Lower Shore Research Articles

Microspatial variability in community structure and photophysiology of calcified macroalgal microbiomes revealed by coupling of hyperspectral and high-resolution fluorescence imaging.

Calcifying coralline macroalgae provide biogenic habitats colonised by epiphytic microalgae that contribute significantly to community productivity. Georeferenced hyperspectral and high-resolution fluorescence imaging were coupled to microspatially mapped community composition and relative biomass of macroalgal host and epiphyte microalgal groups, and their weighted contributions to productivity within host fronds of Corallina officinalis on upper and lower zones of a rocky shore were determined. Lower shore epiphytes were dominated by filamentous diatoms (Bacillariophyta), confined to the apex of the frond structure, which were low light acclimated but retained a high capacity for photoprotective down regulation and contributed up to 51% of total community productivity. Upper shore epiphytes were dominated by green algae (Chlorophyta) and single-celled diatoms (principally Cocconeis spp.), which were high light acclimated but present at far lower relative biomass and contributed negligibly to productivity. The host, C. officinalis was the main primary producer. Variation in light environment resulting from differences in shore height and shading within the host macroalga, likely play a large role in determining patterns in epiphyte community structure, biomass and productivity observed. Additionally, microspatial gradients in photophysiological parameters along the host macroalga likely resulted from age-dependent variation in pigments as well as the gradient in light environment.

Diet of an underappreciated benthic intertidal fish, <em>Cryptacanthodes maculatus</em> (Cryptacanthodidae), in eastern Maine, USA

We discovered through gut-content analysis over a 20-month period (June 2009–March 2011) that a little-known benthic fish, the wrymouth, Cryptacanthodes maculatus, preyed upon soft-bottom fauna from 8 phyla, 10 classes, and 28 genera in the lower intertidal/ shallow subtidal zone in Cobscook Bay (eastern Maine, USA). Wrymouth (N = 42; total length = 30–50 cm) live infaunally in extensive subterranean burrows, and consumed mainly polychaetes and amphipods that occurred in 80% and 75% of stomachs, respectively. The two most common polychaetes, Alitta virens and Harmothoe imbricata, were found in 60% and 25% of stomachs, respectively. Gammarideans Leptocheirus pinguis and Ampelisca abdita were the two most common amphipods occurring in 40% and 33% of stomachs, respectively. Benthic core samples taken from the mid- and low shore were ambiguous in helping to understand where wrymouth forage. Wrymouth likely contribute to trophic linkages between the intertidal and subtidal zones in soft-bottoms; however, its relative role in regulating benthic community structure, aspects of its reproductive behavior, and early life-history is unknown due in part to its cryptic lifestyle. In addition to identifying components of the wrymouth’s diet, we document gravid females for the first time, and when they appear in the population.

Hormosira banksii (Phaeophyceae): a tough survivor in the harsh conditions of high intertidal pools in southeast Australia

Hormosira banksii, the most successful intertidal fucoid in the southern hemisphere, usually inhabits only the lower shore. On Kainga Reef, at 36°S on the New South Wales coast, it is one of only two macroalgae in most of the pools on a platform above xthe lowest high water; 29 pools in the middle of the platform were monitored photographically for 12 years. Recruitment was not seasonal. It took about 5–8 months for germlings to become visible, when they consisted of about 3 vesicles. The growth rate of germlings was between linear and exponential. Individuals could become fertile when they were 11–14 months old. Adult frond growth rate in the mid-platform pools, measured in situ, was highest in autumn but similar in the other seasons. In summer, however, in pools at the edge of the reef, often flushed by waves, the growth rate was as fast in summer as in autumn, either because of better provision of scarce nutrients or because of less inhibition by high temperature. Mortality, both of individuals and of fronds, was highest in the summer when pool isolation for one or more tidal cycles, caused by the coincidence of low high tide levels and a calm sea, was more common. Hormosira could tolerate full summer sunlight, water temperatures of up to 40°C, 140 psu (four times the strength of seawater) but not dehydration. Dehydration caused inter-annual variation in cover and in the total number of plants present, but with no overall trend over 12 years. Sand cover and rotting cast weed could also cause mortality. Survivorship was Slobodkin’s Type IV, with few plants reaching 4 years but high longevity after that, due to the establishment of a holdfast which could regenerate new fronds. Compared with other fucoids, growth was slow. The lifestyle resembles that of Ascophyllum nodosum.

