Genetic connectivity of the coral‐eating sea star Acanthaster planci during the severe outbreak of 2006–2009 in the Society Islands,French Polynesia

Occasional population outbreaks of the crown‐of‐thorns sea star, Acanthaster planci, are a major threat to coral reefs across the Indo‐Pacific. The presumed association between the serial nature of these outbreaks and the long larval dispersal phase makes it important to estimate larval dispersal; many studies have examined the population genetic structure of A. planci for this purpose using different genetic markers. However, only a few have focused on reef‐scale as well as archipelago‐scale genetic structure and none has used a combination of different genetic markers with different effective population sizes. In our study, we used both mtDNA and microsatellite loci to examine A. planci population genetic structure at multiple spatial scales (from <2 km to almost 300 km) within and among four islands of the Society Archipelago, French Polynesia. Our analysis detected no significant genetic structure based on mtDNA (global F_ST = ?0.007, P = 0.997) and low levels of genetic structure using microsatellite loci (global F_ST = 0.006, P = 0.005). We found no significant isolation by distance patterns within the study area for either genetic marker. The overall genetically homogenized pattern found in both the mitochondrial and nuclear loci of A. planci in the Society Archipelago underscores the significant role of larval dispersal that may cause secondary outbreaks, as well as possible recent colonization in this area.     

Neurophysiological control of swimming behaviour,attachment and metamorphosis in black-footed abalone (Haliotis iris) larvae

Experiments were conducted to test the effect of a range of chemicals on larval responses in swimming behaviour, attachment and metamorphosis of the black-footed abalone (Haliotis iris). The effect of antibiotics on larval survival was first tested within negative (filtered seawater) and positive (GABA at 10^?5, 10^?4 and 10^?3 mol L^?1) control assays over 3 days. This experiment corroborated the effectiveness of using antibiotics to improve survival of larvae without obvious synergistic interactions with the GABA inducer or confounding effects of potential bacterial interactions. Chemical treatments (acetylcholine, potassium chloride, dopamine and glutamine) were then tested at various concentrations for their ability to modulate swimming behaviour and induce larval attachment and metamorphosis over 14 days. Generally, larval state shifted from swimming to attached, and from attached to metamorphosed, in the control and treatments over time. However, the peak percentage of attached and metamorphosed larvae varied in time among chemicals and concentrations. While overall percent metamorphosis was minimally enhanced after 14 days of exposure to some chemical treatments at certain concentrations, all treatments displayed significant capacities to down-regulate larval swimming and induce early attachment and metamorphosis. Mortality was recorded throughout the duration of the experiment, and was generally low (<20%) across controls and most treatments for exposures of less than 12 days. Interpretations of specific results from this study are used to elucidate neurophysiological control of larval activities for this abalone species. Comparisons with other marine invertebrates highlight the specificities of chemical cues and endogenous regulatory mechanisms across relatively closely related taxa.     

Protracted oogenesis and annual reproductive periodicity in the deep‐sea pennatulacean Halipteris finmarchica (Anthozoa,Octocorallia)

Halipteris finmarchica is one of the most common species of deep‐sea pennatulacean corals in the Northwest Atlantic; it was recently determined to act as a biogenic substrate for other species and as a nursery for fish larvae. Its reproductive cycle was investigated in colonies sampled in 2006 and 2007 along the continental slope of Newfoundland and Labrador (Canada). Halipteris finmarchica exhibits large oocytes (maximum diameter of 1000 μm), which are consistent with lecithotrophic larval development. Female potential fecundity based on mature oocytes just before spawning was ~6 oocytes · polyp^?1 (500–6300 oocytes · colony^?1); male potential fecundity was 16 spermatocysts · polyp^?1 (5500–57,400 spermatocysts · colony^?1). Based on statistical analysis of size‐probability frequency distributions, males harboured one cohort of spermatocysts that matured inside 8–11 months, whereas females harboured two distinct cohorts of oocytes; a persistent pool of small ones (≤400 μm) and a small number (~20%) of larger ones that grew from ~400 to >800 μm over a year. Despite this difference in the tempo of oogenesis and spermatogenesis, a synchronic annual spawning was detected. A latitudinal shift in the spawning period occurred from south (April in the Laurentian Channel) to north (May in Grand Banks and July–August in Labrador/Lower Arctic), following the development of the phytoplankton bloom (i.e. sinking of phytodetritus). Prolonged oogenesis with the simultaneous presence of different oocyte classes in a given polyp is likely not uncommon in deep‐sea octocorals and could hamper the detection of annual/seasonal reproduction when sample sizes are low and/or time series discontinued or brief.     

