Flattening of Caribbean coral reefs: region-wide declines in architectural complexity

Coral reefs are rich in biodiversity, in large part because their highly complex architecture provides shelter and resources for a wide range of organisms. Recent rapid declines in hard coral cover have occurred across the Caribbean region, but the concomitant consequences for reef architecture have not been quantified on a large scale to date. We provide, to our knowledge, the first region-wide analysis of changes in reef architectural complexity, using nearly 500 surveys across 200 reefs, between 1969 and 2008. The architectural complexity of Caribbean reefs has declined nonlinearly with the near disappearance of the most complex reefs over the last 40 years. The flattening of Caribbean reefs was apparent by the early 1980s, followed by a period of stasis between 1985 and 1998 and then a resumption of the decline in complexity to the present. Rates of loss are similar on shallow (<6 m), mid-water (6–20 m) and deep (>20 m) reefs and are consistent across all five subregions. The temporal pattern of declining architecture coincides with key events in recent Caribbean ecological history: the loss of structurally complex Acropora corals, the mass mortality of the grazing urchin Diadema antillarum and the 1998 El Nino Southern Oscillation-induced worldwide coral bleaching event. The consistently low estimates of current architectural complexity suggest regional-scale degradation and homogenization of reef structure. The widespread loss of architectural complexity is likely to have serious consequences for reef biodiversity, ecosystem functioning and associated environmental services.     

Presence of cleaner wrasse increases the recruitment of damselfishes to coral reefs

Mutualisms affect the biodiversity, distribution and abundance of biological communities. However, ecological processes that drive mutualism-related shifts in population structure are often unclear and must be examined to elucidate how complex, multi-species mutualistic networks are formed and structured. In this study, we investigated how the presence of key marine mutualistic partners can drive the organisation of local communities on coral reefs. The cleaner wrasse, Labroides dimidiatus, removes ectoparasites and reduces stress hormones for multiple reef fish species, and their presence on coral reefs increases fish abundance and diversity. Such changes in population structure could be driven by increased recruitment of larval fish at settlement, or by post-settlement processes such as modified levels of migration or predation. We conducted a controlled field experiment to examine the effect of cleaners on recruitment processes of a common group of reef fishes, and showed that small patch reefs (61–285 m²) with cleaner wrasse had higher abundances of damselfish recruits than reefs from which cleaner wrasse had been removed over a 12-year period. However, the presence of cleaner wrasse did not affect species diversity of damselfish recruits. Our study provides evidence of the ecological processes that underpin changes in local population structure in the presence of a key mutualistic partner.     

Holocene reef building on eastern St. Croix, US Virgin Islands: Lang Bank revisited

New core and seismic data suggest that widespread reef building started on Lang Bank by 8,900 CalBP and was dominated by Acropora palmata for the next three millennia. Accretion rates averaged 5.81 m ky^?1, a rate that was sufficient for reefs to keep pace with rising sea level on the bank throughout their history. Seismic data show a deep platform interior that was flooded well in advance of reef building along the elevated rim. As a result, those reefs were buffered from sediment stress by their higher positions and active water flow to the west. A. palmata disappeared from the shallow margin by 6,350 yr ago, and reef building on Lang Bank largely ceased by 5,035 CalBP. The reasons for these dramatic events are unclear. Water depth over the reefs was generally shallower than when they started to build, and sea level was slowing dramatically. The new data described here show that reefs flourished on Lang Bank throughout the hiatus suggested by earlier studies (10–7 kyrs BP), and the ultimate demise of shelf-edge reefs is clearly not associated with either poor water quality or sudden sea-level rise. In addition, accretion rates from eastern St. Croix and throughout the Caribbean were well below the high values (≥10 m ky^?1) that have been widely assumed. These data collectively argue against models that require extreme environmental or oceanographic phenomena to drown reefs on Lang Bank where reef building was too fast to be outpaced by Holocene sea-level rise. This also bears on more generalized Caribbean models that depend on the presumed reef history on eastern St. Croix.     

