Kelp Biomass Research Articles

An empirical test of 'universal' biomass scaling relationships in kelps: evidence of convergence with seed plants.

Biomass allocation patterns have received substantial consideration, leading to the recognition of several 'universal' interspecific trends. Despite efforts to understand biomass partitioning among embryophytes, few studies have examined macroalgae that evolved independently, yet function ecologically in much the same ways as plants. Kelps allocate photosynthate among three organs (the blade(s), stipe(s) and holdfast) that are superficially convergent with organs of land plants, providing a unique opportunity to test the limits of 'universal' trends. In this study, we used an allometric approach to quantify interspecific biomass partitioning patterns in kelps and assess whether embryophyte-based predictions of biomass scaling can be applied to marine macrophytes that lack root-to-leaf hydraulic transport. Photosynthetic area and dry mass were found to scale to approximately the ¾ power and kelp biomass allocation patterns were shown to match closely to empirical measures of allometric scaling among woody plants. Larger kelp species were found to have increased relative stipe and holdfast mass than smaller species, highlighting important consequences of size for marine macroalgae. Our study provides insights into the evolution of size in the largest marine macrophytes and corroborates previous work suggesting that the morphology of divergent lineages of photoautotrophs may reflect similar selective pressures.

Spatial Patterns and Predictors of Drift Algal Subsidy in Deep Subtidal Environments

The movement of resource subsidies across natural systems can have important effects on recipient communities and has emerged as a key research area in ecology. Detrital subsidies are critical in marine ecosystems where communities are reliant on external sources of primary production, yet few studies have quantified the spatial extent of drift algae at coastal scales. Using observations of the seafloor (up to 140 m depth) from tow-camera surveys along 145 km of Nova Scotia coast, and bathymetric data of this region, we created the first predictive map of drift subsidy in a marine ecosystem. We used a random forest model to generate our predictions, which correctly classified 95 % of observations into a presence or absence of drift. Distance from source, slope, and bathymetric position index (elevation relative to surrounding landscape) was the main predictor variables of the occurrence of drift. Drift algae occurred across a range of benthic habitats within our study area, but most frequently within 1.4 km of the coast on flat bottoms or in regions with zero or negative bathymetric position index. Such areas were coincident with seafloor depressions and flat low-energy habitats. Repeated observations at some locations indicated that areas with steep slopes or large curvature tended to have variable patterns of drift compared to areas with little or no slope or curvature. We predict that deep subtidal environments receiving drift subsidy will be impacted by the declines in kelp biomass projected for this region (and others) due to changes in ocean climate.

Environmental controls on spatial patterns in the long‐term persistence of giant kelp in central California

AbstractAs marine management measures increasingly protect static areas of the oceans, it is important to make sure protected areas capture and protect persistent populations. Rocky reefs in many temperate areas worldwide serve as habitat for canopy‐forming macroalgae and these structure‐forming species of kelps (order Laminariales) often serve as important habitat for a great diversity of species. Macrocystis pyrifera is the most common canopy‐forming kelp species found along the coast of California, but the distribution and abundance of M. pyrifera varies in space and time. The purpose of this study is to determine what environmental parameters are correlated with and their relative contribution to the spatial and temporal persistence of M. pyrifera along the central coast of California and how well those environmental parameters can be used to predict areas where this species is more likely to persist. Nine environmental variables considered in this study included depth of the seafloor, structure of the rocky reef, proportion of rocky reef, size of kelp patch, biomass of kelp within a patch, distance from the edge of a kelp patch, sea surface temperature, wave orbital velocities, and population connectivity of individual kelp patches. Using a generalized linear mixed effects model (GLMM), the persistence of M. pyrifera was significantly associated with seven of the nine variables considered: depth, complexity of the rocky reef, proportion of rock, patch biomass, distance from the edge of a patch, population connectivity, and wave orbital velocities. These seven environmental variables were then used to predict the persistence of kelp across the central coast, and these predictions were compared to a reserved dataset of M. pyrifera persistence, which was not used in the creation of the GLMM. The environmental variables were shown to accurately predict the persistence of M. pyrifera within the central coast of California (r = 0.71, P < 0.001). Because persistence of giant kelp is important to the community structure of kelp forests, understanding those factors that support persistent populations of M. pyrifera will enable more effective management of these ecosystems.

