History of kelp beds (Macrocystis) in Orange and San Diego Counties,California

Areas of Macrocystis canopies, as recorded by infrared aerial photography, are presented for about 140 km of the southern California coastline for the 25 year period 1967 to 1991. Several surveys per year were conducted and the largest size canopy per year was selected for presentation. Possible effects from various influences were examined: El Nino and La Nina episodes, storms, rainfall, and human-associated influences such as discharged wastewaters.     

Colony Structure and Seasonal Differences in Light and Nitrogen Modify the Impact of Sessile Epifauna on the Giant Kelp Macrocystis pyrifera (L.) C Agardh

The presence of the stoloniferous hydroid Obelia geniculata (L.) had no effect on the pigment concentration or nitrogen status of underlying blade tissue of the giant kelp Macrocystis pyrifera (L.) C. Agardh. The sheet-like colonies of the bryozoan Membranipora membranacea (L.) markedly reduced the pigment concentration of colonized blade tissue, but only during winter. Reductions in pigment concentration are most likely a result of damage to underlying tissue due to some factor related to the presence of bryozoan colonies on blade surfaces. Blade tissue colonized by M. membranacea also had higher δ¹⁵N signatures than surrounding bryozoan-free tissue, possibly indicating the provision of nitrogen to M. pyrifera by bryozoan colonies. Results show that seasonal changes in nitrogen and colony size can strongly modify the effect of epifauna on macroalgae they colonize. Unlike bryozoans, hydroid colonies provided no barrier to nitrogen uptake by colonized M. pyrifera tissue and enhanced ammonium uptake was observed for tissue colonized by O. geniculata during nitrogen limitation. Epifauna with stoloniferous growth forms such as hydroids are more likely to have benign or even mutualistic relationships with macroalgae they colonize than the sheet-like colonies of bryozoans.     

Reproduction strategies of Macrocystis pyrifera (Phaeophyta) in Southern Chile: The importance of population dynamics

Macrocystis pyrifera is an ecologically dominant species along the temperate Northern and Southern Pacific Coast of America, showing some similarities and differences at population and community level. In general, this kelp is reported to be reproductive all year round. Annual populations present in wave-protected areas of southern Chile suggest that the reproductive strategies of this population can be different. In this study we explore the reproductive strategies of annual M. pyrifera present in wave-protected areas and perennial populations encountered in exposed areas of southern Chile (41^∘S). Our results show that M. pyrifera present in wave-exposed locations has a reproductive strategy that is similar to populations in the northern hemisphere. These populations reproduce all year round and their strategy is to produce high numbers of sporophylls and ensure that most of them (over 90%) become sporogenous. On the other hand, the protected populations with an annual life cycle, produce more spores per area of sorus. In a few months, they are able to produce sufficient propagules to recolonize areas before the adult plants disappear in autumn.     

Changes in the fish fauna associated with a sub-Antarctic <Emphasis Type="Italic">Macrocystis pyrifera</Emphasis> kelp forest in response to canopy removal

The fish fauna associated with a Macrocystis pyrifera forest and the effects of the canopy removal on this fauna were studied in the Beagle Channel, Tierra del Fuego. Seasonal changes and differences in the fish communities that inhabit the canopy and the holdfast were also studied. Two patches of kelp forest separated by 200 m were selected. In one, the canopy was removed periodically while the other was used as a control. Samples were collected seasonally, from autumn 1999 to 2001. Fish fauna in the water column was sampled using trammel nets and holdfast fish fauna was sampled by removing the complete holdfast. Different assemblages of fish species were captured in the water column (surface and bottom) and in the holdfast. In the former there were mainly pelagic and benthopelagic species and the latter predominantly demersal species. The principal effect of the canopy removal was a drop in the abundance (and total weight) of Paranotothenia magellanica (doradito), the species with the strongest relationship with the canopy, principally at the surface of the treated patch probably due to a reduction in the availability of refuges. A high degree of seasonality was observed for fish species’ total weight, abundance and diversity, with higher values in summer and autumn. Taking into account our data and available data on kelp growth in the same locality, we suggest of cutting the kelp forest (preferably those farther away from the coast) once a year in winter or early spring, in order to minimize impact on the fish community.     

