Animal-sediment relations in Cape Cod Bay,Massachusetts I. A transect study

Benthic macrofauna and bottom sediments were sampled at 7 stations along a 24 km long onshore-offshore transect ranging in depth from 12 to 42 m in Cape Cod Bay, Massachusetts, USA. High faunal density, biomass and species diversity were recorded at stations densely populated by tubicolous polychaetes. These tube mats bind and stabilize the substratum, providing solid surfaces for attachment of epizoans. Three suspension-feeding species, Euchone incolor (polychaete), Thyasira gouldi (bivalve) and Aeginina longicornis (amphipod), co-occur with deposit-feeding species on muds resuspended by tidal currents. Hydrographic profiles of temperature, salinity and turbidity indicate that resuspended silt-clay particles are entrapped in dense water below the summer thermocline, which persists from mid-April to mid-October. The zone of intersection of the thermocline with the sea floor in about 22 m of water defines a major biofacies-lithofacies transition. This ecotone is characterized by high faunal density, biomass, and species diversity. Benthic populations of macrofauna from Cape Cod Bay are larger than those from Buzzards Bay, Massachusetts, and have a widely different taxonomic and trophic composition.Contribution No. 235 of the Systematics-Ecology Program, Marine Biological Laboratory, Woods Hole, Massachusetts, USA.     

Succession and growth limitation of phytoplankton in the Gulf of Bothnia (Baltic Sea)

A one year field study of four stations in the Gulf of Bothnia during 1991 showed that the biomass was ca. two times, and primary productivity ca. four times, lower in the north (Bothnian Bay) than in the south (Bothnian Sea) during the summer. Nutrient addition experiments indicated phosphorus limitation of phytoplankton in the Bothanian Bay and the coastal areas in the northern Bothnian Sea, but nitrogen limitation in the open Bothanian Sea. A positive correlation between the phosphate concentration and the production/biomass ratio of phytoplankton was demonstrated, which partly explained the differences in the specific growth rate of the phytoplankton during the summer. Differences in photosynthetic active radiation between the stations also showed a covariation with the primary productivity. The relative importance of nutrient or light limitation for photosynthetic carbon fixation could not, however, the conclusively determined from this study. Marked differences in phytoplankton species composition from north to south were also observed. The number of dominating species was higher in the Bothnian Sea than in the Bothnian Bay. The distribution of some species could be explained as due to nutrient availability (e.g. Nodularia spumigena, Aphanizomenon sp.), while salinity probably limits the distribution of some limnic as well as marine species. The potentially toxic phytoplankton N. spumigena, Dinophysis acuminata and Chrysochromulina spp. were common in the Bothnian Sea but not in the Bothnian Bay. The pico- and nanoplankton biomass during late summer was higher than previously reported due to a revised carbon/volume ratio.     

Spatio-temporal changes in diversity and community structure of planktonic copepods in Sagami Bay, Japan

Seasonal changes in diversity and community structure of planktonic copepods at a shelf site in Sagami Bay, Japan was studied in relation to cross-shelf interaction of species components. Seasonal mesozooplankton samples were collected from the shelf station (St. M) of the north-west part of Sagami Bay from 1995 to 1997. Vertical multi-layered samples were collected near the center of Sagami Bay (St. P) in June 1996. A total 185 copepod species were identified from the two stations. We observed a clear seasonal succession in calanoid diversity and community structure at St. M from a simple shelf water community (>11 species) during spring blooming periods to highly diverse and mixed communities (ca 20–30 species) of shelf water species coupled with various Kuroshio Current species during late summer to autumn. Cluster and non-metric multidimensional scaling ordination analyses showed two distinct calanoid community groups. One group, which included samples of St. M and the surface layer of St. P, consisted of shelf water species, such as Calanus sinicus, Ctenocalanus vanus, Paracalanus spp., and Kuroshio species, such as, Canthocalanus pauper, Scolecithrix danae, etc. The other cluster was restricted to the samples collected from mid and deep layers at St. P, which consisted of meso- and bathypelagic species and Oyashio species (cold-current species, such as Neocalanus cristatus, Pseudocalanus spp., Eucalanus bungii and Metridia pacifica). In the mid and deep layers at St. P, the population of dormant copepodid stage V (CV) of Eucalanus californicus and C. sinicus were dominant. The deep CV population of C. sinicus might be ecologically discriminated from the surface and shelf water population due to their larger body length and dormant life cycle. E. californicus was also collected at the shelf site during each spring bloom period, whereas the population might descend into the mid- and deep-layers of the central bay before summer. Our results suggest that the seasonal fluctuation of community structure in the shelf water was controlled by both physical (Kuroshio Current) and biological factors, i.e., spring bloom and ontogenetic vertical migration of E. californicus. In particular, transport and diffusion processes of Kuroshio Current in Sagami Bay played a key role in controlling the shelf water calanoid community.     

