Intertidal Invertebrates Research Articles

Are Mussels Always the Best Bioindicators? Comparative Study on Biochemical Responses of Three Marine Invertebrate Species to Chronic Port Pollution.

Bivalves have traditionally been considered good bioindicators due to their sensitivity to pollution, among other features. This characteristic is shared by several other non-bivalve species as well, though studies in this respect remain scarce. This work aims to compare biomarker sensitivity to chronic port pollution among three intertidal invertebrate species with good bioindicator characteristics. Mussels' immunological (phenoloxidase and peroxidases) and biotransformation (glutathione-S-transferase) responses were contrasted against those of limpets and barnacles. The three species under study evidenced activity of all the enzymes measured, although with differences. Barnacle Balanus glandula was the most sensitive species showing pollution modulation of the three enzymes, which suggests that mussels would not always be the best bioindicator species among marine invertebrates depending on the responses that are assessed.

Molecular evidence of distinct evolutionary units in the sandhopper Talorchestia capensis (Amphipoda, Talitridae) along South African coasts

Marine geographical and ecological barriers often reflect intraspecific genetic discontinuities among populations which may experience different selective pressures and undergo evolutionary divergence. While the phylogeography of marine intertidal invertebrates across the Atlantic/Indian Ocean transition received more attention, the population genetic structures of supralittoral direct developers across such transition area have been poorly investigated. Sandhoppers are supralittoral invertebrates characterised by a direct developmental mode (low dispersal ability), and Talorchestia capensis (Amphipoda, Talitridae) represents the most abundant species of sandhoppers along the South African coasts. To define population structure of T. capensis, we used a mitochondrial marker (the cytochrome oxidase subunit I gene, COX1). T. capensis showed a clean population structure with three main haplogroups genetically well separated, although this separation is not perfectly in line with geographical boundaries described for this area. The presence of separate evolutionary significant units is also confirmed by the shape of mismatch distribution, as well as the p distance values among groups. The overall results confirm the importance of mtDNA to retrieve information on the evolutionary history of species. This study suggests the evidence of a complex-species for this sandhoppers, which have never been considered before, providing fundamental basis for further studies.

Effects of beach replenishment on intertidal invertebrates: A 15-month, eight beach study.

Beach replenishment is an increasingly popular means to remediate coastal erosion, but no consensus exists regarding how long replenishment affects sandy beach intertidal invertebrates, key components of beach ecosystems. We monitored the intertidal invertebrate community for fifteen months following a replenishment project at eight beaches, each with replenished and control sections, across San Diego County. Nearly all taxa showed major declines in abundance immediately following replenishment. Populations of talitrid amphipods and the bean clam Donax gouldii recovered within one year, sooner than in previous studies. On some beaches, populations of the mole crab Emerita analoga bloomed four months after replenishment and were more numerous on replenished portions of beaches at that time. Mole crab populations subsequently declined and no longer differed by treatment. The polychaete community, composed of Scolelepis sp. and several other numerically important taxa, showed a strong replenishment-induced reduction in abundance that persisted through the end of the study. The large negative effect of replenishment on polychaetes, coupled with their overall importance to the invertebrate community, resulted in a more than twofold reduction in overall invertebrate abundance on replenished beaches at 15 months. Such reductions may have far reaching consequences for sandy beach ecosystems, as community declines can reduce prey availability for shorebirds and fish. As this and other recent studies have revealed longer times for the recovery of intertidal invertebrates than previously observed, longer study periods and more cautious estimates regarding the magnitude, variability, and duration of impacts of beach replenishment for management decision-making are warranted.

Facing the Heat: Does Desiccation and Thermal Stress Explain Patterns of Orientation in an Intertidal Invertebrate?

