The fisheries and growth of Ark Clams (Arcoida: Arcidae) Anadara tuberculosa in Málaga Bay, Colombian Pacific, 2005-2007

A. tuberculosa, is the most important bivalve species under exploitation in Colombia. Here, this species is found from Cabo Corrientes (Chocó) to the Ecuador border, in muddy substrates of mangrove forests. In order to determine the growth and the state of fisheries of A. tuberculosa, between December 2005 and April 2007, both, biological (in situ) and commercial studies were performed at Bahia Malaga (Colombian Pacific). The growth was estimated using the general equation of von Bertalanffy, with prior application of the methods of Bhattacharya and Powell-Wetherall. Mortality and exploitation rate were determined using the inverse model of von Bertalanffy. For the biological samplings, a total of 446 individuals of A. tuberculosa (0.64 +/- 0.13 individuals/m2) and 53 individuals (0.05 +/- 0.049 individuals/m2) of Anadara similis were collected. 79% of the catch was below 51mm. In the commercial samplings, 836 individuals of A. tuberculosa (size range: 31.1-92.2mm) were measured, but no A. similis samples were available for this. Recruitment of A. tuberculosa was higher during March, May, July and November. According to the data, A. tuberculosa might be reproducing during December, February, April and August. The data gathered with the biological samples were more reliable on explaining the growth of A. tuberculosa (K=0.332 per year, L(infinity)=88.256mm, t0=0.0556 years) than the one taken from market samples (K=0.256 per year, L(infinity)=89.77mm, t0=0733 years). The high exploitation rate (77%), the low density and the high mortality suggest that A. tuberculosa is in overexploitation state in Bahia Malaga and management strategies are urgently required.     

The red tide event in El Salvador, August 2001-January 2002

A red tide event occurred in El Salvador from August 2001 to January 2002. National health authorities usually measured toxin levels in Ostrea iridescens, however other species were analyzed during this microalgae bloom: Anadara similis, Anadara tuberculosa and Modiolus sp. El Salvador authorities consider 400 mouse units/100 g the highest value that is safe for human health. During this period toxin levels in 0. iridescens and Modiolus sp. increased from values under 400 to 3977 and 15,468 mouse units/100 g, respectively. Persistent and higher levels were recorded in oyster and mussel banks on the west part of the country. The Ministry of Health and Social Assistance treated 41 slight to moderate intoxications associated to bivalve mollusks consumption.     

A matter of size: the population structure of the smallest known living shark,Etmopterus perryi (Springer & Burgess, 1985), from deep waters off the Colombian Caribbean coast

The dwarf lanternshark (Etmopterus perryi) is the smallest known described shark, and practically no information has been available on this species since first described in the mid-1980s. Therefore, the aim of this work is to describe, for the first time, the population structure regarding dwarf lanternshark in the Colombian Caribbean Sea. During deep-water research surveys conducted along the Colombian Caribbean coast, 87 stations were sampled using the swept area method. A total of 153 dwarf lanternshark individuals were caught in depths ranging from 230 to 530 m. This information was used to describe the size structures, morphological measurements including length-at-weight relationship, length at maturity in females and the spatial distribution of mean length and biomass of the species. The lengths of individuals ranged from 78.02 to 289.00 mm total length (TL), which is a new record of maximum length for this species. The spatial distribution of mean lengths and biomass distributions show high abundances and high relative mean lengths in the northeast area off Santa Marta and the area northwest of Riohacha. The mean biomass density in the whole prospected area was 5.52 kg km⁻². Length at 50% maturity in females was estimated in 203 mm TL (95% C.I. : 190–214 mm). Deep-water elasmobranch species, such as the dwarf lantern shark, are expected to show extremely low resilience to fishing exploitation, even when they are not targeted by commercial fishing. Therefore, the information reported in this study can serve as a baseline upon which management measurements can be proposed for the conservation of this shark species.     

Damage to different motor units from active lengthening of the medial gastrocnemius muscle of the cat.

Slow-twitch motor units in the medial gastrocnemius muscle of the anesthetized cat were found to have an average optimum length for active tension that was 0.8 +/- 0.5 (SE) mm longer than the whole muscle optimum. For fast-twitch units (time to peak < 50 ms), the average optimum was 1.3 +/- 0.3 mm shorter than the whole muscle optimum. After the muscle had been subjected to 10 stretches while maximally activated, beginning at the whole muscle optimum length, the optimum lengths of the 27 fast-twitch motor units shifted significantly further in the direction of longer muscle lengths (mean 4.3 +/- 0.3 mm) than for the eight slow-twitch units (2.1 +/- 0.4 mm). A shift in the muscle's length-tension relation was interpreted as being due to sarcomere disruption. Statistical analysis showed that a motor unit's optimum length for a contraction, relative to the whole muscle optimum, was a better indicator of the unit's susceptibility to damage from active lengthenings than was motor unit type.     