Highly restricted gene flow between disjunct populations of the skunk clownfish (Amphiprion akallopisos) in the Indian Ocean

The skunk clownfish (Amphiprion akallopisos) has a disjunct distribution, occurring in the Eastern Indian Ocean (EIO) and the Western Indian Ocean (WIO), separated by several thousands of kilometres. Information on connectivity of marine species is very important for the correct spacing of marine protected areas, a powerful instrument for the protection of coral reefs. The population genetic structure of A. akallopisos was analysed in order to investigate connectivity amongst populations and to explain the disjunct distribution of the species. A fragment of the mitochondrial control region was used to investigate the genetic population structure. Fin clips were collected from 263 individuals at 14 sites in the WIO and three sites in the EIO. The obtained DNA sequences were used to calculate genetic diversity, evaluate demographic history and to construct a haplotype network. An analysis of molecular variance (AMOVA) was conducted to evaluate the significance of the observed genetic population structure. None of the identified 69 haplotypes was shared between the WIO and EIO. Haplotype as well as nucleotide diversity was considerably higher in the EIO than in the WIO. Significant genetic population structure was revealed by an AMOVA with an overall φ_st‐value of 0.28 (P < 0.001) in the Indian Ocean. The overall AMOVA (φ_st = ?0.00652) was not significant in the EIO, but was significant in the WIO (φ_st = 0.016; P < 0.01). Demographic analysis indicated population expansion in the EIO and WIO. Population genetic analysis revealed highly restricted gene flow between the EIO and WIO. Genetic diversity was much higher in the EIO than in the WIO, suggesting that the EIO is the geographical origin of the species. Given the large distance between the disjunct populations and the short pelagic larval duration, long‐distance dispersal is rather unlikely. A stepping stone model involving islands in the Central Indian Ocean is a more likely scenario for colonization of the WIO.     

Effects of dietary and water-borne oil exposure on larval pacific herring (Clupea harengus pallasi)

Pacific herring (Clupea harengus pallasi) larvae were exposed either directly to the water-soluble fraction (WSF) of crude oil or indirectly via oil-contaminated prey (OCP) (Artemia salina) for <- 28 days, to determine the relative effects of diet and water as routes of contamination. Larvae were affected rapidly by 0·9 ppm WSF, which caused high larval mortality, reduced swimming ability and rapid reductions in feeding rates. Larval length was significantly reduced by 0·7 ppm WSF in 7 days and by 0·3 ppm WSF within 14 days. The WSF exposure also caused similar reductions in larval weights. Highly contaminated prey (6 ppm prey exposure) caused significant mortality, but surviving larvae appeared robust. The OCP did not affect swimming, feeding, or growth. Exposure of larvae was not significantly extended by OCP, which rapidly depurated WSF in clean water (98% in 1 day). Therefore, OCP is probably not an important source of low molecular weight petroleum contamination to larval fish in the marine environment.     

