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The recent surge in interest for restoring kelp forests in California has created a confusing and crowded landscape to navigate. Additionally, most existing resources are in the form of formal reports or journal articles, both of which rely heavily on specific terminology and can be physically locked behind a paywall. It is therefore unreasonable to assume interested members of the public and policy makers can reliably access or understand the intricacies of the kelp restoration landscape. To address these gaps, this project develops a multimedia web-based resource that provides unique access to kelp restoration projects happening in California. Through photos, videos, audio and maps, users can interact with the StoryMap and learn directly from stakeholders and learn how they are using various methodologies to restore kelp in California.See media created for this project here:https://storymaps.arcgis.com/stories/d35a011b5dd747b89d4d94d324e62693

Macrocystis pyrifera (giant kelp), a haplodiplontic brown macroalga that alternates between a macroscopic diploid (sporophyte) and a microscopic haploid (gametophyte) phase, provides an ideal system to investigate how ploidy background affects the evolutionary history of a gene. In M. pyrifera, the same genome is subjected to different selective pressures and environments as it alternates between haploid and diploid life stages. We assembled M. pyrifera gene models using available expression data and validated 8,292 genes models using the model alga Ectocarpus siliculosus. Differential expression analysis identified gene models expressed in either or both the haploid and diploid life stages while functional annotation identified processes enriched in each stage. Genes expressed preferentially or exclusively in the gametophyte stage were found to have higher nucleotide diversity (π = 2.3 × 10–3 and 2.8 × 10–3, respectively) than those for sporophytes (π = 1.1 × 10–3 and 1 × 10–3, respectively). While gametophyte-biased genes show faster sequence evolution, the sequence evolution exhibits less signatures of adaptations when compared to sporophyte-biased genes. Our findings contrast the standing masking hypothesis, which predicts higher standing genetic variation at the sporophyte stage, and support the strength of expression theory, which posits that genes expressed more strongly are expected to evolve slower. We argue that the sporophyte stage undergoes more stringent selection compared with the gametophyte stage, which carries a heavy genetic load associated with broadcast spawning. Furthermore, using whole-genome sequencing, we confirm the strong population structure in wild M. pyrifera populations previously established using microsatellite markers, and estimate population genetic parameters, such as pairwise genetic diversity and Tajima’s D, important for conservation and domestication of M. pyrifera.

Significance Landscapes are spatially heterogeneous, and the measurement of spatial pattern is dependent upon observation scale. Understanding plant populations requires assessing their extrinsic interactions with the environment as well as intrinsic biological processes and has been difficult because of the inability to track both plant abundance and health on appropriate scales. We introduce remote sensing observations that assess the abundance and health of giant kelp, an important ecosystem-structuring species, over regional and local scales. We find that both extrinsic nutrient availability and intrinsic senescence processes regulate population dynamics but on regional and local scales, respectively. This suggests that future satellite missions will be able to assess plant abundance and health and their interactions with the environment on local to global scales., Disentangling the roles of the external environment and internal biotic drivers of plant population dynamics is challenging due to the absence of relevant physiological and abundance information over appropriate space and time scales. Remote observations of giant kelp biomass and photosynthetic pigment concentrations are used to show that spatiotemporal patterns of physiological condition, and thus growth and production, are regulated by different processes depending on the scale of observation. Nutrient supply was linked to regional scale (>1 km) physiological condition dynamics, and kelp forest stands were more persistent where nutrient levels were consistently high. However, on local scales (

