Marina Meadows Research Articles

조도계수를 이용한 거머리말 해초지의 조석류에 대한 수치실험

Spatial distribution of water flow generated by tidal current was investigated within a Zostera marina(seagrass) bed in Wonpo Bay. Water flow and elevation were observed during the seagrass growing season. The spatial distribution of water flow was numerically estimated using roughness coefficient. Water flow inside the seagrass meadow was compared with the observed values. Velocity in Zostera marina vegetated areas was approximately <TEX>$25{\sim}84%$</TEX> lower than that of unvegetated areas. However, flow direction was the same. Intensity of the flood tide diminished appreciably within the seagrass bed, while its pattern was also affected. It is therefore concluded that water flow is influenced by Zostera marina meadows.

Effects of filamentous algal mats on sulfide invasion in eelgrass ( Zostera marina)

The effect of filamentous algae invasion into Zostera marina meadows on water quality, sediment sulfur pools and sulfide invasion into plant tissues was studied experimentally. Sulfide invasion was assessed through analysis of sulfur isotopic composition ( δ 34S) and total sulfur (TS) concentrations in plant tissues. The algal mats (5 and 10 cm thickness) depleted oxygen in the mats and increased the pools of sulfides in the sediments. Plants exposed to algal mats had δ 34S signals closer to the δ 34S of sediment sulfide, whereas plants with no mats present had δ 34S signals closer to the δ 34S of seawater sulfate, indicating a higher sulfide invasion in plants exposed to algal mats. The δ 34S varied between the plant tissues with the leaves having more positive δ 34S signals than roots and rhizomes, indicating that sulfide was invading into the roots and moved to the other tissues through the lacunae. TS concentrations were higher in plants exposed to algal mats suggesting that sulfur derived from sediment sulfide accumulated in the plants. F sulfide showed that up to 50% of the sulfides in the plants were derived from sedimentary sulfides. The combined effect of water column anoxia in the lower parts of the meadow and high sulfide invasion into the plants lead to significantly reduced growth rates after 3 weeks and the below-ground tissues showed signs of degradation suggesting that algal mats invasion in to Zostera marina meadows can result in seagrass decline.

Habitat selection and spatial segregation in three pipefish species

Habitat partitioning was investigated within a guild composed of three sympatric pipefish species, namely Syngnathus typhle, Syngnathus abaster and Nerophis ophidion. Field surveys of patterns of pipefish abundance among different seagrass habitats (each dominated by a different seagrass species) were combined with laboratory studies on habitat choice and microhabitat use in the three species. Results showed that S. typhle and N. ophidion occurred with higher abundance in the Cymodocea nodosa meadow, which is characterised by longer leaves and intermediate shoot density compared to the Zostera marina and Nanozostera noltii habitats. By contrast, S. abaster showed higher abundance in the Z. marina meadow than in the other meadows. Males of N. ophidion also showed significant habitat choice in behavioural tests, preferring long over short seagrass leaves, whereas in the other species habitat choice experiments did not show any significant results. In terms of microhabitat use, the three species tended to segregate along the vertical axis, with S. abaster spending significantly more time near the bottom, while N. ophidion and S. typhle preferred to use the intermediate and the top portion of the artificial seagrass. Results are discussed in the light of the current knowledge on habitat partitioning within fish guilds, especially in relation to vegetated aquatic systems.

The Brachyura (Decapoda) community of Zostera marina meadows in the coastal area of the southern Black Sea (Sinop Peninsula, Turkey)

