Coral reef functioning in a highly variable environment : Effects of upwelling on Pacific coral reefs of Costa Rica

With increasing local and global stressors on coral reef ecosystems, the future stability of environmental conditions for coral reefs is in question. The capacity of reef organisms and ecosystems to adapt to such variable environments in terms of functions and services is a current topic in coral reef research, yet related knowledge, especially on the ecosystem level, is scarce. Marginal reefs that thrive in highly fluctuating or limiting environments, such as upwelling systems, provide natural laboratories to study the acclimatization and adaptation potential of reef organisms. This thesis aimed to contribute to the understanding of coral reef functioning in variable environments by investigating the impact of the Papagayo upwelling at the northern Pacific coast of Costa Rica. A series of interconnected studies was conducted in upwelling exposed reefs at weekly intervals over an entire observation year (April 2013 - April 2014). These studies monitored (i) a range of inorganic and organic water parameters, (ii) in situ primary production rates, (iii) benthic and herbivore community composition, and (iv) responses of algal and invertebrate settlement to simulated overfishing. Upwelling events between February and April 2014 decreased water temperatures by 7 - 9 °C for several hours or days, while inorganic nutrient concentrations increased 3 - 16-fold. Sequentially, organic matter concentrations in the water column above the reef doubled and remained elevated for 2 - 3 months (Chapter 2). Surprisingly, the strong seasonality in environmental conditions did not significantly influence benthic community productivity or composition in the studied reef. Upwelling-impacted water parameters negated each other in their effects on primary production of reef organisms. Corals were the only primary producers that benefitted from upwelling conditions, while production rates of all investigated algal taxa decreased (Chapter 3). Instead of following a seasonal cycle, benthic cover of the scleractinian corals Pocillopora spp. increased continuously and at an exceptionally high rate over the monitoring year (from 20 % to 50 % relative cover), while turf algal cover dropped significantly (from 60 % to 20 %). This shift in community composition was supported by high abundances of the herbivorous sea urchin Diadema mexicanum, which controlled turf algal cover in the reef community (Chapter 4). Fish exclusion significantly altered benthic communities on settlement tiles from short turf algae and crustose coralline algae dominance towards long turf algae, fleshy macroalgae and ascidians (Chapter 5). The results of this thesis indicate that the investigated benthic reef community is physiologically acclimatized to seasonal changes in environmental conditions, and that the local herbivore community effectively controls algae growth in the studied reef. However, high abundances of sea urchins potentially threaten the reef structure through bioerosion, and overexploitation of herbivorous reef fish may result in benthic community shifts. Additionally, repeated disturbances such as coral diseases (Chapter 6), El Niño events and harmful algal blooms likely prevent the coral community from increasing in diversity or developing a resistant reef structure. Upwelling-influenced reefs in the Gulf of Papagayo provide an example of how reefs may look like in the future, when anthropogenic chronic stressors will select for a minority of resilient coral species to dominate reef ecosystems. The results of this thesis suggest that those future reefs may still be highly productive and have a high resilience towards prevailing stressors in their ecosystem. Despite this, the reefs will be vulnerable to the intervention of acute stressors such as disease outbreaks or El Niño events due to low genetic diversity and functional redundancy in the coral populations

