Ecological indices tracking distinct impacts along disturbance-recovery gradients in a temperate NE Atlantic Estuary – Guidance on reference values

Results gathered from a monitoring programme on the Mondego Estuary (Western Coast of Portugal) were compliant with findings drawn from other studies, which pointed out that unstable environments, namely estuarine systems, constitute a great challenge for the use of environmental tools such as ecological indices. The Margalef Index, the Shannon–Wiener Index and AMBI were proposed to evaluate the ecological status of benthic communities in the scope of the European Water Framework Directive (WFD) in Portugal and other European member states. In this system these indices were not equally effective in tracking changes in benthic communities that expressed obvious responses to anthropogenic disturbances (eutrophic situations and severe physical disturbance) and to subsequent impacts' cessation. Natural variability played an important role on the indices' response, with estuarine gradient and habitat heterogeneity affecting the ranges of values obtained, and with extreme climate events slowing down the ongoing recovery process. Nonetheless, both natural and anthropogenic variability during the study period could be satisfactorily detected if we accounted for the information provided by all three indices. Based on the whole range of variation observed (a) as a response to different kinds of impacts, and (b) along recovery gradients, as well as accounting for the natural driving forces acting upon estuarine benthic invertebrate communities, we propose a set of reference values for these three indices. This proposal aims at contributing to the implementation of classification tools within the scope of the European WFD.     

Effects of the suspension feeding mussel Mytilus trossulus on a brackish water macroalgal and associated invertebrate community

The importance of suspension-feeding mussels is particularly apparent in benthic communities; however, the role of this feeding strategy on the development of macroalgal and associated invertebrate communities is in general poorly known. The effect of suspension-feeding mussels Mytilus trossulus on benthic communities was studied in an in situ factorial field experiment in the Northern Baltic Sea over one ice-free season. The experiment was performed under different regimes of wave exposure (low and moderate) and on different sedimentary habitats (soft bottom with high organic content, soft bottom with low organic content, and hard bottom). In general the presence of mussels was associated with increased biomass of filamentous algae, herbivores and deposit feeders and decreased biomass of charophytes. The effect of M. trossulus interacted with the effect of exposure and substrate. Stronger responses were observed in moderately exposed than in sheltered areas. The presence of M. trossulus affected charophytes and deposit feeders on sand with low content of organic matter and filamentous algae on pebbles but not on other substrate types. The magnitude of the effects varied between months. The results suggest that (i) even in dynamic coastal systems the biodeposits and excretions of mussels are at least partly assimilated locally and are not flushed away to the open sea, (ii) the accumulation of faecal material induced elevated growth of deposit feeders, (iii) mussels enhanced the growth of ephemeral macroalgae and reduced the growth of perennial macroalgae, and (iv) together with increasing benthic primary production, mussels indirectly increase the production of herbivores.     

Distribution patterns of benthic juvenile gobies in and around seagrass habitats: effectiveness of seagrass shelter against predators

The significance of a sheltering effect of seagrass against predators influencing the distribution patterns of benthic juveniles of the streaked goby Acentrogobius sp. was investigated by field experimentation in and around seagrass habitats at Moroiso and Aburatsubo Bays, Miura Peninsula, Japan. In the former bay, juveniles were always restricted to the seagrass bed, whereas at the latter, they also occurred over the surrounding bare sand substrate. Juveniles never occurred inside predator-exclusion cages over unvegetated sand in Moroiso Bay. Additionally, a tethering experiment resulted in similarly small numbers of juveniles being preyed upon in both the seagrass bed and over bare sand, suggesting that the predation risk for juveniles may not differ between the habitat types and was thus not responsible for their distribution patterns. The availability of symbiotic shrimp burrows, which were scarce in bare sand in Moroiso Bay but abundant in a similar area in Aburatsubo Bay, was also hypothesized as a determinant of distribution pattern. In a manipulative experiment at Aburatsubo Bay, however, juveniles showed no response to alterations in the availability of symbiotic shrimp burrows, indicating that neither the sheltering effect of seagrass against predators nor the availability of symbiotic shrimp burrows was a significant factor in streaked goby juvenile distribution. Food availability may be a determinant, because food abundance patterns were concordant with the juvenile distribution pattern.     

YSDP102钻孔有孔虫动物群与南黄海东南部古水文重建

所研究的YSDP1 0 2钻孔岩心 (33°49.496′N ,1 2 5°45.0 0 9′E)是由韩国能源研究所和中国国土资源部海洋地质研究所于 1 995年 8月联合取自南黄海东南部水深 62m的巨厚泥质沉积区内 ,岩心长 60 65m。通过对岩心沉积物中浮游和底栖有孔虫动物群的分析 ,结合相应的AMS1 4 C测年数据 ,对黄海暖流及与其相伴生的南黄海东南部冷水体的形成及演化进行了初步的探讨。结果表明 ,黄海暖流及与其相伴生的南黄海东南部冷水体形成于距今约640 0日历年前。形成伊始 ,冷水体处于明显的强势状态 ,而暖流的强度却相对较弱 ,这一过程约持续了 2 2 0 0年左右 ,是南黄海东南部巨厚泥质沉积区的主要堆积期。直到距今 42 0 0日历年前后 ,黄海暖流的影响强度开始加强 ,冷水体相对减弱 ,直至达到现代的水文状态。     

Dissolved Fe2+ and ∑H2S Behavior in Sediments Seasonally Overlain by Hypoxic-to-anoxic Waters as Determined by CSV Microelectrodes

