Ecology of Echinometra mathaei (Echinoidea: Echinodermata) at Diani Beach,Kenya

Studies were carried out on the inner and outer coral reefs at Diani Beach on the Kenya coast to assess the distribution, density and behaviour of Echinometra mathaei (de Blainville). Transects 1 m wide were run on the two reefs in April, June and September, 1970. Test measurements on representative samples from the animal populations on both reefs were also taken. Direct observations on specimens of E. mathaci in selected rock pools on the outer reef were made to determine their movement, gregariousness, homing and feeding behaviour. Population density was higher on the inner reef furthest from the sea at low tide than on the outer reef. On the submerged inner coral reef at low tide, E. mathaei occurred mainly exposed on the seaweeds, but, on the exposed outer reef, its main niches were crevices in rock pools and under coral ledges. Sizefrequency distributions revealed that smaller individuals occurred on the inner reef and larger ones on the outer reef. The growth rate of E. mathaei was estimated from the positions of modal values, calculated from size-frequency distributions. No gregarious or homing behaviour was observed and, once settled in a suitable crevice, E. mathaei showed little movement.     

Growth and production of Sterechinus neumayeri (Echinoidea: Echinodermata) in McMurdo Sound,Antarctica

Population dynamics of Sterechinus neumayeri were investigated at four sites in McMurdo Sound: Cape Evans, McMurdo Station, East Cape Armitage and New Harbor. The annual formation of natural growth bands in the jaws of the Aristotle's lantern was verified by a tagging-recapture experiment. Growth functions based on natural growth bands indicated differences among stations but showed S. neumayeri to be a slow growing species, reaching its maximum diameter of 70 mm at an age of about 40 yr. Annual production ranged between 2.4 (C. Evans) and 0.65 g ash free dry mass m^-2 (New Harbor) and was related to differences in food conditions. More than 95% of total production was invested in reproduction, and less than 5% was invested in somatic growth. Consumption estimates for S. neumayeri showed this species to play a significant role in the benthic trophic web of McMurdo Sound.     

Growth pattern of the sea urchin, Loxechinus albus (Molina, 1782) in southern Chile: evaluation of growth models

The growth pattern of Loxechinus albus in southern Chile was studied using size-at-age data obtained by reading growth bands on the genital plates. The scatter plots of sizes-at-age for samples collected in three different locations indicated that growth is linear between ages 2 and 10. Five different growth models, including linear, asymptotic and non-asymptotic functions, were fitted to the data, and model selection was conducted based on the Akaike information criteria (AIC) and the Bayesian information criteria (BIC). The AIC identified the Tanaka model as the most suitable for two of the three sites. However, the BIC led to the selection of the linear model for all zones. Our results show that the growth pattern of L. albus is different from the predominantly asymptotic pattern that has been reported for other sea urchin species.     

Growth and spatial distribution of Cassidulus mitis (Echinodermata: Echinoidea) on a sandy beach in Southeastern Brazil

Using a hand dredge, a population of Cassidulus mitis Krau, 1954 was sampled monthly from February 1986 to January 1987 at 15 stations offshore from Vermelha Beach (22°5718 S; 43°948 W), in water depths ranging from 0 to 6 m. The sex ratio indicated a slight numerical dominance of females for adults and a larger numerical female dominance for juveniles. A von Bertalanffy growth curve was estimated as L=71.00 (1-e^(-0.390t)), where L=length (mm) and t=time (yr). The instantaneous natural mortality rate (M) was estimated as 0.812. The population occupies a zone parallel to the beach, and displays a spatially aggregated pattern, with higher densities in areas characterized by coarse and very well sorted sand containing low amounts of organic matter.     

Mass mortality of Strongylocentrotus droebachiensis (Echinodermata: Echinoidea) off Nova Scotia,Canada

