Compensatory growth of the kelp Macrocystis integrifolia (Phaeophyceae, Laminariales) against grazing of Peramphithoe femorata (Amphipoda, Ampithoidae) in northern-central Chile

Compensation of tissue loss has been considered an alternative strategy for seaweeds that have no or only minor chemical or structural defense against herbivory. Compensatory responses are facilitated by resource transfer among different tissues and have been suggested for large kelps. Macrocystis integrifolia (Bory) is a common kelp species from northern-central Chile, which is characterized by high growth rates and the absence of lipophilic chemical defenses against herbivore grazing. Herein, we used the giant kelp M. integrifolia to test for compensatory growth in response to grazing by the nest-dwelling amphipod Peramphithoe femorata (Krøyer). Amphipods were allowed to graze inside nests on subapical blades of M. integrifolia sporophytes for 14 days. We measured growth and chemical composition (C, N, laminaran and mannitol) of apical and subapical blades of grazed and ungrazed (control) sporophytes. Our results revealed the capability of M. integrifolia to maintain elongation rates in grazed subapical blades, which were similar to those of subapical blades from ungrazed sporophytes. Apical blades grew slower in grazed than in ungrazed sporophytes indicating a trade-off between apical and subapical blades when herbivores were present. Thus, compensation occurs in blades directly attacked by grazers and is probably mediated by vertical resource allocation within sporophytes to subapical blades, a suggestion supported by the fact that stipe internodes in these regions grew more on grazed sporophytes. In general, our study indicates that M. integrifolia exhibits compensatory growth against the herbivore amphipod P. femorata, and we suggest that this could be an important strategy of large kelp species to tolerate moderate grazing intensities.     

GIANT KELP (MACROCYSTIS PYRIFERA, PHAEOPHYCEAE) RECRUITMENT NEAR ITS SOUTHERN LIMIT IN BAJA CALIFORNIA AFTER MASS DISAPPEARANCE DURING ENSO 1997–1998

During the ENSO event of 1997–1998, density and population structure were evaluated in a Macrocystis pyrifera forest located in Bahía Tortugas, Baja California, Mexico, near the southern limit of the species' distribution in the Northern Hemisphere. Observations in Bahía Tortugas were made quarterly from January 1997 to September 1998 using SCUBA diving surveys. No macroscopic plants were found in the Bahía Tortugas area from October 1997 to April 1998, a local absence of at least 7 months. Aerial surveys further suggest regional disappearance along most of the Baja California coast during the event. Unexpectedly, plants were found in Bahía Tortugas again in July 1998, in spite of the widespread disappearance of the species less than a year earlier. Long-distance spore dispersal was an unlikely cause of the recruitment because: 1) the nearest spore source was more than 100 km away; 2) recruitment appeared to be simultaneous at many sites and occurred rapidly after the cessation of the ENSO event; and 3) the recruits occurred in the same areas as before disappearance. We suggest that a microscopic stage that was not visible during dive surveys survived the stressful conditions of ENSO and caused the recruitment event, supporting the hypothesis that a bank of microscopic forms can survive conditions stressful to macroscopic algae.     

Microbiota within the perennial ice cover of Lake Vida, Antarctica

Lake Vida, located in the McMurdo Dry Valleys, Antarctica, is an 'ice-sealed' lake with approximately 19 m of ice covering a highly saline water column (approximately 245 ppt). The lower portions of the ice cover and the lake beneath have been isolated from the atmosphere and land for circa 2800 years. Analysis of microbial assemblages within the perennial ice cover of the lake revealed a diverse array of bacteria and eukarya. Bacterial and eukaryal denaturing gradient gel electrophoresis phylotype profile similarities were low (<59%) between all of the depths compared (five depths spanning 11 m of the ice cover), with the greatest differences occurring between surface and deep ice. The majority of bacterial 16S rRNA gene sequences in the surface ice were related to Actinobacteria (42%) while Gammaproteobacteria (52%) dominated the deep ice community. Comparisons of assemblage composition suggest differences in ice habitability and organismal origin in the upper and lower portions of ice cover. Specifically, the upper ice cover microbiota likely reflect the modern day transport and colonization of biota from the terrestrial landscape, whereas assemblages in the deeper ice are more likely to be persistent remnant biota that originated from the ancient liquid water column of the lake that froze.     

Species composition and distribution of free-living marine nematodes in Vostok Bay, Sea of Japan

The qualitative and quantitative composition of free-living marine nematodes have been studied in Vostok Bay (Peter the Great Bay, Sea of Japan). It is found that the population density of nematodes in the bottom sediments of Vostok Bay shows an uneven distribution. The mean population density equaled 56800 ± 23400 specimens/m². A correlation has been revealed between the population density of nematodes and the substrate type. Altogether, 85 species of nematodes have been found; they were dominated by Sabatieria palmaris, Rhabdodemania orientalis, Araeolaimus parvibulbosus, Oncholaimium paraolium, Doryolaimopsis peculiaris, and Metachromadora itoi. Six taxocenoses of nematodes were distinguished, taking into account the species dominating in the population density and using cluster analysis of the obtained data. The dominating trophic assemblage of nematodes was “scrapers.” In general, the species composition of nematodes in Vostok Bay is characterized by the relatively great similarity with that in other areas of Peter the Great Bay (Sea of Japan).