Rapid bioerosion in a tropical upwelling coral reef

Coral reefs persist in an accretion-erosion balance, which is critical for understanding the natural variability of sediment production, reef accretion, and their effects on the carbonate budget. Bioerosion (i.e. biodegradation of substrate) and encrustation (i.e. calcified overgrowth on substrate) influence the carbonate budget and the ecological functions of coral reefs, by substrate formation/consolidation/erosion, food availability and nutrient cycling. This study investigates settlement succession and carbonate budget change by bioeroding and encrusting calcifying organisms on experimentally deployed coral substrates (skeletal fragments of Stylophora pistillata branches). The substrates were deployed in a marginal coral reef located in the Gulf of Papagayo (Costa Rica, Eastern Tropical Pacific) for four months during the northern winter upwelling period (December 2013 to March 2014), and consecutively sampled after each month. Due to the upwelling environmental conditions within the Eastern Tropical Pacific, this region serves as a natural laboratory to study ecological processes such as bioerosion, which may reflect climate change scenarios. Time-series analyses showed a rapid settlement of bioeroders, particularly of lithophagine bivalves of the genus Lithophaga/ Leiosolenus (Dillwyn, 1817), within the first two months of exposure. The observed enhanced calcium carbonate loss of coral substrate (>30%) may influence seawater carbon chemistry. This is evident by measurements of an elevated seawater pH (>8.2) and aragonite saturation state (Ωarag >3) at Matapalo Reef during the upwelling period, when compared to a previous upwelling event observed at a nearby site in distance to a coral reef (Marina Papagayo). Due to the resulting local carbonate buffer effect of the seawater, an influx of atmospheric CO2 into reef waters was observed. Substrates showed no secondary cements in thin-section analyses, despite constant seawater carbonate oversaturation (Ωarag >2.8) during the field experiment. Micro Computerized Tomography (μCT) scans and microcast-embeddings of the substrates revealed that the carbonate loss was primarily due to internal macrobioerosion and an increase in microbioerosion. This study emphasizes the interconnected effects of upwelling and carbonate bioerosion on the reef carbonate budget and the ecological turnovers of carbonate producers in tropical coral reefs under environmental change.Sistema Nacional de Áreas de Conservación/[028-2013-SINAC]/SINAC/Costa RicaSistema Nacional de Áreas de Conservación/[72-2013-SINAC]/SINAC/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Funktionsweise von Korallenriffen in variablen Lebensräumen : Einfluss von Auftrieb auf Korallenriffe an der Pazifikküste von Costa Rica

With increasing local and global stressors on coral reef ecosystems, the future stability of environmental conditions for coral reefs is in question. The capacity of reef organisms and ecosystems to adapt to such variable environments in terms of functions and services is a current topic in coral reef research, yet related knowledge, especially on the ecosystem level, is scarce. Marginal reefs that thrive in highly fluctuating or limiting environments, such as upwelling systems, provide natural laboratories to study the acclimatization and adaptation potential of reef organisms. This thesis aimed to contribute to the understanding of coral reef functioning in variable environments by investigating the impact of the Papagayo upwelling at the northern Pacific coast of Costa Rica. A series of interconnected studies was conducted in upwelling exposed reefs at weekly intervals over an entire observation year (April 2013 - April 2014). These studies monitored (i) a range of inorganic and organic water parameters, (ii) in situ primary production rates, (iii) benthic and herbivore community composition, and (iv) responses of algal and invertebrate settlement to simulated overfishing. Upwelling events between February and April 2014 decreased water temperatures by 7 - 9 °C for several hours or days, while inorganic nutrient concentrations increased 3 - 16-fold. Sequentially, organic matter concentrations in the water column above the reef doubled and remained elevated for 2 - 3 months (Chapter 2). Surprisingly, the strong seasonality in environmental conditions did not significantly influence benthic community productivity or composition in the studied reef. Upwelling-impacted water parameters negated each other in their effects on primary production of reef organisms. Corals were the only primary producers that benefitted from upwelling conditions, while production rates of all investigated algal taxa decreased (Chapter 3). Instead of following a seasonal cycle, benthic cover of the scleractinian corals Pocillopora spp. increased continuously and at an exceptionally high rate over the monitoring year (from 20 % to 50 % relative cover), while turf algal cover dropped significantly (from 60 % to 20 %). This shift in community composition was supported by high abundances of the herbivorous sea urchin Diadema mexicanum, which controlled turf algal cover in the reef community (Chapter 4). Fish exclusion significantly altered benthic communities on settlement tiles from short turf algae and crustose coralline algae dominance towards long turf algae, fleshy macroalgae and ascidians (Chapter 5). The results of this thesis indicate that the investigated benthic reef community is physiologically acclimatized to seasonal changes in environmental conditions, and that the local herbivore community effectively controls algae growth in the studied reef. However, high abundances of sea urchins potentially threaten the reef structure through bioerosion, and overexploitation of herbivorous reef fish may result in benthic community shifts. Additionally, repeated disturbances such as coral diseases (Chapter 6), El Niño events and harmful algal blooms likely prevent the coral community from increasing in diversity or developing a resistant reef structure. Upwelling-influenced reefs in the Gulf of Papagayo provide an example of how reefs may look like in the future, when anthropogenic chronic stressors will select for a minority of resilient coral species to dominate reef ecosystems. The results of this thesis suggest that those future reefs may still be highly productive and have a high resilience towards prevailing stressors in their ecosystem. Despite this, the reefs will be vulnerable to the intervention of acute stressors such as disease outbreaks or El Niño events due to low genetic diversity and functional redundancy in the coral populations

