Beds Of Giant Kelp Research Articles

Persistence of southern California giant kelp beds and alongshore variation in nutrient exposure driven by seasonal upwelling and internal waves

Kelp beds provide significant ecosystem services and socioeconomic benefits globally, and prominently in coastal zones of the California Current. Their distributions and abundance, however, vary greatly over space and time. Here, we describe long-term patterns of Giant Kelp (Macrocystis pyrifera) sea surface canopy area off the coast of San Diego County from 1983 through 2019 along with recent patterns of water column nitrate (NO3-) exposure inferred from in situ temperature data in 2014 and 2015 at sites spanning 30 km of the coastline near San Diego California, USA. Site-specific patterns of kelp persistence and resilience were associated with ocean and climate dynamics, with total sea surface kelp canopy area varying approximately 33-fold over the almost 4 decades (min 0.34 km2 in 1984; max 11.25 km2 in 2008, median 4.79 km2). Site-normalized canopy areas showed that recent kelp persistence since 2014 was greater at Point Loma and La Jolla, the largest kelp beds off California, than at the much smaller kelp bed off Cardiff. NO3- exposure was estimated from an 11-month time series of in situ water column temperature collected in 2014 and 2015 at 4 kelp beds, using a relationship between temperature and NO3- concentration previously established for the region. The vertical position of the 14.5°C isotherm, an indicator of the main thermocline and nutricline, varied across the entire water column at semidiurnal to seasonal frequencies. We use a novel means of quantifying estimated water column NO3- exposure integrated through time (mol-days m-2) adapted from degree days approaches commonly used to characterize thermal exposures. Water column integrated NO3- exposure binned by quarters of the time series showed strong seasonal differences with highest exposure in Mar - May 2015, lowest exposure in Sep - Dec 2014, with consistently highest exposure off Point Loma. The water column integrated NO3- signal was filtered to provide estimates of the contribution to total nitrate exposure from high frequency variability (ƒ >= 1 cycle 30 hr-1) associated predominantly with internal waves, and low frequency variability driven predominantly by seasonal upwelling. While seasonal upwelling accounted for > 90% of NO3- exposure across the full year, during warm periods when seasonal upwelling was reduced or absent and NO3- exposure was low overall, the proportion due to internal waves increased markedly to 84 to 100% of the site-specific total exposure. The high frequency variability associated with internal waves may supply critical nutrient availability during anomalously warm periods. Overall, these analyses support a hypothesis that differences in NO3- exposure among sites due to seasonal upwelling and higher frequency internal wave forcing contribute to spatial patterns in Giant Kelp persistence in southern California. The study period includes anomalously warm surface conditions and the marine heatwave associated with the “Pacific Warm Blob” superimposed on the seasonal thermal signal and corresponding to the onset of a multi-year decline in kelp canopy area and marked differences in kelp persistence among sites. Our analysis suggests that, particularly during periods of warm surface conditions, variation in NO3- exposure associated with processes occurring at higher frequencies, including internal waves can be a significant source of NO3- exposure to kelp beds in this region. The patterns described here also offer a view of the potential roles of seasonal and higher frequency nutrient dynamics for Giant Kelp persistence in southern California under continuing ocean surface warming and increasing frequency and intensity of marine heatwaves.

Standing Crop, Turnover, and Production Dynamics of Macrocystis pyrifera and Understory Species Hedophyllum nigripes and Neoagarum fimbriatum in High Latitude Giant Kelp Forests.