Population ecology and fishery of Cittarium pica (Gastropoda: Trochidae) on the Caribbean coast of Costa Rica

The West Indian Topshell Cittarium pica is artisanally collected on rocky shores along the Caribbean Coast of Costa Rica. There are neither data on the state of its exploitation nor exist any regulation of the fishery From October 2000 to March 2001, the population dynamics of this species were studied at an unexploited and two exploited sites to determine the present impact of the fishery on the resource. Average population density with 14 ind./m2 about three times higher at the unexploited than at the exploited sites. Length-frequency histograms showed a strong shift towards smaller specimens at the exploited sites, which is also reflected in significantly higher rates of total mortality (Z = 4.05 and 4.47) when compared to the unexploited site (Z = 1.47). Von Bertalanffy growth parameters were estimated as k = 0.19-0.28 (yr-1) and L infinity = 104 mm. No significant differences were found among sites. From these values a range of the growth performance index phi was computed (phi = 3.31-3.48) which lies at the lower end of the values reported for other tropical marine gastropods. The size at first maturity for both sexes combined was estimated as 29.20 +/- 1.14 mm. Exploitation rates > 0.6 for both exploited sites and a large fraction of small specimens (< 30 mm) in the catches suggest overexploitation and recruitment overfishing. Based on the estimated maximum sustainable yield we recommend regulative measures for the fishery such as a control of a minimum landing size of 40 mm and a closure of the fishery during its reproductive period (from July to November).     

Ashworthius Patriciapilittae n. sp. (Trichostrongyloidea: Haemonchinae), an abomasal nematode in Odocoileus virginianus from Costa Rica,and a new record for species of the genus in the Western Hemisphere

A species of Ashworthius is reported for the first time in the Western Hemisphere, and A. patriciapilittae n. sp. is described on the basis of specimens in white-tailed deer Odocoileus virginianus from Costa Rica. Among 8 known species, A. patriciapilittae is morphologically similar to A. tuyenquangi in red muntjac Muntjacas muntjak from northern Vietnam. The synlophe in A. patriciapilittae is composed of 26 ridges in the cervical zone and is continuous to the caudal extremity in males and females. Males are characterized by a complex dorsal ray and narrow trifurcate spicules (351-356 microm long) lacking an "eyelet." with dissimilar ventral and dorsal processes; the gubernaculum is 45-48% of the spicule length. Females have a prominent linguiform flap at the vulva and large eggs (108-142 microm long). The presence of A. patriciapilittae in Costa Rica is examined in the context of competing hypotheses for cospeciation or contemporary host-switching in cervids: either A. patriciapilittae is a component of an endemic Central and South American fauna that has diversified through coevolution of Ashworthius and cervid hosts or it has been introduced. Among haemonchines in the Western Hemisphere, specimens of A. patriciapilittae may be confused with 3 species of Haemonchus, including H. contortus, H. placei, and H. similis, that occur in both domestic and wild ruminants. Discovery of A. patriciapilittae emphasizes the continued need for survey and inventory to define the structure and distribution of parasite faunas in wild and domestic ruminants from the Nearctic and Neotropical regions.     

Relationship of density to growth and metamorphosis of caged larval sea lampreys, Petromyzon marinus Linnaeus, in Michigan streams

Larval sea lampreys, Petromyzon marinus , of the 1976 year class were studied between May 1977 and October 1981 in five Michigan streams to determine the relationship of density to growth and metamorphosis. Two cages were placed in each stream; one cage contained 25 larvae (low density group) and the other 75 larvae (high density group). Changes in body length, as an indicator of growth, were monitored in all streams from age I to V. Mean lengths ranged from 25 to 55 mm at the beginning of the study and from 102 to 158 mm at the end. Some ammocoetes attained lengths greater than 160 mm. Growth was related mainly to density; crowding affected growth from age I to metamorphosis. Mean increases of total length ranged from 90 to 128 mm among low-density groups and from 54 to 97 mm among high-density groups. Growth was typically greater in the cage with fewer lampreys in each stream. Most growth occurred from May to October when stream temperatures were highest. In two streams in which cages were not vandalized, 96% and 92% of the lampreys in the low-density groups and 68% and 52% in the high-density groups survived to age V. Metamorphosis occurred at age V in low-density groups. Five lampreys (2.4%; range, 133–145 mm long) metamorphosed among the 207 that survived until completion of the study.     

