Giant Kelp Macrocystis Pyrifera Research Articles

Trophic versus structural effects of a marine foundation species, giant kelp (Macrocystis pyrifera).

Foundation species create milieus in which ecosystems evolve, altering species abundances and distribution often to a dramatic degree. Although much descriptive work supports their importance, there remains little definitive information on the mechanisms by which foundation species alter their environment. These mechanisms fall into two basic categories: provision of food or other materials, and modification of the physical environment. Here, we manipulated the abundance of a marine foundation species, the giant kelp Macrocystis pyrifera, in 40×40-m plots at Mohawk Reef off Santa Barbara, California and found that its biomass had a strong positive effect on the abundance of bottom-dwelling sessile invertebrates. We examined the carbon (C) stable isotope values of seven species of sessile invertebrates in the treatment plots to test the hypothesis that this positive effect resulted from a nutritional supplement of small suspended particles of kelp detritus, as many studies have posited. We found no evidence from stable isotope analyses to support the hypothesis that kelp detritus is an important food source for sessile suspension-feeding invertebrates. The isotope composition of invertebrates varied with species and season, but was not affected by kelp biomass, with the exception of two species: the tunicate Styela montereyensis, which exhibited a slight enrichment in C stable isotope composition with increasing kelp biomass, and the hydroid Aglaophenia sp., which showed the opposite effect. These results suggest that modification of the physical habitat, rather than nutritional subsidy by kelp detritus, likely accounts for increased abundance of sessile invertebrates within giant kelp forests.

Nitrogen fixation associated with the decomposition of the giant kelp Macrocystis pyrifera

The seaweed Macrocystis pyrifera plays an important role in the coastal zone as a result of its global distribution, high productivity and detrital export, and the high diversity of the ecological communities that it supports. Growth of the giant kelp Macrocystis, like other seaweeds, is often limited by the availability of fixed nitrogen. Several other macroalgal species have been reported to harbor microbial symbionts that fix ubiquitous dissolved N2, converting it into bioavailable forms, and potentially making a significant contribution to algal nutrition. Our investigation shows that N2 fixation on living Macrocystis (mean 0.17μmol g−1d−1) was more than 10 times greater than that associated with all but one of the 14 other macroalgal species we studied. However, this rate is insufficient to contribute significantly to Macrocystis growth. Instead, we reported much higher rates of N2 fixation (up to 23μmol g−1d−1) associated with detrital or decomposing Macrocystis. Decomposition-related N2 fixation on Macrocystis is stimulated both by anaerobic conditions and amendment with mannitol or phosphate, but is inhibited by light, and is therefore, likely a heterotrophic process in contrast to the cyanobacterial N2 fixation reported for Codium and Sargassum. Using O2 microsensors, we show that anaerobic conditions around the Macrocystis blade are unlikely to develop in attached plants. Nitrogen fixation may be important in kelp rafts and wrack, where it could contribute as much as a 4-fold increase in the availability of nitrogen to support microbial and invertebrate communities.

Bioeconomic analysis of giant kelp Macrocystis pyrifera cultivation (Laminariales; Phaeophyceae) in northern Chile

This study analyzed the economic feasibility of offshore commercial cultivation of Macrocystis pyrifera in northern Chile. To achieve this objective, a continuous-time model including biological, technological, and economic aspects was developed. To implement this model, the biomass growth until marketable size is reached was estimated for three periods of the year. A periodic system of cultivation and harvesting is described, and the main investments, operation costs, remunerations, and operational costs of cultivation and harvesting are defined. The results of the baseline model show that cultivation is not profitable in the long term considering the selling price and the harvest yield. Additionally, at baseline, the revenue is unable to cover the investment costs or the operation costs. However, in a scenario in which productivity is 211 % higher than the base harvest and prices are 25 % higher, cultivation becomes profitable, with positive net present values (NPV) after 14 years. Despite the aforementioned considerations, the opportunity for generating greater value from this type of cultivation is discussed, taking into account its characteristics as units that provide ecosystem services, which is a feature that is starting to be discussed in relation to marine environments.

