Microsatellite markers for the giant kelp Macrocystis pyrifera

We report the isolation and characterization of 16 microsatellite loci to study the population genetics of the giant kelp, Macrocystis pyrifera. Markers were obtained by screening a genomic library enriched for microsatellite motifs. Of the 37 primer pairs defined, 16 amplified clean polymorphic microsatellites and are described. These loci identified a number of alleles ranging from three to forty (mean = 16.5, and gene diversity ranging from 0.469 to 0.930 (mean = 0.774). The isolation and characterization of these highly polymorphic markers will greatly benefit much needed studies on the molecular ecology of this important macroalga.     

Resource translocation drives 13C fractionation during recovery from disturbance in giant kelp,Macrocystis pyrifera

Resource allocation and translocation are fundamental physiological functions for autotrophs. The mobilization and use of resources drive population dynamics by regulating growth and recovery of individuals, but also influences ecosystem‐level processes such as primary productivity and carbon cycling. This study provides the first observation of translocation‐driven gradients of δ¹³C in macroalgae, a critically important phenomenon recognized in vascular plants for decades. A ~10‰ δ¹³C increase in new giant kelp (Macrocystis pyrifera) fronds relative to mature canopy blades was produced after 5 weeks following a biomass removal experiment, more than twice the variation typical for macroalgae. The observed δ¹³C patterns are consistent with tissue enrichment following resource translocation in vascular plants. The analogous source‐sink relationships and consistent translocation patterns in Macrocystis and vascular plants suggest that translocation of stored resources is critical for structuring productivity and recovery from disturbance in important, habitat‐forming macroalgae such as kelps and fucoids.     

Factors correlating with deterioration of giant kelp Macrocystis pyrifera (Laminariales, Heterokontophyta) in an aquarium setting

Survival of the giant kelp, Macrocystis pyrifera (Linnaeus) C. Agardh, in its natural habitat is governed by abiotic and biotic factors such as temperature, light, nutrients, current velocity, and predators. Factors affecting the survival of the alga in an aquarium setting, however, have not been investigated. The National Museum of Marine Biology and Aquarium (NMMBA), in subtropical Taiwan, is the only aquarium in the world that displays giant kelp that does not have naturally occurring specimens in nearby waters. Giant kelp displayed in aquaria often deteriorates within a 3-month period, yet the cause of this mortality is unknown. We investigated abiotic and biotic parameters affecting survival of giant kelp in aquaria over a 3-month period. The results indicated that temperature, salinity, pH, light, and nutrient concentrations did not affect giant kelp survival. However, the massive proliferation of epiphytic diatoms on kelp blades (from 7?×?10² cells cm^?2 initially to 3?×?10⁴ cells cm^?2 after 1 month) was identified as being the most likely candidate affecting survival of giant kelp in an aquarium setting. Potential factors that may stimulate epiphyte proliferation include lack of epiphytic algae control via predation, high nutrient concentrations, a weak current, and a generally stable environment.     

Persistence and transport of fauna on drifting kelp (Macrocystis pyrifera (L.) C. Agardh) rafts in the Southern California Bight

Drifting rafts of Macrocystis pyrifera may connect isolated kelp forests in the Southern California Bight. To determine which species might utilize this dispersal mechanism, faunal samples from natural drifting rafts and attached M. pyrifera plants were collected during five cruises between March 1995 and December 1997. These rafts, which can be considered as floating islands, were aged and the macroinvertebrate assemblage enumerated. There was no significant relationship between raft age and species richness, or between species richness and distance offshore, which contrasts with predictions based on island biogeography. Species richness, however, was related to raft weight. Patterns of species presence and density were investigated relative to raft age for the species most frequently associated with rafts. Only one species, the isopod Idotea resecata, was found on all sampled rafts. Some species increased in frequency with raft age and others decreased, but only one relationship, a decline in the frequency of the anemone Epiactis prolifera with raft age was significant. When species density was examined over all cruises, only I. resecata had a significant change in density (an increase) with raft age, but additional significant relationships were found when species density patterns were considered by cruise. The results of all the tests were combined to provide a measure of "raft success". Nine of the most frequent 19 species had a positive score, indicating a favorable response to rafting, seven were unaffected, and two species had negative responses to rafting. Extinction times were calculated using species abundance and raft age relationships. Two species (E. prolifera and Paracerceis cordata), were predicted to persist on rafts for only about 100 days, which is the maximum estimated raft lifetime. All other species were predicted to persist for longer periods if the rafts floated longer. Kelp fauna that begin rafting appear to be largely unaffected by rafting, and hence dispersal on kelp rafts is possible for many members of the kelp forest community.     

