Ana Vila-Concejo

Long-term empirical evidence of ocean warming leading to tropicalization of fish communities, increased herbivory, and loss of kelp

Significance Most studies of the impact of global warming focus on the direct physiological impacts of climate change. However, global warming is shifting the distribution of many species and leading to novel interactions between previously separated species that have the potential to transform entire ecological communities. This study shows that an increase in the proportion of warmwater species (“tropicalization”) as oceans warm is increasing fish herbivory in kelp forests, contributing to their decline and subsequent persistence in alternate “kelp-free” states. These tropical and subtropical herbivores are increasingly impacting temperate algal communities worldwide, posing a significant threat to the long-term stability of these iconic ecosystems and the valuable services they provide. Some of the most profound effects of climate change on ecological communities are due to alterations in species interactions rather than direct physiological effects of changing environmental conditions. Empirical evidence of historical changes in species interactions within climate-impacted communities is, however, rare and difficult to obtain. Here, we demonstrate the recent disappearance of key habitat-forming kelp forests from a warming tropical–temperate transition zone in eastern Australia. Using a 10-y video dataset encompassing a 0.6 °C warming period, we show how herbivory increased as kelp gradually declined and then disappeared. Concurrently, fish communities from sites where kelp was originally abundant but subsequently disappeared became increasingly dominated by tropical herbivores. Feeding assays identified two key tropical/subtropical herbivores that consumed transplanted kelp within hours at these sites. There was also a distinct increase in the abundance of fishes that consume epilithic algae, and much higher bite rates by this group at sites without kelp, suggesting a key role for these fishes in maintaining reefs in kelp-free states by removing kelp recruits. Changes in kelp abundance showed no direct relationship to seawater temperatures over the decade and were also unrelated to other measured abiotic factors (nutrients and storms). Our results show that warming-mediated increases in fish herbivory pose a significant threat to kelp-dominated ecosystems in Australia and, potentially, globally.

The first two years of an inlet: sedimentary dynamics

Abstract A monitoring program, including the acquisition of a series of topo-bathymetric surveys and oblique aerial photos, has been carried out at Ancao Inlet since its artificial opening in June 1997. This paper presents morphological and volumetric results, including inlet channel evolution (in terms of width, depth and cross-sectional area) and tidal delta formation. The results are analysed in relation to the prevailing oceanographic conditions. This allows the development of a conceptual evolutionary model for the natural evolution of artificially opened inlets with four stages: Stage 1 is the artificially opened inlet; Stage 2 represents the inlet after reaching dynamic equilibrium for the channel while ebb- and flood-tidal deltas are still developing; Stage 3 is the “mature” migrating inlet; and Stage PS (stage post-storm) is the inlet situation after high-energy conditions. The transition from Stage 1 to Stage 3 is a continuous process with intermediate sub-stages. Transition to Stage PS is a discrete phenomenon, caused by high-energy events, after which the inlet gradually changes back to the previous stage. Ancao Inlet was in Stage 1 in June 1997. In April 1998 the inlet channel reached dynamic equilibrium, thus beginning Stage 2. One year after the opening (July 1998) the inlet showed fully developed ebb and flood deltas, reaching the end of Stage 2. Transition to Stage 3, with the beginning of the downdrift migration and bypassing processes, took place during the second year. Stage PS characteristics were observed in January 1999 after high-energy storm conditions, with strong evidence of landward sediment transport. Although the conceptual model was developed for Ancao Inlet, it is envisaged that it could be applicable to other mixed-energy migrating inlets opened in an artificial way.

Recent Evolution of the Natural Inlets of a Barrier Island System in Southern Portugal

ABSTRACT Four natural inlets, existing in a multi-inlet, barrier island system, were studied for the period between the 1940s and 1996. Inlet width and position of the inlet channel were determined using a series of vertical aerial photos and charts. The objective of the work was to determine the association between inlet migration patterns and different hydrodynamic conditions, major storms and engineering interventions. Results indicate that natural inlet opening and evolution were mainly affected by three factors: (a) existence of sub-embayments (western and eastern) inside the system, (b) exposure to wave energy, and (c) inlet efficiency. Two distinctive eastward migration patterns were found by analysing the correlation coefficient (r) between inlet width evolution and inlet migration and by the comparison of the shape of the curves fitted to the inlet migration behaviour.Typical migration of the high-energy flank (on the west side of the system) is characterised by an initial stage of readjustment, with low migration rates, followed by a stage of high eastwards migration rates, up to a limiting position. Inlet width remains reasonably constant during the entire migration cycle, thus the correlation between inlet width and position is very low.Typical inlets on the low-energy flank (east side of the system) are formed by barrier breaching during major storms and produce initially very wide inlets. Eastward inlet migration on the low-energy flank follows a natural logarithmic curve where channel migration is accompanied by strong constructional processes on the updrift barrier. Due to subsequent inlet width reductions, the correlation between inlet width and position is significant.