The DOD relies heavily on UUVs for mine countermeasure missions to provide safe passage for their ships. Unwanted interactions between UUVs and marine vegetation present in littoral areas pose a threat to their mission success. Not much is known about the mechanisms of these interactions. This thesis studies the interactions between a box-shaped UUV and two types of marine vegetation found in littoral regions. The equipment and procedures used closely followed previous work done with a torpedo-shaped UUV. To estimate the vehicle’s speed, calibration runs were performed. Experimental runs were done, at different speeds, both with and without the UUV constrained. The runs were conducted in different settings consisting of synthetic giant kelp or eelgrass and different density configurations. The resulting interactions were dependent on the vegetation type, vegetation density, vehicle speed, and vehicle geometry. The synthetic giant kelp caused interactions such as blockage and entanglement with the vehicle’s body and propellers. The only adverse interactions caused by the synthetic eelgrass were entanglement with the propellers, but they were severe. The best results were those at lower densities and higher speeds, while higher densities and lower speeds had the worst prognosis. The constrained UUV runs resulted in fewer unwanted interactions. When comparing previous results, the torpedo-shaped UUV had more success at going through the vegetation than the box-shaped UUV. Lieutenant, United States Navy Approved for public release. Distribution is unlimited.

The emerging sector of offshore kelp aquaculture represents an opportunity to produce biofuel feedstock to help meet growing energy demand. Giant kelp represents an attractive aquaculture crop due to its rapid growth and production, however precision farming over large scales is required to make this crop economically viable. These demands necessitate high frequency monitoring to ensure outplant success, maximum production, and optimum quality of harvested biomass, while the long distance from shore and large necessary scales of production makes in person monitoring impractical. Remote sensing offers a practical monitoring solution and nascent imaging technologies could be leveraged to provide daily products of the kelp canopy and subsurface structures over unprecedented spatial scales. Here, we evaluate the efficacy of remote sensing from satellites and aerial and underwater autonomous vehicles as potential monitoring platforms for offshore kelp aquaculture farms. Decadal-scale analyses of the Southern California Bight showed that high offshore summertime cloud cover restricts the ability of satellite sensors to provide high frequency direct monitoring of these farms. By contrast, daily monitoring of offshore farms using sensors mounted to aerial and underwater drones seems promising. Small Unoccupied Aircraft Systems (sUAS) carrying lightweight optical sensors can provide estimates of canopy area, density, and tissue nitrogen content on the time and space scales necessary for observing changes in this highly dynamic species. Underwater color imagery can be rapidly classified using deep learning models to identify kelp outplants on a longline farm and high acoustic returns of kelp pneumatocysts from side scan sonar imagery signal an ability to monitor the subsurface development of kelp fronds. Current sensing technologies can be used to develop additional machine learning and spectral algorithms to monitor outplant health and canopy macromolecular content, however future developments in vehicle and infrastructure technologies are necessary to reduce costs and transcend operational limitations for continuous deployment in an offshore setting.

Modern multibeam echosounders can record backscatter data returned from the water above the seafloor. These water-column data can potentially be used to detect and map aquatic vegetation such as kelp, and thus contribute to improving marine habitat mapping. However, the strong sidelobe interference noise that typically contaminates water-column data is a major obstacle to the detection of targets lying close to the seabed, such as aquatic vegetation. This article presents an algorithm to filter the noise and artefacts due to interference from the sidelobes of the receive array by normalizing the slant-range signal in each ping. To evaluate the potential of the filtered data for the detection of aquatic vegetation, we acquired a comprehensive water-column dataset over a controlled experimental site. The experimental site was a transplanted patch of giant kelp (Macrocystis pyrifera) forest of known biomass and spatial configuration, obtained by harvesting several individuals from a nearby forest, measuring and weighing them, and arranging them manually on an area of seafloor previously bare. The water-column dataset was acquired with a Kongsberg EM 2040 C multibeam echosounder at several frequencies (200, 300, and 400 kHz) and pulse lengths (25, 50, and 100 μs). The data acquisition process was repeated after removing half of the plants, to simulate a thinner forest. The giant kelp plants produced evident echoes in the water-column data at all settings. The slant-range signal normalization filter greatly improved the visual quality of the data, but the filtered data may under-represent the true amount of acoustic energy in the water column. Nonetheless, the overall acoustic backscatter measured after filtering was significantly lower, by 2 to 4 dB on average, for data acquired over the thinned forest compared to the original experiment. We discuss the implications of these results for the potential use of multibeam echosounder water-column data in marine habitat mapping.

