World Seas: An Environmental Evaluation (Second Edition)
Chapter 3 - Status and Trends for the World’s Kelp Forests
Abstract
Kelp forests are extensive underwater habitats that range along 25% of the world’s coastlines, providing valuable resources, habitat, and services for coastal communities. They grow best in cold, nutrient-rich water, where they attain some of the highest rates of primary production of any natural ecosystem. Kelps exhibit a great diversity of growth forms and life strategies, with the largest individuals reaching lengths of > 30 m and biomasses of 42 kg. In the past half century, threats to kelp forests have increased in number and severity, leading to a global decline of kelp abundances of ~ 2% per year. Trajectories of change vary considerable across regions and include range contractions, range expansions, species replacements, establishment of invasive kelps, replacement by turf algae reefs, or regime shifts to sea urchin barrens. These changes will likely have significant impacts on marine biodiversity and ecosystem functioning because kelps are foundation species for a plethora of habitat-associated plants and animals, many of which are socioeconomically important. Some forms of management have been effective in restoring kelp forests, but in many cases the threats facing kelp forests in the future greatly exceed local conservation strategies, necessitating novel conservation solutions to protect and conserve these ecosystems. Although the diversity of changes to kelp forest globally make it challenging to generalize about their future, it seems almost certain that many kelp forests a few decades from now will differ substantially from what they are today.
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Variations in the chemical composition of Norwegian cultivated brown algae Saccharina latissima and Alaria esculenta based on deployment and harvest times
2024, Algal ResearchBrown algae exhibit large seasonal variation in their composition based on nutrient and sunlight access, as well as other environmental factors. The continued growth of brown algae cultivation in Europe is dependent on increased knowledge of these variances, to ensure optimal growth conditions, predict quality prior to harvest, and determine suitability of the biomasses' composition for different markets and applications. In the present study, cultivated sugar kelp (Saccharina latissima - SL) and winged kelp (Alaria esculenta - AE) were collected from seeded lines deployed at two different times (October 2020 and January 2021). Samples were collected from the two deployment groups throughout the harvesting season (April–June 2021) from a single site (Frøya, Norway). The collected biomasses were analyzed with respect to lamina elongation, dry matter content, ash content, elemental composition, soluble protein, amino acid composition, and monosaccharide composition. The results showed that SL was more influenced by deployment time compared to AE, where earlier deployed biomass showed larger lamina size, lower iodine content, and later accumulation of mannitol and laminarin. The study further showed the compositional variation in each of the species and deployment groups throughout the harvesting seasons, indicating ideal harvesting times for different applications of the biomass.
Sea urchin Arbacia punctulata feeding preference for algal turf over kelp in a degraded kelp forest ecosystem
2024, Journal of Experimental Marine Biology and EcologyClimate change is driving a shift in the distribution of global kelp forests, with the contraction of kelp habitats occurring at warm range edges. Declining kelps often have been replaced by novel algal turf assemblages, which are reinforced by ecological feedback mechanisms and provide fewer ecosystem services. Trophic interactions among marine herbivores, algal turfs, and kelps on algal turf-dominated reefs remain poorly resolved but could have important implications for the stability of algal turf reefs and the potential for kelp forest recovery. Here, we examine herbivory by the Atlantic purple sea urchin, Arbacia punctulata, in a degraded kelp forest ecosystem dominated by algal turf in southern New England, USA. In a localized field survey, we observed lower algal turf cover on reef areas containing A. punctulata (mean ± SE: 62 ± 12% turf cover) as compared to areas with no sea urchins present (92 ± 4% turf cover). Reef areas with and without sea urchins had similarly low cover of the previously dominant kelp, Saccharina latissima (6–8% kelp cover). In laboratory and field experiments, individuals or groups of A. punctulata enclosed with a diet choice of algal turf versus kelp had higher grazing rates on the algal turf. A. punctulata in the laboratory also exhibited greater attraction to algal turf over kelp, physically moving towards this food source. In combination, the results provide evidence that A. punctulata has a feeding preference for algal turf over kelp in southern New England. Future research is warranted to further examine the grazing ecology of A. punctulata, particularly in the context of ongoing kelp forest restoration efforts in this region.