Changes in kelp forest biomass and depth distribution in Kongsfjorden, Svalbard, between 1996–1998 and 2012–2014 reflect Arctic warming

Arctic West Spitsbergen in Svalbard is currently experiencing gradual warming due to climate change showing decreased landfast sea-ice and increased sedimentation. In order to document possible changes in 2012–2014, we partially repeated a quantitative diving study from 1996 to 1998 in the kelp forest at Hansneset, Kongsfjorden, along a depth gradient between 0 and 15 m. The seaweed biomass increased between 1996/1998 and 2012/2013 with peak in kelp biomass shifted to shallower depth, from 5 to 2.5 m. The kelp biomass at 2.5 m was 8.2-fold higher in 2012/2013 (14 kg fresh biomass m−2) than in 1996/1998 and mostly due to an increase in the kelp Laminaria digitata. This resulted in a very high density of 2- to 8-year-old kelp (70 ind. m−2) and a high leaf area index of nearly 10 at 2.5 m. The entire zonation seemed to have shifted upwards to shallower depth, since also the lower depth limit of most dominant brown algae was shallower as well as the biomass maximum of several taxa. The cumulated annual photosynthetic active radiation at 15 m depth (42 mol m−2 year−1) determined the current depth limit of kelps. Changes also resulted in an altered seaweed community pattern. The complex pattern of change was probably driven by opposing effects of co-acting environmental drivers, namely lack of ice-scouring, elongation of the open-water period and deterioration of the underwater irradiance climate. The results are interpreted as a consequence of Arctic warming probably reflecting a typical scenario for change along other Arctic shores in near future.

Top predators rely on carbon derived from giant kelp Macrocystis pyrifera

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 537:1-8 (2015) - DOI: https://doi.org/10.3354/meps11467 FEATURE ARTICLE Top predators rely on carbon derived from giant kelp Macrocystis pyrifera Craig Koenigs, Robert J. Miller*, Henry M. Page Marine Science Institute, University of California, Santa Barbara, California 93106-6174, USA *Corresponding author: miller@msi.ucsb.edu ABSTRACT: Net primary production (NPP) fundamentally shapes ecosystems, but the fate of NPP and its transfer through the food web varies depending on its appeal and availability to consumers. Kelp forests are complex and diverse marine ecosystems, and kelp biomass and NPP can vary widely due to processes including trophic cascades and consequent changes in grazing pressure, storm wave disturbance, and changes in ocean climate and nutrients. Kelp, like other foundation species, clearly modulates the physical environment in which species interact: dense canopies of giant kelp Macrocystis pyrifera shade the reef, shaping the benthic community, and dampen flow through the forest. Yet little quantitative work has investigated the trophic contribution of kelps to kelp forest food webs. Here, we show that giant kelp provides significant trophic support to fishes living in the canopy of the kelp forest. Carbon contributions from kelp, via mesograzer prey, relative to pelagic carbon sources, increased with increasing trophic level of fishes, showing that giant kelp is particularly important to top predators. These findings suggest that losses of giant kelp would have significant consequences for coastal ecosystems and have important implications for the conservation and management of temperate reef ecosystems. KEY WORDS: Ecosystem engineers · Stable isotopes · Trophic subsidy · Detritus · Grazing · Benthic Full text in pdf format Information about this Feature Article NextCite this article as: Koenigs C, Miller RJ, Page HM (2015) Top predators rely on carbon derived from giant kelp Macrocystis pyrifera. Mar Ecol Prog Ser 537:1-8. https://doi.org/10.3354/meps11467 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 537. Online publication date: October 14, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Herbivory drives kelp recruits into ‘hiding’ in a warm ocean climate

