Taraba Sound is located north of the Magallanes Region (henceforward Magellan Region), the southernmost administrative region of Chile. It spans approximately 31 km in length and is bordered on the east side by the Benson Peninsula and on the west by the Sarmiento Mountain Range, where the Zamudio and Bernal snowdrifts descend into the Fjord of the Mountains (Fig. 1). The interior of the sound is surrounded by mountains and steep rock walls, with temporary freshwater effluents from melting snow on top of the mountains; certain areas are influenced by freshwater runoff from adjacent glaciers. Three main types of environment were observed in the area: strip cliffs, large and rounded cobble fields and gravel and pebble beaches. The last type was used as a protected study site.

Figure 1.  

Study area and sampling sites, Taraba Sound.

The study was carried out on 18 and 19 January 2013 (during the austral summer) on three beaches on the eastern side of the interior of Taraba Sound and one on the west side of the sound. The sampling areas were selected for their easy access during low tide.

The study areas were accessed using a Zodiac® inflatable boat launched from the fishing vessel Mary Paz II. The intertidal benthic macrofauna (> 1 mm) was manually collected and by means of a palette knife to collect sediment between stones directly from the shoreline along transects perpendicular to the coastline on each beach (T1–T4; Table 1). In each transect, samples were taken at specific points determined by the beach profile between high and low tide levels (supralittoral, mesolittoral and infralittoral), N1–N3. In each sampling level, three replicates (R1–R3) were collected using a 0.25 m² quadrat (50 cm x 50 cm) for each beach level. The collected benthic macrofauna was separated, fixed with 5% formalin and preserved in 95% ethanol buffered with saturated sodium borate on board the vessel.

At each sampling site, the geographic coordinates were recorded with an Etrex H® GPS, salinity (‰) was recorded with a handheld refractometer (RHS-10 ATC) and temperature (°C) with a mercury thermometer. In addition, each intertidal sector was photographed using a digital camera (Canon PowerShot A470).

The collected macrofauna was sorted and identified to the lowest possible taxonomic level (i.e. genus or species) starting with specialised literature available for the region (e.g. Forcelli (2000), Zagal and Hermosilla (2007), Häussermann and Försterra (2009)). Some experts assisted in the identification of different taxa (see Acknowledgements). Species records and their respective geographic positions of the sites were entered into a spreadsheet, structured using the Standard Darwin Core format (Wieczorek et al. 2012). The data were submitted in the Integrated Publishing Toolkit, following the GBIF's standards (GBIF: The Global Biodiversity Information Facility 2024).

The data were analysed using PRIMER-E v.6.0 (Clarke and Gorley 2005). The community structure parameters included total abundance of individuals (N), species richness = number of species (S), Shannon's diversity index = number of species as a function of each species’ abundance (H’; Shannon (1948)), Pielou's evenness index = measurement of how even the abundance of all species is (J’; Pielou (1966)), taxonomic diversity = average taxonomic distance between all pairs of species (∆) and taxonomic distinctness = average path length between two random individuals from different species (∆*), including the taxonomic levels of phylum, class, order, family, genus and species (Warwick and Clarke 1995). To identify groupings or assemblages within areas, we employed non-parametric multivariate analysis techniques using PRIMER-E v.6.0 software (Clarke and Gorley 2005). First, an abundance matrix was developed for the sampling sites and previously transformed using fourth root transformation. To assess biological parameters, the Bray-Curtis similarity index (Bray and Curtis 1957) was then calculated. Following this, to asses other biological parameters, a Non-Metric Multidimensional Scaling (MDS) ordination analysis (Kruskal and Wish 1978) was conducted, along with the creation of a cluster classification dendrogram, based on the average similarity of the sites using the SIMPROF test (Clarke et al. 2008). The similarity percentage (SIMPER) analysis (Clarke 1993) was applied to determine the species contributing most to the observed clusters. Spatial differences in cluster structure were assessed using the one-way ANOSIM non-parametric test (Clarke and Green 1988).

To test for significant differences between study areas (transects) and intertidal levels, a one-way analysis of variance (ANOVA) was performed, followed by post hoc Tukey tests. Before performing these analyses, we verified the normality of the data using the Kolmogorov-Smirnov test with SPSS 15.0 statistical software. A significance level of 0.05 was assumed for the tests to evaluate the null hypothesis.

Pearson correlation coefficients were calculated to explore the relationships between various ecological variables, including species richness, abundance, diversity, uniformity and evenness, in relation to salinity and temperature. Data were analysed using RStudio software (R Core Team 2022), with the ‘ggcorrplot’ and ‘corpmat’ packages employed for visualisation of the correlation matrix via ‘ggplot2’. Coefficients were computed alongside p-values to assess the significance of the correlations. A significance level of p < 0.05 was used to identify the variables most notably related to biological diversity and abundance.

A data package entitled “Biodiversity of intertidal invertebrates of Taraba Sound (Magellan Region, Chile)” was uploaded to GBIF (Aldea et al. 2024). All material was catalogued with the voucher “intertidal-benthic-invertebrates-taraba-sound2013” and was deposited in the collection of CEQUA Foundation, Punta Arenas city.

Our study reveals important patterns in the structure of intertidal communities. While we did not observe significant differences in alpha diversity between intertidal levels, we found notable variations in organism abundance across the four pebble beaches studied. Although species richness (S) remains relatively consistent across levels, the composition and abundance of individuals vary, indicating that certain taxonomic groups are more sensitive to environmental factors, such as habitat stability.

