Long-lived groupers require structurally stable reefs in the face of repeated climate change disturbances

Abstract

Benthic recovery from climate-related disturbances does not always warrant a commensurate functional recovery for reef-associated fish communities. Here, we examine the distribution of benthic groupers (family Serranidae) in coral reef communities from the Lakshadweep archipelago (Arabian Sea) in response to structural complexity and long-term habitat stability. These coral reefs that have been subject to two major El Nin ˜o Southern Oscillation-related coral bleaching events in the last decades (1998 and 2010). First, we employ a long-term (12-yr) benthicmonitoring dataset to track habitat structural stability at twelve reef sites in the archipelago. Structural stability of reefs was strongly driven by exposure to monsoon storms and depth, which made deeper and more sheltered reefs on the eastern aspect more stable than the more exposed (western) and shallower reefs. We surveyed groupers (species richness, abundance, biomass) in 60 sites across the entire archipelago, representing both exposures and depths. Sites were selected along a gradient of structural complexity from very low to high. Grouper biomass appeared to vary with habitat stability with significant differences between depth and exposure; sheltered deep reefs had a higher grouper biomass than either sheltered shallow or exposed (deep and shallow) reefs. Species richness and abundance showed similar (though not significant) trends. More interestingly, average grouper biomass increased exponentially with structural complexity, but only at the sheltered deep (high stability) sites, despite the availability of recovered structure at exposed deep and shallow sites (lower-stability sites). This trend was especially pronounced for long-lived groupers (life span [10 yrs). These results suggest that long-lived groupers may prefer temporally stable reefs, independent of the local availability of habitat structure. In reefs subject to repeated disturbances, the presence of structurally stable reefs may be critical as refuges for functionally important, long-lived species like groupers.

Potential and Risk of Grouper (Epinephelus spp., Epinephelidae) Stock Enhancement in Indonesia

“…Assuming that about 10% are grouper, then grouper biomass can reach 120 kg ha -1 . This value is close to the highest grouper biomass found in the marine protected area of 130 kg ha -1 [26]. Comparing the grouper biomass that can be reached in the marine protected area with the grouper biomass in Taka Malang and Cemara Kecil Island, it should be possible to enhance the stock of grouper at both release sites.…”

Changing role of coral reef marine reserves in a warming climate

“…4b, c). This is quite likely due to population declines driven by erosion of their prey base following reef structural loss 32,33 , coupled with slow life histories of species which require long recovery times in intact coral habitats 34 .…”

Catch rates and income are associated with fisheries management restrictions and not an environmental disturbance, in a heavily exploited tropical fishery

“…Some of these small-bodied prey species are typically dependent on hard coral cover for recruitment, survival, and growth and are therefore sensitive to losses in coral cover (Graham et al 2007. Karkarey et al (2014) showed that grouper numbers declined on reefs where structural complexity was lost after coral mortality, which is likely due to a loss in their coral-dependent prey. Consequently, the issues of what species are caught in the fishery, their reliance on coral reefs and prey, and the extent of the disturbance may all play a role in the outcomes of the disturbance on the fishery.…”

“…Nevertheless, the subsequent effects on the fisheries have been less clear and difficult to study because of the expected time lag responses between losses of smaller and prey species on the larger and predatory fish and their potential interactions with fisheries management (Graham et al 2007, 2008, Karkarey et al 2014. Further, management restrictions might improve the outcomes and hide the full effects of environmental degradation expected from climate change.…”