Exploitation and habitat degradation as agents of change within coral reef fish communities

Abstract

Over-exploitation and habitat degradation are the two major drivers of global environmental change and are responsible for local extinctions and declining ecosystem services.Here we compare the top-down effect of exploitation by fishing with the bottom-up influence of habitat loss on fish communities in the most diverse of ecological systems, coral reefs. Using a combination of multivariate techniques and path analyses, we illustrate that the relative importance of coral cover and fishing in controlling fish abundance on remote Fijian reefs varies between species and functional groups. A decline in branching Acropora coral is strongly associated with a decline in abundance of coral-feeding species, and a decrease in coral-associated habitat complexity, which has indirectly contributed to reduced abundance of small-bodied damselfish. In contrast, reduced fishing pressure, brought about by declining human populations and a shift to alternate livelihoods, is associated with increased abundance of some piscivores and fisheries target species. However, availability of prey is controlled by coral-associated habitat complexity and appears to be a more important driver of total piscivore abundance compared with fishing pressure. Effects of both fishing and coral loss are stronger on individual species than functional groups, as variation in the relative importance of fishing or coral loss among species within the same functional group attenuated the impact of either of these potential drivers at the functional level. Overall, fishing continues to have an influence on Fijian fish communities; however, habitat loss is currently the overriding agent of change. The importance of coral loss mediated by climate change is expected to have an increasing contribution to fish community dynamics, particularly in remote locations or where the influence of fishing is waning.

A test of trophic cascade theory: fish and benthic assemblages across a predator density gradient on coral reefs

“…Declines in acroporid cover, and thus habitat complexity, are associated with the loss of small-bodied coral-associated fishes, such as territorial damselfishes Brandl et al 2016), which may explain the lower density and biomass of territorial grazers in the Swains compared to the Ribbons. Bottom-up effects that shape habitat complexity and populations of small-bodied fishes likewise drive prey availability to large piscivores (Alvarez-Filip et al 2011a), and in Fiji, the loss of habitat complexity and thus prey availability is a more important driver of piscivore assemblages than fishing pressure (Wilson et al 2008). Further, the architectural complexity offered by acroporid cover may drive additional ecosystem services such as wave energy and nutrient upcycling, thus further impacting the trophic structure of fish assemblages (Alvarez-Filip et al 2011b).…”

Distribution and drivers of coral disease at Ningaloo reef, Indian Ocean

“…Characteristics of this family, including investment in energy towards growth and dominance of reef substratum, rather than resistance to disease (Jackson & Hughes 1985, Palmer & Gates 2010, are likely to contribute to the susceptibility of this family to disease globally (Gladfelter 1982, Patterson et al 2002, Willis et al 2004, Hobbs & Frisch 2010. Acroporids are major reef builders, their diversity of growth forms contributing significantly to structural complexity and diversity of reefs (Lirman 1999, Graham et al 2006, Wilson et al 2008), including fish and invertebrates which closely associate with Acropora corals (Munday et al 1997, Vytopil & Willis 2001, Pratchett 2005. At Ningaloo Reef, the threat to Acropora corals from disease is currently low; however, given the vulnerability of this genus to disease and a variety of other stressors (Precht et al 2002), the potential loss of Acropora corals from reefs is of global concern because such a loss could have far-reaching effects on the abundance and distribution of many reef-associated animals (Pratchett et al 2009).…”

The Dynamics of Coral-Algal Interactions in Space and Time on the Southern Great Barrier Reef

“…Although herbivorous fish abundances were not directly measured, the northeast study area is the only area investigated outside of the Marine National Park management zone, where fishing is permitted. Furthermore, the reduction in coral cover due to cyclone damage may have led to a decline in structural complexity, further reducing fish populations (Wilson et al, 2008), and ultimately leading to a greater abundance of Halimeda.…”