NITROGEN EXCRETION IN THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL, 1908)

Excretion of ammonia, urea and primary amines (assayed as fluorescamine-positivesubstances, FPS) was measured in the Antarctic limpet Nacellaconcinna. The mean contributions to overall excretion rate were89% ammonia, 8% urea and 3% FPS, although in some individualsurea formed almost 40% total excreted nitrogen and in othersprimary amines formed over 30%. Ammonia and urea excretion rateswere not correlated, suggesting the ureagenesis has a specificphysiological role and is not simply an alternative end-pointto ammonia. In starved limpets urea excretion at first increasedby at least x2, and then declined to low levels after 44 days.Ammonia excretion also increased, but only after 20 days, andthen stayed high until at least day 44. These different patternsconfirm the independent roles of ammonia and urea productionin Nacella. (Received 10 June 1993; accepted 25 August 1993)     

Enzymatic indices of respiration and ammonia excretion: relationships to body size and food levels

Enzyme indices of zooplankton respiration, citrate synthase(CS), and ammonia excretion rate, glutamate dehydrogenase (GDH),were measured in cultures of Artemia franciscana (San FranciscoBay) feeding in a 25-fold range of concentration of the algaDunaliella salina. Enzyme activities per animal were regressedagainst body size (expressed as dry weight or protein) in theform of the allometric equation, log Y = log a + b logW. CSactivity was related to size with a scaling exponent (b) of1.133 in terms of dry weight and 0.864 in terms of protein.GDH scaling exponents were 1.283 and 0.978 for dry weight andprotein, respectively. In cases where these variables are measured,it is essential that the size structure of populations and communitiessampled is taken into account, otherwise false conclusions maybe drawn. Despite specific growth rate variation from 0.117to 1.188 day^–1, no differences in CS or GDH activity couldbe attributed to feeding level or growth rate effects. Suchenzymatic indices, which represent only maximum potential metabolicrates, may therefore be poor predictors of actual rates in vivo.     

FORAGING ACTIVITY OF HELCION PRUINOSUS (PATELLOGASTROPODA) ON A SOUTH AFRICAN BOULDER SHORE

Foraging activity of the mid-shore limpet Helcion pruinosuswas monitored on an exposed boulder beach in the Eastern Capeof South Africa. Numbers of limpets active in 10 fixed quadratswere monitored and compared in different seasons and during springand neap tides. Foraging excursions were mainly associated with nocturnallow tides, limpets only emerging from beneath rocks when theywere completely uncovered by the receding tide, and they hadall retreated to beneath rocks before being splashed by theadvancing tide. The number of animals active was greater onfull moon spring tides. Significantly more limpets were activeon an autumn spring tide than on similar tides in other seasons. ^* To whom correspondence should be addressed. (Received 27 March 2000; accepted 5 July 2000)     

STUDIES ON THE METABOLISM OF UREA AND OTHER NITROGENOUS COMPOUNDS IN CHLORELLA ELLIPSOIDEA: III ASSIMILATION OF UREA

Assimilation of urea by Chlorella ellipsoidea was investigatedby using ¹⁴C-urea. It was revealed that urea carbon metabolizedby the N-starved cell was almost quantitatively recovered incarbon dioxide under dark-aerobic conditions. The rate of ureaconsumption was considerably influenced by the N-content ofalgal cells, practically no metabolism of urea being observedwith the cells containing more than 7 per cent N on a dry weightbasis. Similar results were also obtained when urea was replacedwith ammonia as nitrogen source. Based on the results obtained,a tentative scheme for the assimilation process of urea in Chlorellawas proposed. (Received February 7, 1960; )     

Energetics and feeding dynamics of Euphausia superba in the South Georgia region during the summer of 1994