Effect of inorganic fertilizer and farmyard manure on soil physical properties, root distribution, and water-use efficiency of soybean in Vertisols of central India

A field experiment was conducted on a Vertisol for three consecutive years (1998-2000) to study the effects of combined use of inorganic fertilizer (NPK) and organic manure (farmyard manure) on soil physical properties, water-use efficiency, root growth and yield of soybean [Glycine max (L.) Merr.] in a soybean-mustard cropping system. Application of 10 Mg farmyard manure and recommended NPK (NPK+FYM) to soybean for three consecutive years improved the organic carbon content of the surface (0-15 cm) soil from an initial value of 4.4 g kg(-1) to 6.2 g kg(-1) and also increased seed yield and water-use efficiency by 103% and 76%, respectively, over the control. The surface (0-15 cm) soil of the plots receiving both farmyard manure and recommended NPK had larger mean weight diameter (0.50 mm) and a higher percentage of water stable aggregates (55%) than both the inorganically fertilized (NPK) (0.44 mm and 49%) and unfertilized control plots (0.41 mm and 45.4%). The saturated hydraulic conductivity (13.32 x 10(-6) m s(-1)) of the NPK+FYM treatment of the 0-7.5 cm depth was also significantly greater than that of the NPK (10.53 x 10(-6) m s(-1)) and control (8.61 x 10(-6) m s(-1)) treatments. The lowest bulk density (1.18 Mg m(-3)) in the 0-7.5 cm layer was recorded in NPK+FYM whereas it was highest in the control plots (1.30 Mg m(-3)). However, at sub-surface (22.5-30 cm) layer, fertilizer and manure application had little effect on bulk density and saturated hydraulic conductivity. Root length density (RLD) up to the 30 cm depth was highest in the NPK+FYM plots and it was 31.9% and 70.5% more than NPK and control plots. The RLD showed a significant and negative correlation (r=-0.88( * *)) with the penetration resistance.     

Composition, growth and conditionindex for a population of Poecilia reticulata (Pisces: Poeciliidae), in a pond in Heredia, Costa Rica

A pond population of Poecilia reticulata was studied in Santo Domingo, Heredia, Costa Rica, between September and November of 1998. The sex ratio was 1:0.49 (males:females). The mean total length was 34.43 +/- 7.26 mm for females, 23.50 +/- 2.24 mm for males and 12.27 +/- 3.41 mm for juveniles. The mean total weight was 0.69 +/- 0.48 g for females: and 0.16 +/- 0.05 g for males and 0.026 +/- 0.027 g for juveniles. The total length-weight relationship for the total population was P= 6 x 10(-5) Lt 3.3272 (r2 = 0.9613). The condition index equation was K = 25.755 e(0.004Lt) (r2 = 0.8925) for females and K = 26.767 e(0.003Lt) (r2 = 0.907) for males. The mean condition index was 31.29 +/- 0.55% for females and 28.52 +/- 0.19% for males. Both sexes reached the sexual maturity when the males and females overcame the 20.00 mm and 23.5 mm of Lt respectively.     

黄渤海鹰爪虾Trochypenaeus curvirostris(Stimpson)种群结构特征的初步研究

本文探讨了鹰爪虾黄渤海群系的种群结构特征。结果如下:1.种群体长范围、生殖群体为20—107mm;越冬群体为13—101mm。2.种群的年龄结构为3个年龄组,4个世代(0—3龄)。3.头胸甲长和体重关系W=0.002421L~(2.5173),r=+0.9961。4.雌、雄性比组成为1.35:1;性成熟的年龄一般为2龄虾。     

Growth, mortality and exploitation rate of Priacanthus arenatus (Perciformes: Priacanthidae), in the trawl fisheries of northeast Venezuela

We analyzed growth, mortality and exploitation rate of Priacanhus arenatus, captured by the shrimp trawling fishery (1989-1996), in northeastern Venezuela. The growth coefficient (K) and the asymptotic length (L8) were estimated by length-frequency data using the Battacharya method and other routines of the FISAT program. Total mortality (Z) and exploitation (E) rates were obtained by length-converted catch curve analysis, based on length-frequency data, and the Berverton and Holt's yield per recruit model, respectively. The mean growth parameters L and K were estimated as 474.7 mm and 0.69 year(-1), respectively. Mean total mortality was 4.03 and the exploitation rate range was 0.70-0.80. Results indicated that the population is overexploited.     

