Paulo Vasconcelos

Shell morphometric relationships of the most common bivalve species (Mollusca: Bivalvia) of the Algarve coast (southern Portugal)

This study reports shell morphometric relationships (height/length and width/length) for the most common and abundant bivalve species of the Algarve coast (southern Portugal). The individuals were caught during periodic exploratory fishing surveys carried out during 2000 using artisanal fishing gears (clam dredge and razor clam dredge), on soft bottoms in the subtidal zone down to 25 m depth. For this particular study, a total of 7497 bivalves were sampled, belonging to 25 species distributed in 9 Families. Almost all regressions were significant (P<0.05 = 52%) or highly significant (P<0.01 = 44%), the only exceptions being the W/L relationships for two bivalve species (n.s. = 4%). The results revealed that both for height/length and width/length morphometric relationships most species presented positive allometric growth (H/L = 11 species; W/L = 15 species), followed by isometric growth (H/L = 7 species; W/L = 6 species) and by negative allometric growth (H/L = 7 species; W/L = 4 species). Data were compared with some morphometric relationships available for the same species in other geographical areas and several ecological hypotheses or explanations were formulated for the distinct types of growth exhibited by different bivalve species.

Spawning of Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) in the laboratory: description of spawning behaviour, egg masses, embryonic development, hatchling and juvenile growth rates

Summary Some authors have studied and described different aspects of the reproductive cycle of Hexaplex (Trunculariopsis) trunculus, but most data are quite ancient and fragmented, lacking information in important respects on the reproductive cycle of this species. Based on several individual and collective spawns deposited in laboratory aquaria, this study provides additional and more detailed information on the spawning behaviour and egg-laying pattern, description of the general morphology and dimensions of the spawns, egg capsules, eggs, embryos and early post-metamorphic juveniles, as well as the first data available on the growth rate of T. trunculus hatchlings and juveniles (until 4 months old). Females deposited an average of 118 ± 89 tongue-shaped egg capsules per individual spawn, measuring on average 5.5 mm length x 4.7 mm width x 2.6 mm thickness. These egg capsules contained 723 ± 66 eggs with an average diameter of 240 ± 8 μm. T. trunculus is a direct developer species (metamorphosed hatchlings) with an incubation period of approximately 1 month. At hatching, individuals measured 1.64 ± 0.22 mm shell length and presented a growth rate of 2.5 mm/month at the end of 4 months. The breeding habits, embryonic development, hatchling and juvenile growth rates are discussed in terms of their implications for the management of the artisanal fishery for T. trunculus in the Ria Formosa lagoon and the assessment of the potential of this muricid species for molluscan aquaculture.

Weight-length relationships of 25 bivalve species (Mollusca : Bivalvia) from the Algarve coast (southern Portugal)

Weight-length relationships of some of the most abundant bivalve species from the Algarve coast (southern Portugal) captured during several exploratory fishing surveys carried out during 2000 on a soft bottom in the subtidal zone down to 25 m depth are reported. For this study a total of 7429 individuals were sampled, belonging to 25 bivalve species in nine families. The most represented families were Mactridae and Veneridae with six species, immediately followed by the families Cardiidae (five species) and Donacidae (three species). The results revealed that most species presented isometric (11 species) or positive allometric relationships (11 species), while only a small minority of species displayed negative growth (three species).

Comparison of indices for the assessment of reproductive activity in Hexaplex trunculus (Gastropoda: Muricidae)