A mass mortality of Strongylocentrotus droebachiensis, attributed to disease, was monitored in an echinoiddominated barren ground at Eagle Head on the south-western coast of Nova Scotia, Canada, in 1982. Mortality was 70% in a shallow (3 m) nearshore area, resulting in a loss of echinoid biomass of 2 042 g fresh weight m^-2, and 6% in deeper (7 m, 10 m) offshore areas. Echinoid density, size and nutritional condition (gonad index) were highest in the nearshore area. Survivorship was higher in juveniles (<15 mm diameter) than in adults resulting in the formation of a bimodal size distribution in the nearshore area. Mortality began around early October, near the peak of the annual cycle of seawater temperature (15°C), and was arrested by early December (seawater temperature 7°C) when morbid echinoids appeared to recover. In laboratory experiments, time to morbidity of S. droebachiensis exposed to morbid conspecifics increased exponentially with decreasing temperature (20° to 8°C). There was no survival at 20° and 16°C, 20% survival at 12°C and 100% survival at 8°C after 60 d; suggesting a lower temperature limit (between 12° and 8°C) for possible transmission of a pathogenic agent. Morbid laboratory echinoids from experiments at 16°C, and recovering echinoids collected in the nearshore area in early December, showed 100 and 85% survival respectively at <=8°C, and 0 and 15% survival respectively at 16°C, after 30 d. Time to morbidity was not affected significantly by nutritional condition and was similar for juvenile and adult echinoids. Time to morbidity was greater in echinoids exposed to one or three morbid individuals continuously, or seven morbid individuals for 1 h, relative to higher levels of exposure (up to seven morbid individuals continuously). Recent mass mortalities in S. droebachiensis have occurred in years of record high sea surface temperatures. The extent of mortality is correlated with the magnitude and duration of temperatures above a lower limit.     

Electron microscope study of the digestive system of Strongylocentrotus droebachiensis (Echinodermata: Echinoidea)

The fine structure of esophagus, stomach and intestinal epithelial cells of the sea urchin Strongylocentrotus droebachiensis have been examined. Three types of mucosal cells secreting neutral, acid and sulfated mucopolysaccharides have been found in the esophagus. The modes of origin of different types of mucous granules are described. Storage and zymogen cells have been identified in the stomach epithelium. Storage cells are adapted for intracellular digestion and synthesis of nutritive substance. Zymogen cells are adapted for enzyme synthesis. The columnar cells occur in the intestinal epithelium; they are adapted for nutrient absorption and lipid storage. Digestion in different parts of the digestive tract is considered in context with the ultrastructural and histochemical data obtained. Some problems concerning the relation between intracellular and extracellular digestion are discussed.     

Response of sea urchin pluteus larvae (Echinodermata: Echinoidea) to reduced seawater pH: a comparison among a tropical, temperate, and a polar species

Ocean acidification, as a result of increased atmospheric CO₂, is predicted to lower the pH of seawater to between pH 7.6 and 7.8 over the next 100 years. The greatest changes are expected in polar waters. Our research aimed to examine how echinoid larvae are affected by lower pH, and if effects are more pronounced in polar species. We examined the effects of lowered pH on larvae from tropical (Tripneustes gratilla), temperate (Pseudechinus huttoni, Evechinus chloroticus), and a polar species (Sterechinus neumayeri) in a series of laboratory experiments. Larvae were reared in a range of lower pH seawater (pH 6.0, 6.5, 7.0, 7.5, 7.7, 7.8 and ambient), adjusted by bubbling CO₂ gas. The effect of pH on somatic and skeletal growth, calcification index, development and survival were quantified, while SEM examination of the larval skeleton provided information on the effects of seawater pH on the fine-scale skeletal morphology. Lowering pH resulted in a decrease in survival in all species, but only below pH 7.0. The size of larvae were reduced at lowered pH, but the external morphology (shape) was unaffected. Calcification of the larval skeleton was significantly reduced (13.8–36.9% lower) under lowered pH, with the exception of the Antarctic species, which showed no significant difference. SEM examination revealed a degradation of the larval skeletons of Pseudechinus and Evechinus when grown in reduced pH. Sterechinus and Tripneustes showed no apparent difference in the skeletal fine structure under lowered pH. The study confirms the need to look beyond mortality as a single endpoint when considering the effects of ocean acidification that may occur through the 21st century, and instead, look for a suite of more subtle changes, which may indirectly affect the functioning of larval stages.     