青杨人工林根系生物量、表面积和根长密度变化

在植物生长季节,采用钻取土芯法对秦岭北坡50年生青杨人工林根径≤2 mm和2～5 mm根系的生物量、表面积和根长密度进行测定.结果表明：在青杨人工林根系(＜5 mm)中,根径≤2 mm根系占总生物量的77.8%,2～5 mm根系仅占22.2%;根径≤2 mm根系表面积和根长密度占根系总量的97%以上,而根径2～5 mm根系不足3%.随着土层的加深,根径≤2 mm根系生物量、表面积和根长密度数量减少,根径2～5 mm根系生物量、表面积和根长密度最小值均分布在20～30 cm土层.≤2 mm根系生物量、表面积和根长密度与土壤有机质、有效氮呈极显著相关,而根径2～5 mm根系的相关性不显著.     

黄土丘陵沟壑区黄土坡面侵蚀过程及其影响因素

降雨强度、坡长、坡度是影响坡面产流产沙的重要因素。为定量分析降雨强度、坡长、坡度对黄土丘陵沟壑区安塞黄土坡面侵蚀过程的影响,本研究基于室内人工模拟降雨试验,分析2个坡长(5、10 m)、3个坡度(5°、10°、15°)、2个降雨强度(60、90 mm·h^-1)下安塞黄土坡面产流产沙规律。结果表明: 初始产流时间随坡长增加呈减小趋势,但总体变化不大;初始产流时间随降雨强度增加而减小,与60 mm·h^-1相比,90 mm·h^-1下缩短5.7～18 min;10°坡度上的径流起始时间最快。随降雨历时延长,产流率先快速增加,最终逐渐稳定在某一产流率值上下波动;产沙率在产流初期短时间内突然升高,达到最大值后减小,再逐渐达到稳定。产流率和产沙率随坡长和降雨强度的增加而增加,但随坡度变化规律不明显。随着降雨强度、坡长和坡度的增加,总产沙量相应增加。在降雨强度90 mm·h^-1时,坡长和坡度分别为10 m和15°的坡面产生了细沟,导致总侵蚀量最大(11885.66 g)。降雨强度为60 mm·h^-1时,随着坡长增加单位面积侵蚀量减小,在5～10 m坡段存在临界侵蚀坡长。坡长、坡度和降雨强度对坡面径流过程均有促进作用,降雨强度、坡长和两者之间交互作用对产流率和总侵蚀量的贡献率较大,其中,对产流率贡献最大的影响因素是降雨强度,贡献率为49.8%;坡长对总侵蚀的贡献率最大,为37.8%。     

珍稀植物蒜头果野生植株结实量及果实特征研究

该研究对云南省广南县不同分布点的野生植株大小与结实量,果实、果核性状特征,果皮与果核性状间的关系进行了分析。结果表明:(1)野生成年植株个体间结实量差异大,单株结实量从几十个至几千个,变异系数可达136.38%。结实量与冠幅有正相关关系(R=0.592,P0.01),与胸径和树高无相关关系(P0.05)。(2)扁球型果实平均纵径37.10~40.36 mm,变异系数7.28%~8.65%;平均横径41.15~45.03mm,变异系数6.44%~9.31%;平均果实重量35.77~47.29 g,变异系数18.99%~21.44%。野生蒜头果果实大小差异明显,单个果实重量差别为3.4倍。(3)果核平均纵径27.50~31.69 mm,变异系数7.13%~10.99%;平均横径30.94~34.16 mm,变异系数6.47%~9.41%;平均果核重量14.03~18.77 g,变异系数17.37%~22.68%。单个果核重量差别为3.7倍。(4)平均果皮纵向厚度4.33~4.80 mm,变异系数20.22%~26.91%;平均横向厚度5.10~5.44 mm,变异系数12.92%~20.98%;平均果皮重21.62~28.51 g,变异系数20.01%~24.12%。该研究结果表明野生蒜头果单株结实量、果实和果核大小、果皮厚等表型性状存在广泛的多样性,其资源为人工定向培育和开发利用提供了较为丰富的选择材料。     

Population dynamics and stock assessment for Octopus maya (Cephalopoda: Octopodidae) fishery in the Campeche Bank, Gulf of Mexico