Copper tolerance and distribution of epibiotic bacteria associated with giant kelp Macrocystis pyrifera in southern California.

Kelp forests in southern California are important ecosystems that provide habitat and nutrition to a multitude of species. Macrocystis pyrifera and other brown algae that dominate kelp forests, produce negatively charged polysaccharides on the cell surface, which have the ability to accumulate transition metals such as copper. Kelp forests near areas with high levels of boating and other industrial activities are exposed to increased amounts of these metals, leading to increased concentrations on the algal surface. The increased concentration of transition metals creates a harsh environment for colonizing microbes altering community structure. The impact of altered bacterial populations in the kelp forest have unknown consequences that could be harmful to the health of the ecosystem. In this study we describe the community of microorganisms associated with M. pyrifera, using a culture based approach, and their increasing tolerance to the transition metal, copper, across a gradient of human activity in southern California. The results support the hypothesis that M. pyrifera forms a distinct marine microhabitat and selects for species of bacteria that are rarer in the water column, and that copper-resistant isolates are selected for in locations with elevated exposure to transition metals associated with human activity.

Effects of ocean acidification on the photosynthetic performance, carbonic anhydrase activity and growth of the giant kelp Macrocystis pyrifera.

Under ocean acidification (OA), the 200 % increase in CO2(aq) and the reduction of pH by 0.3-0.4 units are predicted to affect the carbon physiology and growth of macroalgae. Here we examined how the physiology of the giant kelp Macrocystis pyrifera is affected by elevated pCO2/low pH. Growth and photosynthetic rates, external and internal carbonic anhydrase (CA) activity, HCO3 (-) versus CO2 use were determined over a 7-day incubation at ambient pCO2 400 µatm/pH 8.00 and a future OA treatment of pCO2 1200 µatm/pH 7.59. Neither the photosynthetic nor growth rates were changed by elevated CO2 supply in the OA treatment. These results were explained by the greater use of HCO3 (-) compared to CO2 as an inorganic carbon (Ci) source to support photosynthesis. Macrocystis is a mixed HCO3 (-) and CO2 user that exhibits two effective mechanisms for HCO3 (-) utilization; as predicted for species that possess carbon-concentrating mechanisms (CCMs), photosynthesis was not substantially affected by elevated pCO2. The internal CA activity was also unaffected by OA, and it remained high and active throughout the experiment; this suggests that HCO3 (-) uptake via an anion exchange protein was not affected by OA. Our results suggest that photosynthetic Ci uptake and growth of Macrocystis will not be affected by elevated pCO2/low pH predicted for the future, but the combined effects with other environmental factors like temperature and nutrient availability could change the physiological response of Macrocystis to OA. Therefore, further studies will be important to elucidate how this species might respond to the global environmental change predicted for the ocean.

