Crab Burrow Density Research Articles

Spatial difference of salt dynamics within burrows in high salinity zone (high intertidal zone & supratidal zone) of mudflat

Surface evaporation and seawater concentration in the tidal flat have been demonstrated as sources of salt for phreatic brine layers. However, the mechanisms of salt replenishment in such layers remain unclear. Here, the transport processes and factors influencing surface salt in mudflat under the influence of bioturbation were examined in the high salinity zone (high intertidal zone & supratidal zone) along the southern coast of Laizhou Bay, China. In this study, the laboratory model and numerical model of salt transport in the mudflat brine distribution area under the influence of crab burrows were constructed through in-situ investigation to simulate the salt transport process in the mudflat brine distribution area under different tidal amplitudes and different beach salinity, and the influence of the diameter and density of crab burrows on the water-salt exchange process was analyzed. The results indicate that in the salt-crust-free region, the salinity change in burrow-dense area (BDA) lags behind that of independent burrow (IB). At the same time, the salinity increase of IB is at most 17 ppt higher than that of BDA, and the salinity decrease of IB is at most 9 ppt lower than that of BDA, which made BDA promoting more salt accumulation and facilitating the salt transport to deeper layers. In the salt-crust-bearing region, due to the high salt content on the beach surface and the weak tidal amplitude, salt is continuously released and accumulated in the surface during multiple tidal cycles, but the ability to transport to the deep layer is weak. In this case, burrows characterized by larger diameters become the preferential paths for salt transport. In addition, crab burrows affect the evaporation of sediments. In this study, the surface salinity of sediments under the influence of burrows is around 10–45 ppt higher than that without burrows.

Effects of burrowing crabs on coastal sediments and their functions: A systematic meta‐analysis

AbstractBurrowing ecosystem engineers, such as termites, crabs, marmots, and foxes, can profoundly affect the biological structure and ecosystem functions of their environments. However, the relative importance of the effects of burrowing engineers on sediments are challenging to predict and are expected to be influenced by engineer density, engineer functional traits (e.g., burrow morphology), and environmental conditions (e.g., geomorphology, vegetation presence). To develop robust hypotheses predicting the impacts of burrowing ecosystem engineers, we conducted a systematic meta‐analysis evaluating the effects of burrowing crabs on sediment properties, nutrient stocks, and ecosystem functions in soft‐sediment coastal habitats (e.g., salt marshes, mangrove forests, tidal flats). Additionally, we tested the impacts of crab burrow density, burrowing crab superfamily (a proxy for crab burrow morphology and diet), and biotic conditions (i.e., vegetation) on the effects of burrowing crab engineers on coastal sediments. Burrowing crabs rework and oxygenate sediments and accelerate rates of nutrient cycling (i.e., nitrification and CO2 flux). However, the magnitude and direction of burrowing crab effects depend on burrowing crab superfamily, the presence of vegetation, and their interaction. Crab burrow density did not consistently predict burrowing engineer effects on sediments. Future efforts need to focus on implementing rigorous manipulative experiments to assess crab ecosystem engineering effects, since methodological variation has hindered efforts to generalize their effects. Our findings suggest that crab engineering effects are predictable across environmental contexts, and understanding the context dependency of crab engineering effects may promote the management and restoration of the critical ecosystem services that are mediated by crab engineers.

Role of abiotic drivers on crab burrow distribution in a saltmarsh wetland

Crab burrows play an important role in saltmarsh wetlands and are a useful indicator of wetland condition. The spatiotemporal distribution of crab burrows varies considerably in tidal wetlands. However, the reasons for these variations are poorly understood, in part, due to the limited availability of comprehensive field data. Based on a two-year continuous observation at a tidal wetland in the northern Jiangsu Coast, China, this study explored the relationship between crab burrow density and environmental variables, including median grain size, water content, organic matter content, soil salinity, and elevation. Our results show that the distribution of crab burrows was unimodal across the shore in winter and spring (Nov-Apr) when air temperature was relatively low, while bimodal in summer and autumn (May-Oct) when temperature was relatively high. The density of crab burrows was larger at areas with higher water content, higher organic matter content, and lower soil salinity, while it was lower with stronger hydrodynamics and lower suspended sediment concentration. Crab burrows were more abundant in vegetated areas than in un-vegetated areas. A backward stepwise model selection was performed based on R-square and Akaike information criterion (AIC) to distinguish the main driving factors that determine crab burrow distribution. Results suggested that the principal driving factors were organic matter content and soil salinity in all the seasons, with the addition of water content in warm seasons. Overall, this study provides a comprehensive field dataset for a more in-depth understanding of crab burrow distribution and a scientific basis for sustainable management of tidal wetlands.