Effects of grazing and damselfish territoriality on internal bioerosion of dead corals : indirect effects

An experiment was performed on Britomart Reef, Great Barrier Reef (central region), to determine the relationship between fish grazing, damselfish territoriality, and internal bioerosion of dead coral substratum. The damselfish Hemiglyphidodon plagiometopon Bleeker (Pomacentridae) was used for the study because it actively excludes herbivorous fish, particularly scarids and acanthurids, from its territories, creating undergrazed patches in the environment. Its territories simulated conditions of naturally reduced grazing. Freshly killed pieces of the plating coral Pachyseris speciosa Dana were placed under four experimental conditions: (1) within cages, excluding grazing fish; (2) within damselfish territories; (3) beneath shade tops to control for light; and (4) outside damselfish territories, fully exposed to grazers. Internal bioeroders were identified by pattern of substratum excavation and characterization of borings, and were quantified by digitizing x-ray radiographs of the substratum. Three major categories of borers were identified: Cliothosa hancocki Topsent, “other sponges” (of the Cliona viridis Schmidt species complex), and “worms” (including polychaetes and sipunculids). Variations in grazing pressure were found to significantly alter the taxonomic composition of the bioeroder community. Bioerosion by C. hancocki, a boring sponge with large exposed papillae, was found to increase significantly when grazing was reduced within damselfish territories. By contrast, other boring sponges of the C. viridis complex decreased in abundance; they were not affected by higher sedimentation in cages. The response of bioerosion by “worms” was less clear but increased slightly within damselfish territories. This was due primarily to a shift in taxonomic composition and dominance from polychaetes to sipunculids (particularly Cleosiphon aspergillum Quatrefages). The effects of grazing on the internal bioeroder community were often altered or obscured in the caged treatments; this was most likely due to caging artifacts such as increased sedimentation and decreased light. In general, bioerosion rates of the substratum P. speciosa were low in comparison to rates established or estimated for corals with less dense skeletons. Total internal bioerosion rates did not vary significantly with changes in grazing pressure. This study implies that, overall, reduced grazing pressure will lead to production of fine sediments derived from internal bioeroders. Under high grazing pressures, the addition of external bioerosion effected directly by grazers would also produce coarse sediment, resulting in an increase in total bioerosion rates (internal and external) and an increased contribution of both coarse and fine sediments to the reef environment.     

Impact of cyclones on hard coral and metapopulation structure,connectivity and genetic diversity of coral reef fish

Cyclones have one of the greatest effects on the biodiversity of coral reefs and the associated species. But it is unknown how stochastic alterations in habitat structure influence metapopulation structure, connectivity and genetic diversity. From 1993 to 2018, the reefs of the Capricorn Bunker Reef group in the southern part of the Great Barrier Reef were impacted by three tropical cyclones including cyclone Hamish (2009, category 5). This resulted in substantial loss of live habitat-forming coral and coral reef fish communities. Within 6–8 years after cyclones had devastated, live hard corals recovered by 50–60%. We show the relationship between hard coral cover and the abundance of the neon damselfish (Pomacentrus coelestis), the first fish colonizing destroyed reefs. We present the first long-term (2008–2015 years corresponding to 16–24 generations of P. coelestis) population genetic study to understand the impact of cyclones on the meta-population structure, connectivity and genetic diversity of the neon damselfish. After the cyclone, we observed the largest change in the genetic structure at reef populations compared to other years. Simultaneously, allelic richness of genetic microsatellite markers dropped indicating a great loss of genetic diversity, which increased again in subsequent years. Over years, metapopulation dynamics were characterized by high connectivity among fish populations associated with the Capricorn Bunker reefs (2200 km²); however, despite high exchange, genetic patchiness was observed with annual strong genetic divergence between populations among reefs. Some broad similarities in the genetic structure in 2015 could be explained by dispersal from a source reef and the related expansion of local populations. This study has shown that alternating cyclone-driven changes and subsequent recovery phases of coral habitat can greatly influence patterns of reef fish connectivity. The frequency of disturbances determines abundance of fish and genetic diversity within species.

