Multiple stressors on coral reefs: A long ‐term perspective

Abstract

Coral reefs are subject to a high frequency of recurrent biological and physical disturbances. The temporal and spatial scales of these are often large and difficult to study, so that most of our knowledge of disturbances on coral reefs comes from investigations conducted at one or a few sites, over short periods of time. We argue that studying single events in isolation can be misleading and that a longer term approach is necessary for understanding the responses of coral reef assemblages to multiple stressors. We present first a brief review of the impacts of physical disturbance (e.g., cyclones, hurricanes) on the community dynamics of coral reefs, with special attention to the effects of recurrent events. We then examine two unusually detailed, long-term data sets from Heron Island, Australia, and Jamaica which demonstrate some of the complexities of multiple stressors (broadly defined as natural or man-made disturbances).Both case studies illustrate that the effect of a particular disturbance often depends critically on the impact of previous perturbations. Consequently, even the same type of recurrent stressor can have different effects at different times, depending on history. Accordingly, when the added dimension of time is considered, the distinction between single and multiple stressors becomes blurred. Even a single event such as a hurricane can be viewed mechanistically as a multiple stressor, with short-and long-term impacts. We emphasize that multiple stressors often have significant effects on recruitment and regenerative processes of assemblages. These impacts are much less obvious than catastrophic or chronic mortality, but they play a crucial role in community dynamics over longer time scales. Importantly, chronic anthropogenic impacts can impede the ability of coral assemblages to recover from natural disasters, even where there is little detectable effect on rates of adult mortality. Once a reef has been degraded, it is usually impossible to ascertain retrospectively the precise mechanisms that were involved or the relative importance of different events. A single survey will provide a snapshot of the status of coral reefs, but a longer term approach is required to understand the processes underlying changes in assemblages.Stress is often considered in the coral reef literature as a sublethal effect on the physiology of an animal or plant, e.g., a decline in feeding, growth, or fecundity, or a biochemical change. The term has also been used at the population or demographic level, usually in terms of an acute or chronic disturbance that causes a decline in the number of organisms. Increasingly, scientists, reef managers, and the general public also refer to stressed or degraded assemblages of species or ecosystems affected by natural and anthropogenic impacts, and there is growing concern about the health of coral reefs (e.g., see Brown and Howard 1985;Ginsberg 1993;Richmond 1993).The concerns for the declining status of many coral reefs are legitimate, although we caution that some of...

Coral recruitment and potential recovery of eutrophied and blast fishing impacted reefs in Spermonde Archipelago, Indonesia

“…Eutrophication, pollution and sedimentation were found to hamper gamete production, alter the timing of spawning and decrease the fertilization success (Gilmour, 1999;Loya et al, 2004). They were found to slow the development and metamorphosis of the larvae and decrease the survival of the coral recruits (Gilmour, 1999;Hughes and Connell, 1999;Abelson et al, 2005). Eutrophication is also known to foster the growth of potential space competitors of coral recruits (Tomascik, 1991;Dunstan and Johnson, 1998;Abelson et al, 2005), toxic cyanobacteria or macroalgae inhibiting coral larvae settlement (Kuffner and Paul, 2004).…”

“…Overfishing could lead to a significant decimation of grazers, which control e.g. algae growth, hence controlling potential space competitor for coral recruits (Hughes and Connell, 1999). Furthermore, reef destruction through blast fishing was shown to increase the proportion and spatial extent of coral rubble, which because of its low resistance to physical dislodgement by waves and currents may provide a killing field for coral spat (Harrison and Wallace, 1990;Fox et al, 2003).…”

Biological community structure on patch reefs in Biscayne National Park, FL, USA

“…Physical disturbances can have lasting effects on coral communities (Hughes and Connell 1999;Bythell et al 2000), and impact studies following Hurricane Andrew revealed that disturbance was very patchy (Tilmant et al 1994;Blair et al 1994). Further, historical changes to coral communities can affect competitive interactions among benthic organisms many years after the disturbance event (Hughes 1989).…”

Ecological Shifts along the Florida Reef Tract: The Past as a Key to the Future

“…Disease pathogens are still present (Santavy et al 2001;Aronson and Precht 2001c;Patterson et al 2002), cold-weather fronts still occur, bleaching events are increasing in frequency and intensity, hurricanes can set back reef development, and predators are continuing to take their toll on remnant populations (Knowlton, Lang, and Keller 1990;Miller 2001), especially when other stressors are also present (Hughes 1989(Hughes , 1994Knowlton 1992;Hughes and Connell 1999). Suitable substrate may also limit larval recruitment where algal populations remain high (Hughes and Tanner 2000).…”