Abundance Of Macroalgae Research Articles

Spatial Variation in Upper Limits of Coral Cover on the Great Barrier Reef

ABSTRACTAimIdentifying the maximum coral cover that a coral community can sustain (i.e., its ‘upper limit’) is important for predicting community dynamics and improving management strategies. Here, we quantify the relationship between estimated upper limits and key environmental factors on coral reefs: hard substrate availability, temperature and water clarity.LocationGreat Barrier Reef (GBR), Australia (over 1400 km).Time Period1990 to 2022.Major Taxa StudiedScleractinian corals.MethodsWe used 32 years of data on coral cover around reef perimeters. Each reef was divided into four wave‐exposure habitats depending on prevailing wind conditions. For each site, we determined if hard coral cover had reached a plateau or upper limit. Next, we extracted existing estimates of hard substrate availability, modelled water temperature and Secchi depth. Then, we quantified the relationship between these environmental variables and the upper limits.ResultsWe found varying upper limits across the GBR, with a median of 33% coral cover and only 17% of the estimated upper limits exceeded 50% coral cover. Upper limits increased towards the southern reefs. Our results show that upper limits increased with increasing hard substrate availability and decreased with temperature and, to a lesser extent, with water clarity.Main ConclusionsThe upper limits estimated in this study are much lower than what is commonly assumed when modelling ecological dynamics, most likely resulting in predicted recovery rates being inappropriately high. Although hard substrate ultimately restricted upper limits, there are mechanisms constraining the proportion of hard substrate that is covered by hard corals. The negative relationship between temperature and upper limits cannot be explained by changes in macroalgal abundance but may be related to changes in species composition. The quantitative relationships between the upper limits of coral cover and environmental variables will provide critical information to prioritise sites for management interventions.

The sea urchin Diadema antillarum facilitates recruitment of the Critically Endangered Caribbean coral species Acropora palmata

The functional extinction of the herbivorous sea urchin Diadema antillarum in the 1980s has contributed to the degradation of Caribbean coral reefs. In the early 2000s, recovering populations of D. antillarum were observed in several locations with mixed consequences for coral recruitment: D. antillarum improved habitat quality for settling coral larvae and recruits, but also contributed to settler mortality through (incidental) predation. To determine the relative importance of both mechanisms, tiles were deployed in the absence and presence of naturally occurring D. antillarum aggregations (2.0-2.8 sea urchins m-2) in Curaçao, after which benthic community composition, ex situ settlement, and long-term (2.5 yr) in situ post-settlement survival of Acropora palmata larvae were quantified. After 3 mo, the presence of D. antillarum resulted in 44% more crustose coralline algae and 52% less turf algae, and a 75% canopy height reduction on the tiles’ exposed habitats. On the cryptic undersides of the tiles, the presence of D. antillarum was linked to lower abundances of sessile invertebrates and macroalgae. Larval settlement was almost 2 times higher on tiles conditioned in the presence of D. antillarum, with a strong preference (>70%) for the cryptic sides of tiles. Settlers returned to areas of reef encompassing D. antillarum populations were twice as likely to survive to the age of 2.5 yr. These findings support the beneficial role of D. antillarum in promoting coral recruitment by creating preferred settlement habitat and by increasing settler survival, and could be leveraged to improve coral restoration practices through dual-species conservation and/or co-culture strategies.

Living under Arctic kelp forests: linking soft-bottom communities to kelp cover in the Canadian Arctic

Kelp forests are dominant habitats along Canadian Arctic coastlines. While their extent and productivity are expected to change dramatically due to global warming, their role in supporting Arctic coastal biodiversity remains poorly explored. Leveraging an extensive data set encompassing core samples, video transects, and environmental data, this study explores the patterns and drivers of benthic diversity, particularly focusing on kelp cover, across 4 Eastern Canadian Arctic regions. We show that the widespread soft bottoms in many subtidal coastal Arctic areas are associated with high densities of the kelp Saccharina latissima, often growing in mixed stands with Laminaria solidungula and Alaria esculenta. These kelps enhance the diversity of invertebrate communities thriving in the sediment below, increasing densities in specific groups and promoting subsurface feeding activity. Interregional comparisons indicate that high turbidity conditions typically lead to low macroalgal cover and low invertebrate richness, whereas extensive sea ice cover can favor high macroalgal abundance and unique diverse communities. Conditions of intermediate open-water duration and high water clarity support tall kelp forests, hosting approximately 70% of local rare taxa. Based on these surveys, we provide a list of Arctic invertebrate taxa according to their level of selectivity for kelp forests as habitats. Despite variation among regions, kelp forests enhance biodiversity and drive unique benthic communities in the Canadian Arctic. Due to their ecological significance and potential vulnerability, we recommend efforts to integrate kelp forests into marine protected areas and minimize human-induced damaging activities within or near these habitats.