[The brachyuran (Decapoda) taxocoenosis of a shallow meadow of Zostera marina was studied in a coastal area of the Sinop Peninsula (southern Black Sea, Turkey). Specimens were collected monthly between February 2002 and January 2003 with a beam trawl at depths of 5-20 m during benthic surveys carried out off the Sinop coast. A total of 3206 individuals belonging to 9 species was collected. The structure of the taxocoenosis along the year is dominated by portunid crabs; among these, Liocarcinus vernalis (Risso, 1816) is the most dominant species (36.87%). The largest Brachyura community in the Zostera marina beds was recorded in the summer months (June and July). La taxocenose de crabes (Decapoda) d'un herbier peu profond a Zostera marina a ete etudiee dans une region cotiere de la peninsule de Sinop (mer Noire meridionale, Turquie). Les specimens ont ete collectees chaque mois, entre fevrier 2002 et janvier 2003 a l'aide d'un chalut a perche a des profondeurs de 5 a 20 m au cours des campagnes benthiques menees au large de la cote de Sinop. Un total de 3206 individus appartenant a 9 especes a ete collecte. La structure de la taxocenose tout au long de l'annee est dominee par les crabes Portunidae; parmi ceux-ci, Liocarcinus vernalis (Risso, 1816) est l'espece dominante (36,87%). La communaute de brachyoures la plus dense dans les lits de Zostera marina a ete observee au cours des mois d'ete (juin et juillet)., The brachyuran (Decapoda) taxocoenosis of a shallow meadow of Zostera marina was studied in a coastal area of the Sinop Peninsula (southern Black Sea, Turkey). Specimens were collected monthly between February 2002 and January 2003 with a beam trawl at depths of 5-20 m during benthic surveys carried out off the Sinop coast. A total of 3206 individuals belonging to 9 species was collected. The structure of the taxocoenosis along the year is dominated by portunid crabs; among these, Liocarcinus vernalis (Risso, 1816) is the most dominant species (36.87%). The largest Brachyura community in the Zostera marina beds was recorded in the summer months (June and July). La taxocenose de crabes (Decapoda) d'un herbier peu profond a Zostera marina a ete etudiee dans une region cotiere de la peninsule de Sinop (mer Noire meridionale, Turquie). Les specimens ont ete collectees chaque mois, entre fevrier 2002 et janvier 2003 a l'aide d'un chalut a perche a des profondeurs de 5 a 20 m au cours des campagnes benthiques menees au large de la cote de Sinop. Un total de 3206 individus appartenant a 9 especes a ete collecte. La structure de la taxocenose tout au long de l'annee est dominee par les crabes Portunidae; parmi ceux-ci, Liocarcinus vernalis (Risso, 1816) est l'espece dominante (36,87%). La communaute de brachyoures la plus dense dans les lits de Zostera marina a ete observee au cours des mois d'ete (juin et juillet).]

Biogeochemical implications for phosphorus cycling in sandy and muddy rhizosphere sediments of Zostera marina meadows (Denmark)

To date, few studies have investigated the implications of sediment biogeochemical con- ditions on differences in sediment phosphorus (P) pools and P availability in sandy (low-P) and muddy (high-P) siliclastic seagrass sediments. To determine the role of seagrass activity on seasonal changes in sedimentary P, we investigated the solid-phase P pools in seagrass Zostera marina sedi- ments in a Danish fjord. During the Z. marina growth season sediments were fractionated by sequen- tial extractions into 3 (and once into 5) chemically defined groups: loosely adsorbed inorganic P, inor- ganic P bound to oxidized metals (primarily Fe-bound), P adsorbed to clay minerals, Al and humic acids, Ca-bound P, and refractory organic P. Fe-bound P accounted for about 30% of total P in the muddy sediments, whereas this pool was small in the sandy sediment ( 80%). The Fe-bound P at the muddy site showed seasonal variations with lower pools during late summer, and it was always lower in the vegetated sediment, except dur- ing maximum biomass in July, where Fe-bound P was higher in the deep rhizosphere sediments. The seasonal variation was less at the sandy site, and there was little difference between unvegetated and vegetated sites, suggesting that the vegetation had a limited effect on the sedimentary P pools. How- ever, the presence of vegetation increased the availability of P in the water column at both types of site, as P was released across the sediment-water interface at the vegetated sites compared with an uptake during most of the sampling period at the unvegetated sites, although the fluxes were low and could only account for a minor fraction (<10%) of the seasonal changes in the sedimentary P pools. Estimates of P incorporation in seagrass biomass showed that the seasonal variation in sedimentary P pools were more than sufficient to support the P demand. We hypothesize that the higher P contents in seagrass tissues and the larger biomass at the muddy site are due to high P availability from the redox-sensitive Fe-bound and organic P pools at this site, whereas P may be a limiting factor for growth at the sandy site, where the mobility of P is lower due to binding in the Ca fraction.

