Las esponjas como ingenieros ecosistémicos en el mesolitoral de la Bahía de San Antonio : evaluación de efectos físicos en el componente biótico y posibles mecanismos

Abstract

Los ingenieros ecosistémicos (IE) son organismos que, con su presencia o actividad, producen cambios estructurales que modulan la distribución de recursos y condiciones abióticas para los demás organismos. Mediante su estructura biogénica, las esponjas proveen microhábitats que son utilizados por otros organismos. En esta tesina se estudió el rol de las esponjas como IE en el mesolitoral de la Bahía de San Antonio (BSA), evaluando sus efectos físicos sobre la abundancia y diversidad de macroinvertebrados asociados.

Ecosystem engineers modulate the distribution of resources and abiotic conditions for other organisms through structural changes caused by their activity or presence. Sponges through their biogenic structure provide microhabitats that are used by other organisms. This study evaluated the role of sponges as ecosystem engineers in the midlittoral of San Antonio Bay (SAB), assessing their physical effects in the abundance and diversity of the associated macroinvertebrates. The study was carried out at the low midlittoral zone of SAB. The effect of sponges was evaluated with in situ experiments, encompassing both sponge remotion and the addition of sponge’s inert copies (mimics). In addition, the effect of sponge structure on the substrate heterogeneity, flow velocity, sedimentation rate and organic matter content were assessed as the mechanisms involved in the engineering process. In sites with sponges, we observed an increase of 36% in species richness and the organism’s abundance was six times higher compared to sites without the sponges. At the same time, sponges’ biogenic structure explains between 37 and 87% of changes in richness and abundance, respectively, of the associated macroinvertebrates assemblage. The substrate heterogeneity was higher in sites with sponges. Despite that, no significant effect of sponges was observed in the other physical variables measured. These findings suggest that in areas exposed to physical stress, like the midlittoral zone, sponges act as ecosystem engineers through their structure that increases microhabitats availability and substrate heterogeneity. Consequently, they increase species richness and abundance of the associated macroinvertebrates. Finally, the role of other mechanism that may interfere besides those mechanisms studied here are discussed.