Predatory behavior and preference of a successful invader, the mud crab Dyspanopeus sayi (Panopeidae), on its bivalve prey

Predator-prey relationships between the panopeid crab, Dyspanopeus sayi, and the mytilid, Musculista senhousia, were investigated. Through laboratory experiments, prey-handling behavior, prey size selection, predator foraging behavior and preferences for two types of prey (M. senhousia and the Manila clam Ruditapes philippinarum) were assessed. Handling time differed significantly with respect to the three prey sizes offered (small: 15.0-20.0 mm shell length, SL; medium: 20.1-25.0 mm SL; and large: 25.1-30.0 mm SL); mud crabs were more efficient in predating medium-small than large prey. Although differences in prey profitability were not evident, D. sayi exhibited a marked reluctance to feed on larger-sized prey whilst smaller, more easily predated mussels were available. Size selection may be the result of a mechanical process in which encountered prey are attacked but rejected if they remain unbroken after a certain number of opening attempts. D. sayi exhibited inverse density-dependent foraging. A significant higher mortality of prey was evident at low prey density. Thus, at low predator density, the D. sayi-M. senhousia interaction was a destabilizing type II functional response. Interference responses affected the magnitude of predation intensity by D. sayi on M. senhousia, since as the density of foraging crabs increased, their foraging success fell. At high density (4 crabs tank⁻¹), crabs engaged in a high amount of agonistic activity when encountering a conspecific specimen, greatly diminished prey mortality. Finally, presenting two types of prey, Manila clam juveniles were poorly predated by mud crabs, which focused their predation mostly on M. senhousia. It is hypothesized that, when more accessible prey is available, mud crabs will have a minimal predatory impact on commercial R. philippinarum juvenile stocks.     

菲律宾蛤仔(Ruditapes plilippinarum)大连群体两种壳型家系生长发育比较

通过对菲律宾蛤仔大连群体壳宽的选择,于2006年5月建立了壳宽型(WS)和壳扁型(PS)两个家系.对两种壳型亲本的鲜重、性比、产卵量及其子代的生长与存活进行了比较.结果表明:两种亲贝的鲜重差异显著(P＜0.05),WS、PS亲贝的雌雄比例分别为0.88 : 1、0.62 : 1,产卵量分别为124.19万/粒和408.50万/粒;两家系子代的卵径、D形幼虫大小、变态规格无显著差异(P＞0.05),但单水管、双水管稚贝的大小差异显著(P＜0.05);幼虫浮游期间(0～16日龄),WS和PS幼虫平均生长速度分别为(9.46±1.56)ìm d-1和 (9.60±0.38)ìm d-1,差异不显著(P＞0.05).12日龄前,WS和PS幼虫存活率差异不显著(P＞0.05),但16日龄时,WS幼虫存活率明显低于PS (P＜0.05).变态期间(16～24日龄),WS家系的生长速度((2.64±0.34)ìm d-1)显著地小于PS家系((3.91±0.67)ìm d-1) (P＜0.05),WS家系的变态率(5.32%±1.53%)也显著地小于PS家系(15.68%±3.06%) (P＜0.01).PS家系在稚贝的室内培育期间(24～60日龄)和生态池育成阶段(60～180日龄)的生长速度均显著地快于WS家系(P＜0.05);PS家系的存活率也均显著地高于WS家系(P＜0.05).     