Thermoplastic polyurethanes with isosorbide chain extender

ABSTRACTIsosorbide, a renewable diol derived from starch, was used alone or in combination with butane diol (BD) as the chain extender in two series of thermoplastic polyurethanes (TPU) with 50 and 70% polytetramethylene ether glycol (PTMEG) soft segment concentration (SSC), respectively. In the synthesized TPUs, the hard segment composition was systematically varied in both series following BD/isosorbide molar ratios of 100 : 0; 75 : 25; 50 : 50; 25 : 75, and 0 : 100 to examine in detail the effect of chain extenders on properties of segmented polyurethane elastomers with different morphologies. We found that polyurethanes with 50% SSC were hard elastomers with Shore D hardness of around 50, which is consistent with assumed co‐continuous morphology. Polymers with 70% SSC displayed lower Shore A hardness of 74–79 (Shore D around 25) as a result of globular hard domains dispersed in the soft matrix. Insertion of isosorbide increased rigidity, melting point and glass transition temperature of hard segments and tensile strength of elastomers with 50% SSC. These effects were weaker or non‐existent in 70% SSC series due to the short hard segments and low content of isosorbide. We also found that the thermal stability was lowered by increasing isosorbide content in both series. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42830.

Mudflow gully characteristics, formation and impact on reservoir heterogeneity – A gas field in the Yinggehai Basin, South China Sea

Mudflow gullies are well developed in offshore areas and on the upper deepwater slope. In this paper, we discuss the formation and characteristics of mudflow gullies in a gas field in the Yinggehai Basin along the northwestern South China Sea margin, and address their impacts on sand body distribution, reservoir heterogeneity, and hydrocarbon accumulation.The geological setting and sedimentary characteristics indicate that the sedimentary environment of the study intervals is located in an area between lower shore face and offshore. The gullies are several meters to a few tens of meters wide, and are filled mainly with thick mudstones interbedded with thin siltstones. Gully fills show an overall fining upward depositional trend, and exhibit a high value, low-amplitude linear GR wireline log shape. Mudflow gullies always incise the underlying sand bars or sand sheets, are overlain by offshore shales and are therefore considered to have developed in a transgressive setting. They are of three basic types, i.e., deep-, moderate- and shallow-classes according to the incision depth. The mudflows developed in offshore environment with rapidly varying topography, and deeply cut the underlying sand bars in lower shore face environment. Influenced by diapiric events, plastic mud-rich sediments were apt to slump, yielding the studied gullies. Gullies can converge to generate a lobe at front of them. In particular, during marine transgression, due to the high depositional rate of muddy sediments and tectonic activity, marine transgression offered the most favorable scenario for the development of these gullies. The mudflows also slumped down the slope into the deep water areas of the basin.Because of the incision of mudflow gullies and transgressive wave ravinement from the southeast, the pre-existing sand bars on the lower shore face were reworked by waves and oriented in a NE–SW direction, perpendicular to the east shoreline to Hainan Island. The sand bars were affected by the mudflow gullies and diapir faults, often isolated from each other, resulting in a weak sand connectivity vertically and laterally. The degree of erosion of the sand bodies by mudflows decreases with depth. In addition, diapiric activity not only induces the formation of mudflow, but also causes CO2 in the deep buried intervals to migrate into gas reservoir attached by faults. The mudflow gullies are important causes of gas reservoir compartmentalization. CO2 filling process and gully development in the area resulted in more heterogeneity than the areas without them. Therefore, mudflow gullies control not only the reservoir compartments but also the gas content in the reservoir.

