Using multivariate analysis and stable isotopes to assess the effects of substrate type on phytobenthos communities

For more than a century, artificial substrates have been employed in phytobenthos studies. In the present study, we compared the phytobenthos community structure in a field experiment over 3 seasons (summer, autumn, and winter) on 3 types of artificial substrates (brick, brown clay tiles, and grey clay tiles) and 3 natural substrates (macrophytes, rocks, and sediment) in a small, temperate system. A combination of multivariate analyses (cluster, multi-response permutation procedure, indicator species [IndVal], and canonical correspondence analysis [CCA]) and stable isotope analysis was used. We identified 96 total phytobenthos taxa. Artificial substrates resulted in different substrate communities, as shown by stable isotope analysis, cluster analysis, and a multi-response permutation procedure, with only those communities growing on grey tiles being similar to natural substrate communities. Overall, artificial substrates exhibited slightly higher species richness compared to natural substrates over the 3 seasons, although there were no significant differences (p > 0.05). Phytobenthos grown on brown tiles, rocks, and bricks showed seasonal variability of the carbon isotope δ13C values using one-way ANOVA (p < 0.05). Phytobenthos community structure did not show great seasonal variation; however, CCA identified water flow, conductivity, ammonium, phosphate, and water depth as important in structuring phytobenthos communities on different substrates. IndVal analysis showed that common phytobenthos taxa were not restricted to a single substrate, but preference was generally high for natural substrate, especially rocks, compared to artificial substrates. Substrate microhabitat type seems to influence the communities within the study areas

Physical and biological processes at the Subtropical Convergence in the South-west Indian Ocean

A detailed hydrographic and biological survey was conducted in the region of the Subtropical Convergence in the Indian sector of the Southern Ocean in April 2007. Hydrographic data revealed that the subsurface expression of the Subtropical Convergence (at 200 m), marked by the 10°C isotherm, appeared to meander considerably between 41°S and 42°15’S. Total surface chlorophyll- a concentration was low and ranged from 0.03 to 0.42 µg l–1 and was always dominated by the pico- ( 0.05). The zooplankton community was dominated, numerically and by biomass, by mesozooplankton comprising mainly copepods of the genera, Oithona,Paraeuchaeta, Pleuromamma, Calanus and Clausocalanus. An exception was recorded at those stations in the region of the front where the tunicate, Salpa thompsoni, dominated the total zooplankton biomass

The regulation of particle transport within the ventral groove of the mussel gill (Mytilus edulis) in response to variations in envrionmental conditions

In order to understand thoroughly the feeding processes of the blue mussel, Mytilus edulis, in response to the variable environmental conditions it experiences in nature, it is important to examine individually the different components that comprise its feeding system. The ciliated ventral food groove represents one of these primary components, within which the majority of food particles trapped by the gill are transported to the labial palps and gut. The ability of mussels to adjust food transport rates within this groove could serve as an important feeding regulatory mechanism in response to variations in the environment. -- Using video endoscopy, mucous strand velocities in the ventral groove of mussels Mytilus edulis were determined over variable time periods and in response to short-term manipulations of ambient particle concentration, temperature and particle type. Mucous strand velocities decreased with increasing ambient particle concentration and particle load on the gill, and also when particle type was switched from algae to sediment. This evidence supports the hypothesis that M. edulis possesses compensation mechanisms involving particle transport at the level of the ventral groove cilia to deal with short-term changes in the environment. Furthermore, mucous strand velocity in the ventral groove increased when the ambient temperature of mussels acclimated to 4.5ﾟC was increased to 15ﾟC. This response is consistent with standard physiological responses of ciliary systems to changes in temperature. Changes in velocity over time were also observed, but there was no consistent pattern

Population dynamics and seasonal lipid cycles in hyperbenthic crustaceans from a cold-ocean environment (Conception Bay, Newfoundland): Mysis mixta (Mysidacea) and Acanthostepheia malmgreni (Amphipoda)