The octopus (Octopus maya) is one of the most important fish resources in the Mexican Gulf of Mexico with a mean annual yield of 9000 ton, and a reasonable number of jobs created; O. maya represents 80% of the total octopus catch, followed by Octopus vulgaris. There are two artisanal fleets based on Octopus maya and a middle-size fleet that covers both species. Catch-at-length structured data from the artisanal fleets, for the 1994 season (August 1st to December 15th) were used to analyze the O. maya population dynamics and stock and to estimate the current level of exploitation. Von Bertalanffy growth parameters were: L infinity = 252 mm, mantle length; K = 1.4 year-1; oscillation parameters C = 1.0, WP = 0.6; and tz = 0.842 years. A rough estimate of natural mortality was M = 2.2, total mortality from catch curve Z = 8.77, and exploitation rate F/Z = 0.75. This last value suggests an intensive exploitation, even when yield per recruit analysis indicates both fleets may increase the minimum legal size on about 10% to increase yields. The length-based VPA also shows that the stock is being exploited under its maximum acceptable biological limit. These apparently contradictory results are explained by biological and behavioral characteristics of this species. Because most females die after reproduction, a new gross estimation of natural mortality was computed as M = 3.3. The new estimate of exploitation rate was F/Z = 0.57. This new value coincides with results from the length-VPA and the Thompson and Bell methods, the former suggesting that a reduction of 20% in fishing mortality may provide larger yields. This fishery resource is fully exploited and current management measures must be revised to sustain and probably optimize yields.     

新疆乌伦古湖拟鲤生长退算材料和方法的比较研究

研究以鳞片和微耳石为生长退算材料, 用4 种常用的鱼类生长退算方法(Dahl-Lea、Regression、Fraser-Lee 和BPH 方法)对新疆乌伦古湖拟鲤(Rutilus rutilus Linnaeus, 1758)的生长进行了退算, 比较分析了退算材料和方法对退算全长的影响, 以此确定适宜的生长退算材料和方法。结果显示, 无论采用哪种退算方法, 用微耳石退算拟鲤生长的结果均好于鳞片, 表现为退算全长更接近实测全长, 与实测体长之间的差异百分比更小。用鳞片退算时, Dahl-Lea 方法退算全长远小于实测全长, 整体差异百分比高达?26.0%, 与其他方法之间的差异也较大, 效果最差; Regression、Fraser-Lee 和BPH 三种方法退算全长与实测全长之间的差异相近, 差异百分比分别为?6.7%、7.0%和7.0%。用微耳石退算时, Dahl-Lea 方法退算全长最接近实测全长, 退算全长与实测全长之间的差异百分比最小, 总体仅为?1.9%, 效果最好; Fraser-Lee 和BPH方法各龄退算全长与实测全长之间的差异百分比相等, 在?1.4%— ?3.2%之间, 总体均为?2.6%, 效果次之; Regression 方法与Fraser-Lee 和BPH 方法之间虽然无显著差异, 但退算全长与实测全长之间的差异百分比最大, 总体为?4.5%,效果最差。       

Studies on Chironomidae in experimental recirculating stream systems. II. The growth, development and production of a spring generation of Orthocladius (Euorthodadius) calvus Pinder

SUMMARY.

• 1 Orthodadius (Euorthodadius) calvus Pinder. similar to Orthocladius (Euorthodadius) thienemanni Kieffer. colonized a new gravel substratum in two recirculating stream channels. A maximum population density of 68.621 m^-2 was attained after only 16 days. This had fallen to a negligible density by the thirty-third day.
• 2 Some recruitment occurred over most of the study period (April-May 1981) and no single sharply defined cohort was evident. There was a large range of body lengths within each instar. and considerable overlap between instars. The population density estimates for instars I and II were low compared with instars III and IV.
• 3 The relationship between instantaneous growth rate (g) and geometric mean length indicated that growth was best described by a Gompertz curve. Growth rate decreased with increasing length from a value of about 40% length day^-1 at 2 mm body length to about 5% length day^-1 at 9 mm.
• 4 Growth rates for individual larvae, kept in culture, were very variable with maximum rates close to the values determined from the field data. Mean duration of larval life was 16 days.
• 5 Estimates of production for the study period ranged from 13.5 g dry wt m^-2 (Channel III, size-frequency method) to 34.2 g dry wt m^-2 (Channel II, Allen's graphical method, values corrected for non-linear growth).
• 6 Gut contents were estimated to represent about 55% of the total weight therefore production values should be reduced by this amount.