The annual cycle of Synechococcus (cyanobacteria) in the northern Levantine Basin shelf waters (Eastern Mediterranean)

Abundance of picoplanktonic chroococcoid marine cyanobacteria Synechococcus was monitored weekly over the year 1998 in shallow coastal waters of the northern Levantine Basin. The ambient physical, chemical and biological variables (temperature, salinity, Secchi disk depth, total suspended sediment, nitrate, phosphate, Chl a and phytoplankton) were also measured. Synechococcus was found to be more abundant during summer and early autumn and less during winter and early spring. At the surface and 15 m depth, cell concentrations were in the range 6.4 × 10³–1.5 × 10⁵ and 3.2 × 10³–1.6 × 10⁵ cells·ml⁻¹, respectively. Based on the Pearson product–moment correlation analysis, a highly significant correlation between Synechococcus abundance and ambient temperature was observed (n = 40, r = 0.558, P < 0.01). As Synechococcus forms blooms that usually do not last more than a week, the short time‐scale survey achieved in this study was appropriate to reveal its abundance dynamics. Several factors such as rapid changes in nutrient concentration (especially nitrate), phytoplankton, light availability, temperature, salinity, freshwater input and vertical mixing played a relevant role on the abundance of Synechococcus over the year in the highly dynamic shallow coastal waters of the Levantine Basin.     

The effect of temperature and salinity on survival and growth of Crangon uritai (Decapoda: Crangonidae) larvae reared in the laboratory

Larvae of the decapod Crangon uritai were reared in the laboratory in a factorial experiment employing three temperatures (9, 12 and 15 °C) and three salinities (29‰, 32‰ and 35‰) from hatching to the post‐larval stage. The effects of temperature and salinity on survival, intermolt period (IP) and molt increment (MI) were investigated. Larvae from one brood were subdivided into groups of 20 and reared in glass bowls containing filtered sea‐water at a number of temperature–salinity combinations. The reared larvae were transferred daily to the clean bowls prepared with newly hatched Artemianauplii, and number of molts and mortality within each bowl were recorded. The zoeal size (carapace length) was determined from exuvia and dead larvae, and the IP was also recorded. Larvae of C. uritai completed larval development only at 15 °C temperature. The first zoeal stage completed their development at all temperature–salinity combinations and exhibited the highest survival rate. IP at each stage increased with increasing size and greatly decreased with increasing temperature, and intermolt duration (range of days) increased with larval development especially at the lower temperature. Although the MI decreased with increasing size, it was little affected by temperature. This led to a better growth rate with increasing temperature.     

Ocean currents determine functional connectivity in an Antarctic deep‐sea shrimp

The coherency among larval stages of marine taxa, ocean currents and population connectivity is still subject to discussion. A common view is that organisms with pelagic larval stages have higher dispersal abilities and therefore show a relatively homogeneous population genetic structure. Contrary to this, local genetic differentiation is assumed for many benthic direct developers. Specific larval or adult migratory behavior and hydrographic effects may significantly influence distribution patterns, rather than passive drifting abilities alone. The Southern Ocean is an ideal environment to test for the effects of ocean currents on population connectivity as it is characterized by several well‐defined and strong isolating current systems. In this study we studied the genetic structure of the decapod deep‐sea shrimp Nematocarcinus lanceopes, which has planktotrophic larval stages. We analysed 194 individuals from different sample localities around the Antarctic continent using nine microsatellite markers. Consistent with a previous study based on mitochondrial DNA markers, primarily weak genetic patterns among N. lanceopes populations around the continent were found. Using ocean resistance modeling approaches we were able to show that subtle genetic differences among populations are more likely explained by ocean currents rather than by geographic distance for the Atlantic Sector of the Southern Ocean.     