Effects of kelp (Macrocystis integrifolia) on soil chemical properties and crop response

In 1981 a two-year field plot experiment was established to assess the effects of quantities (0, 7.5, 15, 30, 60 and 120 t ha⁻¹) of fresh kelp (Macrocystis integrifolia) on crop growth and nutritional response and chemical properties of a fine-textured soil. Soil was analyzed for NO₃−N, NH₄−N, electrical conductivity, pH, Cl and exchangeable cations (K, Mg, Ca, Mn and Na). The plots were planted to beans (Phaseolus vulgaris) in the first year and peas (Pisum sativum) in the second year. Marketable bean yields increased in the first year with kelp applications up to 60 t ha⁻¹, with yields, emergence and flowering being reduced by the 120 t ha⁻¹ application. Soluble salts (EC) and Cl concentrations in the soil eight days after application increased linearly and sharply with increasing quantities of kelp. Increased K concentration and moisture content, characteristics of plants growing in a salt-stressed soil environment, were measured. A subsequent companion greenhouse experiment confirmed that the reduced bean emergence and growth with 120 t ha⁻¹ applications of kelp were primarily due to soluble salts. The only growth effects upon peas in the second year was a slight reduction in leaf plus stem yields with increasing applications of kelp.     

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.     

A unique pattern of F-actin organization supports cytokinesis in vacuolated cells of Macrocystis pyrifera (Phaeophyceae) gametophytes

Summary. The organization of actin filaments and their role in cytokinesis was studied in regenerating protoplasts and thallus cells of gametophytes of the brown alga Macrocystis pyrifera. Before the onset of cytokinesis, a ring of actin filaments appeared on the putative cytokinetic plane just under the plasmalemma. Light and electron microscopy of cytokinetic cells revealed that large vacuoles occupy the space between the daughter nuclei, which very often are eccentrically positioned at the cell cortex. By the progress of cytokinesis, actin filament bundles emanating from the cytokinetic ring tend to form an actin plate that enters cytoplasmic pockets in which the cytokinetic diaphragm develops. The mechanism of this cytokinetic pattern that has not been reported so far for brown algae is discussed. Correspondence and reprints: Department of Botany, Faculty of Biology, University of Athens, Athens 157 84, Greece.     

Effects of kelp (Macrocystis integrifolia andEcklonia maxima) foliar applications on bean crop growth

In 1983 and 1984 field plot experiments were established to assess the effects of a foliar applied (2 or 4L ha^–1×four applications per season) kelpMacrocystis integrifolia, concentrate on growth and nutrition of bean,Phaseolus vulgaris. A commerical kelp concentrate, prepared fromEcklonia maxima, was also used as a test comparison. In the first year a phytohormonal extract of theM. integrifolia concentrate, designed to extract the cytokinin, auxin and gibberellin phytohormones, was also applied to the crop to test the thesis that these phytohormones are active constitutents. In each of the two field seasons the kelp concentrates increased harvestable bean yields on average by 24%. The phytohormonal extract also increased yields, but was less effective than the kelp concentrate itself. Bioassay results demonstrated the presence of phytohormone-like substances in this crude extract.     

Characterisation of microsatellite loci in the habitat-forming kelp, Ecklonia radiata (Phaeophyceae, Laminariales)

Habitat forming algae play an important role in the ecology of temperate reefs worldwide. Despite this, our understanding of levels of gene flow within and among populations of algae is largely limited to studies on intertidal species; we know comparatively little about important habitat-forming subtidal algae. Here, we develop eight polymorphic microsatellite markers for the characterisation of population genetic diversity and structure in the subtidal kelp, Ecklonia radiata. This large macroalga is the most abundant habitat-forming kelp on the subtidal rocky reefs of temperate Australia and New Zealand where it forms extensive forests that support an astounding diversity of associated taxa.     