Measurements of adult Antarctic krill (Euphausia superba) gutcontents, evacuation and egestion rates, as well as digestiveefficiency, were carried out during February-March 1994 in thevicin ity of South Georgia to estimate in situ daily ration.These were combined with acoustically derived biomass data tocalculate the grazing impact of Antarctic krill and its contributionto the carbon flux in the region. Individual levels of gut pigmentconcentrations and evacuation rates ranged from 27 to 1831 ngchlorophyll a-eq. ind.^–1 and from 0.133 to 0.424 h^–1,respectively. Losses of pigment fluor escence during digestionwere very high, ranging from 58 to 98% of the total pigmentdigested. Daily carbon consumption estimated using the gut fluorescencemethod varied from 0.234 to 0.931 mg C ind.^–1 day^–1(or 0.4–1.7% of body carbon), compared to {small tilde}2.73mg C ind.^–1 day^–1 (or {small tilde}5% of body carbon)using the faecal pellet production data. The 3-fold higher dailyration estimated using egestion rate data may be explained bypredation on micro-and mesozooplankton. Maximum krill grazingimpact ranged from 0.4 to 1.9% of the total phytoplankton stockor from 10 to 59% of the total daily primary production. However,grazing impact on the microphytoplankton (>20 µm) wassubstantially higher, at times exceeding 100% of the daily microphytoplanktonproduction. It is suggested that to meet its energetic demands,kriil must consume a substantial proportion of heterotrophiccarbon. ³Present address Zoology Department, University of Fort Hare,P/Bag X1314, Alice, 5700, South Africa     

Metabolism and elemental composition of aggregate and solitary forms of Salpa thompsoni (Tunicata: Thaliacea) in waters off the Antarctic Peninsula during austral summer 1999

Oxygen consumption, ammonia excretion and phosphate excretionrates were measured on the aggregate form (aggregated sexualblastozooid generation) and solitary form (solitary asexualoozooid generation) of Salpa thompsoni sampled from waters offthe Antarctic Peninsula from December 1999 to February 2000,in conjunction with body composition analysis (water, ash, carbon,nitrogen and phosphorus). The specific metabolic rates of S.thompsoni were weight-independent. No significant differencesbetween the aggregate and solitary forms were observed for theweight-specific rates with the exception of the oxygen consumptionrate on phosphorus weight. Metabolic loss estimated for theaggregate and solitary forms was 3.0 and 3.5% day^–1 forbody carbon, 1.6 and 1.8% for body nitrogen, 3.9 and 10.6% forbody phosphorus, respectively. Contents of carbon (6.0% of dryweight for the aggregate form and 5.1% for the solitary form),nitrogen (1.5 and 1.3%) and phosphorus (0.15 and 0.11%) tendedto decrease with the increase of dry weight. All mean valuesof each body constituent (water, ash, C, N and P) for the aggregateand solitary forms were not significantly different in the samedry weight ranges.     

Studies on the Expansion of the Leaf Surface: II. THE INFLUENCE OF LIGHT INTENSITY AND DAYLENGTH

The parts played by constant amounts of visible radiation perday and its two components—daylength and intensity—ininfluencing the growth of Cucumis sativus have been investigated.The amount of radiation per day had a far greater influencethan either of its components per se. Nevertheless, small significanteffects of photoperiod were found, leaf expansion and dry weightincrease being greatest at daylengths between 10 and 15 hr.rather than with longer days which, with similar daily totals,would be expected to give the greatest amounts of assimilation. Rates of leaf production and appearance were greatest with thehighest amounts of radiation, but the rates of expansion ofindividual leaves and their maximum areas were greatest withintermediate amounts of radiation. This response resulted inan optimum curve relating the leaf surface and the dry weightattained after a given period to radiation. The amount of radiationgiving the maximum leaf surface and dry weight decreased withage and with external nutrient supply, but at any one age washigher for increase in dry weight than for increase in leafsurface; stem and root tissues responded more to high radiationthan did the leaf surface. The net assimilation rate was a linearfunction of visible radiation over the range of 15–120cal. cm.^-2 day^-1 explored, the highest value of radiation usedrepresenting the intensity at which photosynthesis would beexpected to be maximal over a 12–15 hr. day. The inhibitory effect of high radiation on leaf expansion andthe resultant influence on the growth of the plant are explainedin terms of the number and intensity of ‘sinks’for carbohydrate and mineral nutrients within the plant.     

