Network properties and keystoneness assessment in different intertidal communities dominated by two ecosystem engineer species (SE Pacific coast): A comparative analysis

Abstract

Multispecies quantitative and qualitative models of the kelp Lessonia nigrescens and the tunicate Pyura praeputialis were constructed for intertidal areas of northern Chile (SE Pacific). Information on biomass, P/B ratios, catches, food spectrum, consumption and dynamics of commercial and non-commercial species was obtained and examined using Ecopath with Ecosim and Loop Analysis theoretical frameworks. The biomass of L. nigrescens and P. praeputialis constituted the most important compartments, exceeding 97% of the total biomass in each model system. Based on Pp/R, the system of P. praeputialis appeared to be the most developed. However, according to Pp/B, A/C, Ai/Ci, and redundancy, the L. nigrescens system was the most developed and, in turn, the least resistant to disturbances. The results obtained using mixed trophic impacts (MTI), Ecosim simulations, and system recovery time (SRT) showed different response patterns. The tunicate species propagated higher effects on the remaining species, whereas the kelp species presented the longest SRT (as a resilience measure). The model keystone species indices suggested that each model system contained a core of ecologically related species. In the L. nigrescens system, core was made up of the filter feeders Semimytilus algosus, barnacles, and small epifauna herbivores (SEH) and the predators Concholepas concholepas and Heliaster helianthus. In the P. praeputialis system, the core consisted of phyoplankton, zooplankton, other filter feeders and the predators C. concholepas, H. helianthus, other starfish, and large epifauna. The outcomes obtained in the current work did not indicate that the alien tunicate P. praeputialis was a better or superior bio-engineer when compared to the system constructed by the kelp L. nigrescens. Rather, each species was relevant and relied on different ecological mechanisms.