The burrowing shrimp Neotrypaea californiensis is an important ecosystem engineer that inhabits estuaries along the US Pacific Northwest coast. This species plays an important role in the estuarine ecosystem but negatively impacts oyster aquaculture through its burrowing activities. Development of population models for burrowing shrimp management requires more detailed life history information and accurate estimates of age. Ageing studies have been limited for crustaceans because it is generally believed that they do not retain structures with annual deposits commonly used to age other marine organisms, when they moult their exoskeletons. A mesocosm growth experiment and field surveys were combined to compare the performance of two ageing techniques, quantification of autofluorescent lipofuscin and gastric mill ossicular lamellae, for estimating age in N. californiensis. Animals of known age were grown in outdoor mesocosms and sampled regularly to correlate age metrics with body size and true age. Lipofuscin concentration increased with time across multiple cohorts at the rate of 1.430 ± 0.060 ng µg−1 year−1. Lamellae counts also increased with time (4.922 ± 0.337 lamellae year−1). While age estimates based on lipofuscin concentration and lamellae counts generally agreed, carapace size did not correlate to either age metric. Lamellae counts from field collections suggest they are added sequentially with age but the relationship can vary by location. When used together, the application of both techniques may provide robust estimates of crustacean age especially when size-based measurements are imprecise.

Depletion of phytoplankton biomass by the introduced reef-forming polychaete Ficopomatus enigmaticus has previously been observed in the Mar Chiquita lagoon (37°40′S 57°23′W; Argentina), but the effect of polychaetes on the higher trophic levels is still unknown. To evaluate the effect of this polychaete on the zooplankton assemblage, replicated mesocosm experiments (N = 10) were performed during spring, summer and winter. Mesocosms with reefs and without reefs were installed and grazing intensity and the effect on the zooplankton assemblage by the polychaetes were assessed. Our results show that the reefs of F. enigmaticus generate minor changes in overall composition of zooplankton assemblage. Although the structure of the zooplankton assemblage was different between seasons, the impact of the reefs was not significant in any of them. There was no relationship between the decline of food resource by grazing and changes in the structure of the zooplankton assemblage. Thus, contrary to our hypothesis, the grazing impact of the invasive polychaete on the biomass of primary producers did not generate cascading effects to higher trophic levels. However, changes in some components of the zooplankton assemblage (e.g. cladocerans) clearly show that the reefs of F. enigmaticus have the potential to affect the structure of the zooplankton community. The lack of data of community composition and abundance of zooplankton before the invasion limits the understanding of how this polychaete might have affected the structure and abundance of the zooplankton of this lagoon. Nevertheless this work suggests that these changes may not be so significant.

Aquarium systems allow technically sophisticated experiments that promise new opportunities to answer urgent questions about reef coral biology, for instance assessing the responses to decreasing environmental pH and/or increased temperatures. Over recent years, long-term culture and (predominantly asexual) propagation of corals has become possible in such systems. At present however, only limited data are available that clarify whether or not responses of the coral holobiont are dominated by the acclimatization to life in captivity or continue to reflect, for example, taxonomic differences seen in nature. We studied the diversity of the symbiotic algae in corals and sea anemones after long-term aquaculture by analysis of their small subunit (SSU) ribosomal DNA gene. A field sample of Acropora clathrata from the Arabian Gulf which was used as a control contained clade C zooxanthellae. The aquarium corals also harboured clade C symbionts, but sequencing of the SSU DNA suggested that the analysed animals host different subclades. A prevalence of clade C is also found among corals from the Indo-Pacific region, the origin of most of the aquarium samples. An individual of the temperate sea anemone Anemonia sulcata (viridis) contained clade A symbionts, similar to those found in nature, even after nearly 10 years of co-culture with sea anemones (Entacmaea quadricolor) and corals hosting clade C symbionts. The results indicate that the specific host–symbiont association occurring in nature appears to persist over >2 years timescales in captivity, with no mixing of symbionts between hosts maintained in the same aquarium or apparent selection of stress-tolerant symbiont strains such as clade D.

Transgenic fish in development for aquaculture could escape from farms and interbreed with wild relatives in the nearby environment. Predicting whether escapes would result in transgene introgression is a major challenge in assessing environmental risks of transgenic fish. Previous studies have simulated gene flow from transgenic fish using mathematical modeling of fitness traits to predict the relative selective value of transgenic genotypes. Here, we present the first study of gene flow over the full life cycle in openly-breeding populations of transgenic animals, along with measurement of fitness traits. We conducted two invasion experiments in which we released two lines of growth-enhanced transgenic fish (T67 and T400), Japanese medaka (Oryzias latipes), into populations of wild-type (W) medaka in structured mesocosms. After several generations, the frequency of transgenic fish varied across replicates in the first invasion experiment (6 months), but the frequency of transgenic fish decreased in the second experiment (19 months). We also measured selected fitness traits in transgenic and wild-type medaka because these traits could be used to predict the relative selective value of a genotype. We found that: T400 males were more fertile than W males; offspring of W females lived longer than those with transgenic mothers; and W and T67 females reached sexual maturity sooner than T400 females. In contrast with other research that reported larger transgenic males had a mating advantage, we found that W males obtained more matings with females than T males; genetic background effects may account for our differing results as we compared W and T fish derived from different strains. The decreasing frequency of transgenic fish in the second invasion experiment suggests that transgenic fish had a selective disadvantage in the experimental environment. Our finding of transgenic advantage of some fitness traits and wild-type advantage in others is consistent with our invasion experiment results.