Abstract The present study compares the ability of conventional condition indices (based on weight of the whole organism, weight of its flesh, and/or its shell weight) and visual quantitative indices (based on measures of the digestive gland, gonad, and capsule gland on digitized images of sections of these organs) for the assessment of reproductive activity in Hexaplex trunculus. To estimate conventional indices, a total of 120 standard-sized specimens (50 males and 70 females) in the 60–70 mm shell length interval were analysed. To estimate visual quantitative indices, a total of 903 specimens (501 males and 402 females) were analysed for the gonadosomatic index (GSI); females were also analysed for the capsule gland index (CGI). Compared to conventional indices, the visual quantitative indices (GSI and CGI) followed seasonal variations of the species reproductive cycle and identified broad changes in reproductive development (being highly accurate in detecting the main period of gonad maturation and spawning that occurred between May and June). Results indicate that both GSI and CGI constitute simple, practical and efficient indices for the routine assessment of reproductive activity in H. trunculus, providing a useful and reliable alternative to conventional condition indices and to histological analyses. Results of this study encourage the use of similar sampling procedures and analytical techniques, and analogous visual quantitative indices, to assess reproductive activity in other gastropod species.

Gametogenic cycle of Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) in the Ria Formosa lagoon (Algarve coast, southern Portugal)

The gametogenic cycle of the banded murex, Hexaplex (Trunculariopsis) trunculus, from the Ria Formosa lagoon (Algarve coast, southern Portugal) was studied through macro- and microscopic analyses of the gonads during a i -year study period (March 2003 -February 2004). The overall samples presented a balanced sex ratio, with males dominating among smaller individuals and females predominating in larger size-classes. The gametogenic cycle of T. trunculus in the Ria Formosa lagoon comprised an extensive period of gonadal activity, with the simultaneous occurrence of distinct developmental stages of gametogenesis in both sexes almost year-round, and with males invariably presenting gonads in more developed stages of gametogenesis than females. Spawning occurred mainly from May to June 2003, apparently triggered by the rising seawater temperature during spring. Due to the extensive period of gonadal activity, T. trunculus exhibited a short resting phase that occurred simultaneously in both sexes between June and August 2003 and coincided with the period of warmest seawater temperatures. Considering these findings, a closed season in the fishing activity should be implemented during the main spawning period of T. trunculus (May and June), in order to protect the female broodstock and collective spawns.

Reproductive cycle and size at first sexual maturity of Hexaplex trunculus (Gastropoda: Muricidae) in the Gulf of Gabès (southern Tunisia)

Abstract The reproductive cycle and size at first sexual maturity of the banded murex (Hexaplex trunculus) from the tidal areas of the Gulf of Gabès (southern Tunisia) were investigated from June 2007 to May 2008 through macroscopic analysis of the gonads and monthly variations in the general condition (K) and gonadosomatic indices (GSI). This muricid gastropod is gonochoristic (separate sexes throughout life) and lacks external sexual dimorphism. The overall sex-ratio of the population was significantly unbalanced, with a predominance of females (M:F = 1:1.6). The monthly variation in the gonad maturation stages, K and GSI revealed that H. trunculus has a yearly reproductive cycle, with both sexes showing a long period of gonadal activity and slightly asynchronous gametogenic cycle. Gametogenesis occurred during most of the year (11 out of 12 months examined) and almost every gametogenic stage was observed throughout the study period. Ripe males were found mainly from November to January, preceding the main period of gametic emission (between January and May). Ripe females occurred mainly from February to April, preceding the main spawning season (between April and May), apparently triggered by the increasing daylength and seawater temperature during this period (from 13.2 to 14.2 h and from 19.3 to 23.4°C, respectively). Both sexes displayed a relatively short resting phase (males: June—July; females: June—September), coincident with the highest daylength and seawater temperature during summer in the Gulf of Gabès. The first sexual maturity was reached at a smaller size in males (SL50 = 36.9 mm SL) than in females (SL50 = 50 50 40.3 mm SL). The information gathered in this study allowed preliminary management measures for the fishery to be proposed, including a closed season during the main spawning season (April—May) and the establishment of a minimum landing size (of at least 40 mm SL) for H. trunculus from the Gulf of Gabès.