Relative impacts at sites of dredged-material relocation in the coastal environment: a phylum-level meta-analysis approach

Phylum-level meta-analysis was applied to 192 samples from a variety of dredgings disposal and relocation sites around the coast of England and Wales. No consistent relationship was found between the disturbance status of macrobenthic communities within disposal sites and the nature or amount of dredgings disposed. Differences between samples within and outside disposal sites were generally smaller than differences between different sites and various patterns of impact were detected. It is concluded that dredgings disposal has two contrasting impacts on benthic communities. One, associated with organic enrichment, leads to communities dominated by annelids and nematodes. The other, associated with intense physical disturbance, favours large motile or armoured forms, such as bivalve molluscs and crustaceans. These effects may act antagonistically, and in a phylum-level meta-analysis may cancel each other out. None of the samples examined from offshore disposal sites was grossly disturbed, in terms of the proportional contribution to production from different phyla, and overall most samples ranged from moderately disturbed to undisturbed. The ecological impacts associated with the intertidal placement of material (beneficial use schemes) were comparable to those observed for the conventional sea disposal sites.     

福建北部海域浙闽沿岸流消亡期浮游植物的种类组成与分布特征

根据2009年4月在福建北部海域(24°47’17.0"~26°48’02.9"N,119°29’36.0"~120°57’13.8"E)所获浮游植物网采样品和同步观测的理化参数,并结合2007年"908专项"春季航次相应范围的调查资料,分析该海域浮游植物种类组成、分布特点、年际变化及其与环境因子的关系.本航次共记录浮游植物3个门类85种,其中硅藻75种、甲藻9种、蓝藻1种.物种组成以广温种为主(占47.06%),其次为暖水种(占36.47%),温带种仅占7.06%.调查区浮游植物丰度平均为137.89×104cells m-3,其平面分布呈现从近岸往外海、从北往南递增的态势.聚类分析显示本海区浮游植物可划分为2个群落,群落Ⅰ主要由近岸低盐种组成,仅分布于受浙闽沿岸流影响较直接的闽江口以北的近岸测站;群落Ⅱ主要为外海高盐种和广温广盐种,广泛分布于受台湾暖流影响较大的闽江口以南及三沙湾外侧水域.主成分分析(PCA)表明,对本海区浮游植物的分布起主导作用的是温度和盐度,而与营养盐的关系不密切,反映调查期间浙闽沿岸流已基本退出本海区,浮游植物的分布主要受制于台湾暖流.浮游植物丰度的平面分布格局与以往的调查结果基本一致,但其群落结构存在年际变化,"908专项"春季航次的优势种为近岸低盐种和广温广盐种,优势种突出,多样性指数低;而本次调查外海性广温种成为优势种之一,多样性指数(H’)和均匀度(J’)均较高,这可能与考察期间受东北季风强度所左右的浙闽沿岸流强弱有关.     

Zooplankton community structure across an eddy-generated upwelling band close to a tropical bay-mangrove ecosystem

