A method to establish an “immortalized F2” sporophyte population in the economic brown alga Undaria pinnatifida (Laminariales: Alariaceae)

Studies of quantitative trait loci based on genetic linkage maps require the establishment of a mapping population. Permanent mapping populations are more ideal than temporary ones because they can be used repeatedly. However, there has been no reported permanent sporophyte population of economically important kelp species. Based on the characteristics of the kelp life cycle, we proposed a method to establish, and then constructed experimentally, an “immortalized F₂” (IF₂) population of Undaria pinnatifida. Doubled-haploid “female” and “male” sporophytes were obtained through the parthenogenesis of a female gametophyte clone and the selfing of a “monoicous” gametophyte clone (originally male), respectively, and they were used as the parents. The F₁ hybrid line was generated by crossing the female and male gametophytes derived from the respective female and male parents. Full-sibling F₂ gametophyte clones, consisting of 260 females and 260 males, were established from an F₁ hybrid sporophyte. Thirty-five females and 35 males were randomly selected and paired to give rise to an IF₂ population containing 35 crossing lines. A parentage analysis using 10 microsatellite markers confirmed the accuracy of the IF₂ population and indicated the feasibility of this method. This proposed method may be adapted for use in other kelp species, and thus, it will be useful for genetic studies of kelp.     

Induction of metamorphosis in the sand dollar Peronella japonica by thyroid hormones

The larva of the sand dollar Peronella japonica lacks a mouth and gut, and undergoes metamorphosis into a juvenile sand dollar without feeding. In the present study, it was found that thyroid hormones accelerate the metamorphosis of P. japonica larvae. The contents of thyroid hormones in larvae increased gradually during development. Thiourea and potassium perchlorate, inhibitors of thyroid hormone synthesis, delayed larval metamorphosis and simultaneously repressed an increase in the content of thyroxine in the larval body. These results suggest that the P. japonica larva has a system for synthesis of thyroid hormones that act as factors for inducing metamorphosis.     

Complete regulation of development throughout metamorphosis of sea urchin embryos devoid of macromeres

The developmental potential of the animal cap (consisting of eight mesomeres) recombined with micromeres or of micromere progeny was examined in sea urchin embryos. The embryos derived from the animal cap recombined with a quartet of micromeres or their descendants developed into four-armed plutei. After feeding, the larvae developed into eight-armed plutei. The left-right polarity of the larvae, recognized by the location of the echinus rudiment, was essentially normal, regardless of the orientation of animal-vegetal polarity in micromeres combining with the animal cap. The larvae had sufficient potential to metamorphose into complete juvenile sea urchins with five-fold radial symmetry. Cell lineage tracing experiments showed that: (i) macromere progeny were not required for formation of the typical pattern of primary mesenchyme cells derived exclusively from large micromeres; (ii) the progeny of large micromeres did not contribute to cells in the endodermal gut with three compartments of normal function; (iii) the presumptive ectoderm had the potential to differentiate into endodermal gut and mesodermal secondary mesenchyme cells, from which pigment cells likely differentiated; and (iv) behavior of the progeny of small micromeres was the same as that in normal embryos through the gastrula stage. These results indicate that the mesomeres respecify their fate under the inductive influence of micromeres so perfectly that complete juvenile sea urchins are produced.     

Bacterial diversity in relation to secondary production and succession on surfaces of the kelp Laminaria hyperborea

Kelp forests worldwide are known as hotspots for macroscopic biodiversity and primary production, yet very little is known about the biodiversity and roles of microorganisms in these ecosystems. Secondary production by heterotrophic bacteria associated to kelp is important in the food web as a link between kelp primary production and kelp forest consumers. The aim of this study was to investigate the relationship between bacterial diversity and two important processes in this ecosystem; bacterial secondary production and primary succession on kelp surfaces. To address this, kelp, Laminaria hyperborea, from southwestern Norway was sampled at different geographical locations and during an annual cycle. Pyrosequencing (454-sequencing) of amplicons of the 16S rRNA gene of bacteria was used to study bacterial diversity. Incorporation of tritiated thymidine was used as a measure of bacterial production. Our data show that bacterial diversity (richness and evenness) increases with the age of the kelp surface, which corresponds to the primary succession of its bacterial communities. Higher evenness of bacterial operational taxonomical units (OTUs) is linked to higher bacterial production. Owing to the dominance of a few abundant OTUs, kelp surface biofilm communities may be characterized as low-diversity habitats. This is the first detailed study of kelp-associated bacterial communities using high-throughput sequencing and it extends current knowledge on microbial community assembly and dynamics on living surfaces.     

