Seventeen-year study reveals fluctuations in key ecological indicators on two reef crests in Cuba.

Reef crests in the Caribbean have lost approximately 80% of the foundational habitat-forming coral Acropora palmata (Lamarck, 1816), with declines registered as early as the 1950s mainly from anthropogenic causes. We studied two reef crests in the northwestern region of Cuba over 17 years (2005 to 2021) to evaluate temporal changes in coral cover, dominated by A. palmata, and their potential drivers. The density of A. palmata generally showed a negative trend at both reefs, with the lowest density recorded in 2021 at 0.2 ± 0.05 col. m-2 at Playa Baracoa and 1.0 ± 0.1 col. m-2 at Rincon de Guanabo. The mean size of the colonies in the two reefs also decreased over time. In Playa Baracoa, the mean diameter of A. palmata colonies decreased from 2012 at 67 ± 5.9 cm to 2013 at 34 ± 2.2 cm, whereas in Rincon de Guanabo, a change in diameter was evident from 2015 at 44.3 ± 2.3 to 2021 at 21.6 ± 0.9 cm. Adult colonies (10 cm-50 cm diameter) predominated in most years on both reefs. The populations of A. palmata on both reefs were healthy, with an average of 70% colonies in good condition during the study period. However, A. palmata cover decreased by almost half by 2021, to 8.6% in Playa Baracoa and 16.8% in Rincon de Guanabo. By contrast, macroalgal cover increased two-fold to 87.1% in Playa Baracoa and four-fold to 77.2% in Rincon de Guanabo. The density of the sea urchin Diadema antillarum was higher in Playa Baracoa than in Rincon de Guanabo. The highest densities were 2.8 ± 0.2 ind. m-2 in Playa Baracoa in 2005 and 0.1 ± 0.03 ind. m-2 in Rincon de Guanabo in 2008. Although our results show an overall decline of A. palmata (density and percent cover) and an increase in macroalgae, these two reef crests are in better condition than most reefs in the Caribbean in terms of the density and health of A. palmata populations, and the density of D. antillarum at Playa Baracoa. Our results are important in establishing a management plan to ensure the condition of these reef crests does not degrade further.

Intestinal microbes: an axis of functional diversity among large marine consumers.

Microbes are ubiquitous throughout the world's oceans, yet the manner and extent of their influence on the ecology and evolution of large, mobile fauna remains poorly understood. Here, we establish the intestinal microbiome as a hidden, and potentially important, 'functional trait' of tropical herbivorous fishes-a group of large consumers critical to coral reef resilience. Using field observations, we demonstrate that five common Caribbean fish species display marked differences in where they feed and what they feed on. However, in addition to space use and feeding behaviour-two commonly measured functional traits-we find that interspecific trait differences are even more pronounced when considering the herbivore intestinal microbiome. Microbiome composition was highly species specific. Phylogenetic comparison of the dominant microbiome members to all known microbial taxa suggest that microbiomes are comprised of putative environmental generalists, animal-associates and fish specialists (resident symbionts), the latter of which mapped onto host phylogeny. These putative symbionts are most similar to-among all known microbes-those that occupy the intestines of ecologically and evolutionarily related herbivorous fishes in more distant ocean basins. Our findings therefore suggest that the intestinal microbiome may be an important functional trait among these large-bodied consumers.

Sediment associated with algal turfs inhibits the settlement of two endangered coral species.

Populations of Acropora palmata and Orbicella faveolata, two important reef-building corals, have declined precipitously across the Caribbean region since at least the 1970s. Recruitment failure may be limiting population recovery, possibly due to lack of suitable settlement habitat. Here, we examine the effects of algal turfs and algal turfs + sediment, two widely abundant substrate types across the Florida Keys, on the settlement of these two ecologically-important species. We show that sediment significantly impedes coral settlement, reducing settlement 10- and 13-fold for A. palmata and O. faveolata, respectively, compared to turf algae alone. This result is corroborated by our field survey data that showed a strong, negative relationship between the abundance of turf + sediment and the abundance of juvenile corals. Turf algae alone did not reduce coral settlement. Our results suggest that sediment-laden turf algae are detrimental to settling corals, but that turf algae alone may be relatively benign.

