Combinations of biological attributes predict temporal dynamics of fish species in response to environmental changes

Assessing species vulnerability to environmental changes is a major challenge for conservation. Combinations of biological attributes have already been successfully used for this purpose, allowing large-scale prediction of inter-specific differences in demographic parameters (e.g. abundance) or endangered status. However, studies investigating whether biological attributes could be used to predict the temporal demographic responses of species in a changing environment are still scarce. In this work, we tackled this issue by taking advantage of a multi-decadal survey of concomitant changes in fish communities and environmental conditions within the Terminos lagoon (Mexico). Based on this rare dataset, we first characterized changes in abiotic parameters that occurred in this ecosystem since the 80s. Then, we adapted a multivariate index accounting for changes in both species abundance and occurrence to assess concomitant demographic changes for the 25 dominant fish species in the lagoon, classifying them into five various types of trajectories (“Increasing”, “Decreasing”, “Constant”, “Hump-shape” and “U-shape”). Finally, we assessed the accuracy in prediction of these temporal responses for all possible combinations of 15 biological attributes including taxonomy, ecological and life-history traits.Our results showed that fish specific demographic changes over the last 30 years could be accurately predicted (72% accuracy) using a combination of five biological attributes (spawning season, order, maximum salinity, width of salinity range, oocyte size) among which three could be related to the increase in average salinity occurred in the lagoon over this period. Appropriate sets of complementary biological attributes could similarly allow prediction of inter-specific differences in demographic changes in other areas, thereby offering an additional pragmatic tool for ecosystem managers to identify vulnerable species at the local scale.     

Identification and characterization of humic substances-degrading bacterial isolates from an estuarine environment

Bacterial isolates were obtained from enrichment cultures containing humic substances extracted from estuarine water using an XAD-8 resin. Eighteen isolates were chosen for phylogenetic and physiological characterization based on numerical importance in serial dilutions of the enrichment culture and unique colony morphology. Partial sequences of the 16S rRNA genes indicated that six of the isolates were associated with the alpha subclass of Proteobacteria, three with the gamma-Proteobacteria, and nine with the Gram-positive bacteria. Ten isolates degraded at least one (and up to six) selected aromatic single-ring compounds. Six isolates showed ability to degrade [(14)C]humic substances derived from the dominant salt marsh grass in the estuary from which they were isolated (Spartina alterniflora), mineralizing 0.4-1.1% of the humic substances over 4 weeks. A mixture of all 18 isolates did not degrade humic substances significantly faster than any of the individual strains, however, and no isolate degraded humic substances to the same extent as the natural marine bacterial community (3.0%). Similar studies with a radiolabeled synthetic lignin ([beta-(14)C]dehydropolymerisate) showed measurable levels of degradation by all 18 bacteria (3.0-8.8% in 4 weeks), but mineralization levels were again lower than that observed for the natural marine bacterial community (28.2%). Metabolic capabilities of the 18 isolates were highly variable and generally did not map to phylogenetic affiliation.     

How is ecosystem health defined and measured? A critical review of freshwater and estuarine studies

Assessing ecosystem health is an ongoing priority for governments, scientists and managers worldwide. There are several decades of scientific literature discussing ecosystem health and approaches to assess it, with applications to aquatic and terrestrial environments incorporating economic, environmental and social processes. We conducted a systematic review of studies that assess ecosystem health to update our current understanding of how ecosystem health is being defined, and provide new ideas and directions on how it can be measured. We focused the review on studies that used the term ‘ecosystem health’ or the equivalent terms ‘ecosystem integrity’, ‘ecosystem quality’ and ‘ecosystem protection’, in lotic freshwater and estuarine environments, and examined how many of these included explicit definitions of what ecosystem health means for their study system. We collected information about the temporal and geographical distribution of studies, and the types of indicators (biological, physical or chemical) used in the assessments. We found few studies clearly defined ecosystem health and justified the choice of indicators. Given the broad use of the term it seems impractical to have an overarching definition of ecosystem health, but rather an approach that is able to define and measure health on a case by case basis. A combination of biological, physical and chemical indicators was commonly used to assess ecosystem health in both estuarine and freshwater studies, with a strong bias towards fish and macroinvertebrate community metrics (e.g. diversity, abundance and composition). We found only two studies that simultaneously considered both freshwater and estuarine sections of the ecosystem, highlighting the significant knowledge gap in our understanding of the transfer of flow, nutrients and biota between the different systems—all key factors that influence ecosystem health. This review is the first to combine knowledge from both freshwater and estuarine ecosystem assessments and critically review how aquatic ecosystem health is defined and measured since the late-1990s, providing the basis for setting achievable management goals relating to ecosystem health into the future.     