Ecology of Australian Temperate Reefs

book reviews ISSN 1948-6596 Ecology of Australian Temperate Reefs Ecology of Australian Temperate Reefs: The Unique South. Scoresby Shepherd & Graham Edgar (editors), 2013, CSIRO Publishing. 520 pp. AU$130.00 (hardback) ISBN: 9781486300099; http://www.publish.csiro.au/ This book is a lavishly-produced text that links geological history, oceanography, and biogeogra- phy with future threats to Australian temperate marine ecosystems and their biodiversity. The Preface claims that the book is directed at three audiences. One, marine ecologists who want to broaden their background knowledge; the book certainly would be useful in this regard. Two, un- der- or post-graduate students; the book would be a useful main or supplemental text for a course. Three, as a reference work for “skilled amateur divers and underwater photographers (page xi)”; I disagree, as it's perhaps a bit too de- tailed for the most part, despite what may have been a Publisher’s imperative to sell copies. There are five main parts to the book. A pot- ted summary of the geology, oceanography and biogeographic history of the Southern Ocean. The ecologies of each of the three main taxa: the algae, the invertebrates, and the vertebrates. The last sec- tion covers ecosystems and their conservation. Part One, the backdrop to modern biodiver- sity, was very informative and unusual in a text on marine ecology, providing (in the book’s Table 1.1) a useful summary of the events from 100 Mya to the present, in terms of climatic, tectonic, oceano- graphic and biotic events. Given the current con- cerns about ocean acidification, the section on carbon dioxide in a historic context was very use- ful in terms of past impacts. The rapid summaries of marine taxa in terms of their evolution and his- toric constraints quickly gets the reader up to speed, and includes all key fossil taxa that remain today. Table 3.2 lists the main marine taxa, with information on species diversity, endemism and dispersal potential. However, boundaries of the area of endemism are not stated, and whether they are the same for each taxon is unclear, which would be important to know since endemism is related to habitat area. Also, some of the calcula- tions appear to be in error. For instance, the per- centage of global species richness in temperate Australia for molluscs is given as ca. 8% of 96,850 species, but this should be 20% (19,000 Southern Australian species). And 71 of 1250 species of pycnogonids is 6% not 11%. Evolution and radia- tion of taxa are examined in some detail for many well known—for instance Haliotis abalones and cowries—and less well known taxa—such as the odacine marine fishes. Despite the preface claiming that modeling is not a focus of the volume, Part One ends with several pages comparing the expectations of two key models of southern biodiversity. This may be too much for lay readers but I feel rounds off the section nicely. Parts Two to Four address higher taxa, in turn algae, invertebrates and vertebrates. In Part Two, the algae chapters, case studies fol- low two key habitat formers, Ecklonia radiata and the giant kelp Macrocystis pyrifera. Each case study considers morphology and growth forms, then demographic parameters and their spatial variation. Table 4.1 is a very useful com- parison of growth, biomass and survival charac- teristics around southern Australia for the ubiquitous Ecklonia radiata. The relationship between depth and biomass is explored further in Figure 4.3 however the potential confound- ing effect of latitude (the shallowest sites ap- pear to be at lower latitudes) isn’t discussed. The giant kelp’s role in the ecosystem is em- phasised including interesting facts such as its ability to enhance lobster puerulus (larvae) re- tention. Pages 99—104 contain an extensive examination of the role of exposure and water movement on algal species distribution across the region. While interesting, I felt that it probably could have been summarised in a ta- ble and in shorter prose. As in previous parts, there is a synthesis and modelling section at the end, although the very simplistic state- change model shown in Fig 5.16 could probably have been described in a sentence instead. frontiers of biogeography 6.3, 2014 — © 2014 the authors; journal compilation © 2014 The International Biogeography Society

Interactive effects of elevated temperature and pCO2 on early-life-history stages of the giant kelp Macrocystis pyrifera

Rising atmospheric CO2 is expected to increase global temperatures and partial pressure of CO2 in surface waters, causing ocean warming and acidification. These changes may have important consequences for the physiological performance of early life-history stages of marine organisms. In this study we investigated the potential for interactive effects of ecologically relevant levels of temperature and pCO2 on germination, dormancy and mortality of zoospores of the giant kelp Macrocystis pyrifera, a foundation species of temperate reef ecosystems. Newly settled kelp spores were cultured in the laboratory for seven days in a factorial design with temperature (13°C and 18°C) and pCO2 (~370 and ~1800μatm) as experimental factors. The two levels of temperature and the low-pCO2 treatment in our design were consistent with present-day environmental conditions in the kelp forest as measured by autonomous temperature and pH sensors, while the high-pCO2 treatment reflects an extreme, future acidification scenario. Our results revealed that the combined effects of increased temperature and pCO2 can significantly decrease germination rates and increase the mortality of kelp spores. Interactive effects of temperature and pCO2 were detected on spore mortality and dormancy. Spore mortality only differed between pCO2 treatments at high temperature. In contrast, spore dormancy was higher in the treatment with low temperature and high pCO2, which is similar to the environmental conditions experienced during upwelling events in southern California. Our results highlight the importance of considering multiple stressors to understand how the early-stages of foundation species such as M. pyrifera will be affected by global change.