The ecology of an epibiont may depend not only on the dynamics of its biogenic habitat but also on microclimate variation generated within aggregations of its host, a process called physical ecosystem engineering. This study explored variation in the abundance and demography of Membranipora, a suspension-feeding bryozoan, within forests of giant kelp (Macrocystis pyrifera) off the coast of Santa Barbara, California, USA. First, we assessed differences in Membranipora abundance between the edge and interior of kelp forests. The occurrence of Membranipora on kelp blades and its percent cover on occupied blades were higher along forest edges than interiors. Second, we conducted observational studies and field experiments to understand spatial variation in substrate longevity, colony mortality, larval recruitment, and colony growth rates. A higher density of recruits and colonies occurred along forest edges than interiors, suggesting kelp acts like a sieve, whereby larvae settle to edge blades first. Moreover, growth rates along the edge were up to 45% higher than forest interiors. Reduced current speeds, combined with feeding by exterior colonies, may have lowered the uptake of suspended food particles by interior colonies. These results suggest that variation in Membranipora abundance is due in part to differences in colony growth between forest edges and interiors, and not solely the result of recruitment limitation. Our results highlight the importance of ecosystem engineers in influencing the ecological dynamics of epiphytic flora and fauna in marine systems.

In 2014-2016 the west coast of North America experienced a marine heatwave that was unprecedented in the historical record in terms of its duration and intensity. This event was expected to have a devastating impact on populations of giant kelp, an important coastal foundation species found in cool, nutrient rich waters. To evaluate this expectation, we used a time series of satellite imagery to examine giant kelp canopy biomass before, during, and after this heatwave across more than 7 degrees of latitude in southern and Baja California. We examined spatial patterns in resistance, i.e. the initial response of kelp, and resilience, i.e. the abundance of kelp two years after the heatwave ended. The heatwave had a large and immediate negative impact on giant kelp near its southern range limit in Baja. In contrast, the impacts of the heatwave were delayed throughout much of the central portion of our study area, while the northern portions of our study area exhibited high levels of resistance and resilience to the warming, despite large positive temperature anomalies. Giant kelp resistance throughout the entire region was most strongly correlated with the mean temperature of the warmest month of the heatwave, indicating that the loss of canopy was more sensitive to exceeding an absolute temperature threshold than to the magnitude of relative changes in temperature. Resilience was spatially variable and not significantly related to SST metrics or to resistance, indicating that local scale environmental and biotic processes played a larger role in determining the recovery of kelp from this extreme warming event. Our results highlight the resilient nature of giant kelp, but also point to absolute temperature thresholds that are associated with rapid loss of kelp forests.

Giant kelp (Macrocystis pyrifera) is the most widely distributed kelp species on the planet, constituting one of the richest and most productive ecosystems on Earth, but detailed information on its distribution is entirely missing in some marine ecoregions, especially in the high latitudes of the Southern Hemisphere. Here, we present an algorithm based on a series of filter thresholds to detect giant kelp employing Sentinel-2 imagery. Given the overlap between the reflectances of giant kelp and intertidal green algae (Ulvophyceae), the latter are also detected on shallow rocky intertidal areas. The kelp filter algorithm was applied separately to vegetation indices, the Floating Algae Index (FAI), the Normalised Difference Vegetation Index (NDVI), and a novel formula (the Kelp Difference, KD). Training data from previously surveyed kelp forests and other coastal and ocean features were used to identify reflectance threshold values. This procedure was validated with independent field data collected with UAV imagery at a high spatial resolution and point-georeferenced sites at a low spatial resolution. When comparing UAV with Sentinel data (high-resolution validation), an average overall accuracy ≥ 0.88 and Cohen’s kappa ≥ 0.64 coefficients were found in all three indices for canopies reaching the surface with extensions greater than 1 hectare, with the KD showing the highest average kappa score (0.66). Measurements between previously surveyed georeferenced points and remotely-sensed kelp grid cells (low-resolution validation) showed that 66% of the georeferenced points had grid cells indicating kelp presence within a linear distance of 300 m. We employed the KD in our kelp filter algorithm to estimate the global extent of giant kelp and intertidal green algae per marine ecoregion and province, producing a high-resolution global map of giant kelp and intertidal green algae, powered by Google Earth Engine.