Population biology and secondary production of the harvested clam Tivela mactroides (Born, 1778) (Bivalvia,Veneridae) in Southeastern Brazil

The population structure, growth and production of the trigonal clam Tivela mactroides were investigated by monthly sampling between January 2003 and October 2004 in two areas (southern and northern) of the intertidal and subtidal zones of Caraguatatuba Bay, Southeastern Brazil. Intertidal sampling was carried out in each area along eight transects perpendicular to the shoreline. In the subtidal zone of both areas, one 50‐m dredging was performed along five sampling stations arranged on three transects perpendicular to the coast. The intertidal abundance of T. mactroides was higher in the southern (more dissipative conditions) than in the northern area. High abundances occurred in February–March 2004 in the south and in September 2004 in the north. The size structure showed that younger individuals dominated in the sublittoral, indicating that recruitment occurs in this zone, followed by the migration of these individuals to the intertidal, where they complete their life cycle. Tivela mactroides showed continuous reproduction, with 26 cohorts detected in the study period. The lower estimates for the growth index (?′ = 3.22), mortality rate (Z = 2.10 year^?1) and turnover rate (P/B = 1.21 year^?1), and conversely the longer life span (2.5 years) of T. mactroides in Caraguatatuba Bay (24°S) compared with Venezuelan populations (10°N) suggests a latitudinal pattern of these life‐history traits. The high production of T. mactroides in Caraguatatuba Bay was due to continuous recruitment and rapid and continuous growth, and demonstrates the importance of T. mactroides as a biological resource for many marine species and for the local residents.     

Wax and wane of Chattonella (Raphidophyceae) bloom with special reference to competition between Skeletonema (Bacillariophyceae) in the Ariake Sea, Japan

The raphidophyte Chattonella and the bacillariophyte Skeletonema are representative bloom-causing organisms in the Ariake Sea, Japan. Changes in their abundance were monitored to clarify the role of river discharge in the red tides caused by these organisms in the innermost area of the sea. In late June 2010, heavy rain occurred and subsequently river discharge increased. A Chattonella bloom occurred after heavy rain on July 5, although Chattonella abundance was very low (<1?cell?ml^?1) before the heavy rain (June 29). Maximum cell density reached 4.2?×?10³?cells?ml^?1 at the surface. Thus, the bloom developed as the river plume extended in the estuary. During the course of extension of the river plume, the Chattonella population rapidly developed using the nutrients supplied by the river. Just after the Chattonella bloom, heavy rain occurred again and a very large quantity of river water flowed into the estuary. Consequently, the salinity of the surface decreased to 5 in the study area on July 16. Chattonella did not migrate to the surface probably because of the overlying low-salinity water; Chattonella formed a thin layer (20–50?cm in thickness) at the depth where salinity was 10. However, a Skeletonema population developed at the surface. On July 20, Skeletonema density at the surface exceeded 10⁵?cells?ml^?1. With the decline of the Skeletonema abundance due to the nutrient limitation, Chattonella again formed bloom probably using deep-nutrient pool by their vertical migration behavior. The present study clearly demonstrates that the Chattonella can form dense bloom after the heavy rain. The seed population awaiting the river discharge is probably essential to the rapid development of Chattonella in the estuary.     

Small macro‐benthic invertebrates influence the survival,growth and behaviour of juvenile green sea urchins Strongylocentrotus droebachiensis in the laboratory

Recent settlers of many marine benthic invertebrates are cryptic, which exposes them to a suite of animals that differs from those they may experience as adults, potentially resulting in interactions causing mortality and/or reducing growth. Previous field experiments have indicated that such is the case with small juvenile green sea urchins Strongylocentrotus droebachiensis but which taxa are responsible for the mortality and reduced growth was not determined. A laboratory study was conducted to examine the effects of small macro‐benthic invertebrates, specifically chitons, scaleworms and larger juvenile conspecifics, as well as the full suite of cobble‐dwelling organisms, on the mortality, growth and behaviour of small (<3 mm) juvenile sea urchins. The likelihood of survival of small juvenile sea urchins was lower in the presence of larger juvenile sea urchins or with the full suite of cobble‐dwelling organisms than in the absence of animals. The small juvenile sea urchins survived and grew the best when they were with chitons and scaleworms. The behaviour of small sea urchins with the full suite of cobble‐dwelling organisms was more cryptic than the behaviour of urchins with scaleworms. This study indicates that interactions with the suite of small organisms living amongst cobbles can affect survival, growth and behaviour of small juvenile sea urchins, and that larger juvenile sea urchins can be a source of mortality for smaller conspecifics.     