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 536:1-9 (2015) - DOI: https://doi.org/10.3354/meps11445 FEATURE ARTICLE Herbivory drives kelp recruits into ‘hiding’ in a warm ocean climate João N. Franco1,2,*, Thomas Wernberg3, Iacopo Bertocci1, Pedro Duarte4, David Jacinto5, Nuno Vasco-Rodrigues6, Fernando Tuya7 1CIIMAR/CIMAR, Centro Interdisciplinar de Investigação Marinha e Ambiental, Rua dos Bragas 289, 4050-123 Porto, Portugal 2Departamento de Biologia, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre s/n, 4150-181 Porto, Portugal 3School of Plant Biology & UWA Oceans Institute (M470), University of Western Australia, Crawley, Western Australia 6009, Australia 4Norwegian Polar Institute, Fram Centre, Post Box 6606 Langnes, 9296 Tromsø, Norway 5MARE - Marine and Environmental Sciences Centre, Laboratório de Ciências do Mar, Universidade de Évora, Apartado190, 7521-903 Sines, Portugal 6MARE - Marine and Environmental Sciences Centre, ESTM, Polytechnic Institute of Leiria, 2520-641 Peniche, Portugal 7Grupo en Biodiversidad y Conservación, Universidad de Las Palmas de Gran Canaria, Canary Islands, Spain *Corresponding author: joaonunofranco@gmail.com ABSTRACT: Assessing effects of herbivory across broad gradients of varying ocean climate conditions and over small spatial scales is crucial for understanding its influence on primary producers. Effects of herbivory on the distribution and abundance of kelp recruits were examined experimentally at two regions under contrasting ocean climate. Specifically, the abundance and survivorship of kelp recruits and the abundance of macro-herbivores were compared between a ‘cool’ and a ‘warm’ region in northern and central Portugal, respectively. In each region, the abundance of kelp recruits and the intensity of grazing were compared between habitats of different topography within reefs (open reef vs. crevices). Compared to the ‘warm’ region, the abundance of kelp recruits was 3.9 times greater in the ‘cool’ region, where 85% of recruits were found in open reef habitats. In contrast, 87% of recruits in the ‘warm’ region were restricted to crevices. The ‘warm’ region had 140 times greater abundances of sea urchins, 45 times more herbivorous fish and 4.1 times more grazing marks on kelp recruits than the ‘cool’ region. Grazing assays showed ca. 50 times higher rates of kelp biomass consumption, mainly by fishes, and zero survivorship of kelp recruits in the ‘warm’ relative to the ‘cool’ region. This study suggests both temperature and herbivores affect abundances of kelp recruits across latitudes, and demonstrates how herbivores affect their distribution at local scales, driving kelp recruits into ‘hiding’ in crevices under intense herbivory. Consequently, where net recruitment success is compromised by herbivory, the persistence of kelps will be contingent on availability of topographical refuges. KEY WORDS: Atlantic Ocean · Portugal · Habitat complexity · Climate · Kelp forests · Grazing · Range limit Full text in pdf format Information about this Feature Article Supplementary material NextCite this article as: Franco JN, Wernberg T, Bertocci I, Duarte P, Jacinto D, Vasco-Rodrigues N, Tuya F (2015) Herbivory drives kelp recruits into ‘hiding’ in a warm ocean climate. Mar Ecol Prog Ser 536:1-9. https://doi.org/10.3354/meps11445 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 536. Online publication date: September 29, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Application of species distribution models to explain and predict the distribution, abundance and assemblage structure of nearshore temperate reef fishes

