Els fons rocosos profunds amb Osmundaria volubilis (Linné) R. E. Norris a les Balears

Abstract not availabl

Els herbeis de Caulerpa prolifera (Forskal) Lamouroux de la Badia de Pollença (Mallorca, Mediterrània Occidental)

Abstract not availabl

Addicions a la fauna d'invertebrats bentònics marins de l'Arxipèlag de Cabrera (Illes Balears, Mediterrània Occidental)

Abstract not availabl

Contribució al coneixement algològic de la Mediterrània espanyola, II

7 páginas, 1 figura.Amb aquesta nota pretenem d'ampliar el coneixement sobre la flora de la Mediterrània amb citacions d'espècies rares, intéressants o no trobades abans a les costes espanyoles. Fem referencia en cada cas a la bibliografía consultada per a la determinado dels nostres exemplars i afegim els aclariments o les descripcions que hem considérât necessaris per obtenir una caracterització mes fídel de les mostres recollides. També comentem la localitat on han estât recol-lectades les algues i la comunitat de que feien part. Les especies s'han ordenat alfabéticament.Peer reviewe

Estructura i dinàmica del poblament algal de les fulles de Posidonia oceanica (L.) Delile als herbeis de Tossa de Mar (Girona)

18 páginas, 7 tablas, 7 figuras.Research on leaf-epiphyte community structure and dynamics was carried out in Posidonia oceanica beds from Tossa de Mar (Western Mediterranean) . Three sampling stations w here chosen at 2, 9 and 23 m depth . Seasonal community structu re was studiea along the year 1982 in the 9 m station. Species composition, species covering , species richness , specific distribution , homogeneity (Kulczynski 's simi larity index) , species diversity, pattern diversity and the qualitative and quantitative minimal areas were obtained from each sample. These parameters were estimated from the species/ number of shoots curves, the diversity (Shannon index ) / number of shoots curves and the similarity/ number of shoots curves as indicated by BALLESTEROS (1986). Structura l changes in the epiphyte community have been observed; there is an increase in species richness and a decrease in the specific distribution and pattern-diversity from autumn to summer. Two different phases can be distinguished : a settling phase, where different shoots have a rather different species composition, that begins in October, just after the fall of senescent Posidonia leaves; and a cana li zation phase, where there is a prog ressive concurrence in the qualitative and quantitative composition of leaf-epiphytes between shoots. Comparison with other Medi t erranean algal communiti es shows t he miniaturization, the great homogeneity and the scanty structure of the Posidonia leaves ep iphytic community. Dynamics were studied in the three sampling stati ons. Species composition of Posidonia leaves is well cllaracterized by the abundance of Fosliella species and the encrusting pllaeophycean Myrionema magnusii. Other species such as Giraudia sphacelarioides, Ca stagnea irregularis, C. cylindrica, Giffordia mitchelliae, Myriactula gracilis, Ectocarpus siliculosus V . confervoides and Feldmannia globifera llave a spring maxima in tlle shallow stations. Zooepiphytes are more abundant, in relative terms , in the deepest station (basically the hydrozoan Sertularia perpusilla and bryozoans Electra posidoniae and Fenestrulina joannae) . Mean phytoepiphyte biomass vari es from 12 to 495 mg dw/ shoot (11 -470 9 dw/ m2) in tlle slla llow stations and 4 to 335 mg dw/ shoot (1 -82 9 dw/ m2) in the deepest station. Zooepiphytes biomass varies from 5 to 188 mg dw/ shoot (2-180 9 dw/ m2). A t ime delay between the sha llowest and the deepest stations has been found for all leaf features and phytoepipllyte composition and biomass, but not for zooep iphyte biomass. A time delay in terms of production and biomass maxima between shallow and deep phytobenthos communities is something general in the Mediterranean (BA~LESTEROS, 1984) . This appears to be an adaptation of different species and communities in order to couple their life-cycle to the seasonal pattern of the limiting factor (or factors) , usually light (in deep communities) and nutrient avai lability (in shallow ones); this could be also the case of Posidonia and its epiphytes. Production estimates of leaf-epiphytes vary from 70 9 C/ m2 year in shallow stations to 12 9 C/ m2 year in the deepest one, that is, between the 10 and the 20 % of the whole Posidonia meadow production .Peer reviewe

Structure and dynamics of North-Western Mediterranean phytobenthic communities: a conceptual model

