Coral Reefs最新文献

Reef functionality depends on the coral community’s species composition, abundance, and on the capacity of corals to build carbonate structures. Nevertheless, the coral’s contribution to functionality remains hidden in species morphological variation displayed. Here, we use three-dimensional (3D) models to estimate the morpho-functional space of 14 Caribbean coral species by combining information from five morphological traits (sphericity, convexity, packing, first moment of surface area, and first moment of volume). Based on a principal component analysis, we selected the trait that captured most of the coral morphological variation to address the effect of colony size on structural complexity, shelter volume, and efficiency of resource use in terms of colony volume and calcium carbonate (CaCO₃) investment. At the species level, structural complexity increased as a function of coral colony size in branching, digitate, and columnar coral species. Shelter volume increased with colony size in all species; however, branching species such as Acropora palmata not only provide more shelter volume than species with simpler morphologies, but they do so more efficiently, investing less colony volume and CaCO₃ mass for attaining the same shelter volume. Tracking changes in coral morphologies and colony size can improve our ability to predict functional repercussions from modifications to coral assemblages that are caused by, for example, disease outbreaks or environmental disturbances.

Abstract

Function-based studies have opened a new chapter in our understanding of coral reefs. Unfortunately, we are opening this chapter as the world’s reefs rapidly transform. In this context, one of the most important roles of function-based studies is to inform coral reef conservation. At this critical juncture, we have a chance to reflect on where we have come from, and where we are going, in coral reef functional ecology, with specific consideration of what this means for our approaches to conserving reefs. As focal examples, we examine the role of corals on reefs, and the practice of culling crown-of-thorns starfish, from a functional perspective. We also consider how the papers in this special issue build on our current understanding. Ultimately, we highlight how robust scientific investigation, based on an understanding of ecosystem functions, will be key in helping us navigate reefs through the current coral reef crisis.

Abstract

Coral reefs harbor 30% of oceanic biodiversity, but many species remain undiscovered. Indeed, coral reef taxonomic inventories are heavily skewed toward large, conspicuous organisms, leaving numerous smaller, cryptic species undescribed. Cryptobenthic reef fishes, such as gobies, can speciate rapidly due to short lifespans and limited dispersal, and ecological specialization may facilitate their diversification. Here, we examine whether habitat specialization correlates with genetic and phenotypic divergence in Risor ruber, a sponge-dwelling goby distributed across the western Atlantic Ocean. By integrating phylogenetic evidence, morphometrics, and network analysis, we identify seven distinct genetic lineages within Risor and reveal concordant patterns of Risor–sponge specialization. Despite the absence of lineage-specific morphologies, morphological traits are associated with sponge hosts, indicating high phenotypic plasticity within lineages. Two Risor lineages specialize on a single host sponge across the Caribbean, while five lineages are generalists. Finally, high modularity across Risor–sponge networks provides further evidence that ecological specialization contributes to Risor diversification. Given the rapid changes in coral reef benthic communities, habitat specialists are more likely to lose their primary habitat and face extinction. Documenting and understanding genetic diversification is imperative, especially in understudied, vulnerable organisms such as cryptobenthic reef fishes.

The zoanthid Parazoanthus axinellae (Schmidt, 1862) is a widespread coral species in the Mediterranean coralligenous assemblages where two morphotypes are found: Slender and Stocky, differing in size, color, and preferred substrate. Due to these marked differences, Slender and Stocky morphotypes were hypothesized to be two species. Here, we used 2bRAD to obtain genome‐wide genotyped single nucleotide polymorphisms (SNPs) to investigate the genetic differentiation between Slender and Stocky morphs, as well as their population structure. A total of 101 specimens of P. axinellae were sampled and genotyped from eight locations along the Italian coastline. In four locations, samples of the two morphotypes were collected in sympatry. 2bRAD genome-wide SNPs were used to assess the genetic divergence between the two morphotypes (1319 SNPs), and population connectivity patterns within Slender (1926 SNPs) and Stocky (1871 SNPs) morphotypes. Marked and consistent differentiation was detected between Slender and Stocky morphotypes. The widely distributed Slender morphotype showed higher population mixing patterns, while populations of the Stocky morphotype exhibited a stronger genetic structure at a regional scale. The strong genetic differentiation observed between P. axinellae Slender and Stocky morphotypes provides additional evidence that these morphs could be attributed to different species, although further morphological and ecological studies are required to validate this hypothesis. Our study highlights the importance of resolving phylogenetic and taxonomic disparities within taxonomically problematic groups, such as the P. axinellae species complex, when performing genetic connectivity studies for management and conservation purposes.

