Our study provides the first record of scavenging crustacean taxa in an area of the Chilean Patagonia that is highly likely to be impacted by several anthropogenic activities. We report a total of 14 taxa, including 7 Decapoda (the 11% of species reported for the whole Patagonian region14). Most decapod taxa were found within the geographic and bathymetric ranges previously reported14,19, with the exception of M. edwarsii, which was found at deeper areas than previously known (from 60 to 72 m). We also report 5 Amphipoda taxa, with O. chilensis found within the geographic range described20 but at a wider bathymetric range than previously known (from 40 to 67 m). Importantly, we found two species that are new to science, belonging to the genera Pseudorchomene and Isaeopsis, which will be described elsewhere (Pérez-Schultheiss pers. comm.).
A previous study reported 60 benthic taxa from Magdalena sound, including 15 mollusks, 11 cnidarians and 10 sponges)17. This is comparable to the 8 taxa of scavenging crustaceans found in this study for the same area, or the 10 species found in Puerto Cisnes bay. To our knowledge, there are no other studies from the same area. However, studies for the whole Patagonian region have reported 1,650 species of benthic organisms21 and 3,776 species of eukaryotes22, which suggests that the number of scavenging crustaceans in the whole Patagonian region will be high.
The bathymetric distribution of scavenger crustaceans in Magdalena sound indicated a decrease in diversity (Shannon-Wiener index) and dominance (Simpson index) with increasing depth, despite the low dominance in general. A decreased diversity gradient with depth has also been reported for benthic fauna in the same area17. In Puerto Cisnes bay, despite the absence of differences in diversity and dominance between the two layers, we observed that the Decapoda dominated the bathymetric stratum 1 (brackish water) while the Amphipoda were more abundant in stratum 2 (sea water). Although the diversity of both areas was not statistically compared, Shannon-Wiener values in strata 1 and 2 of Puerto Cisnes bay tended to be lower (0.08–0.31 on average, respectively) than those of the same strata in Magdalena sound (0.68 and 0.87, respectively). Although both areas show similar stratification regarding these two layers, which are composed of brackish and sea water respectively17, there are important differences between them, mostly to the fact that Magdalena sound is deeper and has more vertical walls.
Species richness in both areas decreased with depth, a similar pattern reported by Smith and Brown23 for fish, where the greatest abundance was found in the intermediate depth water layer, in relation to favorable environmental conditions, such as maximum productivity and temperature. However, this pattern has also been attributed to the characteristics of the substrate, abiotic stress or seasonality. Betti et al.17 identified 60 Operative Taxonomic Units (OTUs) in the vertical rock walls of the Magdalena sound, of which only one was a sessile crustacean (Balanus laevis, Brugiere, 1789), and all were different from the 14 species recorded in the sand and rock substrates in the present study. The number of OTUs was distributed with a pattern similar to those already mentioned, with a peak at 10 m depth (12.2 ± 0.6).
Regarding the primary productivity of the area, others have reported seasonal variations over 20 m of depth, which could explain the community patterns detected here. Gross primary production and annual community respiration were 533 and 537 gC m2 year−1, respectively24, primary production was 800 mgC m2 day−1 and there was a vertical flow of particulate organic carbon that doubled in spring (266 mgC m2 day−1) compared to winter (168 mgC m2 day−1)25. The depth-integrated gross primary production varied from the period of highest productivity from August to April (0.1 to 2.9 gC m2 day−1) to a shorter period of lower productivity from May to July (0.03 to 0.3 gC m2 day−1)26.
The physicochemical profiles of water reported by Betti et al.17 were similar to those reported here. The surface strata presented great seasonal and spatial variability, identifying in spring-summer a superficial estuarine layer up to 10 m (15 PSU and 15 °C), an intermediate level of salinity (31–33 PSU), and then one of greater salinity (>33 PSU) and lower temperature (10.5 °C) below 50 of depth. In winter, thermal stratification decreased and was inverted with 4 °C in the surface layer and 8 °C below 50 m of depth. Therefore, the productivity and development of benthic mobile crustaceans at greater depth could be limited by the gradual decrease in surface oxygen concentration, caused by large allochthonous particulate matter revenues, which would characterize most of the 90 gulfs, channels and Patagonian fjords27.
Scavenging crustaceans constitute an important food component for fish species such as the Patagonian blenny Eleginops maclovinus (Cuvier, 1830) and dolphins that inhabit the study area, which are recognized as one of the main tourist attractions28,29. Moreover, these crustaceans are likely to be severely affected by pollution in the area as a result of salmon farming30,31, including substances used for pest control, as well as harmful algal blooms31,32. Our results thus provide background information about the diversity of an important group of organisms in Chilean Patagonia, an understudied and vulnerable area of the world, and evidence the need for further research that may contribute to safeguarding crustacean biodiversity in future scenarios of intense anthropogenic activities.
Source: Ecology - nature.com
