Oceanologica Acta最新文献

{"title":"Life cycles in brackish habitats: adaptive strategies of some polychaetes from the Venice lagoon","authors":"Daniela Prevedelli,&nbsp;Roberto Simonini","doi":"10.1016/S0399-1784(02)01232-X","DOIUrl":"https://doi.org/10.1016/S0399-1784(02)01232-X","url":null,"abstract":"<div><p><span>The life cycle of five species of polychaetes living in the Venice lagoon is analysed with the aim of finding out if some traits can be interpreted as an adaptation to brackish environments<span>. The studied species are characterized by different sizes and reproductive strategies. </span></span><em>Marphysa sanguinea</em> is a large-sized, annual iteroparous species belonging to the Eunicidae family that reproduces without epitokal modification. <em>Perinereis cultrifera</em> and <em>P. rullieri</em><span> are large-sized semelparous species belonging to the Nereididae family: the first reproduce with epitokal metamorphosis, the second do not. </span><em>Ophryotrocha labronica</em> and <em>Dinophilus gyrociliatus</em> are small iteroparous species with semi-continuous reproduction belonging to the Dorvilleidae and Dinophilidae families, respectively. All the species are gonochoric. The larger species often have a sex ratio close to 1:1, while in the smaller ones the sex ratio is biased toward the female sex (2:1 in <em>O</em>. <em>labronica</em> and 3:1 in <em>D</em>. <em>gyrociliatus</em>). Moreover, <em>D</em>. <em>gyrociliatus</em><span> exhibits strong sexual dimorphism: the males are dwarf and short living. All the large-sized species have external fertilization, while the small-sized </span><em>O</em>. <em>labronica</em> and <em>D</em>. <em>gyrociliatus</em><span> exhibit external fertilization with pseudo-copulation and internal fertilization, respectively, that ensure a high reproductive success. All the species produce lecitotrophic eggs, protect young stages from at least some environmental stresses and reduce larval dispersion. The role of the suppression of epitoky and protection structure for developing eggs in limiting the dispersal phase is discussed. All species, independent of reproductive strategies, are characterized by high fecundity and reproductive effort. In the small-sized species, the marked bias of the sex ratio in favour of the female sex and, in </span><em>D</em>. <em>gyrociliatus</em>, the reduction in the size of the male eggs, are significant factors in the increasing rate of the populations, enabling them to tolerate sharp variation in density due to environmental unpredictability.</p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 77-84"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01232-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91725580","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Genetic diversity and adaptability of two species of Mugilidae (Teleostei: Perciformes) of the Po river delta coastal lagoons","authors":"Riccardo Papa ,&nbsp;Francesco Nonnis Marzano ,&nbsp;Valeria Rossi ,&nbsp;Gilberto Gandolfi","doi":"10.1016/S0399-1784(02)01235-5","DOIUrl":"https://doi.org/10.1016/S0399-1784(02)01235-5","url":null,"abstract":"<div><p><span>Molecular polymorphisms (allozyme and amplified fragment length polymorphisms<span> (AFLP)) were investigated in the mullet specie's </span></span><em>Liza ramada</em> and <em>Liza saliens</em><span> to determine levels of genetic variability and assess possible correlations between the population genetic structure and the specie's adaptability to shallow water environments. The thinlipped (</span><em>L. ramada</em>) and the sharpnose (<em>L. saliens</em><span>) mullets are diadromous species that enter coastal lagoons during early life stages to complete growth previous to sexual maturation. Bi-monthly samples (</span><em>n</em><span> = 30–50) were collected in the period 2000–2002 in different sites of the Sacca di Goro (Po river delta) and a nearby aquaculture lagoon (Valle Bertuzzi). Biochemical analyses were carried out by means of starch gel electrophoresis<span> (SGE) on 24 genetic loci corresponding to 15 gene–enzyme systems. In addition, molecular species-specific AFLP (15 primer combinations) were obtained by means of capillary electrophoresis. The degree of allozyme variability determined at three polymorphic loci, GPI-A, GPI-B and G3PDH in </span></span><em>L. saliens</em> and <em>L. ramada</em> (polymorphic loci <em>P</em><span> = 0.08; mean heterozygosity </span><em>H</em> = 0.010–0.022) and AFLP diversity (<em>P</em> = 0.110–0.430), seems lower than the one reported in the literature for ecologically similar teleost species. The identification of diagnostic alleles at GPI-A, G3PDH, AK-2, CK-A, CK-B, AAT, IDH, PGM-1, PGM-2 loci in the two mullet species was used for the taxonomic classification of <em>L. saliens</em> and <em>L. ramada</em><span>. Molecular taxonomy (allozyme and AFLP) demonstrated that the presence of small individuals inside the lagoons previously identified according to morphological characters has often been misinterpreted. The results are discussed in relation to the adaptive role of genetic variation<span> and the migratory characteristics of Mugilidae.