Ocean acidification reduces biomineralization-related gene expression in the sea urchin, Hemicentrotus pulcherrimus

Although recent studies have demonstrated that calcification in a wide range of marine organisms is profoundly affected by CO₂-induced ocean acidification, the mechanism of this phenomenon is still unclear. To clarify the effects of ocean acidification on the calcification process at the molecular level, we evaluated the expression of three biomineralization-related genes in the sea urchin Hemicentrotus pulcherrimus exposed under control, 1,000, and 2,000?ppm CO₂ from egg to pluteus larval stage. We found that the expression of the gene msp130, which is proposed to transport Ca²⁺ to the calcification site, is suppressed by increased CO₂ at pluteus larval stage. Meanwhile, expression of the spicule protein matrix genes SM30 and SM50 was apparently not affected. The results suggest that the combined effects of ocean acidification on the expression of skeletogenesis-related genes as well as the change in seawater carbonate chemistry affect the biomineralization ability of sea urchins.     

Predicted impact of ocean acidification on a marine invertebrate: elevated CO<Subscript>2</Subscript> alters response to thermal stress in sea urchin larvae

Ocean acidification (OA) and the biological consequences of altered seawater chemistry have emerged as a significant environmental threat to healthy marine ecosystems. Because a more acidic ocean interferes with fixation of calcium carbonate to form shells or calcified skeletons, future ocean chemistry may significantly alter the physiology of calcifying marine organisms. These alterations may manifest themselves directly in the calcification process, or have synergistic effects with other environmental factors such as elevated temperatures. New tools permit us to explore subtle changes in gene expression patterns in response to environmental conditions. We raised sea urchins (Strongylocentrotus franciscanus) under conditions simulating future atmospheric CO₂ levels of 540 and 970 ppm. When larvae raised under elevated CO₂ conditions were subjected to 1-h acute temperature stress, their ability to mount a physiological response (as measured by expression of the molecular chaperone hsp70) was reduced relative to those raised under ambient CO₂ conditions. These results represent the first use of gene expression assays to study the effects of OA on sea urchin development. They highlight the importance of looking at multiple environmental factors simultaneously as this approach may reveal previously unsuspected biological impacts of atmospheric changes.     

Experimental determination of Cd2+ adsorption mechanism on low-cost biological waste

Carbonate shells have an astonishing ability in the removal of Cd²⁺ in a short time period with emphasis on being a low cost adsorbent. In the present study, the sorption capacity of carbonate shells was studied for Cd²⁺ in batch experiments. The influence of different carbonate shell sizes and physico-chemical factors were evaluated and the results were analyzed for its correlation matrices by using Predictive Analytics Software (PASW). The mineralogy state of aqueous solution regarding the saturation index was simulated using PHREEQC to identify the Cd²⁺ uptake mechanism. The Cd uptake rates were calculated as well as Ca²⁺, HCO ₃ ^? concentration, pH, ambient humidity and temperature were measured. Cd²⁺ removal of 91.52% was achieved after 5 h adsorption. The adsorption efficiencies were significantly influenced by pH as they increased with the increase of pH from acidic solution (5.50±0.02) to slightly alkaline (7.60±0.05). In addition, the mineralogy state of aqueous solution calculated from PHREEQC confirmed that the increment of Ca²⁺ and HCO ₃ ^? concentrations in solution was attributed to the dissolution of carbonate shells. Moreover, the ion exchange adsorption mechanism of Cd²⁺ toward Ca²⁺ was identified as the process involved in Cd²⁺ uptake.     

Influence of some coral reef communities on the calcium carbonate budget of Tiahura reef (Moorea,French Polynesia)

The calcium carbonate budget of coral reefs is the result of the interaction of the processes of calcification and biological degradation, and is reflected in the chemical properties of the seawater overlying the reefs. A series of experiments at Moorea Island (French Polynesia) in 1988 monitored the diurnal and nocturnal variations in the chemical properties of seawater under field and laboratory conditions. Our results revealed that in the study area (Tiahura barrier reef flat), the calcium carbonate budget varied over space and time as a function of location in the water current. Two in-situ sites were investigated; one was situated 100 m from the algal crest of the barrier reef, the other 300 m further downstream. As a result of cumulative upstream events, the daily net calcification was ten times higher at the downstream (5.22 gm^-2 d^-1) than at the upstream (0.45 gm^-2 d^-1) site. The carbonate uptake by in situ Porites lobata in enclosures (8 kgm^-2 yr^-1) was ten times higher than the uptake by the whole community in the surrounding water (0.8 kgm^-2 yr^-1) and five times higher than that recorded for P. lobata in laboratory experiments (1.4 kgm^-2 yr^-1), where illumination levels were 10% of in situ levels. In laboratory experiments, the planktonic fraction of the seawater had no perceptible influence on the calcium carbonate budget. In the absence of bioeroders, living coral totally depleted the carbonate content of the seawater (3.7 gm^-2d^-1). Bioerosive organisms played an important role in restoring this calcium carbonate; e.g. sea urchins grazing on algal turf covering dead coral ingested CaCO₃ and released this as a carbonate powder (1.26 gm^-2d^-1); a form of carbonate which is extremely accessible to chemical dissolution.     