Identity of coral reef herbivores drives variation in ecological processes over multiple spatial scales.

Overexploitation of key species can negatively impact ecosystem processes, so understanding the ecological roles of individual species is critical for improving ecosystem management. Here, we use coral reefs and the process of herbivory as a model to examine how species identity of consumers influence ecosystem processes to inform management of these consumers. Herbivorous fishes can facilitate the recruitment, growth, and recovery of corals by controlling the fast-growing algae that can outcompete corals for space. However, herbivorous fish guilds are species rich with important differences among species in diet, movement, and habitat preferences. Yet, we lack a general understanding of (1) how these species-specific differences in feeding and behavior scale up to reef-wide rates of ecosystem processes and (2) how species identity and diversity impact these processes. To address these knowledge gaps, we used field observations to derive key species- and size-specific foraging parameters for nine herbivorous parrotfish species on coral reefs in the Florida Keys, USA. We then combined these foraging parameters with fish survey data spanning multiple spatial scales to estimate the rates of three ecosystem processes: area of reef grazed, amount of macroalgae removed, and rate of bioerosion. We found that predicted rates of ecological processes varied dramatically among habitats and among reef zones within habitats, driven primarily by variation in abundance among species with different foraging behaviors. In some cases, assemblages with similar levels of total biomass had different rates of ecological processes, and in others, assemblages with different biomass had similar rates of ecological processes. Importantly, our models of herbivory using species-specific parameters differed from those using genus-level parameters by up to 300% in rates of ecological processes, highlighting the importance of herbivore identity in this system. Our results indicate that there may be little overlap in the roles species play, suggesting that some systems may be vulnerable to loss of ecological function with the reduction or loss of just a few species. This work provides a framework that can be applied across the region to predict how changes in management may affect the ecological impact of these important herbivores.

Interactive effects of herbivory and substrate orientation on algal community dynamics on a coral reef.

Herbivory is a significant driver of algal community dynamics on coral reefs. However, abiotic factors such as the complexity and orientation of the benthos often mediate the impact of herbivores on benthic communities. We experimentally evaluated the independent and interactive effects of substrate orientation and herbivorous fishes on algal community dynamics on a coral reef in the Florida Keys, USA. We created horizontal and vertical substrates, mimicking the trend in the reduction of vertical surfaces of coral reefs, to assess how algal communities developed either with herbivory (open areas) or without herbivory (herbivore exclosures). We found that substrate orientation was the dominant influence on macroalgal community composition. Herbivores had little impact on community development of vertical substrates as crustose algae dominated these substrates regardless of being in exclosures or open areas. In contrast, herbivores strongly impacted communities on horizontal substrates, with upright macroalgae (e.g., Dictyota spp., articulated coralline algae) dominating herbivore exclosures, while filamentous turf algae and sediment dominated open areas. Outside of exclosures, differences between vertical and horizontal substrates exposed to herbivores persisted despite similar intensity of herbivory. Our results suggest that the orientation of the reef benthos has an important impact on benthic communities. On vertical surfaces, abiotic factors may be more important for structuring algal communities while herbivory may be more important for controlling algal dynamics in flatter areas. Thus, the decline in structural complexity of Caribbean coral reefs and the flattening of reef substrates may fundamentally alter the impact that herbivores have on benthic community dynamics.

Seasonal recruitment and survival strategies of Palisada cervicornis comb. nov. (Ceramiales, Rhodophyta) in coral reefs.

