Seasonal growth of the giant kelp Macrocystis pyrifera in New Zealand

The seasonal growth pattern of Macrocystis pyrifera (L.) C. Agardh in New Zealand was determined from measurements of blade-elongation rates between March 1986 and December 1987. Growth rates remained relatively constant throughout most of the year, but declined significantly during the summer months. Seawater nitrate levels had a marked seasonal cycle, with concentrations of 0.3 μM detected in summer. The timing of the decline in internal nitrogen concentrations varied for different-aged blades, but occurred ∼1 mo after the decrease in seawater nitrate concentrations. Sufficiently high irradiance levels and seawater nutrient concentrations support active growth for most of the year, but growth is nutrient-limited during summer. No carbon accumulation during summer was observed. Between March and August 1988, growth estimates were also derived from node-initiation rates and stipe-elongation rates to permit comparisons with previous studies from the northern and southern hemispheres. Direct comparisons of the three growth parameters determined for non-terminated canopy and sub-surface fronds were used to assess possible differential resource allocation in the two frond classes. Received: 16 May 1997 / Accepted: 28 May 1997     

Modelling the growth and harvest yield of the giant kelp Macrocystis pyrifera

The giant kelp Macrocystis pyrifera is one of the largest and fastest growing seaweeds and is dominant over large areas of the west coast of North America. A model of its growth has been developed which describes plant biomass and production over the course of a year as a function of environmental parameters which affect the light flux. Such parameters include water clarity, spacing between plants, bottom depth, latitude, harvesting activity, and photosynthetic response (P _max and I _k ). Model results for a standard set of conditions (latitude 33°N, 3 m plant spacing, water absorbance of 0.115 m^-1 and 12 m depth) yield a peak daily gross production of almost 6 g C m^-2 d^-1, peak daily net production of almost 3 g C m^-2 d^-1, and a peak specific growth rate of about 0.022 d^-1. Annual gross production for this case is 1 567 g C m^-2 yr^-1; annual net production is 537 g C m^-2 yr^-1. These values are comparable to those from field measurements. Size and timing of biomass and production peaks are affected by changes in the parameters describing the light field, with peaks usually occurring later in the year for more adverse circumstances. Inhigher latitudes, the seasonal variation is so extreme that the plant could not last the year at 53° N in 12 m of water, although it is able to survive the year in shallower water. Harvesting has severe effects on biomass and production. Model results suggest that light limitation is a very important constraint on kelp growth that should not be overlooked. This implies that differences in parameters describing two environments must be considered when comparing results obtained at different locales.     

In vivo accumulation of radioactive polonium by the giant kelp Macrocystis pyrifera

The in vivo accumulation rate of ²¹⁰Po by Macrocystis pyrifera (L) Ag. has been determined by the tagging of specific parts of young, growing lamina in La Jolla kelp beds and their subsequent collection for ²¹⁰Po analysis. The rates of accumulation for observed and growth-corrected data were, respectively, 0.78x10^-9 pCi/cm² sec (1.73x10^-9 dpm/cm² sec) and 1.17x10^-9 pCi/cm² sec (2.60x10^-9 dpm/cm² sec). Invert, but biologically foulable, glass-slide surfaces exposed to the kelp bed environment yielded ²¹⁰Po accumulation rates of 0.64x10^-9 pCi/cm² sec (1.42x10^-9 dpm/cm² sec), slightly less than those of M. pyrifera. Distinction is made between observed net accumulation rate and gross rates or total flux. Several factors contributing to the final net accumulation rate are discussed.     

Photosynthetic characteristics of giant kelp (Macrocystis pyrifera) determined in situ

Rates of net photosynthesis and nocturnal respiration by individual blades of the giant kelp Macrocystis pyrifera (L.) C. Agardh in southern California, were determined in situ by measuring oxygen production in polyethylene bags during spring/summer of 1983. Mature blades from different depths in the water column exhibited different photosynthetic characteristics. Blades from the surface canopy (0 to 1 m depth) exhibited higher photosynthetic capacity under saturating irradiance and higher photosynthetic efficiency at low irradiances than blades from 3 to 5 or 7 to 9 m depths. Saturating irradiance was lower for canopy blades than for deeper blades. Canopy blades showed no short-term photoinhibition, but photosynthetic rates of deeper blades were significantly reduced during 1 to 2 h incubations at high irradiances. Results of 1 to 2 wk acclimation experiments indicated that differences between photosynthetic characteristics of blades from different depths were primarily attributable to acclimation light conditions. Vertical displacement of blades within the kelp canopy occurred on a time-scale of 1 min to 1 h. Blades continually moved between the unshaded surface layer and deeper, shaded layers. Vertical movement did not maximize photosynthesis by individual blades; only a small proportion of blades making up a dense surface canopy maintained light-saturated photosynthetic rates during midday incubations. The relatively high photosynthetic rates exhibited by canopy blades over the entire range of light conditions probably resulted from acclimation to intermittent high and low irradiances, a consequence of vertical displacement. Vertical displacement also reduced the afternoon depression in photosynthesis of individual canopy blades. The overall effect of vertical displacement was optimization of total net photosynthesis by the kelp canopy and, therefore, optimization of whole-plant production.     