     

Artificial reef design affects benthic secondary productivity and provision of functional habitat

1. Novel hard substratum, introduced through offshore developments, can provide habitat for marine species and thereby function as an artificial reef. To predict the ecological consequences of deploying offshore infrastructure, and sustainably manage the installation of new structures, interactions between artificial reefs and marine ecosystem functions and services must be understood. This requires quantitative data on the relationships between secondary productivity and artificial reef design, across all trophic levels. Benthic secondary productivity is, however, one of the least studied processes on artificial reefs.
2. In this study, we show that productivity rates of a common suspension feeder, Flustra foliacea (Linnaeus 1758), were 2.4 times higher on artificial reefs constructed from “complex” blocks than on reefs constructed from “simple” blocks, which had a smaller surface area.
3. Productivity rates were highest on external areas of reefs. Productivity rates decreased by 1.56%, per cm distance into the reef on complex reefs and 2.93% per cm into the reef on simple block reefs. The differences in productivity rates between reefs constructed from simple and complex blocks are assumed to reflect different current regimes and food supply between the external and internal reef areas, according to reef type.
4. Synthesis and applications. Our results show that artificial reef design can affect secondary productivity at low trophic levels. We demonstrate that the incorporation of voids into reef blocks can lead to a greater proportion of the structure serving as functional habitat for benthic species. By including such modifications into the design of artificial reefs, it may be possible to increase the overall productivity capacity of artificial structures.

     

Effect of habitat characteristics on the distribution and abundance of damselfish within a Red Sea reef

For coral reef fish with an obligate relationship to their habitat, like Pomacentrid damselfish, choosing a suitable home amongst the reef structure is key to survival. A surprisingly small number of studies have examined patterns in adult damselfish distributions compared to other ontogenetic phases. The aim of this study was to determine which reef and coral colony characteristics explained adult damselfish distribution patterns in a Red Sea reef. The characteristics investigated were reef type (continuous or patchy), coral species (seven species of Acropora), and coral morphology (coral size and branching density). The focal damselfish species were Dascyllus aruanus, D. marginatus, Chromis viridis, and C. flavaxilla. Occupancy (presence or absence of resident damselfish), group size and fish species richness were not significantly different between the seven Acropora species. However, within each coral species, damselfish were more likely to occupy larger coral colonies than smaller coral colonies. Occupancy rates were also higher in patchy reef habitats than in continuous sections of the reef, probably because average coral colony size was greater in patchy reef type. Fish group size increased significantly with coral colony volume and with larger branch spacing. Multi-species groups of fish commonly occurred and were increasingly likely with reduced branching density and increased coral size.     

The Acropora inheritance: A reinterpretation of the development of fringing reefs in Barbados,West Indies

The discovery of the widespread occurrence of the remains of the reef coral Acropora palmata within the fabric of the fringing reefs on the west coast of Barbados requires a new interpretation of their Holocene development. Radiocarbon dating of the A. palmata framework suggests that reef construction by this species began as early as 2,300 years B.P. A. palmata probably flourished in Barbados into the present century but has now declined. The present fringing reefs are characterized by a core and base of A. palmata upon which subsequent colonization took place, especially by Montastrea annularis, Porites porites and coralline algae.     

Interactions between herbivorous fish guilds and their influence on algal succession on a coastal coral reef

Herbivory is an important mechanism affecting algal succession, particularly on coral reefs where the relationship between algae and corals is largely controlled by herbivores. However, different functional groups of herbivores may have contrasting effects on succession, which may explain different trajectories of coral reef recovery after disturbance. Here, the effects of different herbivore groups (roving herbivores = foragers and territorial damselfish = farmers) were isolated by a multi-factorial experiment carried out on a coastal coral reef with high macroalgal cover, high farmer densities and relatively low forager abundance. The effects of foragers and farmers were distinguished by monitoring algal succession on settlement tiles placed inside and outside exclusion cages, with orthogonal treatments established inside and outside damselfish territories (with appropriate cage controls). Within 12 months, algal assemblages on ungrazed tiles inside exclusion cages proceeded rapidly from fine filamentous turfs, to corticated algae, to tough erect (e.g. Amphiroa spp.) and foliose (e.g. Peyssonnellidae) calcified algae. Farmers had a dramatic impact on succession, essentially arresting the development of the algal community at a point where it was dominated by palatable filamentous algae of the genus Polysiphonia. Fleshy macroalgae such as Sargassum spp. were excluded from farmer territories. In contrast, foragers did not suppress fleshy macroalgae, but rather, appeared to decelerate succession and promote a relatively diverse assemblage. In contrast to forager-dominated reefs, farmer territories did not appear to function solely as forager exclusion areas or promote algal diversity as a result of intermediate grazing pressure. The relatively strong effects of farmers observed here may represent a future scenario for coral reefs that are increasingly subject to overfishing of large grazing fishes.     