As marine tropical ecosystems deteriorate and lose biodiversity, their communities are shifting to being dominated by a few species, altering ecosystem's functioning and services. Macroalgae are becoming dominant on coral reefs, and are frequently observed outcompeting corals. Turf algal assemblages are the base of energy flow in these systems and one of the most abundant types of macroalgae on coral reefs, but little is known about their biology and diversity. Through molecular and morphological analyses, we identified the turf-forming species Laurencia cervicornis, and by studying seasonal recruitment and the impact of herbivorous fishes on its abundance, we describe its survival strategy. The molecular analyses used a total of 45 rbcL gene sequences including eight current genera within the Laurencia complex and two new sequences of L. cervicornis and strongly support the new combination of Palisada cervicornis comb. nov. In addition, a detailed morphological characterization including the description of reproductive structures is provided. Palisada cervicornis was seen recruiting in all seasons but was typically in low abundance. Specimens grown on tiles in fish exclosure cages were devoured in less than 4 h when offered to fishes. Even though many species of the Laurencia complex have chemicals that deter herbivory, species within the genus Palisada lack feeding deterrents and thus are highly palatable. We suggest that P. cervicornis is a palatable species that seems to survive in the community by obtaining a size-refuge from herbivory within turf communities.

Seasonal regulation of herbivory and nutrient effects on macroalgal recruitment and succession in a Florida coral reef.

Herbivory and nutrient enrichment are drivers of benthic dynamics of coral reef macroalgae; however, their impact may vary seasonally. In this study we evaluated the effects of herbivore pressure, nutrient availability and potential propagule supply on seasonal recruitment and succession of macroalgal communities on a Florida coral reef. Recruitment tiles, replaced every three months, and succession tiles, kept in the field for nine months, were established in an ongoing factorial nutrient enrichment-herbivore exclusion experiment. The ongoing experiment had already created very different algal communities across the different herbivory and nutrient treatments. We tracked algal recruitment, species richness, and species abundance through time. Our results show seasonal variation in the effect of herbivory and nutrient availability on recruitment of coral reef macroalgae. In the spring, when there was higher macroalgal species richness and abundance of recruits, herbivory appeared to have more control on macroalgal community structure than did nutrients. In contrast, there was no effect of either herbivory or nutrient enrichment on macroalgal communities on recruitment tiles in cooler seasons. The abundance of recruits on tiles was positively correlated with the abundance of algal in the ongoing, established experiment, suggesting that propagule abundance is likely a strong influence on algal recruitment and early succession. Results of the present study suggest that abundant herbivorous fishes control recruitment and succession of macroalgae, particularly in the warm season when macroalgal growth is higher. However, herbivory appears less impactful on algal recruitment and community dynamics in cooler seasons. Ultimately, our data suggest that the timing of coral mortality (e.g., summer vs. winter mortality) and freeing of benthic space may strongly influence the dynamics of algae that colonize open space.

[The feeding activity of herbivorous fishes and their impact on coral reefs with different levels of anthropogenic degradation]. / Actividad alimentaria de los peces herbívoros y su impacto en arrecifes con diferente nivel de degradación antrópica.

The feeding activity of three herbivorous fishes (Sparisoma viride, Scarus iserti and Acanthurus coeruleus) and its impact on two coral reefs were studied during the dry (February) and rainy (August) seasons of 2006 in Cuba. One of the reef stations is at the "Acuario" dive point in the Guanahacabibes National Park, and is relatively pristine. The second one is located at the north coast of Havana City facing the Instituto de Oceanología (IdO) and is subject to pollution and fishing pressures. Herbivore fish composition was analized, and foraging intensity was measured for all Acanthurid and Scarid species, by counting fish bites in 1 m2 during five minute intervals (25 replicates). Concurrently, species foraging intensity was measured for juvenile, intermediate, and adult phases, counting fish bites during 10 minutes intervals (10 replicates). Algal consumption rate was estimated using a coefficent of consumed biomass per bite, for each size class. The algal cover was sampled at 20 m linear transects with four replicates at each site. Food items were assessed sampling algae at the observed bitten substrates. Compared to Acuario, herbivores in IdO showed lower species richness and higher density of small size fishes, but large-sized parrotfish was almost absent due to intense fishing. The highest bite rate was observed for the smallest fish size, but net consumption rate was three times greater for medium and great size fishes, which were more abundant in the protected area. Algal cover was lower in Acuario, while in IdO it was very high, and coral cover was very low. In both locations epiphytic algae were the preferred food. These results support generalizations referring to the importance of great size herbivores fishes in controlling excesive algal proliferation on coral reefs.

