Miguel B. Gaspar

Doubly uniparental inheritance (DUI) of mitochondrial DNA in Donax trunculus (Bivalvia: Donacidae) and the problem of its sporadic detection in Bivalvia.

Abstract Mitochondrial DNA is transmitted maternally in metazoan species. This rule does not hold in several species of bivalves that have two mtDNA types, one that is transmitted maternally and the other paternally. This system of mitochondrial DNA transmission is known as doubly uniparental inheritance (DUI). Here we present evidence of DUI in the clam Donax trunculus making Donacidae the sixth bivalve family in which the phenomenon has been found. In addition, we present the taxonomic affiliation of all species in which DUI is currently known to occur and construct a phylogeny of the maternal and paternal genomes of these species. We use this information to address the question of a single or multiple origins of DUI and to discuss whether failed attempts to demonstrate the presence of DUI in several bivalve species might be due to problems of detection or to genuine absence of the phenomenon.

Growth and reproductive cycle of Donax trunculus L., (Mollusca : Bivalvia) off Faro, southern Portugal

Abstract The shell growth and reproductive cycle of Donax trunculus (Mollusca: Bivalvia) from southern Portugal were studied from December 1993 to November 1994. Both the acetate peel method and quantification of surface growth rings were used to establish age and estimate growth rate. Widely spaced growth bands were formed in spring and summer whilst narrowly spaced bands were deposited in late summer and early autumn. No cessation of growth was observed during the winter. The von Bertalanffy growth curve estimated from the internal bands did not differ significantly from that obtained from the surface rings. However, the age of clams can be determined more accurately from acetate peels than directly from surface rings. Laboratory experiments demonstrated that periodicity of the deposition of microgrowth bands was related to an innate rhythm. Gonadal development was monitored using standard histological methods. Both males and females showed synchronism in gonadal development. The gametogenic cycle began in late November and ended in late August. Spawning occurred between March and August with two major spawning phases: March and May–August. D. trunculus reached maturity during the first year of life.

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.

A comparison of direct macrofaunal mortality using three types of clam dredges

The white clam Spisula solida is harvested along the entire coast of Portugal using mechanical dredges. In this study, the total direct mortality of the macrobenthic community caused by three types of clam dredges (north dredge—ND, traditional dredge—TD, and the metallic grid dredge—GD) used in the S. solida fishery was determined and compared. The relationship between mortality and catching efficiency for each type of dredge was also assessed. Our results showed significant differences for total direct mortality between the ND and both the GD and TD dredges. This difference was largely attributed to the mortality of animals that died in the dredge track as a direct result of the physical damage inflicted by the dredge passing. It was also found that the damage to uncaught individuals is directly related to gear efficiency. The lower catching efficiency of the ND (64%) led to a higher proportion of damaged individuals being left in the dredge path, when compared with the more efficient GD (98%) and TD (90%) dredges. Short and long-term implications of the impact of dredging on the composition of benthic communities are discussed. From fisheries management and ecological points of view, there are obvious advantages to introduce into the bivalve dredge fisheries more efficient and selective dredges in order to reduce the number of damaged individuals and by-catch, and consequently decreasing the impact on the macrobenthic communities.

Ecological characterization of dredged and non-dredged bivalve fishing areas off south Portugal

Macro and meiobenthic communities of two fishing areas (Vilamoura and Lagos) in the western part of south Portugal (Algarve coast) were analysed. Both locations had been under severe dredge-fishing impact until four years previously. Vilamoura has since continued to be dredged, while fishing activity in Lagos was stopped in 1995 as a response to overfishing. For each location, three replicate areas were analysed at depths of 7–9 m. In each of these areas, 18 quadrats for macrofauna and 12 cores for meiofauna were randomly sampled by SCUBA divers during September 1999. The Shannon–Weiner diversity index was higher for meiofauna in the fished area, whereas macrofauna diversity was higher in the recently non-fished area. Bray–Curtis dissimilarity between the two areas was 87·82%. Major differences were found between Ampeliscidea, Amphiura mediterranea , Spisula solida , Haustoriidae, Nemertinea and Diogenes pugilator populations at the two sites. There was higher abundance but lower biomass of potential macrofaunal scavengers in the fished area, and carnivore biomass was also higher in this area. Deposit-feeders dominated meiofauna abundance in both study areas. The community structure of the continuously fished area was dominated by small, opportunistic, short-lived species while the community structure of the recently non-fished area was dominated by more fragile and long-living sessile organisms.

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.

Short-term environmental impact of clam dredging in coastal waters (south of Portugal): chemical disturbance and subsequent recovery of seabed

The physical and chemical changes in sediment and near bottom water caused by clam dredging were examined during July and September 1999, at two locations Vilamoura (VL) and Armona (AR), south coast of Portugal. Sediment cores and near bottom water were collected simultaneously before dredging (control samples) and within short time intervals (min-h) after dredging. After dredging operations, microphytobenthos coming from the path were accumulated in the re-worked sediment (ridge). Chlorophyll a in superficial sediment increased from 1.2 microg x g(-1) before dredging to 1.7 microg x g(-1) after dredging and these higher values remained for a few hours. However, the expected increase of chlorophyll a in near bottom water due to re-suspension was not observed. After sediment disturbance an instantaneous sorption of phosphorus onto iron oxides occurred in the upper sediment layers (from 2 to 3 micromol x g(-1) before dredging to 4-5 micromol x g(-1) after dredging). A microcosm experiment showed that after sediment disturbance HPO(4)(2-) dissolved in pore water decreased from 40 to 10 microM being simultaneously sorbed onto iron oxides formed in the top layer of sediment. The ammonium, nitrates, organic nitrogen, phosphate and silicate dissolved in pore water decreased immediately after dredging activity and simultaneously an increase in near bottom water was sporadically observed. Generally, the re-establishment of seabed was reached within a short time (min-h), at both stations (VL and AR).

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.

The influence of dredge design on the catch of Callista chione (Linnaeus, 1758)

To evaluate a possible introduction of a new dredge in the fishery of Callista chione (Linnaeus, 1758), IPIMAR has conducted a study with the objective of comparing the efficiency of two dredges (traditional dredge and the new dredge design) and evaluating their impact on the benthic community. The experiments were carried out during March 1999 on the Southwest coast of Portugal, from a site off Troia. Three different tow durations of 5, 10 and 20 min were investigated. A total of 24 hauls were accomplished, 4 for each tow duration and dredge. The experiments were conducted by attaching a cover bag with a 20 mm mesh to the gear. After each haul, the catches in the bag and in the cover were sorted separately. All individuals retained were attributed scores on a scale of 1–4 in which 1 equates to good and 4 equates to dead. The results obtained showed that catches from the traditional dredge (TD) are composed of a great fraction of juveniles of C. chione, while in the new dredge (NDD) catches are composed, almost entirely, by individuals with a superior size to the minimum legal length (50 mm). This result indicates that the mesh of the bag of the TD used in the exploitation of this resource is not adequate. For the 3 different tow durations, the mean fishing yield obtained for the NDD was always superior to the TD, due to its greater efficiency in capture. The proportion of by-catch is significantly higher when the TD is used. For all 3 tow duration, the TD caused mortalities on the target species and on the macrobenthic community in the same order of magnitude as the NDD. Since the fishery of C. chione is managed by daily quotas per boat, when using the NDD the impact on the macrobenthic community is reduced by about 50% due to its greater efficiency of capture. Another advantage in the usage of the NDD relatively to the TD, is to allow the smallest individuals (independently of the species) to escape rapidly through the metallic bars on the grid, increasing their probability of survival.