In the present study we aim to describe the diatom communities associated to some Gelidiacean species (Rodophyta) from Gran Canaria (Canary Islands) considering their seasonal and spatial variability, in terms of abundance, biomass and community structure. Five Gelidiacean species (Gelidium arbuscula, Gelidium canariense, Gelidium pusillum, Pterocladiella capillacea e Pterocladiella melanoidea) has been collected in different coastal localities of Gran Canaria Island (Boccabarranco (Galdar), Agaete e Quintanilla (Ba?aderos) during winter and summer season 2007-2008. Gelidium arbuscula, G. canariense e P. capillacea appeared distributed in clumps consisting of several ramets; thalli of G. pusillum e P. melaoidea looks liked to small carpet adhering to rocks. Sampled ramets were cut in a apical, central and basal fragment except in the case of G. pusillum e P. melanoidea for their reduced size (about 1cm). In order to preserve the integrity of the epiphytic diatom communities and to analyze them at Scanning Electron Microscope, ramets were fixed with glutaraldehyde 2.5% in filtered seawater and placed on a polycarbonate filter in a "Swinnex" filtration apparatus (Millipore). A second filter was placed over the first to form a sandwich in which the sample was trapped. A dehydration and Critical Point Dryer treatment were respectively carried out by directly immersing the Swinnex into specific containers in alcohol at increasing alcoholic strength and finally in a Critical Point Dryer. At the end of this treatments, each fragment was placed on a stub and covered with gold-palladium to be observed using SEM Total abundances of epiphytic diatoms in all Gelidiacean species studied were low in both the sampling seasons ranging from 200-480 cell/mm2 in winter to 150-300 cell/mm2 in Summer. Spatial distribution of epiphytic diatoms communities showed a marked increasing gradient form the basal to the apical part of the ramets. Considering the growth forms of diatom species, adnate forms (Amphora and Cocconeis spp.) were distributed mainly in the basal and central part of ramets whereas erect forms (mainly Grammatophora, Licmophora, and Achnantes spp.) were mainly distributed in the apical part of the colonies. Motile species were rarely found without showing a clear distribution pattern in the three portion of the ramets. Adnate diatoms were more abundant on those Gelidiaceae having harder, microstructurally complex and ramified thalli respect than with soft and smooth ones. This is due to the presence, in the former, of an higher number of microenvironments to which the adnate diatoms can adhere using their entire valve faces. Erected diatom species were less affected by these constrains since their adhesion to the substrate was mediated by mucilage pads or peduncles.
TAXONOMICAL AND ECOLOGICAL ANALYSIS OF EPIPHYTIC DIATOM COMMUNITIES ON GELIDIACEAN (RHODOPHYTA) SPECIES FROM GRAN CANARIA (CANARY ISLANDS)
DE STEFANO, Mario
2011
Abstract
In the present study we aim to describe the diatom communities associated to some Gelidiacean species (Rodophyta) from Gran Canaria (Canary Islands) considering their seasonal and spatial variability, in terms of abundance, biomass and community structure. Five Gelidiacean species (Gelidium arbuscula, Gelidium canariense, Gelidium pusillum, Pterocladiella capillacea e Pterocladiella melanoidea) has been collected in different coastal localities of Gran Canaria Island (Boccabarranco (Galdar), Agaete e Quintanilla (Ba?aderos) during winter and summer season 2007-2008. Gelidium arbuscula, G. canariense e P. capillacea appeared distributed in clumps consisting of several ramets; thalli of G. pusillum e P. melaoidea looks liked to small carpet adhering to rocks. Sampled ramets were cut in a apical, central and basal fragment except in the case of G. pusillum e P. melanoidea for their reduced size (about 1cm). In order to preserve the integrity of the epiphytic diatom communities and to analyze them at Scanning Electron Microscope, ramets were fixed with glutaraldehyde 2.5% in filtered seawater and placed on a polycarbonate filter in a "Swinnex" filtration apparatus (Millipore). A second filter was placed over the first to form a sandwich in which the sample was trapped. A dehydration and Critical Point Dryer treatment were respectively carried out by directly immersing the Swinnex into specific containers in alcohol at increasing alcoholic strength and finally in a Critical Point Dryer. At the end of this treatments, each fragment was placed on a stub and covered with gold-palladium to be observed using SEM Total abundances of epiphytic diatoms in all Gelidiacean species studied were low in both the sampling seasons ranging from 200-480 cell/mm2 in winter to 150-300 cell/mm2 in Summer. Spatial distribution of epiphytic diatoms communities showed a marked increasing gradient form the basal to the apical part of the ramets. Considering the growth forms of diatom species, adnate forms (Amphora and Cocconeis spp.) were distributed mainly in the basal and central part of ramets whereas erect forms (mainly Grammatophora, Licmophora, and Achnantes spp.) were mainly distributed in the apical part of the colonies. Motile species were rarely found without showing a clear distribution pattern in the three portion of the ramets. Adnate diatoms were more abundant on those Gelidiaceae having harder, microstructurally complex and ramified thalli respect than with soft and smooth ones. This is due to the presence, in the former, of an higher number of microenvironments to which the adnate diatoms can adhere using their entire valve faces. Erected diatom species were less affected by these constrains since their adhesion to the substrate was mediated by mucilage pads or peduncles.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
