The theoretical basis for estimating phytoplankton production and specific growth rate from chlorophyll, light and temperature data

Phytoplankton maximum specific growth rate, μ_max, and maximum photosynthetic quantum yield, Φ_max, can be related mathematically via the photosynthetic light curve, P(I). A model is presented in which maximum quantum yield defines the initial slope of the light curve and is assumed to be a known constant, while maximum specific growth rate defines the light-saturated region of the curve and is assumed to be a known function of temperature. The effect of introducing μ_max(T) into P(I, Φ_max) is to replace the unknown, temperature-dependent light saturation parameter with a term involving the ratio μ_max/Φ_max. The advantage of writing P(I) in terms of both μ_max and Φ_max is that those parameters are particularly well documented in the literature. Consequently, estimates of nutrient-unlimited phytoplankton growth and production rates can be based solely on the constants μ_max, Φ_max and k_c (light absorption per unit of chlorophyll) and the free variables light, temperature and chlorophyll concentration. Rate estimates appear to be accurate to within a factor of two for an extremely wide range of conditions.One particularly significant result of introducing μ_max into P(I, Φ_max) is that the carbon : chlorophyll ration, θ, appears explicitly. It is possible to derive an expression for optimum θ based on the assumption that adaptive changes in carbon/chlorophyll occur so as to maximize the specific growth rate for given conditions of light and temperature. Laboratory and field data are compiled from the literature to test the formulae presented here.     

Enforcement missions: Targets vs budgets

Enforcement of policy is typically delegated. What sort of mission should the head of an enforcement program be given? When there is more than one firm being regulated the firms’ decision problems—otherwise completely separate—become linked in a way that depends on that mission. Under some sorts of missions firms compete to avoid the attention of the enforcer by competitive reductions in the extent of their non-compliance, in others the interaction encourages competitive expansions. We develop a general model that allows for the ordering of some typical classes of missions. We find that in plausible settings ‘target-driven’ missions (that set a hard target in terms of environmental outcome but flexible budget) achieve the same outcome at lower cost than ‘budget-driven’ ones (that fix the enforcement budget). Inspection of some fixed fraction of firms is never optimal.     

Potential impact model to assess agricultural pressure to landscape ecological functions

Conservation and protection of soil and water resources and visual aspects of landscape, as well as the promotion of biodiversity, are some of the central tasks of environmental policy development and social politics in the future. One of the main questions is: ‘which agricultural systems are able to guarantee sustained resource-conserving land use?’ Based on the ecological risk concepts of the 1970s and 1980s, a potential impact model was developed using a universal assessment algorithm derived from fuzzy logic. The model estimated the potential impact of agricultural land use on ecosystem function using a few resource indicators. Intervention intensities of agricultural land-use are set in relation to site conditions and aggregated for each of several defined potential impact categories. The interpretation with respect to risk and the calculation of potential impact values are explained.     

Photosynthetic performance of Laminaria solidungula measured in situ in the Alaskan High Arctic

Photosynthetic performance in the kelp Laminaria solidungula J. Agardh was examined from photosynthesis irradiance (P-I) parameters calculated from in situ ¹⁴C uptake experiments, using whole plants in the Stefansson Sound Boulder Patch, Alaskan Beaufort Sea, in August 1986. Rates of carbon fixation were determined from meristematic, basal blade, and second blade tissue in young and adult sporophytes. Differences in saturating irradiance (I _k, measured as photosynthetically active radiation, PAR), photosynthetic capacity (P _max), and relative quantum efficiency () were observed both between young and adult plants and between different tissue types. I _k was lowest in meristematic tissue (20 to 30 E m^–2 s^–1) for both young and adult plants, but consistently 8 to 10 E m^–2 s^–1 higher in young plants compared to adults in all three tissues. Average I _k for non-meristematic tissue in adult plants was 38 E m^–2 s^–1. Under saturating irradiances, young and adult plants exhibited similar rates of carbon fixation on an area basis, but under light limitation, fixation rates were highest in adult plants for all tissues. P _max was generally highest in the basal blade and lowest in meristematic tissue. Photosynthetic efficiency () ranged between 0.016 and 0.027 mol C cm^–2 h^–1/E m^–2 s^–1, and was highest in meristematic tissue. The relatively lower I _k and higher exhibited by L. solidungula in comparison to other kelp species are distinct adaptations to the near absence of light during the eight-month ice-covered period and in summer when water turbidity is high. Continuous measurement of in situ quantum irradiance made in summer showed that maximum PAR can be less than 12 E m^–2 s^–1 for several days when high wind velocities increase water turbulence and decrease water transparency.The Univeristy of Texas Marine Science Institute Contribution No. 695     