Importance of kelp detritus as a component of suspended particulate organic matter in giant kelp Macrocystis pyrifera forests

Importance of kelp detritus as a component of suspended particulate organic matter in giant kelp Macrocystis pyrifera forests

Benthic community structure in kelp forests from the Southern California Bight

The United States and Mexico share the Southern California Bight (SCB) ecosystem in the Northeast Pacific Ocean where marine wildlife and habitats historically have been disturbed by human activities. Within this ecosystem, forests of the giant kelp Macrocystis pyrifera are critical habitats that sustain diverse biological assemblages and important fishery species. We studied patterns of temporal and spatial variability within the benthic communities of five transboundary kelp forests in California (USA) and Baja California (Mexico) over a fouryear period that included a moderate El Niño event. While the benthic marine communities shared some species, they varied significantly in community structure from each other, and the degree of dissimilarity was not related to the geographic distances among the studied habitats. Rather, species richness was significantly related to local substratum rugosity, suggesting it could be used as a proxy of relative benthic biological diversity. Temporal changes in the benthic assemblages were not consistent across all forests, and contrary to observations made during previous El Niño events in the SCB, the benthic communities did not change significantly following the 2009–2010 El Niño. Such an unexpected community response may be explained by the fact that the 2009–2010 El Niño was linked to the Modoki phenomenon, where warm sea surface temperature is focused in the central equatorial Pacific and not in the eastern Pacific Ocean. We propose that long-term conservation efforts should incorporate this ecological knowledge to support science-based decisions, binational coordination of policies, and coherent management practices including the design of transboundary conservation networks as spatial management tools for the protection, conservation, and/or restoration of the SCB ecosystem.

The ecological importance of Macrocystis pyrifera (Phaeophyta) forests towards a sustainable management and exploitation of Chilean coastal benthic co-management areas

The giant kelp Macrocystis pyrifera forms dense aggregations in rocky subtidal areas along the Chilean coast. Seasonal abundance of seaweed and invertebrate populations associated with kelp forests and control sites without forests were monitored for two years in Southern Chile. Monitoring took place in areas under co-management fisheries administration provision entitled 'Management and exploitation areas for benthic resources (MEABR)' where several species that are under commercial exploitation have to be monitored. This study provides evidence indicating the importance of giant kelp in the maintenance of exploited organisms and biodiversity in general. The results showed that kelp influences the abundance of other macroalgae and benthic invertebrates, including species exploited by the local fisheries. Kelp size and density varied seasonally, generating cyclical variation in habitat, species composition and community structure. A consequence of the exploitation and depletion of Macrocystis forests will be a decrease in the abundance of other economically important species and therefore the sustainable development of coastal communities may be compromised.

Can giant kelp (Macrocystis pyrifera) forests enhance invertebrate recruitment in southern Chile?

Macrocystis pyrifera is a foundation species that modifies the environment in complex ways and provides food and refuges for a variety of coastal organisms, some of which are important for local fishery communities in the south of Chile. In this study we tested the effect of Macrocystis forests on recruitment of benthic organisms within Management and Exploitation Areas for Benthic Resources (MEABR). We placed artificial Tuffy collectors to sample recruits in three MEABRs during three different seasons. In each MEABR we installed 60 Tuffy collectors inside the kelp forest and an additional 60 outside the forest. Eight groups of invertebrate recruits were found abundantly in the study areas. The most common recruits belonged to the Mytilidae family, as well as the gastropod Tegula spp., the crabs Taliepus spp. and Pilumnoides perlatus, the keyhole limpet Fissurella spp., the sea urchin Loxechinus albus, the ascidian Ciona intestinalis and polychaetes. The kelp forest effect interacts significantly with season and locality for all eight invertebrates, the a-posteriori HSD Tukey test shows a significantly higher recruitment under the kelp forest than outside for Fissurella spp., polychaetes, Ciona, Pilumnoides and the family Mytilidae. On the other hand, only the sea urchin Loxechinus albus presented a significantly higher recruitment outside the kelp forest. As Macrocystis forests favoured the recruitment of several invertebrates, conservation of kelp forests is important for maintaining invertebrate biodiversity and science-based benthic fisheries management plans for its exploitation are required.