Mesoscale eddies in the world’s oceans are ubiquitous and bring about episodic pulses of nutrients into the photic zone. Transient in nature, the role of eddy pumping in coastal enrichment via plankton production, and subsequent organic flux is not yet fully realised. In the context of a cyclonic cold-core eddy that propagates annually under the influence of the East India Coastal Current and enriches coastal waters in the western Bay of Bengal north of 16°N, a detailed study on zooplankton community structure along with phytoplankton composition and associated water quality was undertaken during April–May 2002 coinciding with the spring intermonsoon. Zooplankton samples were collected at 32 hydrographically different (salinity 24.5–35.6 PSU) GPS fixed locations representing bay-mangrove areas and nearshore waters (30 m) close to the River Godavari, which is one of India’s largest estuarine systems. During the study, the bay-coastal waters were typified by elevated nutrient levels (nitrate 10.73–22.04 μM), high salinity (27.98–35.52 PSU), and relatively low temperatures (30.63–31.40°C). Altogether, 95 zooplankton taxa were encountered with copepods forming the predominant population. Agglomerative Hierarchical Cluster Analysis (AHCA) and Non-metric Multidimensional Scaling (NMDS) based on Bray–Curtis similarity (PRIMER) analysis revealed appreciable alterations in zooplankton structure across bay-mangrove locations and coastal waters (Stress 0.11; ANOSIM test Global R: 0.94, P = 0.1%). Similarity Percentage (SIMPER) analysis revealed zooplankton associations through “discriminating species” for each location (Kakinada Bay, Cluster I, 27.9 ± 3.0 PSU; upwelling band, cluster II, 35.5 ± 0.2 PSU; offshore waters, cluster III, 34.2 ± 0.4 PSU; mangrove outlets, cluster IV, 32.7 ± 1.3 PSU and mangrove creeks, cluster V, 33.5 ± 0.6 PSU). The index of multivariate dispersion (IMD) illustrated high variability in zooplankton standing stock for mangrove/sea locations relative to the bay. Concurrent observations on phytoplankton revealed the importance of diatoms (r: 0.640, P ≤ 0.05). Within the eddy-generated band of upwelled water, a significant top-down control of diatoms by herbivorous zooplankton resulted in a comparative increase in abundance of dinophyceans. Based on zooplankton abundance data and species association patterns, it was possible to distinguish different zooplankton/copepod communities in accordance with mesoscale variability in physical, chemical and biological processes under tropical conditions. This was confirmed through canonical correspondence analysis (CCA) that represented coastal-offshore waters and the Bay environment in this area.     

Classification and ordination of benthic samples from Bedeque Bay,an estuary in Prince Edward Island,Canada

An attempt was made to identify the causes of the distribution of benthos within Bedeque Bay using multivariate techniques programmed for the computer. Both classification by a hierarchical cluster analysis, and ordination by principal components analysis suggested that a large proportion of the variance in the data was directly or indirectly correlated with a salinity gradient. Classification divided the species into two main groups, a in the upper half of the estuary where lower salinities and larger salinity fluctuations occurred, and group b in the lower half of the estuary with a more stable salinity regime. The group b species were further subdivided into those preferring soft mud and those preferring sandier sediments. The group a species were divided into a well-developed oyster association and various sub-groups less strongly associated with oysters. Five principal components were required to account for 50% of the variance in the data. The first axis accounted for 20% of the variance and was shown by a non-parametric test to be correlated with the salinity gradient. Axes II to V could not be interpreted, but possibly represented complex species interactions. By providing hard substrates and altering the natura of the sediment, oysters and mussels produced conditions suitable for many other species.     

Mercury bioaccumulation in estuarine food webs

We tested for unintended mercury contamination problems associated with estuarine floodplain restoration projects of the Louisiana coastal zone, USA. Barataria Bay and Breton Sound are two neighboring deltaic estuaries that were isolated by levees from the Mississippi River about 100 years ago. These estuaries recently have been reconnected to the nutrient-rich Mississippi River, starting major river diversion (input) flows in 1991 for Breton Sound and in 2004 for Barataria Bay. We collected > 2100 fish over five years from 20 stations in these estuaries to test two hypotheses about Hg bioaccumulation: (H1) Background Hg bioaccumulation in fish would be highest in low-salinity upper reaches of estuaries, and (H2) recent river inputs to these upper estuarine areas would increase Hg bioaccumulation in fish food webs. For H1, we surveyed fish Hg concentrations at several stations along a salinity gradient in Barataria Bay in 2003-2004, a time when this estuary lacked strong river inputs. Results showed that average Hg concentrations in fish communities were lowest (150 ng/g dry mass) in higher salinity areas and -2.4x higher (350 ng/g) in low-salinity oligohaline and freshwater upper reaches of the estuary. For H2, we tested for enhanced Hg bioaccumulation following diversion onset in both estuaries. Fish communities from Breton Sound that had long-term (> 10 years) diversion inputs had -1.7x higher average Hg contents of 610 ng/g Hg vs. 350 ng/g background values. Shorter-term diversion inputs over 2-3 years in upper Barataria Bay did not result in strong Hg enrichments or stable C isotope increases seen in Breton Sound, even though N and S stable-isotope values indicated strong river inputs in both estuaries. It may be that epiphyte communities on abundant submerged aquatic vegetation (SAV) are important hotspots for Hg cycling in these estuaries, and observed lesser development of these epiphyte communities in upper Barataria Bay during the first years of diversion inputs may account for the lessened Hg bioaccumulation in fish. A management consideration from this study is that river restoration projects may unintentionally fertilize SAV and epiphyte-based food webs, leading to higher Hg bioaccumulation in river-impacted floodplains and their food webs.     