The effect of natural variation in substrate architecture on the survival of juvenile bicolor damselfish

Coral reefs offer settling fish larvae a spatial mosaic of microhabitats that differ not only in structural complexity but also in the abundance and diversity of predators. This paper provides evidence that interactions between predators and prey are causally linked to variation in relevant architectural characteristics of natural substrates. Juvenile bicolor damselfish, Stegastes partitus, experienced greater mortality on Montastrea annularis boulder coral than on piles of Porites porites coral rubble. This pattern was consistent on both back and fore reef habitats. Architectural differences, variable encounter rates with predators, and access to different food sources all contributed to higher mortality. Spatial and structural differences among refuges provided by the two substrates were most important in affecting survival. Porites rubble contained almost three times the number of crevices (39.9 vs. 14.3 crevices m^–2AM²), had a much smaller mean crevice size (15.9 vs. 48.5 cm²), and had a more complex internal structure than Montastrea coral. Survival of juvenile fish living on Montastrea coral was positively correlated with crevice density (r² = 0.41) whereas survival of fish living on Porites rubble was negatively correlated with crevice size (r² = 0.43). These patterns were evident on fore reef habitats only, whereas on back reef habitats no clear patterns emerged. The effect of these natural differences in architecture on mortality rates of juvenile S. partitus was experimentally tested in the field using a combination of natural and artificial substrates. As the number of large shelters was increased I found that the density of potential predators increased but the survival rates of juvenile bicolor damselfish declined. These results highlight the importance of structural architecture among common reef substrates in affecting predator-prey relationships and in determining the survivorship and small-scale distribution patterns of juvenile reef fish.     

Regional and local variability in recovery of shallow coral communities: Moorea,French Polynesia and central Great Barrier Reef

Coral communities at Moorea, French Polynesia, and on the Great Barrier Reef (GBR), Australia, were severely depleted by disturbances early in the 1980s. Corals were killed by the predatory starfish Acanthaster planci, by cyclones, and/or by depressed sea level. This study compares benthic community structure and coral population structures on three disturbed reefs (Vaipahu-Moorea; Rib and John Brewer Reefs-GBR) and one undisturbed reef (Davies Reef-GBR) in 1987–89. Moorea barrier reefs had been invaded by tall macrophytes Turbinaria ornata and Sargassum sp., whereas the damaged GBR reefs were colonised by a diverse mixture of short macrophytes, turfs and coralline algae. The disturbed areas had broadly similar patterns of living and dead standing coral, and similar progress in recolonisation, which suggests their structure may converge towards that of undisturbed Davies Reef. Corals occupying denuded areas at Vaipahu, Rib and John Brewer were small (median diameter 5 cm in each case) and sparse (means 4–8 m^-2) compared to longer established corals at Davies Reef (median diameter 9 cm; mean 18 m^-2). At Moorea, damselfish and sea urchins interacted with corals in ways not observed in the GBR reefs. Territories of the damselfish Stegastes nigricans covered much of Moorea's shallow reef top. They had significantly higher diversity and density of post-disturbance corals than areas outside of territories, suggesting that the damselfish exerts some influences on coral community dynamics. Sea urchins on Moorea (Diadema setosum Echinometra mathaei, Echinotrix calamaris) were causing widespread destruction of dead standing coral skeletons. Overall, it appears that the future direction and speed of change in the communities will be explicable more in terms of local than regional processes.     

Reduced Diversity and High Sponge Abundance on a Sedimented Indo-Pacific Reef System: Implications for Future Changes in Environmental Quality

Although coral reef health across the globe is declining as a result of anthropogenic impacts, relatively little is known of how environmental variability influences reef organisms other than corals and fish. Sponges are an important component of coral reef fauna that perform many important functional roles and changes in their abundance and diversity as a result of environmental change has the potential to affect overall reef ecosystem functioning. In this study, we examined patterns of sponge biodiversity and abundance across a range of environments to assess the potential key drivers of differences in benthic community structure. We found that sponge assemblages were significantly different across the study sites, but were dominated by one species Lamellodysidea herbacea (42% of all sponges patches recorded) and that the differential rate of sediment deposition was the most important variable driving differences in abundance patterns. Lamellodysidea herbacea abundance was positively associated with sedimentation rates, while total sponge abundance excluding Lamellodysidea herbacea was negatively associated with rates of sedimentation. Overall variation in sponge assemblage composition was correlated with a number of variables although each variable explained only a small amount of the overall variation. Although sponge abundance remained similar across environments, diversity was negatively affected by sedimentation, with the most sedimented sites being dominated by a single sponge species. Our study shows how some sponge species are able to tolerate high levels of sediment and that any transition of coral reefs to more sedimented states may result in a shift to a low diversity sponge dominated system, which is likely to have subsequent effects on ecosystem functioning.     