Metabolism,enzymic activities and cold adaptation in Antarctic mesopelagic fishes

Several species of Antarctic mesopelagic fishes that have different minimal depths of occurrence but the same environmental temperature were collected in November–December 1983 and in March 1986 between 0 and 1 000 m in the open water near the marginal ice zone in the vicinity of 60°S 40°W (1983) and 65°S 46°W (1986), and oxygen consumption rate (V _{O 2}) and the activity of two metabolic enzymes, lactate dehydrogenase (LDH, an indicator of the anaerobic potential of locomotory muscle) and citrate synthase (CS, an indicator of citric acid cycle activity or aerobic potential), were determined. In four dominant species, whole-individual oxygen-consumption rate (y, ml O₂ individual^–1 h^–1) varied with weight (X, g) according to the equation y=aX ^b, with b values falling between 0.889 and 1.029. The relation of weight-specific LDH activity (y, U g^–1 wet wt) with weight (x, g) was also described by the equation y=aX ^b, with b values varying between 0.229 and 1.025. Weight-specific CS activity declined with weight, with b values from-0.031 to-0.369. V _{2 O}, LDH activity and CS activity all declined markedly with increased species' minimum depth of occurrence (the depth below which 90% of a species' population lives). Comparisons with previous studies on ecologically equivalent species of the California Borderland indicate that depth-related decreases in metabolism are the result of adapted traits of deeper-living species, not declining temperature within the water column. The metabolic rate of Antarctic mesopelagic fishes is approximately twice that of California species at equivalent temperatures; similar rates were found at the normal habitat temperatures of the two groups. Thus, a well-developed compensation for temperature is present in the Antarctic fishes: cold adaptation. Differences in enzymic activity among species, and among different sized individuals of a species are related to differences in metabolic rate and locomotory capacity. Enzymic indices can be used to estimate metabolic rates and evaluate ecological parameters such as predatory strategies and niche separation.     

Photosynthesis, respiration and calcification of a zooxanthellate scleractinian coral under submerged and exposed conditions

An experimental set-up was designed to investigate photosynthesis, respiration and calcification of zooxanthellate scleractinian corals under submerged and exposed conditions. The results of experiments to determine the effect of exposure to air on the metabolism of Stylophora pistillata (Esper, 1797) revealed that: (1) maximum gross photosynthesis ( p _{g max}) is 3.6 times higher in water than in air; (2) an indicator of photoadaptation (I _k ) does not reveal any difference between water and air; (3) the difference between submerged and aerial respiration is not statistically significant; (4) aerial photosynthesis–irradiance (P–I) curves display lower initial slopes (α) than aquatic P–I curves; (5) there is no calcification in air. Received: 7 February 1997 / Accepted: 4 March 1997     

Comparing discriminant analysis, neural networks and logistic regression for predicting species distributions: a case study with a Himalayan river bird