Life cycles and seasonal changes in density, biomass, growth, secondary production and lipids in Mysis mixta and Acanthostepheia malmgreni from a 240-m deep site in Conception Bay, Newfoundland, were studied from October 1998 to November 2000. The primary aim was to provide life-history and ecological information on populations inhabiting the hyperbenthos of Conception Bay, and to relate the seasonal lipid and fatty acid dynamics to each species' life cycle and to the occurrence and quality of the annual phytoplankton bloom. -- Life spans and reproductive cycles were remarkably similar in the two species, with the release of free-living juveniles from mature females occurring in April and May when bloom material was settling to the hyperbenthos. Females reproduced once and then died at age-2.5 years following a 5-month brooding period of larval stages. The biennial life cycles of both populations resulted in the presence of 2 cohorts of each species co-existing at most times, although a marked annual alternation in cohort dominance occurred in the amphipod population. Annual production:biomass (P/B) ratios in the mysid population were similar in both years, indicating consistent recruitment from year to year. In contrast, the alternation in cohort strength in A. malmgreni had significant repercussions in the success of this population, reflected in a lower P/B ratio in 1999 than in 2000. -- Divergent patterns in lipids, fatty acids, and specific fatty acid marker ratios reflected differing life styles, diets and critical periods of energy accumulation and utilisation in M. mixta and A. malmgreni . Influenced by the seasonally productive and perpetually cold environment created by the Labrador Current, M. mixta and A. malmgreni both accumulated high levels of lipid reserves similar to those attained by other cold-water zooplankton. Maximum lipid stores were observed in females, although the maximum lipid content in M. mixta was over twice that in A. malmgreni. Lipid levels increased with maturity, and developing mysids exhibited a particularly rapid accumulation of triacylglycerols and diatom-associated fatty acids at the start of the spring bloom. Unlike the mysids, juvenile amphipods did not begin to develop sexual characteristics or accumulate significant amounts of triacylglycerol or phytoplanktonic fatty acids until after the spring bloom material had already reached the hyperbenthos in May. This study reveals a dependence of M. mixta and A. malmgreni on seasonal lipid accumulation for reproduction, and the existence of trophic links between their populations and the pelagic production cycle (i.e. benthic-pelagic coupling). Increased mobility and a broad range of prey types provided M. mixta with sufficient opportunities to accumulate essential fatty acids rapidly. However, A. malmgreni was restricted to a lower quality diet than was M. mixta, and the trophic connection between A. malmgreni and production in the euphotic zone was less pronounced

Seasonal and developmental variation in the fatty acid composition of Mysis mixta (Mysidacea) and Acanthostepheia malmgreni (Amphipoda) from the hyperbenthos of a cold-ocean environment (Conception Bay, Newfoundland)

Fatty acid composition in different life-history stages of Mysis mixta (Crustacea, Mysidacea) and Acanthostepheia malmgreni (Crustacea, Amphipoda) from Conception Bay, Newfoundland, was examined throughout 1999 and 2000. The primary aim was to relate the seasonal fatty acid dynamics to each species’ life cycle and to published information on the occurrence and quality of the annual phytoplankton bloom. Divergent patterns in fatty acid composition and specific fatty acid marker ratios reflected different life styles, diets and critical periods of energy accumulation and utilization in M. mixta and A. malmgreni. Changes in fatty acids reflected the sequence of plankton taxa during and following the spring bloom, starting with diatoms and dinoflagellates and ending with copepods. Immature mysids exhibited a particularly rapid accumulation of diatom-associated fatty acids at the start of the spring bloom, probably owing to the high degree of motility of M. mixta and the broad range of prey types available to this species. In contrast, immature amphipods did not begin to accumulate significant amounts of phytoplankton fatty acids until after the spring bloom material had settled to the hyperbenthos in May. Differences in fatty acid composition indicated that A. malmgreni was restricted to a lower quality diet than was M. mixta and that the trophic connection between A. malmgreni and production in the euphotic zone was weaker

Distribution of benthic diatom communities in a permanently open temperate estuary in relation to physico-chemical variables

