Beach Species Research Articles

Splitting light pollution: Wavelength effects on the activity of two sandy beach species

Artificial Light at Night (ALAN) threatens to disrupt most natural habitats and species, including those in coastal settings, where a growing number of studies have identified ALAN impacts. A careful examination of the light properties behind those impacts is important to better understand and manage the effects of this stressor. This study focused on ALAN monochromatic wavelengths and examined which types of light spectra altered the natural activity of two prominent coastal species from the Pacific southeast: the talitroid amphipod Orchestoidea tuberculata and the oniscoid isopod Tylos spinulosus. We compared the natural daylight/night activity of these organisms with the one they exhibit when exposed to five different ALAN wavelengths: lights in the violet, blue, green, amber, and red spectra. Our working hypothesis was that ALAN alters these species’ activity at night, but the magnitude of such impact differs depending on light wavelengths. Measurements of activity over 24 h cycles for five consecutive days and in three separate experiments confirmed a natural circadian activity pattern in both species, with strong activity at night (∼90% of probability) and barely any activity during daylight. However, when exposed to ALAN, activity declined significantly in both species under all light wavelengths. Interestingly, amphipods exhibited moderate activity (∼40% of probability) when exposed to red lights at night, whereas isopods shifted some of their activity to daylight hours in two of the experiments when exposed to blue or amber lights, suggesting a possible alteration in this species circadian rhythm. Altogether, our results were consistent with our working hypothesis, and suggest that ALAN reduces night activity, and some wavelengths have differential effects on each species. Differences between amphipods and isopods are likely related to their distinct adaptations to natural low-light habitat conditions, and therefore distinct sensitivity to ALAN.

No man’s land support the endemic Red Sea ghost crab (Ocypode saratan) in the Gulf of Eilat

Tourism pressure on the Red Sea ecosystem have posed significant threats to numerous endemic species, including the Ghost Crab Ocypode saratan, which is exclusively found along a small stretch of beach in the Eilat/Aqaba Red Sea Gulf. Due to the limited understanding of their ecology, we investigated how tourism impacts the behavior of this species. Employing a natural setup, we compared burrow dimensions, pyramid structures, and density across three distinct beach sections subjected to varying levels of human interference. Access to a secluded beach, referred to as “No Man’s Land,” provided a crucial control for our study. This facilitated a comparative analysis of ghost crab activity among beaches experiencing differing levels of human disturbances: (1) a tourist beach characterized by continual high disturbance, (2) a naval beach subject to moderate and sporadic disturbances, and (3) the isolated “no man’s land” beach devoid of human presence. Our observations revealed notable differences in ghost crab density among the three beaches. Furthermore, we observed that on the secluded beach, larger individuals tended to establish burrows farther from the waterline and construct taller sand pyramids. Given the significance of sexual selection processes, their conservation becomes imperative for the survival and potential expansion of the ghost crab population across the Gulf of Eilat/Aqaba. We propose a straight-forward and cost-effective strategy: the designation of short, secluded beach enclaves along this gulf. We believe that this approach will mitigate adverse impacts of tourisms while simultaneously benefiting various sandy beach species.

Unveiling coastal diversity: An inventory and conservation report of beach forest flora of Surigao del Sur, Philippines

