Shallow-water Habitats Research Articles

Coarse- and fine-scale acoustic telemetry elucidates movement patterns and temporal variability in individual territories for a key coastal mesopredator

Great barracuda (Sphyraena barracuda) are a high trophic level predator that uses a wide variety of habitats globally throughout tropical and subtropical waters. Despite the important top-down pressure this species likely exerts on fish communities within its foraging territories, the specifics of spatial ecology remain relatively unknown. This study tracked 17 great barracuda throughout Buck Island Reef National Monument, a marine-protected area located in St. Croix, U.S. Virgin Islands (17.786944° N, − 64.620556° W) from July 2014 to May 2016. Broad- and fine-scale acoustic telemetry was used to examine individual variability and study population patterns in residency, site fidelity, territoriality, and complexity of spatial use within home ranges. Network analysis of broad-scale data revealed spatial and temporal differentiation among the population in location of core use areas and showed that these areas contained multiple unique receiver groups or communities, a product of spatial or temporal variation within core activity spaces. Results from the fine-scale positioning system reinforced spatial and temporal partitioning in core use areas between individuals, indicating territorial behaviors, and showed evidence for both resident and transient movements. Preliminary fine-scale analysis also suggested diel variation in location of activity spaces. Although ubiquitous throughout all shallow water habitats, detection patterns for the study population appear to be influenced by high residency, territoriality, spatial partitioning, and diel variation. Understanding the complexities of individual space use is fundamental to ecologically founded and effective area-based spatial management frameworks at community scales.

Intensified Ocean Deoxygenation During the end Devonian Mass Extinction

AbstractThe end‐Devonian mass extinction (~359 Ma) substantially impacted marine ecosystems and shaped the roots of modern vertebrate biodiversity. Although multiple hypotheses have been proposed, no consensus has been reached about the mechanism inducing this extinction event. In this study, I/Ca ratio of carbonate was used to unravel the changes in local oxygen content of the upper water column during this critical interval. The Devonian‐Carboniferous boundary was recorded in two shallow water carbonate sections in south China. I/Ca values at both locations show a clear decline in the Middle and Upper Siphonodella praesulcata conodont zones, which coincides with a positive shift in carbonate carbon isotope composition and a negative shift in nitrogen isotope composition. These results suggest that deoxygenation was intensified during this critical interval, which likely influenced shallow water habitats, lending support to the notion that oxygen deficiency likely was a direct mechanism impacting the end‐Devonian mass extinction.

PEMETAAN HABITAT PERAIRAN DANGKAL DI KAWASAN PADAT WISATA TANJUNG BENOA BALI MENGGUNAKAN DATA REMOTE SENSING

Tourism is a sector that is prioritized in various countries. Most of the tourist objects are distributed along the coast that intersects directly with those that result in the degradation of the ecosystem inside. The southern region of Bali is one of the regions that has experienced rapid development of tourism activities. The expansion of the tourism area in Tanjung Benoa occurs in coastal areas and directly contacts underwater ecosystems such as seagrass beds and coral reefs, which it have an impact on changes in the area of the ecosystem. Information about the form of distribution of underwater objects can be the first step in making ecological-based tourism policy. Satellite imagery can be used to detect shallow-water habitats. The purpose of this study was to determine the effectiveness of sentinel-2 A images to map shallow water habitat in densely packed tourist areas Tanjung Benoa. The results showed that there were three types of land cover in Tanjung Benoa area, such as seagrass, coral and sand, the accuracy results showed landsat 8 images had higher accuracy than Sentinel-2 A images with total accuracy of 74.83% and kappa accuracy of 46.59%. There are 8 types of seagrasses species in the coastal area of Tanjung Benoa, namely Cymodocea rotundata, Enhalus acoroides, Halodule pinifolia, Halodule uninervis, Halophila ovalis, Thalassia hemprichi Syringodium isoetifolium dan Thalassodendron Ciliatum.
 Keywords: Remote Sensing; Shallow Water Habitat; Tanjung Benoa; Sentinel-2 A; Landsat 8

Exceptionally species-rich assemblages of modern larger benthic foraminifera from nearshore reefs in northern Palawan (Philippines)