An economical non-destructive method for estimating eelgrass, Zostera marina (Potamogetonaceae) leaf growth rates: formal development and use in northwestern Baja California

Seagrass beds provide much of the primary production in estuaries; host many fishes and fish larvae, and abate erosion. The present study presents original analytical methods for estimating mean leaf-growth rates of eelgrass (Zostera marina). The method was calibrated by using data collected in a Z. marina meadow at Punta Banda estuary in Baja California, Mexico. The analytical assessments were based on measurements of leaf length and standard regression procedures. We present a detailed explanation of the formal procedures involved in the derivation of these analytical methods. The measured daily leaf-growth rate was 10.9 mm d(-1) leaf(-1). The corresponding value projected by our method was 10.2 mm d(-1) leaf(-). The associated standard errors were of 0.53 and 0.56 mm d(-1) leaf(-1) respectively. The method was validated by projecting leaf-growth rates from an independent data set, which gave consistent results. The use of the method to obtain the mean leaf growth rate of a transplanted plot is also illustrated. Comparison of our leaf-growth data with previously reported assessments show the significant forcing of sea-surface temperature on eelgrass leaf dynamics. The formal constructs provided here are of general scope and can be applied to equivalent eelgrass data sets in a straightforward manner.

Genetic structure of eelgrass Zostera marina meadows in an embayment with restricted water flow

Genetic structure of the seagrass Zostera marina in a coastal lagoon with restricted water flow, and with heterogeneous water residence times and oceanographic characteristics, was assessed using 8 polymorphic microsatellite loci. Analyses of genetic differentiation (θ) and Bayesian clustering suggested that the Z. marina population in San Quintin Bay (SQB) is genetically substructured, with at least 4 genetically different groups: (1) West Head, (2) Mouth, (3) East Arm, and (4) East Head. The greatest θ value was observed between the most distant sites (θ = 0.095). The lowest values were found among sites closest to the mouth of the coastal lagoon (θ = 0.000 to 0.009). The maximum likelihood approach showed that the sites at the mouth have a mixed pattern of gene flow without a unidirectional pattern. In contrast, there was a clear pattern of asymmetrical gene flow from the mouth towards the West Head. These results suggested that the restriction of water flow at the heads, current pattern, and the distance between sites can reduce genetic flow and promote genetic differences within Z. marina meadows in small water embayments such as SQB. Though the population is genetically substructured and a 14% decline in cover has been detected, this study did not show evidence of a recent genetic bottleneck. In contrast, mouth sites have experienced a recent expansion in their population size, and also perhaps a recent influx of rare alleles from genetically distinct immigrants.

Comparison of Zostera marina and maerl community metabolism

The photosynthetic and repiratory metabolism of Zostera marina and maerl communities was compared, in the same area of the Bay of Brest in March–April, using benthic chambers. P– E curves for both oxygen and carbon were established for bottom irradiances between 0 and 525 μmol m −2 s −1. An exponential function was fitted to calculate daily production. Community metabolic quotients did not differ for maerl and seagrass beds. Community photosynthetic quotients were significantly higher (1.19) whereas community respiratory quotients were lower (0.70) than 1. Maerl and seagrass bed P– E curves mainly differed by the minimum saturating irradiance ( E k). Net community production was estimated to 26.8 mmol C m −2 d −1 for Z. marina meadows and 8.6 mmol C m −2 d −1 for maerl beds. The two communities can, therefore, be considered as autotrophic during the March–April period. Community respiration did not differ between Z. marina meadows and maerl beds, with an average value of 53.8 mmol C m −2 d −1 during a day. In similar environmental conditions, the production of maerl beds corresponds to approximately one third that of seagrass meadows. The maerl communities, therefore, form productive ecosystems, relevant to temperate coastal ecosystems functioning.

Seasonal and spatial variation in the organic carbon and nitrogen concentration and their stable isotopic composition in Zostera marina (Denmark)

The spatial and seasonal variation in the concentration and stable isotopic composition of carbon and nitrogen was studied in Zostera marina (eelgrass) meadows in Roskilde Fjord and Oresund, Denmark. Organic carbon (C org) and nitrogen (Norg) concentrations in new tissues (leaf, rhizome, roots) ranged from 11 to 40 mmol g 21 C and 0.4 to 3.6 mmol g 21 N, whereas their stable isotopic composition in new leaf ranged from 222‰ to 28‰ ( d 13 Cleaf) and 17‰ to 120‰ ( d 15 Nleaf). The d 13 Cleaf correlated weakly (r 2 ; 0.3) with the d 13 C of total dissolved inorganic carbon (DIC) in the surface waters (d 13 CDIC range: 25.4‰ to 20.3‰). The temporal change was more pronounced than the spatial change for Norg, the atomic C : N ratio, and d 13 Cleaf but was much smaller for Corg and d 15 Nleaf. Eelgrass plants had higher Norg concentrations, lower C : N ratios, and more depleted d 13 Cleaf in winter than summer, reflecting the temporal imbalance between inorganic nutrient supply and plant demand imposed by seasonality in the growth rate. The apparent carbon isotope enrichment factor of new leaf relative to external DIC («eelgrass-DIC range: 212.1‰ to 25.3‰) indicated that eelgrass must be reliant on direct HCO uptake, especially during the period of high 2 3 growth rate (May to September). The steep spatial gradient of d 15

