SEASONAL PHOTOSYNTHETIC PERFORMANCE OF MACROCYSTIS INTEGRIFOLIA (PHAEOPHYCEAE)1

The seasonal photosynthetic performances of three age classes of blades of Macrocystis integrifolia Bory were estimated by studying their photosynthetic rate vs. irradiance curves and pigment contents for 15 months. All blade types were irradiance-saturated between 25 and 70 μE · m^?2· S^?1. Young and mature blade tissues had higher photosynthetic maxima and initial slopes on an area basis than older blade tissue. The latter, however, had pigment concentrations similar to those in mature blade tissues. All these parameters varied on a seasonal basis. The photosynthetic maxima ranged from 0.1–0.8 μmol · C · cm^?2· h^?t and showed two peaks, one in late summer-early fall and the other in late winter. Changes in initial slope and pigment concentrations in the blade tissues suggest that, changes in the size or efficiency of electron transfer in the photosynthetic unit occur. These data are discussed in relation to changes in seawater temperature and nitrate concentrations.     

Photosynthesis of Marine Macroalgae from Antarctica: Light and Temperature Requirements

The photosynthetic performance of macroalgae isolated in Antarctica was studied in the laboratory. Species investigated were the brown algae Himantothallus grandifolius, Desmarestia anceps, Ascoseira mirabilis, the red algae Palmaria decipiens, Iridaea cordata, Gigartina skottsbergii, and the green algae Enteromorpha bulbosa, Acrosiphonia arcta, Ulothrix subflaccida and U. implexa. Unialgal cultures of the brown and red algae were maintained at 0°C, the green algae were cultivated at 10°C. I_K values were between 18 and 53 μmol m^?2 s^?1 characteristic or low light adapted algae. Only the two Ulothrix species showed higher I_K values between 70 and 74 μmol m^?2 s^?1. Photosynthesis compensated dark respiration at very low photon fluence rates between 1.6 and 10.6 μmol m^?2 s^?1. Values of α were high: between 0.4 and 1.1 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the brown and red algae and between 2.1 and 4.9 μmol O₂ g^?1 FW h^?1 (μmol m^?2 s^?1)^?1 in the green algal species. At 0°C P_max values of the brown and red algae ranged from 6.8 to 19.1 μmol O₂ g^?1 FW h^?1 and were similarly high or higher than those of comparable Arctic-cold temperate species. Optimum temperatures for photosynthesis were 5 to 10°C in A. mirabilis, 10°C in H. grandifolius, 15°C in G. skottsbergii and 20°C or higher in D. anceps and I. cordata. P: R ratios strongly decreased in most brown and red algae with increasing temperatures due to different Q₁₀ values for photosynthesis (1.4 to 2.5) and dark respiration (2.5 to 4.1). These features indicate considerable physiological adaptation to the prevailing low light conditions and temperatures of Antarctic waters. In this respect the lower depth distribution limits and the northern distribution boundaries of these species partly depend on the physiological properties described here.     

Photosynthesis and respiration of a deep-water periphyton community (Macclesfield Bank,South China Sea)

The production parameters of the deep-water periphyton were investigated on the Macclesfield Bank (South China Sea) at depths down to 240 m. At 70–90 m depths the substrate is composed of the remains of dead corals and fragments of porous calcareous material overgrown with red coralline and articulated thalline algae Halimeda sp. At 220–240 m depths the substrate consists of rhodolites, which are individual unattached nodules encrusted mainly with red calcareous coralline algae Lithophyllum sp., Porolithon sp. and red lamellar alga Hypoglossum sp. At all depths the substrate is pierced with green filiform algae Ostreobium sp. and covered with benthic diatom algae. The zooperiphyton in the studied area is comprised of bryozoans, sponges, foraminifers and drilling mollusks. Respiration (R) and the gross (Pg) and net (Pn) primary production of the deepwater periphyton community were determined using the oxygen technique (polarographic electrode) at values of photosynthetically active radiation (PAR) close to natural levels. At 70–90 m depths the Pg of the photoperiphyton was 23.3 mg O₂/(m² h), and the Pn of the community had negative values due to respiration of phytoand mainly zooperiphyton and bacteria. At 220–240 m depths, where less than 0.001% of the surface PAR penetrates, the Pg of the phytoperiphyton decreased to 9.6 mg O₂/(m² h), and the R of the community was 25.9 mg O₂/(m² h). A high efficiency of light energy utilization by the phytoperiphyton was found. The apparent quantum yield (Fa) for algae collected at 70–90 m depths was close to the maximum level of 0.097. The values of Fn that we obtained for 220–240 m depths and calculated from identical data [27], were much higher than theoretical values, which cannot be explained based on modern views on the mechanisms of photosynthesis. Possible sources of errors are discussed. It is proposed that we observed additional evolution of oxygen as the result of H₂O₂ degradation.     

Farming of the Giant Kelp Macrocystis Pyrifera in Southern Chile for Development of Novel Food Products

This study explores the potential cultivation of the giant kelp Macrocystis pyrifera (L.) C.A. Agardh in southern Chile, for the development of novel food products. The study demonstrates the importance of considering the collection site of the parent sporophytes for successful cultivation. This study also shows that the ropes must be seeded with 10,000 to 40,000 spores ml⁻¹, depending on the culture method used. We also demonstrated that under environmental conditions in southern Chile, the seeded ropes must be put at sea at the latest during autumn (April) in order to reach the harvesting season in December. However, several other management aspects must be considered to improve the quality of the product. Our final estimation indicates that over 14.4 kg m⁻¹of rope (fresh weight) can be produced and from this total production, over 70% can reach the quality to produce different food products that are already being introduced in oriental countries. The remaining 30% can be used for abalone feeding and is also available for the organic fertilizer industry located in Chile.     