A key challenge for ecologists is to quantify, explain and predict the ecology and behaviour of animals from knowledge of their basic physiology. Compared to our knowledge of many other types of distribution and behaviour, and how these are linked to individual function, we have a poor level of understanding of the causal basis for orientation behaviours. Most explanations for patterns of animal orientation assume that animals will modify their exposure to environmental factors by altering their orientation. We used a keystone grazer on rocky shores, the limpet Cellana tramoserica, to test this idea. Manipulative experiments were done to evaluate whether orientation during emersion affected limpet desiccation or body temperature. Body temperature was determined from infrared thermography, a technique that minimises disturbance to the test organism. No causal relationships were found between orientation and (i) level of desiccation and (ii) their body temperature. These results add to the growing knowledge that responses to desiccation and thermal stress may be less important in modifying the behaviour of intertidal organisms than previously supposed and that thermoregulation does not always reflect patterns of animal orientation. Much of what we understand about orientation comes from studies of animals able to modify orientation over very short time scales. Our data suggests that for animals whose location is less flexible, orientation decisions may have less to do with responses to environmental factors and more to do with structural habitat properties or intrinsic individual attributes. Therefore we suggest future studies into processes affecting orientation must include organisms with differing levels of behavioural plasticity.

Response of Native Species 10 Years After Rat Eradication on Anacapa Island, California

Abstract Measuring the response of native species to conservation actions is necessary to inform continued improvement of conservation practices. This is particularly true for eradications of invasive vertebrates from islands where up-front costs are high, actions may be controversial, and there is potential for negative impacts to native (“nontarget”) species. We summarize available data on the response of native species on Anacapa Island, California, 10 y after the eradication of invasive black rats Rattus rattus. Native marine taxa hypothesized to respond positively to rat eradication increased in abundance (Scripps's murrelet Synthliboramphus scrippsi; International Union for Conservation of Nature Vulnerable, and intertidal invertebrates). Two seabird species likely extirpated by rats—ashy storm-petrel Oceanodroma homochroa (International Union for Conservation of Nature Endangered) and Cassin's auklet Ptychoramphus aleuticus—are now confirmed to breed on the island. Long-term negative effects from nontarget impacts are limited. Rufous-crowned sparrows Aimophila ruficeps obscura are still present, although likely in lower abundance. The endemic Anacapa deer mouse Peromyscus maniculatus anacapae population increased with no loss in heterozygosity, but with reduced genetic differentiation on East Anacapa and the loss of some alleles across the islets. Intertidal invertebrate cover increased while algal cover decreased. These findings clarify the pervasive effects of invasive rats on a wide variety of taxa, the short- and long-term impacts of eradication, and the ability of some island fauna to passively recover following a carefully planned rat-eradication project.

Alutiiq Subsistence Economy at Igvak, a Russian-American Artel in the Kodiak Archipelago

Igvak was a Russian-American Company fur-hunting outpost ( artel ) on the south end of Afognak Island that was occupied from the 1790s to about 1830. Midden samples were recovered from deposits adjacent to the Alutiiq workers’ barracks as part of the Dig Afognak program. Although small amounts of European domesticates were identified, the bulk of the diet focused on traditional local foods. The dominant species included cod, harbor seals, and puffins, with a mix of intertidal invertebrates such as mussels, butter clams, and periwinkles. Also common were salmon, cormorants, sea otters, and sea lions. A single species of whale barnacle was identified. The high number of puffin remains may be related to the production of puffin-skin parkas for the Russian-American Company. The site was likely occupied year-round, but the presence of the bones of harbor seal pups and puffin and cormorant chicks confirms a summer occupation.

Shore-level size gradients and thermal refuge use in the predatory sea star Pisaster ochraceus: the role of environmental stressors

The body size of a mobile intertidal invertebrate can determine its access to different microhabitats, and thus alter its exposure to environmental stressors. We surveyed a rocky inter- tidal keystone predator, the sea star Pisaster ochraceus, and characterized size-dependent distribution, defined by individuals' shore level and refuge use. At 2 field sites (in California and Oregon, USA) we examined temporal and geographical variability in habitat selection. We evalu- ated the hypothesis that environmental drivers measured on-site and body temperatures meas- ured using biomimetic sensors (i.e. 'robo-sea stars'), explained the observed distribution patterns, including shore-level size gradients, with larger animals lower on the shore. We tested the effect of size on animals' thermo- and desiccation-tolerance. Using robo-sea star data, thermal perform- ance curves and critical temperatures of different size classes, we investigated potential physio- logical and survival consequences of microhabitat use (shaded vs. sun-exposed). Pisaster is mostly found in thermal refugia during low tide even when the risk of thermal stress in sun-exposed areas is low, suggesting a risk-avoidance strategy. In sheltered microhabitats, Pisaster exhibited shore-level size gradients; in sun-exposed microhabitats, this pattern disappeared. The proportion of individuals found in shaded microhabitats increased with air temperature, solar radiation, and body temperature. Size-dependent sensitivity to stressful temperatures and wind speed did not explain the observed distribution patterns, suggesting that in the field, size constraints prevent larger animals from occupying refuges that small individuals can use. Our data reveal that, despite generally mild conditions, Pisaster risk-avoidance strategy buffers against rare but poten- tially highly stressful events.