Acid-base status in the sea urchins Psammechinus miliaris and Echinus esculentus (Echinodermata: Echinoidea) during emersion

The acid-base status of two sea urchins, Psammechinus miliaris (Gmelin) and Echinus esculentus (L.) during experimental emersion has been investigated. Sea urchins were collected from the Firth of Clyde between August and September 1987. The carbon dioxide capacity of the coelomic fluid of P. miliaris was greater than that of E. esculentus, although both were low and only marginally greater than that of sea water. The pH of the coelonic fluid was also low (7.05 to 7.17) and was influenced mainly by the internal partial pressure of CO₂ (P_{CO 2}). Acid-base disturbance in the coelomic fluid of both species during emersion, although minimal, was more pronounced in E. esculentus than in P. miliaris and was due primarily to an increase in the internal P_{CO 2}, although there was an increase in the concentration of L-lactate in the coelomic fluid of E. esculentus. The coelomic fluid of both species was in a state of perfectly compensated respiratory acidosis. An increase in the concentration of divalent ions (Ca²⁺ and Mg²⁺) may be related to the dissolution of the test as a source of carbonate buffer.     

Water geochemistry and dissolution rates of the karst-dominated Houzhai River basin,China

ABSTRACT

Houzhai (Guizhou Province, Southwest China) is a typical karstification area, with dolomite and limestone constituting the major rock types. The aim of this study was to utilize major element mass-balance and multivariate statistical methods to analyze the chemical composition of water in the Houzhai River catchment area with regard to seasonal variations in ion content, dissolution reactions, and rates. Data demonstrated that the Houzhai's hydrochemical composition is dominated by calcium (Ca²⁺), magnesium (Mg²⁺), bicarbonate (HCO₃^?), and sulfate (SO₄^2?) which predominantly originated from chemical weathering of carbonate rocks like limestone and dolomite. Carbonate weathering contributes 83% of the dissolved Ca²⁺. Sulfuric acid also plays an important role in rock weathering. Our analysis identified three principal sources of hydrochemical variation in the study area, including dolomite dissolution, limestone dissolution, and anthropogenic activities. In addition, the identified two main hydrochemical facies were characterized by the predominance of Ca-Mg-HCO₃ and Ca-Mg-HCO₃-SO₄. In terms of temporal variation, all of the examined parameters showed strong inter-annual and seasonal variations of concentration distribution, except pH levels and potassium and sodium (K⁺+Na⁺). The dissolution rate of carbonate was estimated using the concentration of Ca²⁺ and discharge rate, which constitutes a simple, practical, and innovative method. Compared with other research methods, our strategy was found to be simple, feasible, readily adaptable, and less demanding of data inputs.     

Tough as a rock-boring urchin: adult Echinometra sp. EE from the Red Sea show high resistance to ocean acidification over long-term exposures

Ocean acidification, a process caused by the continuous rise of atmospheric CO₂ levels, is expected to have a profound impact on marine invertebrates. Findings of the numerous studies conducted in this field indicate high variability in species responses to future ocean conditions. This study aimed at understanding the effects of long-term exposure to elevated pCO₂ conditions on the performance of adult Echinometra sp. EE from the Gulf of Aqaba (Red Sea). During an 11-month incubation under high pCO₂ (1,433 μatm, pH_NBS 7.7) and control (435 μatm, pH_NBS 8.1) conditions, we examined the urchins’ somatic and gonadal growth, gametogenesis and skeletal microstructure. Somatic and gonadal growths were exhibited with no significant differences between the treatments. In addition, all urchins in the experiment completed a full reproductive cycle, typical of natural populations, with no detectable impact of increased pCO₂ on the timing, duration or progression of the cycle. Furthermore, scanning electron microscopy imaging of urchin tests and spines revealed no signs of the usual observed effects of acidosis, such as skeletal dissolution, widened stereom pores or non-smoothed structures. Our results, which yielded no significant impact of the high pCO₂ treatment on any of the examined processes in the urchins studied, suggest high resistance of adult Echinometra sp. EE to near future ocean acidification conditions. With respect to other findings in this area, the outcome of this study provides an example of the complicated and diverse responses of echinoids to the predicted environmental changes.     

