Parrotfish movement patterns vary with spatiotemporal scale

Abstract

Herbivorous fishes are being increasingly valued for their ecological function in coral reef systems, and consequently they have become the focus of management actions on many reefs around the world. Because many conservation actions require an understanding of the space use patterns of species of interest, there has been an increased effort in recent years to study the movement patterns and home range sizes of many herbivorous taxa. Also of great interest are the fine-scale foraging patterns of parrotfishes and the spatial and temporal scale of their interactions with benthic organisms. In this study, we performed a comprehensive evaluation of the movement patterns of the parrotfish Chlorurus microrhinos at multiple spatial and temporal scales at Palmyra Atoll in 2013−2015. We found that these fish have large home ranges when accounting for migrations to spawning and night refuge sites, but that within feeding territories, their activity is highly non-random and is quite spatially constrained and temporally episodic, indicating a high level of feeding selectivity. These patterns of foraging activity result in the patchy removal of algae from the reef, which may have consequences for the space competition between algae and corals.

Patchy delivery of functions undermines functional redundancy in a high diversity system

“…Such small, highly focussed feeding areas have been previously reported for one functionally critical herbivore species, the steephead parrotfish Chlorurus microrhinos (Davis et al, ; Welsh & Bellwood, ). We found this pattern to be common across the entire observed herbivore assemblage; all functional groups had consistently small feeding areas.…”

“…The href smoothing parameter was utilised to allow conservative estimations across a range of sample sizes (Supporting Information Figure S1c, d). Maximum utilised area (95% contour) and core usage area (50% contour) were identified (Davis, Carlson, Lowe, Warner, & Caselle, ; Welsh & Bellwood, ). All area values were calculated from the KUDs using the r ‐package raster (Hijmans, ) and standardised by “feedable area.” Feedable area represents the space that was available for feeding at each site, that is the experimental 36 m 2 minus live coral or sand cover as well as areas that were not visible on video recordings.…”

“…The href smoothing parameter was utilised to allow conservative estimations across a range of sample sizes (Supporting Information Figure S1c, d). Maximum utilised area (95% contour) and core usage area (50% contour) were identified (Davis, Carlson, Lowe, Warner, & Caselle, 2017;Welsh & Bellwood, 2012). All area values were calculated from the KUDs using the r-package raster (Hijmans, 2017) and standardised by "feedable area."…”

Seascapes as drivers of herbivore assemblages in coral reef ecosystems

“…Similarly, excavating parrotfish (namely Chlorurus microrhinos ) that play an important role in coral reef resilience by actively eroding reef substrates and opening up substrates for coral recruitment (Green and Bellwood , Davis et al. ) were preferentially associated with western barrier reef sites and emergent carbonate banks and were depauperate from the eastern reefs. Thus, geographic partitioning of herbivore communities driven by habitat associations at archipelago scales may intrinsically affect the resilience of reefs following disturbance.…”

The commercially important shoemaker spinefoot, Siganus sutor, connects coral reefs to neighbouring seagrass meadows

“…Consequently, improved fishery resource management efforts are presumed to be caused by the effective conservation of these networked habitats since they are known to promote fish biomass and species richness on neighbouring coral reefs (e.g., Nagelkerken et al, 2002;Olds et al, 2012). The spatial extent of fishes can primarily be determined by observing environmental cues such as the diel cycle (Davis et al, 2017;Honda et al, 2016). Accordingly, monitoring the use of different habitats during different times of the day can further explain important biological and ecological processes of fish species, such as foraging, predator avoidance and resting, and thus help support mobile link evidence.…”