Trophic interactions and ecological stability across coral reefs in the Marshall Islands

Abstract

Coral reef assemblages, trophic interactions, and food web stability were examined across a remote and densely populated atoll, in the Republic of the Marshall Islands (RMI). The biomass of sharks, large-bodied piscivores, and secondary invertebrate consumers was expectedly larger in the absence of major human populations. Less intuitively, we report a doubling in the density and biomass of small-bodied acanthurids with significant human presence, whereas large-bodied parrotfishes were halved. These trends provided evidence for prey release of small acanthurids, but also indicated a reduction in grazing function given that power-law relationships govern fish size and physiology. Path analyses supported the conjecture that apex predator biomass enhanced the abundance of large-bodied herbivores, with ensuing benefits to calcifying benthic substrates and coral diversity. Human populations, as low as 40 individuals, had opposing linked interactions. The study next used species abundances to depict food chain interaction strengths, and multivariate measures of heterogeneity to depict food chain diversity. The removal of few strong links along the gradient of investigation (i.e. Acropora corals and sharks), as well as numerous weak links, was associated with fish assemblages and benthic substrates that had reduced grazing and calcification potential, respectively. The results inferred that a reduction in the functional response time of trophic guilds will follow perturbations (i.e. reduce stability), synonymous to food webs with low return rates to their modeled, stable con figuration. This study provides a broader perspective for interpreting how humans and apex predators influence ecological stability across (RMI) coral reef ecosystems.

Managing coral reef fish community biomass is a priority for biodiversity conservation in Madagascar

“…The human influence metric does not take account of resource abundance metrics, such as reef area, nor of human infrastructure and travel time, or livelihood alternatives such as agriculture and animal husbandry among other socioeconomic attributes that should influence fishing pressure . Given the better predictions of human influence and environmental factors in other regions (Friedlander et al 2003, Brewer et al 2013, Houk & Musburger 2013, Williams et al 2015, Maire et al 2016, Mellin et al 2016a, the weaker responses found here suggests the need for an evaluation of fishing pressure and the factors that promote it at smaller spatial scales. Good models must account for various local factors influencing the balance between fish production and human impacts.…”

The effects of modern war and military activities on biodiversity and the environment

“…With the exception of a few specialized species, scleractinian coral diversity has rebounded on a number of reefs affected by nuclear testing . As well, the size-frequency distribution, an indicator of biomass, of many fish taxonomic groups within former blast sites have been observed to be much greater than that of the surrounding waters unaffected by nuclear testing (Houk and Musburger 2013). While nuclear testing is devastating on an acute timescale, it may prove to be beneficial to the local ecosystem over a more chronic duration through human exclusion.…”

“…Indeed, these areas have been demonstrated to have quite diverse and thriving ecosystems that are often in a better ecological state when compared to similar areas where routine human activity is present (see Fig. 2; Gray and Rickard 1989;Whicker et al 2004;Davis 2007;Richards et al 2008;Houk and Musburger 2013). Thus, sites devoted to nuclear arms production and testing can still be considered a positive feature in maintaining biodiversity despite the potential for chronic health impacts in resident organisms.…”

“…However, over a more chronic duration, these impacts are likely to be minimal as populations and diversity could recover through dispersal to the area as well as contributions from surviving organisms. Indeed, this has been observed in a number of plant (Palumbo 1962;Shields and Wells 1962;Shields et al 1963;Beatley 1966;Fosberg 1985;Hunter 1991Hunter , 1992 and animal (Jorgensen and Hayward 1965;O'Farrell 1984;Hunter 1992;Wills 2001;Kolesnikova et al 2005;Pinca et al 2005;Planes et al 2005;Richards et al 2008;Houk and Musburger 2013) communities from a diversity of testing site environments. In some instances, the exclusion of human activity from test sites has been quite beneficial to the recovery and prosperity of organisms found in these areas, as in the case of the atolls of the Marshall Islands (see Fig.…”

“…In some instances, the exclusion of human activity from test sites has been quite beneficial to the recovery and prosperity of organisms found in these areas, as in the case of the atolls of the Marshall Islands (see Fig. 2; Davis 2007;Richards et al 2008;Houk and Musburger 2013).…”