Simulated overfishing and natural eutrophication promote the relative success of a non-indigenous ascidian in coral reefs at the Pacific coast of Costa Rica

Colonial ascidians of the genus Didemnum are common fouling organisms and are typically associated with degraded ecosystems and anthropogenic structures installed in the sea. In this study, however, the non-indigenous ascidian Didemnum cf. perlucidum Monniot F., 1983 was discovered in coral reef environments on the Pacific coast of Costa Rica. Its role in the succession of a benthic community and the impact on biogeochemical features (i.e. reef cementation) was assessed by deploying terracotta settlement tiles on the reef for 24 weeks. Predator exclusion in experimental plots and naturally elevated nutrient concentrations during seasonal coastal upwelling gave insights on how settlers of D. cf. perlucidum succeed under projected environmental change. Exclusion of larger predators and grazers caused an increase of D. cf. perlucidum coverage on tiles from 7 to > 80%. Due to its rapid proliferation, D. cf. perlucidum grew over calcifying reef organisms, such as barnacles, polychaetes, and crustose algae, and significantly decreased the accumulation of inorganic carbon on the settlement tiles by one order of magnitude (4.6 to 0.4 mg C cm- ²). The combination of reduced predation and eutrophication revealed negative synergistic effects on the accumulation of inorganic carbon. The opportunistic reaction of D. cf. perlucidum to environmental changes was further evident by 2-fold increased growth rates that were positively correlated (r² = 0.89) to seawater particulate organic matter (POM) concentration during coastal upwelling. These results suggest that D. cf. perlucidum is a strong spatial competitor in Eastern Tropical Pacific coral reefs that face changing environmental conditions, e.g. overfishing and eutrophication. The effects of this species on disturbed benthic communities, but also its potential role as a habitat modifier, is likely significant. Thus, a continuous monitoring of D. cf. perlucidum is recommended to better understand their effects on post-disturbance dynamics in coral reef ecosystems.UCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR)UCR::Vicerrectoría de Docencia::Ciencias Básicas::Facultad de Ciencias::Escuela de Biologí

Effects of simulated overfishing on the succession of benthic algae and invertebrates in an upwelling-influenced coral reef of Pacific Costa Rica

Overfishing and nutrient enrichment are among the major local stressors to coral reefs worldwide, as they can alter the benthic reef community by promoting fast growing algae and bioeroders. The Northern coast of Pacific Costa Rica is strongly influenced by seasonal upwelling events that naturally increase nutrient concentrations between December and March. This study therefore investigated the combined effects of simulated overfishing and naturally increased nutrients on benthic community composition and succession on settlement tiles over a period of 24 weeks (October 2013 until March 2014) using exclusion cages deployed in a coral reef in the Gulf of Papagayo. Tile cover of functional groups and development of organic C and N on light-exposed and –shaded tile sites were assessed. Results revealed that the exclusion of fish significantly increased the development of organic C and N and decreased the C/N ratio on light-exposed tiles. Large filamentous algae (> 2 mm), fleshy macroalgae and the colonial ascidian Didemnum sp. (Savigny 1816) (up to 80% tile coverage) were dominant on both tile sites. A significant peak of filamentous algae growth and associated organic matter C/N ratio occurred on light-exposed tiles throughout all treatments in February when nutrient concentrations were elevated. These results suggest that both herbivore exclusion and natural eutrophication have a strong influence on the benthic reef community composition and its early succession patterns. The presence of Didemnum sp. and turf algae could represent good early warning bioindicators for local overfishing and eutrophication and may therefore be included in management and monitoring strategies.German Leibniz Association/[]/WGL/AlemaniaGerman Academic Exchange Service/[]/DAAD/AlemaniaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Upwelling Increases Net Primary Production of Corals and Reef-Wide Gross Primary Production Along the Pacific Coast of Costa Rica

