Latitudinal, seasonal and depth-dependent variation in growth, chemical composition and biofouling of cultivated Saccharina latissima (Phaeophyceae) along the Norwegian coast

The Norwegian coastline covers more than 10° in latitude and provides a range in abiotic and biotic conditions for seaweed farming. In this study, we compared the effects of cultivation depth and season on the increase in biomass (frond length and biomass yield), chemical composition (protein, tissue nitrogen, intracellular nitrate and ash content) and biofouling (total cover and species composition) of cultivated Saccharina latissima at nine locations along a latitudinal gradient from 58 to 69° N. The effects of light and temperature on frond length and biofouling were evaluated along with their relevance for selecting optimal cultivation sites. Growth was greater at 1–2 m than at 8–9 m depth and showed large differences among locations, mainly in relation to local salinity levels. Maximum frond lengths varied between 15 and 100 cm, and maximum biomass yields between 0.2 and 14 kg m−2. Timing of maximum frond length and biomass yield varied with latitude, peaking 5 and 8 weeks later in the northern location (69° N) than in the central (63° N) and southern (58° N) locations, respectively. The nitrogen-to-protein conversion factor (averaged across all locations and depths) was 3.8, while protein content varied from 22 to 109 mg g−1 DW, with seasonality and latitude having the largest effect. The onset of biofouling also followed a latitudinal pattern, with a delayed onset in northern locations and at freshwater-influenced sites. The dominant epibiont was the bryozoan Membranipora membranacea. Our results demonstrate the feasibility of S. latissima cultivation along a wide latitudinal gradient in North Atlantic waters and underscore the importance of careful site selection for seaweed aquaculture.

Identification of early biomarkers in proteomic profiles of the phaeophyte Saccharina japonica proximal to and beneath the front of bryozoan colonies

The sessile bryozoanMembranipora membranaceafrequently colonizes the phaeophyteSaccharina japonica.Identifying early colonization markers using proteomics could assist in the early detection of epiphytic contamination. Different sections of thallus tissue proximal to the bryozoan (i.e. the 1-cm zone beyond the boundary of the colony) and tissue from the colony-front (i.e. the narrow zone under the newly formed front of the colony after removing the bryozoans) were separated. From the proteomic profiles ofS. japonica, we detected 151 protein spots (99 up-, 50 down-, and 2 similarly regulated) from proximal tissues and 151 spots (69 up-, 75 down-, and 7 same-regulated) from colony-front tissues. Hundred and ten spots were detected from distal healthy thallus tissue, used as a control. The protein SSP15 was specifically up-regulated in the proximal tissues by ca. 1395-fold, while it exhibited little expression at the colony-front and in distal healthy tissues. ATPases were markedly up-regulated in both the proximal and colony-front tissues by 3198- and 2475-fold, respectively. Rpl1P and SRSF proteins were specifically up-regulated only in colony-front tissues by 5724- and 273-fold, respectively. Therefore, these proteins may be used as specific biomarkers for the early detection of bryozoan colonization on each tissue type of the seaweed.

Embryonic chirality and the evolution of spiralian left–right asymmetries

The group Spiralia includes species with one of the most significant cases of left–right asymmetries in animals: the coiling of the shell of gastropod molluscs (snails). In this animal group, an early event of embryonic chirality controlled by cytoskeleton dynamics and the subsequent differential activation of the genes nodal and Pitx determine the left–right axis of snails, and thus the direction of coiling of the shell. Despite progressive advances in our understanding of left–right axis specification in molluscs, little is known about left–right development in other spiralian taxa. Here, we identify and characterize the expression of nodal and Pitx orthologues in three different spiralian animals—the brachiopod Novocrania anomala , the annelid Owenia fusiformis and the nemertean Lineus ruber —and demonstrate embryonic chirality in the biradial-cleaving spiralian embryo of the bryozoan Membranipora membranacea . We show asymmetric expression of nodal and Pitx in the brachiopod and annelid, respectively, and symmetric expression of Pitx in the nemertean. Our findings indicate that early embryonic chirality is widespread and independent of the cleavage programme in the Spiralia. Additionally, our study illuminates the evolution of nodal and Pitx signalling by demonstrating embryonic asymmetric expression in lineages without obvious adult left–right asymmetries. This article is part of the themed issue ‘Provocative questions in left–right asymmetry’.

Cleavage modification did not alter early blastomere fates during bryozoan evolution

Stereotypic cleavage patterns play a crucial role in cell fate determination by precisely positioning early embryonic blastomeres. Although misplaced cell divisions can alter blastomere fates and cause embryonic defects, cleavage patterns have changed several times during animal evolution. Here, we analyze the evolutionary transition from spiral cleavage – a stereotypic pattern remarkably conserved in many protostomes – to the biradial cleavage of bryozoans. We characterize the cell lineage, MAPK signaling and expression of several developmental genes in the bryozoanMembranipora membranacea, and found that the fate and the genes expressed in the early bryozoan blastomeres are similar to their putative homologous blastomeres in spiral-cleaving embryos. The data indicate that cleavage geometry evolved independent from other developmental traits during the transition from spiral to biradial cleavage in the bryozoan lineage, revealing that stereotypic cleavage patterns can be evolutionarily modified without major changes to the molecular identity and fate of embryonic blastomeres.

Invasive bryozoan alters interaction between a native grazer and its algal food

The epiphytic bryozoan Membranipora membranacea encrusts the surface of kelp blades, causing recurrent large-scale defoliation events in kelp beds off the Atlantic coast of Nova Scotia, Canada. The gastropod Lacuna vincta grazes kelp, creating perforations that weaken blade tissues and increase the fragmentation rate. We assess the interaction between M. membranacea and L. vincta by measuring the grazing rate of snails on bryozoan-encrusted and non-encrusted kelp (Saccharina latissima) in no-choice and choice experiments in the laboratory conducted in November and December 2010. There was no effect of diet on grazing rate in no-choice experiments. In choice experiments, however, L. vincta grazed significantly more non-encrusted than encrusted kelp (7.1 versus 1.1 mg snail−1 d−1), and grazing rate of non-encrusted kelp was almost twice that in the no-choice experiment (3.8 mg snail−1 d−1), indicating that snails may avoid colonies of M. membranacea on partially encrusted kelp blades. We found no effect of diet on growth, reproduction and survival of snails maintained for four weeks on encrusted or non-encrusted kelp. By concentrating grazing damage on non-encrusted areas of blades, L. vincta may act synergistically with M. membranacea to increase the likelihood of blade breakage and canopy loss. This indirect effect of the invasive bryozoan could augment its direct effect on the standing biomass of native kelp beds and detrital export to adjacent communities.