Linking macrobenthic communities structure and zonation patterns on sandy shores: Mapping tool toward management and conservation perspectives in Northern France

In a context of intensifying anthropogenic pressures on sandy shores, the mapping of benthic habitat appears as an essential first step and a fundamental baseline for marine spatial planning, ecosystem-based management and conservation efforts of soft-sediment intertidal areas. Mapping allows representing intertidal habitats that are basically characterised by abiotic (e.g sediments, exposure to waves…) and biotic factors such as macrobenthic communities. Macrobenthic communities are known to show zonation patterns across sandy beaches and many studies highlighted the existence of three biological zones. We tested this general model of a tripartite biological division of the shore at a geographical scale of policy, conservation and management decisions (i.e. Northern France coastline), using multivariate analyses combined with the Direct Field Observation (DFO) method. From the upper to the lower shores, the majority of the beaches exhibited three macrobenthic communities confirming the existence of the tripartite biological division of the shore. Nevertheless, in some cases, two or four zones were found: (1) two zones when the drying zone located on the upper shore was replaced by littoral rock or engineering constructions and (2) four zones on beaches and estuaries where a muddy-sand community occurred from the drift line to the mid shore. The correspondence between this zonation pattern of macrobenthic communities and the EUNIS habitat classification was investigated and the results were mapped to provide a reference state of intertidal soft-sediment beaches and estuaries. Our results showed evidence of the applicability of this EUNIS typology for the beaches and estuaries at a regional scale (Northern France coastline) with a macroecological approach. In order to fulfil the requirements of the European Directives (WFD and MFSD), this mapping appears as a practical tool for any functional study on these coastal ecosystems, for the monitoring of anthropogenic activities and for the implementation of management plans concerning effective conservation strategies.

Determination of key environmental factors responsible for distribution patterns of fiddler crabs in a tropical mangrove ecosystem.

In tropical regions, different species of fiddler crabs coexist on the mangrove floor, which sometimes makes it difficult to define species-specific habitat by visual inspection. The aim of this study is to find key environmental parameters which affect the distribution of fiddler crabs and to determine the habitats in which each species was most abundant. Crabs were collected from 19 sites within the mudflats of Sepang-Lukut mangrove forest. Temperature, porewater salinity, organic matter, water content, carbon and nitrogen content, porosity, chlorophyll content, pH, redox potential, sediment texture and heavy metals were determined in each 1 m2 quadrate. Pearson correlation indicated that all sediment properties except pH and redox potential were correlated with sediment grain size. Canonical correspondence analysis (CCA) indicated that Uca paradussumieri was negatively correlated with salinity and redox potential. Sand dwelling species, Uca perplexa and Uca annulipes, were highly dependent on the abundance of 250 μm and 150 μm grain size particles in the sediment. Canonical Discriminative Analysis (CDA) indicated that variation in sediment grain size best explained where each crab species was most abundant. Moreover, U. paradussumieri commonly occupies muddy substrates of low shore, while U. forcipata lives under the shade of mangrove trees. U. annulipes and U. perplexa with the high number of spoon tipped setae on their second maxiliped are specialized to feed on the sandy sediments. U. rosea and U. triangularis are more common on muddy sediment with high sediment density. In conclusion, sediment grain size that influences most sediment properties acts as a main factor responsible for sediment heterogeneity. In this paper, the correlation between fiddler crab species and environmental parameters, as well as the interaction between sediment characteristics, was explained in order to define the important environmental factors in fiddler crab distributions.