AbstractAimThe purpose of this study was to create predictive species distribution models (SDMs) for temperate reef‐associated fish species densities and fish assemblage diversity and richness to aid in marine conservation and spatial planning.LocationCalifornia, USA.MethodsUsing generalized additive models, we associated fish species densities and assemblage characteristics with seafloor structure, giant kelp biomass and wave climate and used these associations to predict the distribution and assemblage structure across the study area. We tested the accuracy of these predicted extrapolations using an independent data set. The SDMs were also used to estimate larger scale abundances to compare with other estimates of species abundance (uniform density extrapolation over rocky reef and density extrapolations taking into account variations in geomorphic structure).ResultsThe SDMs successfully modelled the species–habitat relationships of seven rocky reef‐associated fish species and showed that species’ densities differed in their relationships with environmental variables. The predictive accuracy of the SDMs ranged from 0.26 to 0.60 (Pearson's r correlation between observed and predicted density values). The SDMs created for the fish assemblage‐level variables had higher prediction accuracies with Pearson's r values of 0.61 for diversity and 0.71 for richness. The comparisons of the different methods for extrapolating species densities over a single marine protected area varied greatly in their abundance estimates with the uniform extrapolation (density values extrapolated evenly over the rocky reef) always estimating much greater abundances. The other two methods, which took into account variation in the geomorphic structure of the reef, provided much lower abundance estimates.Main conclusionsSpecies distribution models that combine geomorphic, oceanographic and biogenic habitat variables can reliably predict spatial patterns of species density and assemblage attributes of temperate reef fishes at spatial scales of 50 m. Thus, SDMs show great promise for informing spatial and ecosystem‐based approaches to conservation and fisheries management.

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.

Geographical variability in the controls of giant kelp biomass dynamics

AbstractAimCoastal marine environments experience a wide range of biotic and abiotic forces that can limit and punctuate the geographical range and abundance of species through time. Determining the relative strengths and nonlinear effects of these processes is vital to understanding the biogeographical structures of species. There has been an ongoing discussion concerning the relative importance of these processes in controlling the dynamics of giant kelp, Macrocystis pyrifera, an important structure‐forming species on shallow reefs in the eastern Pacific. We used novel spatial time‐series that span nearly three decades to determine the dominant drivers of giant kelp canopy biomass and the temporal and spatial scales over which they operate across the dominant range of the giant kelp in North America.LocationNear‐shore areas from Año Nuevo, California, to the USA/Mexico border.MethodsWe employed empirical orthogonal functions to elucidate the primary drivers of giant kelp canopy biomass across space and time and then fit generalized additive and linear models to determine the nonlinear effect and relative importance of each of these potential drivers along the c. 1500‐km study region over a 25‐year period.ResultsWave disturbance, nitrate availability and the state of the North Pacific Gyre Oscillation were the most important environmental predictors of giant kelp canopy biomass, explaining 24.5%, 12.7% and 6.1% of the variance, respectively. Environmental drivers of canopy biomass exhibited profound spatial differences in relative effect sizes. Nonlinear effect shapes of each potential biomass driver were determined, which explained these spatial differences.Main conclusionsThese large‐scale analyses help to reconcile the local‐scale conclusions of canopy biomass dynamics across the California coastline and show that these dynamics differ predictably in space and time in accordance with local and regional differences in environmental drivers. By characterizing the nonlinear effects of these drivers, we identified spatio‐temporal patterns of processes that cannot be detected by remote sensing.

Multi-approach mapping to help spatial planning and management of the kelp species L. digitata and L. hyperborea: Case study of the Molène Archipelago, Brittany

