Type II diabetes is considered the most common metabolic disorder in the developed world and currently affects about one in ten globally. A therapeutic target for the management of type II diabetes is the inhibition of α- glucosidase, an essential enzyme located at the brush border of the small intestinal epithelium. The inhibition of α-glucosidase results in reduced digestion of carbohydrates and a decrease in postprandial blood glucose. Although pharmaceutical synthetic inhibitors are available, these are usually associated with significant gastrointestinal side effects. In the present study, the impact of inhibitors derived from edible brown algae is being investigated and compared for their effect on glycaemic control. Carbohydrate- and polyphenolic-enriched extracts derived from Ascophyllum nodosum, Fucus vesiculosus and Undaria pinnatifida were characterised and screened for their inhibitory effects on maltase and sucrase enzymes. Furthermore, enzyme kinetics and the mechanism of inhibition of maltase and sucrase were determined using linear and nonlinear regression methods. All tested extracts showed a dose-dependent inhibitory effect of α-glucosidase with IC50 values ranging from 0⋅26 to 0⋅47 mg/ml for maltase; however, the only extract that was able to inhibit sucrase activity was A. nodosum, with an IC50 value of 0⋅83 mg/ml. The present study demonstrates the mechanisms in which different brown seaweed extracts with varying composition and molecular weight distribution differentially inhibit α-glucosidase activities. The data highlight that all brown seaweed extracts are not equal in the inhibition of carbohydrate digestive enzymes involved in postprandial glycaemia.

The north-west Pacific kelp, Undaria pinnatifida, was first discovered in Europe on the Mediterranean coast of France (1971) and introduced to Brittany for aquaculture (1983). In the north-east Atlantic, it occurs in Spain, France, the British Isles, Belgium and Holland. The first UK record was in the Hamble estuary (1994) and it was found off Plymouth in 2003. The UK distribution is presently restricted to the south of England and the northern Irish Sea. We assessed the distribution of U. pinnatifida and native kelps and their allies in Plymouth Sound (at 0 to +1 m relative to Chart Datum). Undaria pinnatifida was widespread along rocky shores, on other hard substrata and grew in the same areas as Saccharina latissima and Saccorhiza polyschides. Undaria pinnatifida was significantly more abundant on vertical substrata than on upward-facing hard substrata. It was almost as common as all of the other kelp species combined on vertical substrata but was outnumbered by native species on upward-facing substrata. Undaria pinnatifida has become the visually dominant macroalga in marinas and has spread to surrounding natural habitats in Plymouth Sound. The extent to which it will outcompete native kelps requires monitoring, especially in conservation areas.

Biological invasions can alter the biodiversity of native communities generating an ecological impact that in many cases is irreversible. In 2001, Undaria pinnatifida invaded Macrocystis pyrifera kelp in Cracker Bay (42°56′S, 64°27′W; Northern Patagonia, Argentina). The possible impact of that invasion was evaluated in March 2004 with a study of population and morphological parameters of both kelp species and their associated holdfast biodiversity. Three nearby areas of spatial distribution of the kelps were differentiated, one dominated by M. pyrifera (M), an intermediate area characterized by M. pyrifera and U. pinnatifida (M+U), and another dominated by U. pinnatifida (U). In each area, sporophytes in nine quadrats of 1 m2 were collected. The density and biomass m−2, the height of the sporophytes and the size of the holdfast of  M. pyrifera did not diminish in the presence of  U. pinnatifida. The richness, abundance and diversity of the flora associated with the holdfast of both kelps were similar, whereas these parameters were higher in the case of the fauna associated to M. pyrifera than U. pinnatifida Results obtained in this work suggest that, at this invasion stage, there is no evidence of interspecific competition. Nevertheless, since density and diversity of the fauna associated with the holdfast is different, we expect community changes if the U. pinnatifida invasion continues to expand.

The invasive kelp Undaria pinnatifida was observed for the first time in the Nuevo Gulf (Patagonia, Argentina) in December 1992. At the present time, with the exception of sandy bottoms, the coasts of the Nuevo Gulf are almost entirely colonized. From October 1997 to February 2000, the characteristics of this population, i.e. the relationships between morphological features and seawater temperature, the seasonality in sporophyll development and the proportions of different reproductive stages during its life cycle, were analysed. The observations confirmed that the maximal mean densities of sporophytes (149.1 plants m−2) occurred in winter while the mean tallest sporophytes (88.5 cm) and the mean highest biomass (16501 g m−2) were registered in spring and at the beginning of the summer. Coexisting juvenile and mature sporophytes were found. Sporophylls showed also seasonal characteristics, with maximal width in summer. Manipulative experiments conducted for testing the recruitment pattern of Undaria pinnatifida confirmed that the presence of juvenile individuals was uninterrupted. Thus, in this paper, we denote that U. pinnatifida has a constant recruitment, together with high reproductive rates, which are some of the characteristics of an introduced species, which explains why they became a highly invasive species or ‘pest species’, with negative environmental and economic effects.

La tolérance aux basses températures des gamétophytes de l'algue alimentaire Undaria pinnatifida est examinée selon différentes méthodes de cryoconservation. La conservation à -80 °C dans une solution glycérolée à 28 % et celle à −196 °C dans une solution en eau de mer de glycérol à 5 ou 10 % ne permettent que des survies de, respectivement, 9 et 4 jours. Par ailleurs, la viabilité n'est pas affectée par un refroidissement de 5 °C/min et une conservation de 15 minutes à −15 °C sans milieu de cryoprotection mais est fortement diminuée par un stockage de 15 minutes à −30 ou −196 °C, même en présence de DMSO. La réduction de la survie des gamétophytes se traduit morphologiquement par une dépigmentation et/ou une contraction des cellules.