Age of drifting Macrocystis pyrifera (L.) C. Agardh rafts in the Southern California Bight

Macrocystis pyrifera plants that detach from the substratum float to the surface and, if they do not become entangled or wash immediately to the shore, may drift at the surface for an unknown period of time. These rafts provide habitat for a variety of coastal and pelagic fauna. The distances dispersed and the period available for species to utilize these habitats, however, depend on the longevity of the raft and methods for determining the age of rafts are unknown. A method to age drifting M. pyrifera rafts based on a change in length of blades (BL) following detachment is validated here. This technique determines the period of time since detachment and not the actual age of the plant. In general, average BL decreases from initial attached values of 50-60 to about 0 cm, when rafts sink. The rate of aging, or deterioration of BL, is related to water temperature, and sets the period a raft stays afloat. Maximal estimates of ages of rafts were between 63 and 109 days, depending on the exact method used. Their lifetime will limit the distances dispersed by kelp rafts in Southern California, and this methodology will be useful for determining the temporal patterns of abundance of fauna associated with rafts.     

The giant kelp Macrocystis pyrifera presents a different nonphotochemical quenching control than higher plants

Here the mechanisms involved in excitation energy dissipation of Macrocystis pyrifera were characterized to explain the high nonphotochemical quenching of chlorophyll a (Chla) fluorescence (NPQ) capacity of this alga. We performed a comparative analysis of NPQ and xanthophyll cycle (XC) activity in blades collected at different depths. The responses of the blades to dithiothreitol (DTT) and to the uncoupler NH4Cl were also assayed. The degree of NPQ induction was related to the amount of zeaxanthin synthesized in high light. The inhibition of zeaxanthin synthesis with DTT blocked NPQ induction. A slow NPQ relaxation upon the addition of NH4Cl, which disrupts the transthylakoid proton gradient, was detected. The slow NPQ relaxation took place only in the presence of de-epoxidated XC pigments and was related to the epoxidation of zeaxanthin. These results indicate that in M. pyrifera, in contrast to higher plants, the transthylakoid proton gradient alone does not induce NPQ. The role of this gradient seems to be related only to the activation of the violaxanthin de-epoxidase enzyme.     

Abiotic influences on bicarbonate use in the giant kelp,Macrocystis pyrifera,in the Monterey Bay

In the Monterey Bay region of central California, the giant kelp Macrocystis pyrifera experiences broad fluctuations in wave forces, temperature, light availability, nutrient availability, and seawater carbonate chemistry, all of which may impact their productivity. In particular, current velocities and light intensity may strongly regulate the supply and demand of inorganic carbon (Ci) as substrates for photosynthesis. Macrocystis pyrifera can acquire and utilize both CO₂ and bicarbonate (HCO₃^?) as Ci substrates for photosynthesis and growth. Given the variability in carbon delivery (due to current velocities and varying [DIC]) and demand (in the form of saturating irradiance), we hypothesized that the proportion of CO₂ and bicarbonate utilized is not constant for M. pyrifera, but a variable function of their fluctuating environment. We further hypothesized that populations acclimated to different wave exposure and irradiance habitats would display different patterns of bicarbonate uptake. To test these hypotheses, we carried out oxygen evolution trials in the laboratory to measure the proportion of bicarbonate utilized by M. pyrifera via external CA under an orthogonal cross of velocity, irradiance, and acclimation treatments. Our Monterey Bay populations of M. pyrifera exhibited proportionally higher external bicarbonate utilization in high irradiance and high flow velocity conditions than in sub‐saturating irradiance or low flow velocity conditions. However, there was no significant difference in proportional bicarbonate use between deep blades and canopy blades, nor between individuals from wave‐exposed versus wave‐protected sites. This study contributes a new field‐oriented perspective on the abiotic controls of carbon utilization physiology in macroalgae.     

Seasonal variation in epifaunal communities associated with giant kelp (Macrocystis pyrifera) at an upwelling‐dominated site