The Molène Archipelago in Brittany (France) hosts one of the largest kelp forests in Europe. Beyond their recognized ecological importance as an essential habitat and food for a variety of marine species, kelp also contributes towards regional economies by means of the alginate industry. Thousands of tons of kelp are collected each year for the needs of the chemical and food industries. Kelp harvesting in Brittany mainly concerns two species, Laminaria digitata (59,000t) and Laminaria hyperborea (24,000t), that, together, represent approximately 95% of the national landings. Estimating the available standing stock and its distribution is a clear need for providing appropriate and sustainable management measures.Prior to estimating the spatial distribution of biomasses, we produced a detailed seabed topography map with accurate hard substrate delineation thanks to surveys and appropriate processing of airborne optical and acoustic imaging. Habitat suitability models of presence–absence and biomass were then developed for each species by relating in situ observations from underwater video and sampling to the many biotic and abiotic factors that may govern kelp species distribution. Our statistical approach combining generalized additive models (GAM) in a delta approach also provided spatial uncertainty associated with each prediction to help management decisions.This study confirmed that the adopted strategy, based on an integrated approach, enhanced knowledge on kelp biomass distributions in the Molène Archipelago and provided a promising direct link between research and management. Indeed, the high resolution topography and hard substrate maps produced for the study greatly improved knowledge on the sea bottom of the area. This was also of major importance for an accurate mapping of kelp distribution. The quality of the habitat suitability models was verified with fishing effort data (RECOPESCA program) and confirmed by local managers and kelp harvesters. Based on the biomass maps produced and their associated confidence intervals, we proposed more precise management rules than those already in use for both L. digitata and L. hyperborea. Our mapping approach is a first step towards sustainable kelp species management in the area. Introducing higher resolution environmental variables and population dynamics would help interannual management.

Remote monitoring of giant kelp biomass and physiological condition: An evaluation of the potential for the Hyperspectral Infrared Imager (HyspIRI) mission

This study examines the potential of the Hyperspectral Infrared Imager (HyspIRI) mission for monitoring the biomass and physiological condition of giant kelp forests on local to global scales. Giant kelp is a highly dynamic foundation species that supports an ecologically and economically important ecosystem found throughout the globe. Satellite, airborne, and field data are used to evaluate the suitability of HyspIRI's spatial, temporal, and spectral coverage for capturing variability in giant kelp biomass and physiological state. We analyze a 28-year time series of giant kelp biomass derived from Landsat satellite imagery in order to identify the dominant temporal modes of variability in giant kelp biomass using the California coast as a model region likely to be relevant to other regions of the globe. Temporal variability in California kelp canopy biomass is compared to the expected availability of cloud-free HyspIRI Visible Shortwave Infrared (VSWIR) views for regions of the world that contain giant kelp populations. Spectral variability is explored by assessing how changes in the physiological condition of giant kelp canopy are exhibited in the reflectance and transmittance of kelp fronds. We compare chlorophyll a to carbon ratios (Chl:C) of kelp fronds collected off the coast of California to laboratory and airborne measurements of hyperspectral reflectance in order to develop metrics of kelp physiological condition.The seasonal cycle dominates giant kelp canopy biomass temporal variability. However, the strength and timing of this cycle varies in both space and time. Our projections of cloud-free HyspIRI coverage indicate that the sensor will be able to capture at least 1 cloud free view each season for nearly all of the global giant kelp habitats, thereby illustrating that HyspIRI will resolve the dominant seasonal cycles in giant kelp biomass. A novel spectral index developed here from field observations explained 76% of the variance in Chl:C and was applied to hyperspectral aircraft observations. These results demonstrate that the spatial, temporal, and spectral coverage provided by HyspIRI has the potential to provide new insights into the ecology and biophysiology of giant kelp.

Biosorption characteristics of uranium(VI) and thorium(IV) ions from aqueous solution using CaCl2-modified Giant Kelp biomass

The CaCl2-modified Giant Kelp biomass (Ca-GK) showed a higher adsorption capacity for U(VI) and Th(IV) ions than the unmodified biomass. FTIR analysis indicates that carboxylic (as main adsorption sites), hydroxyl, sulfonate, and amino groups are responsible for U(VI) and Th(IV) adsorption. The kinetic analysis indicates that the rate-limiting step is the chemical sorption process. The maximum mono-layer adsorption capacities of Ca-GK in mono-component systems were 156 and 135 mg g−1 for U(VI) and Th(IV) ions, respectively. In bi-component systems, the adsorption capacities for both U(VI) and Th(IV) were reduced significantly, and the Ca-GK showed a slight adsorption preference for U(VI) over Th(IV).