Assessing the diversity of New Zealand freshwater harpacticoid copepods (Crustacea: Copepoda) using mitochondrial DNA (COI) barcodes

Taxonomic and ecological studies of freshwater harpacticoid copepods are limited globally by the ability to easily and accurately identify specimens. Here, we test the use of the mitochondrial cytochrome c oxidase subunit I (COI) gene locus as a tool for assessing the diversity of freshwater Harpacticoida. We obtained sequences from New Zealand harpacticoid copepods, representing two families, five genera and nine species, including the non-indigenous Elaphoidella sewelli. All species were delineated by the COI gene. However, high intraspecific diversity was evident among populations of Elaphoidella bidens (>12%), and between North and South Island populations of Bryocamptus pygmaeus (>18%), potentially indicating the presence of morphologically cryptic taxa. We suggest that mitochondrial DNA (COI) sequences can provide a useful tool for the routine identification of freshwater harpacticoid copepods. Applications of these data will include assessing species diversity and biogeography as well as assisting with the detection of non-indigenous species.     

Diapause of copepods as an element for stabilizing the parasite system of some fish helminths

The analysis of infection dynamics of copepods, which are the intermediate hosts of three helminth species of freshwater fishes (Triaenophorus crassus, Proteocephalus exiguus and P. percae), has shown that diapause in the life cycle of the copepods is favourable for preserving the infection in the waterbody until physiological prerequisites for successful infection of the final host are acquired. The peculiarity of a copepod's life cycle may determine the strategy of a parasite in its preimaginal phase as a waiting stage, and the duration of the residence of helminth larvae in copepods that have an obligatory diapause, is one of the elements the provide stability in parasite systems.     

Vulnerability of microcrustaceans to predation by the invasive filter-feeding mussel Limnoperna fortunei (Dunker)

Limnoperna fortunei is an Asian mussel introduced to South America around 1990. One of the most important impacts of this invader is probably its grazing on the plankton. In this study we evaluate the vulnerability of several planktonic microcrustaceans from the Paraná River floodplain to predation by adult L. fortunei. We conducted 2-h laboratory feeding experiments where the bivalves were offered microcrustaceans differing in overall body shape, size, and locomotive abilities. Ingestion and clearance rates for each taxon were estimated. Results suggest that, in addition to detritus and phytoplankton, microcrustaceans may be a very important food item for this invasive mollusc. Limnoperna fortunei can prey on larger organisms (up to 1100?µm) than Dreissena polymorpha, the European and North American invasive mussel.     

Spatial and temporal variation in the diet of the Pacific sand lance Ammodytes hexapterus in waters off the coast of British Columbia,Canada

Variation in the diet of the Pacific sand lance Ammodytes hexapterus was examined in three years (2009–2011) at four sites in British Columbia, Canada. There were 12 major taxa of prey in diets, eight of which were Crustacea, with copepods being by far the dominant taxon in all 12 site‐years. Of the 22 copepod taxa recorded, only Calanus marshallae and Pseudocalanus spp. occurred in all collections, and these two calanoid species dominated diets in terms of frequency of occurrence and total numbers of prey (Pseudocalanus spp. in most collections), and total prey biomass (C. marshallae in all collections). Based on an index of relative importance, C. marshallae was the primary prey at the two southerly sampling sites (Pine and Triangle Islands) and Pseudocalanus spp. at the two northerly sites (Lucy Island and S'G ang Gwaay). Based on an index of dietary overlap, the species composition of the copepod component of A. hexapterus diets overlapped very strongly at the northerly and the southerly pairs of sites in both a cold‐water La Niña year (2009) and a warm‐water El Niño year (2010), but overall there was more homogeneity amongst all four sites in the La Niña year.     

PLASTICITY OF OXYLIPIN METABOLISM AMONG CLONES OF THE MARINE DIATOM SKELETONEMA MARINOI (BACILLARIOPHYCEAE)1

Diatom oxylipins have been observed to deleteriously impact copepod reproductive success. However, field studies have revealed very variable and case‐dependent results. Therefore, the plasticity of diatom oxylipin metabolism was studied among four clones of the marine diatom Skeletonema marinoi Sarno et Zingone. Diatom oxylipin metabolism was studied by two lipoxygenase (LOX) activity assays carried out at different pH values and by oxylipin quantification. The four clones showed no major metabolic differences in terms of protein content or growth rate. However, two of the clones produced significantly higher levels of oxylipins than the other two. LOX activity measurements also indicated clonal variability in fatty acid oxidative metabolism. The presence of clone‐specific differences in oxylipin metabolism may play a role in shaping diatom population dynamics by conferring selective advantages to certain clones.