We assessed the occurrence of a common river bird, the Plumbeous Redstart Rhyacornis fuliginosus, along 180 independent streams in the Indian and Nepali Himalaya. We then compared the performance of multiple discrimant analysis (MDA), logistic regression (LR) and artificial neural networks (ANN) in predicting this species’ presence or absence from 32 variables describing stream altitude, slope, habitat structure, chemistry and invertebrate abundance. Using the entire data (=training set) and a threshold for accepting presence in ANN and LR set to P≥0.5, ANN correctly classified marginally more cases (88%) than either LR (83%) or MDA (84%). Model performance was assessed from two methods of data partitioning. In a ‘leave-one-out’ approach, LR correctly predicted more cases (82%) than MDA (73%) or ANN (69%). However, in a holdout procedure, all the methods performed similarly (73–75%). All methods predicted true absence (i.e. specificity in holdout: 81–85%) better than true presence (i.e. sensitivity: 57–60%). These effects reflect species’ prevalence (=frequency of occurrence), but are seldom considered in distribution modelling. Despite occurring at only 36% of the sites, Plumbeous Redstarts are one of the most common Himalayan river birds, and problems will be greater with less common species. Both LR and ANN require an arbitrary threshold probability (often P=0.5) at which to accept species presence from model prediction. Simulations involving varied prevalence revealed that LR was particularly sensitive to threshold effects. ROC plots (received operating characteristic) were therefore used to compare model performance on test data at a range of thresholds; LR always outperformed ANN. This case study supports the need to test species’ distribution models with independent data, and to use a range of criteria in assessing model performance. ANN do not yet have major advantages over conventional multivariate methods for assessing bird distributions. LR and MDA were both more efficient in the use of computer time than ANN, and also more straightforward in providing testable hypotheses about environmental effects on occurrence. However, LR was apparently subject to chance significant effects from explanatory variables, emphasising the well-known risks of models based purely on correlative data.     

Temperature acclimation of respiration and photosynthesis in the brown algaLaminaria saccharina

Sporophytes of the brown algaLaminaria saccharina (L.) Lamour grown at 15°C contained significantly more chlorophylla (chla) than did similar plants grown at 5°C. The increase in chla in 15°C plants was due to increased numbers of photosystem II reaction centes, and possibly to increased photosynthetic unit size, compared with 5°C plants. These changes were associated with increased values (photosynthetic efficiencies) in 15°C-grownL. saccharina relative to 5°C-grown plants. The changes in together with reduced respiration rates allowed 15°C-grownL. saccharina to achieve net photosynthesis and light-saturated photosynthesis at a lower photon fluence rate (PFR) than 5°C plants when both groups were assayed at the same temperature (15°C). The photon fluence rates necessary to reach the compensation point and achieve light-saturated photosynthesis (I _c andI _k , respectively) increased with increasing incubation temperature inL. saccharina grown at both 5 and 15°C. However, acclimation responses to growth temperature compensated for the short-term effect of temperature onI _c andI _k . Consequently, plants grown at 5 and 15°C were able to achieve similar rates of light-limited photosynthesis, and similarI _c andI _k values at their respective growth temperatures. These responses are undoubtedly important for perennial seaweeds such asL. saccharina, which frequently grow in light-limited habitats and experience pronounced seasonal changes in water temperature.Please address all correspondence and requests for reprints to I.R. Davison     

Effects of salinity and possible interactions with temperature and pH on growth and photosynthesis of <Emphasis Type="Italic">Halophila johnsonii</Emphasis> Eiseman

The effects of salinity, temperature, and pH variations on growth, survival, and photosynthetic rates of the seagrass Halophila johnsonii Eiseman were examined. Growth and survival responses to salinity were characterized by aquarium experiments in which plants were exposed to seven different salinity treatments (0, 10, 20, 30, 40, 50, and 60 psu) during 15 days. Photosynthetic behavior was assessed for short-term salinity exposures (1 or 20 h) by incubation experiments in biological oxygen demand (BOD) bottles and by measuring photosynthesis versus irradiance (PI) responses in an oxygen electrode chamber. In the bottle experiments the possible effects of interactions between salinity and temperature (15, 25, and 35°C) or pH (5, 6, 7, and 8.2) were also examined. Growth and survival of H. johnsonii were significantly affected by salinity, with maximum rates obtained at 30 psu. Salinity also altered the parameters of the PI curves. Light-saturated photosynthesis (P _max) and the photosynthetic efficiency at subsaturating light (α) increased significantly up to an optimum of 40 psu, decreasing again at the highest salinities. Dark respiration rates and compensating irradiance (I _c) showed minimum values at 40 and 50 psu, while light-saturation point (I _k) was maximum at 30–50 psu. An interaction between salinity and temperature was not found although an increase of temperature alone produced an increase in α, P _max, respiration rates, and I _k. An interaction between salinity and pH was only found in the P _max response: P _max increased with pH=5 at 30 psu. In addition, reducing the pH increased α significantly. In the BOD bottles experiment a significant reduction in the dark respiration with decreasing pH was observed, but the opposite trend was observed in the photosynthetic rate. These results suggest that the endemic seagrass H. johnsonii could be negatively affected by hypo- or hypersalinity conditions, although salinity changes did not seem to alter the tolerance of this species to other environmental factors, such as temperature or pH.     