</span></span></p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 121-128"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01235-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91726554","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Role of macroalgal biomass and clam fishing on spatial and temporal changes in N and P sedimentary pools in the central part of the Venice lagoon","authors":"Adriana Sfriso,&nbsp;Chiara Facca,&nbsp;Sonia Ceoldo,&nbsp;Silvia Silvestri,&nbsp;Pier Francesco Ghetti","doi":"10.1016/S0399-1784(02)00008-7","DOIUrl":"10.1016/S0399-1784(02)00008-7","url":null,"abstract":"<div><p><span>Nutrient concentrations have been investigated in the Venice lagoon for three scenarios: abnormal growth of nuisance macroalgae, decrease of macroalgal dominance and intense catching of the bivalve </span><span><em>Tapes philippinarum</em></span><span> Adams and Reeve by means of hydraulic and mechanical dredges. Total nitrogen and organic and total phosphorus monitored in June 1987, 1993 and 1998 showed significant changes both in concentrations and distribution. The disappearance of macroalgal blooms and the starting of intense clam fishing activities affected mainly organic phosphorus concentrations which, between 1987 and 1998, decreased from 104 ± 42 to 59 ± 31 μg cm</span>^–3, accounting for 27% (1987) and 16% (1998) of total phosphorus, respectively. Peak values also decreased significantly: they changed from 246 to 124–146 μg cm^–3. Similar results were recorded both for the mean total nitrogen concentrations, which decreased from 1.21 ± 0.60 to 0.93 ± 0.48 mg cm^–3, and the highest total nitrogen values which collapsed from 2.98 to 1.37 mg cm^–3. It was also observed that spatial nutrient distribution was more homogeneous because of the high sediment re-suspension and spreading over the whole lagoon. The mean values of nutrient concentrations monitored one to three times per month per year in 1989–1990 (first scenario) and 1998–1999 (third scenario) at three stations located in the lagoon inlet (Alberoni, station A), in the central lagoon (Sacca Sessola, station B) and in proximity of the mainland (San Giuliano, station C) confirm the nutrient decrease recorded in the surface sediments of the whole central lagoon. At station B, an area characterised by a macroalgal biomass up to 20 kg m^–2, wet wt., in 1989, the mean total nitrogen concentration decreased from 1.43 ± 0.42 mg cm^–3 in 1989–1990 to 0.75 ± 0.15 mg cm^–3 in 1998–1999. Similarly, organic phosphorus decreased from 106 ± 39 to 62 ± 23 μg cm^–3. Station C showed similar changes, whereas at station A, recently colonised by seagrasses, the opposite results were found.</p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 3-13"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)00008-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"56208754","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Phytoplankton abundance, community structure and diversity in the eutrophicated Orbetello lagoon (Tuscany) from 1995 to 2001","authors":"Caterina Nuccio,&nbsp;Chiara Melillo,&nbsp;Luca Massi,&nbsp;Mario Innamorati","doi":"10.1016/S0399-1784(02)00007-5","DOIUrl":"10.1016/S0399-1784(02)00007-5","url":null,"abstract":"<div><p>The Orbetello lagoon consists of two coastal ponds, Laguna di Ponente and Laguna di Levante, characterized by high nutrient concentrations, very poor exchanges with the sea and subjected to recurrent eutrophication crisis mainly in the past decades. To assess its current trophic status<span><span>, from 1995 to 2001 the temporal evolution<span> and spatial distribution of environmental factors, phytoplankton biomass and composition have been investigated. In this paper, the mean annual cycles of phytoplankton abundance, community structure and diversity are discussed. The seasonal cycles of micro- and nanophytoplankton densities are characterized by high frequency oscillations with fast increasing and decreasing blooms, but generally the lowest densities occur in winter, except for the peaks of December, and the highest ones during spring and summer. Despite the variability at short time scale of phytoplankton density, composition and diversity, a recurrent pattern was evidenced. Nanoplanktonic flagellates were the dominant fraction, mainly cryptophyceans during winter and early spring, while diatoms showed high summer blooms of nanoplanktonic centric genera and were very scarce during the other seasons, mainly with pennate genera. The phytoplankton community structure appeared to be more diversified from early summer to fall with the variable contribution of diatoms, </span></span>dinoflagellates and other flagellates. Phytoplankton diversity, computed by means of the Shannon index, was relatively low (mean of 1.96 bit per cell) and two phases, common to the whole lagoon, have been evidenced: a first phase of lower diversity during winter and early spring, followed by an increasing trend that reached the highest diversity in late summer-fall. The pattern of nutrients' (DIN and DIP) availability and depletion leads to a seasonal change of the N/P ratio that seems to play a role as regards the phytoplankton community succession and then diversity, favoring or limiting the growth of the different groups.