Low Tidal Zone Research Articles

Response of suspension-feeding clams to natural removal of bioturbating shrimp on a large estuarine intertidal sandflat in western Kyushu, Japan

On a 3.4-km2 intertidal sandflat in Ariake Sound, Japan, four phytoplankton-feeders were dominant in the benthic community in terms of abundance and biomass in spring–summer, 2004: ghost shrimp, Nihonotrypaea japonica, mud shrimp, Upogebia major, and clams, Ruditapes philippinarum and Mactra veneriformis, each occupying a specific one-fourth area of the sandflat. N. japonica is a deposit feeder, while the others are suspension feeders. N. japonica and U. major dwell in 0.7- and 2-m deep burrows, respectively. Subsequent monitoring conducted every spring during 2005 to 2008 revealed that (1) probably due to typhoon- and stingray-induced substratum disturbances for mud and ghost shrimp populations, respectively, these had greatly shrunk from their original mid- to low-tide habitat in 2005 and high- to mid-tide one in 2006, respectively, (2) vacated space was colonized by juveniles of both clams and a formerly subdominant, suspension-feeding clam, Meretrix lusoria, (3) only Ma. veneriformis and Me. lusoria were found as adults there, with R. philippinarum adults remaining limited to the low-tide zone, and (4) loss in sum total population biomasses due to that in the shrimp' was compensated by the gain in the clam species'. These findings suggest that the five species compete for (1) space, with superiorities exerted by shrimps to clams through the former's intense bioturbating activities and by Ma. veneriformis and/or Me. lusoria to R. philippinarum in the high- to mid-tide zone and vice versa in the low-tide zone, and (2) food to the limit of the carrying capacity provided by the sound. Furthermore, estimates were made of the benthic community biomass in the past based on a long-term record (or estimate) of chlorophyll-a concentrations (proxy measure for food) for the sound water column and of the R. philippinarum population biomass based on its fishery-landing record. The latter estimate would account for 60% of the former one in the late 1970s, when the first eutrophication is believed to have been in progress. The subsequent decrease in benthic community biomass was suggested in response to that in phytoplankton abundance, reaching the one-fourth level in 2004–2008. In the long run, three alternative states would have occurred in the benthic community, from (1) R. philippinarum population boom in the 1970s, through (2) remarkable increases in the populations of the shrimps and Ma. veneriformis in place of R. philippinarum in the early to mid-1980s, followed by a plateau until 2004, to (3) the one described here for the 2004–2008 period.

Use of beach galleries as an intake for future seawater desalination facilities in Florida and globally similar areas

Desalination of seawater using the reverse osmosis process can be made less costly by the use of subsurface intake systems. Use of conventional open-ocean intakes requires the addition of a number of pretreatment processes to protect the primary RO process. Despite using the best designs possible for the pretreatment, seawater RO membranes tend to biofoul because of the naturally-occurring organic material and small bacteria present in seawater. These materials are not completely removed by the pretreatment system and they pass through the cartridge filters into the membranes, thereby causing frequent and expensive cleaning of the membranes. Quality of the raw water can be greatly improved by the use of subsurface intakes which can substantially reduce the overall treatment cost. There are a number of possible subsurface designs that can be used including conventional vertical wells, horizontal wells, collector wells, beach galleries, and seabed filters. The key selection criteria for the type of subsurface intake most suited and most cost-effective for a site are based on the required volume of raw water and the local geology. The active shorelines of Florida are very well-suited for the development of beach gallery intake systems. These systems are installed beneath the active beach between the high and low tide zones of the beach. Since they are constructed with a depth to the screens between 3 and 5 m, they cannot be observed at surface and persons using the beach would be unaware of their existence. These galleries are simple to construct and they tend not to clog because the active wave action within the intertidal zone provides mechanical energy that continuously cleans the filter face. They also have other advantages, including: the water quality is seawater unaffected by substances present in freshwater aquifers occurring landward of the shoreline, the salinity of the water is generally constant, and there are no impacts on water users located inland from the shoreline. A comprehensive study of the grain size characteristics of Florida beaches has allowed an assessment to be made of the hydraulic conductivities of the Florida beach sands. Hydraulic conductivity values generally range from 1.8 to 24 m/day, which is more than sufficient to allow the design and construction of high-capacity galleries at a reasonable cost. This type of intake is particularly relevant to the northeast Florida shoreline adjacent to an area being considered for development of a large-capacity seawater desalination system.