In situ water motion and nutrient uptake by the giant kelp Macrocystis pyrifera

Rates of NO ₃ ^- uptake by individual blades of Macrocystis pyrifera (L.) C. Agardh were measured at different flow rates in the laboratory. Dissolution rates of hemispherical, plaster buttons attached to the blade surface provided a relative measure of flow rates over blades used in uptake experiments and also over intact blades of adult kelp plants in situ (Laguna Beach, California, USA; 1981). Laboratory results indicated that uptake was saturated at a flow rate equivalent to 2.5 cm s^-1 current velocity. Flow rates over intact blades in situ always exceeded this uptake saturation level. Wave surge and movement of plant surfaces relative to the surrounding water provided sufficient flow to saturate uptake, even in a dense kelp canopy during low-current and calm sea-state conditions.     

Interactive effects of light and temperature on sporophyte production in the giant kelp Macrocystis pyrifera

Laboratory experiments were conducted in 1984 to test for an interaction between irradiance and temperature in controlling sporophyte production in the giant kelp Macrocystis pyrifera. Gametophytes from plants in the San Onofre kelp forest were cultured under a combination of seven irradiance (2.9 to 30 E m^-2 s^-1) and ten temperature (11° to 20°C) levels. The minimum daily quantum dose for fertility of female gametophytes during the 42 d culture-period was 0.25 E m^-2 d^-1. The saturation quantum dose was approximately 0.60 E m^-2 d^-1. Temperatures between 11° and 20°C had little effect on the fertilityirradiance relationship, except at irradiations near the threshold and saturation levels. Cultures at 0.60 E m^-2 d^-1 had significantly lower fertility after 6 wk at 20°C than at the lower temperatures and there was a trend toward lower fertility at temperatures greater than 15°C in cultures at 0.25 E m^-2 d^-1. These differences were also reflected in the development time for female gametophytes. The 11°C cultures reached 50% fertility slightly faster and the 20°C cultures slower than cultures at intermediate temperatures.     

Effect of boundary layer transport on the fixation of carbon by the giant kelp Macrocystis pyrifera

The uptake of inorganic carbon into the thallus of Macrocystis pyrifera (L.) C. Ag. requires first that the inorganic carbon pass through the water medium to the plant surface. This transfer of inorganic carbon to the thallus must take place through a boundary layer. Experiments in water tunnels indicate that the boundary layer adjacent to the M. pyrifera blade may be turbulent in water speeds as low as 1 cm sec^-1. Photosynthetic output of the blade can be increased by a factor of 300% by increasing water speeds over the blade surface from 0 to 4 cm sec^-1. This is consistent with a decrease in the thickness of the boundary layer. Above 4 cm sec^-1, the assimilation of carbon was limiting. The assimilation of carbon is generally known to follow Michaelis-Menten-like kinetics. Combining the two uptake steps into an overall model of carbon uptake agrees well with photosynthetic data obtained from M. pyrifera under varying conditions of water speed and bicarbonate concentrations in the laboratory. The ecological and morphological consequences of these findings are discussed.     

Growth and utilization of internal nitrogen reserves by the giant kelp Macrocystis pyrifera in a low-nitrogen environment

An adult giant kelp plant (Macrocystis pyrifera), moved from an inshore kelp forest to an offshore, low-nitrogen environment near Santa Catalina Island, California (USA), maintained growth for 2 wk on internal nitrogen reserves. Frond elongation rates decreased significantly during the third week, and plant growth rate (wet wt) dropped from an initial inshore rate of 3.6 to 0.9% d^-1. During this 3 wk period, nitrogen contents and free amino acid concentrations decreased, while mannitol and dry contents increased in frond tissues. After depletion of internal nitrogen reserves, the nitrogen content of lamina and stipe tissues averaged 1.1 and 0.7% dry wt, respectively. The experimental plant was exposed to higher ambient nitrogen concentrations during the last 2 wk. Rates of frond elongation and plant growth increased, but nitrogen content and amino acids in frond tissues remained low. Of the total nitrogen contained in frond tissue of the plant before transplantation, 58% was used to support growth in the absence of significant external nitrogen supply. Amino acids constituted a small proportion of these internal nitrogen reserves. Net movement of nitrogen occurred within large fronds, but not between different frond size classes. The nitrogen content of holdfast tissue remained relatively constant at 2.4% dry wt and accounted for 18 to 29% of the total nitrogen. Holdfast nitrogen was not used to support growth of nitrogen-depleted fronds. In comparison to Laminaria longicruris, which is adapted to long seasonal periods of low nitrogen availability, M. pyrifera has small nitrogen-storage capacity. However, internal reserves of M. pyrifera appear adequate to make nitrogen starvation uncommon in southern California kelp forests.     