不同年龄段大连群体菲律宾蛤仔EST-SSR多样性

为查明年龄结构对菲律宾蛤仔同一群体内遗传多样的影响,采用14个SSR分子标记对大连石河不同年龄段的野生蛤仔进行了检测。结果表明:不同年龄段(1龄-Age1、2龄-Age2、3龄-Age3)蛤仔均维持着较高的遗传多样性。根据POPGENE 1.31和SPSS16.0统计分析显示,位点Rp-11、Rp-12、Rp-19对3个年龄段蛤仔的等位基因数差异极显著(P<0.01);位点Rp-20、Rp-24、Rp-27、Rp-30对其差异显著(P<0.05);剩余7个位点表现为差异不显著(P>0.05)。在平均水平上,每位点等位基因数目Na为4.3095,有效等位基因数目Ne为2.3729,多态位点百分数P(%)为14。观察杂合度和期望杂合度都比较高,观察杂合度平均为Ho=0.2335,期望杂合度平均为He=0.5140。而且,Ne和He随年龄的变化表现出Age2>Age3>Age1的趋势。各年龄段蛤仔——Age1、Age2、Age3的平均观察杂合度(Ho)和平均期望杂合度(He)分别为0.2357、0.2546、0.2159和0.4951、0.5286、0.5184。Age2的遗传多样性指数高于Age1及Age3,遗传分化相对较低。其中,Age1与Age3蛤仔遗传距离最小,D为0.0195,即变异很小;而Age1与Age2遗传距离较大,D为0.0437,变化范围不大(0.0195—0.0437)。从遗传一致度的数值上看了3个年龄段蛤仔的遗传相似程度很大,平均为0.9655。Age1与Age3遗传相似程度高达0.9807,而Age1与Age2相似程度较小为0.9572。说明不同年龄段蛤仔相似程度非常高。根据不同年龄段蛤仔的遗传距离,采用UPGMA平均聚类方法对其进行聚类可知,Age3与Age1蛤仔间遗传距离较小,与Age2蛤仔差异较大。通过对等位基因频率进行卡方检验发现,随着年龄结构的变化,部分基因基因频率减小;同时随着年龄的增长,有部分等位基因得到了纯化。大连群体蛤仔总的遗传分化较低,其遗传分化指数Fst为0.0248(Fst<0.05),遗传分化系数为0.02,说明总的遗传变异中有2%来自于不同年龄段的蛤仔之间。遗传距离和遗传一致度均值分别为0.035和0.9655,基因流(Nm=9.8238)相对流畅,进一步表明年龄结构对蛤仔种群内遗传分化的影响较小。     

Impact of Brown Ring Disease on the energy budget of the Manila clam Ruditapes philippinarum

Brown Ring Disease (BRD) is a bacterial disease caused by the pathogen, Vibrio tapetis. The disease induces formation of a brown deposit on inner shell of the Manila clam, Ruditapes philippinarum. Development of this disease is correlated with a decrease in the condition index of infected clams. Experiments were conduced in order to assess the effect of the development of BRD on two parameters affecting the energy balance of the clams: the clearance and the respiration rates. Experiments were performed in a physiological measurement system that allowed simultaneous measures of clearance and respiration rates. During both acclimation and measurements clams were fed with cultured T-iso and temperature was close to seasonal field temperature (10°C). Our results showed that severely diseased clams (conchiolin deposit stage, CDS ≥ 4) are subject to weight loss in comparison to uninfected ones, indicating that BRD induces a disequilibrium in the energy balance. We demonstrated a reduction of the clearance rate of severely diseased clams which led to a decrease in energy acquisition. Respiration rate showed a significant decrease with BRD symptoms, but evidence in the literature allowed us to hypothesize that energy mobilised for an immune response and lesion repair increases overall organism maintenance costs. Both factors should thus contribute to the degradation of the energy balance of diseased clams. Because effects of BRD on naturally infected clams only appears significant for CDS ≥ 4, when brown ring assumes a significant place on the inner shell, we consider that the Manila clam is tolerant of low disease levels.     

Spatial and seasonal biomarker responses in the clam Ruditapes decussatus

The clam Ruditapes decussatus is an important resource to preserve in coastal lagoon systems around the Mediterranean including the South Portugal. To assess spatial and temporal biomarker responses to contamination in the species, a multibiomarker approach was conducted using antioxidant enzymes, MFO system phase I and II; acetylcholinesterase, metallothionein (MT), δ-aminolevulinic acid dehydratase and lipid peroxidation (LPO). The condition index (CI), metals and polycyclic aromatic hydrocarbons (PAHs) were also determined. The levels of contaminants were not particularly high and the antioxidant enzymes, acetylcholinesterase (AChE), MT in the digestive gland, and δ-aminolevulinic acid dehydratase (ALAD) do not provide a suitable seasonal and spatial discrimination reversely to that regarding CYP450, glutathione-S-transferase (GST), MT in the gills, and LPO in both tissues. However, even those could vary with natural variables that may act as confounding factors. Thus, seasonal variability and natural range of biomarker responses must be carefully and accurately taken into account in ecotoxicological approaches of environmental quality assessment programmes.     

