Benthic communities depend on receiving much of their food from the water column. While sinking, particles are transformed in a discontinuous process and are temporally retained in transitional physical structures, which act as boundaries and contribute to their further transformation. Motile organisms are well-acquainted with boundaries. The number, width and placement of boundaries are related to the degree of particle degradation or transformation. Progressively deepening within each boundary, particles are degraded according to their residence time in the discontinuity and the activity of the organisms temporarily inhabiting that boundary. Finally, particles reach the seafloor and represent the main food source for benthic organisms; the quality and quantity of this food have a strong impact on the development of benthic communities. However, benthic communities not only play the role of a sink of matter: they act as an active boundary comparable to other oceanic boundaries, in accordance with the boundary concept proposed by the ecologist Ramon Margalef.

Macrocystis pyrifera kelp beds play a significant ecological role along the coast of Chile. Besides their importance as food, protection structures, substrata, microhabitats and nurseries, regularly occurring natural disturbances (e.g. extremes of the climate variability El Niño–Southern Oscillation) and increased kelp exploitation affect these habitats. The present study aimed to test the dependence of reef fishes on Macrocystis pyrifera and to evaluate the effect of an enhanced habitat structure (experimental M. pyrifera bed) on the abundance, composition and spatial distribution on rock, on macroalgae, in the water column and on sand of the reef fish community. Boulders colonised by M. pyrifera were transported into three replicated experimental areas (9 m 2 each) located in a barren ground area. Three barren ground areas (9 m 2 each) without manipulation were selected as controls. The fish abundance, composition and spatial distribution on rock, on macroalgae, in the water column and on sand were recorded weekly by scuba diving over a period of 3 months, between 15 February 2007 and 13 June 2007 (4 months). Results indicate significantly higher abundances (mean = 225%) of fishes in the forested areas compared to the barren ground controls (mean = 3.71 fishes/9 m 2 and 1.14 fishes/9 m 2 , respectively). Scartichthys gigas / viridis , Chromis crusma , Cheilodactylus variegatus and Isacia conceptionis numerically dominated the fish assemblages of the experimental kelp patches. Each fish species revealed different distributions in the forested areas: Scartichthys gigas / viridis was more abundant on rocks and C. variegatus in the macroalgae, whereas C. crusma and I. conceptionis preferred the water column above the experimental kelp bed. During the experimental time, the kelp lost some blades and some plants became detached. The overall number of fishes correlated with the declining kelp abundance ( r = 0.964, p < 0.05). The fish species showed different responses to these changes in the experimental areas: C. variegatus and I. conceptionis declined in abundance, whereas the abundance of Scartichthys gigas / viridis remained constant.

The trophic structure of the German Bight soft-bottom benthic community was evaluated for potential changes after cessation of bottom trawling. Species were collected with van-Veen grabs and beam trawls. Trophic position (i.e. nitrogen stable isotope ratios, δ15N) and energy flow (i.e. species metabolism approximated by body mass scaled abundance) of dominant species were compared in trawled areas and an area protected from fisheries for 14months in order to detect trawling cessation effects by trophic characteristics. At the community level, energy flow was lower in the protected area, but we were unable to detect significant changes in trophic position. At the species level energy flow in the protected area was lower for predating/scavenging species but higher for interface feeders. Species trophic positions of small predators/scavengers were lower and of deposit feeders higher in the protected area. Major reasons for trophic changes after trawling cessation may be the absence of artificial and additional food sources from trawling likely to attract predators and scavengers, and the absence of physical sediment disturbance impacting settlement/survival of less mobile species and causing a gradual shift in food availability and quality. Our results provide evidence that species or community energy flow is a good indicator to detect trawling induced energy-flow alterations in the benthic system, and that in particular species trophic properties are suitable to capture subtle and short-term changes in the benthos following trawling cessation.

Total lipid and fatty acid concentrations were studied in a late spring-early summer flagellate-dominated bloom in the Weddell Sea.These indicators were considered a good tool for assessing the quality of organic matter settling from surface to deep-water layers (epibenthic water layers).The results showed different patterns between the early (11-15 December 2003) and the late sampling period (18-27 December 2003) at all studied depths (5 m, 50 m and near-bottom water layers).Low phytoplankton biomass (mainly flagellates) in the first half of the study corresponded to low total lipid and fatty acid concentrations.In the second sampling period a spring bloom (mainly flagellates and diatoms) was detected, increasing the total lipid and fatty acid concentrations in the water column.The amount of settling organic matter from surface waters to the near-bottom water layers was high, especially in the late sampling period.Trophic markers showed evidence of a sink of available organic matter rich in quality and quantity, especially in terms of polyunsaturated fatty acids, for benthic organisms from surface layers to bottom layers in only a few days.The importance of studying short-time cycles in order to detect organic matter availability for benthic biota in view of the pulse-like dynamics of primary production in Antarctic waters is discussed.