Abstract. Ramos GB, Panduyos JB, Caray RE, Bacquial LS. 2024. Unveiling coastal diversity: An inventory and conservation report of beach forest flora of Surigao del Sur, Philippines. Biodiversitas 25: 421-430. Coastal greenbelts, comprise mangroves and beach forest trees, are pivotal in disaster mitigation and climate change resilience. Despite the evident importance of these coastal ecosystems, they are often overlooked in research due to a lack of comprehensive data on species community structure and their broader ecological importance. Hence, this present study was conducted to document beach forests composition and conservation status in selected coastal municipalities of Surigao del Sur, Philippines. The study was conducted in five sampling locations, namely, La Paz, Bil-at, Balibadon, Poblacion Cagwait and Arangasa Island. At each sampling location, a 2 km transect line, parallel to the beach’s shoreline, was established having a 100 square meter sampling plots spaced 50m apart. Beach species frequency counts, percentages, and diversity indices were quantified. The study documented 27 beach forest species belonging to 21 families and 25 genera with the dominant species being Crinum asiaticum, Cocos nucifera, Millettia pinnata, Timonius compressicaulis, and Terminalia catappa. Both Arangasa Island and La Paz beach forests have the highest species diversity (H’ = 2.04); however, Cagwait has the highest species richness (Margalef = 2.34). This study has potential to significantly contribute in addressing existing data gap regarding beach forest species in the Philippines. With the looming threat of extinction due to infrastructural development and anthropogenic activities, the study's outcomes stand as an urgent call to action; thus, a collaborative endeavor of Local Government Units, academicians, and community for conservation and protection before these species succumb to the threat of extinction.

Ingestion of marine debris by juvenile Magellanic penguins (Spheniscus magellanicus) in wintering grounds of coastal Argentina

The occurrence of marine debris in the stomach contents of young male and female Spheniscus magellanicus stranded along the Atlantic coast of northern Argentina during its post-breeding exodus is reported for the first time. Marine debris was found in 15.5 % of 148 dead penguins, with a higher proportion of debris found in females when compared to males. A total of 81 debris items was recorded; plastic and paper each contributed with an equal number of debris whereas rubber contributed with a single item. Chemical identification performed using FTIR/ATR revealed that plastic items were largely LDPE and PA; other polymers included HDPE, PP and PS. The average length of fragmented plastic debris are in line with those reported from penguins stranded along the southern Brazilian coasts. Our study indicates that loads of ingested marine debris were roughly five times lower when compared to the estimates for the species in Brazilian beaches.

Multiple species ingest microplastic but few reflect sediment and water pollution on sandy beaches: A baseline for biomonitoring

Databases recording the ingestion of microplastics by marine animals are growing. This is also recurrent on sandy beaches, where different biomonitors have been proposed to monitor the impacts of plastic pollution. We aimed to record the occurrence of suspected microplastic (SMP) in the digestive tract of multiple taxa (n = 45 identified species) and test whether some macroinvertebrates and fishes ingested SMPs proportionally with the pollution level of sediment and water; thus, we aimed to depict which sandy beach species could be used as biomonitors. Among all taxa, 10 macroinvertebrates and 12 fish species were reported to ingest SMP for the first time. SMP morphotypes proportion differed between abiotic and biotic compartments. Moreover, 10 of 12 taxa did not have SMP concentration linearly related with SMP in sediment and water. Our findings suggest that few species from sandy beaches can be used as efficient biomonitors, although almost all ingest plastic polymers.

Exposure of Loggerhead Sea Turtle Nests to Waves in the Florida Panhandle

Wave wash-over poses a significant threat to sea turtle nests, with sustained exposure to waves potentially resulting in embryonic mortality and altered hatchling locomotor function, size, and sex ratios. Identifying where and under what conditions wave exposure becomes a problem, and deciding what action(s) to take (if any), is a common issue for sea turtle managers. To determine the exposure of sea turtle nests to waves and identify potential impacts to hatchling productivity, we integrated a geographic information system with remote sensing and wave runup modeling across 40 nesting beaches used by the Northern Gulf of Mexico Loggerhead Recovery Unit. Our models indicate that, on average, approximately 50% of the available beach area and 34% of nesting locations per nesting beach face a significant risk of wave exposure, particularly during tropical storms. Field data from beaches in the Florida Panhandle show that 42.3% of all nest locations reported wave exposure, which resulted in a 45% and 46% decline in hatching and emergence success, respectively, relative to their undisturbed counterparts. Historical nesting frequency at each beach and modeled exposure to waves were considered to identify priority locations with high nesting density which either experience low risk of wave exposure, as these are good candidates for protection as refugia for sustained hatchling production, or which have high wave exposure where efforts to reduce impacts are most warranted. Nine beaches in the eastern Florida Panhandle were identified as priority sites for future efforts such as habitat protection or research and development of management strategies. This modeling exercise offers a flexible approach for a threat assessment integration into research and management questions relevant to sea turtle conservation, as well as for other beach species and human uses of the coastal environment.