Effects of high temperature on larval development and metamorphosis of Arachnoides placenta (Echinodermata: Echinoidea)

Adults of the sea urchin Arachnoides placenta (L.) were induced to spawn, and eggs were fertilized at 28°C in September 1989. After 5 min, eggs were transferred to 28, 31, 34, or 37°C and reared to metamorphosis. Embryos were observed at 20-min intervals during the first 2 h; larvae were observed daily. The cleavage was higher at higher temperatures. Embryos reared at 28°C were still at the 4th cleavage (16-cell stage) after 100 min, while those at 34°C had reached the 5th cleavage (32-cell stage). All embryos reared at 37°C died on the second day. Incidence of abnormality was 20 to 30% at 28 and 31°C, 48% at 34°C, and 77% at 37°C. The 8-arm stage was reached after 4 d at 28°C, 3 d at 31°C and 2 d at 34°C. Larvae displayed decreasing body length and arm length with increasing temperature. Larvae at 31°C have relatively long arms, as a result of a decrease in body length, not because of increased arm length. Incidence of metamorphosis was 43.9±1.7% (mean/plusmn;SD) at 28°C, 24.5±1.9% at 31°C, and 5.3% at 34°C. The size of metamorphosed juveniles was significantly larger at 28°C than at 31 and 34°C. Temperatures of 31°C negatively affect larvae and juveniles of the sand dollar.     

Population dynamics of Diadema antillarum (Echinodermata: Echinoidea) following mass mortality in Panamá

In 1983, Diadema antillarum suffered mass mortality throughout the Caribbean Sea and the western Atlantic Ocean. I followed the dynamics of populations at the San Blas Islands, Panamá from April 1983 to November 1987. Density measurements indicate that populations of D. antillarum have not recovered from the die-offs that killed nearly 97% of the individuals. There was recruitment to the 1 to 1.5 cm class immediately after the mass mortality, but there has been little additional influx of juveniles since then. The low number of observable juveniles could not be attributed to elevated rates of predation on very small individuals. Rates of recruitment did not differ between reefs with artificially increased densities of D. antillarum and reefs kept free of sea urchins; thus, the lack of recruitment did not arise from absence of adults that could provide settlement cues to the larvae or protection to newly settled juveniles. Other species of sea urchins did not show a clear pattern of increase after the demise of D. antillarum. Therefore, interspecific competition directed towards D. antillarum juveniles did not increase after the mass mortality. Two reefs where Echinometra viridis, Eucidaris tribuloides and Lytechinus williamsi, were removed showed no significant differences in recruitment of D. antillarum relative to two reefs where these species were allowed to remain at their natural densities. Resident D. antillarum after the mass mortality produced gametes with the same per capita intensity and lunar synchrony as before the mass mortality. However, it is possible that the probability of fertilization of their gametes decreased because of low population density. The most likely explanation for lack of recruitment is that the reduced numbers of reproducing adults at Panamá and upstream locations resulted in levels of larval supply that were inadequate to sustain recruitment on Panamanian reefs.     

Responses of ovaries and testes of Lytechinus variegatus (Echinodermata: Echinoidea) to dietary administration of estradiol, progesterone and testosterone

 In many vertebrates, environmental factors influence gamete differentiation and growth of the mature gonad through alteration of sex steroid production or action; however, it is unclear how gamete differentiation and gonadal growth are regulated in echinoids. The purpose of this study was to examine the influence of dietary administration of estradiol (E2), progesterone (P4), testosterone (T) and finasteride (F, a 5α-reductase inhibitor) on the ovaries and testes of mature Lytechinus variegatus (Lamarck) during gonadal growth. Echinoids were fed a formulated diet supplemented with steroids or steroids in combination with finasteride for 36 d. The effects of dietary administration of steroids on L. variegatus were both steroid- and sex-specific. The mean ovary index was 54% greater in individuals fed E2 than from individuals fed the control (C) diet (10.0 ± 1.1 vs 6.5 ± 0.7, respectively; P < 0.05). Individuals fed E2, P4, E2/P4, and P4 in combination with F had significantly smaller oocytes (P < 0.005) than individuals fed C. The volume fraction occupied by nutritive phagocytes in ovarian tubules from individuals fed E2/P4 or P4 were significantly larger than the volume fraction occupied by nutritive phagocytes from individuals fed C, indicating that E2 and 5α-reduced progestins may promote nutrient allocation to nutritive phagocytes. Although oocytes from the individuals fed T alone were significantly smaller than those fed T in combination with F, oocytes from individuals in both treatments were significantly larger compared to oocytes from individuals fed C. These data suggest that upon removal of 5α-reduced androgens, T is able to promote an increase in oocyte diameters. In contrast, the mean testis index was 56% greater in individuals fed P4 than in individuals fed C (8.9 ± 0.6 vs 5.7 ± 0.9, respectively; P < 0.05); the testis index did not increase in individuals fed P4/F, suggesting that 5α-reduced progestins stimulate testicular growth. Testes growth in the presence of 5α-reduced progestins was accomplished by significant increases in the volume fraction occupied by nutritive phagocytes and by a significant reduction in the volume fraction occupied by spermatogenic columns in testicular tubules. These data further indicate that 5α-reduced progestins (or 5α-reduced androgens) may inhibit spermatogenic column formation. In conclusion, E2 stimulated ovarian growth but inhibited oocyte growth, whereas T had no affect on ovarian growth but promoted oocyte growth in L. variegatus. We hypothesize that the E2 (or E2 metabolites) and/or 5α-reduced androgens in combination with T regulate oocyte growth in the echinoid L. variegatus. In addition, 5α-reduced progestins promoted nutrient accumulation in nutritive phagocytes within the ovaries and the testes. Furthermore, 5α-reduced progestins stimulated growth of the testes and inhibited spermatogenic column formation, suggesting that 5α-reduced progestins regulate nutrient accumulation into nutritive phagocytes and spermatogenic column formation in L. variegatus. The differences in estrogen effects between echinoids and asteroids may be related to differences in gonad morphology and, ultimately, the differences in cellular signalling pathways (paracrine vs endocrine). Received: 22 May 1999 / Accepted: 24 May 2000     