Antarctic marine ecosystems are increasingly threatened by climate change and are considered to be particularly sensitive because of the adaptation of most organisms to cold and stable environmental conditions. Fishes play a central role in the Antarctic marine food web and might be affected by climate change in different ways: (i) directly by increasing water temperatures, decreasing seawater salinity and/or increasing concentrations of CO2; (ii) indirectly by alterations in the food web, in particular by changes in prey composition, and (iii) by alterations and loss of habitat due to sea ice retreat and increased ice scouring on the sea floor. Based on new data and data collected from the literature, we analyzed the vulnerability of the fish community to these threats. The potential vulnerability and acting mechanisms differ among species, developmental stages and habitats. The icefishes (family Channichthyidae) are one group that are especially vulnerable to a changing South Polar Sea, as are the pelagic shoal fish species Pleuragramma antarcticum. Both will almost certainly be negatively affected by abiotic alterations and changes in food web structure associated with climate change, the latter additionally by habitat loss. The major bottleneck for the persistence of the majority of populations appears to be the survival of early developmental stages, which are apparently highly sensitive to many types of alterations. In the long term, if climate projections are realized, species loss seems inevitable: within the demersal fish community, the loss or decline of one species might be compensated by others, whereas the pelagic fish community in contrast is extremely poor in species and dominated by P. antarcticum. The loss of this key species could therefore have especially severe consequences for food web structure and the functioning of the entire ecosystem.

Normal 0 21 false false false PT-BR X-NONE X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Tabela normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin-top:0cm; mso-para-margin-right:0cm; mso-para-margin-bottom:10.0pt; mso-para-margin-left:0cm; line-height:115%; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi; mso-fareast-language:EN-US;} The relevance of faunistic intercontinental comparisons is discussed here in the context of the past and current projects related to Antarctic biodiversity research. Some of these have focussed on questions regarding Antarctic isolation and evolutionary pathways between South America and that continent, such as the ‘Investigación Biológica Marina en Magellanes relacionada con la Antártida'(IBMANT), ‘Ecology of the Antarctic Sea Ice Zone' (EASIZ), and more recently the ‘Evolution and Biodiversity in the Antarctic' (EBA) as well as the ‘Census of Antarctic Marine Life' (CAML) and the ‘Scientific Committee on Antarctic Research Marine Biodiversity Information Network' (SCARMarBIN). The Latin American subproject of the ‘Census of Antarctic Marine Life' (LA-CAML) provided a landmark to collect data on the biodiversity and life history for all groups of organisms ranging from microbes to endotherms. In addition to such fundamental knowledge the application of molecular techniques and highly sophisticated methods to study macroecological processes are necessary to better understand ecosystem functioning and large-scale comparisons in the southern hemisphere, especially between South America and Antarctica. More cooperation between scientists and more interdisciplinary approaches are required to develop reliable projections for the future of our biosphere under anthropogenic stress and its ecosystem services.

Biochemical characteristics of seafloor sediment off Austasen in the southeastern Weddell Sea were assayed in samples recovered in the early autumn and late spring of 2000 and 2003, respectively. Sediment was separated in the grain-size fractions >200 μm and <200 μm to distinguish biochemical characteristics in the fraction available for benthic suspension feeders (<200 μm). In the bulk sediment, the lipid (LPD) and carbohydrate (CHO) contents were significantly different between seasons with higher LPD content in the early autumn and higher CHO content in the late spring. In the grain-size fractions <200 μm, the LPD and protein (PRT) contents were significantly higher in the early autumn meaning that in this season the fraction available for benthic suspension feeders presented higher nutritive value. The relatively higher CHO concentrations observed in each fraction in the late spring were attributed to refractory matter, whereas the higher PRT and LPD concentrations found during the early autumn were associated with planktonic material settled after the summer phytoplankton bloom. Our results suggest that there is seasonal variation in the composition of organic matter in the sediment, with better nutritive quality in the early autumn, especially in the grain-size fraction available for benthic suspension feeders. These variations also suggest that the benthic community exploits the fresh organic matter accumulated after the summer throughout the Antarctic dark months leaving the sediment almost exhaust of LPD and with higher CHO contents, presumably of refractory nature, at the onset of the seasonal phytoplankton bloom of the following year.