Genetic signatures of rafting dispersal in algal-dwelling brooders Limnoria spp. (Isopoda) along the SE Pacific (Chile)

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 455:111-122 (2012) - DOI: https://doi.org/10.3354/meps09673 Genetic signatures of rafting dispersal in algal-dwelling brooders Limnoria spp. (Isopoda) along the SE Pacific (Chile) Pilar A. Haye1,*, Andrea I. Varela1,2, Martin Thiel1 1Departamento de Biología Marina, Facultad de Ciencias del Mar, Universidad Católica del Norte, Larrondo 1281, and Centro de Estudios Avanzados en Zonas Áridas (CEAZA), Coquimbo, Chile 2Present address: School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand *Email: phaye@ucn.cl ABSTRACT: Brooding marine isopods of the genus Limnoria inhabit and feed on kelp holdfasts and wood. These substrata have high floating potential, making these species ideal organisms to study the effects of rafting-mediated connectivity on the population structure of brooders living on rafting substrata. It is hypothesized that rafting leaves particular genetic signatures such as low differentiation among distant local populations and absence of isolation by distance (IBD) at a macro-geographic scale (thousands of km). Using cytochrome oxidase I (COI) sequences, we tested the effects of rafting-mediated gene flow with respect to genetic differentiation on L. quadripunctata (from wood and also the holdfasts of the giant kelp Macrocystis pyrifera) and L. chilensis (mainly from the bull kelp Durvillaea antarctica) sampled across 2400 km of the Chilean coast. Analyses of COI data for both species indicated low differentiation between distant locations along the Chilean coast and lack of IBD, bearing the expected genetic signatures of rafting dispersal. Phylogenetic analyses were performed with COI and the nuclear gene 28S to place the genetic diversity of Chilean Limnoria spp. into a wider geographical context. Both markers revealed that L. quadripunctata from Chile is a sister clade to other Limnoria spp. analyzed (L. chilensis, L. segnis, and L. stephenseni), which mainly inhabit D. antarctica. L. chilensis from Chile and subantarctic islands form a tight monophyletic group. Phylogenetic and phylogeographic analyses show that along the studied area, L. quadripunctata and L. chilensis have the genetic signatures of relatively recent or ongoing rafting. KEY WORDS: Peracarids · Rafting · Biogeography · Mitochondrial DNA · COI · 28S · Phylogeny · Phylogeography Full text in pdf format Supplementary material PreviousNextCite this article as: Haye PA, Varela AI, Thiel M (2012) Genetic signatures of rafting dispersal in algal-dwelling brooders Limnoria spp. (Isopoda) along the SE Pacific (Chile). Mar Ecol Prog Ser 455:111-122. https://doi.org/10.3354/meps09673 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 455. Online publication date: May 30, 2012 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2012 Inter-Research.

Uptake and transport of nitrogen derived from sessile epifauna in the giant kelp Macrocystis pyrifera