Variability of dissolved Fe²⁺ and ∑H₂S concentrations in porewaters were studied, using cathodic stripping voltammetry (CSV) microelectrodes, in sediments overlain by hypoxic waters in the summer from the southeastern region of Corpus Christi Bay, Texas (CCB) and the Mississippi River Bight (MRB), Louisiana. These measurements were complimented by sediment microcosm studies where oxygen concentrations in the overlying water were manipulated. Sulfate reduction rates, benthic oxygen demand, total reduced sulfide, porewater sulfate, and total organic carbon were also determined. Fe²⁺ and ∑H₂S were the major dissolved redox-reactive dissolved species in these sediments. During hypoxic conditions, an upward migration of porewater Fe²⁺ and ∑H₂S occurred, with Fe²⁺ reaching much higher maximum concentrations than ∑H₂S. Statistically significant (p < 0.05) differences in both Fe²⁺ and ∑H₂S occurred between sediments at the CCB and MRB study sites. Although both sites were Fe-dominated, reactive and dissolved iron were higher while ∑H₂S was lower at the MRB site. However, there were no statistically significant (p > 0.05) difference in regard to ∑H₂S between microcosm and field monitoring studies. Results indicated that, for Fe²⁺ and ∑H₂S, relatively large and rapid changes occurred in both the concentrations and distributions of these important porewater constituents in response to relatively short-term changes in overlying water oxygen content. Model calculations indicated that conditions in the sediments can be responsible for the induction of hypoxic conditions in the formation of hypoxic overlying waters in <6 days at CCB and ~20 days at MRB.     

Long-term hydrological,biogeochemical, and ecological data for the Kuparuk River,North Slope,Alaska

The Kuparuk River, located on Alaska's North Slope, is one of the most studied rivers in the Arctic. For nearly 40 seasons, physical, chemical, and biological parameters have been monitored continuously in a 5 km, 4th-order reach of the river during the short summer season when there is flow in this river. Flow decreases as the tundra begins to refreeze in the late autumn and these streams normally remain frozen until the spring freshet. The monitoring program has supported a 34-year phosphorus enrichment experiment conducted by the Arctic Long Term Ecological Research (LTER) program. Enrichment with phosphorus dramatically changed the structure and function of the primary producer community in the fertilized reach, with cascading effects in higher trophic levels. The datasets generated by this experiment have revealed significant increases in flow-weighted mean concentrations of nitrate and significant decreases in flow-weighted mean concentrations of dissolved organic N and P over time. In this paper, we present an overview of the nutrient concentration, discharge, macroinvertebrate, and Arctic grayling population datasets we have collected. The purposes of these datasets are to track changes resulting from the enrichment experiment, support ancillary research on responses of an Arctic stream to climate warming and permafrost thaw, and to provide input and validation data for models to predict future changes in Arctic streams.     

The European Water Framework Directive 2000/60/EC in the evaluation of the ecological status of watercourses. Case study: the river Chienti (central Apennines,Italy)

The quality of the river Chienti (eastern‐central Apennines, Italy) has been evaluated according to the Water Framework Directive 2000/60/EC, taking into consideration both biotic (animal and vegetable) and chemical parameters. In studying the biotic component, two indices were used: the E.B.I, Extended Biotic Index (version adapted to the Italian rivers), based on macroinvertebrates, and the EPI‐D, the Eutrophication and/or Pollution Index, based on diatoms. For both macroinvertebrates and diatoms, two samplings were conducted, one in June and the other in October 2003. Instead, according to the Italian Law 152/99 the chemical and bacteriological analyses were conducted monthly for the entire year. The results of biomonitoring and chemical‐bacteriological analyses unanimously demonstrated a good ecological situation for the upper section of the Chienti, though the situation tends to worsen as the river continues its descent and undergoes increased anthropogenic pressure. Data obtained were correlated with Spearman's coefficients and principal component analysis. Both statistical calculations showed clear, direct correlation between the two biotic indices and an inverse correlation between these and the chemical and bacteriological parameters. However, a few differences of judgement that emerged among the various indices highlight the importance of using them simultaneously in order to obtain a more accurate diagnosis of the ecological status of the watercourses.     

Detecting Vulnerable Marine Ecosystems in the Southern Ocean using research trawls and underwater imagery

To ensure that destructive bottom fishing activities do not have significant adverse impacts on Vulnerable Marine Ecosystems (VMEs) in high seas areas of the World Ocean, as required by United Nations General Assembly Resolution 61–105, knowledge of the locations of VMEs is required. Quantifying the occurrence and abundance of VME indicator taxa in research bottom-trawl samples, as well as from in situ observations with underwater photography, provides methods for detecting these ecosystems. A case study is presented in which a threshold density of indicator taxa was used as the basis for VME designation. In 2009, high densities of VME indicator taxa were encountered at 11 sites off th`e South Orkney Islands in the Atlantic sector of the Southern Ocean. In most cases, thresholds were exceeded by a limited number of VME indicator taxa, primarily representatives of the class Demospongiae (siliceous sponges), Hexactinellida (glass sponges) and Ascidiacea (tunicates). In situ imagery further showed the importance of bryozoans (lace corals), scleractinians (stony corals) and stylastrids (hydrocorals) in the study region. The approach outlined here, which relies on widely used sampling techniques, could be employed throughout the World Ocean to detect and document the presence of VMEs from existing datasets. To illustrate this point, the method was applied to a separate dataset, collected in 2006, from a research cruise off the northern Antarctic Peninsula, which led to the detection of 17 VMEs. The VMEs from both the 2006 and 2009 data are now registered and influence the management of fisheries in the Southern Ocean.