3Dealing with climate change in polar and subpolar waters of the southern hemisphere, the Magellan region is in a particularly favourable position. During geological history up to the present time, this area has been influenced by, and many times involved in, Antarctic and Subantarctic climate change. Life in its waters is still reflecting the consequences of the latest glaciation. Of all land masses surrounding the Antarctic, it lies at a relatively close distance, is the only one connected by a bridge of islands and shallows, and its marine fauna shows the greatest similarity with that of South Polar regions. Furthermore, scientists of most countries doing Antarctic marine research pass the Magellan region on their way to and from the Antarctic, and many research vessels use Punta Arenas (Chile) or Ushuaia (Argentina) as their last continental base for refuelling and replenishing provisions. In the past decades, Antarctic research has increased in importance, and various cooperative projects have made use of the facilities and research opportunities offered in the Cono Sur. In particular the IBMANT project has made an effort to study the biological interactions between the Magellanic and Antarctic provinces, revealing a considerable degree of relatedness. The data collected in this project and

Human-induced habitat destruction, overexploitation, introduction of alien species and climate change are causing species to go extinct at unprecedented rates, from local to global scales. There are growing concerns that these kinds of disturbances alter important functions of ecosystems. Our current understanding is that key parameters of a community (e.g. its functional diversity, species composition, and presence/absence of vulnerable species) reflect an ecological network’s ability to resist or rebound from change in response to pressures and disturbances, such as species loss. If the food web structure is relatively simple, we can analyse the roles of different species interactions in determining how environmental impacts translate into species loss. However, when ecosystems harbour species-rich communities, as is the case in most natural systems, then the complex network of ecological interactions makes it a far more challenging task to perceive how species’ functional roles influence the consequences of species loss. One approach to deal with such complexity is to focus on the functional traits of species in order to identify their respective roles: for instance, large species seem to be more susceptible to extinction than smaller species. Here, we introduce and analyse the marine food web from the high Antarctic Weddell Sea Shelf to illustrate the role of species traits in relation to network robustness of this complex food web. Our approach was threefold: firstly, we applied a new classification system to all species, grouping them by traits other than body size; secondly, we tested the relationship between body size and food web parameters within and across these groups and finally, we calculated food web robustness. We addressed questions regarding (i) patterns of species functional/trophic roles, (ii) relationships between species functional roles and body size and (iii) the role of species body size in terms of network robustness. Our results show that when THE ROLE OF BODY SIZE IN COMPLEX FOOD WEBS: A COLD CASE 183 Author's personal copy analyzing relationships between trophic structure, body size and network structure, the diversity of predatory species types needs to be considered in future studies.

Human-induced habitat destruction, overexploitation, introduction of alien species and climate change are causing species to go extinct at unprecedented rates, from local to global scales. There are growing concerns that these kinds of disturbances alter important functions of ecosystems. Our current understanding is that key parameters of a community (e.g. its functional diversity, species composition, and presence/absence of vulnerable species) reflect an ecological network's ability to resist or rebound from change in response to pressures and disturbances, such as species loss. If the food web structure is relatively simple, we can analyse the roles of different species interactions in determining how environmental impacts translate into species loss. However, when ecosystems harbour species-rich communities, as is the case in most natural systems, then the complex network of ecological interactions makes it a far more challenging task to perceive how species’ functional roles influence the consequences of species loss. One approach to deal with such complexity is to focus on the functional traits of species in order to identify their respective roles: for instance, large species seem to be more susceptible to extinction than smaller species. Here, we introduce and analyse the marine food web from the high Antarctic Weddell Sea Shelf to illustrate the role of species traits in relation to network robustness of this complex food web. Our approach was threefold: firstly, we applied a new classification system to all species, grouping them by traits other than body size; secondly, we tested the relationship between body size and food web parameters within and across these groups and finally, we calculated food web robustness. We addressed questions regarding (i) patterns of species functional/trophic roles, (ii) relationships between species functional roles and body size and (iii) the role of species body size in terms of network robustness. Our results show that when analyzing relationships between trophic structure, body size and network structure, the diversity of predatory species types needs to be considered in future studies.