Sessile epifauna that excrete ammonium as a waste product are often closely associated with surfaces of macroalgae that are able to absorb and use ammonium for growth. This close association means that nitrogen provisioning from epifauna to host macroalgae is probable, but barriers to uptake, formed by epifaunal colonies, and the physiological status of colonised macroalgal tissue may limit the amount of ammonium absorbed by colonised macroalgae. Evidence for the movement of nitrogen from sessile epifauna into and around the giant kelp Macrocystis pyrifera was gathered using a 15N-enriched stable isotope tracer. Experiments in which 15N-labelled phytoplankton was fed to the epifaunal bryozoan Membranipora membranacea did not to find conclusive evidence for the flow of nitrogen released by bryozoan colonies into colonised M. pyrifera tissue. The low degree of transmission of 15N observed may be due to the barrier to nitrogen uptake that is formed by M. membranacea tissue and the low affinity for ammonium uptake by M. pyrifera blades during winter. M. membranacea is unlikely to provide significant benefits to host macroalgae via nitrogen provision in many situations, due to its sheet-forming habit and its absence during summer low-nitrogen periods. In situ incubations of M. pyrifera blades in 15N-enriched ammonium were used to determine if ammonium provided by epifaunal colonies could be taken up by mature blades tissue and exported to the stipe for long-distance transport to actively growing meristems. Uptake and export of labelled nitrogen from basal blades into the stipe was measured, and the potential for longdistance transport of nitrogen from older blades was confirmed. Active transport of nitrogen from older macro algal tissue colonised by epifauna such as hydroids could be an important mechanism allowing kelp with specialised long-distance solute transport systems to tolerate nitrogen limitation.

Wave disturbance overwhelms top-down and bottom-up control of primary production in California kelp forests.

We took advantage of regional differences in environmental forcing and consumer abundance to examine the relative importance of nutrient availability (bottom-up), grazing pressure (top-down), and storm waves (disturbance) in determining the standing biomass and net primary production (NPP) of the giant kelp Macrocystis pyrifera in central and southern California. Using a nine-year data set collected from 17 sites we show that, despite high densities of sea urchin grazers and prolonged periods of low nutrient availability in southern California, NPP by giant kelp was twice that of central California where nutrient concentrations were consistently high and sea urchins were nearly absent due to predation by sea otters. Waves associated with winter storms were consistently higher in central California, and the loss of kelp biomass to winter wave disturbance was on average twice that of southern California. These observations suggest that the more intense wave disturbance in central California limited NPP by giant kelp under otherwise favorable conditions. Regional patterns of interannual variation in NPP were similar to those of wave disturbance in that year-to-year variation in disturbance and NPP were both greater in southern California. Our findings provide strong evidence that regional differences in wave disturbance overwhelmed those of nutrient supply and grazing intensity to determine NPP by giant kelp. The important role of disturbance in controlling NPP revealed by our study is likely not unique to giant kelp forests, as vegetation dynamics in many systems are dominated by post-disturbance succession with climax communities being relatively uncommon. The effects of disturbance frequency may be easier to detect in giant kelp because it is fast growing and relatively short lived, with cycles of disturbance and recovery occurring on time scales of years. Much longer data sets (decades to centuries) will likely be needed to properly evaluate the role of disturbance relative to other processes in determining patterns of NPP in other systems.

Herbivorous amphipods inhabit protective microhabitats within thalli of giant kelp Macrocystis pyrifera

Many small marine herbivores utilize specific algal hosts, but the ultimate factors that shape host selection are not well understood. For example, the use of particular microhabitats within algal hosts and the functional role of these microhabitats have received little attention, especially in large algae such as kelps. We studied microhabitat use of the herbivorous amphipod Peramphithoe femorata that inhabits nest-like domiciles on the blades of giant kelp Macrocystis pyrifera. The vertical position of nest-bearing blades along the stipe of the algal thallus and the position of the nests within the lateral blades of M. pyrifera were surveyed in two kelp forests in northern-central Chile. Additionally, we conducted laboratory and field experiments to unravel the mechanisms driving the observed distributions. Peramphithoe femorata nests were predominantly built on the distal blade tips in apical sections of the stipes. Within-blade and within-stipe feeding preferences of P. femorata did not explain the amphipod distribution. Amphipods did not consistently select distal over proximal blade sections in habitat choice experiments. Mortality of tethered amphipods without nests was higher at the seafloor than at the sea surface in the field. Nests mitigated mortality of tethered amphipods, especially at the seafloor. Thus, protective microhabitats within thalli of large kelp species can substantially enhance survival of small marine herbivores. Our results suggest that differential survival from predation might be more important than food preferences in determining the microhabitat distribution of these herbivores.