Sulfonated reduced graphene oxide catalyzed fatty acid methyl ester production from macroalgae Dictyota dichotoma in supercritical conditions

Despite proposed alternative fuels in the recent past, the race for a natural substitute still exists. In this research work, we suggest biodiesel preparation from the rarely explored macroalgae D. dichotoma using a supercritical fluid system of ethanol/ THF. Reduced graphene oxide was prepared using dried jasmine powder as bio-reductant. Reduced graphene oxide was sulphonated using sulfanilic acid, and the catalysts were characterized by XRD, BET surface area, FTIR, and SEM techniques. The reaction conditions for algal oil conversion into biodiesel in supercritical ethanolysis were optimized. FTIR, and GCMS were eployed as analytical tools to analyze the produced biodiesel. The optimized reaction conditions were 265 °C, ethanol: algal oil= 15:1, Reaction time = 10 min, catalyst loading = 5% GO, and THF: ethanol −0.4 for 78% FAEE yield using GO. 10 wt% S-rGO yielded a maximum of 89% FAEE; and 22.55% C18:2. The catalyst was efficient till five cycles. The work assures the utility of abundant macroalgae for alternative fuel production.

The effects of atmospheric nitrogen deposition in coral-algal phase shifts on remote coral reefs

Remote seawater has been considered a potential refuge for corals in the face of anthropogenic disturbances. However, these remote areas may receive increased atmospheric N deposition, and the ecological consequences remain unclear. This field survey revealed coral-algal phase shifts in the mid-north of the South China Sea. These shifts were observed in 44%, 13.6%, and 26.5% of the sampled reef sites at depths of 1-4 m, 5-8 m, and 10-15 m, respectively. Over 50% of sections in the deeper depths hosted fewer corals compared to shallower areas, coinciding with a higher abundance of macroalgae in the deeper layers. Furthermore, based on long-term observation of atmospheric N flux, laboratory experiments were conducted to explore the cause of coral declines. The results indicate that N supply efficiently promoted macroalgae growth. The saturation of N absorption by macroalgae occurred within 2 weeks, leading to nutrient accumulation in seawater, especially nitrate, which had a direct impact on corals. While moderate N fluxes appeared to mitigate coral bleaching, high N fluxes, even with a balanced P supply or medium level of nutrients with an imbalanced N/P ratio, can both increase the susceptibility of corals to heat bleaching. This study explains the coral-algal phase shift in remote and relatively deep seawater and improves understanding of the cause-and-effect relationship between atmospheric N deposition and coral reef decline.

Dietary macroalgae Chaetomorpha linum supplementation improves morphology of small intestine and pectoral muscle, growth performance, and meat quality of broilers.

Over the last decades, the poultry industry has experienced steady growth. Although the industry is gradually expanding in Indonesia, poultry feed production has always been expensive. There is a need to study alternative ingredients to obtain affordable feed from natural resources. Chaetomorpha linum (CL) is an abundant macroalgae available throughout the year in Indonesia. This study aimed to determine the effect of CL on the histological structure of the small intestine, pectoralis muscle, growth performance, and meat quality of broilers. This study used 300-day-old chick (DOC) male broilers that were reared until they were 21 days old. This study used a completely randomized design with four treatment groups and five replications, and each replication group contained 15 DOC individuals. The treatment groups consisted of Control (CON), CON basal feed (BF), CL1 (0.75%/kg BF), CL2 (1.5%/kg BF), and CL3 (3%/kg BF) groups. The histological structure of the small intestine, pectoralis muscle, growth performance, and meat quality of the broiler was examined. Small intestine and pectoral muscle histomorphology, growth performance, and meat quality were significantly improved in the CL2 (1.5%) and CL3 (3%) groups compared with the CL1 (0.75%) and CON groups. Dietary CL supplementation ameliorates small intestine and pectoral muscle histomorphology, growth performance, and meat quality of broilers.