Mass spawning by the sea urchin Evechinus chloroticus (Echinodermata: Echinoidea) in a New Zealand fiord

A mass synchronous spawning of the sea urchin Evechinus chloroticus (Valenciennes) was observed in situ in Doubtful Sound, a large New Zealand fiord. Spawning occurred between 17:30 hrs and 18:30 hrs on 27 January 1994 and coincided with a full moon, spring tides and a period of decreasing sea temperatures. During spawning, the sea urchins formed a dense spawning aggregation of both sexes, with >90% of the urchins observed spawning at the time. Spawned gametes clouded the water column, and some were eaten by small labrid fish species. The spawning, which may have been as widespread as 40 km, marked a 42 to 50% decrease in gonad indices and resulted in a widespread, dense cohort of  E. chloroticus larvae within the fiord. Received: 25 September 1997 / Accepted: 6 March 1998     

The effect of depth on the reproductive cycle ofBrissopsis lyrifera (Echinoidea,Echinodermata) in the Gulf of Lions,Mediterranean Sea

A sample of 227Brissopsis lyrifera were collected in the Gulf of Lions in the Mediterranean Sea between 60 and 1000 m depth over a 21/2-yr period (June 1983 to November 1985). Males and females were sexually mature at the end of summer. After a period of gonadal inactivity during winter, gametogenesis resumed at the beginning of spiring. The cycle was synchronous over the entire bathymetric range studied. Variations in environmental conditions may be one factor inducing gametogenesis.     

Effects of temperature and salinity acclimation of adults on larval survival,physiology, and early development of Lytechinus variegatus (Echinodermata: Echinoidea)

Larval survival and developmental rates of Lytechinus variegatus (Lamarck) were determined as a function of temperature and salinity in two experiments by: (1) directly transferring fertilized eggs to 35, 30, 27.5, 25, 20, 15, and 10S seawater at 18 and 23°C, and (2) acclimation of adult sea urchins to the conditions described above for 1 to 4 wk prior to spawning. Developmental rates and percent survival of larvae prior to metamorphosis decreased at salinities below 35 (Q₁₀ values for metamorphosis=0.380 to 0.384). Temperature and salinity significantly (P<0.05) affected metabolic rates of L. variegatus plutei. These results show that L. variegatus larvae are stenohaline when compared to larvae of other echinoderm species. LC₅₀ values (S), developmental rates, and survival to metamorphosis indicate that acclimation of adult sea urchins to lower salinity prior to spawing and fertilization does not enhance development or survival of embryos exposed to low salinity.     