Fiddling with the blue carbon: Fiddler crab burrows enhance CO2 and CH4 efflux in saltmarsh

Saltmarshes are important global carbon (C) sinks, but the considerable uncertainty in the C budget and the underlying mechanisms limit the estimation of greenhouse gas emissions (GHG, e.g., CO2 and CH4) in the context of global climate change. To ascertain the mechanistic understanding, we assessed how crab burrows morphology and greenhouse gas effluxes changed in response to interactions of fiddler crab burrow density, soil organic matter content (high vs low), and presence/absence of Spartina alterniflora (vegetated saltmarsh vs nearby unvegetated mudflat) on the coast of New England (USA). The crab burrow volume in the vegetated saltmarsh was smaller than that in the mudflat, and crab burrow volume greatly correlated with soil CO2 efflux, indicating that crab activities could enhance coastal wetland CO2 efflux. Soil CO2 and CH4 effluxes rates were significantly positively correlated with crab burrow density, organic matter content, and vegetation types. Specifically, the higher soil organic matter content and crab burrow density greatly increased soil heterotrophic respiration in the saltmarsh. Overall, with crab disturbances, soil CO2 and CH4 efflux increased by 32.1% and 47.9%, respectively. This study highlights that fiddler crab burrowing activity plays an important role in the C sequestration of coastal blue C ecosystems (BCEs).

Combined influence of human disturbance and beach geomorphology on Ghost Crab, Ocypode cursor, burrow density and size in the eastern Mediterranean

Ghost Crabs, Ocypode cursor (Linnaeus, 1758), are used as a bioindicator species to evaluate the ecological condition of sandy beaches. Studies using Ghost Crabs as bio-indicator have often focused on the influence of human disturbance and beach geomorphology, separately. However, the relative importance of these variables should be assessed to maintain community structure. Here, I used an indirect burrow examination technique to understand whether Ghost Crabs respond to human disturbance stronger than to geomorphological properties of the sites. I analysed sand compaction rate, sand grain size, beach width, and beach slope as geomorphological features and urbanization index as a measure of human disturbance on each site. I further examined Ghost Crab burrows by counting and measuring the openings. Ghost Crabs showed lower population density and individual body sizes as a response to human disturbance, and the level of this response was partly related to the geomorphological features of the sites. However, human disturbance explained approximately 72% of the variation in the Ghost Crab burrow density and about 70% of the variation in the burrow size, alone. The findings of this study corroborate the use of Ghost Crabs as an efficient bioindicator species of human disturbance on sandy shores to achieve efficient beach management, yet suggest that managers and scientists should combine the influences of geomorphological features of the beaches and the degree of human disturbances in their ecological assessments.

Responses of a tidal freshwater marsh plant community to chronic and pulsed saline intrusion