STRUCTURE OF THE CEPHALIC TENTACLES OF SOME SPECIES OF PROSOBRANCH LIMPET (PATELLIDAE AND FISSURELLIDAE)

The morphology and ultrastructure of the cephalic tentaclesand eye (optic vesicle) of some patellid and a fissurellid limpetspecies are described. The epithelium of the tentacle bearsciliated cells which have neural connections suggesting a sensoryfunction. In patellid limpets the density of these cells variesbetween species, with the greatest density (18 ciliated tufts.100 µm^–2) being recorded in the territorial limpet,Patella cochlear. The surface of the tentacle of a fissurellidlimpet, Fissurella mutabilis, is papillate, which contrastswith the smooth surface of a patellid tentacle. Ciliated tuftsare borne at the tip of most papillae. Movement of the tentacleis controlled by longitudinal muscle and a radial muscle-collagentissue association, which function as a muscular hydrostat.The eye of a patellid consists of a simple open vesicle anda retina which is comprised of one type of cell. By contrastthe optic vesicle of a fissurellid contains a lens, enclosedby a cornea and a retina which is composed of two types of cell,pigmented and photoreceptive. The ultrastructural features ofthe cells resemble those described for other molluscan eyes. (Received 5 June 1989; accepted 16 August 1989)     

TEMPORAL VARIATION IN FORAGING BEHAVIOUR OF PATELLA GRANULARIS (PATELLOGASTROPODA) AND SIPHONARIA CONCINNA (BASOMMATOPHORA) ON A SOUTH AFRICAN SHORE

Foraging activity of two mid- to low- shore species of limpet,Patella granulans (Prosobranchia) and Siphonaria concinna (Pulmonata)from an exposed shore on the Eastern Cape coast of South Africawas monitored. In both species, activity was compared duringspring and neap tides and, in P. granularis between summer andwinter. Rhythms of activity of the two species were similar,with foraging excursions being mainly associated with nocturnallow tide times, although some P. granularis foraged during daytimelow tides. It is suggested that foraging excursions in P. granularisare triggered by wave action. Both species foraged further onspring tides than on neap tides and this is suggested to bea result of the limited time limpets have to forage. P. granulariswas also found to forage further during summer when comparedto winter and the possibility that seasonal micro-algal productivityinfluences foraging distances in limpets is discussed. The foraging activity of both species could be divided into3 distinct phases, a relatively rapid outward phase, a muchslower foraging phase and a rapid homeward phase. Whether ornot these limpets graze throughout an excursion is not known.S. concinna was found to home to a fixed scar, although duringthe experiment some scar-swapping occurred. P. granularis didnot home to a fixed scar but possessed a ‘home range’(approx. 5 cm²) to which it returned after each excursion. Patella granularis was found to move randomly during foraging,whilst S. concinna foraged in a non-random direction -whichtook individuals upshore. No tidal-influence is thought to bepresent in this case and the possibility of a learning componentin the foraging behaviour of certain limpet species in relationto the return to optimal feeding patches is discussed. (Received 18 May 1996; accepted 2 September 1996)     

Quantification of the phosphorus released by zooplankton in an oligotrophic lake (La Caldera, Spain): regulating factors and adjustment to theoretical models

Using an in situ approach, we have evaluated the phosphorusinputs from zooplankton in a high-mountain oligotrophic lake.Values of the specific gross release rate (SGRR) fluctuatedbetween 0.2 and 2.9 µg P mg^–1 dry weight h^–1,and were higher when the nauplii of Mixodiaptomus laciniatusdominated the zooplankton community. The rate of P recyclingby the zooplankton was high, reaching 1.6 µg P l^–1day^–1, and showed a highly consistent seasonal patternfrom one year to the next, with maxima in midsummer. Zooplanktonsize accounted for as much as 85% of the variance obtained inthe measurements of the specific rate of P release, while otherfactors, such as the quality or quantity of food, did not significantlyinfluence the SGRR changes. Among the models tested, only theone proposed by Peters (Int, Ver. Theor. Angew. Limnol. Verh.,19, 273–279, 1975) was useful for predictions in thissystem. The stoichiometric model of Hessen and Andersen (Arch.Hydrobiol., 35, 111–120, 1992), applied in this oligotrophicsystem, adequately predicted the phyto- and zooplankton dynamics,whereas the values of P release estimated using this model werefar higher than the excretion rates obtained experimentally.These differences were related to the type of egestion (formationof faecal pellets) of metazooplankton and to the relative importanceof the food resistance to digestion. We believe that in communitieswhere copepods constitute a substantial percentage of the zooplankton,an evaluation of the P release which is readily available [solublereactive phosphate (SRP), total dissolved phosphate (TDP)] toalgae and bacteria would not fit the predictions of generalmodels of mass balance; under these circumstances, assimilationefficiency proves to be the key parameter for predicting thereadily available P (excreted P).     