Egg masses of the Patagonian squid Doryteuthis (Amerigo) gahi attached to giant kelp ( Macrocystis pyrifera ) in the Magellanic channels of the sub-Antarctic ecoregion in southern South America is documented for the first time. Of seven egg masses observed between 2008 and 2011, one was taken to the laboratory to be analysed and photographed. Comprising long transparent capsules containing eggs, the masses were strongly attached to the stipes of M. pyrifera . This macroalgae is a potentially important economic resource due to its multiple industrial uses; this study shows that it also serves an important ecological role as a spawning substrate for D. gahi . Keywords: Doryteuthis ; egg masses; giant kelp; Patagonian squid; sub-Antarctic ecoregion (Published: 5 November 2014) Citation: Polar Research 2014, 33 , 21636, http://dx.doi.org/10.3402/polar.v33.21636

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.

Patterns of spatial genetic structure (SGS), typically estimated by genotyping adults, integrate migration over multiple generations and measure the effective gene flow of populations. SGS results can be compared with direct ecological studies of dispersal or mating system to gain additional insights. When mismatches occur, simulations can be used to illuminate the causes of these mismatches. Here, we report a SGS and simulation-based study of self-fertilization in Macrocystis pyrifera, the giant kelp. We found that SGS is weaker than expected in M. pyrifera and used computer simulations to identify selfing and early mortality rates for which the individual heterozygosity distribution fits that of the observed data. Only one (of three) population showed both elevated kinship in the smallest distance class and a significant negative slope between kinship and geographical distance. All simulations had poor fit to the observed data unless mortality due to inbreeding depression was imposed. This mortality could only be imposed for selfing, as these were the only simulations to show an excess of homozygous individuals relative to the observed data. Thus, the expected data consistently achieved nonsignificant differences from the observed data only under models of selfing with mortality, with best fits between 32% and 42% selfing. Inbreeding depression ranged from 0.70 to 0.73. The results suggest that density-dependent mortality of early life stages is a significant force in structuring Macrocystis populations, with few highly homozygous individuals surviving. The success of these results should help to validate simulation approaches even in data-poor systems, as a means to estimate otherwise difficult-to-measure life cycle parameters.

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.

Chile is an important producer of brown seaweeds representing 10% of world supply. Landings of Chilean kelp fluctuated between 40,000 t.year−1 in the early ‘80s to 250,000 t.year−1 more recently. Commercialized algae come from natural populations and no mass-cultures of involved species have been established. Four species of brown algae are commercially collected in the country: Lessonia trabeculata, L. nigrescens, Macrocystis pyrifera and M. integrifolia. Since 2000, the demand of alginate sources and food for cultivated abalones dramatically raised the harvesting of these species. Direct evaluations of Lessonia spp. and Macrocystis standing-stocks were made along 700 km of coast in northern Chile. Lessonia spp. estimated populations exceed 900,000 t, whereas M. integrifolia does not exceed 300 t. The insights provided indicate that sustainability of Chilean kelp subjected to intense harvesting would require management programs including the following bio-ecological recommendations: (1) to harvest the entire plant including the holdfast; (2) to harvest plants larger than 20 cm in diameter; (3) to harvest plants sparsely, selecting mayor specimens; (4) rotation of harvesting areas; and (5) for Macrocystis, to cut the canopy 1–2 m from the surface. They must be implemented in a National Program of Kelp Management, elaborated by government, scientists, fisherman, and industry.