Reproduction of the commercial sea cucumber Holothuria scabra (Echinodermata: Holothuroidea) in the Solomon Islands

Over a 3-year period (1996-1998), reproduction of the commercial sea cucumber Holothuria scabra (Jaeger, 1833) was investigated in the Solomon Islands to determine the spawning pattern and whether gametogenesis is continuous or seasonal. The gonad consisted of a single cohort of tubules that developed uniformly. Macroscopic examination of the gonads revealed that mature gametes were present throughout the year. Individuals with gonads at different stages of maturity were present in most samples. Partly spawned gonads were prevalent in females, whereas mature gonads were prevalent in males. The time at which the peak gonad index was recorded differed among years. Although gametogenesis was continuous, with a potential for prolonged gamete release, a period of enhanced spawning occurred during the dry season, from September to December. Maximum gonad indices were reached prior to and during this period of enhanced spawning. Histology revealed that gametogenesis reinitiated in partly spawned gonads, resulting in the presence of gametes at different stages of development in the gonad. The uniform growth of gonad tubules indicated that H. scabra does not conform to the progressive tubule recruitment model described for holothurian oogenesis. Continuous reproduction in H. scabra and prolonged availability of mature gametes would facilitate use of this species for aquaculture.     

Patterns of abundance, population size structure and microhabitat usage of Paracentrotus lividus (Echinodermata: Echinoidea) in SW Portugal and NW Italy

In coastal habitats, wave exposure influences several aspects of the life history of marine organisms. Here, we assess how hydrodynamic conditions can generate variation in density, size structure and microhabitat usage of Paracentrotus lividus and whether these effects are consistent between regions that are markedly different for oceanic climate, such as the coasts of SW Portugal and NW Italy. The abundance of P. lividus was ~4 times higher in SW Portugal than in NW Italy, but within each region, there was no effect of wave exposure. In SW Portugal, higher urchin abundances were found at shallower depths, while no effect of depth on urchin abundance emerged in NW Italy. Most of the variation in urchin abundance occurred at small spatial scales (metres), and our results suggest that habitat complexity, that is, the presence of cracks and crevices, is an important determinant of patterns of distribution of this species. The population in NW Italy was characterized by a unimodal size distribution, with a higher proportion of medium-sized individuals. In contrast, in SW Portugal, smaller individuals represented a large proportion of the populations. Size structure varied between exposed and sheltered habitats in SW Portugal, suggesting that the proportion of individuals from different size cohorts may vary along wave-exposure gradients as a result of direct or indirect effects of hydrodynamic forces. In SW Portugal, most urchins occurred in burrows, while in NW Italy, urchins were mainly observed in crevices. These results suggest that creating/occupying burrows might be an adaptive behaviour that allows sea urchins to better withstand stressful hydrodynamic conditions and, therefore, are more common on exposed Atlantic coasts. Overall, our study suggests that the effects of hydrodynamic forces on sea urchin populations are context dependent and vary according to background oceanic climate.     

Reef coral reproduction in the eastern Pacific: Costa Rica,Panama, and Galapagos Islands (Ecuador)

Reproductive ecology of two major reef-building corals in the eastern Pacific [Pocillopora damicornis (Linnaeus) andPocillopora elegans Dana] was investigated between 1984 and 1990 in Costa Rica, Panama (Gulf of Chiriqui and Gulf of Panama), and the Galapagos Islands (Ecuador) following the 1982–83 El Niño disturbance. Mature spermatocytes and oocytes were found in both species and were usually present in the same polyp in nearly equal ratios. Numerous zooxanthellae were observed in mature, unfertilized oocytes. Although spawning in field populations was not observed, it is likely that both pocilloporids are simultaneous hermaphroditic spawners, as evidenced by the disappearance of mature gametes after full moon. This is in contrast with most known pocilloporid corals that brood and release planula larvae. Corals were reproductively most active in the thermally stable environments of Costa Rica and the Gulf of Chiriqui (Panama) where 32 to 90% of all colonies contained gametes. In the moderately varying thermal conditions in the Galapagos Islands, 16 to 40% of colonies contained gametes, and in the pronounced seasonal upwelling environment of the Pearl Islands (Panama) only 6 to 18% of colonies contained gametes. Year-round reproduction occurred in Costa Rica and the Gulf of Chiriqui, whereas reproduction was confined to warm periods in the seasonally varying environments of the Galapagos Islands and the Gulf of Panama. Pocilloporid corals in Costa Rica and the Gulf of Chiriqui demonstrated lunar spawning activity, with mature gametes present a few days before and after full moon. Some limited spawning may have occurred also at new moon. While frequent gamete maturation has been demonstrated in this study, the relatively low rates of larval recruitment occurring on eastern Pacific coral reefs disturbed by the 1982–83 El Niño suggest that the recovery of important frame-building corals could be greatly prolonged.     