Survival of kelp adjacent to areas grazed by sea urchins in New South Wales,Australia

Abstract The sea urchin Centrostephanus rodgersii grazes areas of reef free of large brown algae (the barrens habitat). Survival of the kelp Ecklonia radiata adjacent to patches of barrens habitat was compared to that in the centre of kelp forests (centre) and edges of forests not adjacent to patches of barrens habitat (ungrazed). Estimates of rates of instantaneous mortality for tagged plants, as described by the slope of a negative exponential model (± 95% CI) were: barrens, 0.078 ± 0.004; centre, 0.051 ± 0.004 and ungrazed edge, 0.065 ± 0.007. Survival of plants was greatest in the middle of forests and least on the margins of patches of barrens habitat. A significant proportion of mortality in the barrens and centre positions was caused by herbivorous fish. When these plants were excluded from analysis there were no significant differences in survival between the barrens and ungrazed positions. It is concluded that C. rodgersii has little impact on the abundance of Ecklonia outside sharply defined boundaries.     

Algal biochar: effects and applications

Algae represent a promising target for the generation of bioenergy through slow pyrolysis, leading to the production of biochar. This study reports experiments conducted on the production of freshwater and saltwater macroalgal biochar in pilot‐scale quantities, the physical and chemical characteristics of the biochars, and their impact on plant growth. The biochars are low in carbon (C) content, surface area and cation exchange capacity, while being high in ash and nutrients. Trace element analysis demonstrates that macroalgal biochar produced from unpolluted water does not contain toxic trace elements in excess of levels mandated for unrestricted use as a biosolids amendment to soils. Pot trials conducted using a C and nutrient‐poor soil, without and with additional fertilizer, demonstrate dramatic increases between 15 and 32 times, respectively, in plant growth rate for biochar treatments compared with the no biochar controls, with additional smaller increases when fertilizer was added. Pot trials conducted using a relatively fertile agricultural soil showed smaller but significant impacts of biochar amendment over the controls.     

Does restoration of a habitat‐forming seaweed restore associated faunal diversity?

Declines of habitat‐forming organisms in terrestrial and marine systems can lead to changes in community‐wide biodiversity. The dominant habitat‐forming macroalga Phyllospora comosa (Fucales) went locally extinct along the metropolitan coastline of Sydney in the 1980s. However, the consequences of that disappearance to the associated faunal diversity in these habitats, and whether Phyllospora is ecologically redundant with respect to the biodiversity it supports, are not known. Efforts are underway to restore Phyllospora, and the capacity to enhance local biodiversity is an important component of the rationale for restoration. We compared epifaunal diversity (abundances and composition) between Phyllospora and two other co‐occurring habitat‐forming algae, the kelp Ecklonia radiata and the fucoid Sargassum vestitum, and determined whether Phyllospora transplanted to Sydney developed different epifaunal communities than undisturbed thalli and controls. Where the 3 species naturally co‐occurred, Phyllospora supported different abundances of taxa than Ecklonia and Sargassum, as well as different composition at finer scales, which suggests that this species is not completely redundant and that its disappearance may have affected local biodiversity. Similarly, assemblages on transplanted Phyllospora differed from those on Ecklonia and Sargassum at restored sites, but did not always resemble assemblages from extant natural Phyllospora populations, even 18 months after transplantation. These experiments indicate that restoration of key habitat‐forming seaweeds not only recovers the algal species but also reduces risks of losing habitat diversity for epifauna and their consumers. However, restoration of all the original biodiversity associated with these seaweeds can be a difficult, complex, and long‐term process.     