Factors influencing the distribution of coastal lichens Hydropunctaria maura and Wahlenbergiella mucosa

AbstractResponses to abiotic and biotic stresses that potentially drive the vertical zonation of the intertidal lichens Hydropunctaria maura, an upper littoral lichen, and Wahlenbergiella mucosa, a lower littoral lichen, were investigated in field and laboratory experiments. When transplanted, both lichens exhibited an inability to survive outside their normal vertical distribution range. W. mucosa appeared to be unable to tolerate prolonged periods of desiccation following translocation from lower to upper littoral regions, whereas H. maura was unable to survive in lower littoral zones possibly owing to increased grazing pressure. The effect of desiccation in both lichens was compared using pulse amplitude modulated chlorophyll fluorescence and infra‐red gas analysis; results indicated a more hydration‐dependent nature of W. mucosa. Photosynthetic (algal) pigments and phenolic compounds were determined in both lichen thalli, and a range of additional coastal lichens occupying a natural gradient from upper to lower shore levels. Pigment composition and concentration in both lichen thalli were similar whereas levels of phenolic compounds were up to three times higher in W. mucosa than H. maura. Pigment and phenolic concentration and composition exhibited some seasonality across 13 different lichens originating from different shore levels. Phenolic concentration increased towards the lower shore, suggesting a potential anti‐herbivory function. This marks the first study of pigments and phenolics in coastal lichen communities, and prompts further investigations on the particular physiological features of marine and maritime lichens that enable them to thrive in this extreme environment.

Different settlement strategies explain intertidal zonation of barnacles in the Eastern Mediterranean

The Mediterranean mid-littoral zone is inhabited by two sympatric chthamalid barnacles: Chthamalus stellatus and Euraphia depressa, C. stellatus extends from the high midtidal zone, above the algal belt, to the supra-littoral fringe, E. depressa is restricted to the uppermost intertidal levels in wave-beaten places and to cryptic habitats lower on the shore within the belt of C. stellatus. Previous studies have suggested that the reason for the fragmented distribution pattern of E. depressa is competitive displacement by the sympatric C. stellatus, following random settlement. This hypothesis is in agreement with the common model of zonation suggested by Connell that lower distribution limits are determined by biotic factors (competition and predation), while upper limits are set by physical factors. It is hard to test the validity of this model for this barnacle pair since the early ontogenetic stages of the species are morphologically indistinguishable, hindering our ability to understand distribution processes. Using 16S mtDNA as a genetic marker in a multiplex PCR system, cyprids and spats were individually identified. Settlement and recruitment rates were assessed using settlement plates, and the effect of post-settlement processes was tested with transplantation of settlers between zones. Results showed different strategies in each species: settlement of E. depressa was habitat-specific, while settlement of C. stellatus was random. Shifting individuals of C. stellatus to the high and cryptic zones resulted in high mortality; however, exposing juveniles of E. depressa that settled in artificially cryptic low shore habitat to C. stellatus presence had no effect on their survival. These finding do not agree with the formerly suggested hypothesis that zonation is mainly determined by post-settlement factors, and that the interspecies boundary is determined by interspecific competition, implying that competition model cannot be adapted to Mediterranean intertidal zonation and that other models, dominated by physical enforcement and pre-settlement recruitment-limiting factors, may prevail in this ecosystem.

Structure of intertidal sessile communities before and after the invasion of Isognomon bicolor (C.B. Adams, 1845) (Bivalvia, Isognomonidae) in southeastern Brazil

Scientists recognize the importance of ecological data prior to invasion by non-native species in order to evaluate changes in the recipient community. Here we assess the potential impact of the invasion of the bivalve Isognomon bicolor (C.B. Adams, 1845) on Brazilian rocky shores through the use of surveys both before and after the arrival of this non–native species. The invader was mostly distributed across the mid and low shore levels of the intertidal zone with relative abundance ranging from 9.0 to 36.7 percent cover. The mid shore, previously dominated by the native barnacle Tetraclita stalactifera (Lamarck, 1818), was co-dominated by this barnacle species and I. bicolor after invasion. The relative abundance of these species, and presumably the interaction strength between them, differed between sites. At the site where I. bicolor reached the highest abundance (around 30% on average), the abundance of T. stalactifera decreased on average 70% compared to baseline values obtained before the I. bicolor invasion. Finally, conspicuous and extensive I. bicolor beds such as those observed in this study have not been reported in its original distribution range. Beds of I. bicolor may create a much more intricate biogenic matrix than the extents of bare rock and barnacle clumps it replaced. This bivalve may act as an ecosystem engineer and, thus a functionally different component of the intertidal community in its invaded range compared to its native distribution.