Abstract Climate change causes both chronic and pulsed environmental changes to ecosystems. In estuaries, tidal freshwater marshes experience both extended and episodic periods of elevated salinities due to sea level rise, reduced river discharge during drought and storm surge, but most research has focused on extended (press) perturbations. Over a 4‐year period, we added diluted seawater to replicated plots in a tidal freshwater marsh in Georgia, USA to raise porewater salinities from freshwater to oligohaline. We assessed the ecosystem effects of press (continuous) and pulse (2 months per year) changes in salinity by measuring the responses of dominant angiosperms, benthic microalgae and dominant macro‐invertebrates (fiddler crabs). We transplanted angiosperms typical of oligohaline and mesohaline conditions into plots as bioindicators (phytometers) to assess potential for vegetation changes over longer time periods. In the press treatment, the cover of all common plant species decreased. Ludwigia repens almost disappeared within the first month; Polygonum hydropiperoides nearly disappeared within the first growing season; Pontederia cordata and Zizaniopsis miliacea declined over the 4 years but did not completely disappear. The decline in the four most dominant plant species decreased total above‐ground plant biomass, leading to an increase in light penetration and increased densities of benthic diatoms and cyanobacteria. The density of fiddler crab burrows was not significantly affected by the treatments, but was positively related to above‐ground plant biomass across all replicates. Transplant experiments indicated that plants typical of higher salinity conditions (e.g. Schoenoplectus sp.) performed well under conditions prevalent in the press plots. In the pulse treatment, only L. repens declined, and there was no effect on community‐level above‐ground biomass or other community variables. Synthesis. Our results indicate that tidal freshwater marsh plant and animal communities are vulnerable to extended periods of salinization but resilient to short saline pulses. Although saline pulses did not impair most ecosystem functions, the decline in a single species (L. repens) in the pulse treatment was associated with reduced marsh accretion and no elevation gain—factors which must be positive for wetland survival in an era of rising seas. Thus, periodic salinization may threaten the long‐term persistence of freshwater wetlands even before dramatic changes in community structure occurs.

Ghost crab predation of loggerhead turtle eggs across thermal habitats

The reproductive success of sea turtles is highly influenced by the environmental and biological conditions of the nesting beach. Maio Island, Cabo Verde, one of the main nesting sites for the Northeast Atlantic loggerhead subpopulation, displays marked heterogeneity of sand coloration, with dark, mixed and light sandy beaches, resulting in different thermal habitats. Considering that sand temperature can influence both sea turtle embryo development and predatory activity by ghost crabs – the main predators of clutches and hatchlings at Cabo Verde – we surveyed loggerhead nesting beaches at Maio Island, with three sand colorations (‘beach type’), to assess: 1) the density and size of ghost crab burrows, as a proxy for ghost crab density and size, and 2) ghost crab predation on 70 loggerhead nests. We further assessed nest site selection, by considering the number of nesting activities and clutches laid across beach type. There were no evident trends in the distributions of ghost crab density and size between years or beach type. We found that ghost crab predation is a major source of mortality in Maio Island, affecting 67.8% (n = 59) of the nests. Ghost crab predation was variable between beaches, but generally, at the warmer dark sand beaches, clutch mortality was mostly caused by ghost crab predation (53.2%, n = 17), while at the mixed sand beaches mortality by predation was low (7.5%, n = 18), compared to mortality due to other causes (49.9%), indicating that other factors can also significantly impact clutch survival. The mixed sand beaches had more nesting activities and higher nest density (2.29/m2; 1.25/m2, respectively), compared to the light sand (0.72/m2; 0.35/m2) and the dark sand beaches (0.73/m2; 0.27/m2), suggesting a possible predation-free nesting preference. Our findings show that some beaches are in need of nest protection, thus we recommend both in situ nest protection and egg translocation to safe hatcheries, depending on the threats identified, to enhance clutch survival at such heterogeneous nesting areas as Maio Island.

Disturbance is complicated: Headward‐eroding saltmarsh creeks produce multiple responses and recovery trajectories

AbstractDisturbances are one of the most important processes affecting natural systems, but there is a gap between simple conceptual models of disturbance and complex empirical studies. We studied the perturbation caused by headward‐eroding creeks in southeastern USA salt marshes. We measured disturbance responses (magnitude and recovery trajectory) of 19 variables. Some variables (shoot density, root biomass, snail density, soil pH, soil strength, soil temperature, elevation) declined sharply, while other variables (crab burrow density, soil organic matter, soil redox) increased sharply, in response to the burrowed and grazed conditions at the creek head. These variables recovered over subsequent years or decades. Other variables (shoot height, aboveground biomass, rhizome biomass, light interception) declined sharply in the creek head, then overshot control values before recovering. Some variables (benthic algae, soil salinity) did not appear to be disturbed by the creek head. As hypothesized, plants recovered before soils and snails. Disturbance magnitude and time to recovery were often greater directly adjacent to the new creekbank than for the same variables in a parallel transect further away from the creekbank, and in some cases variables never converged with control values, indicating a persistent state change. Reducing the dimensionality of the data set into principal component axes obscured the diverse ways in which different aspects of the system responded to and recovered from the perturbation. Our study illustrates the challenges in moving from simple conceptual models of disturbance to empirical studies in which multiple variables are likely to be affected differently and follow different recovery trajectories.