Positive feedback between large-scale disturbance and density-dependent grazing decreases resilience of a kelp bed ecosystem

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 522:1-13 (2015) - DOI: https://doi.org/10.3354/meps11193 FEATURE ARTICLE Positive feedback between large-scale disturbance and density-dependent grazing decreases resilience of a kelp bed ecosystem John M. O’Brien1,*, Robert E. Scheibling1, Kira A. Krumhansl1,2 1Department of Biology, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada 2Present address: Hakai Institute, Simon Fraser University, Burnaby, British Columbia V5A 1S6, Canada *Corresponding author: jh876261@dal.ca ABSTRACT: We examined how large-scale disturbances that defoliate kelp beds (outbreaks of an invasive bryozoan, hurricanes) alter local-scale grazing dynamics of an abundant herbivore, the gastropod Lacuna vincta, on the Atlantic coast of Nova Scotia, Canada. From field observations and a 5 wk kelp-thinning experiment that simulated disturbance, we found that snail density and grazing intensity on the kelp Saccharina latissima increased non-linearly with decreasing kelp biomass, as it varied within a site. Grazing intensity on S. latissima also increased non-linearly with decreasing standing kelp biomass across 5 sites spanning 40 km (linear distance) of coast and 2 yr, but we did not find strong support for this relationship for the kelp Laminaria digitata. Intensification of grazing augments the indirect effect of L. vincta on S. latissima (increased blade erosion and fragmentation), and drives it beyond a threshold for further losses of kelp biomass with subsequent storms. This positive feedback between large-scale disturbances and local-scale grazing could reinforce the depletion of kelp and facilitate the establishment of turf-forming algae on Nova Scotian rocky reefs. We conclude that interactions of large external perturbations with local natural perturbations must be considered to understand how drivers of ecosystem change collectively disrupt the balance of top-down and bottom-up forces to cause shifts to unexpected community states. KEY WORDS: Kelp · Turf-forming algae · Feedback · Synergy · Disturbance · Grazing · Hurricanes · Invasive species Full text in pdf format Information about this Feature Article Supplementary material NextCite this article as: O’Brien JM, Scheibling RE, Krumhansl KA (2015) Positive feedback between large-scale disturbance and density-dependent grazing decreases resilience of a kelp bed ecosystem. Mar Ecol Prog Ser 522:1-13. https://doi.org/10.3354/meps11193 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 522. Online publication date: March 02, 2015 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2015 Inter-Research.

Phenological decoupling of mortality from wave forcing in kelp beds.

Kelps often live in a harsh hydrodynamic environment where wave-driven dislodgement of individuals can alter the biodiversity and functioning of reef systems, and increase production in coastal ecosystems adjacent to reefs. The current paradigm is that winter storms tear kelps from reefs once hydrodynamic forces exceed attachment or tissue strength--a threshold response that implies a pulsed relationship between wave forces and dislodgement. Here, we challenge this understanding by showing how kelp phenology can decouple susceptibility to dislodgement from seasonal patterns in wave forces. We measured kelp dislodgement rates and hydrodynamic forces at nine subtidal reefs over two years (n = 4320 kelps tagged and monitored). Contrary to expectation, we found relatively low and constant dislodgement rates for all reefs (13% +/- 6% [mean per season +/- SD]) in spite of a strong temporal pattern in wave action and extreme water velocities (winter peaks up to 3-4 m/s). A biomechanical model, based on the balance between kelp attachment strength and hydrodynamic drag, demonstrated that severe reduction in individual kelp size toward winter (>50% decrease in biomass for all sites) minimized drag and made the kelps less susceptible to high water velocities, allowing individuals to survive storm velocities over 3-4 m/s. We conclude that the timing of reduced susceptibility to disturbance, through the seasonal reduction of individual kelp biomass that coincides with times of highest water velocities is critical to the dynamics of kelp dislodgement and survival. We propose that phenological processes maintain many kelp beds in a higher degree of population stability and equilibrium with hydrodynamic forces than previously believed.