Graphical Abstract

Schematic overview of the main genetic structuring patterns observed in this study. Coral polyps were colored to intuitively associate the reader to Parazoanthus axinellae morphotypes, with orange tones being attributed to the Stocky morphotype, and yellow tones to the Slender morphotype. Bidirectional arrows represent gene flow between coral individuals, with the number and thickness of arrows corresponding to the intensity of gene flow rates. The red dashed line represents the potential reproductive isolation between Slender and Stocky morphs

Outbreaks of crown-of-thorns starfish (COTS) pose a major threat to coral reefs in the Ashizuri-Uwakai National Park, Japan, which is partially affected by the Kuroshio Current. The purpose of this study was to identify the upstream areas of the Kuroshio significantly contributing to the supply of larvae to this area, where the larvae are most likely to reach within the Ashizuri-Uwakai area (inter-connectivity), and to clarify the connectivity within the park (intra-connectivity). Using a hydrodynamic model based on a 12-year dataset with a high spatial resolution (ca. 2 km), this study evaluated the transport and dispersion processes into and within the region, although the proportion of particles reaching the Ashizuri-Uwakai area the major sources were Tanegashima and Yakushima islands and the east coast of Kyushu. Grid cells with a high supply from these source areas were identified within Ashizuri-Uwakai and quantitatively shown to have high sink strength in the southwestern and cape areas. We were also able to show where particles released within Ashizuri-Uwakai tend to accumulate. Since locations with high sink strength generally coincided with diving sites and areas where conservation activities have been conducted, strengthening conservation activities in these locations can be considered to be effective in controlling outbreaks of COTS.

Over the past few decades, tool use has been described in a variety of animals across taxa. However, there are relatively limited reports and studies of tool use in marine environments. Among marine fish though, labrids have been reported to be proficient at using tools. Here, we describe the first observations of tool use in two species of tropical wrasses—Halichoeres hortulanus (checkerboard wrasse) and Thalassoma jansenii (Jansen’s wrasse)—and the first report of tool use from the wild for the wrasse Thalassoma lunare (Moon wrasse). These observations were made incidentally as part of size-specific predation assays for a small burrow-dwelling sea urchin (Echinostrephus molaris) in the Lakshadweep Archipelago, Indian Ocean. We documented multiple instances of anvil use by the wrasses H. hortulanus, and T. jansenii, and one instance of anvil use by T. lunare. All three species were recorded carrying the assay urchins to a nearby coral or benthic substrate and striking them repeatedly to break off their spines and crack their tests before consuming them. The behaviour was observed multiple times in different wrasse individuals. Also, sea urchin test size was a good predictor of the size of the fish that preyed on them. As naturalists spend more time observing fish in their natural environment, records of tool use in fish are increasing. Often these observations are incidental, yet documenting them carefully is critical, so we can ask larger questions about the evolution and development of animal intelligence. This study adds to observations of predation-associated tool use by fishes expanding reports of this behaviour taxonomically as well as geographically.

Deposits of seabird guano on marine shores have drawn the attention of companies and naturalists for centuries. Among notable effects, allochthonous energy/matter inputs by seabirds are responsible for shifts in ecosystem functioning next to colonies. Here, we used stable isotopes of nitrogen-15 (ratios of ¹⁵N:¹⁴N, expressed as δ¹⁵N) to trace guano incorporation in the intertidal reef community (fish and crab). The study areas were the Saint Peter and Saint Paul Archipelago (SPSPA), a remote and very small group of islets in the equatorial Atlantic Ocean, and two reference Atlantic islands where intertidal environments are not subject to the influence of guano. SPSPA intertidal reef fauna presented 3–7‰ higher δ¹⁵N values in comparison with local seabirds and with the intertidal reef fauna of reference islands. The intertidal food web of SPSPA appears supplemented by guano subsidies with carnivores, omnivores and herbivores ¹⁵N-enriched in relation to a local seabird. While no difference in intertidal biota δ¹⁵N values was detected between references sites, ¹⁵N-enrichement observed for SPSPA intertidal reef fauna is supported by guano subsidies. With emerged area < 0.02 km², SPSPA is one of the world’s smallest archipelagos and only its main islet (Belmonte Island) has a few tidepools apt to be inhabited by fish. As guano readily drains into tidepools and reef crevices adjacent to the seabird colony, allochthonous nutrients become available and support habitat-restricted species in this small and isolated location.