Bioaccumulation of copper and zinc by the giant kelp Macrocystis pyrifera

This study examined the bioaccumulation of the heavy metals copper (Cu) and zinc (Zn) by the giant kelp, Macrocystis pyrifera, by exposing meristematic kelp tissue to elevated metal concentrations in seawater within laboratory aquaria. Specifically, we carried out two different experiments. The first examined metal uptake under a single, ecologically-relevant elevation of each metal (30 ppb Cu and 100 ppb Zn), and the second examined the relationships between varying levels of the metals (i.e., 15, 39, 60, 120, 240, and 480 ppb Cu, and 50, 100, 200, 300, 500, and 600 ppb Zn). Both experiments were designed to contrast the uptake of the metals in isolation (i.e., when only one metal concentration was elevated) and in combination (i.e., when both metals` concentrations were elevated). Following three days of exposure to the elevated metal concentrations, we collected and analyzed the M. pyrifera tissues using inductively coupled plasma atomic emissions spectroscopy. Our results indicated that M. pyrifera bioaccumulated Cu in all treatments where Cu concentrations in the seawater were elevated, regardless of whether Zn concentrations were also elevated. Similarly, M. pyrifera bioaccumulated Zn in treatments where seawater Zn concentrations were elevated, but this occurred only when we increased Zn alone, and not when we simultaneously increased Cu concentrations. This suggests that elevated Cu concentrations inhibit Zn uptake, but not vice versa. Following this, our second experiment examined the relationships among varying seawater Cu and Zn concentrations and their bioaccumulation by M. pyrifera. Here, our results indicated that, as their concentrations in the seawater rise, Cu and Zn uptake by M. pyrifera tissue also rises. As with the first experiment, the presence of elevated Zn in the water did not appear to affect Cu uptake at any concentration examined. However, although it was not statistically significant, we observed that the presence of elevated Cu in seawater appeared to trend toward inhibiting Zn uptake, especially at higher levels of the metals. This study suggests that M. pyrifera may be useful as a bio-indicator species for monitoring heavy metal pollution in coastal environments.

Photosynthetic oxygen flux by Macrocystis pyrifera: a mass transfer model with experimental validation

The present paper elaborates the development of a mass transfer model to determine rates of photosynthetic oxygen flux from the giant kelp Macrocystis pyrifera in a moving fluid. The model can be used to calculate local dissolved oxygen flux, blade-averaged oxygen flux and daily average net primary productivity for a kelp forest. Predicted rates of photosynthetic oxygen flux agree well with previously reported direct measurements. This model was derived from the fundamental principles of conservation of mass and momentum over a flat plate using an integral method approach and is applicable in laminar, transitional and turbulent flows. It predicts oxygen flux as an explicit function of fluid flow conditions above the kelp blade. Experimental velocity profiles and dissolved oxygen concentration profiles, measured under a range of fluid flow conditions, followed power-law scaling and demonstrated local similarity between oxygen and velocity distribution within the boundary layers above the kelp blade. The proposed model provides a useful tool for estimating rates of photosynthesis with minimal data collection.

Environmental controls of giant-kelp biomass in the Santa Barbara Channel, California