Global regime shift dynamics of catastrophic sea urchin overgrazing

A pronounced, widespread and persistent regime shift among marine ecosystems is observable on temperate rocky reefs as a result of sea urchin overgrazing. Here, we empirically define regime-shift dynamics for this grazing system which transitions between productive macroalgal beds and impoverished urchin barrens. Catastrophic in nature, urchin overgrazing in a well-studied Australian system demonstrates a discontinuous regime shift, which is of particular management concern as recovery of desirable macroalgal beds requires reducing grazers to well below the initial threshold of overgrazing. Generality of this regime-shift dynamic is explored across 13 rocky reef systems (spanning 11 different regions from both hemispheres) by compiling available survey data (totalling 10 901 quadrats surveyed in situ) plus experimental regime-shift responses (observed during a total of 57 in situ manipulations). The emergent and globally coherent pattern shows urchin grazing to cause a discontinuous ‘catastrophic’ regime shift, with hysteresis effect of approximately one order of magnitude in urchin biomass between critical thresholds of overgrazing and recovery. Different life-history traits appear to create asymmetry in the pace of overgrazing versus recovery. Once shifted, strong feedback mechanisms provide resilience for each alternative state thus defining the catastrophic nature of this regime shift. Importantly, human-derived stressors can act to erode resilience of desirable macroalgal beds while strengthening resilience of urchin barrens, thus exacerbating the risk, spatial extent and irreversibility of an unwanted regime shift for marine ecosystems.     

Ichtyotoxic activity of extracts from Mexican marine macroalgae

Seventy-three species of macroalgae from the Mexican Pacific, Atlantic and Caribbean coast were screened for ichtyotoxic activity. Ethanolic, acetonic and aqueous extracts were prepared and tested against the fish Carassius auratus. The extracts were classified on the basis of their effects as: toxic if the fish died in two hours or less; moderately toxic, if the organism behaved abnormally but death did notoccur, and non-toxic if the fish did not display any change. 79% species were ichtyotoxic to some degree. Extracts of 39 species were toxic, with at least one extract with lethal effects, 19 were moderately toxic and 15 species were non-toxic. Only the extracts ofDictyota bartayresiana, Dictyota cervicornis,Lobophora variegata, Bryothamnion triquetrum and Laurencia obtusa were toxic in all three solvents. The acetone and ethanol extracts were more active, and therefore are more suitable for extraction of toxic substances. This revised version was published online in August 2006 with corrections to the Cover Date.     

Diversity of carbon use strategies in a kelp forest community: implications for a high CO2 ocean

Mechanisms for inorganic carbon acquisition in macroalgal assemblages today could indicate how coastal ecosystems will respond to predicted changes in ocean chemistry due to elevated carbon dioxide (CO₂). We identified the proportion of noncalcifying macroalgae with particular carbon use strategies using the natural abundance of carbon isotopes and pH drift experiments in a kelp forest. We also identified all calcifying macroalgae in this system; these were the dominant component of the benthos (by % cover) at all depths and seasons while cover of noncalcareous macroalgae increased at shallower depths and during summer. All large canopy‐forming macroalgae had attributes suggestive of active uptake of inorganic carbon and the presence of a CO₂ concentration mechanism (CCM). CCM species covered, on average, 15–45% of the benthos and were most common at shallow depths and during summer. There was a high level of variability in carbon isotope discrimination within CCM species, probably a result of energetic constraints on active carbon uptake in a low light environment. Over 50% of red noncalcifying species exhibited values below ?30‰ suggesting a reliance on diffusive CO₂ uptake and no functional CCM. Non‐CCM macroalgae covered on average 0–8.9% of rock surfaces and were most common in deep, low light habitats. Elevated CO₂ has the potential to influence competition between dominant coralline species (that will be negatively affected by increased CO₂) and noncalcareous CCM macroalgae (neutral or positive effects) and relatively rare (on a % cover basis) non‐CCM species (positive effects). Responses of macroalgae to elevated CO₂ will be strongly modified by light and any responses are likely to be different at times or locations where energy constrains photosynthesis. Increased growth and competitive ability of noncalcareous macroalgae alongside negative impacts of acidification on calcifying species could have major implications for the functioning of coastal reef systems at elevated CO₂ concentrations.