Can we use plant performance as indicators to infer plant-crab interactions in coastal saltmarshes?

Increasing effort has been devoted to restoring coastal ecosystems to counteract their degradation globally. Restoration success of coastal ecosystems often relies on harnessing biotic interactions that shape the performance of foundation plant species. Crabs acting as essential ecosystem engineers and consumers are commonly present in coastal saltmarshes. Previous work has focused on the grazing effect of crabs on plants. In line with the idea of top-down control, plant performance (in terms of biomass or height) is often used as indicators of plant-animal interactions. However, crabs could also produce facilitative effects through non-consumptive behavior. It remains unclear if and to what extent the net effect of crabs on coastal plants is dependent on environmental context. Therefore, systematic assessments are needed to test if the reliability of plant performance as an indicator of plant-crab interactions is context-dependent. Here, we conducted field survey in two similar intertidal saltmarsh ecosystems along the Yellow Sea coast, eastern China, and examined the effects of crab burrowing, soil properties, and nutrient availability on plant (Suaeda salsa) performance using multiple regression and structural equation models. We found that crab burrow density was significantly correlated with plant height, which signals strong plant-crab interactions. Surprisingly, we observed opposite signs (positive vs. negative) of plant-crab relationships between the two study sites that have highly similar composition and structure of plant communities. A possible explanation is that soil compactness can mediate crab burrowing behavior, resulting in differential facilitative effects on the plants. Thus, the usefulness of plant height serving as an indicator of plant-crab interactions depends on environmental context to a substantial degree. More comprehensive indicators taking into account soil compactness may facilitate robust inference of plant-crab interactions. Our results highlight landscape-scale spatial heterogeneity and context-dependency of plant-animal interactions in coastal saltmarshes, and provide a useful implication to inferring nuanced biotic interactions using compressive biotic and abiotic indicators in coastal ecosystems.

Reciprocal facilitation between annual plants and burrowing crabs: Implications for the restoration of degraded saltmarshes

Abstract Increasing evidence shows that facilitative interactions between species play an essential role in coastal wetland ecosystems. However, there is a lack of understanding of how such interactions can be used for restoration purposes in saltmarsh ecosystems. We therefore studied the mechanisms of reciprocal facilitative interactions between native annual plants, Suaeda salsa, and burrowing crabs, Helice tientsinensis, in a middle‐elevation saltmarsh (with generally high plant density and moderate tides) in the Yellow River Delta of China. We investigated the relationship between the densities of the plants and crab burrows in different seasons. Then, we tested whether and how saltmarsh plants and crabs indeed facilitate each other in a series of field and laboratory experiments. Finally, we applied the results by creating a field‐scale artificial approach for microtopographic modification to restore a degraded saltmarsh. We found that the density of plant seedlings in spring was positively correlated with the density of crab burrows in the previous autumn; moreover, the density of crab burrows was correlated with the density of plants in summer. The concave–convex surface microtopography created by crabs promoted seed retention and seedling establishment of saltmarsh plants in winter and spring. These plants in turn facilitated crabs by inhibiting predators, providing food and reducing physical stresses for crabs in summer and autumn. The experimental removal of saltmarsh plants decreased crab burrow density, while both transplanting and simulating plants in bare patches promoted crabs. The microtopographic modification, inspired by our new understanding of the interactions between saltmarsh plants and crabs, showed that these degraded saltmarsh ecosystems can be restored by a single ploughing intervention. Synthesis. Our results suggest a reciprocal facilitation between annual plants and burrowing crabs in a middle‐elevation saltmarsh ecosystem. This knowledge yielded new restoration options for degraded coastal saltmarshes through the one‐time ploughing initiation of microtopographic variation, which could promote the re‐establishment of ecosystem engineers and lead to the efficient recovery of pioneer coastal vegetation and associated fauna.