From frontier military post to Hong Ngu district-level town

Hong Ngu Town is currently the only town of Dong Thap Province. Place name Hung Ngu dates back from early times and was officially recorded in many of Nguyen Dysnasty’s historical records. The place name Hong Ngu originated from Hung Ngu which was the name of the Nguyen Lords’ army troup assigned to guard the border and to collect taxes. The place where the Nguyen Lords’s army troup stationed was named Bao Hung Ngu. The land was garrisoned by the army troup of the same name. Through long-time contact, the land’s name was set as Hung Ngu. For convenience of sound pronunciation, “hung” was pronounced a little bit inclined to “hong”; thereby, “hung ngu” to “hong ngu”. The place name Hung Ngu (now called Hong Ngu) may have been formed in the late 18th Century or the early 19th Century. Bao Hung Ngu troup originally stationed at Rach Doc Vang rivulet mouth (at Thanh Binh rural district), then moved to the lower shore of Hiep An river, now is the Mekong resort of Dong Thap Tourist Company. Over 200 years, Hong Ngu constantly developed. It took 85 years sharp for the frontier military post in the Nguyen Lords’ times to become an administrative unit at rural district level (1029); now it has been the district-level town of the province for 5 years (2009-2014). The paper points out the continuity of the formation and development process as mentioned above. Hong Ngu continues to rise to become an urban area and the clue of an economic focal point of the North of Dong Thap Province, and towards the near future, a city in the sea area.

Influence of habitat heterogeneity on the assemblages and shell use of hermit crabs (Anomura: Diogenidae)

BackgroundTwo contrasting intertidal habitats on the western Sabah coast (Malaysia), one is a rocky-sandy-mud flat at Sepangar (N6°02′18.57″; E116°06′40.07″) and the other is a mangrove foreshore at Sulaman (N6°15′33.00″; E116°18′49.80″), are characterized by substrate zonation and homogeneous substrate (mud), respectively. Hermit crabs are one of the most conspicuous benthic macrofauna at both sites. The study examined the influence of habitat heterogeneity on the assemblages and shell use pattern of hermit crabs.ResultsThe heterogeneous intertidal flat at Sepangar (five species) supported a higher diversity and abundance of hermit crabs compared to Sulaman mangrove foreshore (two species). Hermit crabs at Sepangar used a greater variety of shells (30 species) compared to those at Sulaman (two species). Zonation of hermit crab species occurred at Sepangar where Diogenes klaasi dominated at the high-tide mark and two Clibanarius species (C. striolatus and C. merguiensis) dominated at the low-tide mark. Considerable overlap in habitat use (mid- and lower shore) occurred between D. tumidus and the two Clibanarius species which appeared to influence shell use pattern.ConclusionsThis study supports the work of others showing that structurally complex habitats will allow habitat partition among species thus explaining the greater diversity and abundance of hermit crabs. Such a heterogeneous habitat provides a wider choice of shells for the hermit crabs, minimizing interspecific competition for the available shell resources.

