Kelp

Kelp forests (Order Laminariales) form key biogenic habitats in coastal regions of temperate and Arctic seas worldwide, providing ecosystem services valued in the range of billions of dollars annually. Although local evidence suggests that kelp forests are increasingly threatened by a variety of stressors, no comprehensive global analysis of change in kelp abundances currently exists. Here, we build and analyze a global database of kelp time series spanning the past half-century to assess regional and global trends in kelp abundances. We detected a high degree of geographic variation in trends, with regional variability in the direction and magnitude of change far exceeding a small global average decline (instantaneous rate of change = −0.018 y −1). Our analysis identified declines in 38% of ecoregions for which there are data (−0.015 to −0.18 y −1), increases in 27% of ecoregions (0.015 to 0.11 y −1), and no detectable change in 35% of ecore-gions. These spatially variable trajecto...

This is the first scientific work about the populational and taxonomic aspects of Laminaria abyssalis and L. brasiliensis in their natural habitat, as well as their relation with physical and chemical habitat properties and its associated flora. The two Brazilian Laminaria species occur at a biotope characterized by depth between 45 and 120 meters, temperature between 15 and 19ºC, low light intensity and have rhodoliths as substrate. For taxonomic, biometric, population density and chemical analysis, two Brazilian Laminaria populations were sampled at the south of Espirito Santo State. Through the annual determination of the temperatures lower than 18°C it was possible detected the presence of upwelling waters at the study site, which was more frequent between August of 2006 and February of 2007. Even though the two Brazilian Laminaria species have been distinct to each other by the blade shape, morphological and anatomical comparisons indicate an overlap of its taxonomic characters, as shape of the blade base and blade dimensions. As it was observed by the morphological results, the molecular analysis based on plastidial (rbcL), nuclear (ITS) and mitochondrial (cox1) markers indicates that both species, in fact corresponds to just one Laminaria species. The sporophyte morphological variation observed in this study reinforces the suggestion that the Laminaria species from Brazil, in fact, corresponds to a gradient of morphological forms of just one species: L. abyssalis. L. abyssalis dimensions tended to present higher values at the summer, whereas the higher proportions of fertile L. abyssalis sporophytes and the higher fertile area percentage were seen at the winter period. The percentage of carbohydrate, total nitrogen and phosphorus in relation L. abyssalis dry biomass were: 29,19 ± 4,63 %, 1,46 ± 0,14 % and 1,09 ± 0,19 %, respectively, and tended to be higher at spring time. The nitrate, nitrite and phosphate mean concentration in seawater were: 2,68 ± 1,19 M, 0,13 ± 0,08 M and 0,19 ± 0,19 M, respectively. As it was observed with light intensity results, the nutrients concentration in the water were higher in the spring-summer period and lower in the autumn-winter period, allowing in the spring-summer period the better conditions for the L. abyssalis development. During the spring-summer period L. abyssalis stores carbohydrate (spring), and thereafter presents the highest thallus growth in summer. The density and blade area values of L. abyssalis were higher during the period of most frequent upwelling water, whereas the higher fertile area occurs during the period of lowest frequency of upwelling waters. The associated flora was composed by 26 taxa: 5 of rhodolith crustose coralline species and other 21 species of fleshy algae growing upon rhodoliths and/or L. abyssalis stipe.