Links between wave forcing, offshore islands and a macro‐tidal headland‐bound bay beach

ABSTRACTProfiles were analysed in conjunction with wave climate to assess offshore island influences on an embayed beach at Tenby, Wales. Time series analyses showed medium and short‐term beach oscillation, with volume exchanges between zones lagging by up to six months. Dominant southerly and southwesterly waves caused sub and low tidal longshore drift from south towards north, while less frequent southeasterly waves generated counter drift. Modelled inshore breaking waves had less energy than offshore ones and the former behaved differently between the low and high tidal zones (spring tidal range of 7 · 5 m). Variations in wave direction from directly behind the islands resulted in reduced wave heights and statistical analyses agreed with wave model results. These were correlated to morphological change and it was concluded that offshore islands change wave dynamics and modify the morphology of embayed beaches in their lee. Consequently, this work provides significant new insights into offshore island influences, shoreline behaviour and especially tidal setting Copyright © 2013 John Wiley & Sons, Ltd.

Immediate Ecological Impacts of the 2011 Tohoku Earthquake Tsunami on Intertidal Flat Communities

Following the Great East Japan Earthquake in 2011, a large tsunami developed and struck the Pacific coast of eastern Japan. To assess the immediate impacts of the tsunami on coastal communities, changes in taxon composition and richness of macrobenthic animals before and after the tsunami were examined at nine intertidal flats in Sendai Bay and the Sanriku Ria coast. The results showed that 30–80% of taxa indigenously inhabiting intertidal flats disappeared after the tsunami. Among animal types, endobenthic and sessile epibenthic animals were more vulnerable to the tsunami than mobile epibenthic animals like shore crabs and snails. For all the intertidal flats examined, animals that were originally dwellers in lower tidal zones and not recorded before the tsunami were also found right after the tsunami, indicating that the tsunami not only took away many benthic taxa from the intertidal flats but also brought in some taxa from elsewhere. However, overall changes in taxon community composition were greater for intertidal flats that experienced larger inundation heights. These results showed that the ecological impacts of the tsunami were proportional to the physical impacts as gauged by wave height and that mobile epibenthic animals were less vulnerable to the tsunami.

Biogeographic comparisons of the traits and abundance of an invasive crab throughout its native and invasive ranges

High abundances of non-native species in the invaded range may be linked to changes in fitness related traits. However, few studies have compared differences in both life-history traits and abundances of introduced species between their native and invaded ranges. We determined differences in 12 morphological traits, an important fitness related trait (body size), and the abundance of the porcelain crab, Petrolisthes elongatus, in its native (New Zealand) and invasive (Tasmania, Australia) ranges. P. elongatus was more abundant in the introduced range; however, changes in abundance depended on tidal height, with higher abundances only at mid and low tidal zones. The biomass of male crabs was higher in the invaded range compared to the native range, but there was no difference in female biomass between ranges. Despite increases in male biomass, sex ratios between native and invasive populations did not differ. In addition, principal components analysis showed no differences in overall morphology between Tasmania and New Zealand. Our study indicates that increased abundance in the invaded range of P. elongatus may be linked to high values of an important trait (greater biomass) in the invaded range. Importantly, changes in biomass and abundance may be due to P. elongatus being able to utilise mid/low zones more in the invaded range. Furthermore, our findings indicate that understanding how sex specific changes in biomass interact with the recipient environment (biotic and abiotic) in the introduced range will be important for determining the mechanisms underpinning the establishment and spread of P. elongatus.

The Distributional Characteristics of Heavy Metal in Jiangsu Province Shoal Sea

After the analysis of surface samples and core samples collected in Xinyanggang tidal land, the contents of Pb, Cu, Zn, and Cr were obtained and analyzed in this paper. The heavy metal accumulation rule and pollution status were studied by Index of geo-accumulation, latent ecological risk index method, and elements accumulation index method. The research suggests that (1) the contents of heavy metal Pb, Cu, Zn, and Cr in Xinyanggang tidal land have the same change trend, and such trend remains unchanged after the data were normalized, while the fluctuation range becomes smaller. (2) After analyzing the heavy metal content in the surface samples, it was revealed that the contents of heavy metals are getting lower from high tidal zone to low tidal zone, but the ranges of the change were different. Cu, Ni, and Zn emerge obvious decline from supratidal zone to subtidal zone, while the changes of Cr and Pb are not obvious. (3) Pb and Cr contents in Xinyanggang tidal land present accumulative character, as Pb in Xinyanggang is 3 times as much as the local background value, whose EF reaches 3.774. (4) RI value in Xinyanggang is 23.552, which indicates that though Xinyanggang tidal land has some heavy metal pollution and accumulation, there are no ecosystem risks, and the whole Xinyanggang core area environment quality is relatively good.