Rotifers as predators on small ciliates

Clearance rates of Synchaeta pectinata, Brachionus calyciflorus and Asplanchna girodi on Tetrahymena pyriformis (46 µm in length) at a density of 10 cells ml^–1, in the presence of algal food, were 2.5 to 6.1 ml rot.^–1 day^–1. Clearance rates of these rotifers were, respectively, about 2, 3, and 13 times lower on Strobilidium gyrans (58 µm in length) than on T. pyriformis, indicating that the saltations of S. gyrans are an effective escape response. Clearance rates of S. pectinata were considerably lower on Colpidium striatum (81 µm) than on S. gyrans, suggesting that S. pectinata may not be able to ingest ciliates of this size. S. pectinata had a clearance rate of 19 ml rot.^–1 day^–1 on S. gyrans at a density of 1.2 cells ml^–1, in the absence of edible algal food. Rotifers may prey extensively on ciliates in natural plankton communities, ingesting 25 to 50 individuals in the 45–60 µm size range day^–1.     

Toxicity of sewage-contaminated sediment cores to Macrocystis pyrifera (Laminariales,Phaeophyta) gametophytes determined by digital image analysis

Macrocystis pyrifera gametophytes were exposed in batch culture to varying mass concentrations of buried, sewage-contaminated, historically discharged sediment that had been sampled from two sites off Palos Verdes Peninsula, California. Significant gametophytic vegetative growth inhibition was detected in six days, using digital image analysis at sediment loadings ranging from 0.15 to 14.5 g in 500 mL nutrient-enriched seawater. Inhibition declined at low sediment loadings and increased at high loadings as cultures aged. Sediments corresponding to the historic emissions peak taken 2 km from the Joint Water Pollution Control Plant outfall inhibited vegetative growth more than did sediments sampled 13 km distant. Analysis showed elevated aqueous Cd(II), Cr(II) and p,p-DDE concentrations in high sediment-loading culture medium. Inhibition by Zn(II) alone was observed at similar concentrations in other experiments, but synergism or antagonism by other toxicants remains possible.     

Osmoregulatory responses of glaucous-winged gulls (Larus glaucescens) to dehydration and hemorrhage

The effects of dehydration and hemorrhage on plasma ionic, osmotic, and antidiuretic hormone (arginine vasotocin) concentrations and of hemorrhage on salt gland secretion and glomerular filtration rate were evaluated in glaucous-winged gulls, Larus glaucescens. Dehydration for 24 h did not affect plasma ionic, osmotic or arginine vasotocin concentrations; 72 h dehydration significantly elevated plasma osmolality, plasma sodium and chloride concentrations, and plasma arginine vasotocin concentration, but did not affect plasma potassium concentration. Constant infusion of 0.8 mol·l^-1 NaCl increased plasma arginine vasotocin concentration and produced salt gland secretion in seven gulls; four secreted well, while three secreted less well. Removal of 20% blood volume during saline infusion immediately reduced (P<0.001) salt gland secretion rate in all gulls. After bleeding, good secretors maintained glomerular filtration rate and urine flow rate; the poorer secretors increased glomerular filtration rate and became diuretic. Blood replacement returned salt gland secretion rate to the prebleeding level (P<0.05) without affecting salt gland secretions sodium concentration in gulls which secreted well, but did not restimulate salt gland secretion in gulls which secreted poorly. Reinfusion of blood had no effect on glomerular filtration rate. Bleeding and blood replacement did not affect plasma arginine vasotocin concentration.Abbreviations AVT arginine vasotocin - ECF extracellular fluid - ECFV extracellular fluid volume - EDTA ethylenediaminetetra-acetate - EWL evaporative water loss - GFR glomerular filtration rate - Hct hematocrit - LB large blood sample - [Na⁺]_pl plasma sodium concentration - Osm_pl plasma osmolality - PEG polyethylene glycol - RH relative humidity - RIA radioimmunoassay - SB small blood sample - SGS salt gland secretion - T _a ambient temperature - TFA trifluoroacetic acid - UFR urine flow rate     