Production rates reported for canopy-forming kelps have highlighted the potential contributions of these foundational macroalgal species to carbon cycling and sequestration on a globally relevant scale. Yet, the production dynamics of many kelp species remain poorly resolved. For example, productivity estimates for the widely distributed giant kelp Macrocystis pyrifera are based on a few studies from the center of this species' range. To address this geospatial bias, we surveyed giant kelp beds in their high latitude fringe habitat in southeast Alaska to quantify foliar standing crop, growth and loss rates, and productivity of M. pyrifera and co-occurring understory kelps Hedophyllum nigripes and Neoagarum fimbriatum. We found that giant kelp beds at the poleward edge of their range produce ~150 g C · m-2 · year-1 from a standing biomass that turns over an estimated 2.1 times per year, substantially lower rates than have been observed at lower latitudes. Although the productivity of high latitude M. pyrifera dwarfs production by associated understory kelps in both winter and summer seasons, phenological differences in growth and relative carbon and nitrogen content among the three kelp species suggests their complementary value as nutritional resources to consumers. This work represents the highest latitude consideration of M. pyrifera forest production to date, providing a valuable quantification of kelp carbon cycling in this highly seasonal environment.

Giant kelp (Macrocystis) fishery in Atacama (Northern Chile): biological basis for management of the integrifolia morph

In Bahia Chasco, Atacama, the integrifolia morph of Macrocystis forms one of the most important kelp forests in northern Chile. In order to determine effects of local harvesting policies, we evaluated the population dynamics of this resource in intact, frequently disturbed, and permanently and completely harvested areas. Recruitment, frond length, reproductive phenology and standing crop were assessed monthly. In intact areas, frond length and ratio of reproductive individuals were higher, but recruitment was poorly stimulated. On the other hand, complete harvest had an important effect on Macrocystis population dynamics. Whereas recruitment and growth were much higher after harvest events, reproductive phenology was lower. The harvest techniques with different frequencies practiced by Bahia Chasco fishermen were less harmful than complete harvest, and we conclude that current exploitation techniques applied in this location are not deleterious for the giant kelp beds. They even have favorable effects by renewing the population through stimulation of sexual reproduction, recruitment and growth of young individuals.

Differences in growth, morphology and tissue carbon and nitrogen of Macrocystis pyrifera within and at the outer edge of a giant kelp forest in California, USA

To investigate the extent to which alteration of physical factors by giant kelp beds affects the growth of kelp within the bed, we conducted analyses of frond morphometrics at 2 mo intervals, elongation rates and tissue chemistry of individuals of Macrocystis pyrifera on the interior and edge of a kelp bed off the coast of Santa Barbara, California, USA. The density of the kelp canopy varied greatly during the 13 mo study, ranging from 0.03 to 8.03 m 2 blade tissue m -2 sea surface. Time series analysis of flow velocity, light, temperature and seawater nitrate concentrations inside and out- side of the bed indicated that when canopy density was high (May to September) current speeds in the bed were 25% of incident flow, and light below the canopy (at 1 m depth) was reduced to 10% surface irradiance. Nitrate concentrations were highly variable and similar between inside and out- side moorings. When the canopy was well developed, kelp fronds on the seaward edge of the bed had faster elongation rates and larger blades, resulting in higher overall growth rates (mass added per day) than interior fronds. Carbon and nitrogen accumulation by edge fronds was also higher dur- ing this period, which fueled growth rates of edge fronds that were nearly twice as high as interior fronds when the canopy was densest. Thus, the growth and tissue chemistry of M. pyrifera within the kelp bed depended on the extent to which the bed modified ambient physical conditions.

Influence of giant kelp beds ( Macrocystis pyrifera) on diel cycles of pCO 2 and DIC in the Sub-Antarctic coastal area

The partial pressure of CO 2 (pCO 2) and dissolved inorganic carbon (DIC) were monitored in shallow coastal waters located inside and outside giant kelp beds ( Macrocystis pyrifera) located in the Kerguelen Archipelago (Southern Ocean). Photosynthesis and respiration by microplankton and kelp lead to marked pCO 2 and DIC diel cycles. Daily variations of pCO 2 and DIC are significant in the spring and summer, but absent in the winter, reflecting the seasonal cycle of biological activity in the kelp beds. If the kelp beds seem to favour the onset of phytoplankton blooms, most of the primary production inside the kelp beds is due to the kelp itself. The primary production of Macrocystis kelp beds in the Sub-Antarctic high-nutrient, low-chlorophyll (HNLC) waters off the Kerguelen Archipelago is elevated and closely linked to light availability. This production is significant from October to March and reaches its climax in December at the solar radiation maximum.

