Depth-Dependent Diversity Patterns of Rocky Subtidal Macrobenthic Communities Along a Temperate Fjord in Northern Chilean Patagonia

Abstract

Understanding the distribution of biodiversity along environmental gradients allows us to predict how communities respond to natural and anthropogenic impacts. In fjord ecosystems, the overlap of strong salinity and temperature gradients provides us with the opportunity to assess the spatial variation of biodiversity along abiotic environmental gradients. However, in Northern Chilean Patagonia (NCP), a unique and at the same time threatened fjord system, the variation of macrobenthic communities along abiotic environmental gradients is still poorly known. Here, we tested whether macrobenthic species diversity and community structure followed systematic patterns of variation according to the spatial variation in salinity and temperature in Comau Fjord, NCP. A spatially extensive nested sampling design was used to quantify the abundance of subtidal macrobenthic species along the fjord axis (fjord sections: head, middle, and mouth) and a depth gradient (0–21 m). The vertical structure of the water column was strongly stratified at the head of the fjord, characterized by a superficial (depth to ca. 5 m) low-salinity and relatively colder layer that shallowed and decayed toward the mouth of the fjord. The biotic variation followed, in part, this abiotic spatial pattern. Species richness peaked at high salinities (>27 psu) between 5 and 10 m in the head section and between 15 and 21 m in the middle and mouth sections. Diversity and evenness were also highest at these salinities and depth ranges in the head and middle sections, but at shallower depth ranges in the mouth. Information theory-based model selection provided a strong empirical support to the depth- and section-dependent salinity, but not temperature, effects on the three biodiversity metrics. Erect algae and the edible mussel Aulacomya atra numerically dominated in shallow water (0–3 m) at the head and the middle of the fjord, coinciding with the horizontal extension of the low-density water layer—these taxa were further replaced by the crustose algae Lithothamnion sp. and deep-dwelling suspension filters (e.g., corals, polychaetes, and sponges) along depth gradient. Macrobenthic biodiversity correlated, therefore, with the influence of freshwater inputs and the density-driven stratification of the water column in this ecosystem. The spatially variable (across both, horizontal and vertical fjord axes) thresholds observed in our study question the widely accepted pattern of increasing biodiversity with increasing distance from the head of estuarine ecosystems. Finally, non-linear environmental stress models provide us a strong predictive power to understand the responses of these unique ecosystems to natural and anthropogenic environmental changes.

Limited complementarity of functional and taxonomic diversity in Chilean benthic marine invertebrates

“…To some extent, these similarities are expected, given that FRic is influenced by species richness (Mason et al., 2005); however, relationships are not inevitable; for instance, Δ + is formally independent of species richness (Clarke & Warwick, 1998). Overall, our results provide further support for the importance of the diversity of latitudes between 42° and 43°S, an area that has been defined as highly biodiverse for benthic invertebrates in Chile (e.g., Camus, 2001; Fernández et al., 2000; Häussermann, 2006; Hernández et al., 2005; Villalobos et al., 2021; Zapata‐Hernández et al., 2016). Our results show that this finding is robust to different diversity measures, including those that control for sampling effort.…”

“…and polychaetes (e.g. Chaetopterus variopedatus ) increases substrate availability, providing habitats for different taxa (Villalobos et al., 2021; Zapata‐Hernández et al., 2016). Spring–summer phytoplankton blooms driving flows of carbon towards the benthos may also support the diversity of taxa, including invertebrates, bony fishes, rays and sharks (Zapata‐Hernández et al., 2016).…”

The Roles of Alpha, Beta, and Functional Diversity Indices in the Ecological Connectivity between Two Sub-Antarctic Macrobenthic Assemblages

“…However, studies using the β-diversity index are scarce. In fact, Villalobos et al [47] determined the β-diversity for benthic communities, and their results highlighted an important percentage of species (48%) turnover in an environmental gradient along the Comau fjord (Norther Patagonian). In contrast, research conducted on the benthic community of central Patagonia has described a βdiversity along a bathymetric gradient.…”

Filling ecological gaps in Chilean Central Patagonia: Patterns of biodiversity and distribution of sublittoral benthic invertebrates from the Katalalixar National Reserve waters (~48°S)

“…The research of the KNR marine ecosystems is limited, and the sublittoral benthic communities and their ecological patterns are still almost unknown since only a few studies have been made in central Patagonia (e.g., Häussermann and Försterra, 2007;Quiroga et al, 2012;Försterrra et al, 2017;Friedlander et al, 2021). In contrast, most studies about the ecology of sublittoral benthic communities of the CPFC have been carried out mainly in the north (e.g., Häussermann et al, 2013;Zapata-Hernańdez et al, 2016;Betti et al, 2017;Betti et al, 2021;Villalobos et al, 2021) and south (e.g., Gerdes and Montiel, 1999;Montiel et al, 2005;Rıós et al, 2007;Montiel et al, 2011).…”

“…Worldwide research on benthic communities using remotely operated vehicles (ROVs) has increased recently in isolated areas, deep sea areas, or environments with harsh weather conditions that are inaccessible to diving or traditional benthic sampling methods (Costello et al, 2018;Tapia-Guerra et al, 2021). In the CPFC, studies based on underwater photography in northern and southern Patagonia were obtained by SCUBA diving (e.g., Caŕdenas and Montiel, 2015;Betti et al, 2017;Villalobos et al, 2021), or by means of an underwater camera operated from a vessel (e.g., Gutt et al, 1999). Nevertheless, studies using ROV are lacking for central Patagonia, including the surrounding waters of KNR, and even more for benthic communities from the deeper areas of the channels and fjords.…”