Effects of an oil and gas-production effluent on the colonization potential of giant kelp (Macrocystis pyrifera) zoospores

Point sources of pollution (e.g. industrial and municipal outfalls) may produce ecological impacts at distant locations if pollutants affect dispersive propagules. We used laboratory experiments to determine how water-column exposure to produced water (=the aqueous fraction of oil and gas production that is typically discharged into coastal waters) influences the colonization potential of giant kelp (Macrocystis pyrifera) zoospores on the bottom. Zoospores were maintained in suspension at relatively low densities in 18-liter containers and exposed to one of five concentrations of produced water for varying amounts of time. Zoospore swimming generally decreased with increasing produced-water concentration and exposure duration; however, the specific pattern of decrease differed between experimental trials done on different dates. The effect of exposure duration on the ability of swimming zoospores to attach to plastic dishes placed on the bottom varied with produced-water concentration. Zoospores placed in produced-water concentrations of 1 and 10% showed a steady decline in their ability to attach with increased exposure; lower concentrations of produced water had no such effects. The percentage of zoospores that germinated after attachment varied tremendously with exposure duration and date of experimental trial. Zoospores that settled during the first 12 h after release had very poor rates of germination, indicative of a short precompetent period. Surprisingly, exposure of suspended zoospores to high concentrations of produced water during the first 12 h reduced this precompetent period and greatly improved germination success on the bottom. The magnitude of this enhancement, however, varied among dates. The results suggest that adverse effects of discharging produced water on planktonic zoospores of giant kelp would most likely be limited to the immediate vicinity of the outfall.     

Nutrient-limited growth of juvenile kelp,Macrocystis pyrifera,during the 1982–1984 “El Niño” in southern California

The relative growth rates of juvenile Macrocystis pyrifera in southern California kelp forests were substantially reduced during the El Niño of 1982–1984. The lower growth rates were correlated with increased temperature and decreased nitrogen availability. Fertilization of juvenile plants with slow-release nitrogen-phosphorus fertilizer increased their growth rates to levels previously observed when temperatures were low and nutrient levels were high. The limitation in growth of M. pyrifera by levels of available nutrients during El Niño was in contrast to the usual limitation of growth by irradiance during non-El Niño years. Thus, there was a shift in the relative importance of factors controlling growth of juvenile M. pyrifera during El Niño.     

Net primary production, growth, and standing crop of Macrocystis pyrifera in Southern California

Marine macroalgae are believed to be among the most productive autotrophs in the world. However, relatively little information exists about spatial and temporal variation in net primary production (NPP) by these organisms. The data presented here are being collected to investigate patterns and causes of variation in NPP by the giant kelp, Macrocystis pyrifera, which is believed to be one of the fastest growing autotrophs on earth. The standing crop and loss rates of M. pyrifera have been measured monthly in permanent plots at three sites in the Santa Barbara Channel, USA. Collection of these data began in June 2002 and is ongoing. Seasonal estimates of NPP and growth rate are made by combining the field data with a model of kelp dynamics. The purpose of this Data Paper is to make available a time series of M. pyrifera NPP, growth, and standing crop that is appropriate for examining seasonal and interannual patterns across multiple sites. Data on plant density in each plot and censuses of fronds on tagged plants at each site are also made available here. NPP, mass-specific growth rate, and standing crop are presented in four different metrics (wet mass, dry mass, carbon mass, and nitrogen mass) to facilitate comparisons with previous studies of M. pyrifera and with NPP measured in other ecosystems. Analyses of these data reveal seasonal cycles in growth and standing crop as well as substantial differences in M. pyrifera NPP among sites and years.     