Spatial and temporal variations in the species composition and abundance of benthic molluscs along 4 rocky shores of Karachi

A total of 97 species of macromolluscs were collected from 4 rocky beaches (Manora, Buleji, Nathiagali, and Cape Monze) along the Karachi coast from December 1993 to December 1995. More species were recorded from Buleji (68) and Manora (63) than from Nathiagali (55) and Cape Monze (57). Gastropods dominated at all 4 of the sites studied. Four species were commonly abundant at all 4 sites: Turbo coronatus, Nerita albicilla, Morula granulata, and Cerithium rubus. The average number of species decreased with an increase in the tidal heights at Manora, Buleji, and Nathiagali, whereas this was greater in the high tidal zone at Cape Monze's rocky shore. The average number of individuals of molluscs was greater in the midtidal zone at the Manora and Buleji rocky shores, whereas it was greater in the low tidal zone at Nathiagali and Cape Monze. Two-way nested analysis of variance showed that the number of individual molluscs was significantly different among zones and among sites in most of the samples. Species richness, diversity, and evenness, however, were not found to be significantly different among zones and sites. Cluster analyses, derived from Bray-Curtis measures of similarity based on abundance data, showed the discrimination between carnivore gastropods and an increase in the abundance of herbivore gastropod molluscs. Differences in community structure amongst sites appeared to be due to habitat structure, substrate instability, human disturbances, and degree of exposure.

崇明东滩湿地不同潮汐带入侵植物互花米草根际细菌的多样性

The invasive species of Spartina alterniflora,as an 'ecosystem engineer' was introduced into many places in China,now,had rapidly and widely invaded into the Chongming Dongtan wetland since 1990s.Microorganisms are important components of wetland ecosystems,performing a range of vital ecosystem functions.But,we have not known how microorganisms have an influence on the invasion of Spartina alterniflora in Chongming Dongtan.In order to study the bacterial diversity and abundance in rhizosphere of invasive plants Spartina Alterniflora growing in different tidelands of Chongming Dongtan Wetlands for different seasons,we selected 10 samples collection points,which distributed on the tidal zones with plant and the blare flat zone without plant in Chongming Dongtan wetlands.The tidal zones contain low-tide zone,mid-tide zone and high-tide zone.Total DNA was extracted from soil samples,and 16S rRNA gene-based PCR was performed.A comparative study of diversity of microorganisms in rhizosphere soils of invasive exotic species(Spartina alterniflora) and two native species(Phragmites australis and Scirpus mariqueter) was conducted by denaturing gradient gel electrophoresis(DGGE) of these PCR products,representing microorganisms in rhizosphere soils..Results showed that diversity and abundance of bacterial community were different in the rhizosphere of Spartina alterniflora,Phragmites australis and Scirpus mariqueter in the low-tide zone,mid-tide zone and high-tide zone in Chongming Dongtan wetlands..We found that,in summer,rhizosphere bacterial communities in mid-tide zone had higher abundance than those in low-tide zone and high-tide zone(P = 0.021 0.05).A higher diversity of bacteria in the rhizosphere soils of these plants was observed in summer than in other seasons.The average diversity index of bacterial community was calculated and was found to be the highest in mid-tide zone(H = 4.20).The abundance and diversity of bacterial community in invasive species Spartina alterniflora rhizosphere were significantly higher than in the local plants P.australis and S.mariqueter in mid-tide zone,and the abundance and diversity of S.mariqueter rhizosphere bacteria in summer slightly higher than in other seasons.Also the abundance and diversity of S.alterniflora rhizosphere bacteria were significantly higher in tidal soils than those in the mudflat soils.Overall,these results indicated the tides had a strong influence on the abundance and diversity of the plants rhizosphere bacteria.And the exotic species Spartina alterniflora had a favorable influence on soil microbial community in wetland.We reasoned that high diversity and abundance bacteria in rhizosphere maybe were an important for the invasion of Spartina alterniflora.A higher diversity of bacteria in the rhizosphere soils of these plants observed in summer revealed that the summer is more beneficial for bacteria living in vicinity of plant roots.The fact that the flourishing Spartina rhizosphere was associated with large bacteria assemblage suggested that the high diversity and abundance of microorganisms might be identified as one of the important factors of Spartina invasion mechanisms.

