Interannual variability and decadal stability of benthic organisms on an Indonesian coral reef

Abstract

The availability of colonizable substrate is an important driver of the temporal dynamics of sessile invertebrates on coral reefs. Increased dominance of algae and, in some cases, sponges has been documented on many coral reefs around the world, but how these organisms benefit from non-colonized substrate on the reef is unclear. In this study, we described the temporal dynamics of benthic organisms on an Indonesian coral reef across two time periods between 2006 and 2017 (2006–2008 and 2014–2017), and investigated the effects of colonizable substrate on benthic cover of coral reef organisms at subsequent sampling events. In contrast with other Indonesian reefs where corals have been declining, corals were dominant and stable over time at this location (mean ± SE percentage cover 42.7 ± 1.9%). Percentage cover of turf algae and sponges showed larger interannual variability than corals and crustose coralline algae (CCA) (P < 0.001), indicating that these groups are more dynamic over short temporal scales. Bare substrate was a good predictor of turf cover in the following year (mean effect 0.2, 95% CI: 0–0.4). Algal cover combined with bare space was a good predictor of CCA cover the following year generally, and of sponge cover the following year but only at one of the three sites. These results indicate that turf algae on some Indonesian reefs can rapidly occupy free space when this becomes available, and that other benthic groups are probably not limited by the availability of bare substrate, but may overgrow already fouled substrates.

The relative influence of sea surface temperature anomalies on the benthic composition of an Indo‐Pacific and Caribbean coral reef over the last decade

“…This stark increase is most strongly related to the Sampela site where high sedimentation has driven sponge dominance (Biggerstaff et al, 2017). However, fine‐scale temporal variation in sponge and algae coverage on the coral reefs of the WNP are well documented (Marlow et al, 2020; Rovellini et al, 2019), along with interannual variability of algae coverage (Marlow et al, 2020; Rovellini et al, 2021), which are likely overlooked based on our findings (e.g., Figure 3). The increase in hard corals at the Indonesia location contradicts the assumed temporal stability of hard coral at these reefs (Marlow et al, 2020; Rovellini et al, 2021) but may be a consequence of recovery from a lower baseline because of the 2010 bleaching event (Watt‐Pringle et al, 2022), or a natural cycle where hard corals are increasing owing to temporal variation (Rovellini et al, 2021).…”

“…However, fine-scale temporal variation in sponge and algae coverage on the coral reefs of the WNP are well documented (Marlow et al, 2020;Rovellini et al, 2019), along with interannual variability of algae coverage (Marlow et al, 2020;Rovellini et al, 2021), which are likely overlooked based on our findings (e.g., Figure 3). The models ran separately for Indonesia and Honduras locations.…”

“…Given that intrinsic site variability between these two locations appears to be the strongest predictor of benthic composition compared with SSTA and time, it is critical to note other potential drivers of composition at these locations. Firstly, the use of mismatched time series methodology does not capture fine‐scale temporal dynamics of species with faster life histories, such as macroalgae and some sponges (Rovellini et al, 2021). These faster life history traits will also influence rock coverage as a bare substrate will be quickly monopolized by these taxa, yet grazing and/or displacement could occur before sampling between years takes place.…”

“…Benthic surveys where SSTA data were not available were excluded from the analysis, leaving a total of 1088 surveys over the 8‐year time period. While there are potential issues (Ferguson et al, 2017) for using mismatched time series (i.e., values over the last 52 weeks before the commencement of the survey), which do not capture fine‐scale variability taxa with fast life histories, such as macroalgae and some sponges (Rovellini et al, 2021), this approach has been successfully employed for assessing coral responses over the time period used (Donovan et al, 2021), which are indicative of coral reef compositional change. Average SSTA values for each location over the course of the previous 52 weeks are summarized in Figure 2.…”

“…The increase in hard corals at the Indonesia location contradicts the assumed temporal stability of hard coral at these reefs(Marlow et al, 2020;Rovellini et al, 2021) but may be a consequence of recovery from a lower baseline because of the 2010 bleaching event F I G U R E 3 Temporal dynamics of each benthic cover for each category at the Indonesia (top) and Honduras (bottom) location (Watt-Pringle et al, 2022),. or a natural cycle where hard corals are increasing owing to temporal variation(Rovellini et al, 2021). This is also indicated by a decrease in coral rubble at the Indonesia location through time, suggesting hard coral cover has displaced dead corals over time.…”