Actividad alimentaria de los peces herbívoros y su impacto en arrecifes con diferente nivel de degradación antrópica

The feeding activity of herbivorous fishes and their impact on coral reefs with different levels of anthropogenic degradation. The feeding activity of three herbivorous fishes (Sparisoma viride, Scarus iserti and Acanthurus coeruleus) and its impact on two coral reefs were studied during the dry (February) and rainy (August) seasons of 2006 in Cuba. One of the reef stations is at the "Acuario" dive point in the Guanahacabibes National Park, and is relatively pristine. The second one is located at the north coast of Havana City facing the Instituto de oceanología (IdO) and is subject to pollution and fishing pressures. Herbivore fish composition was analized, and foraging intensity was measured for all Acanthurid and Scarid species, by counting fish bites in 1 m²during five minute intervals (25 replicates). Concurrently, species foraging intensity was measured for juvenile, intermediate, and adult phases, counting fish bites during 10 minutes intervals (10 replicates). Algal consumption rate was estimated using a coefficent of consumed biomass per bite, for each size class. The algal cover was sampled at 20 m linear transects with four replicates at each site. Food items were assessed sampling algae at the observed bitten substrates. Compared to Acuario, herbivores in IdO showed lower species richness and higher density of small size fishes, but large-sized parrotfish was almost absent due to intense fishing. The highest bite rate was observed for the smallest fish size, but net consumption rate was three times greater for medium and great size fishes, which were more abundant in the protected area. Algal cover was lower in Acuario, while in IdO it was very high, and coral cover was very low. In both locations epiphytic algae were the preferred food. These results support generalizations referring to the importance of great size herbivores fishes in controlling excesive algal proliferation on coral reefs. Rev. Biol. Trop. 57 (3): 687-697. Epub 2009 September 30.

Estudiamos la actividad alimentaria de tres peces herbívoros (Sparisoma viride, Scarus iserti y Acanthurus coeruleus) y su impacto, en dos arrecifes de coral de Cuba, durante la época seca (febrero) y la lluviosa (agosto) del 2006. una de las estaciones en los arrecifes está en el lugar de buceo "Acuario" en el parque nacional Guanahacabibes, y es relativamente prístina. La segunda está en la costa norte de la Habana al frente del Instituto de oceanología (IdO) y es objeto de presiones de contaminación y pesca. La composición de los peces herbívoros fue analizada, y la intensidad de búsqueda de alimento ("forrajeo") medida para todas las especies de acantúridos y escáridos, contando los mordiscos de peces en 1 m2 durante intervalos de cinco minutos (25 repeticiones). La intensidad de forrajeo fue medida para las fases joven, intermedia, y adulta, contando los mordiscos de peces durante intervalos de 10 minutos (10 repeticiones). La tasa de consumo de algas se estimó usando un coeficiente de biomasa consumida por mordisco, para cada clase de tamaño. La cobertura de algas fue muestreada en transectos de 20 m en línea con cuatro repeticiones en cada sitio. Las piezas de comida fueron evaluadas por medio de muestreo de algas en los sustratos observados con mordiscos. En comparación con Acuario, los herbívoros en IdO mostraron riqueza de especies más baja y mayor densidad de peces pequeños, pero los peces loro de gran tamaño estuvieron casi ausentes debido a la pesca intensiva. La tasa de mordisqueo más alta se observó para los peces de tamaño más pequeño, pero la tasa neta de consumo fue tres veces mayor para los peces de mediano y gran tamaño, los cuales fueron más abundantes en el área protegida. La cobertura de algas fue más baja en Acuario, mientras que en IdO fue muy alta, y la cobertura de coral fue muy baja. En ambas localidades las algas epífitas fueron el alimento preferido. Estos resultados apoyan las generalizaciones con respecto a la importancia de los peces de gran tamaño para controlar la proliferación excesiva de algas en arrecifes de coral.