The giant kelp Macrocystis is the world's largest benthic organism and most widely distributed ke... more The giant kelp Macrocystis is the world's largest benthic organism and most widely distributed kelp taxon, serving as the foundation for diverse and energy-rich habitats that are of great ecological and economical importance. Although the basic and applied literature on Macrocystis is extensive and multinational, studies of large Macrocystis forests in the northeastern Pacific have received the greatest attention. This review synthesises the existing Macrocystis literature into a more global perspective. During the last 20 yr, the primary literature has shifted from descriptive and experimental studies of local Macrocystis distribution, abundance and population and community structure (e.g., competition and herbivory) to comprehensive investigations of Macrocystis life history, dispersal, recruitment, physiology and broad-scale variability in population and community processes. Ample evidence now suggests that the genus is monospecific. Due to its highly variable physiology and life history, Macrocystis occupies a wide variety of environments (intertidal to 60+ m, boreal to warm temperate) and sporophytes take on a variety of morphological forms. Macrocystis sporophytes are highly responsive to environmental variability, resulting in differential population dynamics and effects of Macrocystis on its local environment. Within the large subtidal giant kelp forests of southern California, Macrocystis sporophytes live long, form extensive surface canopies that shade the substratum and dampen currents, and produce and retain copious amounts of reproductive propagules. The majority of subtidal Macrocystis populations worldwide, however, are small, narrow, fringing forests that are productive and modify environmental resources (e.g., light), yet are more dynamic than their large southern California counterparts with local recruitment probably resulting from remote propagule production. When intertidal, Macrocystis populations exhibit vegetative propagation. Growth of high-latitude Macrocystis sporophytes is seasonal, coincident with temporal variability in insolation, whereas growth at low latitudes tracks more episodic variability in nutrient delivery. Although Macrocystis habitat and energy provision varies with such ecotypic variability in morphology and productivity, the few available studies indicate that Macrocystis -associated communities are universally diverse and productive. Furthermore, temporal and spatial variability in the structure and dynamics of these systems appears to be driven by processes that regulate Macrocystis distribution, abundance and productivity, rather than the consumptive processes that make some other kelp systems vulnerable to overexploitation. This global synthesis suggests that the great plasticity in Macrocystis form and function is a key determinant of the great global ecological success of Macrocystis .
We use data from San Miguel Island shell middens spanning much of the past 10,000 years in a prel... more We use data from San Miguel Island shell middens spanning much of the past 10,000 years in a preliminary exploration of long-term ecological relationships between humans, sea otters (Enhydra lutris), shellfish, and kelp forests. At Daisy Cave, human use of marine habitats begins almost 11,500 years ago, with the earliest evidence for shellfish harvesting (11,500 cal BP), intensive kelp bed fishing (ca. 10,000-8500 cal BP), and Sea Otter hunting (ca. 8900 cal BP) from the Pacific Coast of North America. On San Miguel Island, Native Americans appear to have coexisted with sea otters and productive shellfish populations for over 9,000 years, but the emphasis of shellfish harvesting changed over time. Knowledge of modern sea otter behavior and ecology suggests that shell middens dominated by large red abalone shells-relatively common on San Miguel between about 7,300 and 3,300 years ago-are only likely to have formed in areas where sea otter populations had been reduced by Native hunting or other causes. Preliminary analysis of sea urchin lenses, in which the remains of urchins are unusually abundant, may also signal an increasing impact of Island Chumash populations on kelp forest and other near shore habitats during the late Holocene. Such impacts were probably relatively limited, however, when compared to the rapid and severe disruption caused by commercial exploitation under the Spanish, Mexican, and American regimes of historic times.
We combined field monitoring and laboratory experiments to examine the population ecology of both... more We combined field monitoring and laboratory experiments to examine the population ecology of both the microscopic and macroscopic stages of a new invasion of Undaria pinnatifida in California. Over the course of 1 yr, we observed 2 distinct recruitment pulses of individuals in the Santa Barbara harbor; the appearance of these pulses was strongly correlated with a 4°C drop in ocean temperature approximately 2 mo prior to recruitment. Cultures of zoospores and successive microscopic stages revealed thermal tolerances consistent with field recruitment data; individuals grown at 13°C had significantly higher survivorship than individuals grown at higher temperatures (harbor temperatures annually ranged from 12 to 21°C). The 2 cohorts also differed greatly in individual size, growth rate, and survival to maturity. Grazing by herbivores, predominately the native kelp crab Pugettia producta, effectively prevented nearly all individuals in the second cohort from reaching reproductive maturity. Grazer control was effective despite far higher rates of recruitment during the second recruitment pulse. Our results highlight the potential for extreme variability in U. pinnatifida demography mediated by local oceanographic and biotic factors. Understanding controls on U. pinnatifida demography helps to explain variation in the spread and impact of this invader worldwide, and allows better prediction of when and where U. pinnatifida may continue its invasion along the west coast of North America.