Distribution and abundance of horseshoe crabs Tachypleus gigas and Carcinoscorpius rotundicauda around the main island of Singapore

A survey and interviews with fishermen to determine the current spatial distribution of coastal Tachypleus gigas and mangrove Carcinoscorpius rotundicauda horseshoe crabs on the main island of Singapore indicated that there are probably no sites that support a breeding population of T. gigas. The only adult T. gigas seen were trapped in nets at 1 site, no juveniles or sub-adults were found at any site, and fishermen see this species infrequently. C. rotundicauda were more abundant, and breeding populations were found on the mudflats, fringed with mangroves. These small areas may be the last sites that support a breeding population of C. rotundicauda. Population density stud- ies of mainly surface crabs on the mudflats at 1 site gave a conservative figure of 0.5 crabs m -2 using non-randomised, longitudinal belt-transects of 5 × 50 m, set from high- to low-tide zones. Smaller ran- domised quadrats, searched for both buried and surface crabs, gave densities of 0.57 to 0.98 individ- uals m -2 , equivalent to a possible abundance ranging from 29 925 to 51 450 individuals in the accessi- ble search area of 52 500 m 2 . Comparisons over different months suggest that density changed little over time. Randomised quadrats and searches to depletion gave higher density figures, but they are labour intensive and difficult to set up in the terrain. Randomised, longitudinal belt- transects of 5 × 50 m are recommended for long-term monitoring of crab density. These findings provide baseline data to monitor the population at the site and to formulate conservation strategies for the 2 crab species.

Phylogeny, biogeography and the stepwise evolutionary colonization of intertidal habitat in the Liparocephalini based on morphological and molecular characters (Coleoptera: Staphylinidae: Aleocharinae).

A phylogenetic analysis of the tribe Liparocephalini Fenyes is presented based on morphological and molecular characters. The data set comprised 50 adult morphological characters, partial COI (907 bp), COII (366 bp) and 12S rDNA (325-355 bp), and nearly complete sequences of 18S rDNA (1768-1902 bp) for 21 species. Eighteen species of liparocephaline beetles from all eight genera and three outgroups, are included. The sequences were analysed separately and simultaneously with morphological characters by direct optimization in the program POY4 and by partitioned Bayesian analysis for the combined data. The direct optimization (DO) tree for the combined data under equal weighting, which also shows a minimum incongruence length difference value, resulted in a monophyletic Liparocephalini with the following patterns of phylogenetic relationships (outgroup ((Baeostethus, Ianmoorea) (Paramblopusa ((Amblopusa, Halorhadinus) (Liparocephalus, Diaulota))))). A sensitivity analysis using 16 different parameter sets for the combined data shows the monophyly of the liparocephalines and all its genera under all parameter sets. Bayesian analysis resulted in topological differences in comparison with the DO tree under equal weighting only in the position of the genus Paramblopusa and clade (Amblopusa + Halorhadinus), which were reversed. Historical biogeography and the stepwise evolutionary colonization of intertidal habitat in the Liparocephalini are discussed. Based on the biogeographical analyses, we hypothesize that the ancestor of the Liparocephalini occurred along the Panthallassan Ocean, the direct antecedent of the Pacific Ocean, followed by repeated dispersals to the Nearctic from the Palearctic. We also hypothesize that ancestors of the Liparocephalini appear to have arisen in the littoral zone of beaches and then colonized rocky reef areas in the low tidal zone later through high- to mid-tide zones. © The Willi Hennig Society 2009.