</span></p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 15-25"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)00007-5","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"97030712","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Recovery of the macrobenthic community in the Valli di Comacchio, northern Adriatic Sea, Italy","authors":"Cristina Munari ,&nbsp;Simone Modugno ,&nbsp;Francesco Ghion ,&nbsp;Giuseppe Castaldelli ,&nbsp;Elisa Anna Fano ,&nbsp;Remigio Rossi ,&nbsp;Michele Mistri","doi":"10.1016/S0399-1784(02)01231-8","DOIUrl":"https://doi.org/10.1016/S0399-1784(02)01231-8","url":null,"abstract":"<div><p><span>The macrobenthic community structure of the Valli di Comacchio (northern Italy) was described in order to assess the ecological conditions of the main basins through 2001. In addition, the biotic data set gathered in 1997–1998 was compared to achieve an estimation of the eventual recovery of the lagoonal benthic assemblages<span>. Four permanent sites (P1, M4, M5 and M6), located along a gradient of sediment texture and confinement, and representing four different areas of the lagoon, were sampled quarterly in 2001 for macrofauna and sedimentary variables (organic content, phytobenthic chlorophyll-a, depth of the </span></span>redox potential<span> discontinuity layer), and fortnightly for water variables (temperature, salinity, dissolved oxygen and planktonic chlorophyll-a). Water and sedimentary variables were typical of eutrophic areas. A total of 52 macrobenthic taxa were identified and, on the basis of the species collected, differences in faunal distribution among the four areas were recognized, although less marked than in previous studies. Sediment trophic status<span> and its seasonal dynamics in the Valli were crucial in determining species distribution among the different areas. The comparison between 1997–1998 and 2001 biotic data indicated that conditions in the lagoon had improved, especially in the formerly most impaired, central area. In the Valli di Comacchio, the recovery of benthic communities after severe disturbance will probably take longer, even if sewage discharges have been removed 11 years ago. Secondary disturbance due to scarce water circulation, sharp temperature and salinity fluctuations, release of toxic substances from sediments influenced animal assemblages along spatial and temporal scales. The interplay of these variables probably caused deviations from the expected improvement in benthic conditions. Nevertheless, clear signs of amelioration, particularly at the previously most impaired area, were detectable.</span></span></p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 67-75"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01231-8","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91599734","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Distribution, persistence and change in the macrobenthos of the lagoon of Lesina (Apulia, southern Adriatic Sea)","authors":"Carlotta Nonnis Marzano ,&nbsp;Lidia Scalera Liaci ,&nbsp;Alessandra Fianchini ,&nbsp;Flavia Gravina ,&nbsp;Maria Mercurio ,&nbsp;Giuseppe Corriero","doi":"10.1016/S0399-1784(02)01229-X","DOIUrl":"https://doi.org/10.1016/S0399-1784(02)01229-X","url":null,"abstract":"<div><p><span><span><span>The benthic community of the lagoon of Lesina was studied from July 2000 to June 2001. The distribution of the main macrophytobenthic species was recorded by visual census at 24 stations in July 2000. The </span>macrofauna, from both hard and soft substrates, was analyzed at five stations with seasonal frequency; in addition, the main hydrologic parameters were recorded monthly. The lagoon was mainly characterized by brackish water, with </span>salinity values decreasing from west to east (annual mean: 23.3 psu). It showed mild water temperatures throughout the year (annual mean: 19.8 °C) and moderately high values of dissolved oxygen (annual mean: 9.9 ppm). No dystrophic crises were observed during the period of study. In the eastern basin, </span><span><em>Zostera</em><em> noltii</em></span> Hornemann, Lissara and <span><em>Ruppia</em><em> cirrhosa</em></span> (Patagna) Grande were the most abundant species of macrophytobenthos. Their distributional pattern was coherent with literature data. Soft bottoms of the western basin were largely occupied by the benthopleustophytic alga <span><em>Valonia</em><em> aegagropila</em></span> C. Agardh, which during the last decade had almost completely replaced <span><em>Cladophora</em><em> prolifera</em></span> (Roth) Kützing and <span><em>Gracilaria</em><em> confervoides</em></span><span> Greville, the latter of which was previously very abundant in the lagoon. Macrozoobenthos consisted of 53 species (1 sponge, 2 cnidarians, 11 molluscs, 14 annelids, 21 crustaceans, 1 insect, 1 bryozoan, 