The Hidden Diversity of Temperate Mesophotic Ecosystems from Central Chile (Southeastern Pacific Ocean) Assessed through Towed Underwater Videos

Abstract

The largely unexplored diversity in temperate mesophotic ecosystems (TME, ~30–150 m depth) has attracted much attention over the past years. However, the number of studies and knowledge of TME diversity and ecology remains limited and geographically restricted. The absence of information on how assemblages vary across environmental gradients and with depth for most regions also limits our capacity to delimit conservation areas and devise management plans effectively. This study focuses on TME from central Chile and describes the depth distribution of reef fishes and benthic invertebrates and algae for the first time. Through the analysis of towed underwater video surveys between 4.7–95.5 m in multiple sites, we show that total reef fish density and richness decrease with depth but increase with local topographic complexity. The depth-related density varies among fish species and trophic groups, and it reverses in the case of Sebastes oculatus, which increases in density with depth. Sponges and gorgonians dominate benthic assemblages below 20 m depth, and brachiopods and anemones increase below 40 and 60 m, respectively. Some of these species form animal forests which, to some extent, replace the shallow-water kelp forests as structural habitat providers. Nevertheless, the reef fish and benthic community do not show a clear structure with depth or across studied sites. We highlight the urgency to intensify and expand the quantitative characterization of these communities, through this and other methodologies, to better define ecological patterns and advance towards conservation plans for TME, including the Souteastern Pacific region.

Environmental DNA reveals temporal variation in mesophotic reefs of the Humboldt upwelling ecosystems of central Chile: Toward a baseline for biodiversity monitoring of unexplored marine habitats

“…We are just beginning to explore Chilean mesophotic reefs, therefore, it is important to note that there is little available data that can be used to compare our results. Nevertheless, a recent study (Campoy et al., 2023 ) explored the diversity in the Chilean central coast (at Algarrobo and Las Cruces) using towed underwater videos (TUVs), focusing mostly on fish. Thirty‐two percent of the genera identified with eDNA were also observed using TUVs, eight genera reported with TUVs were not present in our eDNA data, and 68% of the fish identified with eDNA were not observed with TUVs.…”

“…To our knowledge, neither Pinguipes chilensis nor Cheilodactylus variegatus (unique species for both genera in central Chile) exhibit depth segregation, at least within the evaluated range (down to 60 m). Moreover, P. chilensis is one of the most abundant species occurring at intermediate depths (20–40 m) in relatively high densities (Campoy et al., 2023 ). Therefore, these depth distribution ranges must be taken cautiously when interpreting eDNA signals for cases with only one depth/season occurrence.…”

“…According to a recent review (Bell et al., 2022 ), most studies on TMREs have been conducted in the Mediterranean Sea, Temperate Australasia, the North Pacific, and the North Atlantic oceans. Only two studies document the broad structure of benthic communities near the upper limit of mid‐depths (30 m) (Betti et al., 2017 ) or across mid‐depths encompassing mesophotic reefs (down to 100 m) in the South‐Eastern Pacific (Campoy et al., 2023 ). The Chilean coast is one of the most productive coastal ecosystems on the planet (Carr & Kearns, 2003 ; Thiel et al., 2007 ), fueled by wind‐driven upwelling that brings cold, salty, nutrient‐rich, and oxygen‐poor water inshore.…”

“…However, scarce information exists below 30 m depth regarding the seasonality of TMRE community composition and the spatial scales of variation among sites or across the depth gradient. The only quantitative characterization of mesophotic reefs here is a recent study describing macroscopic invertebrate and fish species using towed underwater videos (Campoy et al., 2023 ). Bycatch fisheries data associated with crustacean trawling fisheries, which are conducted mostly over the soft bottom of the continental shelf, have also provided a coarse characterization of mesophotic and deeper water assemblages (Landaeta et al., 2023 ; Montero et al., 2020 ).…”

“…Baited Remote Underwater Video (unpublished data) Isacia conceptionis Isacia conceptionis Visual surveys (Pérez‐Matus et al., 2007 , 2022 ) Chromis enchrysura * Chromis enchrysura * Most likely C. crusma , but C. crusma is absent from all databases. Visual survey (Pérez‐Matus et al., 2007 , 2022 ), TUV (Campoy et al., 2023 ) Trachurus symmetricus * Trachurus murphyi T. symmetricus absent from 16s database. Visual surveys (Pérez‐Matus et al., 2007 , 2022 ) Sprattus muelleri * Most likely Strangomera bentiki , absent from 16s database.…”