Abstract Background Predation pressure and herbivory exert cascading effects on coral reef health and stability. However, the extent of these cascading effects can vary considerably across space and time. This variability is likely a result of the complex interactions between coral reefs’ biotic and abiotic dimensions. A major biological component that has been poorly integrated into the reefs' trophic studies is the microbial community, despite its role in coral death and bleaching susceptibility. Viruses that infect bacteria can control microbial densities and may positively affect coral health by controlling microbialization. We hypothesize that viral predation of bacteria has analogous effects to the top-down pressure of macroorganisms on the trophic structure and reef health. Results Here, we investigated the relationships between live coral cover and viruses, bacteria, benthic algae, fish biomass, and water chemistry in 110 reefs spanning inhabited and uninhabited islands and atolls across the Pacific Ocean. Statistical learning showed that the abundance of turf algae, viruses, and bacteria, in that order, were the variables best predicting the variance in coral cover. While fish biomass was not a strong predictor of coral cover, the relationship between fish and corals became apparent when analyzed in the context of viral predation: high coral cover (> 50%) occurred on reefs with a combination of high predator fish biomass (sum of sharks and piscivores > 200 g m −2 ) and high virus-to-bacteria ratios (> 10), an indicator of viral predation pressure. However, these relationships were non-linear, with reefs at the higher and lower ends of the coral cover continuum displaying a narrow combination of abiotic and biotic variables, while reefs at intermediate coral cover showed a wider range of parameter combinations. Conclusions The results presented here support the hypothesis that viral predation of bacteria is associated with high coral cover and, thus, coral health and stability. We propose that combined predation pressures from fishes and viruses control energy fluxes, inhibiting the detrimental accumulation of ecosystem energy in the microbial food web.
more »
« less
Fishing degrades size structure of coral reef fish communities
Fishing pressure on coral reef ecosystems has been frequently linked to reductions of large fishes and reef fish biomass. Associated impacts on overall community structure are, however, less clear. In size‐structured aquatic ecosystems, fishing impacts are commonly quantified using size spectra, which describe the distribution of individual body sizes within a community. We examined the size spectra and biomass of coral reef fish communities at 38
- NSF-PAR ID:
- 10027279
- Publisher / Repository:
- Wiley-Blackwell
- Date Published:
- Journal Name:
- Global Change Biology
- Volume:
- 23
- Issue:
- 3
- ISSN:
- 1354-1013
- Page Range / eLocation ID:
- p. 1009-1022
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
more » « less
Abstract Marine food webs are structured through a combination of top‐down and bottom‐up processes. In coral reef ecosystems, fish size is related to life‐history characteristics and size‐based indicators can represent the distribution and flow of energy through the food web. Thus, size spectra can be a useful tool for investigating the impacts of both fishing and habitat condition on the health and productivity of coral reef fisheries. In addition, coral reef fisheries are often data‐limited and size spectra analysis can be a relatively cost‐effective and simple method for assessing fish populations. Abundance size spectra are widely used and quantify the relationship between organism size and relative abundance. Previous studies that have investigated the impacts of fishing and habitat condition together on the size distribution of coral reef fishes, however, have aggregated all fishes regardless of taxonomic identity. This leads to a poor understanding of how fishes with different feeding strategies, body size‐abundance relationships, or catchability might be influenced by top‐down and bottom‐up drivers. To address this gap, we quantified size spectra slopes of carnivorous and herbivorous coral reef fishes across three regions of Indonesia representing a gradient in fishing pressure and habitat conditions. We show that fishing pressure was the dominant driver of size spectra slopes such that they became steeper as fishing pressure increased, which was due to the removal of large‐bodied fishes. When considering fish functional groups separately, however, carnivore size spectra slopes were more heavily impacted by fishing than herbivores. Also, structural complexity, which can mediate predator‐prey interactions and provisioning of resources, was a relatively important driver of herbivore size spectra slopes such that slopes were shallower in more complex habitats. Our results show that size spectra slopes can be used as indicators of fishing pressure on coral reef fishes, but aggregating fish regardless of trophic identity or functional role overlooks differential impacts of fishing pressure and habitat condition on carnivore and herbivore size distributions.
-
more » « less
Abstract Protection of coastal ecosystems from deforestation may be the best way to protect coral reefs from sediment runoff. However, given the importance of generating economic activities for coastal livelihoods, the prohibition of development is often not feasible. In light of this, logging codes of practice have been developed to mitigate the impacts of logging on downstream ecosystems. However, no studies have assessed whether managed land‐clearing can occur in tandem with coral reef conservation goals.