Kelp forests are highly productive and species‐rich benthic ecosystems in temperate regions that provide biogenic habitat for numerous associated species. Diverse epifaunal communities inhabit kelp sporophytes and are subject to variations in the physical environment and to changes experienced by the kelp habitat itself. We assessed seasonal variations in epifaunal invertebrate communities inhabiting giant kelps, Macrocystis pyrifera, and their effects on this seaweed. Six seasonal samplings were conducted over a year at an upwelling‐dominated site in northern‐central Chile where physical conditions are known to fluctuate temporally. More than 30 taxa were identified, among which peracarid crustaceans stood out in both diversity and abundance. Species richness and abundance differed among sporophyte sections (holdfast and fronds) and throughout the year. The frond community was dominated by two grazers (the amphipod Peramphithoe femorata and the isopod Amphoroidea typa), while suspension feeders, grazers, and omnivores (the amphipod Aora typica, the isopod Limnoria quadripunctata, and polychaetes) dominated the holdfasts. Abundances of the dominant species fluctuated throughout the year but patterns of variation differed among species. The most abundant grazer (P. femorata) had highest densities in summer, while the less abundant grazer (A. typa) reached its peak densities in winter. Interestingly, the area of kelp damaged by grazers was highest in autumn and early winter, suggesting that grazing impacts accumulate during periods of low kelp growth, which can thus be considered as ‘vestiges of herbivory past.’ Among the factors determining the observed seasonal patterns, strong variability of environmental conditions, reproductive cycles of associated fauna, and predation by fishes vary in importance. Our results suggest that during spring and early summer, bottom‐up processes shape the community structure of organisms inhabiting large perennial seaweeds, whereas during late summer and autumn, top‐down processes are more important.     

Plant and frond dynamics of the giant kelp,Macrocystis pyrifera,forming a fringing zone in the Falkland Islands

Fluctuations in plant and frond characteristics are described for Macrocystis pyrifera (L.) C. Agardh (Laminariales, Phaeophyta) forming a fringing zone in the Falkland Islands. Giant kelp plants were sampled along a transect in the austral autumn (May 1986) and late spring (December 1986) which, according to previous frond weight analysis, were the times when extremes in population parameters were expected. Plant density and holdfast wet weights were similar for both seasons, but plants had more fronds and the fronds weighed more in spring than in autumn. Consequently, in autumn the frond biomass (1·1 wet kg m^?2) and productivity (34·1 wet g m^?2 d^?1) were lower than in spring, when a biomass of 5·0 wet kg m^?2 and a productivity of 72·4 wet g m^?2 d^?1 were recorded. Production of new fronds and loss of old fronds were determined at monthly intervals between April 1986 and March 1987. New frond production rates followed fluctuations in the quantity of light and varied between 0·08 and 0·48 fronds per plant per day. Frond loss rates did not show a seasonal pattern and fluctuated between 0·05 and 0·42 fronds per plant per day. It is suggested that the Falkland Islands Macrocystis population is more stable than most other giant kelp beds at high latitudes, because of the absence of winter storms.     

Translocation of C in Macrocystis pyrifera (Giant Kelp)

The pattern of import and export of ¹⁴C-labeled assimilates in Macrocystis pyrifera (L.) C. A. Agardh in southern California was studied by labeling single blades on fronds, in situ, with [¹⁴C]NaHCO₃ for 24 hours. The pattern was found to be similar to that known in dicotyledons: actively growing tissue imported and did not export. As a blade reached maturity it began to export, at first only acropetally to the apex which formed it, later also down the frond to sporophylls and frond initials at the base of the frond, and into the apical regions of juvenile fronds; finally there was a phase of declining export, late in the life of the blade, when transport was only downward. Young fronds imported from older fronds until they were approximately 3 meters long, by which time they had developed mature, upward exporting blades. No translocation was found from a younger frond to an older frond, nor was there transport upward from a blade on a frond lacking the apical region.     

Significance of microheterotrophs in relation to the degradation process of subantarctic kelp beds (Macrocystis pyrifera)

Summary The abundances of the heterotrophic bacteria in relation to the degradation of the stranded kelp bed of Macrocystis pyrifera of the Morbihan Bay (Kerguelen Archipelago) were studied. During a one year period between the austral autumns 1982 and 1983 systematic observations of viable and direct counts of bacteria were recorded for three stations along a transect including kelp bed, intertidal and offshore waters. Quantitatively the microflora was very similar to that found in more temperate regions. Seasonal fluctuations were correlated with successive periods of deposit and degradation of the stranded kelp debris. After each new deposit, a very fast growing phase of the microbial population were observed. Doubling time (approximately 1.5 days) and biovolumes of the total bacteria showed rapid increases (from 0.16 to 0.38 m³). At the same time the ratio direct counts/viable counts showed a significant decrease and reached values close to 1. Decreasing number of bacteria were observed along the transect studied but the impact of kelp deposits on bacterial growth reached also offshore waters.     