A note on the measurement of agglomeration economies with compensation for urban disamenities

The net agglomeration and disamenities approaches to the measurement of agglomeration economies are merged. The net agglomeration view is represented by a labor demand function derived from Segal (D. Segal, Rev. Econ. Stat. 48, 339–350 (1976)). The disamenities view is represented by an upward-sloping labor supply function derived from Izraeli (O. Izraeli, Urban Stud. 14, 275–290 (1977)). Three cases are simulated. Case I is the benchmark case and assumes a linear homogeneous production function, no agglomeration economies, and no perceived environmental quality differences between cities. Cases II and III combine Segal and Izraeli by introducing agglomeration economies, an upward-sloping labor supply function, and a change in the level of air pollution. The results demonstrate the feasibility of isolating the output of market goods and environmental goods within a common framework.     

Review and comparison of methods to study the contribution of variables in artificial neural network models

Convinced by the predictive quality of artificial neural network (ANN) models in ecology, we have turned our interests to their explanatory capacities. Seven methods which can give the relative contribution and/or the contribution profile of the input factors were compared: (i) the ‘PaD’ (for Partial Derivatives) method consists in a calculation of the partial derivatives of the output according to the input variables; (ii) the ‘Weights’ method is a computation using the connection weights; (iii) the ‘Perturb’ method corresponds to a perturbation of the input variables; (iv) the ‘Profile’ method is a successive variation of one input variable while the others are kept constant at a fixed value; (v) the ‘classical stepwise’ method is an observation of the change in the error value when an adding (forward) or an elimination (backward) step of the input variables is operated; (vi) ‘Improved stepwise a’ uses the same principle as the classical stepwise, but the elimination of the input occurs when the network is trained, the connection weights corresponding to the input variable studied is also eliminated; (vii) ‘Improved stepwise b’ involves the network being trained and fixed step by step, one input variable at its mean value to note the consequences on the error. The data tested in this study concerns the prediction of the density of brown trout spawning redds using habitat characteristics. The PaD method was found to be the most useful as it gave the most complete results, followed by the Profile method that gave the contribution profile of the input variables. The Perturb method allowed a good classification of the input parameters as well as the Weights method that has been simplified but these two methods lack stability. Next came the two improved stepwise methods (a and b) that both gave exactly the same result but the contributions were not sufficiently expressed. Finally, the classical stepwise methods gave the poorest results.     

Impact of cocoa agricultural intensification on bird diversity and community composition

To meet the growing demand for chocolate, cocoa (Theobroma cacao) agriculture is expanding and intensifying. Although this threatens tropical forests, cocoa sustainability initiatives largely overlook biodiversity conservation. To inform these initiatives, we analyzed how cocoa agriculture affects bird diversity at farm and landscape scales with a meta-analysis of 23 studies. We extracted 214 Hedges' g* comparisons of bird diversity and 14 comparisons of community similarity between a forest baseline and 4 farming systems that cover an intensification gradient in landscapes with high and low forest cover, and we summarized 119 correlations between cocoa farm features and bird diversity. Bird diversity declined sharply in low shade cocoa. Cocoa with >30% canopy cover from diverse trees retained bird diversity similar to nearby primary or mature secondary forest but held a different community of birds. Diversity of endemic species, frugivores, and insectivores (agriculture avoiders) declined, whereas diversity of habitat generalists, migrants, nectarivores, and granivores (agriculture associates) increased. As forest decreased on the landscape, the difference in bird community composition between forest and cocoa also decreased, indicating agriculture associates replaced agriculture avoiders in forest patches. Our results emphasize the need to conserve forested landscapes (land sparing) and invest in mixed-shade agroforestry (land sharing) because each strategy benefits a diverse and distinct biological community.     