Effects of starvation on growth, survival, and body biochemical composition among different sizes of Manila clam Ruditapes philippinarum

A study was conducted to investigate the impact of starvation on different sizes of Manila clam Ruditapes philippinarum (0.66 ± 0.11, 2.12 ± 0.38, and 11.65 ± 0.84 mm in shell length, respectively) in the summer of 2008. Different size clams were starved for 7, 15, 30, 45, and 60 d, respectively, and followed by refeeding for 30 d. During the study, the water temperature ranged 26.2–28.4 °C, salinity 22–24‰, and pH 7.80–8.12. Compensatory growth occurred in the smallest size-group after 7 and 15 d of starvation, respectively. The point-of-no-return (PNR₅₀) was determined to be 18.7 d. However, no compensatory growth was noted in the medium size-group, and the PNR₅₀ for this group was 25.2 d. The complete compensatory growth was observed for the largest size-group following food depravation for 7 and 30 d, respectively. In the same group, over-compensatory growth occurred 15 d post-starvation. The PNR₅₀ for the largest size-group was 46.3 d. The survival rate of different groups decreased as the starvation time prolonged. To discuss the change in body biochemical composition of individuals in the process of starvation and refeeding, the biochemical composition of the largest group individuals at different stages was determined. There were no significant differences in moisture and ash concentrations of the largest size-group during starvation and refeeding (P > 0.05). The relative body protein content increased as the starvation period prolonged and the level returned to normal after refeeding. The lipid content of the clam at the end of starvation was significantly lower than the initial level (P < 0.05), and remained below the initial level at end of the refeeding period.     

温度和盐度突变对菲律宾蛤仔斑马蛤耗氧率和排氨率的影响

为研究温度和盐度对蛤仔新品种斑马蛤耗氧排氨的影响,以野生蛤仔为对照,实验设置15、20、25、30和35℃五个温度梯度和20、25、30、35和40五个盐度梯度,结果表明:温度和盐度对斑马蛤的耗氧率和排氨率影响显著（P < 0.05）。在温度15-35℃内,随着温度的增加,耗氧率和排氨率整体上呈增加的趋势。在20-40盐度内,耗氧率随着盐度的升高先减少后增加,排氨率随着盐度的升高先增加后减少,在盐度为30时达到最高值。在水温为15℃,盐度20-40内,斑马蛤的O:N为9.534-62.008;在盐度为35,水温在15-35℃内,斑马蛤的O:N是20.700-74.138。与野生蛤仔比较,斑马蛤的耐高温能力要强于野生蛤仔,从Q₁₀的变化反映出斑马蛤对温度的敏感性相对较弱,适应温度变化的能力比较强;斑马蛤的耐低盐和耐高盐能力强于野生蛤仔。研究结果为进一步完善蛤仔斑马蛤的人工养殖技术提供参考。     

Toxicity of Chemically Spiked Sediment to the Carpet Shell Clam Ruditapes decussatus Embryos and Larvae

The objective of this research was to assess the toxicity of sediment contaminated with cadmium, DDT, chlorpyrifos, and fluoranthene to embryos and larvae of the European clam Ruditapes decussatus, exposed to two sediment fractions, the whole sediment and elutriate. The percentages of abnormal D-shaped larvae and larval mortality have been investigated. The median effective concentration (EC50) values, reducing 50% of the percentage of D-shaped larvae, in whole sediments and elutriates were, respectively, 1.17 mg/kg and 417.1 μgl^?1 (3.71 μM) for cadmium, 1.66 mg/kg and 97.8 μgl^?1 (0.48 μM) for fluoranthene, 1.71 mg/kg and 384.8 μgl^?1 (1.08 μM) for DDT, and 0.96 mg/kg and 339.5 μgl^?1 (0.96 μM) for chlorpyrifos. The 96h-median lethal concentrations (LC50) reducing larval survival by 50% were 4.04 mg/kg 654.3 μgl^?1 (5.82 μM) for cadmium, 17.41 mg/kg 8666.6 μgl^?1 (42.84 μM) for fluoranthene, 3.93 mg/kg and 457.4 μgl^?1 (1.29 μM) for DDT, and 2.53 mg/kg and 308.06 μgl^?1 (0.87 μM) for chlorpyrifos. Based on EC₅₀ and LC₅₀ comparisons to toxicity data for other marine species, these findings suggest that the R. decussatus embryotoxicity and larvae mortality bioassay were among the most sensitive tools for sediment quality assessment.