High-resolution computed tomography reconstructions of invertebrate burrow systems.

The architecture of biogenic structures can be highly influential in determining species contributions to major soil and sediment processes, but detailed 3-D characterisations are rare and descriptors of form and complexity are lacking. Here we provide replicate high-resolution micro-focus computed tomography (μ-CT) data for the complete burrow systems of three co-occurring, but functionally contrasting, sediment-dwelling inter-tidal invertebrates assembled alone, and in combination, in representative model aquaria. These data (≤2,000 raw image slices aquarium−1, isotropic voxel resolution, 81 μm) provide reference models that can be used for the development of novel structural analysis routines that will be of value within the fields of ecology, pedology, geomorphology, palaeobiology, ichnology and mechanical engineering. We also envisage opportunity for those investigating transport networks, vascular systems, plant rooting systems, neuron connectivity patterns, or those developing image analysis or statistics related to pattern or shape recognition. The dataset will allow investigators to develop or test novel methodology and ideas without the need to generate a complete three-dimensional computation of exemplar architecture.

Temporal variation in intertidal community recruitment and its relationships to physical forcings, chlorophyll-a concentration and sea surface temperature

We investigated the recruitment of intertidal barnacles and mussels at three temporal scales (months, weeks and days), and its relationships to physical forcings, chlorophyll-a concentration (Chla) and sea surface temperature (SST), at both a local (km) and a regional (10–100 km) resolution. The study was conducted in the South Brazilian Bight, a subtropical region influenced by upwelling and meteorological fronts, where recruitment rates were measured monthly, biweekly and daily, from 2012 to 2013 using artificial substrates fixed in the intertidal zone. The strength of the relationship between recruitment and physical forcings, Chla and SST depended on the temporal scale, with different trends observed for barnacles and mussels. Barnacle recruitment was positively correlated with wind speed and SST and negatively related to the wind direction, cold front events and Chla. Wind direction was positively correlated with mussel recruitment and negatively covaried with SST. We calculated net recruitment (NR) to estimate the differences in recruitment rates observed at longer time scales (months and weeks), with recruitment rates observed at shorter time scales (weeks and days), and found that NR varied in time and among taxa. These results suggest that wind-driven oceanographic processes might affect onshore abundance of barnacle larvae, causing the observed variation in recruitment. This study highlights the importance of oceanic–climatic variables as predictors of intertidal invertebrate recruitment and shows that climatic fluctuations might have different effects on rocky shore communities.

Integrating macroecological metrics and community taxonomic structure.

We extend macroecological theory based on the maximum entropy principle from species level to higher taxonomic categories, thereby predicting distributions of species richness across genera or families and the dependence of abundance and metabolic rate distributions on taxonomic tree structure. Predictions agree with qualitative trends reported in studies on hyper-dominance in tropical tree species, mammalian body size distributions and patterns of rarity in worldwide plant communities. Predicted distributions of species richness over genera or families for birds, arthropods, plants and microorganisms are in excellent agreement with data. Data from an intertidal invertebrate community, but not from a dispersal-limited forest, are in excellent agreement with a predicted new relationship between body size and abundance. Successful predictions of the original species level theory are unmodified in the extended theory. By integrating macroecology and taxonomic tree structure, maximum entropy may point the way towards a unified framework for understanding phylogenetic community structure.

Surviving in a semi-marine habitat: Dietary salt exposure and salt secretion of a New Zealand intertidal skink