Diet of four species of deep-sea isopods (Crustacea: Malacostraca: Peracarida) in the South Atlantic and the Southern Ocean

The food of four species of asellote isopods (Crustacea, Malacostraca), Haploniscus rostratus, Haploniscus unicornis, Acanthocope galatheae and Betamorpha fusiformis, was evaluated by analysis of their gut contents. The isopods were sampled at several stations on the abyssal plains of Guinea Basin, Angola Basin and Cape Basin (southeast Atlantic), the Weddell Sea abyssal plain and the Antarctic continental slope during the DIVA and ANDEEP expeditions in 2000, 2001 and 2005. While all species had mineral particles in their guts and mucus material was the most frequent food item, the remaining gut contents differed among species. Betamorpha fusiformis fed mostly on phytodetritus, especially in the Southern Ocean basins and ingested along with it whole calcareous foraminifers. Acanthocope galatheae showed some differences in gut contents between basins, but in the Guinea Basin, the contents were to a large extent stercomata, i.e., waste pellets of soft-walled foraminifers, i.e., the Komokiaceae. Indications were that the haploniscids were feeding on detritus and agglutinating foraminifers (stercomata). This indicates spatial differences in food availability for this diverse group of deep-sea isopods and the importance of poorly known foraminiferal groups, like the Komokiaceae, as a food source in the deep sea.     

Population genetics and systematics of theLeptasterias hexactis (Echinodermata: Asteroidea) species complex

Morphological characters and 14 enzyme loci were examined for 1 040 sea stars, currently recognized as forms ofLeptasterias hexactis, from Lynn Canal, Alaska, and Puget Sound, Washington, USA, between March 1988 and April 1989. Three morphologically and two genetically distinctLeptasterias forms were identified. The most common form found at both localities wasL. epichlora (Brandt)sensu Verrill.L. hexactis (Stimpson)sensu Verrill co-occurred withL. epichlora at all study sites and apparently hybridizes extensively withL. epichlora in the Puget Sound region, but rarely, if at all, in Alaska. The presumptive product of this hybridization morphologically resembledL. aequalis (Stimpson)sensu Fisher, and was conspicuously absent from Alaskan samples. Considerable genetic distance existed betweenL. epichlora andL. hexactis (Nei'sD=0.19±0.01) and moderate genetic differentiation occurred between populations of each species from Alaska and Washington (Weir and Cockerham'sF _RT =0.29±0.04 forL. epichlora and 0.21±0.15 forL. hexactis). A significant (p<0.05) deficiency in the proportion of heterozygous individuals was found compared to Hardy-Weinberg expectations (Wright's fixation index,F _ID=0.12±0.04 and 0.31±0.08 forL. epichlora andL. hexactis, respectively). However, mean observed heterozygosity for each species (0.09±0.03, 0.14±0.04 and 0.14±0.04 forL. epichlora, L. hexactis andL. aequalis, respectively) fell within the range of reported values for other asteroid species (ca. 0.04 to 0.37). The results of this study indicate that considerable genetic integrity is maintained betweenL. epichlora andL. hexactis, which warrants their recognition as distinct species despite their apparent hybridization in the Puget Sound region.     

Life-history biology of Peniagone azorica and P. diaphana (Echinodermata: Holothurioidea) from the north-east Atlantic Ocean

Aspects of the reproduction and population biology of two elasipodid holothurians collected during the period 1973–1984 from the north-east Atlantic Ocean were examined. The reproductive biology of both the benthic species Peniagone azorica and the benthopelagic P. diaphana are similar. A primary oocyte forms from an oogonium and grows to about 100m diameter, whereupon it undergoes vitellogenesis and increases to 300m before being spawned. A high proportion of primary oocytes are not spawned and undergo a complicated breakdown process resulting in the formation of an amorphous sac in the ovary wall. It is possible that when an ovarian tubule is full of these sacs it atrophies and drops off, allowing other tubules to develop. The maximum egg size for both species suggests abbreviated larval development. In P. azorica, juveniles reach sexual maturity for the first time at about 30 mm length. The population structure suggests that the adults grow slowly, although it is possible that the observed unimodal distribution in size-frequencies results from one or several recruitments. Recruitment to the population is probably infrequent and may occur irregularly. Comparison of the population structure of closely spaced samples suggests a patchy distribution on the bottom. The benthopelagic lifestyle of adult P. diaphana suggests that the larvais also planktonic.