Full stomachs at empty tides: tidal cycle affects feeding activity and diet of the sandy beach gastropod Olivella minuta

ABSTRACTOlivella minuta is an abundant neogastropod on sandy beaches from Texas (USA) to southern Brazil. This study aimed to characterize and compare the feeding activity and diet of a Brazilian population of O. minuta in different tidal zones (intertidal and subtidal), and different tidal levels (high and low tides), with three combinations of tidal zone and level being studied (intertidal during low tide, intertidal during high tide and subtidal). The results showed that diet composition was generally similar among tidal conditions, with O. minuta being a generalist, feeding on 45 different food items. Feeding activity, however, was higher in the intertidal during low tide, whereas the richness and diversity of food items were higher in the intertidal during high tide. The higher feeding activity of O. minuta during low tide may be linked to a lower risk of predation; at low tide organisms may be able to feed for a longer time, and this may be particularly true on beaches with fine sand, where water retention is higher than that on beaches with coarse sand. The higher diversity of food items consumed in the intertidal during high tide is likely related to the increased prevalence of planktonic food during high tide. Our results indicate that tidal zone and level may strongly influence the feeding activity of coastal soft-bottom species and that species may show higher feeding activity during low tide. Given the current loss of intertidal habitats due to anthropogenic activity and climate-change associated factors, our study has important implications, highlighting the importance of intertidal areas for the ecology and conservation of sandy beach species.

Supporting sandy beach conservation through comparative phylogeography: The case of Excirolana (Crustacea: Isopoda) in South Africa

Sandy beach ecosystems are ecologically and culturally important, yet they face a wide range of anthropogenic stressors. Their constituent biodiversity is usually poorly resolved, with numerous instances of cryptic species described. In addition, there are few studies on the spatio-temporal patterns of evolutionary diversity, although these are vital for unravelling historical and contemporary processes acting to shape biodiversity, with measures of molecular diversity and differentiation providing important insights towards the conservation and management of beach ecosystems. Here we utilise a comparative phylogeographic approach to describe the mtDNA COI variation of two co-distributed Excirolana (Crustacea, Isopoda) sister-species in South Africa. We found that both species showed medium to high population genetic structure, with many populations isolated from each other. In addition, we describe two deeply divergent lineages for both species in the eastern parts of their ranges, which may constitute two additional Excirolana species in South Africa. We show that populations on the range edge for both species have lower genetic diversity than in the core. Our results on the divergent patterns of molecular diversity, in addition to the high levels of population divergence, highlight the need for the inclusion of molecular indices into conservation planning. This ensures safeguarding not only patterns of species occurrence, but also genetic diversity, critical to maximising resilience of sandy beach species in a changing world.

Resource-use dynamics of co-occurring chondrichthyans from the First Coast, North Florida, USA.