Late Holocene sea-level fall and turn-off of reef flat carbonate production: Rethinking bucket fill and coral reef growth models

Relative sea-level rise has been a major factor driving the evolution of reef systems during the Holocene. Most models of reef evolution suggest that reefs preferentially grow vertically during rising sea level then laterally from windward to leeward, once the reef flat reaches sea level. Continuous lagoonal sedimentation (“bucket fill”) and sand apron progradation eventually lead to reef systems with totally filled lagoons. Lagoonal infilling of One Tree Reef (southern Great Barrier Reef) through sand apron accretion was examined in the context of late Holocene relative sea-level change. This analysis was conducted using sedimentological and digital terrain data supported by 50 radiocarbon ages from fossil microatolls, buried patch reefs, foraminifera and shells in sediment cores, and recalibrated previously published radiocarbon ages. This data set challenges the conceptual model of geologically continuous sediment infill during the Holocene through sand apron accretion. Rapid sand apron accretion occurred between 6000 and 3000 calibrated yr before present B.P. (cal. yr B.P.); followed by only small amounts of sedimentation between 3000 cal. yr B.P. and present, with no significant sand apron accretion in the past 2 k.y. This hiatus in sediment infill coincides with a sea-level fall of ∼1–1.3 m during the late Holocene (ca. 2000 cal. yr B.P.), which would have caused the turn-off of highly productive live coral growth on the reef flats currently dominated by less productive rubble and algal flats, resulting in a reduced sediment input to back-reef environments and the cessation in sand apron accretion. Given that relative sea-level variations of ∼1 m were common throughout the Holocene, we suggest that this mode of sand apron development and carbonate production is applicable to most reef systems.

Artificial Construction of Dunes in the South of Portugal

Abstract The Cacela Peninsula on the south coast of Portugal was, previous to nourishment operations, extremely vulnerable to overwash events. During the 1995–96 winter, extensive overwashing led to the opening of a new inlet. Simultaneously, the lagoon channel in the backbarrier was silting up with the overwash deposits, inlet flood delta sands, and accretion of fine sediments. Between October 1996 and February 1997 the channel was dredged, and the sediments were deposited on the western 2,000 meters of the Cacela Peninsula, forming an artificial dune ridge. The sediment characteristics of the dredge spoils were in contrast with the natural dune sand. The spoils had higher silt and clay content, lower mean grain size, and poorer sorting. In January 1998, three washover breaches were infilled, with sand removed from the foreshore, on the eastern part of the Cacela Peninsula. These sands were coarser and more poorly sorted than the original dune sediments. A 2-year monitoring program, consisting of beach/dune profiling, topographic surveys in specific areas, and sediment analysis, was established to observe the morphological evolution of these areas. The total eroded volume recorded for the dune nourishment project after 2 years was about 106,500 cubic meters, corresponding to 33% of the total 325,000 cubic meters of sediment that was deposited. The washover infilling showed little or no variation. However, the downdrift beaches and foredunes experienced severe erosion. Both protective measures accomplished their purposes in terms of preventing erosion; however, a natural landscape was only created where dune development by aeolian processes was possible.

Evolution of Coral Rubble Deposits on a Reef Platform as Detected by Remote Sensing