This thesis examines the dispute between the Crown and private proprietors over the ownership of the Scottish kelp shores and the Scottish foreshore generally, between the mid 19th century and the mid 20th century and, in particular, the work and membership of the Association of Seaboard Proprietors of Scotland and the contribution of the 9th Duke of Argyll.  The thesis also examines the actions and motivations of proprietors of Highland estates, and their relationship and influence with the Crown and Government departments, in defending their sacred right of property, first in the context of early 19th century threats to the kelp industry are second in the context of later challenges - from the Crown over the ownership of the foreshore, and on behalf of the crofters over the rights to seaware. The existence and facts of the foreshore dispute have not had any attention in the historiography of the Highlands and Islands of Scotland and only the briefest of mentions in the legal historiography.  The examination of the foreshore dispute in this thesis casts new light on the Scottish kelp industry.  The received wisdom as to the economic benefits of the kelp industry appears to be that the benefits accrued to the proprietors through an unchallenged exclusive ownership by the proprietors of the seaware and the foreshore on which the seaware was found.  This thesis suggests we should not accept this received wisdom without, at the very least, acknowledging that for over 100 years the whole question as to ownership was very much a disputed one between the Crown and the private proprietors.  This thesis also draws attention to the previously unacknowledged part which crofters and cottars played in the final determination of ownership of the foreshore through their gathering of seaware for kelp and manure.

The capacity of marine organisms to adapt and/or acclimate to climate change might differ among distinct populations, depending on their local environmental history and phenotypic plasticity. Kelp forests create some of the most productive habitats in the world, but globally, many populations have been negatively impacted by multiple anthropogenic stressors. Here, we compare the physiological and molecular responses to ocean acidification (OA) and warming (OW) of two populations of the giant kelp Macrocystis pyrifera from distinct upwelling conditions (weak vs strong). Using laboratory mesocosm experiments, we found that juvenile Macrocystis sporophyte responses to OW and OA did not differ among populations: elevated temperature reduced growth while OA had no effect on growth and photosynthesis. However, we observed higher growth rates and NO3− assimilation, and enhanced expression of metabolic-genes involved in the NO3− and CO2 assimilation in individuals from the strong upwelling ...

Kelp forests (Order Laminariales) form key biogenic habitats in coastal regions of temperate and Arctic seas worldwide, providing ecosystem services valued in the range of billions of dollars annually. Although local evidence suggests that kelp forests are increasingly threatened by a variety of stressors, no comprehensive global analysis of change in kelp abundances currently exists. Here, we build and analyze a global database of kelp time series spanning the past half-century to assess regional and global trends in kelp abundances. We detected a high degree of geographic variation in trends, with regional variability in the direction and magnitude of change far exceeding a small global average decline (instantaneous rate of change = −0.018 y −1). Our analysis identified declines in 38% of ecoregions for which there are data (−0.015 to −0.18 y −1), increases in 27% of ecoregions (0.015 to 0.11 y −1), and no detectable change in 35% of ecore-gions. These spatially variable trajecto...

Low nitrogen availability is one of the major environmental factors limiting macroalgal growth in temperate marine ecosystems. Macroalgae have overcome the fluctuating nature of nitrogen supply via adjustments to their life-history (e.g. opportunistic versus perennial) and/or their morphophysiology (e.g. type of growth, use of reserves). Fast-growing species dominate when nutrients are elevated but are typically absent in nutrient-poor systems; Macrocystis pyrifera, however, is an exception because it is a perennial species as well as fast-growing. Although its nutrient demands are inherently high (due to its size and productivity), it remains a cosmopolitan species even when nitrogen concentrations are low. The primary objective of this collective work is to refine current knowledge on how the ecophysiology of Macrocystis helps mitigate nitrogen limitation. This is investigated within small communities (i.e. intra-bed mass-transfer) and also within individuals (i.e. endogenous nitrogen use and storage).

Nitrogen uptake is enhanced by increased rates of water mass-transfer, which is largely dictated by water flow. Macrocystis beds modify their physical environment so that flow rates are reduced in the bed's interior. To better understand how macroalgae influence mass-transfer rates within kelp beds, the architecture of a model kelp bed is described, highlighting dominant canopy and subcanopy species. These biogenic structures significantly influenced the rates of masstransfer throughout the bed – rates were highest at the exterior edge and at the surface of the bed, decreasing towards the interior and with depth. Growth and tissue chemistry (e.g. pigmentation, soluble nitrate) of Macrocystis paralleled the intra-bed variability in mass-transfer. This work also provides evidence that the influence of mass-transfer on nitrogen acquisition is a particularly important mechanism when ambient nitrogen is limiting.