https://www.frontiersin.org/articles/10.3389/fmars.2015.00113/fullPhotosynthetic production is a key ecosystem service provided by tropical coral reefs, but knowledge about the contribution of corals and other reef-associated organisms and the controlling environmental factors is scarce. Locations with occurrence of upwelling events can serve as in-situ laboratories to investigate the impact of environmental variability on production rates of reef-associated organisms. This study investigated individual and reef-wide net (Pn) and gross primary production (Pg) for the dominant autotrophic benthic organisms (hard corals Pocillopora spp., crustose coralline algae (CCA), turf algae, and the macroalga Caulerpa sertularioides) associated with a coral reef along the Pacific coast of Costa Rica. Oxygen fluxes by these organisms were measured at a weekly to monthly resolution over 1 year (May 2013–April 2014) via in-situ chamber incubations. The influence of simultaneously measured environmental parameters (temperature, light, inorganic nutrient concentrations, dissolved and particulate organic matter concentrations) on Pn of the different taxa were tested via linear model fitting. Turf algae showed highest individual Pn and Pg rates per organism surface area (35 and 49 mmol O m−2 h−1), followed by Pocillopora spp. (16 and 25 mmol O m−22 2 h−1), CCA (9 and 15 mmol O m−22 h −1), and C. sertularioides (8 and 11 mmol O2 m−2 h −1). Under upwelling conditions (February—April 2014), Pn rates of all algal taxa remained relatively uniform despite high nutrient availability, Pn of corals increased by 70%. On an ecosystem level, corals on average contributed 60% of total Pn and Pg per reef area (73 and 98 mmol O2 m−2 h −1 , respectively), due to high benthic coverage, followed by turf algae (25%). Under upwelling conditions, reef-wide Pg increased by >40%, indicating acclimatization of local reef communities to upwelling conditions.Universidad de Costa Rica/[]/UCR/Costa RicaUCR::Vicerrectoría de Investigación::Unidades de Investigación::Ciencias Básicas::Centro de Investigación en Ciencias del Mar y Limnología (CIMAR

Carbonate chemistry in the Papagayo Upwelling System, Pacific coast of Costa Rica (2012-2013)

In situ measurements were undertaken during two non-upwelling periods (15 days in June 2012 and 7 days in May-June 2013) at a water depth of 1.5 m. pH, pCO2 and seawater temperature were measured with two Submersible Autonomous Moored Instruments (SAMI-pH and SAMI-CO2, deployed at the pier of Marina Papagayo (10.64154,-85.65571). Discrete water samples were used to validate the sensors, and salinity values were obtained from discrete water samples and used for correction of pH values. Wind speed data was obtained from a station of the Instituto Metereológico Nacional (National Metereological Institute of Costa Rica) located at the nearby Liberia airport. Tidal data was provided by Módulo de Información Oceanográfica of the University of Costa Rica

Changes in environmental parameters at Matapalo in a weekly resolution over 12 months.

<p>(a) Seawater temperature (weekly data points measured with MANTA loggers and daily averages calculated from continuous HOBO logger data) and salinity; (b) pH value (total scale) and concentration of dissolved oxygen; (c) concentrations of inorganic nutrients phosphate, ammonia and nitrate; (d) concentration of chlorophyll <i>a</i>; (e) concentrations of particulate organic nitrogen and carbon; (f) concentration of dissolved organic carbon. Error bars indicate ± SE. Shaded area = upwelling period.</p

Changes in meteorological parameters and seawater temperature in 5 m depth at Matapalo over 12 months.

<p>(a) Mean daily air temperature [°C] and daily precipitation [mm]. (b) Mean daily seawater temperature [°C] and mean daily wind speed [m s^-1]. Shaded area = upwelling period.</p