Symbiont-bearing larger benthic foraminifera (LBF) are ubiquitous components of tropical and subtropical carbonate-rich shallow-water habitats and contribute substantially to coral reef accretion and stability. More than 60 species of LBF are currently described from the Indo-Pacific Ocean with the Philippines being recently identified as their potential center of maximum species richness.The Palawan archipelago, also known as the “last ecological frontier” of the Philippines and a hotspot of biodiversity, attracts a growing number of tourists due to its comparatively intact marine environments and picturesque landscapes. Here, we document and illustrate the species-rich fauna of modern LBF from shallow nearshore habitats in northern Palawan. Sampling covered the northernmost part of Palawan's South China and Sulu Sea coasts including the Calamian Islands group. A total of 24 samples were taken from fore-reef slopes, inter-reef areas, a back-reef, seagrass leaves with a nearby mangrove swamp, and a WW2 shipwreck at depths between 0 to 25m. We recorded a total of 44 LBF morphospecies, a number that is among the highest reported so far. Heterostegina depressa and Calcarina mayori were identified as the most widely distributed taxa in the study area. We further describe Peneroplis hoheneggeri nov. sp. as a new species of Peneroplis de Montfort. The newly described peneroplid is characterized by single rows of large pits and was previously also documented from Micronesia. Our survey supports the designation of northern Palawan as an exceptionally biodiverse ecoregion with high priority for marine conservation efforts.

A Bird's Eye View: Hesperornithiforms as Environmental Indicators in the Late Cretaceous Western Interior Seaway

Seabirds are considered indicators of ecological hotspots in modern ecosystems because their biogeographic distribution is correlated with physical, chemical, and biological oceanographic factors. Pursuit diving seabirds – those that actively pursue prey underwater – are generally more limited in distribution and more closely tied to oceanographic factors, as diving ability is often gained at the expense of flight capabilities. Today, wing propelled pursuit diving seabirds are restricted to colder waters; foot propelled divers have a broader latitudinal distribution, but do not forage far from shore in marine environments. In comparison, Late Cretaceous Northern Hemisphere seas were host to foot propelled pursuit diving seabirds called hesperornithiforms. Their Western Interior Seaway fossil record, in particular, reflects the broad latitudinal distribution of modern foot propelled divers, but with occurrences of offshore foraging more typical of modern wing propelled divers. The presence of hesperornithiforms in such a wide variety of environments (Boreal, Tethyan, coastal, nearshore, and offshore) suggests different ecological and oceanographic conditions affected biogeographic patterns of Late Cretaceous divers. The purpose of this study is to explore Late Cretaceous hesperornithiform paleobiogeography in light of what is known about how biotic and environmental factors affect modern pursuit diving seabirds to better understand WIS paleoecology.The Late Cretaceous was characterized by greenhouse climate, high sea levels, and epicontinental seas that provided marine paleoenvironments with no modern analogs. Two notable ecological differences between the Late Cretaceous and today are the presence of marine reptiles (and absence of marine mammals) as apex predators and the lack of acanthomorph fish diversity. Spatio-temporal overlap among hesperornithiforms, marine reptiles, and large predatory fishes implies different competition and predator-prey relationships among marine carnivores than today. Differences in swimming capabilities between marine reptiles and marine mammals may partially account for the presence of hesperornithiforms in warm, offshore waters. Additionally, environmental factors relating to the unique paleoceanography of the WIS would have also influenced hesperornithiform populations. Ample shoreline, abundant shallow water habitats, and high primary production made epicontinental seas hotspots for pursuit diving seabirds, despite warmer temperatures. Together, ecosystem structure and the unique oceanographic factors characterizing epicontinental seas both contribute to differences in seabird biogeography between the Late Cretaceous and today.

Megabenthic communities of the Ligurian deep continental shelf and shelf break (NW Mediterranean Sea).