Abstract: An investigation into the evolution of coral rubble deposits on a coral reef platform is assessed using high-resolution remote sensing data and geospatial analysis. Digital change detection analysis techniques are applied to One Tree Reef in the southern Great Barrier Reef by analysing aerial photographs and satellite images captured between 1964 and 2009. Two main types of rubble deposits were identified: (1) rubble flats that are featureless mass accumulations of coral rubble; and, (2) rubble spits that are shore-normal linear features. While both deposits prograde in a lagoon-ward direction, rubble spits move faster (~2 m/yr) than rubble flats (~0.5 m/yr). The volume of rubble, the underlying substrate, the energy regime, and storm frequency control the rate of progradation. Rubble flat occurrence is restricted to the high-energy (windward) margin of the coral reef platform, while rubble spits are distributed reef wide, both in modal high energy and modal low energy regions of the reef. Rubble spit deposition is considered to be a result of enlarged spur and groove morphology of the forereef, whereby wave energy is focused through the enlarged groove formations causing the preferential deposition of coral rubble in particular zones of the adjacent reef flat. One last control is thought to be the elevation of the reef crest whereby lower areas are more prone to rubble flat development. A vertical and ocean-ward accumulation of rubble is occurring on the windward margin of the reef leading to a build-up and build-out of the reef, governing the expansion of the reef footprint. This study shows for the first time the evolution of a coral reef rubble flat and rubble spits over decadal time scales as detected through remotely sensed images spanning 45 years.

Coral reef sediment dynamics: evidence of sand-apron evolution on a daily and decadal scale

ABSTRACT Vila-Concejo, A. Harris, D.L., Shannon, A.M., Webster, J.M., and, Power, H.E., 2013. Coral reef sediment dynamics: evidence of sand-apron evolution on a daily and decadal scale This paper investigates sand apron progradation on decadal and daily scales on a platform reef (One Tree Reef, OTR) located in the southern Great Barrier Reef. The decadal scale is addressed by analysing sand apron progradation using remotely sensed images (aerial photos and satellite imagery) coupled with wind data and cyclone events. The daily scale is addressed through a field campaign that was undertaken in September-October 2011. The campaign consisted of hydrodynamic measurements in three stations over the southern sand apron in OTR. It was found that while there was a small overall progradation over the last 31 years, the progradation had not occurred continuously or consistently along the entire sand apron. Additionally, the effect of cyclones was not clear on the decadal scale. On the daily scale, it was found that currents are generally weak (<0.4 m/s) and that currents during conditions at which suspended sediment is maximized are ocean-ward directed on the central part of the sand apron and lagoon-ward directed on the easternmost end. As such, daily sediment transport does not represent a gross contribution to lagoon infilling by sand apron progradation. Our results show that sand apron progradation does not occur continuously on the decadal or the daily scale.

Wave transformation on a coral reef rubble platform.

ABSTRACT Harris, D.L. and Vila-Concejo, A., 2013. Wave transformation on a coral reef rubble platform Wave transformation across coral reef platforms is the primary process affecting changes in coral reef geomorphology. Transformation regulates the amount of wave energy entering reef systems, however there have been relatively few hydrodynamic assessments conducted on coral reefs when compared to siliciclastic environments with the effects of common geomorphic features like rubble platforms on wave transformation never specifically examined. This study focuses on the changes in wave characteristics across a rubble platform in a high energy environment (One Tree Reef, southern Great Barrier Reef). Wave conditions were measured at five locations over two days along a cross-reef transect from the reef rim to lagoon. Most of the wave energy was dissipated during wave breaking with energy attenuation due to bottom friction a secondary process. Wave energy attenuation was between 60–99% of the offshore wave conditions only during high tide would wave propagation across the reef platform be capable of affecting reef geomorphology. The wave spectrum also changed with the shorter period gravity wave energy (3 – 20 s) almost completely expending during transformation while longer period infragravity waves (20 – 300 s) were capable of propagating across the reef platform. Wave heights were depth limited and primarily controlled by water depth which suggests that water depth over the reef platform and subsequently elevation of the reef platform above mean sea level govern the amount of wave energy transferred across into reef systems, with most of the gravity wave energy removed during propagation over coral rubble platforms.

Oceanographic Conditions and Human Factors on the Water Quality at an Amazon Macrotidal Beach