Nitrogen supply,tissue composition and frond growth rates for Macrocystis pyrifera off the coast of southern California

Seasonal changes in ambient NO ₃ ^– and NH ₄ ⁺ , tissue composition (N, C, and C/N ratio), and frond growth rates for Macrocystis pyrifera (L.) Agardh were examined. Ambient NO ₃ ^– showed distinct seasonal variations. Frond growth rates were variable, but showed no clear correlation to ambient NO ₃ ^– . The average N content of plant tissue did, however, show the same seasonal variations as ambient NO ₃ ^– . The longitudinal distribution of total tissue N and various components of tissue N along fronds were also analyzed. Several distinct patterns were found: high levels of protein N at growing tips and elevated levels of soluble N in lower parts of the frond. Free amino acids accounted for a major portion of the soluble N, but neither NO ₃ ^– nor NH ₄ ⁺ accumulated in the plant tissue. The longitudinal distribution of N along the fronds is compared to reported variations in C metabolism, and it is concluded that C and N sourcesink relations do not always coincide and bidirectional translocation may occur.     

Algal succession in a Macrocystis pyrifera forest

Algal succession within a subtidal forest of the giant kelp Macrocystis pyrifera was studied by following colonization and community development on concrete blocks fastened to the bottom. Sets of blocks were placed in the bed at 3-month intervals. Subsequent algal development on each set was followed for over a year. All macroscopic species attached to the substrata were noted, and the number and lenght of basal branches determined every 1 to 3 months. Colonizing plants fell into 3 categories: rapid-growing ephemerals, and rapid and slow-growing perennials. Ephemerals such as Giffordia (Ectocarpus) mitchellae, Colpomenia peregrina, and diatom films generally produced and initial bloom on the blocks but were gradually replaced by perennials (articulated corallines, Rhodymenia spp., Gigartina spp.) characteristic of the mature kelp community. These stages, rather than representing “ecological” succession, seemed to reflect differences in growth rate and success in interspecific competition for space and light. Colonization on the blocks varied with season, indicating that most species have either a spring-summer or fall-winter period of maximum reproduction. M. pyrifera sporophyte colonization was greatest in spring. During community development, algal diversity (H), number of species (s) and evenness (J) all reached a peak within 100 to 200 days regardless of the time the blocks were started. Diversity and number of species then fell as ephemeral species disappeared. These species were apparently unable to compete with perennials and, once gone, did not recolonize. Evenness remained high.     

Pigment content and photosynthetic rate of the fronds of Macrocystis pyrifera

The Macrocystis pyrifera (L.) C. Ag. frond is here described in terms of chlorophyll a, fucoxanthin, chlorophyll c and photosynthetic rate. Pigment concentrations increased back from the apical meristem reaching a maximum after 2 to 3 m. Pigment concentrations were then generally constant throughout most of the length of the frond, finally decreasing again in the oldest parts of the frond with the exception of the sporophylls. Pigment ratios remained relatively constant throughout. Maximum net photosynthetic rates on a given frond showed a decrease with tissue age on both an area basis (1040 down to 463 nmol O₂ cm^-2 h^-1) and on a chlorophyll a basis, which was shown as half-saturation constants (quantum irradiance) which dropped on an area basis from 85 mol m^-2 sec^-1 at 4.5 m above the holdfast to 26 mol m^-2 sec^-1 at 15.5 m. Young sporophytes transplanted from the sea floor to the surface (12 m) tended to decrease pigment content, while those transplanted to the bottom tended to increase all pigments, but especially fucoxanthin. Photosynthetic rates, however, changed little on a unit area basis. The results of these data are considered in the light of recent work on photosynthetic units, tissue age effects and general adaptations of the M. pyrifera frond to its light environment.     

Effects of sediments on the development of Macrocystis pyrifera gametophytes

Rocky ocean bottoms are covered from time to time with small amounts of fine sediments. This material may interfere with the development of germling stages of Macrocystis pyrifera. Tests were performed by introducing sediments before and after spores were dispersed in culture dishes. 10 mg cm^-2 of sediment, enough to occlude the surface, prevents spore attachment, greatly reducing the probability of survival. Smothering of established germlings was severe at 108 mg sediment cm^-2. Water motion further reduced spore success where sediments were present, probably because of abrasive scour. Mechanisms of natural and human interference with M. pyrifera reproduction are suggested.     