As the major form of coral reef regime shift, stony coral to macroalgal transitions have received considerable attention. In the Caribbean, however, regime shifts in which scleractinian corals are replaced by octocoral assemblages hold potential for maintaining reef associated communities. Accordingly, forecasting the resilience of octocoral assemblages to future disturbance regimes is necessary to understand these assemblages' capacity to maintain reef biodiversity. We parameterised integral projection models quantifying the survival, growth, and recruitment of the octocorals, Antillogorgia americana, Gorgonia ventalina, and Eunicea flexuosa, in St John, US Virgin Islands, before, during, and after severe hurricane disturbance. Using these models, we forecast the density of populations of each species under varying future hurricane regimes. We demonstrate that although hurricanes reduce population growth, A. americana, G. ventalina, and E. flexuosa each display a capacity for quick recovery following storm disturbance. Despite this recovery potential, we illustrate how the population dynamics of each species correspond with a longer-term decline in their population densities. Despite their resilience to periodic physical disturbance events, ongoing global change jeopardises the future viability of octocoral assemblages.

Rapid recovery of coral cover following acute disturbance has been documented on many reefs. Yet measuring coverage alone can mask shifts in community and demographic structure. Here, we quantify long-term changes in population size structure for three common genera (Acropora, Pocillopora, and Stylophora) at an eastern outer reef in Palau, Micronesia, following catastrophic loss of corals due to typhoon Bopha in 2012, based on size measurements from 3648 coral colonies. Mean colony size returned to pre-disturbance levels within 4 and 6 years for Stylophora and Pocillopora, respectively. By 2020, Pocillopora colony density far exceeded pre-disturbance levels, with rapid successful recruitment following typhoon Bopha. Despite recovery of Acropora colony density by 2020, populations remained dominated by smaller colonies. We demonstrate that full demographic recovery can occur more rapidly for pocilloporids (within 6 years) compared to Acropora which had not fully recovered by 8 years post-disturbance, possibly due to fewer annual recruitment events and larger maximum colony sizes. Our results highlight the value of demographic metrics as early indicators of recovery.

Abstract

Coral reefs are spatially variable ecosystems that form biogenic structures ranging in size from 10 to 1000s of meters. Their changes in response to anthropogenic stress are occurring across increasingly broad scales, yet our ability to detect, understand and respond to these changes at relevant scales is limited. Traditional in-water observation-based coral reef ecology and remote sensing-based methods both offer valuable insights into benthic change, but their relative scalability and use to-date must be understood to inform optimal future research approaches. We conducted a systematic literature review comparing the approaches used to quantify benthic habitat, through traditional in-water ecological studies and remote sensing studies, with respect to: (a) their geographic distribution, (b) reef zone selection, and c) their focal questions. Among the 199 studies reviewed, traditional ecological studies primarily concentrated on community composition (89%), using high-detail direct measurements, especially from the reef slope (80%). By contrast, remote sensing studies provided spatially explicit datasets at coarser spatial and thematic resolutions, with a predominant focus on benthic mapping (72%) across entire reef systems. Only 3% of studies integrated both approaches, combining comprehensive in-situ observations with broadscale remote sensing. As anthropogenic stressors continue to increase in scale, bridging these scientific disciplines offers a promising way to upscale observations to entire reef-scape scales. We identify steps to harness the strengths of both fields and integrate multiple tools at various levels of resolution and scale. Such bridging approaches offer a way forward in understanding and managing coral reef functioning in the Anthropocene.