This study explores the potential cultivation of the giant kelp Macrocystis pyrifera (L.) C.A. Agardh in southern Chile, for the development of novel food products. The study demonstrates the importance of considering the collection site of the parent sporophytes for successful cultivation. This study also shows that the ropes must be seeded with 10,000 to 40,000 spores ml−1, depending on the culture method used. We also demonstrated that under environmental conditions in southern Chile, the seeded ropes must be put at sea at the latest during autumn (April) in order to reach the harvesting season in December. However, several other management aspects must be considered to improve the quality of the product. Our final estimation indicates that over 14.4 kg m−1of rope (fresh weight) can be produced and from this total production, over 70% can reach the quality to produce different food products that are already being introduced in oriental countries. The remaining 30% can be used for abalone feeding and is also available for the organic fertilizer industry located in Chile.

Energy fixed by primary producers supports the vast majority of life on earth. The giant kelp Macrocystis pyrifera is the largest marine alga in the world and supports one of the most productive ecosystems on earth. Carbon fixed by Macrocystis pyrifera on temparate rocky reefs not only provides essential habitat for an entire community of associated species, but also provides carbon subsidies to nearby ecological communities. Net primary productivity (NPP) is often used to quantify energy fixation by autotrophs, and researchers often measure NPP by summing the incremental increases in biomass and foliar losses. While the processes governing incremental increases in biomass have been well studied, the processes that drive the loss of foliar biomass are poorly understood.The main theme of my research is the investigation of the drivers that regulate the lifespan of foliar biomass of giant kelp beds near Santa Barbara, California, USA. Tissue lifepspan in marine macroalgae has not received much attention from either plant ecologists or algal ecologists, despite its potential importance to the dynamics of primary productivity. Macrocystis is an ideal species for investigations on tissue lifespan in macroalgae for two main reasons. First, it is well studied and much of its biology is already known, and second, Macrocystis is locally abundant, grows fast and turns over frequently. In addition, due to relatively benign environmental conditions for Macrocystis growth, the coastal margin along the Santa Barbara Channel is an ideal location to study intrinsic properties in the absence of extreme environmental forcing (such as frequent temperature spikes and severe storm events) that could overwhelm potentially important patterns.I investigated drivers that regulate frond and blade lifespan in Macrocystis, and the consequences of limited frond and blade lifespans. The first chapter is a long-term, multi-site analysis of frond lifetimes and exploration of internal and external drivers that could affect frond lifetime. This study provides broad spatial and temporal scope and identifies progressive senescence as an important driver of Macrocystis biomass dynamics. The second chapter employs a more focused field study to investigate whether spatial variability in light within a kelp forests affects lifespan, size, thickness, nitrogen content and pigment content of Macrocystis pyerifera blades in ways that are predicted by theory developed to predict leaf traits of vascular plants. The last chapter is a mathematical model of the system, which I parameterized with field data, to explicitly quantify the loss of blade tissue via erosion and quantify the amount of biomass not captured in traditional surveys of net primary productivity. I found that the natural course of progressive senescence in fronds can explain much of the variability in frond loss throughout a typical year in a Santa Barbara kelp bed, that kelp blades that have more access to light have shorter lifetimes (as predicted by leaf lifespan theory), and that ignoring the sub-lethal blade area losses can result in significant underestimates of net primary productivity. I believe that internal regulation of tissue turnover is an important mechanism by which giant kelp maximizes carbon gain in a changing environment and that adaptations that increase photosynthetic efficiency may be an important factor in the widespread success and dominance of Macrocystis.

