Many coral reefs have been degraded over the past two to three decades through a combination of human and natural disturbances. In Jamaica, the effects of overfishing, hurricane damage, and disease have combined to destroy most corals, whose abundance has declined from more than 50 percent in the late 1970s to less than 5 percent today. A dramatic phase shift has occurred, producing a system dominated by fleshy macroalgae (more than 90 percent cover). Immediate implementation of management procedures is necessary to avoid further catastrophic damage.

https://science.sciencemag.org/content/sci/265/5178/1547.full.pdf

Catastrophes, phase shifts, and large-scale degradation of a Caribbean coral reef.

Two features characterize all natural communities. First, they are dynamic systems. The densities and age-structures of populations change with time, as do the relative abundances of species; local extinctions are commonplace (37). For many communities, a self-reproducing climax state may only exist as an average condition on a relatively large spatial scale, and even that has yet to be rigorously demonstrated (36). The idea that equilibrium is rarely achieved on the local scale was expressed decades ago by a number of forest ecologists (e.g. 10 1, 168). One might even argue that continued application of the concept of climax to natural systems is simply an exercise in metaphysics (41). While this view may seem extreme, major climatic shifts often recur at time intervals shorter than that required for a community to reach competitive equilibrium or alter the geographical distributions of species (6, 21, 43, 76, 92). Climatic variation of this kind influences ecological patterns over large areas, sometimes encompassing entire continents. Other agents of temporal change in natural communities operate over a wide range of smaller spatial scales (47, 242). Second, natural communities are spatially heterogeneous. This statement is true at any scale of resolution (242), but it is especially apparent on what is commonly referred to as the regional scale. (By region I mean an area that potentially encompasses more than one colonizable patch.) Across any land or seascape, one observes a mosaic of patches identified by spatial discontinuities in the distributions of populations (153, 159, 161, 231, 239, 240). Closer examination often reveals a smaller-scale patchwork of same-aged individuals (e.g. 85-87, 101, 146, 199,204,217-220,235,246). Discrete patch boundaries sometimes reflect species-specific responses to

The Role of Disturbance in Natural Communities

We suggest that relatively few species attributes are of overriding importance to the structure of benthic marine algal communities and that these are often shared among taxonomically distant species. Data from the western North Atlantic, eastern North Pacific and Caribbean suggest that patterns in algal biomass, diversity and dominance are strikingly convergent when examined at a functional group level relative to the productivity and herbivore-induced disturbance potentials of the environment. We present a simple graphical model that provides a way to predict algal community composition based on these two environmental axes. This predictability stems from algal functional groups having characteristic rates of mass-specific productivity, thallus longevity and canopy height that cause them to «behave» in similar ways (...)

http://www.vliz.be/imisdocs/publications/131003.pdf

A functional group approach to the structure of algal-dominated communities

All species have evolved in the presence of disturbance, and thus are in a sense matched to the recurrence pattern of the perturbations. Consequently, disturbances within the typical range, even at the extreme of that range as defined by large, infrequent disturbances (LIDs), usually result in little long-term change to the system's fundamental character. We argue that more serious ecological consequences result from compounded perturbations within the normative recovery time of the community in question. We consider both physically based disturbance (for example, storm, volcanic eruption, and forest fire) and biologically based disturbance of populations, such as overharvesting, invasion, and disease, and their interactions. Dispersal capability and measures of generation time or age to first reproduction of the species of interest seem to be the important metrics for scaling the size and frequency of disturbances among different types of ecosystems. We develop six scenarios that describe communities that have been subjected to multiple perturbations, either simultaneously or at a rate faster than the rate of recovery, and appear to have entered new domains or “ecological surprises.” In some cases, three or more disturbances seem to have been required to initiate the changed state. We argue that in a world of ever-more-pervasive anthropogenic impacts on natural communities coupled with the increasing certainty of global change, compounded perturbations and ecological surprises will become more common. Understanding these ecological synergisms will be basic to environmental management decisions of the 21st century.

/pdf/compounded-perturbations-yield-ecological-surprises-1ooryxcop3.pdf

Compounded Perturbations Yield Ecological Surprises

Phase-shifts from one persistent assemblage of species to another have become increasingly commonplace on coral reefs and in many other ecosystems due to escalating human impacts. Coral reef science, monitoring and global assessments have focused mainly on producing detailed descriptions of reef decline, and continue to pay insufficient attention to the underlying processes causing degradation. A more productive way forward is to harness new theoretical insights and empirical information on why some reefs degrade and others do not. Learning how to avoid undesirable phase-shifts, and how to reverse them when they occur, requires an urgent reform of scientific approaches, policies, governance structures and coral reef management.

https://www.cell.com/trends/ecology-evolution/pdf/S0169-5347(10)00182-5.pdf

Rising to the challenge of sustaining coral reef resilience.

Coral reefs of north Jamaica, normally sheltered, were severely damaged by Hurricane Allen, the strongest Caribbean hurricane of this century. Immediate studies were made at Discovery Bay, where reef populations were already known in some detail. Data are presented to show how damage varied with the position and orientation of the substraturn and with the shape, size, and mechanical properties of exposed organisms. Data collected over succeeding weeks showed striking differences in the ability of organisms to heal and survive.

/pdf/hurricane-allen-s-impact-on-jamaican-coral-reefs-48kbzcaely.pdf

P. A. Clifford

Papers

Hurricane Allen's Impact on Jamaican Coral Reefs