High apex predator biomass on remote Pacific islands

Abstract

Abstract. On coral reefs in Palmyra-a central Pacific atoll with limited fishing pressure-total fish biomass is 428 and 299% greater than on reefs in nearby Christmas and Fanning Islands. Large apex predators -groupers, sharks, snappers, and jacks larger than 50 cm in length-account for 56% of total fish biomass in Palmyra on average, but only 7% and 3% on Christmas and Fanning. These biomass proportions are remarkably similar to those previously reported for the remote and uninhabited Northwest Hawaiian Islands (NWHI) and densely populated Main Hawaiian Islands (MHI), although Palmyra's reefs are dominated in biomass by sharks (44% of the total), whereas the NWHI by jacks (39%). Herbivorous fish biomass was also greater on Palmyra than on Christmas and Fanning (343% and 207%, respectively). These results and previous findings indicate that remote, uninhabited islands support high levels of consumers, and highlight the importance of healthy coral reef ecosystems as reference points for assessment of human impacts and establishment of restoration goals.

Differences in fish-assemblage structure between fished and unfished atolls in the northern Line Islands, central Pacific

“…Our observations of strong indirect effects of piscivores on secondary consumers differ from those of Stevenson et al (2007), who did not detect such effects based on a limited and variable number of transects conducted in different years at Palmyra, Tabuaeran, and Kiritimati only. Low statistical power likely explains why among-atoll differences in secondary consumer biomass were not detected.…”

“…High total fish biomass and disproportionately great representation of piscivores is pervasive across all of these lower latitude (< 2°) reefs except Tabuaeran and Kiritimati, despite striking similarities in elevated planktonic productivities among all that occur within the region of equatorial upwelling (Sandin et al 2008). Our observations provide the detail needed at an expanded spatial scale to conclusively demonstrate patterns of piscivore dominance and the trophic structuring of fish assemblages suggested by the preliminary study of Stevenson et al (2007) in the northern Line Islands.…”

“…The 4 atolls in the northern Line Islands provide a useful (if not perfectly controlled, see 'Materials and methods') natural experiment of predation effects on coral reefs, analogous to the situation in the NWHI. Dramatic variations in apex predator biomass have been noted across these atolls (Stevenson et al 2007, Sandin et al 2008, along with associated changes in the coral, other invertebrate, and algal assemblages (Sandin et al 2008), and in the microbiota (Dinsdale et al 2008). …”

Trophic restructuring of coral reef fish communities in a large marine reserve

“…The large disparity in proportional biomass between reserve and non-reserve sites in the large piscivore category was a major finding of this analysis, given that most other categories also had higher mean biomasses inside the marine reserve. Even so, our results support conclusions from studies of the northwest Hawaiian Islands (Friedlander & DeMartini 2002) and the Line Islands (Stevenson et al 2007, Sandin et al 2008 suggesting that relatively healthy, unfished reefs such as those found within the ECLSP may normally have as much as 50% of the fish biomass concentrated in top-level predatory species. The major reduction in average biomass for small piscivores and large mixed carnivores within the reserve, combined with associated increases in small mixed carnivores and planktivores suggests that reintroduction of these large piscivores can alter the distribution of species in other functional groups.…”

Rapid Effects of Marine Reserves via Larval Dispersal

“…Fishing on Caribbean reefs occurred long before the arrival of European settlers, but has returned increasingly diminished yields over the last 200 years as human populations have escalated in the region [14][15][16]. Similar to industrial and recreational counterparts in developed nations, artisanal fishing tends to target large-bodied, top trophic-level fishes, so greater numbers of fishermen per unit area should result in increased removal of larger species [17][18][19][20]. Indeed, populations of large-bodied fishes have become notoriously impoverished at some Caribbean locations with high densities of human populations (e.g., Jamaica) [21,22].…”