Recent studies on shark assemblages on the northeast Florida and southeast Georgia coast (hereafter referred to collectively as the "First Coast") have demonstrated differences in species and age-class composition of catch from previously characterized estuaries and newly surveyed area beaches, demonstrating that these regions may provide a critical habitat to different segments (i.e., life stages) of local shark populations. In this study, carbon and nitrogen stable isotopes (δ13 C and δ15 N) from muscle tissue and blood plasma were used to examine trophic dynamics (and temporal variability thereof) of the three dominant co-occurring species found along First Coast beaches (the Atlantic Sharpnose shark Rhizoprionodon terraenovae, Blacknose shark Carcharhinus acronotus and Blacktip shark Carcharhinus limbatus) to determine if they exhibit overlap in resource use along with spatial and temporal habitat use. Although considered spatially segregated from the beach species, a dominant, age-class species found in First Coast estuaries (juvenile Sandbar sharks Carcharhinus plumbeus) was also included in this analysis for comparison. Temporal variability of resource-use characteristics was detected at the species level. Resource-use overlap among species varied by tissue type and was generally higher for blood plasma, suggesting greater resource sharing over more recent time periods. Over longer time periods Atlantic Sharpnose and Blacktip sharks exhibited resource-use expansion, whereas Blacknose sharks exhibited a narrowing in resource use, suggesting a more specialized foraging strategy compared to the other species. The resource-use breadth of Sandbar sharks also expanded between blood plasma and muscle tissue. Significant size relationships were detected in Blacktip and Sandbar sharks, indicating ontogenetic resource shifts for both species. A diversity of highly productive resource pools likely support shark populations along the First Coast such that resource-use differentiation is not required to facilitate species co-occurrence. This work may shed light on understanding patterns of species co-occurrence as well as aid in future conservation efforts.

Disentangling the environmental impact of different human disturbances: a case study on islands

Coastal ecosystems suffer substantially from the worldwide population growth and its increasing land demands. A common approach to investigate anthropogenic disturbance in coastal ecosystems is to compare urbanized areas with unaffected control sites. However, the question remains whether different types of anthropogenic disturbance that are elements of an urbanized area have the same impact on beach ecosystems. By investigating small islands that are utilized for tourism, inhabited by the local population, or remained completely uninhabited, we disentangled different anthropogenic disturbances and analysed their impacts on hermit crabs as indicator species. We observed a negative impact on abundance on tourist islands and a negative impact on body size on local islands. In comparison to the uninhabited reference, both disturbances had an overall negative impact. As both forms of disturbance also impacted the underlying food resource and habitat availability differently, we propose that the findings from our study approach are valid for most obligate beach species in the same system. This demonstrates that in urbanized areas, the coastal ecosystem is not always impacted identically, which emphasizes the importance of considering the particular type of anthropogenic disturbance when planning conservation action in urbanized areas.

Artificial light pollution at night (ALAN) disrupts the distribution and circadian rhythm of a sandy beach isopod

Coastal habitats, in particular sandy beaches, are becoming increasingly exposed to artificial light pollution at night (ALAN). Yet, only a few studies have this far assessed the effects of ALAN on the species inhabiting these ecosystems. In this study we assessed the effects of ALAN on Tylos spinulosus, a prominent wrack-consumer isopod living in sandy beaches of north-central Chile. This species burrows in the sand during daylight and emerges at night to migrate down-shore, so we argue it can be used as a model species for the study of ALAN effects on coastal nocturnal species. We assessed whether ALAN alters the distribution and locomotor activity of this isopod using a light system placed in upper shore sediments close to the edge of the dunes, mimicking light intensities measured near public lighting. The response of the isopods was compared to control transects located farther away and not exposed to artificial light. In parallel, we measured the isopods’ locomotor activity in the laboratory using actographs that recorded their movement within mesocosms simulating the beach surface. Measurements in the field indicated a clear reduction in isopod abundance near the source of the light and a restriction of their tidal distribution range, as compared to control transects. Meanwhile, the laboratory experiments showed that in mesocosms exposed to ALAN, isopods exhibited reduced activity and a circadian rhythm that was altered and even lost after a few days. Such changes with respect to control mesocosms with a natural day/night cycle suggest that the changes observed in the field were directly related to a disruption in the locomotor activity of the isopods. All together these results provide causal evidence of negative ALAN effects on this species, and call for further research on other nocturnal sandy beach species that might become increasingly affected by ALAN.

What do we know about Cassis tuberosa (Mollusca: Cassidae), a heavily exploited marine gastropod?