The ecological value of fully enforced, no‐entry, marine protected areas: A case study of harvested limpets

Abstract Harvesting of intertidal gastropods can lead to a direct reduction in the biomass of targeted species through a reduction in the numbers and size of individuals, in turn leading to extensive changes to the structure of intertidal communities. In the Azores, two patellid species co‐occur, and both are exploited for human consumption. However, one of these species, Patella aspera (Röding, 1798), is larger and has a greater economic value and is thus favoured in comparison to the smaller Patella candei (d'Orbigny, 1840). This study investigates the effects of human exploitation on the interaction between these two species by comparing their densities and sizes within two areas of a marine protected area (MPA): a no‐entry area where human access is strictly prohibited and an adjacent area where human access is allowed and collection still occurs despite it being prohibited. Patella aspera attained similar densities in the two areas, but individuals were much larger within the no‐entry MPA. In contrast, P. candei were more abundant in the adjacent area but were of a similar size as in the no‐entry MPA. Limpet biomass was much greater within the no‐entry MPA. The abundance (% cover) of upright macroalgae and barnacles as well as bare rock were also significantly reduced within the no‐entry MPA, where grazer‐resistant algal crusts cover was significantly greater. This study highlights the influence of human activities and how these may affect the complex dynamics of biotic interactions with wider community‐level cascading effects.

Competitive effects of the macroalga Caulerpa taxifolia on key physiological processes in the scleractinian coral Turbinaria peltata under thermal stress.

An increased abundance of macroalgae has been observed in coral reefs damaged by climate change and local environmental stressors. Macroalgae have a sublethal effect on corals that includes the inhibition of their growth, development, and reproduction. Thus, this study explored the effects of the macroalga, Caulerpa taxifolia, on the massive coral, Turbinaria peltata, under thermal stress. We compared the responses of the corals' water-meditated interaction with algae (the co-occurrence group) and those in direct contact with algae at two temperatures. The results show that after co-culturing with C. taxifolia for 28 days, the density content of the dinoflagellate endosymbionts was significantly influenced by the presence of C. taxifolia at ambient temperature (27 °C), from 1.3 × 106 cells cm-2 in control group to 0.95 × 106 cells cm-2 in the co-occurrence group and to 0.89 × 106 cells cm-2 in the direct contact group. The chlorophyll a concentration only differed significantly between the control and the direct contact group at 27 °C. The protein content of T. peltata decreased by 37.2% in the co-occurrence group and 49.0% in the direct contact group compared to the control group. Meanwhile, the growth rate of T. peltata decreased by 57.7% in the co-occurrence group and 65.5% in the direct contact group compared to the control group. The activity of the antioxidant enzymes significantly increased, and there was a stronger effect of direct coral contact with C. taxifolia than the co-occurrence group. At 30 °C, the endosymbiont density, chlorophyll a content, and growth rate of T. peltata significantly decreased compared to the control temperature; the same pattern was seen in the increase in antioxidant enzyme activity. Additionally, when the coral was co-cultured with macroalgae at 30 °C, there was no significant decrease in the density or chlorophyll a content of the endosymbiont compared to the control. However, the interaction of macroalgae and elevated temperature was evident in the feeding rate, protein content, superoxide dismutase (SOD), and catalase (CAT) activity compared to the control group. The direct contact of the coral with macroalga had a greater impact than water-meditated interactions. Hence, the competition between coral and macroalga may be more intense under thermal stress.

Characterization of macroalgal-associated microbial communities from shallow to mesophotic depths at Manawai, Papahānaumokuākea Marine National Monument, Hawai'i.