Assessment of Acropora palmata in the Mesoamerican Reef System

The once-dominant shallow reef-building coral Acropora palmata has suffered drastic geographical declines in the wider Caribbean from a disease epidemic that began in the late 1970s. At present there is a lack of quantitative data to determine whether this species is recovering over large spatial scales. Here, we use quantitative surveys conducted in 107 shallow-water reef sites between 2010 and 2012 to investigate the current distribution and abundance of A. palmata along the Mesoamerican Reef System (MRS). Using historical data we also explored how the distribution and abundance of this species has changed in the northern portion of the MRS between 1985 and 2010–2012. A. palmata was recorded in only a fifth of the surveyed reef sites in 2010–2012. In the majority of these reef sites the presence of A. palmata was patchy and rare. Only one site (Limones reef), in the northernmost portion of the MRS, presented considerably high A. palmata cover (mean: 34.7%, SD: 24.5%). At this site, the size-frequency distribution of A. palmata colonies was skewed towards small colony sizes; 84% of the colonies were healthy, however disease prevalence increased with colony size. A comparison with historical data showed that in the northern portion of the MRS, in 1985, A. palmata occurred in 74% of the 31 surveyed sites and had a mean cover of 7.7% (SD = 9.0), whereas in 2010–2012 this species was recorded in 48% of the sites with a mean cover of 2.9% (SD = 7.5). A. palmata populations along the MRS are failing to recover the distribution and abundance they had prior to the 1980s. Investigating the biological (e.g., population genetics) and environmental conditions (e.g., sources of stress) of the few standing reefs with relatively high A. palmata cover is crucial for the development of informed restoration models for this species.     

Effects of territorial damselfish on an algal-dominated coastal coral reef

Territorial damselfish are important herbivores on coral reefs because they can occupy a large proportion of the substratum and modify the benthic community to promote the cover of food algae. However, on coastal coral reefs damselfish occupy habitats that are often dominated by unpalatable macroalgae. The aim of this study was to examine whether damselfish can maintain distinctive algal assemblages on a coastal reef that is seasonally dominated by Sargassum (Magnetic Island, Great Barrier Reef). Here, three abundant species (Pomacentrus tripunctatus, P. wardi and Stegastes apicalis) occupied up to 60% of the reef substrata. All three species promoted the abundance of food algae in their territories. The magnitudes of the effects varied among reef zones, but patterns were relatively stable over time. Damselfish appear to readily co-exist with large unpalatable macroalgae as they can use it as a substratum for promoting the growth of palatable epiphytes. Damselfish territories represent patches of increased epiphyte load on macroalgae, decreased sediment cover, and enhanced cover of palatable algal turf.     

Systematic Analysis of White Pox Disease in Acropora palmata of the Florida Keys and Role of Serratia marcescens

White pox disease (WPD) affects the threatened elkhorn coral, Acropora palmata. Owing in part to the lack of a rapid and simple diagnostic test, there have been few systematic assessments of the prevalence of acroporid serratiosis (caused specifically by Serratia marcescens) versus general WPD signs. Six reefs in the Florida Keys were surveyed between 2011 and 2013 to determine the disease status of A. palmata and the prevalence of S. marcescens. WPD was noted at four of the six reefs, with WPD lesions found on 8 to 40% of the colonies surveyed. S. marcescens was detected in 26.9% (7/26) of the WPD lesions and in mucus from apparently healthy colonies both during and outside of disease events (9%; 18/201). S. marcescens was detected with greater frequency in A. palmata than in the overlying water column, regardless of disease status (P = 0.0177). S. marcescens could not be cultured from A. palmata but was isolated from healthy colonies of other coral species and was identified as pathogenic pulsed-field gel electrophoresis type PDR60. WPD lesions were frequently observed on the reef, but unlike in prior outbreaks, no whole-colony death was observed. Pathogenic S. marcescens was circulating on the reef but did not appear to be the primary pathogen in these recent WPD episodes, suggesting that other pathogens or stressors may contribute to signs of WPD. Results highlight the critical importance of diagnostics in coral disease investigations, especially given that field manifestation of disease may be similar, regardless of the etiological agent.     