Synthesizing long-term observations at multiple scales is vital for understanding the environ- mental drivers of ecosystem dynamics. We assessed the role of several environmental drivers in explaining temporal and spatial patterns in the abundance of giant kelp Macrocystis pyrifera in the Santa Barbara Channel between 1984 and 2009. We developed a novel method for estimating the canopy biomass of giant kelp from Landsat 5 Thematic Mapper satellite imagery, which allowed us to examine the dynamics of giant-kelp biomass on spatial scales ranging from 100s of m 2 to 100s of km 2 and temporal scales ranging from several weeks to 25 yr. Comparisons of changes in canopy biomass with oceanographic and climatic data revealed that winter losses of regional kelp canopy biomass were positively correlated with significant wave height (r 2 = 0.50), while spring recoveries were negatively correlated with sea surface temperature (r 2 = 0.30; used as a proxy for nutrient availability). On interannual timescales, regional kelp-canopy biomass lagged the variations in wave heights, sea surface tem- peratures, and the North Pacific Gyre Oscillation index by 3 yr, indicating that these factors affect cycles of kelp recruitment and mortality. Results from cluster analysis showed that the response of kelp biomass to environmental conditions varied among different sub- regions of the Santa Barbara Channel. The dynamics of kelp biomass in exposed regions were related to wave disturbance, while kelp dynamics in sheltered regions tracked sea surface temperatures more closely. These results depict a high level of regional hetero- geneity in the biomass dynamics of this important foundation species.

Using Macrocystis pyrifera (L.) C. Agardh from southern Chile as a source of applied biological compounds

The exploitation of seaweeds in Chile has been carried out for more than 60 years. More recently, seaweeds have been used for the production of alginate, agar and carrageenan, agricultural fertilizers and industrial aquaculture (feed for abalone and sea urchins), increasing the added value of this natural resource. In the Magellan Region (56oS), the giant kelp Macrocystis pyrifera (L.) C. Agardh presents the most extensive kelp forest, reaching a biomass of approximately 12 kg.m-2. Recent studies have shown potential benefits from adding M. pyrifera- derived flour to salmonid feed. Research is currently underway to evaluate the useof brown algae-derived products for marine aquaculture feed of Oncorhynchus mykiss in tanks. There was no apparent adverse effect on the evaluated parameters that can be attributed to the incorporation of M. pyrifera meal in the diets fed to salmonids. Even when the control diet had numerically the best performance in zootechnical terms, the analysis of variance of all parameters evaluated showed no significant differences with regard to diets containing M. pyrifera meal. These results demonstrated that seaweed meal has important benefits for animal health and nutrition that could be applied or tested in other marine organisms of commercial importance.

GRAZING ON GIANT KELP MICROSCOPIC PHASES AND THE RECRUITMENT SUCCESS OF ANNUAL POPULATIONS OF MACROCYSTIS PYRIFERA (LAMINARIALES, PHAEOPHYTA) IN SOUTHERN CHILE(1).

The giant kelp Macrocystis pyrifera (L.) C. Agardh is widely distributed in the Northern Hemisphere and Southern Hemisphere, yet it exhibits distinct population dynamics at local to regional spatial scales. Giant kelp populations are typically perennial with the potential for year-round reproduction and recruitment. In southern Chile, however, annual giant kelp populations exist and often persist entirely on secondary substrata (e.g., shells of the slipper limpet Crepipatella fecunda [Gastropoda, Calyptraeidae]) that can cover up to 90% of the rocky bottom. In these populations, the macroscopic sporophyte phase disappears annually during winter and early spring, leaving a 3-4 month period in which a persistent microscopic phase remains to support the subsequent year's recruitment. We tested the effects of a suite of grazers on the recruitment success of this critical microscopic phase at two sites in southern Chile. Field experiments indicated that the snail Tegula atra negatively impacted M. pyrifera sporophyte recruitment, but that recruitment was highest in the presence of sessile female limpets, C. fecunda. Conversely, small male C. fecunda (biofilm grazers) did not regulate kelp recruitment. Laboratory observations showed that C. fecunda males only grazed on microscopic kelp gametophytes and small (<250 μm) sporophytes, rejecting larger sporophytes, whereas T. atra grazed on all the kelp stages. Recruitment to the C. fecunda treatments far exceeded that to bare rock in the absence of grazers but was not due to the physical presence of C. fecunda shells. We concluded that the key to M. pyrifera recruitment success in southern Chile is its capacity to colonize secondary substrates provided by the slipper limpet C. fecunda.