Incidence and biology of Arcotheres tivelae (Crustacea: Decapoda) in Amiantis umbonella (Bivalvia: Veneridae) on the northern coast of the Persian Gulf, Iran

The occurrence of pinnotherid crab Arcotheres tivelae in the bivalve mollusc Amiantis umbonella was investigated for one year on the Bandar Abbas coast (Persian Gulf, Iran). Specimens of A. umbonella were collected monthly from two transects from April 2007 to March 2008 and were investigated for presence of the Arcotheres tivelae. Infestation frequency of A. tivelae was 9.18% in a sample of 893 clams. From a total of 89 specimens of crabs, only eight were male. They were observed in late February and early March, all of them but one in association with female crabs. There was no significant difference between the sexes of the infested clams that pea crabs choose as a host. The mean carapace width of the crab A. tivelae was 7.7 ± 1.7 mm and the mean length of the Amiantis umbonella was 39.84 ± 8.93 mm. Clams in the mid and low tidal zones were more infested. There was no significant relationship between clam length–crab width (R2 = 0.28). The mean fecundity of crabs was 2517 ± 864 eggs. Infection caused a reduction of flesh weight of clams. There was no significant correlation between the frequency of crabs' occurrence and the temporal variability of water temperature, salinity, dissolved oxygen and pH in different months. This study provides the first report of the distribution of pea crabs A. tivelae in A. umbonella, a new clam host record in Iran.

Long-term displacement of intertidal seagrass and mussel beds by expanding large sandy bedforms in the northern Wadden Sea

On aerial photographs, sandy tidal flats display (1) large sandy bedforms (> 10 m long, > 3 m wide), indicating effects of strong hydrodynamics on sediment relief, and (2) beds of seagrass and mussels, indicating stable sediment conditions. These physical and biogenic structures have been mapped from aerial photographs taken in a back-barrier tidal basin of the North Sea coast at low tide between 1936 and 2005. Fields of large intertidal sandy bedforms show a consistent spatial distribution in the central part of the basin, and have increased in area from 7.2 to 12.8 km 2, corresponding now to 10% of the tidal flats. Areal expansion may be linked to a rise in average high tide level and an increase of the expansion rate from the 1960s to the mid 1990s might be traced back to an increased frequency of storm tides during this period. It is shown that expanding fields of large sandy bedforms have replaced mussel beds in the low tidal zone and displaced seagrass beds in the mid tidal zone. Fields of intertidal large sandy bedforms are expected to expand further with an accelerating rise in sea level, and it is recommended to monitor these physical indicators of sediment instability and disturbance of biogenic benthic structures by analysing aerial photographs.

First account of apochlorotic diatoms from intertidal sand of a south Florida beach

During the period January to December 2004, monthly intertidal sand samples were collected from John U. Lloyd State Park beach, Florida. This study is the first to report on spatial and temporal distributions of heterotrophic (apochlorotic) diatoms in a sub-tropical beach, or indeed any sandy beach. Two non-pigmented, apochlorotic diatom morphotypes (strains III and IV) were consistently isolated from two intertidal beach sites and neither conformed to the morphologies of described species. Apochlorotic diatoms were found throughout the year and formed significant peaks in April, attaining total diatom counts of 71.1 and 94.9 cells g −1 wet sand, for the upper tidal zone and lower tidal zone, respectively. Valve morphology is described in detail for the two diatom morphotypes isolated from the beach sites (strains III and IV). Growth responses to changes in salinity (reflecting those of the intertidal zone) were examined in the laboratory for these diatoms. Both morphotypes were euryhaline, tolerating salinities between 10 and 50, and maximum growth rates were achieved at salinities between 20 and 40. Diatoms grew equally well whether grown in the light or the dark and showed no evidence of pigments when viewed by epifluorescence microscopy. The ability of diatoms to burrow into agar and carrageenan at different concentrations was tested. Both morphotypes were observed to develop burrows through non-nutrient agar up to twice the standard concentration (30 g agar l −1). The ease with which these heterotrophic diatoms formed burrows suggests that they were digesting these complex carbohydrates (i.e. phycocolloids) as a nutrient source. Strain IV, however, failed to burrow in a different phycocolloid, carrageenan. Similar degradative actions in the field might have implications for the breakdown of recalcitrant materials or allow diatoms to effectively compete with bacteria for carbon and nutrients.