The Papahānaumokuākea Marine National Monument, Hawai'i, is one of the most isolated and protected archipelagos in the world, making it a natural laboratory to examine macroalgal-microbial diversity because of limited direct anthropogenic impacts. We collected the most abundant macroalgae from nine sites ranging from shallow subtidal (1.5 m) to mesophotic (75 m) depths around Manawai (Pearl and Hermes Atoll). We characterized the macroalgal bacterial communities via high-throughput amplicon sequencing and compared the influence of host phylum, species, site, and depth on these relationships at a single atoll. Ochrophyta species had the lowest bacterial diversity compared to Chlorophyta and Rhodophyta. Site and/or depth may influence the microbial community structure associated with Microdictyon setchellianum, indicating a possible disconnect of these microbial communities among habitats. Chondria tumulosa, a cryptogenic species with invasive traits, differed in associated microbiota compared to the native Laurencia galtsoffii, an alga from the same family collected at the same site and depth. While there was overlap of bacterial communities across sites for some algal species, the majority had minimal macroalgal-microbial community connectivity across Manawai. This mesophotic system, therefore, did not appear to be refugia for shallow water coral reefs at microscopic scales. Additional studies are required to identify other significant influences on microbial community variation.

Status of Coral Reef Communities on the Caribbean Coast of Costa Rica: Are We Talking about Corals or Macroalgae Reefs?

In the past decades, one of the most widely reported phenomena on Caribbean reefs is the general fall in coral cover and rise in macroalgae. Reefs with low coral cover and high macroalgal abundances are often presumed to provide poorer ecosystem functions and services. In this study, we assessed the condition of coral reefs on the Caribbean Coast of Costa Rica and determined how eight key ecosystem metrics varied in response to different coral and fleshy macroalgae covers. Most reefs surveyed had high fleshy macroalgae and low live coral covers, with an average (±SD) of 31 ± 28% and 14 ± 13% per site. The value of many of the ecosystem metrics estimated for coral reefs of the region appears to be lower than what has been reported for other areas in the Caribbean. We found that the rugosity, urchin density, fish richness, total fish biomass, large fish density, and the potential fishery value of the reef were higher in sites with low fleshy macroalgae covers (<10%). Our results concur with the prevailing paradigm that an increase in macroalgae abundance could reduce the ecosystem services provided by coral reefs.

Analysis of marine diversity and anthropogenic pressures on Seixas coral reef ecosystem (northeastern Brazil)

Coral reefs, vital and ecologically significant ecosystems, are among the most jeopardized marine environments in the Atlantic Ocean, particularly along the northeastern coast of Brazil. The persistent lack of effective management and conservation has led to fragmented information on reef use and pressures, hindering the understanding of these ecosystems' health. Major difficulties and challenges include inadequate data, diverse anthropogenic pressures, and the complex interaction between marine species. This study sought to bridge this knowledge gap by conducting a comprehensive analysis of marine diversity and anthropogenic pressures, specifically focusing on Seixas coral reef near João Pessoa city, an area notably impacted by tourism. Utilizing 25 monitoring transects, subdivided into 1 m2 quadrants, the marine diversity was meticulously evaluated through innovative procedures including (a) sedimentological and geochemical field surveys, (b) application of Shannon-Weaver diversity and Simpson dominance indices, (c) cluster analysis, (d) species identification of macroalgae, coral, and fish, and (e) an examination of anthropogenic interactions and pressures on the coral reef. The assessment encompassed three distinct zones: Back Reef, Reef Top, and Fore Reef, and identified a total of 25 species across 15 genera and 10 fish families. The findings revealed the prevalence of brown macroalgae, fish, and coral, with heightened abundance of red macroalgae in the Fore Reef, which also exhibited the greatest diversity (2.816) and dominance (0.894). Original achievements include the identification of specific spatial variations, recognition of the anthropogenic factors leading to ecological changes, and the formulation of evidence-based recommendations. The study concludes that escalating urbanization and burgeoning daily tourist visits to the reef have exacerbated negative impacts on Seixas coral reef's marine ecosystem. These insights underscore the urgent need for strategic planning and resource management to safeguard the reef's biodiversity and ecological integrity.

Short-term response of macroalgal communities to ocean warming in the Southern Bay of Biscay

Climate change is causing significant shifts in biological communities worldwide, including the degradation of marine communities. Previous research has predicted that southern Bay of Biscay canopy-forming subtidal macroalgal communities will shift into turf-forming Mediterranean-like communities by the end of the century. These predictions were based on a community-environment relationship model that used macroalgal abundance data and IPCC environmental projections. We have tested the short-term accuracy of that model by resampling the same communities and locations four years later and found the short-term predictions to be consistent with the observed communities. Changes in sea surface temperature were positively correlated with changes in the Community Temperature Index, suggesting that macroalgal communities had responded quickly to global warming. The changes over four years were significant, but canopy-forming macroalgae were more resilient in local sites with favourable temperature conditions. Our study demonstrated that updating predictive models with new data has the potential to yield reliable predictions and inform effective conservation strategies.