Efficiency of calcein tagging on juveniles of the sea urchins Diadema africanum and Paracentrotus lividus

We evaluated the effectiveness of chemical tagging with the fluorescent marker calcein for two key species of herbivorous sea urchins, Diadema africanum and Paracentrotus lividus, to facilitate medium‐ and long‐term ecological experiments. In total, 98 juveniles of D. africanum and 98 P. lividus were tagged with this fluorescent marker, with 12 combinations of different tagging techniques (chemical bath or injection), concentrations of calcein (2, 10 and 20 mg · l^?1), and soaking times (2, 4 and 24 h). Respective control treatments were conducted by means of seawater injection and bathing. The success of tagging was assessed after a month of feeding individuals ad libitum with the algae Dictyota sp. Sea urchins were dissected and their Aristotle's lanterns cleaned with 10% sodium hypochlorite to examine these structures under UV light using a binocular microscope. Each species was evaluated in terms of survival, percentage of tagged individuals and intensity of the resulting tag. The results showed that the method of soaking individuals of both species for 24 h in concentrations of calcein of 10 and 20 mg · l^?1 gave the highest percentage survival (100%) and the resulting tags were clearly visible.     

Description of the larval development of Galaxies maculatus in landlocked lentic and lotic systems in Western Australia

The larvae and larval development of Galaxias maculatus are described from a freshwater lake and a saline river in southwestern Western Australia. The size at hatching (7.0 mm total length) was similar to that recorded elsewhere for G. maculatus and the sequence of fin development (i.e., caudal, dorsal, anal, pectoral, and pelvic fins) was identical to that recorded for galaxiids generally. There were relative increases in the proportions of head length and body depth with larval growth and a decrease in proportion of pre‐anal length. Larvae from river habitats were smaller throughout larval stages of development than those from the lake. Fins of riverine fish began and completed development at a smaller size of fish than the lacustrine population, presumably as a response to the need for great motility at a smaller fish size in lotic environments.     

Abundance and distribution of rhynchoteuthion larvae of Illex argentlnus (Cephalopoda: Ommastrephidae) in the south-western Atlantic

The results of ichthyoplankton surveys carried out by the Instituto Nacional de Pesca (INAPE) in the Argentine–Uruguayan Common Fishing Zone (AUCFZ) in summer 1980 and the winters of 1980–1982 are presented. In addition, the results of joint research with INIDEP, the Argentine and Japan Fisheries Agency, on larvae, juveniles and adults of the short-finned squid Illex argentinus carried out in winter 1989 are given, as are data obtained during the joint sardine and anchovy recruitment project carried out by R.V. Meteor in November/December 1989. The short-finned squid Illex argentinus is the most important cephalopod resource of the area, and an extended fishery is carried out on the Patagonian shelf and in the proximity of the Falkland Islands. The fishing season in the AUCFZ, for pre-spawning and spawning animals, extends from early autumn to winter (March–August). Abundance of rhynchoteuthion larvae (417–485 larvae·10 m^?2) was greatest in winter in surface temperatures of 12,1–16,9°C and surface salinities of 34,8 – 35,2 × 10^?3. The distribution of the larvae is related to the western boundary of the Brazil Current and the convergence front.     