Cassis tuberosa is a key species in reefs and sandy beaches, where it plays an essential role as a predator of echinoderms (sea urchins and sand dollars). Due to the beauty of its shell, it is one of the most exploited species for trade as marine souvenirs throughout its distribution in the Western Atlantic. Despite its ecological importance, there is little available information about population and biological data or the impacts of its removal from its natural habitats. Considering the economic and ecological importance of this species, this study provides a short review of existing studies and highlights research and conservation needs for this highly exploited marine gastropod.

Life-history, substrate choice and Cytochrome Oxidase I variations in sandy beach peracaridans along the Rio de la Plata estuary

Life-history, substrate choice and Cytochrome Oxidase I (COI) sequences were analysed in populations of two peracaridans, the supralittoral talitrid Atlantorchestoidea brasiliensis and the intertidal cirolanid Excirolana armata. Three populations of each species, from beaches with similar grain size and located at different points along the natural gradient generated by the Rio de la Plata estuary were analysed. Abundance of E. armata increased with distance from the estuary, while the opposite trend was observed for A. brasiliensis. The proportion of females decreased towards high salinities for both species, significantly for E. armata. A test on substrate salinity preference revealed the absence of patterns due to active choice in E. armata. By contrast, A. brasiliensis showed no preference for the population closer to the estuary, while individuals from the other two sites significantly preferred high salinity substrates. Mitochondrial COI sequences were obtained from A. brasiliensis specimens tested for behaviour. Sequence analysis showed the population from the intermediate site to differ significantly from the other two. No significant genetic differentiation was instead found between populations from the two most distant sites, nor between individuals that expressed different salinity preference. Results showed that diverse sets of traits at the population level enable sandy beach species to cope with local environmental changes: life-history and behavioural traits appear to change in response to different ecological conditions, and, in the case of A brasiliensis, independently of the population structure inferred from COI sequence variation. Information from multiple traits allowed detection of population profiles, highlighting the relevance of multidisciplinary information and the concurrent analysis of field data and laboratory experiments, to detect responses of resident biota to environmental changes.

Surface activity patterns of macrofauna on pocket, tidal beaches: Insights into the role of wrack and artificial lighting

This study targets surface activity of mobile macrofauna on pocket tidal beaches, undergoing different human use. We considered two beaches in Pittwater (NSW, Australia): Tennis beach on Scotland Island features artificial structures and provided with artificial lighting, while Portuguese beach (Ku-Ring-Gai Chase National Park) is only accessible by boat and has no artificial structures. At each site we placed pitfall traps across the littoral zone, with replicates at an opposite tidal period. Traps were kept active for 24 hours and emptied every three hours. The beach-hopper Platorchestia smithi was dominant in abundance at both sites; however Portuguese had a higher species number, including the burrowing isopod Actaecia bipleura. Circular summaries and behavioural models were calculated for abundant species. We found two different activity peaks for adults (nocturnal) and juveniles (sunrise) of P. smithi, consistent across sites, and a complex, tide-related pattern for A. bipleura. We also remarked the relevance of wrack presence on the littoral: this factor was found to modulate the activities of specific categories of macrofauna, such as females and juveniles of P. smithi, and A. bipleura. Results finally indicated no effect of artificial lighting on surface activity of abundant beach species.

Beaches under pressure – effects of human access on vegetation at Baltic Sea beaches

AbstractQuestionsHow do cover, richness and composition of plant species vary according to different levels of beach access? What shifts in plant traits occur along gradients of tourism intensity? What recommendations regarding the sustainable management of Baltic Sea beaches can be proposed?LocationSouthern Baltic Sea beaches in Germany.MethodsIn this study, the species composition of vascular plants on beaches with differing accessibility to tourists was analysed at the southwest Baltic Sea coast. In total, 894 vegetation plots were evaluated in order to determine vegetation changes along the sea–inland gradient due to different levels of human accessibility at beaches. Relevés were conducted as repeated transects from the beach ridge to the shore. Shifts in vegetation characteristics due to different levels of tourism access were analysed at the level of plant communities and plant species traits.ResultsSpecies richness did not differ significantly between the levels of accessibility. Vegetation cover significantly increased with distance to the shore and was highest in the upper shore area of closed beaches (52.0 ± 2.7%). Corresponding to the increase in beach access, we observed an increase in ruderal species and a decrease in typical beach species of the vegetation class Honckenyo‐Elymetea. Tourism access and distance to the shoreline had a decisive influence on the distribution of plants with selected plant traits. In particular, at accessible sites, a loss of plants with leaves having high scleromorphy was recorded.ConclusionsIncreased beach access results in a loss of typical beach plant species. Changes in vegetation characteristics are considered to alter the function of the beach ecosystem. Based on these results, we derived spatially differentiated management measures for excluding the most sensitive beach areas from tourism.

