Biotopes of the intertidal zone in Clarence Island (south of the Strait of Magellan)

Abstract Background The characteristics of the Strait of Magellan promote the formation of unique environments, with diverse habitats and marine organisms. This fragmentation of the landscape generates diverse little-explored ecological associations, especially in the zone of sub-Antarctic islands of the Tierra del Fuego archipelago. One way to address this lack of knowledge is through the biotope characterization methodology, with ecological units composed of the habitat and the communities associated with these environments, obtaining data and information on the dominant and incidental taxonomic groups. This is a good research model to conduct baseline studies in coastal benthic marine environments. New information A data set in Darwin Core standard is presented of the species that make up the intertidal biotopes of Clarence Island (Tierra del Fuego Archipelago, south of the Strait of Magellan). This includes 50 identified species and the specific coordinates for each sampled location, with a total of 1400 georeferenced records. Mollusks were the most diverse taxon with 21 species, followed by algae (14 species). Sessile organisms such as the barnacles Elminiuskingii and Austromegabalanuspsittacus predominate in these ecosystems, followed by bivalve mollusks such as Choromytiluschorus and Mytiluschilensis, which together with Nacellamagellanica and the alga Hildenbrandia sp. make up more than 50% of the total records. The inclusion of biotope patterns in this study complements the information on benthic marine flora and fauna in the intertidal zone, including new records for the coast in the Clarence Island area, which is within the boundary of the Kawésqar National Park.


Introduction
The southern Chilean administrative region denominated "Magallanes y la Antártica Chilena" (hereafter Magallanes Region) is made up of a large unique system of sub-Antarctic channels and fjords at the convergence of the Pacific and Atlantic oceans, integrating different masses of water and thus generating a unique habitat for marine life, with high levels of endemism and biodiversity (Fernández et al. 2000, Miloslavich et al. 2011. The presence of these ecological singularities means that the variations in composition, richness and structure of the rocky coastal communities are high in comparison with the rest of the temperate coasts of America (Rosenfeld et al. 2013).
The fragmentation of the landscape significantly affects the diversity of the existing benthic communities of the Magallanes Region (Valdovinos et al. 2008), where the intertidal and shallow subtidal fractions make up the coastal margin, configured mainly by portions of reduced substrate in which macroalgae play a key role as bioengineers and structurers ( Jones et al. 1997). These macroalgae assemblages allow the coexistence of a large number of invertebrates, generating interactions between organisms and coastal morphology, producing the formation of biotopes.
Biotopes are part of ecosystems and refer to environments with dominant organisms and their relationship with the abiotic variables present there, being a habitat and community assemblage (Olenin and Ducrotoy 2006), encompassing organisms and abiotic components in order to describe the landscape and its ecological functionality more broadly (John et al. 2002).
Magellanic macroinvertebrates and macroalgae have developed under the influence of local conditions such as wave intensity, which can have effects on the diversity of intertidal biotopes in a fjord system (Soto et al. 2012). Some biotopes have a restricted distribution and as such are well-defined and are easily recognized as having one or more dominant organisms (John et al. 2003). An example of this is the macroalga Macrocystis pyrifera, which recurrently characterizes its own biotope in the Magallanes Region. In the field of biotope studies, efforts have been made in coastal localities applied to intertidal and subtidal areas during the CIMAR-15 and -16 Fjords cruises (Soto et al. 2012, Soto et al. 2015, Letelier et al. 2013).
The Magallanes Region has been chosen by several expeditions for scientific purposes (Ríos et al. 2003), carrying out studies mainly of marine macroinvertebrates in the different areas of the Strait of Magellan. There have been both compilation (Aldea et al. 2020) and specific studies, the latter in the eastern end , western end (Aldea et al. 2020), channels (Letelier et al. 2013 and Tierra del Fuego (Friedlander et al. 2018), as well as the Francisco Coloane Marine Coastal Protected Area . However, there are still unexplored areas, mostly adjacent islands.
Clarence Island is an important part of this ecosystem, located to the south of Brunswick Peninsula, surrounded by the Cockburn Channel, the Bárbara Channel and the Froward Pass. Administratively, Clarence Island belongs to the Magallanes Region and is within the boundaries of the former Alacalufes National Reserve (today Kawésqar National Park). Kawésqar National Park has a wide biodiversity of flora and fauna and covers the administrative provinces of Última Esperanza and Magallanes; it is one of the largest national parks in the world (Friedlander et al. 2021). This island is the habitat of macroalgae Macrocystis pyrifera (Palacios Subiabre 2008), Durvillaea antarctica (Mansilla et al. 2017) and Mazzaella laminarioides ( Montecinos et al. 2012), and marine invertebrates such as arthropods, polychaetes, echinoderms, nemerteans and mollusks ( Palacios Subiabre 2008, Cañete et al. 2013. The inclusion of biotopes in ecological analyses of marine environments complements the functional studies of the systems, providing information on both taxonomy and associations of organisms (Olenin and Ducrotoy 2006), which when developed on Clarence Island will provide key information on the structure of this ecosystem.
The GBIF network provides data provider institutions around the world with common standards and open source tools that allow them to share information about where and when species have been recorded (GBIF: The Global Biodiversity Information Facility 2022). The databases on this platform are available to any user, contributing knowledge regarding the distribution of species and for future decisions.
Clarence Island, a little-explored ecosystem, is of great importance to obtain more information about these marine biotopes, since although research has been carried out previously, it is of a limited nature and the information is not openly available through the GBIF open access platform. This study aims to sample a large area within the southeastern limits of the Kawésqar National Park, thereby seeking to achieve a precise description of the marine biotopes present in the different intertidal and shallow subtidal strata during the summer and winter, in order to contribute to knowledge and future decision-making in the Magallanes Region.