Influence of anthropogenic pressure and seasonal upwelling on coral reefs in Nha Trang Bay (Central Vietnam)

The growing coastal development, dredging and dumping activities, overfishing and expansion of marine cage culture in Nha Trang Bay (NTB) of Central Vietnam since the beginning of the 2000s have resulted in a dramatic decrease of live coral cover. Surveys conducted in April–May 2013 and the same period in 2014 revealed that with an increase in distance from the outer part of the bay towards the mainland, the rivers’ influxes and dredged areas, coral cover decreased from 75% to 0.6% and species richness from 63 to 5, while the abundance of macroalgae increased from 0% to 56%. These changes correlate with differences in the concentration of suspended sediments on the same gradient. The abundance of the crown‐of‐thorns starfish Acanthaster planci and of the echinoid Diadema setosum significantly increased between the first estimation in 1998 and the survey in 2014, from 0 to 1.7 individuals (ind.) per 100 m^?2 and from 50.8 to 94.5 ind. per 100 m^?2, respectively, contributing to coral loss and intensive bioerosion of the reef framework in the bay. The large sizes of adult colonies of tabulate Acropora on the remote stations with negligible sedimentation and eutrophication loads were inconsistent with the assumptions that temperature‐induced coral bleaching or cyclones could be the major impacts in Nha Trang Bay. Analysis of the 16‐year thermal history of the bay did not reveal any instances in which the coral thermal bleaching threshold had been exceeded up to the present study. Seasonal upwelling, which occurs annually in the vicinity of Central Vietnam, may contribute to mitigation of thermal anomalies within NTB and to the maintenance of healthy coral communities on the remote reefs with relatively low anthropogenic impact.     

Ecological energetics of the tropical sea urchin Diadema antillarum Philippi in Barbados, West Indies

The common tropical sea urchin Diadema antillarum Philippi is the dominant herbivore on fringing coral reefs in Barbados, West Indies. The biological importance of Diadema as an agent of energy transfer was evaluated from energy budgets constructed for the population and for individuals of 10 size groups. Monthly energy budgets for urchins of various size groups balance within 1 kcal except for urchins of the largest size group examined. Approximately 20% of the monthly net benthic primary production of the fringing coral reef is consumed by Diadema. This percentage is considerably larger than the 7% reported for the consumption of benthic algal production by a population of the temperate water sea urchin, Strongylocentrotus droebachiensis, feeding in kelp beds but is lower than the 47% reported for the consumption of sea grass by the tropical urchin Lytechinus variegatus. Higher rates of secondary production of Diadema compared to that of Strongylocentrotus may be in part due to higher net and gross growth efficiencies exhibited by Diadema. It is apparent that Diadema is more efficient at converting its algal food resources into urchin biomass than is Strongylocentrotus of similar size. In comparison to Strongylocentrotus and Lytechinus, Diadema releases as much energy to the benthos in the form of fecal pellet detritus as do the other two species. The production of fecal pellet detritus is the most important pathway of energy transfer on the fringing coral reef. Fecal pellet detritus contributes approximately 26 kcal m⁻² month⁻¹ to the benthic community. This amount is equivalent to 7·4% of the monthly net primary production of the benthic algae or approximately 37% of the caloric intake of the urchin population. In addition fecal pellet detritus produced by Diadema contains about 10 times the caloric content of surface sediments found to the north and south of the fringing reef and approximately 1·7 times the caloric content of sediments within the reef. The utilization of this energy-rich fecal pellet detritus by other reef organisms is discussed briefly.     

Stage‐dependent thyroxine effects on sea urchin development

Thyroxine, one of the iodinated hormones produced by vertebrate thyroids, has been reported to accelerate late larval development in several sea urchins (Chino et al. 1994) and in the crown‐of‐thorns starfish (Johnson & Cartwright 1996), but thyroxine effects on earlier portions of echinoderm development have not been reported. I investigated thyroxine effects on developmental rates during several periods spanning development from early cleavage to metamorphosis in the New Zealand sea urchin Evechinus chloroticus (Valenciennes). Thyroxine treatment slowed development between the eight‐cell stage and assembly of the four‐armed pluteus and mid‐larval development between the four‐armed and six‐armed stages. Thyroxine treatment accelerated progress of eight‐armed plutei toward settling, but did not alter the final percentages of larvae that settled and metamorphosed to juvenile urchins. Acceleration of late larval echinoderm development by thyroxine may indicate a relatively ancient evolutionary origin of thyroxine's effects on developmental processes (Johnson 1997).     