1 echinoderm, 1 tunicate), most of which are typical of brackish water. Highest abundances were found in the eastern area of the basin. Some marine species were recorded in the western area. In contrast with the dramatic changes observed in the floral assemblage, a large amount of species had already been recorded in the lagoon during the last 10 years, pointing out the persistence of the macrozoobenthic community. Nevertheless, the distribution of benthic macrofauna seemed to be greatly influenced by the presence of </span><em>Valonia aegagropila</em><span>, as shown in an ordination model, where station-points were segregated by the presence of the alga rather than by hydrologic parameters. The impact of biotic factors on the community, such as non-indigenous species invasions, was suggested as constraints inducing the temporal variations of benthos.</span></p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 57-66"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01229-X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91726551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Economic modelling as a tool to support macroalgal bloom management: a case study (Sacca di Goro, Po river delta)","authors":"Francesca Cellina ,&nbsp;Guilio A. De Leo ,&nbsp;Andrea E. Rizzoli ,&nbsp;Pierluigi Viaroli ,&nbsp;Marco Bartoli","doi":"10.1016/S0399-1784(02)01238-0","DOIUrl":"https://doi.org/10.1016/S0399-1784(02)01238-0","url":null,"abstract":"<div><p>During the last 20 years, intensive mollusk farming has been developed in coastal waters, mostly in sheltered bays and lagoons. Often, mollusk stocks are threatened by frequent anoxic events from macroalgal blooms. Here, a decision support tool is described to select the optimal short-term strategy to control algal biomasses. Even though long-term and detailed studies of the lagoon systems are required to provide reliable, biologically based policies, we have here developed a simplified analysis that overlooks most of the ecological complexity, but explicitly includes environmental variability and uncertainty in parameter estimation in the economic assessment of the performances of different management strategies. The aim is to quickly screen management alternatives of harvesting <em>Ulva rigida</em> biomass in terms of the control measures considered, i.e. the number of vessels used (the harvesting effort) and the <em>U. rigida</em><span><span> density at which the vessels start to operate. The decision support tool was applied to the Sacca di Goro, the southernmost coastal lagoon of the Italian Po </span>river delta, where intensive farming of the clam </span><span><em>Tapes philippinarum</em></span> occurs. The results of the analysis indicate that an intermediate number of vessels should start operating as soon as <em>U. rigida</em> biomass exceeds low thresholds.</p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 139-147"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01238-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"91726552","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Small-scale morphological and genetic differentiation in the Mediterranean killifish Aphanius fasciatus (Cyprinodontidae) from a coastal brackish-water pond and an adjacent pool in northern Sardinia","authors":"Ferruccio Maltagliati ,&nbsp;Paolo Domenici ,&nbsp;Clara Franch Fosch ,&nbsp;Piero Cossu ,&nbsp;Marco Casu ,&nbsp;Alberto Castelli","doi":"10.1016/S0399-1784(02)01236-7","DOIUrl":"10.1016/S0399-1784(02)01236-7","url":null,"abstract":"<div><p>Two samples of <em>Aphanius fasciatus</em><span> collected in the Pilo pond (northern Sardinia, Italy) and in an adjacent pool of small surface area were analysed morphologically (235 individuals) and genetically (a subsample of 58 individuals). The aims of the present study were (i) to test the hypothesis that different predation pressures may be associated with morphological and/or genetic differences between samples from each habitat and (ii) to assess the level of divergence between the two populations. Morphological analysis was based on the relative size of fins because it has been shown to be associated with predation pressure. The relative caudal fin area (caudal fin area/total body surface) was smaller in specimens from the pool, in both males and females, whereas no differences were found for the dorsal and anal fin areas. Caudal fins with higher aspect ratio<span><span> (fin depth/fin length) were found in fish from the pool but not in the pond, due to a higher fin depth. We hypothesised that specimens from the pool would show smaller caudal fin area, since they are subject to lower predation pressure. Random amplification of polymorphic DNA (RAPD) analysis revealed a relatively high degree of both within- and between-sample genetic heterogeneity. The pond and pool samples exhibited </span>heterozygosities, which did not differ significantly by </span></span><em>t</em><span>-test. Between-sample genetic divergence was highlighted by the coancestry coefficient (θ = 0.301 ± 0.059, </span><em>P</em> &lt; 0.001) and analysis of molecular variance (AMOVA) (variance between sites = 41%, <em>P</em> &lt; 0.001). Genetic divergence between sites with a relatively high genetic diversity within both samples suggested that the population in the pool did not originate from a single colonisation event with a small number of founders. The genetic divergence between the two populations is consistent with their differences in fin size.