Dissolved and particulate organic matter in contrasting Zostera marina (eelgrass) sediments

The influence of seagrass Zostera marina on sediment characteristics was examined in two contrasting sediments, one organic-rich and one organic-poor. The presence of plants leads to reduced sediment redox potential in both sediment types compared to bare sediment with the largest effects in the organic-poor sediment. Z. marina stimulated the sulfate reduction rates in organic-poor sediment with ∼50% and higher pools of dissolved organic carbon (DOC) were found. In contrast, sulfate reduction rates were lower in vegetated compared to bare sites in the organic-rich sediment. Despite a low contribution of dissolved carbohydrate (DCHO) to the DOC pool (<5%), the seagrass vegetation was responsible for an increase of ∼50% in DCHO pools with a peak in the root zone suggesting that Z. marina supplied DCHO to the pore waters. The Z. marina meadows also enhanced the contribution of particulate carbohydrate (PCHO) to sedimentary particulate organic carbon (POC) pools by 6–14% compared to bare sediment. Although the PCHO pools were higher in organic-rich than organic-poor sediments, the analyses of carbohydrate composition revealed that three groups of neutral sugars including glucose, galactose and mannose+xylose were the major compounds of PCHO and contributed with >60% to sedimentary carbohydrate pools at both sites. Only glucose showed depletion with depth in the vegetated sediments, whereas the percentage of ribose and rhamnose increased indicating a selective degradation of labile carbohydrates in the meadows. Galactose and mannose+xylose appeared to represent a refractory part of carbohydrate that remained after degradation of the more labile components. The sugar content was rather constant with depth at the bare organic-rich sediment indicating that only recalcitrant carbohydrate pools were buried. There was less difference in the PCHO composition profiles between vegetated and bare organic-poor sediments.

Improved leaf area index based biomass estimations for Zostera marina L.

The application of special scanning technologies in plant population studies makes it now possible to offer reliable indirect estimations of Leaf Area Index (LAI). This has stimulated the adaptation of related biomass assessment methods and has provided a way to simplify tedious laboratory procedures whilst avoiding destructive sampling. Particularly, aboveground biomass for Zostera marina L. has been expressed depending linearly on Leaf Area Index. Nevertheless, we demonstrate that this approach produces biased estimations. It is also shown that expressing leaf dry weight by means of an allometric function of length and width can eliminate bias. Furthermore, the dominant term of the associated power series expansion becomes the aforementioned linear representation in terms of Leaf Area Index. The consistency of the estimation methods derived from the allometric model was tested using data from a Z. marina meadow. Consequently, the improved method is expected to become a valuable tool for the reduction of the uncertainty associated with the estimation of above‐ground biomass through the use of Leaf Area Index.

Improved leaf area index based biomass estimations for Zostera marina L.

The application of special scanning technologies in plant population studies makes it now possible to offer reliable indirect estimations of Leaf Area Index (LAI). This has stimulated the adaptation of related biomass assessment methods and has provided a way to simplify tedious laboratory procedures whilst avoiding destructive sampling. Particularly, above-ground biomass for Zostera marina L. has been expressed depending linearly on Leaf Area Index. Nevertheless, we demonstrate that this approach produces biased estimations. It is also shown that expressing leaf dry weight by means of an allometric function of length and width can eliminate bias. Furthermore, the dominant term of the associated power series expansion becomes the aforementioned linear representation in terms of Leaf Area Index. The consistency of the estimation methods derived from the allometric model was tested using data from a Z. marina meadow. Consequently, the improved method is expected to become a valuable tool for the reduction of the uncertainty associated with the estimation of above-ground biomass through the use of Leaf Area Index.