Seaweed deforestation (isoyake) is a conspicuous phenomenon in many temperature/polar regions of ... more Seaweed deforestation (isoyake) is a conspicuous phenomenon in many temperature/polar regions of the world and often results in strong ecological and economic impacts to local human communities. The study of isoyake in East Asia (especially in Japan) has a long history, however the resulting literature is generally inaccessible to researchers that do not speak Asian languages. This study integrates knowledge of the causes and consequences of isoyake in East Asia into an emerging global model of the causes of deforestation in non-Asian kelp systems. Isoyake in southern regions of East Asia result from a concurrence of increased herbivory by fish and sea urchins of sub-tropical origin with periods of decreased seaweed production due to poor oceanographic conditions. Such processes are similar to those that cause deforestation in other warm-temperate kelp systems ( southern California and northern New Zealand) and may be enhanced during periods of ocean warming. Alternatively, isoyake in northern regions of East Asia result primarily from uncontrolled sea urchin grazing; inherently low kelp productivity in these regions cannot balance the high rates of kelp consumption. As such, these regions appear similar to other high latitude/low productivity kelp systems in which large enduring sea urchin barrens often exist in the absence of external controls on sea urchin abundance ( predation or harvesting by humans). Therefore, the diversity of causes of isoyake in East Asian systems appears to encompass the full range of deforestation processes described for high-to low-latitude kelp systems worldwide. The unique situation in which high seaweed and herbivore diversity coincide with high variability in oceanographic processes appears may make East Asian seaweed systems more vulnerable to perturbation than other temperate kelp systems.
The Essential Naturalist: Timeless Readings in Natural History
... 6· Michael H. Graham ... Brodo, Sharnoff, and Sharnoff (2000) present lichens as the essence... more ... 6· Michael H. Graham ... Brodo, Sharnoff, and Sharnoff (2000) present lichens as the essence of wildness. As in the other taxon-centric examples, stunning photographs effectively portray the beauty of our organic world while the text devel-ops the underlying Natural History and ...
Phenotypic plasticity allows genotypes to produce alternate phenotypes that enhance survivability... more Phenotypic plasticity allows genotypes to produce alternate phenotypes that enhance survivability and reproductive ability in different environments, creating altered selective pressures, which act on genotypes governing traits such as growth rate, development, and reproductive strategies. The giant kelp, Macrocystis, is able to dramatically reduce sexual reproduction normally utilized by the subtidal morph (M. pyrifera), to asexual growth in the intertidal morph (M. integrifolia). To test for genetic isolation caused by ecological divergence in the intertidal, we performed fine scale spatial sampling and molecular analysis of parapatric, M. pyrifera and M. integrifolia, populations in Central California. Using seven microsatellite markers, we compared genetic differentiation between morphs in the same site and among morphs across different sites. Additionally, we identified the presence of clonal replicates in intertidal populations. Preliminary results from two study sites suggest...
Mounting concern over the loss of marine biodiversity has in- creased the urgency of understandin... more Mounting concern over the loss of marine biodiversity has in- creased the urgency of understanding its consequences. This ur- gency spurred the publication of many short-term studies, which often report weak effects of diversity (species richness) driven by the presence of key species (the sampling effect). Longer-termfield experiments are slowly accumulating, and they more often report strong diversity effects driven
Organisms face continual fluctuations in global climatic processes to which they must adapt or pe... more Organisms face continual fluctuations in global climatic processes to which they must adapt or perish. Considering that many species are key habitat formers and energy producers, such responses to climate change can have significant population, community and even ecosystem consequences. Paleo-records of ecosystem responses to past environmental variability have proven invaluable for studying impacts of climate change on natural systems, yet such records are almost completely lacking for temperate benthic marine systems.