Project description
Title: Determination of intertidal biotopes in the locality of Clarence Island.

Study area description:
Clarence Island is located south of the Brunswick Peninsula and is surrounded by the Strait of Magellan, Barbara Channel, Cockburn Channel, and the narrow Pedro and Acwalisnan Channels.

Description:
The sampling was carried out as part of an exploratory study of the biodiversity of Clarence Island, located in the Magallanes Region, extending into the Chilean Fjords and Channels Ecoregion (Spalding et al. 2007). The contributions of freshwater from the ice fields of glaciers surrounding Clarence Island and the geomorphology of the area cause the studied locality to have particular and unique marine biodiversity. A part of Clarence Island called Seno Duntze, located on the southeast coast of the Island towards the Cockburn Channel and exposed to the prevailing westerly winds, was described by Palacios Subiabre (2008), who indicated that the coast has an intertidal substrate with little slope, pebble and boulder block granulometry, and sedimentary type rocks. Macrocystis pyrifera is mentioned as the predominant algal species, along with several species of marine invertebrates (Palacios Subiabre 2008).

Sampling description:
Units of measurement in the study area were defined following a distance gradient, considering sites of interest in fjords and channels on the east coast of Clarence Island, just inside the southeastern boundary of Kawésqar National Park (Fig. 1). These units were called transects (Table 1). Stations were established in front of, around and in the immediate vicinity of each transect. Between 7 and 9 sampling units (stations ;  Table 1) were defined, spaced approximately every 500 meters, which gave each transect a maximum coastline prospecting distance of 4.5 kilometers. The intertidal zone is regularly exposed to air by tidal movement; the aquatic organisms that live in these habitats are adapted to these periods. The mid-coastal zone is wide and very visible, often dominated by rocks inhabited by attached or mobile organisms which are tolerant of periodic exposure to air and depend on seawater immersion. The middle zone of the coast is preceded by a supralittoral zone, a strip of almost bare rock, although with the presence of some gastropods. Below the middle zone is the infralittoral zone, where there is a margin of dense kelp and other algae that provide shelter for flora and fauna.
The sampling was carried out with high-quality still camera photographs, which allow the identification of the species in the images. The entire bank of photographs was organized and classified by sampling season, summer and winter. All photos were taken by professionals from biological areas; special care was taken to capture the zone and representation of intertidal biotopes, following the recommendations of John et al. (2003) on intertidal biotopes. Location of the study area on the east coast of Clarence Island, which is shown circumscribed within the limits of the Kawésqar National Park (green shading). Each transect (CL1 to CL13; see Table 1) was assigned a different color.

Quality control:
The identification of taxa taken in the photograph was carried out meticulously, using the appropriate specific literature for each taxon plus comparison with samples in institutional collections. 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) and taxonomically adjusted according to the World Register of Marine Species (WoRMS Editorial Board 2022). The data were submitted in the Integrated Publishing Toolkit, following the standards of the Global Biodiversity Information Facility (GBIF).

Geographic coverage
Description: The coast of the Clarence Island, south of the Strait of Magellan, in an intensive sampling area along fjords and channels in the southeast of the island, covering <1 degree of latitude.
The following data fields of the Darwin Core standard were utilized:

Additional information
Based on the methodology proposed by John et al. (2003) for the Aysén Region (Laguna San Rafael National Park, Estero Elefantes, Chonos Archipelago and Katalalixar Reserve), three studies related to intertidal biotopes have been carried out in the southern part of the Chilean Fjords and Channels Ecoregion (Soto et al. 2012, Soto et al. 2015, Letelier et al. 2013, all from the CIMAR-Fjords Cruises (Comité Oceanográfico Nacional 2021). In the first, 13 stations were sampled between Canal Trinidad and Canal Smyth, where 19 biotopes were identified. In the second, a sampling of 14 stations was carried out, recognizing 10 biotopes from the Strait of Magellan to the Beagle Channel. Finally, the latest biotope work carried out so far in the region, also between the Trinidad Channel and Smyth Channel, found 13 recognized biotopes in the intertidal and shallow sublittoral zones. Therefore, until now there was a lack of biotope information in remote locations such as Clarence Island, where its estuarine areas have new biotopes, based on this study. A common biotope throughout the study area is that composed of lichens and mosses (LSUPR.LICH; Fig. 2, Table 2). Other very common biotopes in the study area were those of the barnacle Elminius kingii (LR. Ekin; Fig. 2

Conclusions
This report constitutes the first record of the intertidal coastal biota for the eastern coast of Clarence Island (Tierra del Fuego Archipelago) which is circumscribed in the Kawésqar National Park.
This information intends to contribute to the knowledge of the coastal ecology of fjords and channels in southern Chile, in addition to serving as a basis for establishing new species distribution records.  Table 2 for the biotope codes.