Designing an effective clipping regime for controlling the invasive plant Spartina alterniflora in an estuarine salt marsh

Many invasive plants are highly tolerant of disturbances and can invade various habitats, leading to difficulties in managing them. Most of control techniques need to be performed repeatedly, and the efficiency of the same control method may vary along environmental gradients. To develop a control strategy for an invasive plant in heterogeneous environments, it is important not only to optimize the control regime, but also to consider the efficiency in different habitats. We conducted a field experiment to test how clipping regime (i.e., initial treatment timing and treatment interval) and habitat type (i.e., high and low tidal zones) influence the control efficiency for invasive Spartina alterniflora in an estuarine salt marsh. Among the 12 treatments, double-clipping treatment performed in early July and mid September (9-week-interval) had the highest efficiency, which not only eliminated sexual reproduction of S. alterniflora, but also inhibited its vegetative growth in the current and following years. The clipping efficiency in low tidal zone was higher than that in high tidal zone. Therefore, an optimized control strategy for the invasive plants could be established based on the efficient control regime and habitat types. According to our study, a recommended double-clipping control strategy for S. alterniflora is that the initial clipping treatment is performed in the flowering period and the second one is performed 9 weeks later. In order to effectively reduce proliferation of the invasive plant, we suggest that the clipping regime should be applied for at least 2–3 years in low tidal zone and 3–4 years in high tidal zone.

Clipping at early florescence is more efficient for controlling the invasive plant Spartina alterniflora

AbstractAs invasive plants in different life stages have different recovery potential against devegetation operation, how to optimize the proper timing (the time for single treatment or the starting time for repeated treatments) for eliminating them becomes an important topic in the management of invasive plants. The invasive plant Spartina alterniflora was selected in this study, and it was clipped as a devegetation example to examine how important treatment timing is for increasing control efficiency. The results illustrated that by either single or repeated clipping treatments within 1 year, clipping at florescence was more efficient for controlling S. alterniflora. On the other hand, increasing clipping frequency without proper timing might not enhance control efficiency, suggesting that treatments in proper timing might reduce the clipping frequency required for a specific control target. From a management point of view, each control method has its optimal treatment timing, thus, in order to improve the control efficiency, the control programs should be ideally designed in relation to the phenology of the target plant. Besides, repeated clipping showed significantly higher control efficiency in low tidal zone than in high tidal zone, implying that habitat dependence of invasive plant control efficiency is an important issue in the management of invasive plants.

Odelo geodatabase en la estructuración y almacenamiento de información espacial para la administración y control del litoral Caribe colombiano

In this research the results of using the data model called Geo-database in the structuring and storage of spatial information of the Cartagena de Indias littorals, the Tierra Bomba island, the Morrosquillo Gulf and between Tajamar Occidental of Magdalena river and Puerto Velero during the years 2007 and 2008 in the Colombian Caribbean are presented. The research included identification of the Maritime National Direction corporative Geodatabase requirements, verification of state and structuring of the spatial information obtained by the Oceanographic and Hydrographic Research Center and establishing the procedure for structuring and later storage of the information. The use of the geodatabase model in the study areas, permitted the structuring, storing and quantification of spatial information of 303.44 kilometers of coastline, 1512.31 hectares corresponding to beach areas and 10469.5 hectares of low tidal zones. This information will be used by the National Maritime Authority and its respective Port authorities as technical support for the control, administration and preservation of these govern property located on the Colombian Caribbean littoral.

한국 남해안 중부에 위치한 광양만 조간대의 해조상과 군집

The seasonal variation and vertical distribution of the marine algal community were investigated using the quadrat method from February 2006 to January 2007 at 10 sites in Gwangyang Bay, Korea. In total, 48 red, 17 brown, and 13 green algal taxa were identified. The algal vertical distribution in the intertidal zone was characterized by Ulva pertusa, while the upper tidal zone was dominated by Gelidium divaricatum. The middle zone was primarily composed of Enteromorpha linza, Sargassum thunbergii, and Chondracanthus intermedia, whereas Hizikia fusiformis, Sargassum thunbergii, Gelidium amansii, and Corallina pilulifera characterized the low tidal zone. Results of cluster analysis indicated that algal composition fell into two groups, which were composed of species in the inland and open sea. In conclusion, the number of species, diversity, and abundance of vegetation in this area were remarkably reduced compared to previous studies in Gwangyang Bay.