The mussel Choromytilus chorus dominated the mid-intertidal and infralittoral zones, forming distinct bivalve belts, consistent with the observations of Ríos and Mutschke (1999), where Mytilus chilensis dominated in boulder and cobble intertidal areas, also forming distinct bivalve belts in the Magellan Region. In contrast, amphipods were more abundant in the supralittoral zones, likely due to their greater tolerance to desiccation and wave action. All beaches have similar pebble substrates. However, exposure may vary due to differences in habitat orientation and local hydrodynamic conditions, which could affect the abundance of macrozoobenthos communities.

According to Ríos (2007), local factors like wave exposure and wind significantly shape rocky intertidal communities in the Magellan Region. These factors likely influence the patterns we observed, where sessile bivalves dominate in more stable zones, while amphipods thrive in more variable conditions. To better understand how these communities respond to environmental stressors, future studies should explore the functional traits of key species. Such an approach would offer insights into their ecological roles and help predict responses to environmental changes.

Furthermore, a stable species richness combined with a decrease in taxonomic distinctness (Δ*) might suggest a loss of diversity at higher taxonomic levels. Previous studies have shown that the relationship between species richness (S) and taxonomic distinctness (Δ*) can vary significantly across ecosystems, with some showing a positive correlation and others showing no significant relationship or even a negative correlation (Heino et al. 2005). For example, in freshwater ecosystems, S and Δ* respond differently to various environmental gradients, underscoring the importance of using both measures to comprehensively assess community-level biodiversity (Heino et al. 2005). This highlights the need for a multi-faceted approach when examining biodiversity, as richness alone may not fully capture the effects of environmental variability on community structure.

Some studies have reported the importance of the hydrological factors, including salinity gradients within the region that could play a pivotal role in moulding benthic communities in fjord ecosystems (Cari et al. 2020). Particularly noteworthy is the longitudinal gradient observed within inner fjords, where river discharge into the ocean introduces freshwater, profoundly influencing the composition of organisms and the availability of carbon food sources crucial for their sustenance. This salinity gradient delineates distinct ecological niches along the fjord's inner reaches. Our results showed how salinity variation may alter intertidal marine life’s abundance distribution and composition. However, it is important to consider these results with caution, as only one measurement of salinity and temperature was collected per sampling site. This limitation underscores the need for careful analysis and the importance of future research to obtain multiple data points and a more comprehensive understanding of how salinity, temperature and other variables affect biological diversity by collecting additional measurements across the supralittoral, mesolittoral and infralittoral zones.

Organisms dwelling in these transitional zones must probably adapt to fluctuating salinity regimes, affecting their metabolic processes and resource utilisation strategies (e.g. Javanshir (2013), Telesh et al. (2013), Little et al. (2017)). Further research is needed to investigate the potential impacts of salinity variability on species composition, abundance and diversity, as well as to identify which organisms may be more tolerant or sensitive to these changes and their functional consequences.

Despite the fjords' environmental conditions, such as substrate composition, lack of algal associations and low exposure from wave action, our results reveal a remarkable diversity across the four studied beaches, with 24 OTUs identified on intertidal boulders and cobble terraces. This finding falls within the range of variability documented in other studies within the geographic region of the Patagonian fjords. Cari et al. (2020) reported 15 taxa in the inner section of the Baker fjord (47.5°S), while Bahamonde et al. (2022) found 29 taxa in Fjord of the Mountains (52°S; see Fig. 1). Soto et al. (2012) and Soto et al. (2015) reported 30 OTUs across 12 intertidal stations in an extensive area between Concepción Channel (50.1°S) and Smyth Channel (52.7°S) surveyed by the CIMAR 15 Fjords Cruise (CONA 2010, Aldea et al. 2022). Additionally, Ríos and Mutschke (1999) and Ríos (2007) documented 60 OTUs in the Whiteside Channel (54°S), which highlights the variability in biodiversity observed across a similar geographic range. This variability underscores how local environmental factors, such as glacial influence, ocean currents and substrate characteristics, can influence biodiversity and species distribution in these ecosystems, beyond surface conditions. However, there is still a lack of taxonomic knowledge, even though this is necessary for advancing ecological research. Such knowledge is important for proper descriptions of benthic communities, their structure and composition and other comparisons of species richness and diversity in the region, especially taking into account the Patagonian fjord ecosystems in southern Chile as a highly vulnerable region (Iriarte et al. 2010).

In the present study, species richness and taxonomic diversity showed a natural positive correlation, as expected, given that taxonomic diversity is inherently influenced by the number of species present. This relationship is a well-established baseline in biodiversity studies. However, no significant differences were observed between species richness and evenness in our dataset, suggesting that the community is relatively balanced in terms of species distribution or an empirical relationship between species richness and evenness, considering the number of species (Stirling and Wilsey 2001).

T4 exhibited lower values of species richness and abundance, this trend could be attributed to a lower salinity level (25‰) influenced by freshwater discharges from effluents in the vicinity, originating from a source near the study area (see Fig. 1). Such changes in salinity significantly impact the composition of benthic invertebrate macrofauna, predominantly small bivalve molluscs and amphipod crustaceans, representing three distinct species. Higher salinity environments are associated with greater species diversity, particularly amongst invertebrates (Soto et al. 2012), a pattern observed at higher latitudes as well.

Salinity values in the study ranged from 25 to 30‰, reflecting the influence of nearby freshwater inflow, while a salinity of 35‰ is considered fully marine. Beaches T2 and T4 located near freshwater effluents recorded the lowest salinity values, which might be associated with diminished species richness, abundance, diversity and evenness, especially in the supralittoral and mesolittoral zones. In contrast, beaches T1 and T3 registered higher salinity levels, as they lacked freshwater inflows in their vicinity.

The intertidal fauna of Taraba Sound, overall, inhabits a low-wave energy environment, characterised by semi-protected beaches. This unique setting likely contributes to the specific community structure observed in the region, highlighting the interplay between salinity variations and wave exposure on the biodiversity of these coastal environments.