Abstract Pereira, L.C.C.; Pinto, K.S.T.; Da Costa, K.G.; Vila-concejo, A., and Da Costa, R.M., 2012. Oceanographic conditions and human factors on the water quality at an Amazon macrotidal beach. Atalaia beach is situated in the NE of the Brazilian state of Pará and is one of the most popular with tourists and local beachgoers. This paper describes the seasonal variation in the meteorologic and oceanographic characteristics of the study area, as well as the effects of the lack of a public sanitation system on the quality of the water used by beachgoers. Oceanographic campaigns were carried out between November 2008 and September 2009. The study area is characterized by high rainfall rates (>1900 mm during the rainy season), NE winds with mean speeds of up to 4.36 m/s in the dry season and 3.06 m/s in rainy season, macrotidal conditions (tidal range >4.0 m), moderate tidal current speeds (up to 0.5 m/s), and significant wave heights up to 1.5 m. Water temperature was relatively homogeneous (27.6°C to 29.3°C). Salinity varied from 5.7 (June) to 37.4 psu (November). The water was well oxygenated (up to 9.17 mg/L), turbid (up to 118 nephelometric turbidity units), alkaline (up to 8.68), and eutrophic (maximum of 2.36 µmol/L for nitrite, 24.34 µmol/L for nitrate, 0.6 µmol/L for phosphate, and 329.7 µmol/L for silicate), and it presented high concentrations of chlorophyll a (up to 82 mg/m3). The natural conditions observed in the present study indicate the need for a review of the hydrologic criteria used for the evaluation of beaches by national and international agencies and their adaptation to the reality of the Amazon Coast. The lack of a public sanitation system has led to bacteriologic contamination and the loss of water quality. Resumen A praia de Atalaia está situada no nordeste do estado do Pará (Brasil), e é uma das mais turísticas e populares praias do litoral amazônico. O objetivo deste trabalho foi descrever as variações sazonais das condições meteorológicas e oceanográficas da área estudada, bem como conhecer os efeitos da falta de um sistema público de saneamento básico sobre a qualidade da água utilizada para banho pelos usuários desta praia. Campanhas oceanográficas foram realizadas entre novembro de 2008 e setembro de 2009 e dados meteorológicos foram fornecidos pelo Instituto Nacional de Meteorologia. Os resultados mostraram que a área de estudo é caracterizada por possuir altas precipitações (>1900 mm durante o período chuvoso), ventos de nordeste com velocidades médias de até 4,36 m/s no período seco e 3,06 m/s no período chuvoso, macromarés com alturas acima de 4,0 m, correntes de marés com velocidades médias de até 0.5 m/s, e altura de ondas significantes de até 1,5 m. A temperatura da água foi relativamente homogênea (27,6 a 29,3°C). A salinidade variou de 5,7 (junho) a 37,4 psu (novembro). A água foi bem oxigenada (até 9,17 mg/L), turva (até 118 NTU), alcalina (até 8.68), eutrófica (máximo de 2,36 µmol/L para nitrito, 24,34 µmol/L para nitrato, 0,6 µmol/L para fosfato e 329,7 µmol/L para silicato), e apresentou altas concentrações de clorofila a (até 82 mg/m3). As condições naturais observadas no presente estudo indicam a necessidade da revisão dos critérios de qualidade da água das praias amazônicas, estabelecidos por agencias nacionais e internacionais. Por outro lado, a falta de um sistema público de saneamento tem causado contaminação bacteriológica e comprometido a qualidade da água da praia de Atalaia.

Influence of subtidal sand banks on tidal modulation of waves and beach morphology in Amazon macrotidal beaches

ABSTRACT Pereira, L.C.C., Vila-Concejo, A.and Short, A.D., 2013. Influence of subtidal sand banks on tidal modulation of waves and beach morphology in macrotidal beaches. Amazon beaches are controlled by large tidal ranges, strong tidal currents and an ample supply of sediments, which create subtidal sand banks that modulate wave energy on the shoreline. Given this, the objective this study was to study the effects of tidal modulation of waves on spatial and temporal beach morphodynamics. This paper presents morphological and hydrodynamic data from three beaches on the Amazon coast of Brazil. Data was taken between November, 2008 and October, 2009. This study has two time scales: short term intensive campaigns with hydrodynamic measurements and topographic surveys and medium term measurements that refer to climatologic and offshore wave data obtained from National Institutes. For the analyses considering the ebb tide and flood tide conditions we have found higher RTR modal values and lower Ω modal values during the ebb tide periods, mainly in the most sheltered beach (higher influence of sand banks), showing the influence of tidal modulation. On the more exposed beach (lower influence of sand banks), a greater influence of wind-wave contributed to a similar pattern among the ebb and flood tide phases, prevailing low tide bar and non-barred dissipative characteristics. On the most sheltered area, the tidal processes dominate maintaining ultradissipative beaches and tidedominated tidal flat. On the macrotidal Amazon beaches tidal elevation and subtidal sand banks modulate the wave energy – during low tide, the waves break offshore on the sand banks and they only start to propagate over the banks when tide is increasing, reaching the maximum wave energy during high tides.