Growth is described as Macrocystis' first and primary response to nitrogen enrichment. Enrichment studies, however, typically fertilise experimental kelp beyond naturally occurring nitrogen concentrations and the nuances in physiological responses to realistic nitrogen enhancement (e.g. upwelling) are likely masked. To determine how Macrocystis prioritises the use of nitrogen when concentrations are low, the seawater immediately surrounding fronds were enhanced with ecologically relevant pulses of nitrate. The immediate response to fertilisation was not growth, but instead reduced blade erosion and increased pigmentation in canopy tissues. This work suggests that when nitrogen-stressed, Macrocystis first stabilises tissues important to photosynthesis and that growth responses can be delayed for at least one month after initial nitrate pulses. Due to localised increases in pigmentation and soluble nitrate within fronds, this work also highlights potential functional differentiation across tissues.

Extended periods of low nitrogen can be mitigated using reserves. The reserve dynamics within whole Macrocystis fronds are poorly understood but suggested to be small. This work aimed to determine which compounds (pigments, soluble nitrate, amino acids) are important nitrogen reserves, in which tissues these pools are stored (six distinct tissues analysed), and how they explain growth. Ultimately, the data suggest that pigments are not an important nitrogen reserve in Macrocystis because maximum concentrations are low compared to other potential reserves, and because they fluctuate in synchrony with ambient seawater nitrate (i.e. no lag time). Soluble nitrate pools in mature blades, however, accrue to high concentrations when ambient nitrogen is replete (winter/early spring) and then nitrate is slowly disseminated to canopy tissues to fuel spring/early summer growth. When ambient nitrogen is low (summer), there is evidence that amino acids are reabsorbed from canopy blades and translocated to basal tissues, perhaps acting as reserve pools for growth in the autumn.

This thesis addresses aspects of Macrocystis ecophysiology that are important in mitigating nitrogen limitation. The main findings are (1) that mass-transfer rates within kelp beds are highly variable and that increased mass-transfer is critical in ameliorating limitation events, (2) that Macrocystis uses nitrogen towards tissue maintenance before growth when nitrogen-stressed, facilitating continued nutrient uptake and photosynthesis, and (3) that soluble nitrate and amino acids are important nitrogen reserves, but that the former is more important for spring growth and the latter more important for autumn growth.

Species interactions are integral drivers of community structure and can change from competitive to facilitative with increasing environmental stress. In subtidal marine ecosystems, however, interactions along physical stress gradients have seldom been tested. We observed seaweed canopy interactions across depth and latitudinal gradients to test whether light and temperature stress structured interaction patterns. We also quantified interspecific and intraspecific interactions among nine subtidal canopy seaweed species across three continents to examine the general nature of interactions in subtidal systems under low consumer pressure. We reveal that positive and neutral interactions are widespread throughout global seaweed communities and the nature of interactions can change from competitive to facilitative with increasing light stress in shallow marine systems. These findings provide support for the stress gradient hypothesis within subtidal seaweed communities and highlight the ...

The vast and complex coast of the Magellan Region of extreme southern Chile possesses a diversity of habitats including fjords, deep channels, and extensive kelp forests, with a unique mix of temperate and sub-Antarctic species. The Cape Horn and Diego Ramírez archipelagos are the most southerly locations in the Americas, with the southernmost kelp forests, and some of the least explored places on earth. The giant kelp Macrocystis pyrifera plays a key role in structuring the ecological communities of the entire region, with the large brown seaweed Lessonia spp. forming dense understories. Kelp densities were highest around Cape Horn, followed by Diego Ramírez, and lowest within the fjord region of Francisco Coloane Marine Park (mean canopy densities of 2.51 kg m-2, 2.29 kg m-2, and 2.14 kg m-2, respectively). There were clear differences in marine communities among these sub-regions, with the lowest diversity in the fjords. We observed 18 species of nearshore fishes, with average sp...