Physiological responses of two acorn barnacles, Tetraclita japonica and Megabalanus volcano, to summer heat stress on a tropical shore

Species living on rocky shores are subject to periodic tidal emersions and can experience intense thermal stress during daytime low tides. Tetraclita japonica and Megabalanus volcano are common intertidal barnacles in Hong Kong, with T. japonica occupying the high to mid-intertidal zone where its lower limits overlap with the upper limits of M. volcano, which is found in the lower intertidal to subtidal zone. In this study, daily profiles of body temperature and hemolymph osmolality on the shore, and responses to thermal challenge under laboratory conditions were compared between the two species to investigate their behavioral and physiological responses to heat and desiccation stress. On-shore measurements of body temperature revealed contrasting thermal profiles, with T. japonica from the upper shore experiencing greater thermal stress than T. japonica and M. volcano from the lower shore. Aerial exposure of the barnacles was associated with an increase in hemolymph osmolality. M. volcano, however, showed a greater increase in hemolymph osmolality than T. japonica at similar shore levels. When the two species were exposed to rock temperatures of 40°C for 5h, more individuals (94%) of T. japonica entered a coma state, and at an earlier time than M. volcano (36%). All T. japonica individuals resumed activity when re-immersed in water, whereas in contrast, all M. volcano that went into a coma state did not recover and died within 24h. Quiescence and reversible coma during the early stages of acute heat stress, as observed in T. japonica, could therefore be adaptive responses to cope with thermal stress in the upper rocky shore.

Abundance and Spatio-Temporal Distributional Pattern of Dotilla Myctiroides (Milne-Edwards) on Exposed Sandy Beach of Aksa, Mumbai

The abundance and distributional pattern of Ocypodid crab, Dotilla myctiroides (Milne-Edwards) was studied on a sandy beach of Mumbai from January 2005 to December 2006. The area experiences semidiurnal tides. The beach is intermediate dissipative type and consists of medium to fine grade sand. The data were collected after fixing a transect line from high to low shore zone based on tidal heights. A mean abundance of 40 ± 4.55 ind.m−2 was found during 2005, while it was 37.82 ± 7.31 ind.m−2 during 2006. Although no significant difference (p > 0.05) in abundance was observed on seasonal scale, there was a marked variation (p < 0.05) in the vertical distribution with an obvious increasing trend in abundance from high to low shore zone. The zonal variation in the abundance was distinct in different seasons and it increased from pre- to post-monsoon with decreasing tidal heights during both the years. A significant difference (p < 0.05) in the abundance was recorded between high and mid shore zone during all the seasons while mid shore zone showed significantly higher (p < 0.05) abundance during post-monsoon season. Data on distributional pattern of different maturity stages (juvenile, immature, young adult and adult) based on carapace width were also collected. The juveniles were mostly observed in mid and low shore zone, while adults dominated mostly the high shore areas. The factors like morphodynamic state of beach and behavioural ecology of this species seemed to play important role in its high abundance and vertical distribution on the sandy beach of Aksa, Mumbai.

변산반도 해조류 군집구조의 계절적 변동

We examined seasonal variation in the structure of marine macroalgal communities at five sites around the Byeonsan Peninsula, Korea, from January to October 2011. Sixty eight species were identified, including 11 green, 17 brown and 40 red algae. Species richness was highest at Gyeokpo (51 species) followed by Sambal (47), Gosapo (34), Byeonsan (33), and Habgoo (18). Seaweed biomass ranged from 12.98 to 145.33 g dry <TEX>$wt/m^2$</TEX>, with maximum and minimum biomasses at Gyeokpo and Habgoo, respectively. Sargassum thunbergii was the representative alga species occupying 47.89% of the total biomass. The dominant seaweeds were S. thunbergii, Corallina pilulifera, Ulva spp, Gracilaria vermiculophylla, and Carpopeltis affinis. No distinctive vertical distribution of seaweeds was found because S. thunbergii, Ulva spp, and G. vermiculophylla were all distributed from high to low shore. Community indices were as follows: dominance index (DI), 0.44-0.61; richness index (R), 6.27-10.35; evenness index (J'), 0.38-0.59; and diversity index (H'), 1.48-1.71. Gyeokpo had the most biomass and highest species richness, and the lowest percentage of Ulva species. However, species richness declined at Gyeokpo, from 78 to 51 species within 10 years, implying that eutrophication and sedimentation from Mankyeong and Dongjin rivers have reduced the stability of seaweed communities.