Characterization of a homogeneous taxonomic group of marine magnetotactic cocci within a low tide zone in the China Sea

Magnetotactic bacteria are a heterologous group of motile prokaryotes, ubiquitous in aquatic habitats and cosmopolitan in distribution. Here, we studied the diversity of magnetotactic bacteria in a seawater pond within an intertidal zone at Huiquan Bay in the China Sea. The pond is composed of a permanently submerged part and a low tide subregion. The magnetotactic bacteria collected from the permanently submerged part display diversity in morphology and taxonomy. In contrast, we found a virtually homogenous population of ovoid-coccoid magnetotactic bacteria in the low tide subregion of the pond. They were bilophotrichously flagellated and exhibited polar magnetotactic behaviour. Almost all cells contained two chains of magnetosomes composed of magnetite crystals. Intriguingly, the combination of restriction fragment length polymorphism analysis (RFLP) and sequencing of cloned 16S rDNA genes from the low tide subregion samples as well as fluorescence in situ hybridization (FISH) revealed the presence of a homogenous population. Moreover, phylogenetic analysis indicated that the Qingdao Huiquan low tide magnetotactic bacteria belong to a new genus affiliated with the alpha-subclass of Proteobacteria. This finding suggests the adaptation of the magnetotactic bacterial population to the marine tide.

Mudflat biota since the 1930s: change beyond return?

Where, since the 1980s, patchy and variable green algal mats are prevailing, distinct belts of an amphipod (Corophium volutator) and seagrass (Zostera spp.) had dominated in the 1930s. The zonation between tide marks has been mapped in a sheltered sedimentary bay in the Wadden Sea near the island of Sylt (coastal eastern North Sea). Maps on vegetation from 1924 and on selected macrobenthos from 1932 and 1934 are compared with biannual surveys conducted from 1988 to 2006. Rising high water levels and eutrophication are suggested to be major causes of the observed long-term changes. In front of a saltmarsh, a sandy beach developed and partly displaced former cyanobacterial mats. Advancing sandiness may have inhibited C. volutator and facilitated lugworms, Arenicola marina, in the upper tidal zone. A variable occurrence of green algal mats arising in the 1980s affected infauna and seagrass by smothering the biota underneath. This dissolved a coherent belt of Zostera noltii. In the lower tidal zone, natural disturbances had lasting effects on the occurrence of mussels with attached fucoid algae. The spectrum of species became enriched by alien species (13% of macrobenthic taxa). A reversal to habitat structure and biotic zonation of the 1920–1930s does not seem possible. Aliens, in combination with climate change, are expected to further divert the ecological pattern to new configurations.

SEASCAPE-DEPENDENT SUBTIDAL–INTERTIDAL TROPHIC LINKAGES

In this study, we test in southern New Zealand a conceptual model of food web linkage that is seascape dependent, which can explain some of the variability in rocky shore community structure among sites and coasts. Using a comparative-experimental approach at local and distant sites we demonstrate that mobile subtidal predators (fish and crabs) can exert strong predation pressure on small mussels in the low tidal zone, but only in sites where the seascape includes subtidal reefs. On intertidal benches with adjacent subtidal reefs (+SR), 60-100% of small (5-15 mm) transplanted mussels were removed within a day from experimental tiles on the low shore when unprotected from predation, compared to fully caged controls that had approximately 100% survival over several months. In partial cages that exclude fish but not crabs, survivorship was intermediate. In contrast, on benches without subtidal reefs (-SR) 40-100% of mussels survived for months, even if unprotected. This difference is expressed in lower cover (0-60%) of mussels on rocks at +SR benches compared to -SR benches (70-99%). The central to northern west coast of the South Island is composed mostly of -SR benches, and predation on small mussels there was low and similar to the -SR benches on the east coast, whereas the +SR benches on the east coast had much greater predation. This contrasts to other studies in New Zealand that examined only predation on larger mussels by seastars and concluded that predation is strong on the west coast and weak on the east coast. Excluding large predators from low-shore areas with new recruits for a year in one +SR site showed longer-term predation effects on their abundance and cover. Short-term sampling at the east coast sites showed that mussel settlement was greater in -SR compared to +SR sites, providing some evidence that seascapes may also affect settlement. Overall, predation depended on the local seascape and ultimately affected community structure via suppression of effective recruitment rates. This study emphasizes the importance of predation on early life stages of basal species and the influence of seascapes on top-down interactions between subtidal predators and their intertidal prey.