The late Pleistocene extinction of so many large-bodied vertebrates has been variously attributed to two general causes: rapid climate change and the effects of humans as they spread from the Old World to previously uninhabited continents and islands. Many large-bodied vertebrates, especially large apex predators, maintain their associated ecosystems through top-down forcing processes, especially trophic cascades, and megaherbivores also exert an array of strong indirect effects on their communities. Thus, a third possibility for at least some of the Pleistocene extinctions is that they occurred through habitat changes resulting from the loss of these other keystone species. Here we explore the plausibility of this mechanism, using information on sea otters, kelp forests, and the recent extinction of Steller's sea cows from the Commander Islands. Large numbers of sea cows occurred in the Commander Islands at the time of their discovery by Europeans in 1741. Although extinction o...

The intensive commercial exploitation of California sheephead (Semicossyphus pulcher) has become a complex, multimillion-dollar industry. The fishery is of concern because of high harvest levels and potential indirect impacts of sheephead removals on the structure and function of kelp forest ecosystems. California sheephead are proto-gynous hermaphrodites that, as predators of sea urchins and other invertebrates, are critical components of kelp forest ecosystems in the northeast Pacific. Overfishing can trigger trophic cascades and widespread ecological dysfunction when other urchin predators are also lost from the system. Little is known about the ecology and abundance of sheephead before commercial exploitation. Lack of a historical perspective creates a gap for evaluating fisheries management measures and marine reserves that seek to rebuild sheephead populations to historical baseline conditions. We use population abundance and size structure data from the zooarchaeological reco...

Ecosystem reconfigurations arising from climate-driven changes in species distributions are expected to have profound ecological, social, and economic implications. Here we reveal a rapid climate-driven regime shift of Australian temperate reef communities, which lost their defining kelp forests and became dominated by persistent seaweed turfs. After decades of ocean warming, extreme marine heat waves forced a 100-kilometer range contraction of extensive kelp forests and saw temperate species replaced by seaweeds, invertebrates, corals, and fishes characteristic of subtropical and tropical waters. This community-wide tropicalization fundamentally altered key ecological processes, suppressing the recovery of kelp forests.

The intensive commercial exploitation of California sheephead (Semicossyphus pulcher) has become a complex, multimillion-dollar industry. The fishery is of concern because of high harvest levels and potential indirect impacts of sheephead removals on the structure and function of kelp forest ecosystems. California sheephead are protogynous hermaphrodites that, as predators of sea urchins and other invertebrates, are critical components of kelp forest ecosystems in the northeast Pacific. Overfishing can trigger trophic cascades and widespread ecological dysfunction when other urchin predators are also lost from the system. Little is known about the ecology and abundance of sheephead before commercial exploitation. Lack of a historical perspective creates a gap for evaluating fisheries management measures and marine reserves that seek to rebuild sheephead populations to historical baseline conditions. We use population abundance and size structure data from the zooarchaeological recor...

IN THEIR REPORT “STRONG TOP-DOWN CONtrol in southern California kelp forest ecosystems” (26 May, p. 1230), B. S. Halpern et al. conclude that these forests show strong top-down (consumer-driven) control and that bottom-up (resource-driven) control in such systems may often be overestimated. These conclusions run counter to most of the extensive literature (1–4) on the ecology and natural history of kelp forests in southern California. There are numerous examples of the importance of storms and low nutrients over large spatial and temporal scales, especially during El Niños (3, 5–7) but also from decadal climate shifts (8). Halpern et al. used a short-term data set that did not include El Niño–Southern Oscillation or decadal climate shifts. Moreover, they used satellite-derived offshore chlorophyll a concentration data as a measure of “resources” without establishing that these data were a good proxy for nutrients or primary production in nearshore kelp forests and despite evidence t...

