The ghost of the past anthropogenic impact: Reef-decapods as bioindicators of threatened marine ecosystems
Bruno Welter Giraldes, Petrônio Alves Coêlho, Petrônio Alves Coelho Filho, Thais Peixoto Macedo, Andrea Santarosa Freire
Abstract
This study demonstrated the plasticity of reef-decapod according with the exposed anthropogenic pressure. Comparing the reef-decapods at sites with different anthropogenic pressures in two different ecoregions (tropical and subtropical reef ecotypes), we demonstrated that historical anthropogenic activity is molding directly and indirectly their population. A direct impact over target decapods for fishing (e.g. Lobsters and large crabs) that are removed directly by human activities. A positive indirect impact related to a top-down trophic imbalance with the increase of naturally dominant preys (small decapod) due to the removal of top predators. Thus, insufficient predators to control the abundant prey in a classic unbalanced prey-predator relationship. An indirect and negative impact, related to a bottom-up trophic imbalance, is the exclusion of niche-restricted species in association with benthic cover (e.g. corals). This also has the positive outcome, however, of increasing numbers of herbivores, detritivores and scavengers. As hypothesis, we propose that a current biodiversity balance in anthropogenically impacted ecosystem is just reflecting past trophic cascade events. Where the remaining biodiversity is monopolizing the vacant niches after the removal of components in a trophic chain. Therefore, we are suggesting that reef-decapod biodiversity, observed using visual identification, can be used to highlight the “Ghost of the past anthropogenic impact” in threatened ecosystems.