Vertical zonation of endosymbiotic zooxanthellae within a population of the intertidal sea anemone, Anthopleura uchidai

Intertidal organisms commonly form zonation bands along the shore. Environmental stressors often determine the vertical position of each zonation band. These stressors may similarly affect the distribution pattern of endogenous species in their intertidal hosts. To evaluate this possibility, we investigated the distribution pattern of endosymbiotic zooxanthellae in the genus Symbiodinium in a population of the intertidal sea anemone Anthopleura uchidai. We used molecular genetics to identify the Symbiodinium clades and found that A. uchidai has two clades of Symbiodinium, clades A and F. These Symbiodinium clades were disproportionally distributed along the vertical gradient of the intertidal shore. Anemones on the upper shore exclusively possessed clade F Symbiodinium while clade A Symbiodinium became dominant in the sea anemones on the lower shore. Photosynthesis activity assays showed that these Symbiodinium clades had similar net productivities at 23.3 and 31.8 °C at all irradiance levels. At 35 °C, however, clade A Symbiodinium exhibited substantially lower net productivities than clade F Symbiodinium, demonstrating that these Symbiodinium clades have distinct tolerances to thermal stress. These results suggest that the thermal gradient across tidal height is a major factor shaping the zonation pattern of Symbiodinium clades in A. uchidai.

Assessment of benthic disturbance associated with stingray foraging for ghost shrimp by aerial survey over an intertidal sandflat

One notable type of bioturbation in marine soft sediments involves the excavation of large pits and displacement of sediment associated with predator foraging for infaunal benthos. Batoids are among the most powerful excavators, yet their impact on sediment has been poorly studied. For expansive tidal flats, only relatively small proportions of the habitat can be sampled due to physical and logistical constraints. The knowledge of the dynamics of these habitats, including the spatial and temporal distribution of ray bioturbation, thus remains limited. We combined the use of aerial photogrammetry and in situ benthic sampling to quantify stingray feeding pits in Tomioka Bay, Amakusa, Japan. Specifically, we mapped newly-formed pits over an 11-ha section of an intertidal sandflat over two consecutive daytime low tides. Pit size and distribution patterns were assumed to scale with fish size and reflect size-specific feeding behaviors, respectively. In situ benthic surveys were conducted for sandflat-surface elevation and prey density (callianassid shrimp). The volume versus area relationship was established as a logistic function for pits of varying sizes by photographing and refilling them with sediment. This relationship was applied to the area of every pit detected by air to estimate volume, in which special attention was paid to ray ontogenetic change in space utilization patterns. In total, 18,103 new pits were formed per day, with a mean individual area of 1060cm2. The pits were divided into six groups (G1 to G6 in increasing areas), with abundances of G1, G2+G3, and G4−G6 being medium, high, and low, respectively. Statistical analyses using generalized linear models revealed a marked preference for the higher prey-density areas in G1 and the restriction of feeding grounds of G4−G6 to the lower shore, with G2+G3 being generalists for prey density and sandflat elevation. The lower degrees of overall bioturbation by G1 and G4−G6 were spatially structured for the eight sub-areas demarcated by prey density and sandflat elevation, while G2+G3 homogenized the state over the sandflat. The newly-formed pits׳ sub-areal mean numerical, excavated-areal, and displaced-sediment-volume densities per day were confined to small ranges: 0.14–0.17m−2, 132–223cm2m−2, and 551–879cm3m−2 (latter two including 119 shallow non-pit excavations). These bioturbation rates are positioned at relatively high levels compared with those by rays from other geographic regions. The present procedure is applicable to the assessment of disturbance by any surface-sediment excavators on tidal flats if their pit dimensions are discernible from the air.