Limited coupling of macrophyte production and bacterial carbon cycling in the sediments of Zostera spp. meadows

Two approaches were used to study coupling between seagrass production and bacter- ial processes in the rhizosphere. In the first approach, stable carbon-isotope ratios of bacteria, sedi- ment organic matter and plants were determined to infer sources of organic carbon used by bacteria in the sediments of 4 European Zostera marina and 2 Z. noltii meadows. Bacterial isotope ratios were derived from bacteria-specific polar lipid-derived fatty acids (PLFA), mainly methyl-branched i15:0 and a15:0. Bacterial δ 13 C ratios in the sediment from both vegetated and unvegetated sites were mostly similar and did not resemble Z. marina ratios, suggesting that seagrass material was of limited importance as a bacterial carbon source. Bacterial ratios were in most cases similar to benthic macro- algae and did correlate well with ratios of diatom biomarkers. Sediment organic matter inside the meadows had δ 13 C ratios similar to those of nearby unvegetated sites, and ratios were clearly differ- ent from the material produced by seagrasses, indicating that little seagrass material accumulated. Results from the 2 Z. noltii sites were less conclusive, as there was no clear difference in δ 13 C ratios between the potential source materials. In addition, bacterial δ 13 C ratios were highly variable at one Z. noltii site. In the second approach, cultured Z. marina was labeled with 13 C-bicarbonate to study the short-term transfer of label from plants to bacteria in the rhizosphere. However, no label was detected in bacterial PLFA after 20 h of incubation. In conclusion, a close coupling between macro- phyte production and bacterial carbon cycling could not be detected in the sediment of Z. marina meadows, and benthic production by algae was probably the main carbon source for bacterial growth.

Are seagrass growth and survival constrained by the reducing conditions of the sediment?

A literature review of the effects of the reducing conditions of the sediment on seagrass metabolism, growth and survival, and of the morphological and physiological adaptations that seagrasses show to cope with sediment anoxia is presented and major gaps in knowledge are identified. The hypothesis that sediment anoxia controls the survival of seagrasses was tested experimentally by increasing the oxygen demand of the sediment with the addition of sucrose. Experiments were performed in a tropical (Southeast Asia) multispecific seagrass meadow, a Mediterranean Cymodocea nodosa meadow, and a temperate Zostera marina meadow. Sulfide levels in pore water and vertical redox profiles were used to characterise the effects of the sucrose additions on the sediment, while plant responses were quantified through the changes in shoot density and leaf growth. Sulfide levels in pore water increased and sediment redox potential decreased after the addition of sucrose to the sediment of different seagrass meadows. The effect of the addition of sucrose to the sediment of seagrasses was species-specific. Leaf growth was reduced and shoot mortality increased in some of the tropical species (e.g., Thalassia hemprichii), but not in others. Neither mortality nor leaf growth of the Mediterranean species C. nodosa was affected by sucrose additions, and only leaf growth was reduced two months after the addition of sucrose in Z. marina. Our results suggest that increased sediment anoxia might be a factor promoting growth inhibition and mortality in seagrasses, although strong differences have been found among different species and environments.

Alterations in the structure of the macrobenthic community at Bahía Falsa, Mexico, related to the culture of Crassostrea gigas

The changes in macrobenthic communities in Bahía Falsa, Baja California, induced by an oyster culture are evaluated, in order to understand the actual status of the ecological system and provide the basis for a future management in the area. The study was conducted between 1987 and 1990 in a 15-point grid covering the lagoon. Data obtained were processed for community ordination by a principal components method, and a biological value index was also obtained. The results indicate that the community, in general, and the Zostera marina meadow, in particular, do not show symptoms of alteration and that the annelid community composition is similar to that reported 3 and 21 years ago. Only the area directly associated with the culture installations shows marked eutrophication and a community characteristic of organically polluted areas.

Comparisons of fauna among natural and transplanted eelgrass Zostera marIna meadows: criteria for mitigation

Numencal abundance, species composition and size of fish and shrimp were compared among (1) unvegetated, (2) transplanted (3) recently seed-colonized and (4) matule, natural eelgrass habitats to determine the equivalence of transplanted eelgrass beds to their natural counterparts In general, fish and shrimp were most abundant in mature natulal eelgrass habitats and least abundant in unvegetated habitats We developed a vector-graphical analysls that shows eplbenthic faunal abundance to be closely coupled with eelgrass bed development In an area where transplants performed poorly, the faunal component had a different composition and significantly lower numerical abundance In companson to natural beds Fauna1 abundance and composition in a 1 9-yr-old transplanted bed and a 6-mo-old seed-developed bed were indistinguishable from mature natural eelgrass beds Our data Indicate that recruitment of fish and shrimp to eelglass habitats established through transplantahon can occur in time, though not as rapidly as with naturally-seeded beds Area1 shoot density may serve as an inexpensive diagnostic parameter of functional equivalence for most resident macroeplfauna Abundance data need to be interpreted through functional mechanisms such as predation which act to produce the observed abundances in older to separate habitat function from dysfunchon Restored seagrass habitats have the potential to make substantial contributions to fish and shrimp production provided the habitats persist