Seed longevity of plant species is an important topic in restoration management, and little is known about the effects of environmental conditions on seed survival and longevity under natural conditions. Therefore, the effect of groundwater level on the survival of seeds in the soil seed bank of a natural grassland community was investigated. Large soil cores, mesocosms, were sampled from a grassland site and transferred to two basins under a glass roof. The mesocosms were subjected to different groundwater-level treatments (high and low, respectively 5 and 30 cm below the soil surface) for nearly three years. After that period the soil seed bank of the mesocosms was sampled. In total 15 789 seeds of 38 taxa emerged from the experiment. Significant differences between the number of viable seeds that emerged in the two treatments were found for several species. More seeds of Glyceria fluitans, Cardamine pratensis and Myosotis palustris germinated in the high water-level treatment, whereas fewer seeds of Juncus spp., Cerastium fontanum and Stellaria media were found in this treatment than in the low water-level treatment. The experiment showed that the anoxic conditions prevailing in the high water-level treatment were beneficial to the survival of seeds of species of wet grassland communities. Species of dry grasslands, although represented by only two species, survived better under aerobic conditions.

Recent publications suggest that in large watersheds a large proportion (20 to 70%) of the net nitrogen input to the aquaticenvironment may be removed during water’s downstream path towards the outlet. In small watersheds there are few to no evaluationsof the importance of in-stream processes in the overall nitrogen budget due in part to the lack of simple and robustmethods for measuring in-stream nitrate uptake. We propose a comparative study for laboratory and field measurements on openmesocosms, 30 cm in diameter. Nitrate uptake was evaluated from the kinetics of disappearance of nitrate in water overlyingundisturbed sediment cores, both in the laboratory and in-situ. Using both laboratory and in-situ mesocosms was an effort todetermine whether the methods were comparable and applicable on a routine basis. Nitrate disappearance kinetics in the laboratoryyielded expected results, which are that nitrate uptake rates are linearly correlated to nitrate concentration in the watercolumn. In such conditions, our results show that the potential for nitrate uptake in streams can be calculated from the mass transfercoefficient. Our comparative study shows that incubations conducted in the laboratory intrinsically limit hyporheic exchanges,associated with small water level fluctuations, which may in fact prevail in the field as the in-situ incubations have shown.In-situ experiments yielded unexpected results, such as the succession of disappearance and gain of nitrate in the mesocosmsthrough time. This was attributed to hyporheic exchanges, both natural and artificially induced by the design of the mesocosms.Both methods should be considered for future nitrate uptake studies as they yield complementary results, provided that somesimple changes are made in the design of in-situ mesocosms.

Changes in relative abundance of estuarine epipelic microalgae along an estuarine gradient were investigated, and population densities of different species along a small-scale nutrient gradient generated by a sewage treatment outfall and in laboratory mesocosms enriched with ammonium were also studied. The relative abundance of certain species of epipelic diatoms was related to location along the estuarine salinity and nutrient gradient: Navicula gregaria and N. phyllepta were abundant at oligo- and mesohaline sites respectively, and Pleurosigma angulatum and Plagiotropis vitrea were abundant at polyhaline sites. On a smaller spatial scale, though there were no significant patterns in microalgal biomass in relation to nutrient enrichment, there were significant differences in the population densities of different epipelic species along a multivariate nutrient gradient (decreasing concentrations of ammonium, nitrite, silicate, organic content, and increasing salinity and pore-water nitrate concentrations) away from a sewage outfall along a saltmarsh creek. The diatoms Nitzschia sigma and Gyrosigma limosum and the cyanobacteria Oscillatoria limosa and O. princeps had significantly higher population densities near the outfall, and Navicula phyllepta, N. pargemina, Nitzschia frustulum, Cylindrotheca signata and Pleurosigma angulatum were significantly more abundant at the seaward end of the gradient. In laboratory tidal mesocosms, sediment cores from along the gradient had their pore-water ammonium concentrations increased to 380–450 μM NH4+. After 26 days, the population densities of Gyrosigma fasciola, G. littorale, P. angulatum, N. phyllepta, Cylindrotheca signata, C. closterium and Niztschia apiculata were significantly reduced, while those of G. limosum, N. sigma, Scolioneis tumida and O. limosa were unaffected, or were significantly higher compared with control cores. Laboratory manipulations of ammonium concentrations supported the observed field distributions, indicating that epipelic species do have different trophic preferences and ammonium concentration may be a significant factor in determining estuarine species composition of epipelic algae.