Hydrography and distribution dynamics of larval and juvenile fishes in the coastal waters of the Tanshui River estuary,Taiwan, with reference to estuarine larval transport

Distribution dynamics of fish larvae and juveniles in the coastal waters of the Tanshui River, Taiwan was studied fortnightly using surface horizontal tows with a larval net in daytime during the period from early April through early June 1991. Environmental factors, including water temperature, salinity, dissolved oxygen, pH, transparency and depth at sampling stations, were also monitored. A total of 10737 fish eggs and 1387 individuals, representing 43 families and 93 species, was collected during five cruises from 12 stations in the coastal waters. Most fish were estuarine-dependent marine species. Liza macrolepis, Ambassis gymnocephalus, Terapon jarbua, Mullidae and Gobiidae were the most dominant, making up 64.7% of the total catch. Early life stages, including egg, preflexion, flexion and postflexion larvae were abundant in surface samples. However, yolk-sac larvae were absent in the surface water, probably due to an ontogenetic behavioral shift as a consequence of a change in specific weight during early development. The species composition of fish larvae and juveniles was related to the microhabitats found in the coastal waters. The physico-chemical conditions, along with ontogenetic behavior, played an important role in larval fish distribution in the coastal waters.     

辽东湾大凌河口湿地土壤微生物群落分析

土壤微生物对湿地生态系统的物质转化和能量流动具有重要作用,目前对天然湿地的微生物资源及群落结构缺少研究。应用PCR-DGGE技术研究辽东湾大凌河口湿地土壤中的微生物群落结构,并对其群落组成进行分析,结合冗余分析（RDA）方法考察环境因子对微生物群落结构的影响。共设定7个站位采集土壤样品,直接提取样品中微生物的总DNA,以巢式PCR扩增细菌16S rDNA-V3区片段,应用变性梯度凝胶电泳（DGGE）技术分离片段,研究河口区湿地土壤细菌的群落结构。结果表明：辽东湾大凌河口区土壤具有较为丰富的细菌种群,主要包含Proteobacteria、Actinobacteria和Bacteroidetes几大类门,且同一季节采集的样品在聚类分析图上聚类成簇。RDA分析表明,土壤的温度与盐度2个变量分别解释了6.5%、2.3%的土壤细菌群落结构变化,表明大凌河口区土壤的群落结构变化是多种环境因子共同作用的结果,其中温度的影响略大于盐度。     

Factors affecting macroalgal distribution in a eutrophic tropical lagoon in Taiwan

Factors affecting distribution of macroalgal periphyton were examined during a complete seasonal cycle in Tapong Bay, a eutrophic tropical lagoon in southern Taiwan. Water residence time varied from a few days to weeks. Total biomass and species richness declined with increasing residence time. However, they appeared to exhibit a unimodal seasonal pattern across all study sites, with blooms and greater richness in winter and spring and lower values in summer and fall. Nonmetric multidimensional scaling ordination of macroalgal communities reveals a clear gradual continuum of changes in species composition along the flushing gradient, suggesting the communities were primarily structured by site, and secondarily by season. The fast-flushing region was dominated by the chlorophycean genus Ulva, which was replaced by Enteromorpha intestinalis at mid-flushing levels, while the cyanobacterium Lyngbya majuscula was the dominant species in the slow-flushing region. Tissue nitrogen, but not tissue phosphorus, of these dominant species increased with increasing nutrient availability as a result of slow flushing. Our results suggest that water motion was an important selective factor for the spatial dominance of macroalgal species in Tapong Bay. This study demonstrates that species-dependent ordination is more sensitive in discriminating between sites than are species-independent measures such as total biomass and nutrient content when monitoring coastal eutrophication in the tropics. However, more-sensitive ordination provides only an early warning that a community is changing; less-sensitive measures are also required to indicate the magnitude and type of these environmental changes.Communicated by T. Ikeda, Hakodate     