Kelp cultivation started in Japan, China and Korea, mainly for human consumption; new applications are still expanding. In Chile, three ‘wild’ Lessonia species and Macrocystis pyrifera are under a strong and increasing pressure of exploitation mainly for alginate production and as a source of feed for abalone. Regulatory restrictions for kelp exploitation and the increased demand for biomass provided a positive environment for the installation of a kelp farming industry. Pilot-production studies demonstrated that 200 tonnes (fresh)/ha/year can be achieved and genetic diversity and breeding studies suggested that this volume could be increased. Kelp disease research is a necessary condition for securing the future development of this industry, as are environmental studies on the impacts of large-scale aquaculture. Beyond the positive bioremediation, ecosystem service effects that kelp farming can provide, especially in a region such as in southern Chile, where intensive salmon and mussel cultivation occurs. Life Cycle Assessment suggests that the energy returns on investment in kelp farming are positive, but more detailed data are still required.

1st Mares Conference on Marine Ecosystems Health and Conservation. Olhão, Portugal 17-21 November 2014. Kelp forests represent some of the most conspicuous coastal habitats and today we recognize only one giant kelp species (Macrocystis pyrifera) distributed globally [1, 2]. M. pyrifera is recognized as a perennial kelp species with a low capacity of energy storage, whereas its high productivity is associated the availability of nitrogen from the water column [3]. The relation between M. pyrifera growth and biomass production results from a plastic response of the sporophytes to temporal and spatial variability in nitrogen availability [4, 5]. However, the low storage capacity of giant kelp [6, 7] is clearly disadvantageous during periods of suboptimal environmental conditions; as those that occur seasonally in California and the inland waters of southern Chile. Due to an increased demand for kelp biomass in Chile for the world alginate industry and abalone farming in Chile [8, 9] there is an increased demand of raw material and interest for developing kelp aquaculture technologies [10]. The present study evaluates the effect of different nitrogen availability on the growth and regeneration of juvenile fronds of M. pyrifera sporophytes from southern Chile and explore its consequences for the development of seeding strategies of kelp farming in southern Chile.

Ocean currents are expected to be the predominant environmental factor influencing the dispersal of planktonic larvae or spores; yet, their characterization as predictors of marine connectivity has been hindered by a lack of understanding of how best to use oceanographic data. We used a high-resolution oceanographic model output and Lagrangian particle simulations to derive oceanographic distances (hereafter called transport times) between sites studied for Macrocystis pyrifera genetic differentiation. We build upon the classical isolation-by-distance regression model by asking how much additional variability in genetic differentiation is explained when adding transport time as predictor. We explored the extent to which gene flow is dependent upon seasonal changes in ocean circulation. Because oceanographic transport between two sites is inherently asymmetric, we also compare the explanatory power of models using the minimum or the mean transport times. Finally, we compare the direction of connectivity as estimated by the oceanographic model and genetic assignment tests. We show that the minimum transport time had higher explanatory power than the mean transport time, revealing the importance of considering asymmetry in ocean currents when modelling gene flow. Genetic assignment tests were much less effective in determining asymmetry in gene flow. Summer-derived transport times, in particular for the month of June, which had the strongest current speed, greatest asymmetry and highest spore production, resulted in the best-fit model explaining twice the variability in genetic differentiation relative to models that use geographic distance or habitat continuity. The best overall model also included habitat continuity and explained 65% of the variation in genetic differentiation among sites.

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Giant kelp (Macrocystis spp.) occurs as extensive beds along the coasts of Baja California and California. The kelp beds form desirable habitat for fishes and invertebrates. The kelp plants are harvested and processed to produce food additives and chemicals. Many Califorman kelp beds have dwindled or disappeared since 1940. We have developed a number of aquacultural techniques to reverse trends of deterioration. One important cause of kelp bed damage can arise from grazing by sea urchins or herbivorous fishes. Urchins can be controlled by quicklime or by crushing the animals with hammers. Fishes can be controlled by netting. In areas where kelp is sparse or has disappeared, stands can be recreated by transplantation techniques. Where reproductive processes are not adequate to maintain a stable population, mass cultures of microscopic gametophytes and sporophytes can be introduced.