This paper describes the structural (species richness, species diversity, pattern-diversity, biomass, coverage, specific distribution, homogeneity) and functional (production, PIB ratio) changes observed during the annual cyc1es of eight phytobenthic Mediterranean communities by using PCA analysis. The first axis obtained discriminated between variables related to pattern-diversity and those related to production and coverage (production- diversification or P-D axis). The second axis was mainly related to biomass and homogeneity (biomass-heterogeneity or b-h axis). Shallow-water cornmunities were positioned in the quadrant of the plane associated with high production while deep-water communities were located in the quadrant characterized by high diversification values. The transit of communities through this plane during their annual cyc1es suggests their idealization as geometric figures revolving c10ckwise along the plane defined by the P-D and the b-h axes. These changes allow the distinction of two phases and two stages in the annual cyc1e of the cornmunities, according to the sequence: diversified cornmunity (high heterogeneitY)---7 production phase (high production)---7 developed community (high biomass)---7 diversification phase (high pattern-diversity). Peak production occurs in spring for the mediolittoral cornmunities and is delayed towards summer and autumn at increasing depths. This time lag affects the whole annual cycle described aboye and appears attributable to the adaptation of the different species and communities to the seasonal cyc1e of the main factors limiting their growth (BALLESTEROS, 1 989b). Although production and diversification are inversely related, PIB ratio is not negatively correlated with diversity because of the different mechanisms generating diversity in natural communities: disturbance and evolution. Short-time diversity increases in periods of intense physical disturbance (diversification phases) due to lack of dominance within the cornmunity and the growth of opportunistic species. Thus, short-term diversity and productivity are not inversely correlated. Long-term diversity increases along evolutionary time under environmental stability, explaining the greater diversity of deep-water communities compared to shallow ones, where an inverse correlation between productivity and diversity is observed. An interannual model of the structural and functional performance s of phytobenthic Mediterranean cornmunities can be depicted over the plane defined by the P-D axis and the b-h axis by introducing time as a third axis. In general, the dynamics of persistent communities can be depicted as helicoidal trajectories whose turns represent annual cyc1es. This representation allows the adequate definition of concepts such as persistence, resistance and resilience of cornmunities, and creates an adequate framework for describing successional processes and the effects of all kind of disturbances. The hypothesized existence of multiple stable points in natural communities closely agrees with the model if different degrees of non-punctual, biotic, disturbances are considered. In our opinion this model could also be extended to other temperate seas

Algues bentòniques i fanerògames marines

La flora marina de l'arxipèlag de Cabrera és extraordinàriament rica a causa de la gran amplitud batimètrica dels seus fons i a la gran transparència de les seves aigües. Tot i no haver-se realitzat una recerca florística exhaustiva, en l'actualitat el nombre de tàxons coneguts de l'arxipèlag i els seus voltants és de 437 (274 si excloem les diatomees) (13 Cyanophyta, 163 Chrysophyta, 177 Rhodophyta, 46 Phaeophyta, 35 Chlorophyta, 3 Magnoliophyta). Aquesta gran riquesa florística es tradueix també en l'existència d'un gran nombre de comunitats fitobentòniques, de tal forma que en l'àrea que abasta l'arxipèlag estan representades la pràctica totalitat de comunitats d'algues i fanerògames marines pròpies de la Mediterrània Central que creixen en aigües oligotròfiques. És destacable el caràcter termòfil de l'arxipèlag pel que fa a la seva flora i a les associacions algals que s'hi desenvolupen.The great bathymetric amplitude and the clear waters of the Cabrera archipelago allow the development of a very rich marine flora. Unless an exhaustive research program on marine floristics is lacking, the number of taxa currently known from the archipelago attains 437 (274 if diatoms are excluded) (13 Cyanophyta, 163 Chrysophyta, 177 Rhodophyta, 46 Phaeophyta, 35 Chlorophyta, 3 Magnoliophyta). This high floristic richness is in agreement with a high number of different phytobenthic communities, to such a degree that nearly all the seaweed and seagrass communities from oligotrophic waters described from the Central Mediterranean are present in the area. The thermophilic conditions of the archipelago, in relation to other Mediterranean places, IS reflected both in the species pool and the phytobenthic communities

Small- scale structure of infaunal polychaete communities in an estuarine environment: Methodological approach

12 páginas, 3 figuras, 2 tablasThis study compares different methods for the estimation of minimal areas (viz. species/area curves, diversity/area curves, similarity/area curves, variance/mean ratio vs. area curves) as community structure descriptions. The comparisons are based upon two polychaete taxocoenoses from muddy and sandy habitats, located in a semienclosed shallow-water Mediterranean bay (Alfacs Bay, Ebro Delta, NW Mediterranean).The mud community appeared to be very homogeneous, with very low diversity. This community displayed high structural simplicity (related to various stress factors), and therefore, qualifies as a physically controlled community). The diversity index was stabilized for areas of 37 cm2, quantitative similarity (Kulcznski index) was higher than 0·7 for areas of 90 cm2, and density of individuals was stabilized for areas of 120 cm2. Therefore, and area of 120 cm2 is suggested as being representative of the community structure. However, it was impossible to define a qualitatively adequate sampling area ( more than 300cm2). The sand community displayed hig structural complexity, with hig species richness and high diversity. This community was characterized by high environmental stability and high variability of microhabitats, as is frequent in biologically accomodated communities. Tne number of individuals became homogeneous for areas of 600-1000 cm2, diversity was stabilized around 300 cm2 and a Kulczynski similarity index of 0·7 was alredy attained at areas of 1000cm2. Thus, a quantitatively representative sampling area of between 700 and 1000 cm2 was suggested. Moreover, the more general pattern of species distribution (with an important set of common species) was directly related to the relatively low qualitative minimal area (400 cm2)Peer reviewe