Potential of Red, Brown, and Green Macroalgae from Dato Beach, Majene, Indonesia as Natural Food Preservative

Macroalgae is one of the natural resources present in Indonesian coastline areas – specifically in Dato Beach, Majene, South Sulawesi. The abundance of macroalgae found in Dato Beach can be utilized in various sectors – including health, cosmetics, and food. The aim of this study was to investigate the secondary metabolites of three types of macroalgae in Dato Beach and their potential to inhibit the growth of pathogenic bacteria in food. The three macroalgae utilized in this study were Turbinaria decurrens (brown algae), Galaxaura rugosa (red algae), and Halimeda opuntia (green algae) representing the three groups of macroalgae based on their dominant pigments. Four types of pathogenic bacteria – namely, Staphyloccus aureus and Bacillus cereus as Gram-positive bacteria plus Salmonella typhi and Escherichia coli as Gram-negative bacteria – were collected from the Biology Laboratory at Universitas Sulawesi Barat, as these bacteria are commonly responsible for food spoilage. The study began with a sampling of macroalgae, followed by cleaning and drying, and subsequently extraction using methanol as the solvent. Methanol was chosen as the universal solvent for its ability to extract both polar and nonpolar components. Phytochemical screening was carried out to test for the presence of flavonoids, steroids/terpenoids, and alkaloids, which represent the three groups of secondary metabolites. The antimicrobial test was carried out using the well diffusion method, as a control used 80 ppm of ampicillin. The results of the study indicated that T. decurrens contains flavonoids, steroids, and alkaloids, G. rugosa contains flavonoids, terpenoids, and alkaloids, whereas H. opuntia only contains terpenoids and alkaloids. Furthermore, G. rugosa was found to have the best ability to inhibit bacteria, with an inhibition zone ranging from 22–23 mm; in some treatments, the diameter of the inhibition zone was even larger than the positive control. T. decurrens was only effective in inhibiting the growth of S. aureus, whereas H. opuntia demonstrated the potential to inhibit the growth of S. aureus and E. coli, and for B. cereus and S. typhi, it could only be inhibited by 100% (1000 μL) extract of the H. opuntia extract.

Recent changes on the abundance and distribution of non-indigenous macroalgae along the southwest coast of the Bay of Biscay

Twenty-three rocky shores along approximately 225 km on the southwest coast of the Bay of Biscay were sampled during the springs of 2014 and 2021, to explore changes in the distribution and abundance of four non-indigenous species (NIS) macroalgae (i.e., Asparagopsis armata, Grateloupia turuturu, Sargassum muticum, and Undaria pinnatifida) by using a semi-quantitative scale. Results showed relevant changes in the distribution and abundance of NIS. The kelp U. pinnatifida was recorded in 2021 for the first time on two shores. The distribution of G. turuturu showed an extension in its range of distribution of 200 km to the east. The other two target species S. muticum and A. armata were widely distributed along the whole 225 km of the studied area in 2014 and 2021, with higher abundance in 2021. Therefore, we strongly advise the necessity of future monitoring programs for these four NIS species. These monitoring programs will explore the progress of invasion and resilience of native species.

Distribution and diversity of the sympatric macroalgae of the pelagic Sargassum horneri in the Yellow and East China seas

The massive pelagic Sargassum horneri (Turner) C. Agardh, 1820 has increasingly occurred in the Yellow Sea and East China Sea. Significant intrusion of floating S. horneri into the southwestern Yellow Sea, the major bloom region of the green tides, has aroused speculations on the blooming mechanism and confounded concurrent prevention practices of green tides. The floating S. horneri were surveyed and sampled throughout its distributional range to study the diversity and abundance of sympatric macroalgae, including the epiphytes and non-epiphytes. The study showed that both types of macroalgae commonly coexisted with the pelagic S. horneri and showed distinct distribution patterns. The non-epiphytic green macroalgae, primarily Ulva prolifera, were free floating with S. horneri. They were initiated from the nearshore water of Jiangsu in late April followed by a rapid accumulation and expansion as the green tide developed. The non-epiphytic green algae were mostly restricted in the western coast of southern YS with biomass decreasing evidently toward offshore. Four species in Phaeophyta were commonly detected epiphytic on the pelagic S. horneri in the survey region and Proselachista taeniiformis was dominant. Unlike the co-occurring green algae, the species composition and abundance of epiphytes have no significant variation in the distributional range of the pelagic S. horneri. High frequency (80%) and abundance (0.25 ± 0.17 gEpi/gSar) of epiphytes indicated significant biological interactions with their hosts and ecological functions of this pelagic system, which deserves further investigation.