Damselfish territories as a refuge for macroalgae on coral reefs

Herbivory is widely accepted as a key process determining the benthic community structure and resilience of coral reefs. Recent studies have mostly focused on the importance of roving herbivorous fishes in ecosystem processes. Here, we examine the role of territorial damselfish in shaping patterns of macroalgal distribution based on benthic surveys and macroalgal bioassays. The territory composition and effect of resident damselfish on the removal of Sargassum bioassays were quantified for six species of damselfish on Lizard Island, a mid-shelf reef in the northern Great Barrier Reef (GBR). The functional composition of algal communities within territories varied markedly among species. The territories of four species (Dischistodus perspicillatus, Dischistodus pseudochrysopoecilus, Plectroglyphidodon lacrymatus, and Stegastes nigricans) were characterized by algal turfs, while the territories of two species (Dischistodus prosopotaenia and Hemiglyphidodon plagiometopon) were characterized by foliose and leathery brown macroalgae. Sargassum, a generally rare alga on mid-shelf reefs, was a particularly common alga within D. prosopotaenia territories on the leeward side of the island but absent within their territories on the windward side of the island. D. prosopotaenia was the only species to retain the transplanted Sargassum, with only a minimal reduction in Sargassum biomass (1.1%) being recorded within their territories at both leeward and windward sites over a 24-h period. In contrast, reductions in Sargassum biomass were high in areas adjacent to D. prosopotaenia territories (83.8%), and within and adjacent to the territories of the five remaining damselfish species (76.2–92.5%). Overall, only one of the six damselfish species provided a refuge for leathery brown macroalgae and may facilitate the development of this macroalgae on mid-shelf reefs of the GBR.     

Occupation Dynamics and Impacts of Damselfish Territoriality on Recovering Populations of the Threatened Staghorn Coral,Acropora cervicornis

Large-scale coral reef restoration is needed to help recover structure and function of degraded coral reef ecosystems and mitigate continued coral declines. In situ coral propagation and reef restoration efforts have scaled up significantly in past decades, particularly for the threatened Caribbean staghorn coral, Acropora cervicornis, but little is known about the role that native competitors and predators, such as farming damselfishes, have on the success of restoration. Steep declines in A. cervicornis abundance may have concentrated the negative impacts of damselfish algal farming on a much lower number of coral prey/colonies, thus creating a significant threat to the persistence and recovery of depleted coral populations. This is the first study to document the prevalence of resident damselfishes and negative effects of algal lawns on A. cervicornis along the Florida Reef Tract (FRT). Impacts of damselfish lawns on A. cervicornis colonies were more prevalent (21.6% of colonies) than those of other sources of mortality (i.e., disease (1.6%), algal/sponge overgrowth (5.6%), and corallivore predation (7.9%)), and damselfish activities caused the highest levels of tissue mortality (34.6%) among all coral stressors evaluated. The probability of damselfish occupation increased as coral colony size and complexity increased and coral growth rates were significantly lower in colonies with damselfish lawns (15.4 vs. 29.6 cm per year). Reduced growth and mortality of existing A. cervicornis populations may have a significant effect on population dynamics by potentially reducing important genetic diversity and the reproductive potential of depleted populations. On a positive note, however, the presence of resident damselfishes decreased predation by other corallivores, such as Coralliophila and Hermodice, and may offset some negative impacts caused by algal farming. While most negative impacts of damselfishes identified in this study affected large individual colonies and <50% of the A. cervicornis population along the FRT, the remaining wild staghorn population, along with the rapidly increasing restored populations, continue to fulfill important functional roles on coral reefs by providing essential habitat and refuge to other reef organisms. Although the effects of damselfish predation are, and will continue to be, pervasive, successful restoration efforts and strategic coral transplantation designs may help overcome damselfish damage by rapidly increasing A. cervicornis cover and abundance while also providing important information to educate future conservation and management decisions.     