Rate and extent of decomposition of dissolved organic matter in surface seawater

An experiment on the decomposition of the dissolved organic matter (DOM) in surface seawater was carried out under controlled laboratory conditions during a cruise of the R.V. Hakuho-Maru in the North-Equatorial Pacific (August/November, 1969). Surface seawater was placed in 300 ml oxygen bottles and incubated in the dark at 25°C. After selected time intervals, the dissolved organic-carbon (DOC) and the dissolved oxygen (DO) were determined for each bottle. The DOM in the surface seawater was described in terms of two labile fractions and a refractory one. The DOC decreased from 0.96 to 0.74 mgC/l during the first 50 days of incubation. Approximately 20% of the initial DOC (Fraction F_I) was oxidized. The other labile fraction, F_II was assumed to be 30 to 40% of the total DOM. The remaining half of the total DOM (Fraction F_III) is probably refractory and resistant to biochemical oxidation. The rate constant for decomposition was 0.0052 day^–1 for the total DOM and 0.033 day^–1 for F _I.     

Spatially distributed modeling of the long-term carbon balance of a boreal landscape

Spatially and temporally distributed information on the sizes of biomass carbon (C) pools (BCPs) and soil C pools (SCPs) is vital for improving our understanding of biosphere-atmosphere C fluxes. Because the sizes of C pools result from the integrated effects of primary production, age-effects, changes in climate, atmospheric CO₂ concentration, N deposition, and disturbances, a modeling scheme that interactively considers these processes is important. We used the InTEC model, driven by various spatio-temporal datasets to simulate the long-term C-balance in a boreal landscape in eastern Canada. Our results suggested that in this boreal landscape, mature coniferous stands had stabilized their productivity and fluctuated as a weak C-sink or C-source depending on the interannual variations in hydrometeorological factors. Disturbed deciduous stands were larger C-sinks (NEP₂₀₀₄ = 150 gC m⁻² yr⁻¹) than undisturbed coniferous stands (e.g. NEP₂₀₀₄ = 8 gC m⁻² yr⁻¹). Wetlands had lower NPP but showed temporally consistent C accumulation patterns. The simulated spatio-temporal patterns of BCPs and SCPs were unique and reflected the integrated effects of climate, plant growth and atmospheric chemistry besides the inherent properties of the C pool themselves. The simulated BCPs and SCPs generally compared well with the biometric estimates (BCPs: r = 0.86, SCPs: r = 0.84). The largest BCP biases were found in recently disturbed stands and the largest SCP biases were seen in locations where moss necro-masses were abundant. Reconstructing C pools and C fluxes in the ecosystem in such a spatio-temporal manner could help reduce the uncertainties in our understanding of terrestrial C-cycle.     

Light-dependency of nitrate uptake by phytoplankton over the spring bloom in Auke Bay,Alaska

The effect of light intensity on nitrate uptake by natural populations of phytoplankton was examined by ¹⁵N traceruptake experiments during the spring (March–May 1987) in Auke Bay, Alaska. The data were fit to a rectangular hyperbolic model which included a term for dark uptake. Three types of curves described nitrate uptake as a function of light intensity. The first (Type I) had a low half-saturation light intensity (K _I), low chlorophyll-specific uptakes rates, no dark uptake and occasional photoinhibition. These were observed during a period of biomass decrease, accompanied by low daily light and strong wind, prior to the major bloom. The second type (Type II) had relatively high K _I, high chlorophyll-specific uptake rates, and no dark uptake. Type II curves were observed during most of the period prior to nitrate depletion in the surface waters. Types I and II both appeared prior to nitrate depletion in the water and reflected variations in the light history of the phytoplankton population. The third type (Type III) occurred in nitrate-deplete conditions, when nitrate uptake was less dependent on light intensity (i.e., high rates of dark uptake and lower K _I). Decreased light-dependency during this period was coupled with physiological nitrogen deficiency in the population. Comparing these parameters to those of photosynthetic carbon fixation, K _Ivalues of nitrate uptake were generally higher than those of photosynthesis prior to nitrate depletion, and lower during nutrient-deplete conditions.     

