Ecological States and the Resilience of Coral Reefs

Abstract

ABSTRACT. We review the evidence for multiple ecological states and the factors that create ecological resilience in coral reef ecosystems. There are natural differences among benthic communities along gradients of water temperature, light, nutrients, and organic matter associated with upwelling-downwelling and onshoreoffshore systems. Along gradients from oligotrophy to eutrophy, plant-animal symbioses tend to decrease, and the abundance of algae and heterotrophic suspension feeders and the ratio of organic to inorganic carbon production tend to increase. Human influences such as fishing, increased organic matter and nutrients, sediments, warm water, and transportation of xenobiotics and diseases are common causes of a large number of recently reported ecological shifts. It is often the interaction of persistent and multiple synergistic disturbances that causes permanent ecological transitions, rather than the succession of individual short-term disturbances. For example, fishing can remove top-level predators, resulting in the ecological release of prey such as sea urchins and coraleating invertebrates. When sea urchins are not common because of unsuitable habitat, recruitment limitations, and diseases, and when overfishing removes herbivorous fish, frondose brown algae can dominate. Terrigenous sediments carried onto reefs as a result of increased soil erosion largely promote the dominance of turf or articulated green algae. Elevated nutrients and organic matter can increase internal eroders of reef substratum and a mixture of filamentous algae. Local conservation actions that attempt to reduce fishing and terrestrial influences promote the high production of inorganic carbon that is necessary for reef growth. However, global climate change threatens to undermine such actions because of increased bleaching and mortality caused by warm-water anomalies, weakened coral skeletons caused by reduced aragonite availability in reef waters, and increased incidence of diseases in coral reef species. Consequently, many coral reefs, including those that are heavily managed, have experienced net losses in accumulated inorganic carbon in recent decades and appear likely to continue this trend in coming decades. Reefs urgently need to be managed with a view to strengthening their resilience to the increased frequency and intensity of these pressures. Ecological targets must include the restoration or maintenance of species diversity, keystone species, spatial heterogeneity, refugia, and connectivity. Achieving these goals will require unprecedented cooperative synergy between human organizations at all political levels, from intergovernmental to local.

Spatial distribution of epibenthic molluscs on a sandstone reef in the Northeast of Brazil

“…The higher abundance of few species found on the Maracajaú reef, a result also observed on Caribbean reefs, may be associated to environmental stress (McClanahan, 2002). Additionally, the fact that the lower the number of species that use the same ecological niche is, the lower the competition among them is, also may have favored the increased abundance of dominant and more generalist species.…”

“…In relation to molluscan density, the low value for the species is a common characteristic in coral reef systems (McClanahan, 1990(McClanahan, , 2002Zuschin et al, 2001). The higher abundance of few species found on the Maracajaú reef, a result also observed on Caribbean reefs, may be associated to environmental stress (McClanahan, 2002).…”

“…This change in substrate cover may account for the altered coral reef community structure, which would result in loss of local biodiversity (Done, 1992;Hughes, 1994;McClanahan et al, 2002;Folk et al, 2004) and increased abundance in dominant generalist species. This substrate alteration may be correlated to the fishing activity that has taken place in this region for many years, which would explain the large fleshy alga cover in the entire reef area due to the lack of herbivore fish.…”

Corals shed bacteria as a potential mechanism of resilience to organic matter enrichment

“…There have been substantial discussions in the literature about how to define resilience (Nystrom et al, 2008), how to manage reefs in ways that encourage it (Hughes et al, 2010), and how to synthesize case studies to elucidate the large-scale mechanisms that determine whether a stony-coral-dominated ecosystem can resist a phase-shift or rebound from one (McClanahan et al, 2002;Norstrom et al, 2009). However, very little attention has been given to the small-scale mechanisms relevant to the microbial processes that determine the resilience of individual corals to a given stressor.…”

Spongivory by Fishes on Southwestern Atlantic Coral Reefs: No Evidence of Top-Down Control on Sponge Assemblages

“…Therefore, the top-down control of spongivory on sponge assemblages could also be weak on coral reefs at other Southwestern Atlantic reef sites. In TSB, coral reefs are under intense ornamental fishing and trade (Sampaio, 2006) and combined with organic matter influxes and other factors can result in dominances of non-reef build groups, as sponges (McClanahan et al, 2002;Maliao et al, 2008;Cruz et al, 2014). Furthermore, there is an urgent need to carefully evaluate regulations of fishing and implementation of management plans for TSB, as in many parts of the world.…”