Publisher versionThe spatial and temporal patterns in benthic diatom community structure in temperate permanently open estuaries are poorly understood. In this study, we used a combination of multivariate and diversity indices to elucidate environmental factors associated with diatom community structure in the Kowie Estuary, South Africa. Benthic diatom samples were collected from three sites corresponding to the upper, middle and lower reaches of the estuary on four occasions over the period early spring 2012 to winter 2013. Among the 89 benthic diatoms observed, Entomoneis paludosa (W Smith) Reimer, Nitzschia reversa W Smith, Nitzschia closterium (Ehrenberg) W Smith, Pleurosigma elongatum W Smith, P. salinarum (Grunow) Grunow, Staurosira elliptica (Schumann) DM Williams & Round, Surirella brebissonii Krammer & Lange-Bertalot, and Surirella ovalis Brébisson were the numerically dominant species. Principal component analysis demonstrated that the diatom community structure was determined by a variety of factors including nutrient (ammonia, nitrate) concentrations, hydrology (e.g., water depth and flow) and pH. Hierarchical cluster analysis revealed the absence of any distinct spatial patterns, although distinct benthic diatom communities were recorded during the different sampling periods. The species richness was highest in the middle reach, decreasing from early spring to summer in all reaches. The results of the study provide important insights into the various factors that structure benthic diatom community composition within a permanently open temperate southern African estuary

Developmental and spatial variations in the diet signatures of hyperbenthic shrimp Nauticaris marionis at the Prince Edward Islands based on stable isotope ratios and fatty acid profiles

Publisher versionThe caridean shrimp Nauticaris marionis is an ecologically important species in the benthic community around the sub-Antarctic Prince Edward Islands (PEI) as it represents a key prey item for a variety of top predators breeding on the islands. We hypothesized that the diet of N. marionis shifts during its development, and that spatial variability in food availability results in differentiation in the diet signatures of specimens collected from various locations of the shelf waters around the PEI. Specimens were collected from nine stations (depth range 70 to 240 m) around the PEI at inter-island shelf (from west to east: upstream, between and downstream) and nearshore regions during austral autumn 2009. Stable isotope and fatty acid data both revealed spatial and developmental variations in the shrimp diet. Nearshore shrimp were more 13C-enriched than those from the inter-island region, suggesting increased kelp detritus entered the food web in the nearshore regions. The shrimp showed increases in δ13C and δ15N signatures (and trophic position) with an increase in body size, resulting in distinctions between size classes that reflected shifts in their trophic niche through development. The fatty acid profiles similarly indicated distinctions in diet with increased shrimp size (in the deep regions), and spatial variability was evident in relation to region and depth. All shrimp contained large proportions of polyunsaturated and essential fatty acids, indicating that the quality of food consumed was similar between regions despite the diet variability. Our results provide new dietary information about a key species operating near the base of the food web at the highly productive PEI, and show that there were no areas of enhanced nutrition available to the shrimp. As such, there was no nutritional advantage to shrimp inhabiting any specific region around the PEI

Effects of substrate on essential fatty acids produced by phytobenthos in an austral temperate river system

Publisher versionAquatic and riparian habitats increasingly are affected by anthropogenic stressors, but the effects of these stressors on the nutritional quality of primary producers are often unknown. We compared essential fatty acids (EFAs) in the phytobenthos (benthic algae) growing on different substrate types (bricks, clay tiles, rocks, macrophytes, and sediments) at 2 river sites subject to differing anthropogenic stressors (using nutrient concentration as a proxy) in a temperate southern hemisphere location. We hypothesized that the fatty acid (FA) content of phytobenthos changes in response to shifts in local nutrient availability but not substrate type. EFA content (18∶2ω6, 18∶3ω3, 20∶4ω6, 20∶5ω3, and 22∶6ω3) in the phytobenthos differed overall among substrates, sites, and seasons and was generally greater in summer than in autumn and winter. EFA content was significantly greater on artificial than natural substrates and was greater at the nutrient-enriched downstream site than at the upstream site. The response of EFA content at the downstream site suggests that land use affected the synthesis of EFAs by phytobenthos and, hence, food quality for aquatic consumers. These findings indicate a potential link between physical factors, such as substrate availability and land management, and the quality of basal food resources available to primary consumers in aquatic food webs