A simulation model for the management of vicuña populations

The population dynamics of the vicuña was modelled based on field data from the Central Galeras Sector, Perú. Rains were simulated in order to obtain net primary productivity and grass availability which act upon density-dependent fecundity and mortality. The model produces a population growth curve that tends to stabilize at densities around 100 vicuñas per km². Harvest and shearing processes were simulated as part of the vicuña population management model. Harvest was based upon a fixed threshold density D_e below which no harvest occurs; for densities above D_e harvesting is applied at a rate proportional to the difference between D_e and the current population density (fixed escapement or ‘bang-bang’ harvest rule). Management optimization was analyzed by determining the optimal escapement density D_e, which maximized either net profits or the number of animals harvested. Analyzing the results as cumulative totals over 20 years of simulation, an optimum harvest production was obtained for a D_e of about 40 vicuñas per km², and maximum profit was obtained for a D_e around 70 vicuñas per km². Analyzing the results of 20 years of simulation as annual averages with an original population density of 40 vicuñas per km², the harvest production and profits were maximized for a D_e of 40 and 60 vicuñas per km², respectively.The model was validated using data from the Reserva Nacional San Guillermo, Argentina, where vicuña and guanaco populations coexist (although their interaction was not modelled). The sensitivity analysis was performed with three different techniques: (a) stepwise multiple linear regression, (b) visual graphic analysis based on a polar coordinates system, and (c) direct evaluation of the effect on management decisions. The curve shape parameters of the fecundity and mortality functions proved to be the most important ones in determining the outcome of the model.     

Aspects of iron and nitrogen nutrition in the red tide dinoflagellateGymnodinium sanguineum

Iron-stress-mediated effects on biochemical constituents of the red tide dinoflagellateGymnodinium sanguineum Hirasaka were examined in 1988 by comparing Fe-replete and Fe-deplete batch cultures. The influence of nitrogen source (NO₃ or NH₄) on characteristics of Fe-deplete cells was also studied [i.e., Fe-deplete/NO₃-grown (= — Fe/NO₃) vs Fe-deplete/NH₄-grown (= — Fe/NH₄)]. Common to both N sources were reductions of chlorophylla (chla) and Fe quotas (per cell volume) by 75% and ca. 1.5 orders of magnitude, respectively, under Fe depletion. The Fe requirement ofG. sanguineum exceeded those of certain neritic diatoms by one to two orders of magnitude. — Fe/NH₄ cells exhibited 30 to 50% greater N quotas and free amino acid:protein ratios than did Fe-deplete cells grown on NO₃. In vivo fluorescence:chla increased with Fe deficiency particularly in — Fe/NO₃ cultures, surpassing — Fe/NH₄ values by ca. two-fold. Effects of Fe depletion were consistent with this element's essential role in the biosynthesis of chla and components of the photosynthetic electron transport (PET) system, and also in NO₃ utilization. Fe:N ratios were larger (1.5-fold) for iron-deficient NO₃-grown than NH₄-grown cells, likely reflecting the Fe content of NO₃ assimilatory enzymes [nitrate (NR) and nitrite (NiR) reductase] and of electron transport components needed to provide reductant, coupled with a diminished capacity of — Fe/NO₃ cells to acquire and assimilate nitrogen. Indicators of PET efficiency suggested that under iron stress, supply of Fe for NR and NiR is partly at the expense of iron-containing PET components. Utilization of nitrate by NO₃-grown cells was inhibited sufficiently by Fe depletion to yield symptoms bordering on N deficiency. In an ecological context, the most important effect mediated by nitrogen source may be the determination of critical Q_Fe (i.e., Fe required to just sustain maximal growth), thereby regulating the degree of growth limitation for a given subsaturating iron concentration.     