Bioerosion in coral reef communities in southwest Puerto Rico by the sea urchin<Emphasis Type="Italic"> Echinometra viridis</Emphasis>

Bioerosion is one of the most important structuring forces in coral reef communities. The bioerosion impact of several species of fish, sponges and sea urchins have been estimated in the Caribbean; however, there is no information for one important species, the red sea urchin Echinometra viridis. This species can be found in high densities in many localities. In this study, bioerosion rates for E. viridis were estimated in two patch reefs off La Parguera, southwest Puerto Rico, using the population size-class distribution, average densities, and the CaCO ₃ content in fecal pellets produced over 24 h. Average densities of urchins along four depth intervals were estimated using 40-m transect lines and 1-m ² quadrats. Average size and size-structure distribution were estimated by measuring the diameter of 180–220 urchins haphazardly collected at each of the four depth intervals. The ignition–loss method was used to estimate the daily rate of bioerosion. Fecal pellets produced by the urchins over a 24 h period were collected in buckets, rinsed in fresh water, dried for 24 h at 70°C, and then burned in a furnace at 550°C, first to eliminate organics, and then at 1000°C until constant weight to determine the amount of calcium carbonate (CaCO ₃) in the fecal pellets. HCl (10%) was then added to the remainder of the sample to test for presence of CaCO ₃. Average individual CaCO ₃ bioerosion rates were estimated at 0.181±0.104 g day ^-1. Average densities (0.77–62.0 ind. m ^-2), size (2.01–2.44 cm) and average bioerosion rates (0.114–4.14 kg m ^-2 year ^-1) were significantly higher in shallow areas (1–3 m) in both reefs. Bioerosion rates were low compared to those reported for parrotfish, endolithic sponges and the black sea urchin D. antillarum, but they were higher than those reported for other small-sized sea urchins in the Caribbean and the Indo-Pacific.     

Geochemistry and quality of groundwater of the Yarmouk basin aquifer,north Jordan

Quality of groundwater in the Yarmouk basin, Jordan has been assessed through the study of hydrogeochemical characteristics and the water chemistry as it is considered the main source for drinking and agriculture activities in the region. The results of the relationship between Ca²⁺ + Mg²⁺ versus HCO₃^? + CO₃^2?, Ca²⁺ + Mg²⁺ versus total cations, Na⁺ + K⁺ versus total cations, Cl^? + SO₄^2? versus Na⁺ + K⁺, Na⁺ versus Cl^?, Na⁺ versus HCO₃^? + CO₃^2?, Na⁺ versus Ca²⁺, and Na⁺: Cl^? versus EC describe the mineral dissolution mechanism through the strong relationship between water with rocks in alkaline conditions with the release of Ca²⁺, Mg²⁺, Na⁺, K⁺, HCO₃^?, CO₃^2?, SO₄^2?, and F^? ions in the groundwater for enrichment. Furthermore, evaporation processes, groundwater depletion, and ion exchange contribute to the increased concentration of Na⁺ and Cl^? ions in groundwater. Anthropogenic sources are one of the main reasons for contamination of groundwater in the study area and for increasing the concentration of Mg²⁺, Na⁺, Cl^?, SO₄^2?, and NO₃^? ions. Results show the quality of groundwater in the study area is categorized as follows: HCO₃^? + CO₃^2? > Cl^? > SO₄^2? > NO₃^? > F^? and Na⁺ > Ca²⁺ > Mg²⁺ > K⁺. In conclusion, the results of TDS, TH, and chemical composition showed that 26% of the groundwater samples were unsuitable for drinking. About 28% of groundwater samples in the study area have a high concentration of Mg²⁺, Na⁺, and NO₃^? above the acceptable limit. Also, based on high SAR, 10% of the groundwater samples were not suitable for irrigation purposes.     