Photosynthetic performance of deep-water macroalgae (Phaeophyta,Dictyotales) off Bermuda

Photosynthetic performance and dark respiration rates were determined in situ for abundant macroalgae occurring between 27–49 m depths off Bermuda. Brown algae, particularly members of the order Dictyotales, predominated at all deep-water sites, and Stypopodium zonale was the most abundant species. Species showed net photosynthesis at very low ambient irradiances (<0.01 maximum I_o). Lobophora variegata, a species with a highly decumbent growth form, had low productivity across all irradiances. In contrast, Dictyota spp. (D. bartayresii, D. dichotoma, D. divaricata) and S. zonale had high photosynthetic capacity (ca. 400 µmol O₂ gdw^–1 h^–1), and light saturation was not evidenced at the highest ambient irradiance level (300 µE m^–1 s^–1) for species with thin, flat thalli. Light-harvesting pigment concentrations reflected tissue-nitrogen levels. C:N atom ratios, except for L. variegata and D. divaricata, were within the ratio for balanced growth. The repeated occurrence and photosynthetic efficiency of these Dictyotalean species in subtropical and tropical deep-water habitats emphasize their successful adaptation to low-light, nutrient-poor environments.     

Driven by the West Wind Drift? A synthesis of southern temperate marine biogeography,with new directions for dispersalism

Aim Twentieth century biogeographers developed intriguing hypotheses involving West Wind Drift dispersal of Southern Hemisphere biota, but such models were largely abandoned in favour of vicariance following the development of plate tectonic theory. Here I present a synthesis of southern temperate marine biogeography, and suggest some new directions for phylogeographic research. Location The southern continents, formerly contiguous components of Gondwana, are now linked only by ocean currents driven by the West Wind Drift. Methods While vicariance theory certainly facilitates the development of testable hypotheses, it does not necessarily follow that vicariance explains much of contemporary southern marine biogeography. To overcome the limitations of narratives that simply assume vicariance or dispersal, it is essential for analyses to test biogeographic hypotheses by incorporating genetic, ecological and geological data. Results Recent molecular studies have provided strong evidence for dispersal, but relatively little evidence for the biogeographic role of plate tectonics in distributing southern marine taxa. Despite confident panbiogeographic claims to the contrary, molecular and ecological studies of buoyant macroalgae, such as Macrocystis, indicate that dispersal predominates. Ironically, some of the better supported evidence for marine vicariance in southern waters has little or nothing to do with plate tectonics. Rather, it involves far more localized and recent vicariant models, such as the isolating effect of the Bassian Isthmus during Pleistocene low sea‐level stands (Nerita). Main conclusions Recent phylogeographic studies of southern marine taxa (e.g. Diloma and Parvulastra) imply that passive rafting cannot be ignored as an important mechanism of long‐distance dispersal. I outline a new direction for southern hemisphere phylogeography, involving genetic analyses of bull‐kelp (Durvillaea) and its associated holdfast invertebrate communities.     

The collapse of benthic macroalgal blooms in response to self‐shading

1. Our goal was to use physiological indicators [photosynthesis–irradiance (P–I) response, nutrient status], population level feedbacks (self‐shading) and ambient environmental conditions (dissolved nutrients, light, temperature) to improve our understanding of the seasonal and spatial population dynamics of Cladophora. 2. Cladophora grew in three distinct phases, rapid growth early in the season (May–July), a mid‐season population collapse (July–August) and autumn re‐growth. Across all sites and dates, mean net maximal photosynthesis [P_M (NET)] was 6.9 ± 3.9 mg O₂ g DM^?1 h^?1, and α was 0.055 ± 0.025 mg O₂ g DM^?1 μm photons^?1 m^?2. Mean values for critical irradiance (I_CR) and the half‐saturation light intensity (I_K), were 42.9 ± 32.1 and 189.3 ± 123.8 μm photons^?1 m^?2 s^?1 respectively. 3. At most sites growth was phosphorus‐limited. Values of α were significantly higher at a site influenced by a nutrient enriched river plume, where algal growth was phosphorus‐sufficient. 4. Photoinhibition was not apparent in any of our P–I experiments. Even if photoinhibition had been apparent during in vitro P–I experiments, population level photosynthetic rates in the field would be little affected because intense self‐shading restricts inhibiting irradiances to the upper few mm–cm of the algal canopy. 5. Our physiological (P–I response) experiments contradicted previous assertions that high ambient temperatures, or nutrient deficiency, were primary causes of mid‐summer sloughing. In our study, sloughing occurred simultaneously at nutrient enriched and nutrient deficient sites, at temperatures well below critical values found during in vitro experiments, and our indicator of physiological condition (P–I response) remained unchanged leading up to, or immediately after, the sloughing event. 6. Self‐shading can reduce the convexity of the P–I response within in vitro incubations, even when the amount of algal material is low. Our experiments used 0.08 g DM of algal material that formed clumps c. 1 cm thick. Under these conditions, we estimated negligible (<1%) effects on P_M, a 12% reduction in apparent values of α, and 14% and 17% increases in values of the α‐dependent terms I_CR and I_K, respectively. 7. Our results are consistent with the hypothesis that a population‐level negative feedback (self‐shading) is responsible for sloughing in dense macroalgal beds. Sloughing was probably inevitable once macroalgal bed density and thickness surpassed a critical threshold. Cells towards the base of the bed received insufficient light to maintain metabolic balance, began to decay and weaken, and became increasingly susceptible to physical detachment from shear stress.