Growth in the limpet <Emphasis Type="Italic">Nacella concinna</Emphasis> from contrasting sites in Antarctica

Annual shell growth was determined by mark and recapture in the limpet Nacella concinna (Strebel 1908) at two contrasting sites in Antarctica. At Signy Island, 60°S, growth was moderately fast, comparable with some limpets in more temperate areas. The fluorescent calcium marker calcein was used to validate the results from the mark/recapture study, and fine-scale growth increments showed that shell growth was seasonal. Further south at Rothera Point, 67°S, mean annual growth over a 3-year period was significantly slower than at Signy, and in 1 year was the slowest yet reported for a limpet. Comparison with an earlier mark/recapture study at Arthur Harbour, Palmer Station (64°S) revealed a cline of decreasing growth performance with increasing latitude along the Antarctic Peninsula. It is not clear whether the slower annual growth rate at higher latitude was caused by physiological constraints, a reduced length of growing season, or a combination of both. Limpets show a global cline in growth performance, which decreases towards higher latitudes.     

A QUANTITATIVE STUDY OF A CERASTODERMA -- NEPHTHYS COMMUNITY IN THE LIMFJORD, DENMARK, WITH SPECIAL REFERENCE TO PRODUCTION OF CERASTODERMA EDULE

Cerastoderma edule is the dominant member of a non-random Cerastoderma—Nephthyscommunity, occupying a physically, homogeneous, submerged sandbankin the Limfjord, Denmark. C. edule is patchily distributed withinthis community, growth rates showing a clear density-dependence.Individual production is about 35%lower in high density patchesthan outside them; at low density annual individual flesh dryweight increment is 295 mg. Seasonal variation in water, ash,lipid, protein and glycogen contents is studied, and a sizedependent(= density-dependent) relationship is shown to exist for someparameters. Population production, estimated by a new graphicalmethod, and taking into account gametic and shell protein production,attains 150 g dry flesh weight, m^–2.yr^–1 at meanpopulation density rising to 250 g dry flesh weight. m^–2.yr^–1in the high density patches. ¹Present address: Institut für Physiologische Chemie, Abt.Zellbiochemie, Universitat Hamburg, Martinistrasse 52, 2000Hamburg 20 (Received 10 March 1980;     

MORPHOLOGICAL AND GENETIC VARIATION IN THE ANTARCTIC LIMPET NACELLA CONCINNA (STREBEL, 1908)

Samples of the Antarctic limpet, Nacella concinna (Strebel,1908), were collected from four sites in the South Orkney Islandsand from Stromness in South Georgia during 1988. At three SouthOrkney sites, both littoral and sub-littoral samples of limpetswere taken. Shell dimensions were measured and littoral andsub-littoral limpets were shown to have significantly differentshell shapes. Foot and digestive gland tissues were subjectedto electrophoresis and five polymorphic loci {Es-1, lcd-1, lcd-2,Gpi, Got-1 and Pgm-1) and two monomorphic loci (Es-2 and Got-2)were scored. Genetic identities between littoral and sub-littoralforms and also between sites were calculated. At the loci scored,the littoral and sub-littoral forms were virtually identicaland this suggests that the shell shape differences between theforms are the result of environmentally induced phenotypic plasticity.However, significant genetic differences and some morphologicaldifferences were apparent between the sample of limpets fromSouth Georgia and all other sites. Genetic identity values suggestedthat the South Georgia and South Orkney N. concinna are geographicallyseparated populations of a single species rather than distinctsub-species. (Received 21 November 1990; accepted 17 April 1991)     

Distribution,growth and reproduction of the limpet Nacella (Patinigera) concinna (Strebel 1908) in relation to potential food availability,in Esperanza Bay (Antarctic Peninsula)

The present work addresses the effect of environmental factors (icing, water temperature, food availability) on the ecology of the patellid limpet Nacella (Patinigera) concinna, in a bay on the Antarctic Peninsula. Sampling was conducted at three depths (intertidal, 5m, 10m) from February 1987 to January 1988. Temperature was recorded and concentrations of Chlorophyll a were measured on the bottom, in the water and in the ice-water layer. The limpets were measured, weighed and a condition coefficient for somatic and gonadal mass was calculated. Their ages were estimated through size frequency distribution analysis and a seasonalized von Bertalanffy growth model was applied. The intertidal subpopulation migrated to deeper levels at the beginning of the icing season and recolonized the intertidal zone after ice retreat. The growth rate was very low (von Bertalanffy K 0.08). Growth rates showed important seasonal variations, with maxima during December and January. Nacella (P.) concinna spawns once a year and spawning coincided with raising water temperature (from -1.33°C to-0.84°C), and probably was also related to increasing spring food availability. Body mass increased during periods of high standing stock of microphytobenthos, revealing that ice-algae and phytoplankton were of minor importance as food sources for limpets in Esperanza Bay.     