Alternative camouflage strategies mediate predation risk among closely related co-occurring kelp crabs

Although camouflage is a common predator defense strategy across a wide variety of organisms, direct tests of the adaptive and ecological consequences of camouflage are rare. In this study, we demonstrated that closely related crabs in the family Epialtidae coexist in the same algal environment but use alternative forms of camouflage––decoration and color change––to protect themselves from predation. Decoration and color change are both plastic camouflage strategies in that they can be changed to match different habitats: decoration occurs on a short timescale (hours to days), while color change accompanies molting and occurs on longer timescales (months). We found that the species that decorated the most had the lowest magnitude of color change (Pugettia richii); the species that decorated the least showed the highest magnitude of color change (Pugettia producta), and a third species (Mimulus foliatus) was intermediate in both decoration and color change, suggesting a negative correlation in utilization of these strategies. This negative correlation between color change and decoration camouflage utilization mirrored the effectiveness of these camouflage strategies in reducing predation in different species. Color camouflage primarily reduced predation on P. producta, while decoration camouflage (but not color camouflage) reduced predation on P. richii. These results indicate there might be among-species trade-offs in utilization and/or effectiveness of these two forms of plastic camouflage, with important consequences for distribution of these species among habitats and the evolution of different camouflage strategies in this group.     

Consumption of introduced prey by native predators: Argentine ants and pit-building ant lions

When populations of native predators are subsidized by numerically dominant introduced species, the structure of food webs can be greatly altered. Surprisingly little is known, however, about the general factors that influence whether or not native predators consume introduced species. To learn more about this issue, we examined how native pit-building ant lions (Myrmeleon) are affected by Argentine ant (Linepithema humile) invasions in coastal southern California. Compared to areas without L. humile, invaded areas contained few native ant species and were deficient in medium-sized and large bodied native ants. Based on these differences, we predicted that Argentine ants would negatively affect ant lion larvae. Contrary to this expectation, observational surveys and laboratory growth rate experiments revealed that Myrmeleon were heavier, had longer mandibles, and grew more quickly when their main ant prey were Argentine ants rather than native ants. Moreover, a field transplant experiment indicated that growth rates and pupal weights were not statistically different for larval ant lions reared in invaded areas compared to those reared in uninvaded areas. Argentine ants were also highly susceptible to capture by larval Myrmeleon. The species-level traits that presumably make Argentine ant workers susceptible to capture by larval ant lions—small size and high activity levels—appear to be the same characteristics that make them unsuitable prey for vertebrate predators, such as horned lizards. These results underscore the difficulties in predicting whether or not numerically dominant introduced species serve as prey for native predators.     

Hybridization of glaucous gull (Larus hyperboreus) and herring gull (Larus argentatus) in Iceland: mitochondrial and microsatellite data

Large white-headed gulls provide an interesting group of birds for studies of hybridization. The group is composed of 20 species of recent origin, often with weak reproductive barriers. Here we report the results from a study on the glaucous gull Larus hyperboreus, an Arctic species which has been breeding in Iceland for centuries, and the herring gull Larus argentatus which has a wide distribution in Europe but colonized Iceland in 1920s. Previous studies, based on morphological variation indicated hybridization between the two species in Iceland, have been questioned as it may just reflect variation within the species. Here we evaluate whether hybridization has occurred between the two species in Iceland by studying variation in microsatellites and mtDNA. The analysis is based on feathers taken from wings sampled in Iceland over a period of 40 years. The results are compared with samples obtained from East Greenland and published sequences of samples obtained throughout Europe. The genetic analysis reveals a distinctive grouping of the two species, although they present a shallow genealogy and an extensive sharing of the genetic variants between the two species. Several individuals show admixture for molecular markers, which may result from an incomplete lineage sorting although geographical patterns of both mtDNA haplotypes and microsatellites strongly indicate a recent hybridization in Iceland.