     

南方小花蝽在不同试验空间对西花蓟马的捕食及搜寻效应

【背景】南方小花蝽是一类很有利用前景的捕食性天敌,而有关其在不同捕食空间下对我国局部地区暴发成灾的重要入侵害虫西花蓟马捕食控制效能的研究较少。【方法】在实验室条件下比较研究了南方小花蝽成虫在不同试验空间对西花蓟马成虫、若虫的捕食选择性、捕食功能反应与搜寻效应。【结果】南方小花蝽成虫对西花蓟马若虫的捕食选择性强于成虫;在相同的试验空间,南方小花蝽成虫的日均捕食量随猎物数量的增加而增大,其对西花蓟马成虫和若虫的捕食量在猎物数量为每指形管中60头时最大,分别为15.90和19.30头;而搜寻效应随猎物数量的增加而降低。在各供试条件下,捕食功能反应均符合Holling Ⅱ型方程;南方小花蝽成虫在小饲养容器中对西花蓟马若虫的瞬时攻击率最大,为1.2794;而在大饲养容器中对西花蓟马成虫的瞬时攻击率最小,仅为0.3506,其处理1头西花蓟马成虫的时间约需0.0402d,而处理1头若虫的时间仅需0.0242d。在相同的猎物数量下,南方小花蝽成虫在大饲养容器中对西花蓟马的日均捕食量均低于其在小饲养容器中对西花蓟马的日均捕食量。【结论与意义】南方小花蝽对西花蓟马有很强的捕食效能,对西花蓟马的种群消长具有一定控制作用。本研究旨在为应用南方小花蝽防治西花蓟马积累资料,同时为西花蓟马的综合治理奠定理论基础。     

Fertility, fecundity and gonadosomatic index of Poecilia reticulata (Pisces: Poeciliidae) in Heredia, Costa Rica

Between September and November of 1998, 1 432 females of Poecilia reticulata were collected in a pond in Santo Domingo, Heredia, Costa Rica. The average total length of females was 34.43 +/- 7.26 mm (range 17.80 and 51.50 mm) and the average total weight of 0.69 +/- 0.48 g (range 0.06 and 2.32 g). This species is a viviparous matrotrofic and the specimens were sexually mature. The total length-fertility relationship was F = 0.527e 0.1171Lt (r2 = 0.9404). The average fertility was 56.1 +/- 43.6 (eggs + embryos) (range 8.0 and 197.6). The total length-fecundity relationship was Fo = 0.695e(0.1076Lt (r2 = 0.9376). The average fecundity was of 49.0 +/- 36.0 (oocytes + ova) (range 7.0 and 179.0). The total length-gonadosomatic index relationship was IGS = 0.0014 e0.134 Lt (r2 = 0.8581). The average gonadosomatic index was 0.25 +/- 0.27% (range 0.02 and 1.31%).     

Seagrass monitoring at Perezoso, Cahuita, Costa Rica (CARICOMP site)

The seagrass of Perezoso (Cahuita National Park, Caribbean coast of Costa Rica) was monitored using the CARICOMP protocol. Productivity (2.7 +/- 1.15 g/m2/d; n=74) was intermediate, compared to other Caribbean sites. Total biomass was intermediate to high (750-1500 g/m2) at most CARICOMP sites (Colombia, Cuba, Mexico, Puerto Rico and Venezuela) including Costa Rica (822.8 +/- 391.84 g/m2; n=32). Turnover rates were high (5.5 +/- 1.36%; n=74) compared to what was found in March and August at other sites. Shoot densities average 725 shoots/m2, in the Caribbean region, while in Costa Rica the value was higher (1184 +/- 335.5 shoots/m2). Average leaf length and width in the entire region were 14.4 cm and 10.6 mm, respectively, similar to what we found, but leaf area index average 3.4 m2 m(-2), higher than what was found in Costa Rica (0.92 m2 m(-2)). At Cahuita, seagrass productivity was significantly lower in March 2005 compared with the previous six years, and biomass has decreased with time. Seagrass productivity and biomass are being affected by the maximum temperatures, which increased by almost 10 degrees C from 1999 to 2005, and show a high negative correlation. Turnover rate and temperature were not correlated. Recreational boating, swimming and nutrient loading from deforested lands in the coast, the upstream rivers and local pollution are potential sources of impact to the seagrass beds at Cahuita.