Harvestable yield of the giant kelp, Macrocystis pyrifera (L.) C. Agardh, is important to its use as a commercial source of phycocolloids and to development of marine biomass as an energy resource. Accurate prediction of yields from natural populations and from crop plants on future marine farms is necessary for optimum utilization of the natural resource and for optimum design and management of the cultivated resource. The nature of the yield parameter - a single value integrating a number of dynamic processes over a relatively long time period - makes accurate prediction difficult. Temporal and spatial variability in growth, biomass production and loss, population structure and density might preclude reliable extrapolation of empirical yield values to populations at other sites or times. To determine the magnitude of short-term temporal variability and better to define relationships between kelp growth, biomass production and yield, we held a population of adult M. pyrifera under partially controlled conditions. Nutrient supply, plant density, and holdfast depth were controlled. Irradiance and temperature were not controlled but were monitored continuously. Growth and population parameters were measured over relatively short intervals. Harvestable yield was determined empirically for the entire study period.

Light influences photosynthesis and morphogenesis in both the gametophyte and sporophyte of the giant kelp Macrocystis (Luning & Neushul 1978; Luning 1981, Neushul et al. 1983). However, the large size and morphological complexity of the sporophyte complicates attempts to define clearly the role that light plays. It is reasonable to assume that light influences all stages of development, from the time when the sporophyte begins growth as a microscopic zygote to maturity. It first grows to form a simple single blade which in turn develops into a complex organism that can have over 100 multibladed fronds, a large holdfast, and a complex basal branching system. At maturity, the plant extends from the dimly lit sea floor to full sunlight at the sea surface. The surface canopy shades the deeper blades. It is known that translocation occurs within the plant (Lobban 1978), and that carbon reserves are allocated to the meristems, holdfast and sporophylls. Seasonally the light-climate in the sea is influenced by a combination of climatological and oceanographic factors, adding further complications to an already complex problem (Neushul 1971).

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Kelp species, the larger members of brown-colored marine plants, are widely cultivated and have been utilized by many peoples as food, fertilizer, a source of chemicals, and as fodder for domestic animals. Interest has recently developed in usage as alternative energy sources (kelp tissue would be converted to methane via bacterial fermentation). Kelp life cycles involve an alternation of generations from an entirely microscopic phase to a phase that includes the large macroscopic plant utilized by humans. The complex life history imposes culturing requirements beyond the usual degree of care needed for propagating terrestrial plants. These difficulties notwithstanding, kelp cultivation is successfully practiced, particularly in the Orient. Culturing techniques range from artificially "seeding" an artificial substrate which may eventually be outplanted to the sea, to transplanting large mature individuals to desired locations, allowing them to "seed" naturally and establish their populations. Giant kelp, Macrocystis, is the principal brown alga utilized commercially in the United States. Culturing techniques have been developed for growing Macrocystis. Depleted kelp beds in southern California have been successfully restored utilizing these methods.

Requirements of Macrocystis pyrifera (L.) C.A. Agardh gametophytes for nine nutrients (Co, Cu, Fe, I, Mn, Mo, N, P and Zn) were established by means of the chemically defined, artificial seawater, Aquil. Optimal growth ranges for total concentrations of Co, Cu, Fe, Mn, Zn and NO3-N and for media temperatures were determined. Effects on Macrocystis gametophytic growth within these optimal ranges were then investigated. Mathematical equations modeling gametophytic length as a function of concentrations of NO3-N, Fe and Zn, and Zn, Mn, Cu and Co were generated by least squares fit of experimental data. An Aquil formulation was developed that consistently produced Macrocystis embryonic sporophytes after 12 culturing days. Sporophyte production was achieved in Aquil using sporophylls from a variety of southern California sampling sites to initiate gametophytic cultures. This marks the first instance that any macroalga has been successfully cultured in a chemically defined artificial seawater medium using ultraclean techniques.

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