The spatial distribution of kelp (Laminaria hyperborea) and sea urchins (Strongylocentrotus droebachiensis) in the NE Atlantic are highly related to physical factors and to temporal changes in temperature. On a large scale, we identified borders for kelp recovery and sea urchin persistence along the north-south gradient. Sea urchin persistence was also related to the coast-ocean gradient. The southern border corresponds to summer temperatures exceeding about 10°C, a threshold value known to be critical for sea urchin recruitment and development. The outer border along the coast-ocean gradient is related to temperature, wave exposure and salinity. On a finer scale, kelp recovery occurs mainly at ridges in outer, wave exposed, saline and warm areas whereas sea urchins still dominate in inner, shallow and cold areas, particularly in areas with optimal current speed for sea urchin foraging. In contrast to other studies in Europe, we here show a positive influence of climate change to pr...

Where predator-prey interactions are size-dependent, reductions in predator size owing to fishing has the potential to disrupt the ecological role of top predators in marine ecosystems. In southern California kelp forests, we investigated the size-dependence of the interaction between herbivorous sea urchins and one of their predators, California sheephead (Semicossyphus pulcher). Empirical tests examined how differences in predator size structure between reserve and fished areas affected size-specific urchin mortality. Sites inside marine reserves had greater sheephead size and biomass, while empirical feeding trials indicated that larger sheephead were required to successfully consume urchins of increasing test diameter. Evaluations of the selectivity of sheephead for two urchin species indicated that shorter-spined purple urchins were attacked more frequently and successfully than longer-spined red urchins of the same size class, particularly at the largest test diameters. As a r...

Background South America's western coastline, extending in a near-straight line across some 35 latitudinal degrees, presents an elegant setting for assessing both contemporary and historic influences on cladogenesis in the marine environment. Southern bull-kelp (Durvillaea antarctica) has a broad distribution along much of the Chilean coast. This species represents an ideal model taxon for studies of coastal marine connectivity and of palaeoclimatic effects, as it grows only on exposed rocky coasts and is absent from beaches and ice-affected shores. We expected that, along the central Chilean coast, D. antarctica would show considerable phylogeographic structure as a consequence of the isolating effects of distance and habitat discontinuities. In contrast, we hypothesised that further south - throughout the region affected by the Patagonian Ice Sheet at the Last Glacial Maximum (LGM) - D. antarctica would show relatively little genetic structure, reflecting postglacial recolonisation. Results Mitochondrial (COI) and chloroplast (rbcL) DNA analyses of D. antarctica from 24 Chilean localities (164 individuals) revealed two deeply divergent (4.5 - 6.1% for COI, 1.4% for rbcL) clades from the centre and south of the country, with contrasting levels and patterns of genetic structure. Among populations from central Chile (32° - 44°S), substantial phylogeographic structure was evident across small spatial scales, and a significant isolation-by-distance effect was observed. Genetic disjunctions in this region appear to correspond to the presence of long beaches. In contrast to the genetic structure found among central Chilean populations, samples from the southern Chilean Patagonian region (49° - 56°S) were genetically homogeneous and identical to a haplotype recently found throughout the subantarctic region. Conclusions Southern (Patagonian) Chile has been recolonised by D. antarctica relatively recently, probably since the LGM. The inferred trans-oceanic ancestry of these Patagonian populations supports the notion that D. antarctica is capable of long-distance dispersal via rafting. In contrast, further north in central Chile, the correspondence of genetic disjunctions in D. antarctica with long beaches indicates that habitat discontinuity drives genetic isolation among established kelp populations. We conclude that rafting facilitates colonisation of unoccupied shores, but has limited potential to enhance gene-flow among established populations. Broadly, this study demonstrates that some taxa may be considered to have either high or low dispersal potential across different temporal and geographic scales.