Benthic polychaete assemblages and their relationship to the sediment in Port Madison,Washington

Two indices of community association and a 3 dimensional ordination of stations were used to elucidate the relationship between small-scale changes in species, composition of polychaete assemblages and changes in the physical character of the sediment, at 9 stations along a 1.5 km subtidal transect. There were no faunal or physical discontinuities that might have been used to delineate boundaries of polychaete communities, except at a very shallow station where the effects of extreme fluctuations of temperature and salinity were evident. The degree of similarity between assemblages was related to the similarity of the sediments at the different stations. In particular, the changes in species composition appeared to correspond most clearly to differences in the clay content of the sediment.     

Setting of the American oyster Crassostrea virginica in the James River,Virginia, USA: temporal and spatial distribution

Setting of larvae of the oyster Crassostrea virginica was monitored in the James River, Virginia, USA from 1963 to 1980. Setting patterns were similar in two ways to those described prior to 1960 (before the onset of the oyster pathogen Haplosporidium nelsoni (MSX) in Chesapeake Bay): (1) setting intensity (average number of spat per shell) was greater at stations in the lower than upper estuary, and (2) on the average, 60 to 80% of the total annual set at each station occurred during a 6-week period from mid-August through September. However, annual setting intensity from 1963–1980 was lower than previously recorded, and annual sets occurred as a series of discrete pulses rather than continuously throughout the season. Pulses were each approximately 1 to 2 weeks in duration and separated by a period of diminished or no setting. Cross-correlation analysis of annual setting patterns among stations revealed three zones in the James River: the upper estuary and entire southwest side, the lower estuary, and a mid-estuary transition zone. Setting pulses tended to be synchronous at stations within each zone, but occurred 1 to 2 weeks later at stations in downriver than in upriver zones. The location of zones is related to known aspects of water circulation in the James River estuary. Moreover, pulse setting itself may be related to the absence of strong vertical salinity gradients accompanying the fortnightly stratification-destratification process.Contribution No. 1213 from the Virginia Institute of Marine Science, School of Marine Science, The College of William and Mary     

Benthic fauna of a shallow-water gaseohydrothermal vent area in the Aegean Sea (Milos, Greece)

The benthic community of shallow-water hydrothermal vents (10 m water depth) in a sandy bay on the south coast of Milos, Greece was studied. The macro- and meiofauna, as well as environmental factors such as temperature, salinity, sulfide concentration, grain size composition, ATP concentration, organic carbon, chlorophyll a and phaeopigments were evaluated. Samples were taken along transects from a seagrass meadow into a hydrothermally active area. Hydrothermally active spots were distinguished from the surrounding sediment by their black sediment coloration and an overlying white bacterial mat. For comparison, a control transect from a seagrass meadow into bare sand in a non-vent area in the same bay was studied. Overall, we found decreasing faunal diversity from the seagrass bed towards the hydrothermally active area. Along this gradient, four different zones could be distinguished. (a) The seagrass area had a relatively low diversity compared to the control stations, but much higher diversity than in the areas directly influenced by hydrothermal activity. (b) The border zone between the seagrass and the hydrothermal area, with moderate sulfide concentrations, pH values, seawater salinity and temperatures, was inhabited by an impoverished community dominated by the polychaete Capitella capitata, the nematodes Oncholaimus campylocercoides and Sabatieria sp., and an as yet undescribed chromadorid nematode (Chromadorina sp.). (c) The transition zone at the border of the hydrothermal area proper, with temperatures and sulfide concentrations higher than in the border zone, was characterized by high salinity (60‰) and low pH values. Along with the gastropod Cyclope neritea, single specimens of C. capitata and O. campylocercoides occurred. (d) The hydrothermal area proper, characterized by high sulfide concentrations, had high sediment temperatures and high salinities. The pH was as low as 6. Here, the gastropod Cyclope neritea was the only species occurring in considerable numbers. The gaseohydrothermal activity seems to largely exclude the surrounding fauna in a graded zonal pattern. The increasing hydrothermal stress entrains a change of the ambient biota towards a depauperate consortium of tolerant, opportunistic species, e.g. Capitella capitata (Polychaeta) and Oncholaimus campylocercoides (Nematoda). Although the hydrothermal area proper was characterized by a thick bacterial mat, the benthic community was characterized not by bacteria feeders but by scavenging species. Received: 13 September 1996 / Accepted: 24 October 1996     