Exposure, vegetation and sediment as primary factors for mobile epibenthic faunal community structure and production in shallow marine soft bottom areas

Mobile epibenthic fauna was quantitatively assessed in 22 shallow-water (0–1.5 m), soft-bottom areas on the Swedish west coast. Relationships between faunal structure, density, biomass and annual production on the one hand, and physical factors such as exposure, vegetation cover and sediment structure on the other, were investigated. The areas were grouped according to their physical characteristics into 4 categories: exposed, semi-exposed and sheltered with little or no vegetation and vegetated. Species number, density, biomass and annual production were shown to be significantly higher in vegetated areas ( Zostera marina L.) than in mainly unvegetated ones. The epibenthic production in Z. marina meadows was 6 g (AFDW)-m −2·y −1. Species composition was also different and Carcinus maenas L. was the only dominant species occurring in both vegetated and unvegetated areas. In all unvegetated areas the number and composition of species were about the same, regardless of exposure, whereas biomass and production varied with the degree of exposure. Highest production (3 to 5.5 g (AFDW)-m −2·y −1) in these areas was found in semi-exposed areas. In exposed and sheltered areas production was 1.1 to 3.3 g and 0.6 to 1.7 g (AFDW)-m −2·y −1, respectively. Degree of exposure, vegetation cover and sediment structure are suggested as the primary factors affecting the composition and quantity of mobile epibenthic fauna in the investigated areas. Biotic factors e.g. predation and competition are generally considered to be subordinate to these physical factors.

Epiphyte-Grazer Relationships in Seagrass Meadows: Consequences for Seagrass Growth and Production

Studies of seagrass meadows have shown that the production of algal epiphytes attached to seagrass blades approaches 20% of the seagrass production and that epiphytes are more important as food for associated fauna than are the more refractory seagrass blades. Since epiphytes may compete with seagrasses for light and water column nutrients, excessive epiphytic fouling could have serious consequences for seagrass growth. We summarize much of the literature on epiphytegrazer relationships in seagrass meadows within the context of seagrass growth and production. We also provide insights from mathematical modeling simulations of these relationships for a Chesapeake BayZostera marina meadow. Finally we focus on future research needs for more completely understanding the influences that epiphyte grazers have on seagrass production.

Abundance, biomass and production of mobile epibenthic fauna inZostera marina(L.) meadows, western Sweden

Abstract Mobile epifauna was sampled quantitatively with a drop-trap in three Zostera marina (L.) meadows on the west coast of Sweden, 1980–82. Of 20 species recorded, 10 were crustaceans (mostly shrimps) and 10 fishes (gobies, pipe-fishes and sticklebacks). Crustaceans dominated in abundance and biomass throughout the season and in all areas. Total abundance and biomass varied between 20 and 160 ind. · m−2 and 1 and 12 g (ash-free dry weight, AFDW) · m−2. The shrimp Palaemon adspersus (Rathke) and the shore crab Carcinus maenas (L.) contributed 65 to 90% of the mean seasonal biomass in the three areas, and the dynamics of these two species are described in this paper. Production of the 6–8 dominant species during eight months (May–December) of investigation varied between 2.5 and 6.0 g AFDW · m−2. No relation was found between the biomass of fauna and standing stock of Zostera, but patches of Fucus vesiculosus in the Zostera were shown to play an important role for some species.

Genetic differentiation in populations of two Palaemon prawn species at the Atlantic east coast: does gene flow prevent local adaptation?

Two Palaemon prawn species, P. adspersus Rathke and P. squilla (L.), occur along the European Atlantic coast. In areas heavily affected by tides (Netherlands and France), one species, P. squilla, inhabits the intertidal zone, and P. adspersus is found subtidally in the Zostera marina meadows. In areas with small tidal ranges (Sweden) both species occur in the Z. marina zone, and here the body size of P. squilla is reduced, something that in turn reduces reproductive output in this species. Is adaptive improvement in non-tidal P. squilla populations prevented by too extensive gene flow from tidal areas? To wanswer this, genetic differentiation was studied by horizontal starch gel electrophoresis. Each of the two species was sampled at five sites along the European Atlantic coast. Twenty-two enzymes representing 25 loci were scored. Significant genetic heterogeneity between sites was found in both species. Thus the extensive gene flow hypothesis was not supported by the results, and non-tidal populations ought to have the possibility to adapt to local conditions.