Variations in physiological responses to thermal stress in congeneric limpets in the Mediterranean Sea

Cardiac activity (Arrhenius breakpoint temperatures and Q10 relationships) and heat shock response (hsp70 expression) were measured in the congeneric limpets Patella rustica, P. caerulea and P. ulyssiponensis in order to test the relationship between their vertical distribution and physiological thermal tolerance. These species exhibit different vertical distributions along Mediterranean shores and despite the narrow tidal range in the Mediterranean, they experience different environmental conditions and consequently had specific thermal windows. Cardiac activity of the upper zoned P. rustica was maintained at higher temperatures than its mid- or low shore counterparts, P. caerulea and P. ulyssiponensis. P. rustica had the highest Arrhenius breakpoint temperature (37.9±2.1°C, mean±SD), followed by P. caerulea (35.9±2.6°C), and finally the low-zoned P. ulyssiponensis (32.2±2.3°C). The same pattern was found for Q10 relationships. Expression of hsp70 increased at 34°C and kept increasing with temperature in P. rustica. In P. caerulea, expression reached a maximum at 36°C and decreased at 38°C, suggesting that hsp70 expression in P. rustica provides a more efficient defence against thermal stress than in P. caerulea. As summer environmental temperatures in the Mediterranean regularly reach 35 to 38°C, performances of these limpets suggest that they are already living at the edges of their thermal window, and further temperature changes may have large-scale consequences for these keystone species.

Larval carry‐over effects from ocean acidification persist in the natural environment

An extensive body of work suggests that altered marine carbonate chemistry can negatively influence marine invertebrates, but few studies have examined how effects are moderated and persist in the natural environment. A particularly important question is whether impacts initiated in early life might be exacerbated or attenuated over time in the presence or absence of other stressors in the field. We reared Olympia oyster (Ostrea lurida) larvae in laboratory cultures under control and elevated seawater pCO2 concentrations, quantified settlement success and size at metamorphosis, then outplanted juveniles to Tomales Bay, California, in the mid intertidal zone where emersion and temperature stress were higher, and in the low intertidal zone where conditions were more benign. We tracked survival and growth of outplanted juveniles for 4months, halfway to reproductive age. Survival to metamorphosis in the laboratory was strongly affected by larval exposure to elevated pCO2 conditions. Survival of juvenile outplants was reduced dramatically at mid shore compared to low shore levels regardless of the pCO2 level that oysters experienced as larvae. However, juveniles that were exposed to elevated pCO2 as larvae grew less than control individuals, representing a larval carry-over effect. Although juveniles grew less at mid shore than low shore levels, there was no evidence of an interaction between the larval carry-over effect and shore level, suggesting little modulation of acidification impacts by emersion or temperature stress. Importantly, the carry-over effects of larval exposure to ocean acidification remained unabated 4months later with no evidence of compensatory growth, even under benign conditions. This latter result points to the potential for extended consequences of brief exposures to altered seawater chemistry with potential consequences for population dynamics.

Deja vu? A second mytilid mussel, Semimytilus algosus, invades South Africa's west coast

A second marine mussel is shown to have invaded South Africa's west coast. Molecular techniques, based on intraspecific gene sequence divergences, prove its identity as Semimytilus algosus, a member of the family Mytilidae, native to Chile. The identity of an older introduced population found in Namibia is also confirmed. The present geographic range of S. algosus in South Africa extends some 500 km, from Groenriviersmond in the north to Bloubergstrand in the south. Together with Mytilus galloprovincialis, another previously established invasive mussel, S. algosus has become a dominant intertidal organism on wave-exposed rocky shores across this region. Both species are now much more abundant intertidally than either of the indigenous mussels Aulacomya ater and Choromytilus meridionalis, which have become largely confined to sublittoral and sand-inundated habitats respectively. The two invasive mussels display strong spatial segregation, with M. galloprovincialis dominating the midshore and S. algosus blanketing the lower shore. Through a combination of its small size and high abundance, S. algosus is likely to greatly increase food availability for a range of intertidal predators, many of which cannot consume mussels above a threshold size.