Comparison of larval fish assemblages in three large estuarine systems, KwaZulu-Natal, South Africa

 The structure of the larval fish assemblages in three large estuarine systems on the KwaZulu-Natal coast of South Africa was examined using a combination of univariate, distributional and multivariate techniques. The database was comprised of a full annual set of larval fish samples taken from each estuarine system: Durban Harbour, Richards Bay Harbour and St Lucia Estuary. The mean monthly densities of each species in each system were used in the species matrix, and the mean monthly values of salinity, temperature and turbidity were used in the environmental matrix. The mean species diversity and evenness index were significantly higher in Durban Harbour (H′ = 1.03, J′ = 0.65) than in the other two systems. The cumulative dominance curve showed that St Lucia Estuary has a high dominance of a few species, with Richards Bay Harbour intermediate and Durban Harbour being the most diverse. Classification and MDS (multiple-dimensional scaling) analyses of larval fish densities in all three systems grouped together into three main clusters on the basis of system. The species similarity matrix (inverse analysis) clustered into five groups at the 25% similarity level. The MDS analysis of the same matrix showed that the groups separated out according to the degree of estuarine association of a species and hence habitat type. The species most responsible for system groupings were: Glossogobius callidus, Gilchristella aestuaria, Stolephorus holodon, Croilia mossambica and Gobiid 12. The “best fitting” of the environmental variables to explain the larval fish community patterns in each system was turbidity on its own (weighted Spearman's rank correlation, ρ_w = 0.55). The relationship of larval densities to environmental conditions was shown to be species-specific with estuarine species (e.g. G. callidus and G. aestuaria), having a strong positive correlation with temperature and turbidity but negative correlations with salinity. In summary, much longer term studies with more sites within each system are needed to assess whether the larval fish assemblages are stable or at an equilibrium (both spatially and temporally) and whether these assemblages are indicative of the relative “health” and nursery function of the system. Received: 28 April 1999 / Accepted: 30 May 2000     

Sea-water seasonal changes at a heavy tourism investment site on the Jordanian northern coast of the Gulf of Aqaba,Red Sea

The Gulf of Aqaba exhibits a strong seasonality due to convective mixing during winter and stratification during summer. The present study provides a detailed appraisal of summer and winter sea-water characteristics at the northern coast of the Gulf of Aqaba, that is witnessing rapid development and increasing changes in its geomorphological characteristics. Sea-water temperature, salinity, nutrients, and chlorophyll a concentrations were measured biweekly at five coastal and four cross-sectional stations during the periods February to April and July to September 2004. Meteorological conditions were continuously recorded at the Marine Science Station. The coastal study sites included four open coastal stations and a marina with one-way exchange with the open water. The effect of convective mixing was clearly apparent on the sea-water characteristics. Natural seasonal characteristics of higher nutrients and chlorophyll a concentrations were recorded during winter at most of the open coastal stations. In the cross-sectional stations, the concentrations of nutrients and chlorophyll a were not different between the surface and the bottom during winter, but the bottom waters had generally higher concentrations during summer. Some deviations from the natural seasonal cycle were recorded at the marina and other coastal stations. Here, higher nutrient and chlorophyll a concentrations were recorded in summer than in winter. These deviations that are most likely due to anthropogenic effects are discussed.     