Early life history of the congrid eels gnathophis habenatus and G. incognitos in New Zealand waters

Larvae (leptocephali) of Gnathophis habenatus (Richardson, 1848) and G. incognitas Castle, 1963 occur off Castlepoint throughout most of the year (not sampled December‐February), In general they are smallest in late summer (March) and ilargest in mid‐spring (October‐November), with metamorphosis to the juvenile in early summer of the year of spawning. The two species therefore have a larval life of approximately 10 months. The early life of these two species in Australian waters, and of G. capensis (Kaup) off southern Africa, agrees well with these observations. Eel eggs collected in the East Cape region of New Zealand and tentatively identified as those of Gnathophis confirm the spawning times (March—April) suggested by the sizes of leptocephali.     

盐度对太平洋牡蛎面盘幼虫垂直分布的影响

于1986年夏、秋两季在福建省惠安、罗源采集太平洋牡蛎,以人工授精法获取受精卵,在空调室内研究盐度变化对太平洋牡蛎面盘幼虫趋性行为的影响。结果表明,盐度的提高能促使牡蛎D形面盘幼虫从正趋地性转变为负趋地性,同时幼虫的正趋光性也得到加强。在D形面盘幼虫期,能引起趋光性加强的盐度增加阈值为2.9×10~(-12);在8日龄壳顶面盘幼虫,提高至5.0×10~(-12)以上。当D形面盘幼虫和壳顶面盘幼虫分别从25×10~(-12)移置于30×10~(-12)时,趋光水平能得到明显提高的时间阈值分别为4h和6h。据以上结果,作者认为该种幼虫在河口区有无阻留的主动性取决于该区环境的变化,同时也与幼虫不同发育时期有关。盐跃层的存在对牡蛎幼虫垂直分布的影响表明,只要盐跃层为2.5×10~(-12),即能抑制幼虫的向上游泳;一旦盐跃层增加,其阻抑作用仍维持接近低盐跃层水平。这说明盐跃层的存在对牡蛎幼虫的垂直迁移具有重要作用。     

Spatio‐temporal variation in density and size structure of the endangered sea cucumber Isostichopus fuscus in Huatulco National Park,Mexico

The brown sea cucumber Isostichopus fuscus (Ludwig, 1875) has been subjected to strong fishing pressure and is currently considered an endangered species by the IUCN Red List of Threatened Species. Spatial and temporal variations in density were analysed and population parameters of I. fuscus were estimated in three localities of the Southern Mexican Pacific. Density was estimated using circular transects covering a 300 m² area in each locality. Body length and weight were also measured. The mean density was 0.018 ± 0.013 individuals·m^?2, and was statistically significantly lower during summer. The mean length and weight were 22.4 ± 3.8 cm and 396 ± 130 g, respectively, and statistically significant differences were found among localities. The weight–length relationship was W = 0.28·L^1.32 and the mean relative condition index (Kn) = 1.04 ± 0.31. The von Bertalanffy growth equation was L_t = 38.7·(1–exp^(?0.4·t)). The lowest values of length, weight and age were found at Dos Hermanas, suggesting that this locality could be favorable for the settlement of larvae and recruitment and growth of juveniles. The present study is the second to estimate densities of I. fuscus and the first one to publish data on size structure and growth for the population at Bahias de Huatulco. The densities were so low in the three sampled localities that none of them would be able to support a fishery, even under a sustainable management scheme. The information collected in the present study could be helpful for management programs of the Huatulco National Park, as all the data used for these currently come mainly from the populations of I. fuscus in the Gulf of California.