacium (Bivalvia:Mesodesmatidae).

The effect of sperm ratio on fertilization was evaluated in five sperm:oocytes treatments (10:1, 50:1, 100:1, 500:1 and 1000:1), the effect of temperature on embryonic and larval development in three temperature treatments (13 °C, 16 °C and 19 °C) was recorded and the duration of each stage, the growth rate and survival rate were registered. The oocytes were spherical (67.5 ± 4.2 µm) with a defined nucleus. Spermatozoa had a circular head (2 µm) and a fusiform flagellum (12 µm). The 500:1 sperm:oocytes treatment presented the lowest % of unfertilized oocytes, and lysis was observed in the 1000:1 treatment. An inverse relationship was observed between temperature and the duration of the stages of embryonic development. At 16 °C, veliger D larvae were observed at 41 h 45' pf (88 ± 13.0 µm). Umbonate larvae were obtained at day 16 in the 13 °C culture and at day 10 in the 16 °C and 19 °C treatment (140 µm). On day 16 of culture, advanced umbonate larvae with a well-defined stomach (235 µm) were observed. The larval growth rate was higher in the 19 °C treatment (3.6 µm day-1) than the 13 °C and 16 °C treatment (2, 2.2 µm day-1). The mortality was higher in the 19 °C treatment (91%). These results are an initial contribution towards the culture of M. donacium as part of small-scale aquaculture in South America.

Long-term monitoring for conservation: closing the distribution gap of Arctocephalus australis in central Chile.

OBJECTIVES: Here, we present the first record of stable colonies of the South American fur seal (Arctocephalus australis), in an area where their presence has never been documented (hereafter distribution gap), as well as an update of the current distribution range of the species in central Chile. RESULTS: A national synoptic aerial census of pinnipeds was performed during the austral summer of 2019 on the Chilean coast. An additional aerial census was conducted in the same area during the austral spring of 2019 as well as a maritime census during the austral summer of 2020. The data showed the presence of South American fur seals in central Chile within their well-known distribution gap. The total abundance was registered in three colonies where fur seals were sighted: one non-breeding colony, Punta Topocalma (summer 2019: mean = 46 ± 3; spring 2019: mean = 9 ± 1); and two breeding colonies, Punta Curaumilla (summer 2019: mean = 595 ± 7; spring 2019: mean = 45 ± 4; summer 2020: mean = 744 ± 5) and Isla Santa María (summer 2019: mean = 246 ± 6). Specifically, we suggest that it is crucial to elucidate the origin of the described settled colonies, and to determine whether there has been an augment in the distribution range from either the northern population, the southern population, or both simultaneously.