Voltage-clamp measurements on single split lamellae of posterior gills of the shore crab Carcinus maenas

Single split lamella preparations of posterior gills of low-salt adapted shore crabs Carcinus maenas (collected from the Kiel Bay, Baltic Sea in 1991) were mounted in a micro Ussing-chamber. With NaCl salines on both sides we found an outside positive potential difference (PD) of 6.6±1.3 mV, a short-circuit current (I_sc) of-240±65 Acm^-2 and a resistance (R_t) of 25±3 cm² (n=8). Substitution of Cl^- (gluconate) on both sides of the preparation resulted in a decrease of I_sc by more than 90% at constant R_t. I_sc disappeared and R_t increased after substitution of Na⁺ (choline). When ouabain (2 mmol l^-1) was applied to the internal NaCl-saline, I_sc decreased and R_t remained unchanged. Internal addition of 0.1 mmol l^-1 acetazolamide left I_sc and R_t unaffected. Application of amiloride to the external NaCl saline resulted in a increase of both inward negative I_sc and R_t. The dose dependence of the diuretic showed a maximal effect between 50 and 200 mol l^-1 with a half-maximal blocker concentration (K_AMI) of ca. 10 mol l^-1. The results show that the split lamella preparation of posterior gills of C. maenas is a low resistance epithelium which is able to effect a massive, electrogenic and coupled absorption of Na⁺ and Cl^-.     

Energetic cost of development through metamorphosis for the seastar<Emphasis Type="Italic"> Mediaster aequalis</Emphasis> (Stimpson)

Rates of oxygen consumption were measured for embryos, larvae and juveniles of the seastar Mediaster aequalis for 76 days post-fertilization. The rate increased from 0.65 nmol O₂ ind^–1 h^–1 at 6 h after fertilization to 2.8 nmol O₂ ind^–1 h^–1 at day 35. Larvae became competent to metamorphose around day 35 post-fertilization and began to decrease their metabolic rate after this time. Metamorphosed juveniles consumed 0.74 nmol O₂ ind^–1 h^–1. Eggs contained 138.6 µg lipid ind^–1 and 12.1 µg protein ind^–1. Lipid levels decreased in concentration throughout development while protein levels increased slightly. The lipid levels decreased by 88.5 µg from eggs to day 76 larvae, accounting for 3.5 J of energy. Total oxygen consumption to this point was 3.74 µmol O₂ ind^–1, accounting for 1.84 J. The energetic demand up to day 76 was met completely through the use of lipid reserves. Metamorphosed juveniles expended 0.5 J more than larvae at the same age. Tubes of the polychaete Phyllochaetopterus prolifica were able to induce metamorphosis in M. aequalis larvae and a non-polar extract of these tubes also triggered metamorphosis. Larvae that are delayed to metamorphose can sustain their metabolic rate with lipid reserves for a limited, yet undetermined, period.Communicated by P.W. Sammarco, Chauvin     

A link between ecological diversity indices and measures of biodiversity

The practice of environmental planning and protection frequently necessitates the quantification of ecological diversity. Traditional ‘ecological diversity indices’ are based on the abundances of species present. However, such indices are insensitive to taxonomic or similar differences. With equal species abundances they measure the species richness (species number) only. Conversely, so-called ‘biodiversity indices’ are based on species differences, but are insensitive to the abundance conditions. The quadratic entropy index is the only ecological diversity index, the value of which reflects both the differences ‘and’ abundances of the species. When a species list is given without abundance data, then, using the quadratic entropy index and postulating equal abundances, one gets the only biodiversity index derived from a traditional ecological index of diversity. Its extensive form is identical with the sum of differences or distances between the species present. This index trivially satisfies set monotonicity, an important property for biodiversity indices.