Combined impacts of natural and anthropogenic disturbances on the bioindicator Ocypode quadrata (Fabricius, 1787)

Intense natural disturbances can dramatically affect populations in various ecosystems and existence of human influences can make the impacts of natural disturbance even greater by reducing the resilience of the populations. Here, we determine how the impacts of natural and anthropogenic disturbances alter population structure of a widespread bioindicator, the Atlantic ghost crab (Ocypode quadrata) by examining its burrow density, size and distribution before and after a hurricane on beaches with different levels of human impacts. We predicted that burrow density and size would show a dramatic decline after the hurricane mainly on the most human-impacted beaches. Because the smaller individuals of this species are highly sensitive to desiccation and thus normally occupy the lower parts of beaches, we further predicted that burrow distribution would not show any changes following the hurricane. We found that the density of ghost crab burrows strongly declined, but that this decline was lessdramatic on beaches with higher levels of human impact. However, the decline in the burrow size 4–7 days following hurricane disturbance indicates that the hurricane had greater impact on larger than on smaller individuals. Moreover, we found that the burrow distribution shifted after the hurricane. When the larger individuals were excluded from the system, the smaller individuals occupied the upper parts of the beach, suggesting that intra-specific interactions are the major mechanism determining the distribution pattern of ghost crabs on sandy shores, rather than physiological limitations (desiccation) that have previously been proposed. Our results suggest that, human influences make the populations less resilient against natural disturbances and that natural disturbances have a larger impact on larger individuals of this bioindicator species.

Influence of sediment characteristics on density and distribution of Ocypodoid crab burrows (superfamily: Ocypodoidea) along the coastal areas of Pakistan

Crabs belong to the superfamily Ocypodoidea are a significant component of benthic fauna and considered as ecosystem engineers because of their dynamic role as an active burrower in mangrove and estuarine environment. The current investigation was to evaluate the crab burrow density, diameter and total area of burrow opening along the coast of Pakistan. The variations in burrow properties and their relation to sediment characteristics were also evaluated to recognize the most influencing variables of sediments that effects on crab burrows. All crab burrow and sediment characteristics differed significantly (p<0.05) among the monitoring sites. Regression analysis showed that crab density was significantly correlated with burrow density (P<0.001). Moreover, burrow density was noticed significantly greater (p<0.05) than crab density. Pearson correlation analysis reveals that moisture, porosity, organics, sand and mean grain size observed as most influencing the features of sediment to determine the ecological functioning of crab burrows in mangrove and mudflats of Pakistan.

What drives the distribution of crab burrows in different habitats of intertidal salt marshes, Yellow River Delta, China

Crabs play important roles in coastal ecosystems and are useful indicators for evaluating ecosystem health. Many previous studies have examined the distribution patterns of crabs among different habitats. However, we know little about what the key factors determining crab burrow distribution among types of habitats. Different kind of crab species may have different preferences of environmental conditions, here, we focus on the dominant crab species Helice tientsinensis in the Yellow River Delta. To identify the drivers of crab burrow distribution in intertidal marshes of the Yellow River Delta, we examined crab burrow density among seven habitats across different marsh zones, with reference to abiotic (water depth, soil hardness, water content, bulk density, porewater salinity, organic matter, total nitrogen and total carbon) and biotic (plant coverage, above- and belowground biomass, macrofauna species richness, abundance and biomass) factors that might explain crab burrow distribution patterns. Differences of all above factors were examined by one-way Analysis of Variance (ANOVA) among different habitats. The best single predictors of crab burrow density were tested by liner regression across the entire study area. Our results showed that patterns of crab burrow distribution were more strongly affected by abiotic drivers (water depth, water content, salinity, soil hardness, organic matter and total carbon) than biotic drivers. Crabs prefer habitats with softer and wetter edaphic conditions. In the future of coastal management, building habitats first, thereafter attracting crabs settling down and regulating feeding area of water birds and other benthic communities are good strategies to follow.