DISTRIBUTION AND PRODUCTION OF THREE HYDROBIA SPECIES (GASTROPODA: HYDROBIIDAE) IN A SHALLOW COASTAL LAGOON IN THE BAY OF CADIZ, SPAIN

The abundance, life span, growth and production of the mud snailsHydrobia minoricensis, H. ulvae and H. ventrosa in a semi-naturallagoon system were studied by taking monthly samples at threesites during 1991 and 1992. The most abundant species, H. minoricensisoccurred at mean densities of 12834 to 26264 snails m^–2(10.7 to 25.8g dry weigh m^–2), depending on the site.The least abundant species, H. ulvae, occurred at mean densitiesof 185 to 353 snails m^–2 (3.2 to 2.2g dry weight m^–2).The numerical abundance and biomass of the three Hydrobia specieswere positively related to the biomass of benthic macroalgae(P<0.01). Although H. ulvae egg capsules were recorded throughoutthe year, newly hatched snailsof this species were not observed,in contrast to the other two species. The early spring and summercohorts of H. minoricensis and H. ventrosa seemed to be themost numerous. The average life spans of these two species wereestimated to be about 18 and 13 months respectively. Annualproduction estimates for the whole lagoon system were 29.0 (6.3),5.5 (0.8) and 5.2 (1.0)g dry weight (ash-free dry weight) m^–2yr^–1 for H. minoricensis, H. ulvae and H. ventrosa respectively.The annual P/B ratio was about 2 for H. minoricensis and H.ventrosa. (Received 5 July 1994; accepted 5 October 1994)     

INTERSPECIFIC INTERACTIONS AND SCARCITY OF A TROPICAL LIMPET

The øcmaeid limpet Lottia stipulata occurs in the midintertidal zone of rocky Pacific shores from Colombia to ElSalvador. It is regularly present but rare (<1 m^–2)at wave-exposed to semi-protected sites in Panama. The verticaldistribution of Lottia overlaps that of a pulmonate limpet,Siphonaria gigas, the most abundant molluscan grazer in themid zone (28. m^–2). Manipulations of the density of Siphonariasuggest the pulmonate negatively affects the recruitment, growth,and abundance of Lottia. Observations of populations of limpetsin an area undergoing succession support these results –Lottia recruits quickly and reaches high levels of abundance,but cannot maintain high densities as other benthic consumerslike S. gigas settle and increase in numbers over time. Paradoxically,examination of radulae suggests that if ability to use algalcrusts (the major available food) were of primary importance,Lottia would be the superior competitor. However, competitionneed not be invoked, and results can be explained by a one-wayrelationship between these two limpets. Lottia apparently hasno effect on Siphonaria, but the larger pulmonate probably actsas an agent of disturbance by interfering with foraging by Lottiaand by bulldozing or consuming newly-settled individuals. Predationon Lottia by a predaceous gastropod, Purpura columellaris, andby the American oystercatchcr, Haematopus palliatus, is insignificantat most sites, but may be important where these consumers areabundant. The abundance of Lottia appears to be controlled primarilyby disturbance by Siphonaria and by physical factors, not bypredation or competition. ¹Present address: Department of Zoology, University of Massachusetts,Amherst, Massachusetts 01003 ²Present address: Department of Zoology, University of RhodeIsland, Kingston, Rhode Island 02881 ³Order of authorship determined by coin toss. (Received 31 July 1984;     

The seasonal population changes and carbon budget of the calanoid copepod Boeckella minuta Sars in a newly formed sub-tropical reservoir

The population carbon budget and seasonality of Boeckella minutain a newly formed subtropical reservoir were examined 3 yearsafter the reservoir filled. Average daily biomass was 26.4 mgC m^–3 and the annual population carbon budget was: consumption2470, egestion 1482, assimilation 988, production 493 and respiration495, mg C m^–3 year^–1, and the average P/B and P/Aratios were 0.08 and 0.5 respectively. Clutch size and reproductiveeffort (egg production/assimilation) were low, and the proportionof males decreased throughout the population cycle. The seasonalabundance pattern changed from perennial (pre-filling years)to a 7 month cycle. It is suggested that eutrophication andthe spring bloom of cyanobacteria may have accentuated a seasonaldecrease in reproductive effort and survival, leading to anabsence of planktonic stages during summer, and that restingeggs facilitated population survival during the summer periodof stratification.     