Fiddler crab burrowing affects growth and production of the white mangrove (<Emphasis Type="Italic">Laguncularia racemosa</Emphasis>) in a restored Florida coastal marsh

Positive plant–animal interactions are important in community ecology, but relatively little attention has been paid to their effect on the production of mangroves, dominant halophytic trees in tropical coastal marshes. Here, the role of fiddler crab (Uca spp.) burrowing on the growth and production of the white mangrove, Laguncularia racemosa (<2 years old), was examined in a restored marsh in Tampa Bay, Florida (27°41.65 N, 82°30.34 W) with manipulative experiments from June 2006 to May 2007. Fiddler crab burrowing significantly increased mangrove height by 27%, trunk diameter by 25%, and leaf production by 15%, compared to mangroves in crab exclusion enclosures. Additionally, the exclusion of fiddler crabs significantly increased interstitial water salinity from 32.4 to 44.2, and decreased the oxidation–reduction potential of the low organic sediments, but did not affect soil pH or sulfide concentration. Mangrove height, trunk diameter, and leaf production along a transect that varied in crab burrow density were positively associated with the number of crab burrows. Further, the density of sympatric Spartina alterniflora shoots was positively correlated with crab burrow density along the transect. As in temperate marshes, fiddler crabs can have significant ecological effects on mangrove communities, serving as ecological engineers by modulating the amount of resources available to marsh plants, and by altering the physical, chemical, and biological state of these soft sediment communities. In restored coastal systems that typically have very poor sediment quality, techniques such as soil amendment could be used to facilitate a more natural interaction between crabs and mangroves in ecosystem development.     

Phytoplankton photosynthetic activity and growth rates in the NW Adriatic Sea

Taxonomic composition, biomass, primary production and growth rates of the phytoplankton community were studied in two stations in the NW Adriatic Sea on a seasonal basis, in areas characterized by differing hydrological and trophic conditions. The main differences between the two stations were quantitative rather than qualitative, most phytoplankton species being common to both stations. The effects of differing nutrient concentrations and plume spreading were evident. Biomass and primary production rates were significantly higher in the coastal station (S1), and the phytoplankton distribution in the water column was markedly stratified in S1 and more even in the offshore station (S3). However, chlorophyll a specific production, potential growth rate and production efficiencies were very similar in both stations, even when phosphorus concentrations were limiting. A discrepancy between potential and actual growth rate was observed: as a feature common to both stations, comparisons between potential and actual growth rates revealed that little carbon produced by phytoplankton accumulated as algal biomass; therefore, very high loss rates were estimated.     

Observations on shell form and its ecological significance in thaisid gastropods of the genus Lepsiella in New Zealand

This paper is concerned with the ecological significance of variation in shell form within the thaisid gastropod genus Lepsiella in New Zealand. Shell form has been investigated by measurement of shell height and breadth, aperture length and width, the diameters of consecutive whorls, apical angle, shell weight, and shell capacity, although in many cases shell height and shell breadth could not be measured because of erosion. L.albomarginata has been studied intensively at 4 stations in the South Island, and L. scobina less intensively at 6 stations in the North and South Islands. Comparisons of pairs of characters between stations have been tested by regression analysis and analysis of covariance where appropriate. Shells of L. albomarginata are relatively taller and narrower, and have a thicker wall, at a very sheltered station (Hakahaka Bay) that at more wave-exposed stations. L. scobina (sensu stricto), characterised by the presence of spiral ribs on the shell, exhibits less striking but comparable differences in shell shape. In laboratory tests in a tidal tank the thicker-shelled L. albomarginata from a sheltered station (Hakahaka Bay in Port Underwood) was much better able to resist attack by the shore crab Hemigrapsus edwardsi than was L. albomarginata from a nearby wave-exposed station (Whites Bay, near Cape Campbell, South Island). L. scobina from both stations was resistant to attack. H. edwardsi abounds at sheltered stations, but is missing from wave-exposed rock reefs such as those at Whites Bay, so that the ability to survive encounters with shore crabs is ecologically important to L. albomarginata inhabiting sheltered stations. L. scobina occupies a lower zone on the shore, where it is probably liable to encounter other more powerful predators. Its spiral ribs probably strengthen the shell. We do not know to what extent differences in shell form and thickness depend on environmental factors, and to what extent they originate genetically. Thin shells are associated with an abundance of mussels (Mytilus edulis ssp. aoteanus or Modiolus neozelanicus). There is an interesting possibility that a scarcity of mussels or other food caused by superior nonspecific predators might result in the production of better-protected Lepsiella.