Production and economic assessment of giant kelpMacrocystis pyriferacultivation for abalone feed in the south of Chile

Kelp biomass availability for mass abalone cultivation remains a critical issue in Chile. The technical and economic feasibility of a commercial scale kelp farming activity has not been established. This study describes the production and economic results of a pilot scale unit installed in southern Chile. Our results show 25 kg m−1 of production over a 9-month spring-summer period, and 16.2 kg m−1 during the autumn-winter period. These values indicate that a total biomass production of 41.3 kg (wet) m−1 year−1 can be obtained by placing the culture lines at 4 m intervals. High quality animal food-grade plants with a 9% protein content, over 5 m in length were harvested. Sensitivity analysis showed that by cultivating 30–50 ha with a market value of US$ 78 ton−1, a return on investment can be made after the first year.

Modeling effects of climate change and phase shifts on detrital production of a kelp bed.

The exchange of energy and nutrients between ecosystems (i.e., resource subsidies) plays a central role in ecological dynamics over a range of spatial and temporal scales. Little attention has been paid to the role of anthropogenic impacts on natural systems in altering the magnitude, timing, and quality of resource subsidies. Kelp ecosystems are highly productive on a local scale and export over 80% of kelp primary production as detritus, subsidizing consumers across broad spatial scales. Here, we generate a model of detrital production from a kelp bed in Nova Scotia to hindcast trends in detrital production based on temperature and wave height recorded in the study region from 1976 to 2009, and to project changes in detrital production that may result from future climate change. Historical and projected increases in temperature and wave height led to higher rates of detrital production through increased blade breakage and kelp dislodgment from the substratum, but this reduced kelp biomass and led to a decline in detrital production in the long-term. We also used the model to demonstrate that the phase shift from a highly productive kelp bed to a low-productivity barrens, driven by the grazing activity of sea urchins, reduces kelp detrital production by several orders of magnitude, an effect that would be exacerbated by projected increases in temperature and wave action. These results indicate that climate-mediated changes in ecological dynamics operating on local scales may alter the magnitude of resource subsidies to adjacent ecosystems, affecting ecological dynamics on regional scales.

Variation in morphology and PSII photosynthetic characteristics ofMacrocystis pyriferaduring development from gametophyte to juvenile sporophyte

Currently, there is increasing demand for brown kelp, especially Macrocystis spp., to support the development of the abalone industry and for use as raw material for the production of alginate. Thus, there is a need to supplement the naturally available kelp biomass with the development of mariculture techniques. In this study, we investigated whether it was possible to cultivate Macrocystis pyrifera sporophytes in the laboratory using gametophyte clones. We propagated gametophytes by periodic fragmentation and then mixed aseptically an equal number of male and female gametophytes to induce fertilization. Approximately 60 days after fertilization, numerous embryonic sporophytes emerged on the seed fibre. By using chlorophyll fluorescence technology, we investigated variation in the photosystem II (PSII) characteristics of M. pyrifera during development from the gametophyte to juvenile sporophyte stage. During this growth period, both the optimal (Fv/Fm) and effective (YII) PSII quantum yields increased significantly from the haploid gametophyte to diploid sporophyte stages. In addition, by comparing female gametophytes with male gametophytes, we found that female gametophytes were not only larger and more pigmented than the males, but also recorded higher values of Fv/Fm and YII. Our results supplemented information on the life cycle and PSII photosynthetic performance during the early development and confirmed the possibility of artificial seeding technology, both of which may contribute to mariculture of M. pyrifera in China in the near future.