Nutrient-rich submarine groundwater discharge increases algal carbon uptake in a tropical reef ecosystem

Submarine groundwater discharge (SGD) in high volcanic islands can be an important source of freshwater and nutrients to coral reefs. High inorganic nutrient content is generally thought to augment primary production in coastal systems but when this is delivered via a freshwater vector as is the case with SGD in this study, the effects on productivity are unclear. In the current literature, there is limited evidence for a direct association between SGD and primary productivity of reefs. To elucidate the response of primary productivity to SGD, we conducted spatially and temporally explicit in situ benthic chamber experiments on a reef flat along a gradient of SGD. We found significant quadratic relationships between C-uptake and SGD for both phytoplankton and the most abundant macroalga, Gracilaria salicornia, with uptake maxima at SGD-derived salinities of ~21−22 (24.5−26.6 μmol NO3-L−1). These results suggest a physiological tradeoff between salinity tolerance and nutrient availability for reef primary producers. Spatially explicit modeling of reefs with SGD and without SGD indicate reef-scale G. salicornia and phytoplankton C-uptake decreased by 82% and 36% in the absence of SGD, respectively. Thus, nutrient-rich and low salinity SGD has significant effects on algal C-uptake in reef systems.

The impact of marine heatwaves on rocky intertidal communities: evidence of accumulative carryover effects of marine heatwaves

The frequency and duration of marine heat waves (MHWs) have recently increased. There is therefore an urgent need to understand the response of marine organisms to MHWs. However, most estimates of MHW impacts on abundances include the effects of environmental stochasticity other than the MHWs. In addition, although MHWs sometimes persist for year-round or occur repeatedly for shorter periods, the accumulative carryover effects (ACEs)— the effects of sequential events accumulating additively over time— of MHWs on organisms have never been evaluated. Furthermore, the relationship between species niche traits other than thermal niches and susceptibility to MHWs is unknown. We examined the impacts of MHWs in southeastern Hokkaido, northern Japan, in summer from 2010 to 2016 on rocky intertidal communities by distinguishing MHW effects from environmental stochasticity. We asked (1) Did MHWs have ACEs on four major functional groups: macroalgae, sessile invertebrates, herbivorous invertebrates, and carnivorous invertebrates? (2) Does ignoring ACEs lead to biased assessments? (3) How did the effects of the MHWs on functional groups and their subsequent recovery differ? And (4) How does the susceptibility to MHWs differ with species niche (thermal and vertical) traits? We detected ACEs of MHWs and found that if they are ignored, the effects of MHWs can be underestimated. Although MHWs are known to reduce the abundance of macroalgae and increase that of sessile invertebrates in rocky intertidal habitats, our results show that macroalgal abundance increased during and after MHWs, whereas sessile invertebrates showed no change during or after MHWs. The abundance of herbivorous mollusks decreased during and after MHWs. Carnivorous invertebrates declined during MHWs and in the first year after MHWs. During and after MHWs, abundances of species with low thermal niches decreased and those with high thermal niches increased. There were no differences in response to MHWs between vertical niches when accumulative carryover effects were ignored. These results emphasize the importance of considering ACEs when assessing the response of marine organisms to MHWs, and that more studies of these responses are needed for a variety of ecosystems, regions and organisms to predict the responses of marine organisms.

Coral Gardens Reef, Belize: An Acropora spp. refugium under threat in a warming world.