Assessment of sulfurous springs in the west of Iraq for balneotherapy,drinking, irrigation and aquaculture purposes

This research deals with the sulfurous spring waters flow along the course of the Euphrates River in western Iraq in the area extended between Haqlaniya and Hit within the Al-Anbar governorate. Eleven springs (3 in Haqlanya, 4 in Kubaysa and 4 in Hit) have been addressed for the purpose of water evaluation for balneology, drinking, irrigation and aquaculture (fish farming). In order to meet the objectives of this research, all springs were sampled and analyzed for the total dissolved solid, electrical conductivity, pH, temperature, major cations (Ca²⁺, Mg²⁺, Na⁺ and K⁺), major anions (SO₄ ^2?, Cl^?, HCO₃ ^? and CO₃ ^2?), minor anions (PO₄ ^3?and NO₃ ^?) as well as the trace elements that included Pb, Zn, Cd, Ni, Fe, Mn, Cu, Br, F, Ba, B, Sr, Al, As, Cr, Hg and Se. The International Standards of World Health Organization are used for assessing the water quality. The results revealed that the springs belong to the tepid springs of 27–30 °C and classified as hypothermal to the thermal springs. Lithochemistry and geochemical processes clearly affected the water chemistry. The hydrogeochemical processes are responsible for the element enrichment in water by the chemical dissolution of carbonate and gypsum and evaporation as well. The results of the study indicate the possibility of using spring water for therapeutic purposes, but not allowed for drinking and aquaculture (fish farming), except those free of H₂S gas. On the other hand, it can be used for irrigation with risk. However, soil type as well as proper selection of plants should be taken into consideration.     

Long-term and trans-life-cycle effects of exposure to ocean acidification in the green sea urchin Strongylocentrotus droebachiensis

Anthropogenic CO₂ emissions are acidifying the world’s oceans. A growing body of evidence demonstrates that ocean acidification can impact survival, growth, development and physiology of marine invertebrates. Here, we tested the impact of long-term (up to 16 months) and trans-life-cycle (adult, embryo/larvae and juvenile) exposure to elevated pCO₂ (1,200 μatm, compared to control 400 μatm) on the green sea urchin Strongylocentrotus droebachiensis. Female fecundity was decreased 4.5-fold when acclimated to elevated pCO₂ for 4 months during reproductive conditioning, while no difference was observed in females acclimated for 16 months. Moreover, adult pre-exposure for 4 months to elevated pCO₂ had a direct negative impact on subsequent larval settlement success. Five to nine times fewer offspring reached the juvenile stage in cultures using gametes collected from adults previously acclimated to high pCO₂ for 4 months. However, no difference in larval survival was observed when adults were pre-exposed for 16 months to elevated pCO₂. pCO₂ had no direct negative impact on juvenile survival except when both larvae and juveniles were raised in elevated pCO₂. These negative effects on settlement success and juvenile survival can be attributed to carry-over effects from adults to larvae and from larvae to juveniles. Our results support the contention that adult sea urchins can acclimate to moderately elevated pCO₂ in a matter of a few months and that carry-over effects can exacerbate the negative impact of ocean acidification on larvae and juveniles.     

The association of N2-fixing bacteria with sea urchins

Dinitrogen fixation associated with bacteria in the gastrointestinal tract of sea urchins appears to be a widespread phenomenon: sea urchins from the tropics (Diadema antillarum, Echinometra lacunter, Tripneustes ventricosus), the temperature zone (Strongylocentrotus droebachiensis) and the arctic (S. droebachiensis) exhibited nitrogenase activity (C₂H₂ reduction). Pronounced seasonal variation was found in nitrogenase activity of temperate sea urchins feeding on kelp (Laminaria spp.) and eelgrass (Zostera marina). The mean monthly nitrogenase activity was inversely correlated with the nitrogen content of the sea urchin's food, which varied up to fivefold over the course of a year. The highest rate of nitrogenase activity recorded for a temperate sea urchin during the 14 month sampling period was 11.6g N fixed g wet wt^-1 d^-1, with a yearly mean activity of 1.36 g N fixed g wet wt^-1 d^-1. Studies with ¹⁵N confirmed the C₂H₂ reduction results and showed incorporation of microbially-fixed nitrogen into S. droebachiensis demonstrating that N₂ fixation can be a source of N for the sea urchin. Laboratory experiments indicated that part of the sea urchin's (S. droebachiensis) normal gastrointestinal microflora is responsible for the observed nitrogenase activity.     