Influence of patch size and connectivity on beach and dune species in land-uplift coasts

Background: Land-uplift beaches and adjacent dunes contribute considerably to natural diversity. In such fragmented habitat types, the size and connectivity of a habitat patch are hypothesised to strongly influence the distribution of species, particularly the most habitat-specific ones.Aims: To test this hypothesis, our study compared the effects of habitat pattern (patch size and connectivity) and local environmental factors on the distribution and richness of beach species.Methods: We collected extensive observational data on vegetation and environment from beach systems along a 600-km land-uplift gradient on the Baltic Sea coast. The analyses were repeated with three modelling methods to ensure that the results were independent of the selected method.Results and conclusions: Our results indicate that patch size and connectivity influence the occurrence and richness of habitat specialists, while total beach species richness is less dependent on the habitat pattern. Patch size and connectivity are as influential on beach vegetation as local environmental drivers. Unexpectedly, largest patch size or highest connectivity does not appear to maximise species richness or the probability of species occurrence. Instead, the study highlights species-specific responses and the value of also relatively small and isolated habitat patches. Both the diverse network of habitat patches and local environmental variability should be accounted for to efficiently preserve beach species.

Coastal talitrids and connectivity between beaches: A behavioural test

Beach-hoppers and sandhoppers in the family Talitridae are strongly linked to the supralittoral environment. They are semi-terrestrial animals and because they are direct developers there is potentially no mobility between populations on adjacent beaches. In the case of coastlines fragmented by natural or artificial structures, the assumed lack of inter-connectivity between beaches may represent a severe threat for the resident populations: in case of impacts, they might not be able to recover and the habitat might not be re-colonised. Unless we consider another possible scenario: the potential connectivity of populations via water currents, from individuals swashed accidentally into the sea. We therefore tested two different species, the sandhopper Notorchestia quadrimana and the beach-hopper Platorchestia smithi for features relevant to dispersal and connectivity among beaches: 1) survival in sea-water; 2) orientation (baseline and scototaxis) in sea-water and; 3) behaviour in a current. Talitrid populations were sampled from a sheltered beach and an exposed beach along the New South Wales coast. On the sheltered beach both species were found, co-occurring within the same distance from the shoreline. On the exposed beach only P. smithi was found, in a dune slack far away from the shoreline. All individuals tested survived 96h in immersion, and when subjected to a current they were clinging on the edge of the flume apparatus for most of the duration of the test. Differences emerged when comparing orientation, with the sharpest precision towards a dark pattern (positive scototaxis) in P. smithi from the sheltered beach and bimodal orientation (partly scototactic and partly sun compass) in N. quadrimana. The behavioural differences observed are likely developed as risk-related: sandhoppers burrow in the substrate and are less exposed to occasional swash, while beach-hoppers living in cast wrack displayed the ability of swimming quickly towards a floating object, increasing the likelihood of being passively carried from one beach to another. Different ecological groups such “sandhoppers” and “beach-hoppers” showed different behavioural patterns. The consideration of behavioural answers to swash risk highlighted the possibility of the connectivity of talitrid populations across fragmented beaches.