Live coral cover has declined precipitously on Caribbean reefs in recent decades. Acropora cervicornis coral has been particularly decimated, and few Western Atlantic Acropora spp. refugia remain. Coral Gardens, Belize, was identified in 2020 as a long-term refugium for this species. This study assesses changes in live A. cervicornis coral abundance over time at Coral Gardens to monitor the stability of A. cervicornis corals, and to explore potential threats to this important refugium. Live coral cover was documented annually from 2012-2019 along five permanent transects. In situ sea-surface temperature data were collected at Coral Gardens throughout the study period and compared with calibrated satellite data to calculate Maximum Monthly Mean (MMM) temperatures and Degree Heating Weeks (DHW). Data on bathymetry, sediment, substrate, herbivore abundance, and macroalgal abundance were collected in 2014 and 2019 to assess potential threats to Coral Gardens. Live coral cover declined at all five transect sites over the study period. The greatest loss of live coral occurred between 2016 and 2017, coincident with the earliest and highest maximum average temperatures recorded at the study site, and the passage of a hurricane in 2016. Structural storm damage was not observed at Coral Gardens, though live coral cover declined after the passage of the storm. Uranium-thorium (230Th) dating of 26 dead in situ fragments of A. cervicornis collected in 2015 from Coral Gardens revealed no correlation between coral mortality and tropical storms and hurricanes in the recent past. Our data suggest that several other common drivers for coral decline (i.e. herbivory, predation, sedimentation, pH) may likely be ruled out for Coral Gardens. At the end of the study period, Coral Gardens satisfied most criteria for refugium status. However, the early onset, higher mean, and longer duration of above-average temperatures, as well as intermittent temperature anomalies likely played a critical role in the stability of this refugium. We suggest that temperature stress in 2016 and perhaps 2015 may have increased coral tissue vulnerability at Coral Gardens to a passing hurricane, threatening the status of this unique refugium.

Diversity, Abundance, and Distribution of Macroalgae in Coastal Ecotourism Areas — A Case Study at Baluran National Park, Situbondo, Indonesia

Indonesia is a mega biodiversity country with abundant macroalgae. The macroalgae are distributed along the coast and function to maintain the balance of the coastal marine ecosystem, including in Bama Beach, Baluran National Park, Situbondo, Indonesia. This study was to determine the abundance, distribution, and diversity of macroalgae in Bama Beach Baluran National Park, East Java, between April 2019 and June 2019. The research was conducted with a purposive sampling method at two stations, each consisting of five substations using transect blocks. Five species of macroalgae from the Phaeophyceae class (Padina australis, Sargassum aquifolium, Polycladia myrica, Eucheuma edule, and Dictyota pinnatifida), a Rhodophyta (Jania pumila), and Chlorophyta (Halimeda macroloba) were found in the study site. Padina australis was a species that had the highest abundance and dominated the observation station. Nonetheless, according to the Shannon-Weaver Index in the study area, overall macroalgae diversity was classified as a low category with a value of 0.35. The high availability of nutrients influences these conditions in ecosystems with the domination of Padina australis, followed by Sargassum aquifolium at Station I and II.

Detecting Trends in Abundance and Distribution of Seagrasses in Lake Worth Lagoon, Palm Beach County, Florida

Over the past 15 years, seagrass community stability has varied in estuaries throughout Florida. This study sought to model potential patterns of physiochemical parameters and community composition that may correlate with the fluctuation of seagrass populations in Lake Worth Lagoon (LWL), Palm Beach County, FL over time (2007–2019). Seven transects and 4 polygon areas throughout the LWL were established and stratified along a north—south gradient. Sites were sampled annually (May–August) for water quality, seagrass and macroalgal abundance, and community composition. Models developed to explain macrophyte abundance and composition were assessed using Akaike Information Criterion. Interaction between year and site best explained seagrass abundance and community composition in transect and polygon sites. Transect data revealed that seagrass and macroalgae declined after 2012 and continued until barely detected after 2016. This die off was not consistent for all transects and there was site variability in annual dissolved oxygen, nitrate, phosphate, and salinity levels. Polygon sites exhibited a shift in community composition after 2013, initially dominated by seagrass species Syringodium filiforme and Halodule wrightii before transitioning in 2012–2013 to Halophila decipiens and Caulerpa spp. Central lagoon sites transitioned to communities devoid of nearly all vegetative species. The loss of seagrass and the change in community composition could be explained by a transient dry period in 2012 and a subsequent inflow of freshwater. These events (sudden drought followed by an increase in freshwater) likely compounded the stress on the system between 2011–2014, leading to a drastic change in seagrass community.