Influence of growth and reproductive cycle on the meat yield and proximate composition of Hexaplex trunculus (Gastropoda: Muricidae)

This study aimed to assess the influence of growth and reproductive cycle on the meat yield and proximate composition of the banded murex (Hexaplex trunculus) from the Ria Formosa lagoon (Algarve coast, southern Portugal). Samples of the edible portion (all soft-body tissues) were analysed monthly during one year. The average meat yield was 37 . 9 ± 4 .6%, with females containing more edible content (39.1 + 4.7%) than males (36.8 ± 4.2%). The proximate composition comprised 70.7 ± 1.4% moisture, 20.1 ± 1.2% protein, 1.6 ± 0.3% fat, 3.0 ± 0.3% ash, and 4.6 :t 1.2% carbohydrate, corresponding to an energetic value of 119.2 ± 7.5 kcal/100 g wet weight. The meat yield was influenced by specimen size, increasing significantly during growth. Both meat yield and proximate composition presented seasonal fluctuations related to the reproductive cycle, which coincided mainly with the periods of maturation and spawning of this species in the Ria Formosa. Finally, H. trunculus meat yield and proximate composition were compared with similar information available for other marine gastropods.

The shell of Hexaplex (Trunculariopsis) trunculus (Gastropoda: Muricidae) as a mobile hard substratum for epibiotic polychaetes (Annelida: Polychaeta) in the Ria Formosa (Algarve coast—southern Portugal)

This work reports and illustrates secondary colonisation of Hexaplex (Trunculariopsis) trunculus shells by polychaetes in the Ria Formosa lagoon (Algarve coast—southern Portugal). Information is presented in terms of qualitative and quantitative data on epibiotic polychaetes, fouling frequency, degree of epibiosis, preferential areas for colonisation and incidence of shell damages. A total of 2,880 polychaetes belonging to 10 families were identified. Besides Spirorbidae (not quantified), the most abundant families were Serpulidae (67.5%), Sabellidae (10.2%), Sabellariidae (9.6%) and Cirratulidae (8.5%). From a total of 2,264 T. trunculus individuals analysed for epibiosis, 28.4% were non-fouled, 66.8% were intermediately fouled and 4.8% were heavily fouled. The fouling frequency, degree of epibiosis and incidence of damages in the shell spire increased markedly with T. trunculus shell length. Some epibiotic polychaetes were located preferentially on/or nearby particular features of T. trunculus shells, which probably facilitate settlement and tube construction, in addition to provide some protection against tube damage. The main consequences of epibiosis (benefits and disadvantages) for the gastropod basibiont (T. trunculus) are discussed. The present study apparently indicates that besides burrowing into soft bottom substrates, sporadic inter-tidal exposure and mutual predation on epibiosis, T. trunculus lacks other typical antifouling defence adaptations.

Appraisal of the usefulness of operculum growth marks for ageing Hexaplex trunculus (Gastropoda: Muricidae): Comparison between surface striae and adventitious layers

Abstract This study estimated the age of Hexaplex trunculus (Gastropoda: Muricidae) by analysing operculum growth marks. Surface striae and adventitious layers were counted in opercula of H. trunculus from the Ria Formosa Lagoon (southern Portugal) and from the Bizerte Lagoon (northern Tunisia), and in aquacultured individuals used for validation of the ageing technique. Operculum growth features were also compared between H. trunculus populations under contrasting environmental conditions (namely seawater temperature). Despite high inter-individual variability, all H. trunculus populations displayed a clear increasing trend in the number of striae and layers with increasing specimen size. The operculum marginal growth revealed that opercular deposition is not annual. Instead, a few growth marks are formed in the operculum each year, which was confirmed with reared specimens. In both ageing methods, considerable variation in the number of counts at a determined shell length indicates that operculum growth marks should be interpreted cautiously because they might not correspond accurately with individual age. Because of the subjectivity inherent to either method, counting striae and layers in opercula only provides rough age estimates of H. trunculus.

Northernmost record of Kyphosus sectator (Osteichthyes: Perciformes: Kyphosidae) in the north-eastern Atlantic

This note reports the main morphometric and meristic parameters of a male Bermuda sea chub (khyphosus sectator) caught off the Algarve coast (southern Portugal). This is the first occurrence of this tropical fish species in Portuguese continental waters, and the second and northernmost capture ever reported for the north-eastern Atlantic.