Information on the ecophysiology of macroalgal planktonic propagules (e.g. spores) has been hard ... more Information on the ecophysiology of macroalgal planktonic propagules (e.g. spores) has been hard to obtain, given their small size and low concentration in the water column. Studies of the photo-physiology of macroalgal spores, for example, have been limited by the need to aggregate many spores into bulk samples for analysis. Subsequently, physiological variability among spores (e.g. pigment concentration, absorption characteristics) is lost, and taxonomic comparisons from multi-taxa samples are impossible. Here we present a technique that utilizes a spectral microphotometer to produce visible (400-800 nm) absorption spectra from individual particles; the particles in our case are macroalgal spores. The microphotometer consists of a microscope fitted with a monochromator and spectrophotometer. After mounting spores from laboratory or field suspensions onto transparent membrane filters, absorption characteristics of individual spores, or even individual plastids, can be evaluated independently from the remaining particles in the sample. Use of transparent rather than opaque membrane filters allows for determination of absorption spectra, as well as more traditional microscopic analyses (e.g. bright field, dark field, epi-fluorescence). Glutaraldehyde fixation and cold storage (−10 • C) were found to be appropriate for maintaining the integrity of absorption spectra for at least 3 days. To demonstrate the utility of microphotometry for macroalgal studies, absorption spectra were obtained and analyzed from spores of various kelps and filamentous red algae.
The Journal of Island and Coastal Archaeology, 2015
We explore the ecology of Pacific Rim marine ecosystems and the idea that the broad geographic ra... more We explore the ecology of Pacific Rim marine ecosystems and the idea that the broad geographic range of many nearshore food resources facilitated a dispersal of maritime peoples from Asia to the Americas. Geographically, a coastal route offered less ecological resistance than interior routes, providing a linear corridor entirely at sea level and essentially free of major obstructions after about 16,000 years ago. We show that North Pacific nearshore ecosystems-from Japan to Mexicocontained hundreds of species of edible shellfish, fish, marine mammals, birds, and seaweeds distributed more or less continuously over vast stretches of coast. A coastal route, including kelp forests and estuaries, would have provided a rich mix of marine, estuarine, riverine, and terrestrial resources. A maritime dispersal following Pacific Rim shorelines could have moved relatively rapidly from northeast Asia into the Americas, leaving behind ancestral populations who followed the aquatic corridors of major river drainages deep into the interior. This model, recognizing the importance of aquatic and terrestrial resources, as well as the behavioral flexibility of Homo sapiens, can account for a relatively rapid dispersal of humans throughout the Americas and the full range of diversity of Paleoindian adaptations found in the Americas.
Proceedings of the Royal Society B: Biological Sciences, 2010
Quaternary glacial-interglacial cycles create lasting biogeographic, demographic and genetic effe... more Quaternary glacial-interglacial cycles create lasting biogeographic, demographic and genetic effects on ecosystems, yet the ecological effects of ice ages on benthic marine communities are unknown. We analysed long-term datasets to develop a niche-based model of southern Californian giant kelp (Macrocystis pyrifera) forest distribution as a function of oceanography and geomorphology, and synthesized palaeooceanographic records to show that late Quaternary climate change probably drove high millennial variability in the distribution and productivity of this foundation species. Our predictions suggest that kelp forest biomass increased up to threefold from the glacial maximum to the mid-Holocene, then rapidly declined by 40 -70 per cent to present levels. The peak in kelp forest productivity would have coincided with the earliest coastal archaeological sites in the New World. Similar late Quaternary changes in kelp forest distribution and productivity probably occurred in coastal upwelling systems along active continental margins worldwide, which would have resulted in complex shifts in the relative productivity of terrestrial and marine components of coastal ecosystems.
