Biodiversity and Chemical Interactions in Antarctic Benthic Communities of Deception Island (South Shetland Islands) = Biodiversidad e Interacciones Químicas en las comunidades bentónicas Antárticas en Isla Decepción

Abstract

This Thesis covers two different topics in Antarctic marine benthic invertebrates. The two main goals are: 1) to improve the knowledge of the biodiversity of the shallow water benthic communities inside Deception Island (South Shetland Islands, Antarctica), and 2) to establish the chemical ecology of selected Antarctic organisms, by studying the antifouling and antimicrobial activity of their organic extracts. Deception Island is an active volcano on the southwestern end of the South Shetland Island chain. This island chain parallels the northeastern curvature of the Antarctic Peninsula, but is separated from the Antarctic continent by the narrow Bransfield Strait. Volcanic activity is believed to be the key environmental component that controls epibenthic and infaunal invertebrate populations in Port Foster. Compared to nearby islands, Deception Island is clearly defaunate at depth, and since the last eruption in 1970, has been considerably recolonized. However, many taxa are still very poorly represented and the colonizer species are mainly those with planktotrophic larvae. Interestingly, the soft-bottom benthos communities of the shallowest zone of Port Foster has been barely and poorly explored yet. A complete study of the benthic invertebrate shallow community at Deception Island was conducted, looking for a comprehensive view of this singular spot working at different trophic levels. Shallow-water sediment at Deception Island is inhabited mostly by opportunistic, motile species, living under the influence of serious and long-lasting disturbances, related more to high sedimentation rates within the bay and the absent of hard substrata, than with the ice-scouring or anchor-ice disturbances (mostly absent inside the caldera, but common elsewhere in Antarctica). The trophic relationship between the water and benthic community has been described in four stages; (i) particulate matter is suspended from the seafloor into the water column; (ii) nutrients stimulate bacterial and phytoplankton production, which stimulates zooplankton production; (iii) large suspended particles provide food for planktonic and benthic grazers; and (iv) organisms no consumed sink to the seafloor to be utilized by benthic community. These nutrients would be transmitted to bacterial communities, known to use this abundant material over the year in some sites of the island. This microbial biomass could then be transmitted to the meiofauna, trophic level showing also high densities in Port Foster. Furthermore, Port Foster receives much runoff during the austral summer, and may serve as a “nutrient trap”, thus influencing the meiofaunal organisms. All these, together with the microbial communities, could be behind the high macrofaunal densities observed here. Finally, all these trophic compartments would then be supporting the remarkable density of megafaunal organisms at Port Foster. Antarctic benthos is dominated by biological interactions, and it is expected that many marine invertebrates use chemicals as means of defense from predators, pathogens or preventing overgrowth. Natural products (also called secondary metabolites) are chemicals produced by organisms, which regulate the biology, co-existence, and co-evolution of the species without participating directly in their primary metabolism. The role of these natural products play in the Antarctic benthic communities is one of the main subjects of investigation in the present dissertation through an experimental contribution in the antimicrobial and antifouling field using chemical crude extracts from Antarctic benthic organisms. Marine secondary metabolites may play a role as deterrents against pathogenic microorganisms, fouling organisms, predators and/or competitors. Benthic marine organisms, under intense pressure for space, light and food, have developed a wide range of defensive mechanisms ranging from behavioral to physical and chemical strategies. Competition for space is a remarkable ecological force, comparable to predation that produce a strong selective pressure on benthic invertebrates. Some invertebrates, thus, possess antimicrobial compounds to reduce surface bacterial growth. The ubiquity of fouling organisms in the marine environment and the negative consequences of fouling are likely strong evolutionary pressures for marine organisms to develop defenses to protect their surface from fouling. In summary, marine invertebrates can survive in the highly competitive and hostile environments, mainly relying on their chemical defensive system by accumulating a series of defensive chemicals in their bodies or releasing the compounds to their surroundings.

Isla Decepción es un volcán activo en el extremo suroeste de la cadena de islas Shetland del Sur. Esta cadena de islas discurre paralela a la curvatura noreste de la Península Antártica, pero está separada del continente antártico por el estrecho de Bransfield. Se cree que la actividad volcánica es el componente ambiental clave que controla las poblaciones de invertebrados epibentónicos e infaunales en Puerto Foster. En comparación con las islas cercanas, Isla Decepción está claramente depauperada en profundidad, y desde la última erupción en 1970, sus fondos han sido recolonizados progresivamente. Sin embargo, muchos taxones están poco representados y las especies colonizadoras son principalmente aquellas que tienen larvas planctotróficas. Curiosamente, las comunidades bentónicas de fondos blandos de la zona más somera de Puerto Foster apenas han sido estudiadas. En un contexto en que la Península Antártica está experimentando una de las tasas más rápidas de cambio climático regional en la Tierra, Isla Decepción se presenta como una buena oportunidad de trabajar con escenarios previsibles para las comunidades bentónicas antárticas costeras. Se ha realizado un estudio completo de la comunidad bentónica de invertebrados en aguas poco profundas de Isla Decepción, en busca de una visión integrada de este paraje singular estudiando diferentes niveles tróficos. El bentos antártico está dominado por interacciones biológicas, y es previsible que muchos invertebrados marinos utilicen productos químicos como medio de defensa contra los depredadores, contra patógenos o para evitar el recubrimiento (antifouling). El papel que estos productos naturales desempeñan en las comunidades bentónicas antárticas es uno de los principales temas de investigación en la presente tesis a través de una contribución experimental en el campo de los antimicrobianos y del antifouling utilizando extractos crudos de organismos bentónicos antárticos. Los invertebrados marinos pueden sobrevivir en entornos altamente competitivos y hostiles, confiando principalmente en su sistema defensivo químico mediante la acumulación de una serie de sustancias químicas defensivas en sus cuerpos o liberando los compuestos a su entorno.