Ammonium excretion in a temperate-reef community by a planktivorous fish,Chromis punctipinnis (Pomacentridae), and potential uptake by young giant kelp,Macrocystis pyrifera (Laminariales)

The blacksmith Chromis punctipinnis, an abundant planktivorous damselfish off southern California, USA, shelters along rocky reefs at night. While sheltered, blacksmiths excrete ammonium that could, in turn, be utilized by nearby benthic macrophytes. Laboratory experiments during the summer and fall of 1983 and 1984 indicate that ammonium excretion at night ranged from 18.1 mol h^-1 by a 8.5 g (dry) fish, to 89.1 mol h^-1 by a 27.3 g fish; excretion rates generally declined throughout the night. Field measurements at night indicate that ammonium concentrations were significantly higher in rocky crevices occupied by blacksmiths than in unoccupied shelters, and the ammonium level in one shelter dropped after a blacksmith was experimentally removed. Young kelp plants (Macrocystis pyrifera) are capable of taking up ammonium at night. Ammonium levels in chambers containing both a blacksmith and a young kelp plant were significantly lower than in chambers containing only a fish, and ammonium levels dropped in ammoniumspiked chambers that contained kelp plants. Nighttime ammonium uptake rates by young kelp plants, which averaged 1.6 mol g^-1 (dry) h^-1, were only slightly lower than those during the day. Daytime excretion by blacksmiths occasionally results in elevated ammonium levels in the water column. On two of six days, ammonium concentrations in midwater foraging aggregations were slightly but significantly higher than in upcurrent controls; since blacksmiths typically aggregate at the incurrent margin of kelp beds, the ammonium is swept downcurrent and may be utilized by large M. pyrifera that extend through the water column. Thus, the activities of blacksmiths may results in the importation of extrinsic, inorganic nitrogen to primary producers on temperate reefs.     

Regulation of algal community development in a Macrocystis pyrifera forest

The effects of small and large-scale roughness, overstory development, competition for space with sessile animals, and grazing on algal community development in a subtidal Macrocystis pyrifera forest were examined using specially prepared concrete blocks as substrata. Variation in small-scale roughness (crevices and grooves in the order of 0.1 to 3 mm width and depth) had no significant effects on community composition. However, M. pyrifera colonization, algal diversity, and sessile animal biomass were higher near the upper horizontal edges of blocks and concrete prisms. This “edge” effect may result from a combination of increased spore and larval settlement and enhanced growth of plants and animals associated with the turbulent eddies formed around these obstructions. Natural and experimentally produced variations in the algal overstory demonstrated that the presence of an overstory can reduce algal diversity and cover beneath. Caging experiments suggest that predatory fishes and sea-stars indirectly affect the algal community by removing sessile animals (primarily bryozoans) which compete with the algae for space. The exclusion of grazers resulted in increased growth of Gigartina spp. Selective grazing on this genus may account for its reduced abundance in the study area.     

Morphological variations of Macrocystis pyrifera in the Falkland Islands in relation to environment and season

Some morphological characteristics of the giant kelp Macrocystis pyrifera in the Falkland Islands were studied from December 1985 until March 1987 in a shallow and relatively sheltered coastal zone and from December 1985 until January 1987 in a deeper offshore field exposed to swells. Seasonal fluctuations in lamina wet weight, density and form as well as pneumatocyst wet weight form and stipe density (i.e., wet weight per unit length) paralleled fluctuations in frond wet weight. Morphological differences between canopies of the giant kelp in the coastal zone and the offshore bed were probably mainly due to differences in water movement and depth between the two sites. Laminae and pneumatocysts of submersed-frond sites had different shapes than those of canopy-forming portions of fronds at the same sites, and their internodes were longer.     

Dispersal of faunal and floral propagules associated with drifting Macrocystis pyrifera plants

The potential of drifting Macrocystis pyrifera kelp for transporting associated animals and plants long distances around the southern oceans was assessed by anchoring kelp holdfasts off the Tasmanian coast in 1985, monitoring the turnover of organisms, and relating species survival to water-transport times and species geographic distributions. Although most of the common animal species and approximately half of the plant species associated with Tasmanian M. pyrifera holdfasts were still present on kelp holdfasts after 191 d at sea, very few of these species have been recorded from New Zealand. It therefore seems unlikely that M. pyrifera plants with intact holdfasts are presently drifting to New Zealand. Drifting kelps probably become negatively buoyant in the Tasman Sea because dissolved nitrate concentrations are insufficient for normal plant growth. Moreover, even if some kelp plants do drift to New Zealand it is possible that their holdfasts rapidly disintegrate in the open ocean because of the abundance of the boring isopods Phycolimnoria spp. in Tasmanian holdfasts. In contrast to the restricted distributions of Tasmanian holdfast-inhabiting species, most of the identified species collected from M. pyrifera holdfasts at subantarctic Macquarie Island also occurred 5 000 km west at Kerguelen Island. Because of the extensive ranges of many subantarctic species, the good probability of survival of epifaunal species on drifting kelps, and the high surface-water nitrate concentrations and low holdfast-densities of Phycolimnoria spp. in the higher latitudes, it is likely that M. pyrifera-mediated transport of faunal and floral propagules has recently occurred, and is probably presently occurring, in subantarctic waters.