Dedication

Hydrochemical, multivariate statistical, and inverse geochemical modeling techniques were used to investigate the hydrochemical evolution within the Ain Azel aquifer, Algeria. Cluster analysis based on major ion contents defined 3 main chemical water types, reflecting different hydrochemical processes. The first group water, group 1, has low salinity (mean EC = 735 μS/cm). The second group waters are classified as Cl–HCO₃-alkaline earth type. The third group is made up of water samples, the cation composition of which is dominated by Ca and Mg with anion composition varying from dominantly Cl to dominantly HCO₃ plus SO₄. The varifactors obtained from R-mode FA indicate that the parameters responsible for groundwater quality variations are mainly related to the presence and dissolution of some carbonate, silicate, and evaporite minerals in the aquifer. Inverse geochemical modeling along groundwater flow paths indicates the dominant processes are the consumption of CO₂, the dissolution of dolomite, gypsum, and halite, along with the precipitation of calcite, Ca-montmorillonite, illite, kaolinite, and quartz.     

Effect of sunlight intensity and albinism on the covering response of the Caribbean sea urchin<Emphasis Type="Italic"> Tripneustes ventricosus</Emphasis>

At Discovery Bay, Jamaica, Tripneustes ventricosus lives in beds of the turtle grass Thalassia testudinum. Especially during daylight hours, it covers its aboral surface with fragments of this plant and other objects. Normally pigmented, wild-type sea urchins covered themselves significantly less with Thalassia when sunlight was experimentally decreased to 66% or 32% ambient intensity. Consistent with this result, naturally occurring sea urchins exhibited significantly less covering at a deep (3.5 m) site than at a shallow (1 m) site, where light intensities at the bottom were 619 and 946 mol s^–1 m^–2, respectively. The graded covering response to light intensity suggests that covering is a defense against damaging solar radiation. Albino sea urchins covered themselves significantly more with Thalassia than wild-type sea urchins in both full and 66% sunlight. In addition, at the shallow site where they accounted for about 4% of the population, they showed significantly greater covering than wild-type urchins. The greater covering response of albino sea urchins suggests a greater susceptibility to solar radiation.Communicated by P. W. Sammarco, Chauvin     

Reassessment of the Ocean-To-Atmosphere Flux of Carbon Monoxide

Abstract

Carbon monoxide (CO) in the surface sea waters is produced predominantly by photochemical processes, oxidized by micro-organisms and outgassed to the atmosphere. to assess carbon monoxide flux from the oceans to the atmosphere, the photochemical production and microbial oxidation of carbon monoxide in the oceanic mixed-layer was investigated during several oeanographic cruises and in the laboratory. the photoproduction rate of carbon monoxide was found to be well correlated to the concentration of dissolved organic carbon (DOC) in coastal and open ocean surface waters. Taking a global average carbon monoxide production rate of 10 ± 2 nmole litre^?1 (mg DOC hr)^?1 in the surface open ocean water, and 25 ± 7 nmole litre^?1 (mg DOC hr)^?1 in coastal sea water, at cloud-free summer solar noon, the photochemical production of carbon monoxide in the global oceans is estimated to be at a rate of 1200 ± 200 Tg CO y^?1. the microbial carbon monoxide turnover time in the mixed-layer was observed to range from hours in a coastal estuary to 16 days in the Pacific along 1057deg; W in dark incubations. Natural sunlight can largely inhibit the microbial consumption of carbon monoxide in surface water. On a global scale, microbial consumption is responsible for the loss of less than 10% of photochemical produced carbon monoxide in the surface ocean. Field measurements have shown that the net transport of carbon monoxide from the euphotic zone to the underlying deeper ocean water is limited and that the overall life time in surface sea waters is less than 3-4 hours. When combined, these field measurements with the photoproduction and microbial consumption rates obtained, we estimate the oceanic flux to the atmosphere is about 1000 ± 200 Tg CO y^?1, which represents the largest single source of atmospheric carbon monoxide.     