Millennial-scale change in the structure of a Caribbean reef ecosystem and the role of human and natural disturbance

Caribbean coral reefs have transformed into algal-dominated habitats over the past half-century, but the role of specific anthropogenic drivers is unresolved due to the lack of ecosystem-level data predating human disturbance. To better understand the extent and causes of long-term Caribbean reef declines, we produced a continuous 3000-yr record of the ecosystem state of three reefs in Bocas del Toro, Caribbean Panama. From fossils and sediments obtained from reef matrix cores, we tracked changes in reef accretion rates and the taxonomic and functional group composition of fish, coral, urchin, bivalve and benthic foraminifera. This dataset provided a comprehensive picture of reef community and environmental change. At all sites, reefs shifted from systems with greater relative abundance of herbivorous fish, epifaunal suspension feeding bivalves and Diadema urchins to systems with greater relative abundance of micropredator fish, infaunal bivalves and Echinometra urchins. These transitions were initiated a millennium ago at two less-degraded reefs fringing offshore islands and ~250 yr ago at a degraded patch reef near the continental coast. Ecosystem shifts were accompanied by a decline in reef accretion rates, and at the patch reef, a decline in water quality since the 18th century. Within all cores, synchronous increases in infaunal bivalves and declines in herbivorous fish regardless of water quality suggest a loss of hard substrate and increasingly hypoxic sediment conditions related to herbivore loss. While the early timing of ecosystem transitions at the fringing reefs implicates large-scale hydrological change, the more recent timing of change and loss of water quality at the patch reef implicates terrigenous runoff from land-clearing. Our whole-ecosystem reconstruction reveals that reef ecosystem deterioration appears to follow a predictable trajectory whether driven by natural or anthropogenic disturbances and that historical local human activities have quickly unraveled reefs at a scale similar to longer-term natural environmental change.     

Effects of substrata, resident conspecifics and damselfish on the settlement and recruitment of the stoplight parrotfish, Sparisoma viride

Recruitment plays an important role in the population dynamics of marine organisms and is often quantified as a surrogate for settlement. When quantified, recruitment includes settlement plus a period of time in the benthic habitat. Therefore, it is essential to determine whether post-settlement processes alter patterns established at settlement. I conducted a series of experiments on 2.0 m² patch reefs to examine the importance of pre- and post-settlement processes to the distribution and abundance of recruits of the stoplight parrotfish, Sparisoma viride, on the Tague Bay reef, St. Croix, USVI. Recruitment was higher to the coral Porites porites than to another common coral Montastrea annularis, but there was no evidence of microhabitat choice at settlement. This result, in conjunction with the examination of the size classes of recruits present on P. porites and M. annularis patch reefs in a separate experiment suggested that differences in recruitment were established after settlement. Stoplights settled in higher numbers to patch reefs that contained conspecific residents, and persistence was higher at higher recruit density. Although resident damselfish directed significant amounts of agonistic behavior towards newly stoplight recruits, damselfish presence had no effect on settlement. However, damselfish presence did reduce stoplight recruitment. These results demonstrate that both pre- and post-settlement processes influence the recruitment of stoplight parrotfish. More importantly, these results indicate that benthic processes can alter recruitment patterns from initial settlement patterns, and indicate that workers should be careful in using recruitment as a proxy for settlement.     

Wave-induced abiotic stress shapes phenotypic diversity in a coral reef fish across a geographical cline

While morphological variation across geographical clines has been well documented, it is often unclear whether such changes enhance individual performance to local environments. We examined whether the damselfish Acanthochromis polyacanthus display functional changes in swimming phenotype across a 40-km cline in wave-driven water motion on the Great Barrier Reef, Australia. A. polyacanthus populations displayed strong intraspecific variation in swimming morphology and performance that matched local levels of water motion: individuals on reefs subject to high water motion displayed higher aspect-ratio fins and faster swimming speeds than conspecifics on sheltered reefs. Remarkably, intraspecific variation within A. polyacanthus spanned over half the diversity seen among closely related damselfish species from the same region. We find that local selection driven by wave-induced abiotic stress is an overarching ecological mechanism shaping the inter- and intraspecific locomotor diversity of coral reef fishes.