When I was a student of marine research at Kiel on the Baltic Sea, my studies proceeded very much the way that had developed in the generations before. I had learnt the basics of physics, chemistry and biology at other universities, which entitled me to concentrate on ocean sciences and marine biology. Physical and chemical oceanography, fisheries biology and planktology, marine zoology and botany were taught at four different institutes, and marine geology at yet another institute several kilometres away. These institutes were led by professors, most of whom held a chair at the university, and who violently defended the importance and uniqueness of their respective disciplines. Some of them also wrote important textbooks, which, as was customary, were strictly monodisciplinary. As students, we listened to the details of faunal evolution, the variability of climate systems and ocean currents and the basics of plate tectonics, but hardly anyone cared to explain to us in which way these processes were connected.

The Humboldt Current System is a highly productive ecosystem that is subject to the dynamics of the El Nino Southern Oscillation (ENSO). El Nino (EN, the warm phase or ENSO) causes vital changes in surface water temperature, oxygen levels, and salinity conditions, which are reflected in various responses of coastal pelagic and benthic organisms. For very shallow habitats such as sandy beaches, temperature and salinity are considered the principal parameters changing during strong EN. However, the mechanisms by which these changes effect change on the structure of coastal populations remains largely unknown. The surf clam Donax obesulus is dominant on large sandy beaches of the Humboldt Current System. Its biogeographical distribution is largely influenced by EN-induced environmental changes. Despite the species' key role in the beach ecosystem, the effects of modified abiotic conditions on the meroplanktonic larval stages and threshold temperatures involved have not yet been investigated. After EN episodes, meroplanktonic larval stages play a crucial role in the medium- and long-term stability of shallow-water species. Thus, this study makes a first attempt to describe the ontogeny of D. obesulus and examines the effects on development of EN temperature conditions (ENTC) in comparison with normal temperature conditions (NTC). Results indicate that early life history follows a pattern previously described for other donacid bivalves. Development, growth, and mortality of larvae were assessed during a 3-wk in vitro experiment, indicating that larvae reared under ENTC grew and developed faster in comparison with those reared under NTC; mortality was slightly higher under ENTC. During a 2nd experiment, larvae were exposed for 48 h to a distinct range of different salinities (35, 25, 15, and 5 +/- 1) at 2 different temperatures (NTC and ENTC). At both temperatures, larvae suffered no mortality at medium and low salinity (35, 25, and 15 +/- 1) but showed 100% mortality at very low salinity (5 +/- 1) after 16 h at NTC and 32 h at ENTC. Activity of larvae was highest at medium salinity (25 +/- 1) and lowest at normal salinity (35 +/- 1). The results of this study indicate that early larval stages of D. obesulus can cope with temperature and salinity changes induced during EN. Only extremely low salinity (5 +/- 1) such as that observed close to river mouths may cause high mortality rates in D. obesulus offspring.

Community succession is an important process in modulating the structure of benthic soft-bottom communities. A field experiment was conducted aiming (1) to describe the successional development in a subtidal soft-bottom community over a two-year period, (2) to estimate the time necessary for the developing community to resemble the surrounding natural community, and (3) to evaluate the effect of seasonal onset on the colonization over a one-year period of development. Containers filled with fine sediment without any previous biological conditioning were installed in subtidal soft bottoms off Playa Colorado, Bahía Antofagasta, Chile (Humboldt Current System). The experiment was initiated in June 2006. For 24months three replicate containers together with 4 reference samples from the surrounding natural community were sampled every three months. Succession was detected but did not show a sequential replacement from early to late colonizers, thus did not follow distinguishable seral stages. These results support the tolerance succession model, which states that species dominating later successional stages colonize at the same time as species mainly associated with initial successional stages. Resemblance to the reference community was first recorded after eighteen months. In order to test for seasonal effects of colonization, three containers were installed in each of the four seasons, and the community was allowed to develop for a one-year period. Seasonality had no evident effect, as all establishing communities converged to a similar structure after one year, regardless of the season, when the containers had been installed. This study highlights the strong resilience of northern Chilean sublittoral soft-bottom communities to environmental variations during the cold conditions of the El Niño Southern Oscillation.