</p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"26 1","pages":"Pages 111-119"},"PeriodicalIF":0.0,"publicationDate":"2003-03-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01236-7","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"102279387","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Temporal and spatial changes of seagrass meadows in a Mediterranean coastal lagoon","authors":"Sylvia Agostini ,&nbsp;Bernard Marchand ,&nbsp;Gérard Pergent","doi":"10.1016/S0399-1784(02)01196-9","DOIUrl":"10.1016/S0399-1784(02)01196-9","url":null,"abstract":"<div><p><span>Aerial photographs and in situ data of the Urbinu Lagoon (one of the largest and deepest ponds in Corsica, Mediterranean Sea) permit the establishment of a cartography of its aquatic </span>benthic assemblages<span><span> and types of sea-beds. It was possible to distinguish in the photographs submerged structures such as: sand, pebbles, mud and seagrass meadows. Seagrass beds were the predominant </span>vegetation type in this lagoon (comprising 14–29% of the total area depending on the year studied), and their distribution was incorporated into a geographical information database, and then compared with historical data. Temporal and spatial change in seagrass meadows was assessed between 1990 and 1997. Change in total extent was evaluated through a map to map comparison of data interpreted from image processing using colored aerial photographs (1990, 1994 and 1997). The overall net change was a 12% decrease between 1990 and 1994 and a 16% increase between 1994 and 1997. These observations imply that regressions are not irreversible over the past 7 years, and show that seagrass meadows in this area have been stable despite environmental perturbations, since the lost zones were recolonized.</span></p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"25 6","pages":"Pages 297-302"},"PeriodicalIF":0.0,"publicationDate":"2002-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01196-9","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"56208821","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Hydroid assemblages from Mar del Plata, Argentina, at depths between 0 and 500 m. Distribution and biological substrata","authors":"Gabriel N Genzano,&nbsp;Mauricio O Zamponi","doi":"10.1016/S0399-1784(02)01197-0","DOIUrl":"10.1016/S0399-1784(02)01197-0","url":null,"abstract":"<div><p><span><span>The first studies on hydroids of the subantarctic region<span> (SW Atlantic Ocean) were based on samples from expeditions to the Antarctic at the end of the 19th and beginning of the 20th centuries. In spite of these works, hydroids from the northern Argentine continental shelf remained unknown until the 1960s. In coastal waters off Mar del Plata, studies on hydroids have been few in number and limited to species described from preserved material. Even rudimentary ecological information is lacking in these reports. Over the past few decades, samples from oceanographic expeditions, and specimens collected directly from the intertidal rocky shore or by means of scuba diving and snorkeling, have provided heretofore unpublished information on hydropolyps of the Mar del Plata region. The goal of this work is to analyze the hydroid fauna of the Mar del Plata coast, including bathymetric distributions, frequencies of occurrence, and biological substrata. A total of 36 species were included. Most were found at depths shallower than 8 m, where hard substrates predominated. Numbers of species decreased markedly below 80 m. The shallow-water hydroid fauna of Mar del Plata comprises a large number of cosmopolitan or widely distributed species. In deeper zones, species with subantarctic or south hemisphere distributions predominated. Hard bottom outcrops were surrounded by extensive areas of sand. Although such substrata are unfavorable for most hydroids, many species were found in soft bottom areas on </span></span>polychaete tubes. Stems of hydroids provided the greatest number of epizoic species (18), followed by polychaete tubes (16 species) and sponges (15 species). Hydroids, bivalve mollusks, and sponges were the most frequent substrates. Colonies grew less frequently on </span>bryozoans and tunicates. This general scheme changed at greater depths, where the most frequent substrates were polychaete tubes and sponges.</p></div>","PeriodicalId":100980,"journal":{"name":"Oceanologica Acta","volume":"25 6","pages":"Pages 303-313"},"PeriodicalIF":0.0,"publicationDate":"2002-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1016/S0399-1784(02)01197-0","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82808123","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}