AUTHOR=Villalobos Vicente I. , Valdivia Nelson , Försterra Günter , Ballyram Stacy , Espinoza Juan Pablo , Wadham Jemma L. , Burgos-Andrade Katherine , Häussermann Vreni 

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

JOURNAL=Frontiers in Marine Science

VOLUME=Volume 8 - 2021

YEAR=2021

URL=https://www.frontiersin.org/journals/marine-science/articles/10.3389/fmars.2021.635855

DOI=10.3389/fmars.2021.635855

ISSN=2296-7745

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 distribution of macrobenthic communities 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 and a depth gradient (0 - 21 meters). The vertical structure of the water column was characterized by a superficial (depth to ca. 5 m) low-salinity and layer that shallowed 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 – 10 m in the head section and between 15 – 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 biodiversity metrics. Erect algae and the edible mussel Aulacomya atra numerically dominated in shallow water (0 - 3 meters), 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,) along depth. Macrobenthic biodiversity correlated, therefore, with the influence of freshwater inputs. The spatially variable thresholds observed in our study question the widely accepted pattern of increasing biodiversity with increasing distance from the head of estuarine ecosystems. Finally, nonlinear environmental stress models provide us a strong predictive power to understand the responses of these unique ecosystems to natural and anthropogenic environmental changes.