Influence of subantarctic Macrocystis bed metabolism in diel changes of marine bacterioplankton and CO2 fluxes

The significance of bacterial communities in the fluxes of carbon and energy in giant kelp beds (Macrocystis pyrifera) in Kerguelen Archipelago, subantarctica, was estimated by measuring bacterioplankton biomass and production over diel cycles in surface seawaters located inside and outside of Macrocystis beds. Several physicochemical parameters [temperature, solar radiation, tide level, dissolved oxygen, total inorganic carbon (TCO2), partial pressure of CO2 (pCO2) and dissolved organic carbon (DOC)] were simultaneously recorded in order to establish possible relationships with observed changes in bacterial parameters. Bacterial biomass and production were significantly higher inside the kelp bed than in the surrounding area. Furthermore, the results showed large and clear diel variations of all parameters measured inside the kelp bed. Changes in dissolved oxygen, TCO2 and pCO2 paralleled those of solar radiation, and were obviously related to the metabolic activity of the kelp. Mean cell volumes and saprophytic bacterial abundance varied over the diel cycles in the same way as photosynthetic activity, while DOC, bacterioplankton production and the frequency of dividing cells varied in an opposite way with maximal values at night-time.

Diving Patterns of Full-Grown and Juvenile Rock Shags

Information on diving patterns was obtained for full-grown and juvenile Rock Shags (Phalacrocorax magellanicus) feeding in Port Stanley Harbour, Falkland Islands. Birds dived mainly in, or just outside, beds of giant kelp within 50 m of the shore where the water depth varied from 1-6 m. Mean dive and recovery times were 28 sec and 10 sec respectively, diving rate was 1.8 dives/min and birds spent 75% of the time underwater. Full-grown and juvenile birds both showed a highly significant positive relationship between dive time and water depth. Full-grown individuals also showed a significant increase in recovery time with increasing dive time, but for juveniles recovery time was independent of dive time. This resulted in full grown birds attaining a rate of diving that was 30-50% higher than that of juveniles in shallow water.

Biogenic habitat structure and characteristics of temperate reef fish assemblages

AbstractAssemblages of non‐cryptic, substrate‐oriented species of fish were compared on a series of reefs in Southern California, USA. Reefs were grouped according to algal cover: dense beds of giant kelp (Macrocystis pyrifera) with turf understorey; sparse beds of giant kelp with foliose algae understorey: foliose algae < 1 m in height; and open barrens. Despite affinities to particular algal substrates by many individual species, we detected no differences in fish species richness and only weak differences in species composition among reefs of different habitat types. Planktivores and species that consume macro‐invertebrates were less likely to occur on reefs that supported giant kelp; the frequencies of occurrence of three other trophic groups (piscivores, herbivores and micro‐carnivores) were unaffected by giant kelp.Algal composition on reefs in Southern California is temporally highly dynamic. Changes in macro‐algal composition of reefs influenced population dynamics of two fish species (black surfperch and striped surfperch) examined. Overall, the weak spatial variation in fish assemblages on reefs in Southern California appears to result from relatively unspecialized ecological requirements of many species combined with temporal changes in algal structure on reefs that are rapid relative to generation times of the fish. We hypothesize that the degree of spatial differentiation in assemblages of substrate‐associated species of fish may be inversely related to the temporal constancy of biogenic reef structure.

Modification of coastal currents by power plant intake and thermal discharge systems

Powerplant cooling systems that entrain large volumes of seawater in multiple discharge jets can produce changes in the local field of flow. A case history of observed flow modification is provided by dye studies and records of currents around the diffusers of the San Onofre Nuclear Generating Station (SONGS), which entrain a volume of flow on the order of 1000 m 3 s −1. Field observations of dilutions and velocities in the discharge plume agree well with the results of hydraulic modelling of the diffuser system. Synoptic observations and long-term statistical distributions of current speeds and directions show systematic patterns of altered flow around the diffusers that are more complex than the flow in the model because of interactions with flow modification by local beds of giant kelp.