Major consequences of minor damage: impacts of small grazers on fast-growing kelps.

Damage by small herbivores can have disproportionately large effects on the fitness of individual plants if damage is concentrated on valuable tissues or on select individuals within a population. In marine systems, the impact of tissue loss on the growth rates of habitat-forming algae is poorly understood. We quantified the grazing damage by an isopod Amphoroidea typa on two species of large kelps, Lessonia spicata and Macrocystis pyrifera, in temperate Chile to test whether non-lethal grazing damage could reduce kelp growth rates and photosynthetic efficiency. For L. spicata, grazing damage was widespread in the field, unevenly distributed on several spatial scales (among individuals and among tissue types) and negatively correlated with blade growth rates. In field experiments, feeding by A. typa reduced the concentration of photosynthetic pigments and led to large reductions (~80%) in blade growth rates despite limited loss of kelp biomass (0.5% per day). For M. pyrifera, rates of damage in the field were lower and high densities of grazers were unable to reduce growth rates in field experiments. These results demonstrate that even low per capita grazing rates can result in large reductions in the growth of a kelp, due the spatial clustering of herbivores in the field and the selective removal of photosynthetically active tissues. The impacts of small herbivores on plant performance are thus not easily predicted from consumption rates or abundance in the field, and vary with plant species due to variation in their ability to compensate for damage.

Coalescence in wild organisms of the intertidal population of Lessonia berteroana in northern Chile: management and sustainability effects

Lessonia berteroana is the subject of 85 % of the total harvest of Chilean brown seaweeds, representing close to 10 % of total kelp biomass worldwide harvested for alginic acid extraction. Frequent incidence of coalescent holdfasts was detected in natural populations, and this process gives rise to fused sporophytes. This study presents the coalescence events in natural populations in northern Chile. During 2011, in natural intertidal populations, 435 target sporophytes of different sizes were observed weekly and 63.90 % (278) showed physical signs of coalescent disks. We were able to distinguish five fusion modes depending on the number and size of each of the participant sporophytes and their spatial distribution. There was a progressive decrease of density and an increase in the number of stipes of each sporophyte over time. Two processes were recognized: active fusion of juvenile sporophytes and passive fusion of adult and senescent sporophytes. However, most of the coalescence processes were detected in juvenile sporophytes with a holdfast diameter of 0.5 to 2 cm. The minimum distance between pairs of coalescing sporophytes was 0.5 cm, and the maximum distance was 13 cm. For good harvesting practices, it is recommended that plants with over 20 cm holdfast diameter are harvested from natural populations because over this size, all of the plants have reproduced. Coalescence events would produce plants with legal size requirement; however, these plant units would not be reproductive, affecting the sustainability of this important coastal resource.

Contrasting mechanisms of dislodgement and erosion contribute to production of kelp detritus

We quantified simultaneously dislodgement and erosion for a dominant kelp species (Ecklonia radiata) over 1 yr, and related both to potential explanatory factors (wave exposure, temperature, and kelp fecundity). Erosion was the largest contributor of detritus, accounting for 80% of annual production. Most erosion occurred as a major pulse in autumn, whereas dislodgement was a minor and constant process throughout the year. Neither erosion nor dislodgement was correlated with water velocity (as often proposed), and this finding contradicts the common assumption that high dislodgement rates during peak wave action account for the bulk of detrital production. Together with low growth, the high erosion rate led to a severe reduction of individual kelp biomass in autumn (from 600 g to 300 g fresh weight kelp−1), reducing drag forces on kelp thalli by ∼ 50%, likely reducing their susceptibility to dislodgement during peak wave action. Instead, a pulse of detrital production coincided with periods of peak kelp fecundity. We propose that sporogenesis weakens the tissue, making E. radiata more susceptible to erosion, and that the ensuing changes in kelp morphology decouple detrital production from the wave‐action forces.