Proceedings of the National Academy of Sciences, 2008
Mounting concern over the loss of marine biodiversity has increased the urgency of understanding ... more Mounting concern over the loss of marine biodiversity has increased the urgency of understanding its consequences. This urgency spurred the publication of many short-term studies, which often report weak effects of diversity (species richness) driven by the presence of key species (the sampling effect). Longer-term field experiments are slowly accumulating, and they more often report strong diversity effects driven by species complementarity, calling into question the generality of earlier findings. However, differences among study systems in which short-and long-term studies are conducted currently limit our ability to assess whether these differences are simply due to biological or environmental differences among systems. In this paper, we compared the effect of intertidal seaweed species richness on biomass accumulation in mesocosms and field experiments using the same pool of species. We found that seaweed species richness increased biomass accumulation in field experiments in both short (2-month) and long (3-year) experiments, although effects were stronger in the longterm experiment. In contrast, richness had no effect in mesocosm experiments, where biomass accumulation was completely a function of species identity. We argue that the short-term experiments, like many published experiments on the topic, detect only a subset of possible mechanisms that operate in the field over the longer term because they lack sufficient environmental heterogeneity to allow expression of niche differences, and they are of insufficient length to capture population-level responses, such as recruitment. Many published experiments, therefore, likely underestimate the strength of diversity on ecosystem processes in natural ecosystems. diversity-ecosystem function ͉ seaweed ͉ species identity ͉ intertidal ͉ algae Author contributions:
Proceedings of the National Academy of Sciences, 2002
The strength of interactions between predators and their prey (interaction strength) varies enorm... more The strength of interactions between predators and their prey (interaction strength) varies enormously among species within ecological communities. Understanding the community-wide distribution of interaction strengths is vital, given that communities dominated by weak interactions may be more stable and resistant to invasion. In the oceans, previous studies have reported lognormal distributions of per capita interaction strength. We estimated the distribution of predator-prey interaction strengths within a subtidal speciose herbivore community (45 species). Laboratory experiments were used to determine maximum per capita interaction strengths for eight species of herbivores (including amphipods, isopods, gastropods, and sea urchins) that graze on giant kelp (Macrocystis pyrifera) microscopic stages. We found that maximum per capita interaction strength saturated as a function of individual herbivore biomass, likely caused by predator͞prey size thresholds. Incorporating this nonlinearity, we predicted maximum per capita interaction strength for the remaining herbivore species. The resulting distribution of per capita interaction strengths was bimodal, in striking contrast to previous reports from other communities. Although small herbivores often had per capita interaction strengths similar to larger herbivores, their tendency to have greater densities in the field increased their potential impact as grazers. These results indicate that previous conclusions about the distributions of interaction strength in natural communities are not general, and that intermediate-sized predators can under realistic circumstances represent the most effective consumers in natural communities.
Proceedings of the National Academy of Sciences, 2007
Classic marine ecological paradigms view kelp forests as inherently temperate-boreal phenomena re... more Classic marine ecological paradigms view kelp forests as inherently temperate-boreal phenomena replaced by coral reefs in tropical waters. These paradigms hinge on the notion that tropical surface waters are too warm and nutrient-depleted to support kelp productivity and survival. We present a synthetic oceanographic and ecophysiological model that accurately identifies all known kelp populations and, by using the same criteria, predicts the existence of >23,500 km 2 unexplored submerged (30-to 200-m depth) tropical kelp habitats. Predicted tropical kelp habitats were most probable in regions where bathymetry and upwelling resulted in mixed-layer shoaling above the depth of minimum annual irradiance dose for kelp survival. Using model predictions, we discovered extensive new deep-water Eisenia galapagensis populations in the Galá pagos that increased in abundance with increasing depth to >60 m, complete with cold-water flora and fauna of temperate affinities. The predictability of deep-water kelp habitat and the discovery of expansive deep-water Galá pagos kelp forests validate the extent of deep-water tropical kelp refugia, with potential implications for regional productivity and biodiversity, tropical food web ecology, and understanding of the resilience of tropical marine systems to climate change.
Although analysis of variance (ANOVA) is widely used by ecologists, the full potential of ANOVA a... more Although analysis of variance (ANOVA) is widely used by ecologists, the full potential of ANOVA as a descriptive tool has not been realized in most ecological studies. As questions addressed by ecologists become more complex, and experimental and sampling designs more complicated, it is necessary for ecologists to estimate both statistical significance and fit when comparing the relative importance of individual factors in an explanatory model, especially when models are multi-factorial. Yet, with few exceptions, ecologists are only presenting significance values with ANOVA results. Here we review methods for estimating statistical fit (magnitude of effect) for individual ANOVA factors based on variance components and provide examples of their application to field data. Furthermore, we detail the potential occurrence of negative variance components when determining magnitude of effects in ANOVA and describe simple remediation procedures. The techniques we advocate are efficient and will greatly enhance analyses of a wide variety of ANOVA models used in ecological studies. Estimation of magnitude of effects will particularly benefit the analysis of complex multi-factorial ANOVAs where emphasis is on interpreting the relative importance of many individual factors. OIKOS 93:3 (2001)
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