Aquacultural Techniques for Creating and Restoring Beds of Giant Kelp, Macrocystis spp.

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.

EESECTS OF WASTEWATERS ON MARINE BIOTA

The ocean provides enormous capacity for dispersion and assimilation of human and natural wastes. Indeed marine ecosystems depend on such terrestrial sources for their nutrient supplies. It is incumbent cm man to cause minimal disruption and, if possible, beneficial effects from dispersing his wastes in the sea. The Southern California Bight receives the most intense exposure to discharged sewage of any exposed region along the Pacific coast of North America. Evidences of significantly altered chemical and biological conditions in southern California hare been demonstrated. Elevated concentrations of certain metals occur in sediments near some large sewage outfalls. Pesticide residues were extremely high in sand crabs from southern California. Beds of giant kelp decreased near some, but not all,sewage outfalls. Correctional measures are disoussed. Ecological surveys are currently used to provide early warning of potential biological problems near some southern California outfalls. A survey near an outfall removed from service indicated most changes in fish and macroinvertebrate populations occurred within a few months after the discharge ceased.

Growth Rate as a Measure of Primary Productivity in Benthic Algae

Primary productivity is considered to be the production of organic matter from inorganic matter and the rate of primary production is the amount of organic matter produced per unit time. Gross production is the total amount of organic matter produced and net production is the total production less the amount lost to respiration (Odum and Odum, 1959). Many techniques have been evolved to estimate indirectly rates of primary production. Some of these methods are growth rate and harvest of standing crop, gas exchange rates, radioactive isotope uptake, and chlorophyll concentration. It is the purpose of this paper to consider measurements of growth rates as approximations of primary production in benthic marine algae. The parameter of growth is defined in many ways, and some that have been used are irreversible increases in linear dimensions, dry weight, surface area increase, and cell numbers. The usual estimates of growth in laboratory cultures of unicellular algae arc cell counts, optical density of cultures, total dry weight, and total cell volume (Boalch, 1961). Total dry weight is the only parameter of growth that can ea.~ily be used for multicellular algae. Thus, Boalch (1961) used an increase in dry weight to measure growth in laboratory cultures of Ectocarpus. Dry weight estimates require the destruction of the organism, and thus they are really harvest techniques. The nondestructive techniques for estimating continuous growth rates have evolved around measurements of changes in plant size and they can be used in situ as well as in the laboratory. Neu.-hul and Haxo (1963) have estimated the growth rate of young Macrocystis plants by measuring the change in the blade surface area as a function of time. Growth of Halimeda in laboratory culture was measured by linear increase iu thallus length (Colinvaux et al., 1965). as was growth of Gracilaria cultured on rafts (Jones 1959a, b). Chapman (1961) measured growth in the fronds of Egregia laevigata by measuring the increasing distance between two marks on the stipe. Increases in dry weight per unit time is an estimate of growth. It is also a measure of primary production if the increase in dry weight is organic matter. Since an increase in weight is not always a result of an increase in organic matter, an improvement might be made by taking both dry weight and ash-free measurements (Clendenning, 1962). Harvest techniques for measuring primary production have other drawbacks. A harvest sample for dry weight determination is taken from the standing crop and represents the organic matter that has neither been respired nor consumed. Thus, it represents something less than net production. If independent measurements of respiratory rates are made, better estimates of primary production are obtained but one still has little hope of getting reliable estimates of gross primary production unless consumption by grazers can be estimated (Odum and Odum, 1959). Leighton, et al. (1966) have reported on the effects of grazers in giant kelp beds. All techniques that depend on harvest of standing crops suffer from this difficulty. They are only useful in situations where herbivores are not present and a steady state condition is never reached. This is not the case in corn-