Niche segregation amongst sympatric species at exposed sandy shores with contrasting wrack availabilities illustrated by stable isotopic analysis

Wrack supplies (macroalgae, seagrasses and carrion) are a common feature of sandy beaches worldwide. These allochthonous inputs are a potential high-quality food subsidy for beach fauna, but little is known about the feeding ecology and niche segregation strategies of these species in beaches with limited wrack availabilities. We used stable isotopic ratios of nitrogen and carbon to examine the diets and niche segregation among three sympatric crustaceans, the amphipods Talitrus saltator and Talorchestia brito, and the isopod Tylos europaeus, in two temperate beaches, Cabedelo and Quiaios, on the Portuguese Atlantic coast, with contrasting wrack availabilities, over winter and summer. In the beach with limited wrack (Quiaios), consumers showed significantly different interspecific and temporal isotopic signatures, suggesting a distinct foraging habitat and niche differentiation. Mixing models outputs (SIAR) revealed in this case a seasonal shift in the diet of consumers from terrestrial sources in winter towards marine-based sources (phytoplankton) in the summer. In contrast, at Cabedelo, consumers showed clear overlap in isotopic signatures, with similar contributions of the available wrack to their diets. As a whole, an opportunistic and generalist feeding behaviour was described for these species, namely for T. saltator. Isotopic profiles support the occurrence of spatial overlap during summer but different foraging strategies of the three species in these beaches during winter. Our results show that on temperate beaches with ephemeral wrack supplies, consumers might need to adopt different foraging strategies and niche segregation for their subsistence, and additionally illustrate the viability of using stable isotopes to capture subtle changes in trophic niches.

Spatial structure on ocean-exposed sandy beaches: faunal zonation metrics and their variability

Spatial ecological structure is expected to be amplified at interface regions, such as sandy beaches, which form the globe's largest ecotone between the oceans and the land. Yet, the dynamic and unstable nature of sandy shore habitats, coupled with the great mobility and behav- ioural plasticity of beach species, theoretically counteract the development and maintenance of stable spatial structure, such as faunal zonation across the intertidal. We examined spatial struc- ture across the non-vegetated beach-face, using a large data set (3120 replicate samples distrib- uted across 260 cross-shore transects) of intertidal macrobenthos distribution from eastern Aus- tralia. Most (94%) distribution data of the benthic assemblage contained distinct spatial structure, evident as faunal zonation across the shore from the swash to the dunes. A general model recog- nised a tripartite biological division of the shore, but variability in the number of zones was pro- nounced. This variability implies that designs employing low temporal replication may fail to accurately describe the spatial structure on many ocean-exposed sandy beaches. Overall, our data support the prediction of distinct spatial structure based on the prominent interface traits of beach systems as well as the prediction of heterogeneity in spatial structure based on the mobility of beach species and instability of their habitat.

Exploring Macroinvertebrate Species Distributions at Regional and Local Scales across a Sandy Beach Geographic Continuum

Exposed sandy beaches are highly dynamic ecosystems where macroinvertebrate species cope with extremely variable environmental conditions. The majority of the beach ecology studies present exposed beaches as physically dominated ecosystems where abiotic factors largely determine the structure and distribution of macrobenthic communities. However, beach species patterns at different scales can be modified by the interaction between different environmental variables, including biotic interactions. In this study, we examined the role of different environmental variables for describing the regional and local scale distributions of common macrobenthic species across 39 beaches along the North coast of Spain. The analyses were carried out using boosted regression trees, a relatively new technique from the field of machine learning. Our study showed that the macroinvertebrate community on exposed beaches is not structured by a single physical factor, but instead by a complex set of drivers including the biotic compound. Thus, at a regional scale the macrobenthic community, in terms of number of species and abundance, was mainly explained by surrogates of food availability, such as chlorophyll a. The results also revealed that the local scale is a feasible way to construct general predictive species-environmental models, since relationships derived from different beaches showed similar responses for most of the species. However, additional information on aspects of beach species distribution can be obtained with large scale models. This study showed that species-environmental models should be validated against changes in spatial extent, and also illustrates the utility of BRTs as a powerful analysis tool for ecology data insight.