Species that inhabit marine and intertidal ecosystems face osmoregulatory challenges, risking dehydration and increased ion concentrations in the body. Lizards need to either tolerate or regulate these increased ion concentrations. In this study, we aim to understand how Suter's skink (Oligosoma suteri), an intertidal skink restricted to shoreline habitats, is able to cope with the physiological stress of living in an extreme salt environment. We determined the diet, prey species' salt content, and nasal and cloacal salt excretion on Rangitoto and Motutapu Islands in northern New Zealand, where the skinks have contrasting access to terrestrial invertebrates. Analysis of stable isotopes suggests inter- and intra-population variability in Suter's skink diets. Intertidal invertebrates under washed up seaweed appear to compose a major part of the diet of the Rangitoto population, while the Motutapu population showed evidence for a mixed diet of terrestrial and intertidal invertebrates. Sodium content of prey species decreased with an increasing distance from the seawater. Field secretion of cations through nasal glands consisted primarily of Na+, which is consistent with other marine and intertidal species. Sodium was also the primary cation in urine. In contrast, fecal cations consisted primarily of K+. This first study into the salt secretion of an intertidal skink species provides evidence of Suter's skink's plasticity in secreting excess ions through nasal salt glands. This likely enables it to deal with the challenges of living in a semi-marine habitat.

Latitudinal variability of physiological responses to heat stress of the intertidal limpet Cellana toreuma along the Asian coast

Potential future distribution shifts of intertidal invertebrates along the Asian coast in the face of global change remain unclear. Integrative study that comprise environmental temperature monitoring and comparative physiological study of thermal adaptation among different geographical populations of species are important to identify population-related differences in thermal ecology that could affect the persistence of species in their present distribution ranges. In the present study, in situ operative temperatures were recorded continuously for 5 mo from August 2011 to January 2012, and measurements of lethal temperature, cardiac performance and gene expression were carried out in 3 geographical populations of the limpet Cellana toreuma (tropical shore: Sichang Island, Thailand; subtropical shore: Nanding Island, Zhangzhou, China; temperate shore: Dagong Island, Qingdao, China). Compared to limpets on the tropical shore in Sichang Island with high mean temperature (28.28°C) and narrow thermal range (19.13 to 46.56°C), limpets on the subtropical shore in Nanding Island have to cope with a thermal environment characterized by a wider temperature range (6.42 to 44.98°C). The absence of differences in lethal temperature (LT50) of limpets from all the locations indicates that limpets currently suffer from intensive heat stress across their biogeographic range. Although the populations lacked differences in upper thermal limit, variations were noted among populations in transcriptional responses in genes linked to energy metabolism. Limpets on the subtropical shore in Nanding Island live closer to their upper thermal limits and thus will be very sensitive to future temperature increases.

The relationship between UV-irradiance, photoprotective compounds and DNA damage in two intertidal invertebrates with contrasting mobility characteristics

The photoprotective role of mycosporine-like amino acids (MAA) against the generation of DNA cyclobutane pyrimidine dimers (CPD) was studied in the sessile intertidal anemone Actinia tenebrosa and the mobile intertidal gastropod Diloma aethiops through 27months at a mid-latitude New Zealand location. MAA were sequestered by A. tenebrosa and D. aethiops from their diet, although maximum total MAA levels in both species were not correlated with seasonal variation in maximum ambient UV-B levels recorded at the collection site. Temporal changes in total MAA in A. tenebrosa showed a six months lag-time in their concentration regarding to the environmental UV-B levels. This lag period corresponded to an observed increase in CPD production from spring to summer; suggesting that MAA do not completely protect the anemone from UV-B during summer. For D. aethiops, total MAA concentrations did not change significantly during the study, although qualitative changes in MAA were apparent. A month lag-time in MAA concentration in D. aethiops and possibly the physical barrier that the shell confers to the animal, can explain reduced CPD levels in comparative terms with A. tenebrosa. Although MAA are used by invertebrates for photoprotection, contrasting mobility characteristics and the presence of physical adaptations can confer them important protection levels during temporal changes of UV-B at mid-latitude places of the Southern Hemisphere.

Population attributes and traits of Siphonaria pectinata (Mollusca: Siphonariidae) in range-edge and non range-edge populations at its Eastern Atlantic northern distribution boundary

The attributes and traits of populations of intertidal invertebrates can become modified in response of the environmental pressures. Therefore, comparative studies of biological traits of range-edge populations versus non range-edge ones may provide essential insights into what processes determine their geographical distribution. In recent decades, the range of Siphonaria pectinata has expanded northwards on the Atlantic coast of the Iberian Peninsula, overlapped in time with significant changes in the sea surface temperature owing to weaker upwelling events. The main objective of this study was to explore differences in the traits and attributes between non range-edge and range-edge populations of S. pectinata and the potential role of temperature in shaping these populations as well. For these aims different biological traits were measured for a year in two non range-edge populations and two range-edge populations of S. pectinata. In general, non range-edge populations had higher densities and percentage of juveniles during November and smaller sizes than range-edge populations. The lack of significant differences in the reproductive traits between the two types of populations and the greater egg-ribbon lengths in range-edge populations suggests a high mortality of larvae or settled juveniles in the latter. Larval and juvenile stages are the most vulnerable stage of the life cycle of marine organisms and temperatures close to the tolerance limit may induce stress. Therefore, it is likely that lower water and air temperatures in the north could be responsible for the higher larval or juvenile mortality in range-edge populations of S. pectinata.