This study quantifies the impacts of current land use and the risk of potential logging activities on downstream coral reef condition and fisheries using a novel suite of linked land‐sea models, using Kolombangara Island in the Solomon Islands as a case study. Further, we examine the ability of erosion reduction strategies stipulated in logging codes of practice to reduce these impacts as clearing extent increases.
We found that with present‐day land use, reductions in live and branching coral cover and increases in turf algae were associated with exposure to sediment runoff from catchments and log ponds. Critically, reductions in fish grazer abundance and biomass were associated with increasing sediment runoff, a functional group that accounts for ~25% of subsistence fishing. At low clearing extents, although best management practices minimize the exposure of coral reefs to increased runoff, it would still result in 32% of the reef experiencing an increase in sediment exposure. If clearing extent increased, best management practices would have no impact, with a staggering 89% of coral reef area at risk compared to logging with no management.
Synthesis and applications . Assessing trade‐offs between coastal development and protection of marine resources is a challenge for decision makers globally. Although development activities requiring clearing can be important for livelihoods, our results demonstrate that new logging in intact forest risks downstream resources important for both food and livelihood security. Importantly, our approach allows for spatially explicit recommendations for where terrestrial management might best complement marine management. Finally, given the critical degradation feedback loops that increased sediment runoff can reinforce on coral reefs, minimizing sediment runoff could play an important role in helping coral reefs recover from climate‐related disturbances. -
more » « less
Abstract Marine protected area (
MPA ) networks, with varying degrees of protection and use, can be useful tools to achieve both conservation and fisheries management benefits. Assessing whetherMPA networks meet their objectives requires data from Before the establishment of the network to better discern natural spatiotemporal variation and preexisting differences from the response to protection. Here, we use a Progressive‐ChangeBACIPS approach to assess the ecological effects of a network of five fully and three moderately protectedMPA s on fish communities in two coral reef habitats (lagoon and fore reef) based on a time series of data collected five times (over three years) Before and 12 times (over nine years) After the network's establishment on the island of Moorea, French Polynesia. At the network scale, on the fore reef, density and biomass of harvested fishes increased by 19.3% and 24.8%, respectively, in protected areas relative to control fished areas. Fully protected areas provided greater ecological benefits than moderately protected areas. In the lagoon, density and biomass of harvested fishes increased, but only the 31% increase in biomass in fully protectedMPA s was significant. Non‐harvested fishes did not respond to protection in any of the habitats. We propose that these responses to protection were small, relative to otherMPA assessments, due to limited compliance and weak surveillance, although other factors such as the occurrence of a crown‐of‐thorns starfish outbreak and a cyclone after the network was established may also have impeded the ability of the network to provide benefits. Our results highlight the importance of using fully protectedMPA s over moderately protectedMPA s to achieve conservation objectives, even in complex social–ecological settings, but also stress the need to monitor effects and adapt management based on ongoing assessments. -
more » « less
Abstract Understanding the spatial and environmental variation in demographic processes of fisheries target species, such as coral grouper (Genus:
Plectropomus ), is important for establishing effective management and conservation strategies. Herein we compare the demography ofPlectropomus leopardus andP. laevis between Australia's Great Barrier Reef Marine Park (GBRMP), which has been subject to sustained and extensive fishing pressure, and the oceanic atolls of Australia's Coral Sea Marine Park (CSMP), where there is very limited fishing for reef fishes. Coral grouper length‐at‐age data from contemporary and historical otolith collections across 9.4 degrees of latitude showed little difference in lifetime growth between GBRMP and CSMP regions.Plectropomus laevis populations in GBRMP reefs had significantly higher rates of total mortality than populations in the CSMP. Mean maximum lengths and mean maximum ages ofP. laevis were also smaller in the GBRMP than in the CSMP, even when considering populations sampled within GBRMP no‐take marine reserves (NTMRs).Plectropomus leopardus , individuals were on average smaller on fished reefs than NTMRs in the GBRMP, but all other aspects of demography were broadly similar between regions despite the negligible levels of fishing pressure in the CSMP. Similarities between regions in growth profiles and length‐at‐age comparisons ofP. laevis andP. leopardus suggest that the environmental differences between the CSMP and the GBRMP may not have significant impacts on lifetime growth. Our results show that fishing may have influenced the demography of coral grouper on the GBR, particularly for the slower growing and longer lived species,P. laevis .