Effects of Small-Scale Armoring and Residential Development on the Salt Marsh-Upland Ecotone

Small-scale armoring placed near the marsh-upland interface to protect single-family homes is widespread but understudied. Using a nested, spatially blocked sampling design on the coast of Georgia, USA, we compared the biota and environmental characteristics of 60 marshes adjacent to either a bulkhead, a residential backyard with no armoring, or an intact forest. We found that marshes adjacent to bulkheads were at lower tidal elevations and had features typical of lower elevation marsh habitats: high coverage of the marsh grass Spartina alterniflora, high density of crab burrows, and muddy sediments. Marshes adjacent to unarmored residential sites had higher soil water content and lower porewater salinities than the armored or forested sites, suggesting that there may be increased freshwater input to the marsh at these sites. Deposition of Spartina wrack on the marsh-upland ecotone was negatively related to elevation at armored sites and positively related at unarmored residential and forested sites. Armored and unarmored residential sites had reduced densities of the high marsh crab Armases cinereum, a species that moves readily across the ecotone at forested sites, using both upland and high marsh habitats. Distance from the upland to the nearest creek was longest at forested sites. The effects observed here were subtle, perhaps because of the small-scale, scattered nature of development. Continued installation of bulkheads in the southeast could lead to greater impacts such as those reported in more densely armored areas like the northeastern USA. Moreover, bulkheads provide a barrier to inland marsh migration in the face of sea level rise. Retaining some forest vegetation at the marsh-upland interface and discouraging armoring except in cases of demonstrated need could minimize these impacts.

Shore to landward transect burrow diversity of fiddler crab in a tropical intertidal coast of Chittagong in Bangladesh

Burrows indicate the abundance and distribution of fiddler crab in an intertidal coast that varies with structure and morphology within intertidal habitats. We observed fiddler crab burrow density and characters (burrow length, depth, diameter and volume) within randomly selected six 1m2 quadrate from three intertidal habitats: higher saltmarsh, mangrove pool (a small ditch distributed within mangrove) and mangrove land through field surveys in a coast of Chittagong, Bangladesh. Burrows were observed and counted for density estimation, and burrow characteristics were studied through excavating 10 representative burrows from each quadrate of each habitat. Spearman correlation was used to relate between the distances (from shore towards land) and burrow characters. Transect starting from saltmarsh as base towards mangrove land showed burrow density decreased from shore to higher intertidal habitat. Simultaneously, higher burrow length and diameter were observed landward and contrariwise shoreward. Burrow prevalence in mangrove pools represents fiddler crabs are abundant within land and shore interface presumably due to the dual privilege of easy burrowing and moist condition required for gill ventilation.Res. Agric., Livest. Fish.4(2): 131-140, August 2017

Shoreline oiling effects and recovery of salt marsh macroinvertebrates from the Deepwater Horizon Oil Spill.

Salt marshes in northern Barataria Bay, Louisiana, USA were oiled, sometimes heavily, in the aftermath of the Deepwater Horizon oil spill. Previous studies indicate that fiddler crabs (in the genus Uca) and the salt marsh periwinkle (Littoraria irrorata) were negatively impacted in the short term by the spill. Here, we detail longer-term effects and recovery from moderate and heavy oiling over a 3-year span, beginning 30 months after the spill. Although neither fiddler crab burrow density nor diameter differed between oiled and reference sites when combined across all sampling events, these traits differed among some individual sampling periods consistent with a pattern of lingering oiling impacts. Periwinkle density, however, increased in all oiling categories and shell-length groups during our sampling period, and periwinkle densities were consistently highest at moderately oiled sites where Spartina alterniflora aboveground biomass was highest. Periwinkle shell length linearly increased from a mean of 16.5 to 19.2 mm over the study period at reference sites. In contrast, shell lengths at moderately oiled and heavily oiled sites increased through month 48 after the spill, but then decreased. This decrease was associated with a decline in the relative abundance of large adults (shell length 21–26 mm) at oiled sites which was likely caused by chronic hydrocarbon toxicity or oil-induced effects on habitat quality or food resources. Overall, the recovery of S. alterniflora facilitated the recovery of fiddler crabs and periwinkles. However, our long-term record not only indicates that variation in periwinkle mean shell length and length-frequency distributions are sensitive indicators of the health and recovery of the marsh, but agrees with synoptic studies of vegetation and infaunal communities that full recovery of heavily oiled sites will take longer than 66 months.