A dual stable isotope study for diet composition of juvenile Chinese horseshoe crab Tachypleus tridentatus (Xiphosura) on a seagrass-covered intertidal mudflat

To enhance our understanding on the foraging biology of juvenile Chinese horseshoe crab on a seagrass-covered intertidal mudflat, we used dual stable isotopes δ13C and δ15N to determine the diet composition and trophic position of 6th–11th instar juveniles in summer and winter. The δ13C and δ15N values in tissues of juveniles and their potential food sources suggested that the juveniles consumed a mixed diet mainly comprised a variety of polychaetes, crustaceans and bivalves, in which these food groups were abundantly available in the study site and largely supported by seagrass biomass in both summer and winter. While δ15N values in juvenile tissues were statistically similar between the two seasons, the δ13C values in tissues of juveniles had a minimal seasonal difference which was probably due to variations in the source values rather than the changes in diet composition of juveniles. There were no differences in δ13C and δ15N values among the size groups of juveniles through 6th–11th instars. Although juvenile Chinese horseshoe crabs may consume the prey in response to the seasonal availability on the mudflat, a healthy condition of habitat with high water quality is essential to support the juveniles and a wide range of intertidal invertebrates they consume.

Historical demography of southern African patellid limpets: congruence of population expansions, but not phylogeography

Global climatic oscillations have shaped the contemporary genetic structure of marine taxa in different ways. Previous demographic studies have indicated that various intertidal marine species display genetic signatures of demographic expansion that either pre- or postdate the Last Glacial Maximum. Such expansions and the ability of species to colonise new habitats will influence their genetic structure, but the link between scales of larval dispersal and the strength of phylogeographic structure is not always clear. We analysed a fragment of the mitochondrial COI gene of 11 sympatric species of intertidal southern African patellid limpets to investigate how ancient oceanographic dynamics have shaped and maintained their contemporary spatial genetic variation. Our data show that the patellid limpets investigated display congruent evidence of spatial expansion during the Late Pleistocene or Early Holocene, which corresponds with the establishment of the contemporary southern African shoreline. We argue that closely related and co-distributed southern African intertidal invertebrates responded to ancient climatic oscillations as a cohesive group. In contrast, contemporary oceanographic circulation has shaped the phylogeographic patterns of these limpets in different ways. We show close relationships between phylogeography and biogeography for some species, but not for others, despite the similarities in their life histories and exposure to the same climatic changes.

Using biomimetic loggers to measure interspecific and microhabitat variation in body temperatures of rocky intertidal invertebrates

Until recently, marine scientists have relied heavily on satellite sea surface temperatures and terrestrial weather stations as indicators of the way in which the thermal environment, and hence the body temperatures of organisms, vary over spatial and temporal scales. We designed biomimetic temperature loggers for three species of rocky intertidal invertebrates to determine whether mimic body temperatures differ from the external environment and among species and microhabitats. For all three species, microhabitat temperatures were considerably higher than the body temperatures, with differences as great as 11.1°C on horizontal rocky substrata. Across microhabitats, daily maximal temperatures of the limpet Cellana tramoserica were on average 2.1 and 3.1°C higher than body temperatures of the whelk Dicathais orbita and the barnacle Tesseropora rosea respectively. Among-microhabitat variation in each species’ temperature was equally as variable as differences among species within microhabitats. Daily maximal body temperatures of barnacles placed on southerly facing vertical rock surfaces were on average 2.4°C cooler than those on horizontal rock. Likewise, daily maximal body temperatures of whelks were on average 3.1°C cooler within shallow rock pools than on horizontal rock. Our results provide new evidence that unique thermal properties and microhabitat preferences may be important determinants of species’ capacity to cope with climate change.