Short- and long-term movements of the patellid limpet Patella flexuosa within gaps in intertidal mussel beds

Short-term and long-term movements of the patellid limpet Patellaflexuosa Quoy & Gaimard were studied on an intertidal rockyshore where a mytilid, Hormomya mutabilis (Gould), formed anextensive mussel zone. At low tide, all the limpets were found restingwithin gaps in the mussel zone, which were formed after massdislodgement of the mussels by waves. The foraging areas ofall the marked limpets were restricted to within the gaps duringfour 24h diving observations. All of these limpets displayedhoming behaviour after short excursions with a maximum averagedistance of 6.7 cm from their homes. During short-term observationperiods of about 4–5 days, no marked limpets moved fromone gap to another gap across the mussel bed of H. mutabilis.During long-term observation periods of one month, however,10–30% of marked limpets shifted their homes to differentgaps that had a lower limpet density. The shell length of theseemigrants was, in general, significantly smaller than that ofnon-emigrants. The percentage of emigrants tended to be higherin summer and autumn than in winter and spring. The movementof P. flexuosa within patchy habitats is discussed with a focuson the difference in site fidelity between small and large limpets. (Received 14 April 1998; accepted 7 September 1998)     

The Distribution of Nitrate Assimilation Between Root and Shoot in Vicia faba L.

Nitrate assimilation was examined in two cultivars (Banner Winterand Herz Freya) of Vicia faba L. supplied with a range of nitrateconcentrations. The distribution between root and shoot wasassessed. The cultivars showed responses to increased applied nitrateconcentration. Total plant dry weight and carbon content remainedconstant while shoot: root dry weight ratio, total plant nitrogen,total plant leaf area and specific leaf area (SLA) all increased.The proportion of total plant nitrate and nitrate reductase(NR) activity found in the shoot of both cultivars increasedwith applied nitrate concentrations as did NO₃^–: Kjeldahl-Nratios of xylem sap. The cultivars differed in that a greaterproportion of total plant NR activity occurred in the shootof cv. Herz Freya at all applied nitrate concentrations, andits xylem sap NO₃^–: Kjeldahl-N ratio and SLA were consistentlygreater. It is concluded that the distribution of nitrate assimilationbetween root and shoot of V. faba varies both with cultivarand with external nitrate concentration. Vicia faba L., field bean, nitrate assimilation, nitrate reductase, xylem sap analysis     

AN ENERGY BUDGET FOR THE SOUTH AFRICAN ABALONE HALIOTIS MIDAE LINNAEUS

Existing data on feeding, growth rate, fecundity, absorptionefficiency, respiration and excretion rates in the South Africanabalone Haliotis midae Linnaeus are converted to energy equivalentsand utilised to compile individual energy budgets. About 63%of the energy content of the food consumed (C) is lost as faeces(F) and a further 32% expended on respiration (R). Energy lossesin the form of ammonia excretion are negligible, accountingfor less than 1% of consumption. Some 5% of energy intake, or13% of absorbed ration (Ab) is thus available for growth andreproductive output (Pg & Pr). In juveniles (<100mm)this is all allocated towards somatic growth, while in adultsan increasing proportion of production is expended on reproductiveoutput. Although feeding, respiration and excretion rates allincrease with temperature the proportions of energy allocatedto the various components of the energy budget appear to beconsistent. Population energy budgets are calculated from densityand size distribution surveys at two study sites. At MarcusIsland, on the Cape west coast, the population has a standingstock of 82 g (wet flesh weight) m^–2,.consumes about 3260KJm^–2y^–1 algae and has a P/B ratio of 0.46, whereasat Cape Hangklip, on the Cape south coast, the population biomassis_133gm^–2, consumes 8613KJm^–2y^–1 and hasa P/B ratio of 0.70. These figures indicate that a high proportionof kelp bed primary production is directly consumed by grazingabalone in areas where populations have not been reduced byhuman exploitation (Received 16 March 1987;