No abstract

Pseudechinus magellanicus is one of the most abundant sea urchins in southern South America, but many aspects of its feeding ecology in nearshore environments remain unknown. Here, we aimed to analyze the variability of the diet composition along a coastal depth gradient from intertidal tidepools to upper circalittoral zones and examine the relation between seaweed availability and the diet composition at intertidal tidepools. A total of 118 food items, including seaweeds and animal components, were identified. The diet composition showed a large variation between the different coastal habitats present along the depth gradient studied. In tidepools, articulate coralline seaweeds (Corallina spp.), mussel shell fragments and small crustaceans were frequent in the gut contents, suggesting that this species behaves like a general omnivore but can also act as a mussel bioeroder when consuming epizoic algae and microeuendolithic organisms. In intertidal tidepools, the species showed a negative preference toward typical species of late successional stages such as Dictyota dichotoma, Adenocystis utricularis, Codium fragile and Chondria macrocarpa. Sea urchins from kelp forests showed higher dietary diversity than those from intertidal and deeper subtidal habitats, but with prevalence of kelps. At upper circalittoral soft bottoms, diverse detrital items as benthic diatoms, cyanobacteria and drifted algae were observed in gut contents, usually associated with fine sediments, indicating that P. magellanicus captures drifted algae and behaves like a biofilm feeder. This trophic plasticity may allow this species to occupy contrasting habitats and may also contribute to explain its wide distribution in southern South America.

Undaria pinnatifida is an invasive brown algae that has been found on the Argentine coast since 1992. This work aims to follow the ontogeny of sporophytes, from egg fecundation to thallus senility, and thereby contribute to information on the development of the species in San Jorge Gulf. Sporophytes obtained in the laboratory were used to study the first stages of development, while samples collected from field population were used to describe advanced stages. Morphological observations were carried out on fronds, stipes, midrib, sporophylls and holdfasts of thalli at different developmental stages, and they was interpreted related to its functionality. Sporophytes described as typical and distant forms were found, and their location in the coastal zone was determined. Primary growth of sporophyte begins in the intercalar meristoderm located between the frond and the stipe. The upper portion of the intercalar meristem produces a row of small pinnules, and its lower portion is the origin of the lateral stipe ribbons. The thallus area and growth in thickness occur through a meristoderm in the frond surface. Characteristic morphological structures such as gland cells, filaments and trumpet cells, and cryptostomata were observed. Some of the gland cells lead to the formation of hair-filled cryptostomata. This work contributed to increase the knowledge of anatomical characteristics of the thallus at different moments of development of this invasive species.

La especie tipo, Blidingia minima (Nägeli ex Kützing) Kylin, fue establecida basándose en Enteromorpha minima Nägeli ex Kützing. Esta especie se encuentra en las costas y ambientes estuarinos de casi todo el mundo y se distribuye ampliamente sobre la costa de Argentina (Boraso 1970(Boraso , 2004.