Short‐ and long‐term acclimation patterns of the giant kelp Macrocystis pyrifera (Laminariales,Phaeophyceae) along a depth gradient

The giant kelp, Macrocystis pyrifera, is exposed to highly variable irradiance and temperature regimes across its geographic and vertical depth gradients. The objective of this study was to extend our understanding of algal acclimation strategies on different temporal scales to those varying abiotic conditions at various water depths. Different acclimation strategies to various water depths (0.2 and 4 m) between different sampling times (Jan/Feb and Aug/Sept 2012; long‐term acclimation) and more rapid adjustments to different depths (0.2, 2 and 4 m; short‐term acclimation) during 14 d of transplantation were found. Adjustments of variable Chl a fluorescence, pigment composition (Chl c, fucoxanthin), and the de‐epoxidation state of the xanthophyll cycle pigments were responsible for the development of different physiological states with respect to various solar radiation and temperature climates. Interestingly, the results indicated that phlorotannins are important during long‐term acclimation while antioxidants have a crucial role during short‐term acclimation. Furthermore, the results suggested that modifications in total lipids and fatty acid compositions apparently also might play a role in depth acclimation. In Aug/Sept (austral winter), M. pyrifera responded to the transplantation from 4 m to 0.2 m depth with a rise in the degree of saturation and a switch from shorter‐ to longer‐chain fatty acids. These changes seem to be essential for the readjustment of thylakoid membranes and might, thus, facilitate efficient photosynthesis under changing irradiances and temperatures. Further experiments are needed to disentangle the relative contribution of solar radiation, temperature and also other abiotic parameters in the observed physiological changes.     

Ecophysiological plasticity of annual populations of giant kelp (Macrocystis pyrifera) in a seasonally variable coastal environment in the Northern Patagonian Inner Seas of Southern Chile

Annual populations of Macrocystis pyrifera in Southern Chile have been the main focus of studies intending to understand how these populations can couple consecutive sporophytic generations. Research has included studying the population dynamics and gametophytic responses to environmental conditions and the role of recruitment, grazing, and the use of benthic filter feeders as secondary substrate. Adult sporophytes undergo senescence due to changes in abiotic factors during summer and autumn producing 100 % mortality. This study provides evidence about the environmental factors driving the decline in sporophyte populations occurring in summer and fall by monitoring two independent kelp populations and also by running experiments using 400 L tubular photobioreactors with semicontrolled environmental factors for testing the capacity for new recruits to recover population levels under winter conditions. The study of natural populations of giant kelp indicates that high temperatures (>15–17 °C) explain the high mortality of adult plants in summer. On the other hand, the sporophytes established in late winter/early spring are able, under high nitrogen availability, to increase their chlorophyll content significantly, allowing the individuals to reduce their light saturation point and thus allow a higher productivity under the low light conditions that exist in late winter and early spring. These results, in addition to the recruitment facilitation produced by filter feeders, help to explain how giant kelp can deal with, and couple sporophytic generations, in variable environments. These results also emphasize the highly plastic physiology of giant kelp that enables this species to colonize diverse habitats across its large distributional range.     

In situ rates of nitrate uptake by giant kelp,Macrocystis Pyrifera (L.) C. Agardh: Tissue differences,environmental effects,and predictions of nitrogen-limited growth

NO⁻₃ uptake rates were measured in situ for seven types of tissue of adult sporophytes of Macrocystis pyrifera (L.) C. Agardh. Uptake by mature blades of canopy fronds followed saturation kinetics. At near-saturation concentrations, mean rates of uptake by different tissues ranged from 0.1 to 2.1 μg-at.· g wet wt⁻¹ · h⁻¹ (7–68 ng-at. · cm⁻²· h⁻¹). Different tissues incubated under similar environmental conditions took up NO⁻₃ at different rates, indicating physiological differences. Uptake rates showed no apparent relation to tissue age or nutritional history, but were influenced by certain environmental factors: uptake was 44–48% slower in dark than at ambient mid-day light levels, and dark uptake was 40% slower by blades incubated at 12m depth than by blades incubated at the surface. These physiological and environmental differences resulted in generally rapid uptake by tissues located at or just below the surface and slower uptake by tissues deeper in the water column.Daily NO⁻₃ uptake by M. pyrifera populations was predicted using a model based on in situ NO⁻₃ uptake rates. According to predictions of the model, NO⁻₃ concentrations of 1–2 μM throughout the water column are required to support kelp growth at the 4% · day⁻¹ (wet wt) rate typical of inshore populations. Vertical stratification, with high NO⁻₃ concentrations only at near-bottom depths, would result in severe nitrogen-limitation of growth. Seasonal changes in frond size distribution do not greatly affect nitrogen-limited growth rate. The model was also used to evaluate potential fertilizing methods and problems in management of offshore kelp farms.