海洋酸化对鱼类感觉和行为影响的研究进展

海洋酸化是指大气增多的二氧化碳(CO2)溶解于海水而导致海水p H值降低的过程。海洋酸化将改变海水碳酸盐平衡体系,使依赖于原化学环境的多种海洋生物乃至生态系统面临巨大威胁。海洋酸化对钙质生物影响的研究最早引起大家关注,而海洋鱼类具有较完善的酸碱调节机制,大家普遍认为酸化对其影响不大。但在过去的5年中,不少实验证明海洋酸化会影响海洋鱼类仔稚鱼的感觉和行为,减弱其野外的生存能力及增加被捕食率,很可能将威胁自然种群补给量和影响全球的渔业资源量。本文从嗅觉、听觉、视觉及高级意识和相关行为角度,综述近几年海洋酸化对鱼类感觉和行为影响的研究进展,介绍了鱼类神经行为生物学的研究,为全面了解和预测海洋酸化的生态、经济和社会效应提供科学依据。     

Growth and mortality of subtidal red sea urchins (Strongylocentrotus franciscanus) at San Nicolas Island,California, USA: problems with models

Red sea urchins, Strongylocentrotus franciscanus, were tagged with tetracycline in 1990 at subtidal sites off San Nicolas Island, California, USA. After one year in the field, the sea urchins were collected and growth increments were measured based on tetracycline marks, which indicated initial slow growth, a maximum rate, and finally a prolonged period of very slow growth. Small red sea urchins (4 cm diam) were estimated to be 3 to 4 yr old, which is much older than has previously been reported. It is estimated that about 12 yr would be required to attain 10 cm diam. Survival has previously been modeled assuming a constant rate. If the population of red sea urchins is assumed to be stable and stationary, annual survival rate was between 71 and 77% yr^-1. Census data for the two years of study have permitted annual survival to be estimated without assuming stable and stationary population structure. Under these conditions, annual survival rate was between 79 and 86% yr^-1. Analysis of transitions in the size distributions from 1990 to 1991 suggested that annual survival may have been sizespecific: 91% yr^-1 for individuals 1.1 to 4.0 cm diam, 82% yr^-1 for individuals 4.1 to 7.0 cm diam, and 63% yr^-1 for those of 7.1 to 10.0 cm diam. An alternative explanation to size-specific survival in our study is sizespecific immigration.     

Assessment of the chemical components of Famenin groundwater,western Iran

The Faminin area in the semi-arid Hamadan state, western Iran is facing a serious deficiency in groundwater resources due to an increasing demand associated with rapid population growth and agricultural development. The chemical composition of 78 well samples throughout the Faminin area was determined with the aim of evaluating the concentration of the background ions and identifying the major hydrogeochemical processes that control the groundwater chemistry. The similarity between rock and groundwater chemistries in the recharge area indicates a significant rock-water interaction. The hydrochemical types Na–HCO₃ and Na–SO₄ are the predominate forms in the groundwater, followed by water types Ca–HCO₃ and Na–Cl. The high values of electrical conductivity and high concentrations of Na⁺, Cl⁻, SO₄²⁻ and NO₃⁻ in the groundwater appeared to be caused by the dissolution of mineral phases and would appeared to be caused by anthropogenic activities, such as intense agricultural practices (application of fertilizers, irrigation practice), urban and industrial waste discharge, among others.     

Rate of dissolution of diatom silica walls in seawater

The solubility and dissolution rate of silica were investigated using cell walls prepared from two species of diatoms, Thalassiosira decipiens and Rhizosolenia hebetata forma semispina. The solubility (C _e) as a function of temperature (T, °C) can be described by the following equation: C _e (SiO₂ mg l^-1)=67.8+1.48 T. The first-order reaction equation without the surface-area term was considered to be reasonable in estimating the dissolution rate of biogenic silica in the ocean system. The rate of dissolution differed not only from one species to another but also from one portion to another portion of the same wall. The rate constants of dissolution in the ocean system were estimated to range in the order of from 10^-1 to 10^-9 per hour.     

Reproductive dynamics of the sea urchin Paracentrotus lividus on the Galicia coast (NW Spain): effects of habitat and population density

We studied the spatial variability in the size at first maturity and the reproductive cycle of Paracentrotus lividus in Galicia, contributing key information for the exploitation and management of this resource. The size at maturity varied between 20.4 (±1.2 SE) mm and 27.9 ± 1.2 mm and was smaller in areas of low population density where sea urchins do not form patches. Using a nonlinear model, we analysed the effect of depth, body size, sex and population density on the temporal pattern of the gonad index. The maximum and minimum indices were obtained at 4 m depth in the months before and after the spring spawning, respectively. The depth also affected the cycle phase, and the sea urchins at 4 m depth spawned 9.4 ± 3.0 days later than the sea urchins at 8 m depth and 20.5 ± 3.0 days later than those at 12 m depth. Moreover, the sea urchins living in patches showed a slight increase in gonad size as a consequence of the better-quality habitat. This shows that there is no intraspecific competition in this area despite the high population densities reached (18.5 kg m^?2).