Using terrestrial laser scanning to support ecological research in the rocky intertidal zone

Scale-appropriate, foundational datasets are necessary for ecological analyses of the rocky intertidal ecosystem. We used terrestrial laser scanning (TLS) to characterize and quantify the rocky intertidal zone topography at a western U.S. coastal site (Rabbit Rock, Oregon) to support ecological research relating to potential climate-induced changes in distribution and abundance of intertidal invertebrates and a large-bodied shorebird, the Black Oystercatcher (Haematopus bachmani). Alternate available data (e.g., aerial photography, airborne LIDAR) proved inadequate or infeasible for development of a topographic surface model inclusive of intertidal area from Mean Lower Low Water to Mean Higher High Water tidal elevation. Our TLS-derived topographic surface model competently supported development of an invertebrate distribution model relative to tidal elevation and topography. Using the developed model, we estimated current and future aerial extent of the intertidal zone and potential foraging habitat for Black Oystercatcher in our study area. Intertidal zone area decreased from 7,194 m2 to 6,409 m2 and 3,070 m2 with 1 and 2 m sea-level rise, respectively. Surprisingly, due to the configuration of site substrate, potential foraging habitat for Black Oystercatcher increased from 5,658 to 5,903 m2 with 1 m sea-level rise, but declined to 3,068 m2 with 2 m sea-level rise. Our results demonstrate the utility of TLS for ecological research in the rocky intertidal zone. They further illustrate that climate change effects on ecological conditions may vary considerably depending on local configurations.

Toward predicting community‐level effects of climate: relative temperature scaling of metabolic and ingestion rates

Predicting the effects of climate change on ecological communities requires an understanding of how environmental factors influence both physiological processes and species interactions. Specifically, the net impact of temperature on community structure depends on the relative response of physiological energetic costs (metabolism) and energetic gains (ingestion of resources) that mediate the flow of energy throughout a food web. However, the relative temperature scaling of metabolic and ingestion rates have rarely been measured for multiple species within an ecological assemblage and it is not known how, and to what extent, these relative scaling differences vary among species. To investigate the relative influence of these processes, I measured the temperature scaling of metabolic and ingestion rates for a suite of rocky intertidal species using a multiple regression experimental design. I compared oxygen consumption rates (as a proxy for metabolic rate) and ingestion rates by estimating the temperature scaling parameter of the universal temperature dependence (UTD) model, a theoretical model derived from first principles of biochemical kinetics and allometry. The results show that consumer metabolic rates (energetic costs) tend to be more sensitive to temperature than ingestion rates (energetic gains). Thus, as temperature increases, metabolic rates tend to increase faster relative to ingestion rates, causing the overall energetic efficiencies of these rocky intertidal invertebrates to decline. Metabolic and ingestion rates largely scaled in accordance with the UTD model; however, nonlinearity was evident in several cases, particularly at higher temperatures, in which alternative models were more appropriate. There are few studies where multiple rate dependencies are measured on multiple species from the same ecological community. These results indicate that there may be general patterns across species in the temperature scaling of biological rates, with important implications for forecasting temperature effects on ecological communities.

Temporal shifts in the fatty acid profiles of rocky intertidal invertebrates

Fatty acid profiles were determined in rocky intertidal suspension-feeders (mussels and polychaetes) and grazers (limpets and sea urchins) on a monthly basis over 1 year to assess potential dietary overlap between consumers occupying the same trophic guild, and any temporal shifts in diets. Both reproductive and non-reproductive tissues were assessed in an attempt to separate influences of food quality with those of life cycle. Relative variability in fatty acids over time could not be predicted from the feeding guild occupied by a consumer, and influential factors of the temporal shifts included both dietary and reproductive dynamics (even in muscle tissues). Species in the same trophic guild occupied separate trophic niches throughout the year, hence minimising competitive interactions regarding food acquisition. Based on overall variation in fatty acid profiles of muscle tissues, the suspension-feeders Perna perna and Gunnarea gaimardi and the grazing limpet Cymbula oculus occupied narrower feeding niches relative to the grazing sea urchin Parechinus angulosus. Our results provide compelling evidence for potentially large changes in the lipid composition of intertidal invertebrate populations over relatively small temporal scales (i.e. month to month), and these have important implications for short-term field collections intended for assessing invertebrate diets.