The yellow clam Mesodesma mactroides (Bivalvia: Mesodesmatidae) was once the most abundant intertidal species on the Atlantic coast of northern Argentina and an important commercial resource in South America. This study of a population inhabiting the intertidal zone of the sheltered-dissipative sandy beach Santa Teresita documents the species’ population biology, including demographic structure, growth and production during December 2004 and December 2006, and adumbrates the critical state of M. mactroides at present. A total of 3,015 M. mactroides were collected and measured, whereas individuals were found with an anterior–posterior shell length between 2 and 64 mm. A von Bertalanffy growth function with an asymptotic length ( L ∞ ) of 85 mm and a growth constant ( K ) of 0.47 year −1 was established from length–frequency distributions. The longevity of the species is estimated at approximately 6 years, and instantaneous mortality rate was about three times higher than 40 years ago. Besides, this study confirmed that the overall growth performance index ( OGP ) is habitat-specific and can be used to group M. mactroides and M. donacium from different areas into temperate and upwelling species. Furthermore, OGP is inversely correlated with the latitudinal distribution of Mesodesma populations. The intertidal biomass ranged between 0.06 and 0.07 g AFDM m −2 year −1 . Individual production was observed to be highest at 47 mm length (0.35 g AFDM m −2 year −1 ), and annual production ranged between 0.12 and 0.19 g AFDM m −2 year −1 , resulting in productivity values ( P / B ) between 1.84 and 2.93. The comparison of the results of the present study with those of growth studies conducted on M. mactroides 40 years ago revealed the following considerable differences in the population structure of M. mactroides , indicating the conservation status of this intertidal bivalve as endangered: (1) present growth rates are faster, but that the maximum length attained has decreased, (2) the numbers of individuals per square metre were many times higher in the past than in the present, (3) bivalves from the present work never reached the ‘commercial size’ of 60 mm and (4) 40 years ago, the population of M. mactroides was composed of up to three cohorts, whereas in this study, there was only one single cohort visible.

Die Konzepte fur das Fischereimanagement haben in den vergangenen hundert Jahren eine tiefgreifende Wandlung durchgemacht. Sie entwickelten sich in der zweiten Halfte des vergangenen Jahrhunderts von monospezifi schen Ansatzen, in denen einzelne Populationen oder Bestande weitgehend isoliert betrachtet wurden, zum Multispecies-Management, das auch Wechselbeziehungen zwischen genutzten Arten berucksichtigte. Die stark verbesserten Ortungs- und Fangtechniken und die Nutzung noch unterfi schter Fanggrunde und Bestande hielten die Anlandungen eine Zeitlang auf hohem Niveau. Die rucklaufi gen Weltfi schereiertrage in den letzten Dekaden des vergangenen Jahrhunderts, der Kollaps wichtiger Fischereien und die auch von der Fischerei zu verantwortende fortschreitende Degradierung mariner Okosysteme zeigten jedoch, dass eine nachhaltige Nutzung der fi schereilichen Ressourcen bei gleichzeitiger Erhaltung der Okosysteme mit diesen Konzepten nicht moglich ist. Angesichts dieses Offenbarungseids und unter dem zunehmenden Druck der Naturschutzer wurden daher die Konzepte des okosystemvertraglichen Fischereimanagements (EBFM, ecosystem-based fi sheries management) und des raumlichen Fischereimanagements (SM, spatial management) entwickelt, bei denen die Prioritaten umgedreht sind: Das Management geht nicht mehr vom Fischereiobjekt, sondern vom Okosystem aus, das horizontal und vertikal in Zonen unterteilt wird, die zu verschiedenen Zeiten befi scht oder unter Schutz gestellt werden konnen. EBFM zielt darauf ab, gesunde Okosysteme inklusive der Fischereien zu erhalten, die von diesen Okosystemen ohne Schadigung getragen werden. Moglicherweise sind diese neuen Konzepte nur wenig realistischer als die Ideen vom langfristigen Dauerertrag oder dem der nachhaltigen Fischerei, die der realen Welt uberdimensionierter Fangfl otten, unersattlicher Markte und zahlreicher politischer Fehlentscheidungen nicht standhielten. Die traurige Tatsache ist, dass nicht nur die Fischerei, sondern auch die marinen Okosysteme sich in einem sehr schlechten Zustand befi nden. Um dem abzuhelfen, sind u.a. Schutzgebiete vorgesehen, in denen die Fischerei eingeschrankt oder verboten ist. Zusammen mit anderen Nutzungen wie Offshore-Windparks bedeutet diese neue Raumordnung einen massiven Eingriff in die bisherigen Rechte und Gewohnheiten der Fischer. In dieser Arbeit werden vor dem Hintergrund der Okosystem-Degradierung einige grundlegende okologische Zusammenhange in naturlichen, befi schten und geschutzten marinen Systemen diskutiert. Dabei stutzen wir uns auf empirische und experimentelle Befunde aus Nord- und Ostsee sowie anderen marinen Okosystemen. Unter dem Strich sollten Schutzgebiete im Rahmen der neuen Managementkonzepte langfristig auch der Fischerei dienen; inwieweit allerdings eine Fischerei unter der kunftigen Raumordnung noch sinnvoll ist, steht dahin.