The influence of crab burrows on sediment salinity in a Rhizophora-dominated mangrove forest in North Brazil during the dry season

Many ecological processes are influenced by salinity. Burrowing crabs, abundant fauna of mangrove forests around the world, can facilitate sediment water fluxes, which may decrease the salinity in mangrove sediments. We investigated whether and how crab burrow density and secondary fine root biomass interact to drive sediment salinity during the dry season in a northern Brazilian mangrove forest. Areas with high density of Rhizophora mangle prop roots and areas free of such roots were compared. We found no correlation between burrow density and sediment salinity in areas with dense prop and fine roots, while crab density correlated negatively with sediment salinity in areas without prop roots, where fine root density was low. Hence, the strength of sediment desalination effects of crabs seems to be context dependent, and high root density of a salt-excluding mangrove species (R. mangle) seems to counteract the crabs’ effect. Our results complement those of a former study conducted in the same area during the rainy season, highlighting that the findings are independent from seasonality and should be considered when evaluating the overall ecological effects of crabs in mangrove ecosystems.

Ghost crab burrow density at Watamu Marine National Park: An indicator of the impact of urbanisation and associated disturbance?

Ghost crab (Ocypode species) burrow densities have previously been used as an indicator of anthropogenic impact. This study aimed to assess the burrow density of Ocypode species (O. ryderi and O. cordimanus) at four sites across Watamu Marine National Park, Kenya. Two sites were in front of hotel complexes (denoting a high degree of urbanisation), and two were in front of residential housing among coastal scrub (denoting a low degree of urbanisation). The findings reveal significantly higher burrow densities at sites in front of residential housing, which was the less developed area. This provides further evidence that Ocypode burrow densities can be used, where other methods would be impractical, to estimate the impact of some human activities along beach fronts, such as at Watamu Marine National Park.

Community Structure and Spatial Zonation of Benthic Macrofauna in Mudflats of the Bahía Blanca Estuary, Argentina

ABSTRACT Zapperi, G.; Piovan, M.J., and Pratolongo, P., 2018. Community structure and spatial zonation of benthic macrofauna in mudflats of the Bahia Blanca Estuary, Argentina. The variations in composition of the benthic community and specific physical variables of mudflats in the Bahia Blanca Estuary, across the intertidal gradient, are described. An upper mudflat, with a steeper slope and higher densities of crab burrows exists seaward of a gently-sloped lower zone, where the density of crab burrows progressively diminishes. Monthly samples were collected from both sections of mudflats to analyze the composition of macrozoobenthos, as well as physical and chemical variables in sediments. Neohelice granulata and Polydora sp. were representative species of the upper mudflat. N. granulata had significantly higher densities in January (236 ± 136 individuals per square meter [ind m−2]) and February (200 ± 68 ind m−2), and Polydora sp. had significantly higher densities in May (491 ± 398 ind m−2). N. granula...

Benthic-Pelagic Coupling in an Intertidal Mudflat in the Bahía Blanca Estuary (SW Atlantic)

ABSTRACT Zapperi, G.; Pratolongo, P.; Piovan, M.J., and Marcovecchio, J.E., 2016. Benthic-pelagic coupling in an intertidal mudflat in the Bahia Blanca estuary (SW Atlantic). Benthic-pelagic coupling was evaluated in a shallow, turbid, and nutrient-enriched estuary in the SW Atlantic. We analyzed the annual trends in turbidity, nutrients, and chlorophyll a (Chl a) concentration in the water column and related those changes to benthic fluxes of dissolved inorganic nutrients, estimated through microcosm incubation experiments, as well as seasonal variations in the abundance and composition of macrobenthic communities. The intertidal mudflats of the estuary are characterized by the presence of two subsystems defined by their macroecological features: crab beds, steep areas dominated by the burrowing crab, and Laeonereis flats, plain areas with low crab burrow density. Peak Chl a concentration in the water column occurred in July after turbidity reached its minimum value in June. Dissolved nutrients decreased...