Impact of climate change and anthropogenic activities on aquatic ecosystem – A review
2023, Environmental ResearchAll living things depend on their natural environment, either directly or indirectly, for their high quality of life, growth, nutrition, and development. Due to the fast emissions of greenhouse gases (GHGs), the Earth's climate system is being negatively impacted by global warming. Stresses caused by climate change, such as rising and hotter seas, increased droughts and floods, and acrid waters, threaten the world's most populated areas and aquatic ecosystems. As a result, the aquatic ecosystems of the globe are quickly reaching hazardous conditions. Marine ecosystems are essential parts of the world's environment and provide several benefits to the human population, such as water for drinking and irrigation, leisure activities, and habitat for commercially significant fisheries. Although local human activities have influenced coastal zones for millennia, it is still unclear how these impacts and stresses from climate change may combine to endanger coastal ecosystems. Recent studies have shown that rising levels of greenhouse gases are causing ocean systems to experience conditions not seen in several million years, which may cause profound and irreversible ecological shifts. Ocean productivity has declined, food web dynamics have changed, habitat-forming species are less common, species ranges have changed, and disease prevalence has increased due to human climate change. We provide an outline of the interaction between global warming and the influence of humans along the coastline. This review aims to demonstrate the significance of long-term monitoring, the creation of ecological indicators, and the applications of understanding how aquatic biodiversity and ecosystem functioning respond to global warming. This review discusses the effects of current climate change on marine biological processes both now and in the future, describes present climate change concerning historical change, and considers the potential roles aquatic systems could play in mitigating the effects of global climate change.
The role of kelp availability and quality on the energetic state and thermal tolerance of sea urchin and gastropod grazers
2023, Journal of Experimental Marine Biology and EcologyWidespread decline in underwater forests, formed by kelps and other macroalgae, is occurring in all oceans. Loss of the vulnerable surface canopy typically leads to alternate rocky reef states dominated by substrate-near, understory vegetation, or reefs without any large fleshy macroalgae such as sea urchin barrens. Such alternate reef states represent a major shift in food availability and quality, and may impact kelp-preferring grazers forced to rely on less nutritious foods. Here we investigate the physiological responses of grazers to changes in food quality and quantity. We quantify the mass-independent oxygen consumption (ṀO2), as a proxy of whole-organism physiology, of four grazing invertebrate species (two sea urchins: Mesocentrotus franciscanus and Strongylocentrotus purpuratus; and two gastropods: Pomaulax gibberosus and Tegula pulligo) provisioned with one of three diet treatments over seven weeks: 1) higher quality, canopy kelp, 2) lower quality, substrate-near kelp, or 3) restricted: no kelp. We further test for differences in the heat resistance of four grazers using an acute, near-lethal heat exposure after completion of the provisioning period. Food restrictions had the strongest influence on oxygen consumption in the two urchins (mass-independent ṀO2 was reduced by 26–78%). By contrast, the two gastropod grazers did not display metabolic depression under food restrictions. Although kelp restrictions had clear physiological consequences in sea urchins, overall, the type of kelp provisioned (Macrocystis and Saccharina) did not relate to oxygen consumption after seven weeks. While heat resistance was also similar across food treatments, unfed individuals showed a slight tendency for lower heat tolerance compared to fed individuals. These results suggest a weak coupling between heat resistance and food quality and quantity, at least for these species and at short time spans. Our work highlights the importance of diet diversity and metabolic depression as strategies to cope with the energetic costs of warming.
Prevalent fingerprint of marine macroalgae in arctic surface sediments
2023, Science of the Total EnvironmentMacroalgal forests export much of their production, partly supporting food webs and carbon stocks beyond their habitat, but evidence of their contribution in sediment carbon stocks is poor. We test the hypothesis that macroalgae contribute to carbon stocks in arctic marine sediments. We used environmental DNA (eDNA) fingerprinting on a large-scale set of surface sediment samples from Greenland and Svalbard. We evaluated eDNA results by comparing with traditional survey and tracer methods. The eDNA-based survey identified macroalgae in 94 % of the sediment samples covering shallow nearshore areas to 1460 m depth and 350 km offshore, with highest sequence abundance nearshore and with dominance of brown macroalgae. Overall, the eDNA results reflected the potential source communities of macroalgae and eelgrass assessed by traditional surveys, with the most abundant orders being common among different methods. A stable isotope analysis showed a considerable contribution from macroalgae in sediments although with high uncertainty, highlighting eDNA as a great improvement and supplement for documenting macroalgae as a contributor to sediment carbon stocks. Conclusively, we provide evidence for a prevalent contribution of macroalgal forests in arctic surface sediments, nearshore as well as offshore, identifying brown algae as main contributors.
Impact of kelp forest on seawater chemistry – A review
2023, Marine Pollution BulletinKelp forests, globally distributed in cool temperate and polar waters, are renowned for their pivotal role in supporting species diversity and fostering macroalgae productivity. These high-canopy algal ecosystems dynamically influence their surroundings, particularly by altering the physicochemical properties of seawater. This review article aims to underscore the significance of kelp forests in modifying water masses. By serving as effective carbon sinks through the absorption of bicarbonate (HCO3−) and carbon dioxide (CO2) for photosynthesis, kelp forests mitigate nearby acidity levels while enhancing dissolved oxygen concentrations, essential for sustaining diverse marine communities. Additionally, kelp beds have exhibited the need to use inorganic ions (NO3−, NO2−, PO43−) from seawater in order to grow, albeit with associated increases in NH4+ concentrations. Specific examples and findings from relevant studies will be presented to illustrate the profound impact of kelp forests on seawater chemistry, emphasizing their vital role in marine ecosystems.