The Ligurian Sea is one of the most studied Mediterranean basins. Since the beginning of the last century, many research expeditions have characterized its benthic and pelagic fauna through scuba diving and trawl surveys. However, a large knowledge gap exists about the composition of benthic communities extending into the so-called mesophotic or twilight depth range, currently under intense pressure from commercial and recreational fishing. A series of visual surveys, carried out by means of remotely operated vehicles between 2012 and 2018, were conducted along the Ligurian deep continental shelf and shelf break, between 30 and 210 m depth, in order to characterize the main benthic biocoenoses dwelling at this depth range and to determine the most relevant environmental factors that explain their spatial distribution. Deep circalittoral communities of the Ligurian Sea were represented by a mixture of species belonging to the deepest extension of shallow-water habitats and deep circalittoral ones. Twelve major biocoenoses were identified, each one characterized by specific preferences in depth range, substrate type and seabed slope. Those biocoenoses included gorgonian and hydrozoan forests, dense keratose sponge grounds, Dendrophyllia cornigera gardens, bryozoan beds and soft-bottom meadows of sabellid polychaetes and soft-corals. Other less common aggregations included six forests of black corals and two populations of Paramuricea macrospina. A georeferenced database has been created in order to provide information to managers and stakeholders about the location of the identified communities and high-diversity areas, aiming to facilitate sustainable long-term conservation of the Ligurian benthic ecosystem.

Establishing temperate crustose early Holocene coralline algae as archives for palaeoenvironmental reconstructions of the shallow water habitats of the Mediterranean Sea

AbstractOver the past decades, coralline algae have increasingly been used as archives of palaeoclimate information due to their seasonal growth bands and their vast distribution from high latitudes to the tropics. Traditionally, these reconstructions have been performed mainly on high latitude species, limiting the geographical area of their potential use. Here we assess the use of temperate crustose fossil coralline algae from shallow water habitats for palaeoenvironmental reconstruction to generate records of past climate change. We determine the potential of three different species of coralline algae, Lithothamnion minervae, Lithophyllum stictaeforme and Mesophyllum philippii, with different growth patterns, as archives for pH (δ11B) and temperature (Mg/Ca) reconstruction in the Mediterranean Sea. Mg concentration is driven by temperature but modulated by growth rate, which is controlled by species‐specific and intraspecific growth patterns. L. minervae is a good temperature recorder, showing a moderate warming trend in specimens from 11.37 cal ka BP (from 14.2 ± 0.4°C to 14.9 ± 0.15°C) to today. In contrast to Mg, all genera showed consistent values of boron isotopes (δ11B) suggesting a common control on boron incorporation. The recorded δ11B in modern and fossil coralline specimens is in agreement with literature data about early Holocene pH, opening new perspectives of coralline‐based, high‐resolution pH reconstructions in deep time.

Marine Heatwave, Harmful Algae Blooms and an Extensive Fish Kill Event During 2013 in South Australia

In 2013, South Australia experienced unusually high and variable water temperatures (5°C above the historic average), with a peak sea surface temperature of approximately 27°C over a wide geographic area covering both gulfs and shelf waters. Over the same period and similar geographic area, a prolonged and widespread marine mortality event occurred. From January to May 2013, low level rates of incidental morbidity and mortality of abalone (Haliotis rubra and H. laevigata) and at least 29 fish species were observed. Mortalities were geographically extensive from Port MacDonnell on the South Coast of South Australia to Point Drummond on Eyre Peninsula, and including two gulf systems, spanning approximately 2,900km of coastline. Mortalities were investigated using gross pathology, histopathology, bacterial culture and polymerase chain reaction (PCR) techniques. Water samples were collected to assess water column nutrient status and phytoplankton biomass levels and community composition. High nutrient concentrations were suggestive of high phytoplankton productivity, with conditions conducive to diatom blooms. A harmful (abrasive) diatom, Chaetoceros coarctatus, was observed in higher concentrations than the historical average. Observed fish mortalities were restricted to a small proportion of the populations and primarily comprised of temperate small-bodied benthic inshore species. Fish histopathology was suggestive of prolonged stress (melanomacrophage aggregation in spleens and kidneys), physical gill damage (focal gill lesions likely caused by C. coarctatus) and lethal bacterial septicaemia. Infectious and notifiable diseases were ruled out in all fish and abalone samples. Abalone mortalities were also restricted to a small proportion of the population with thermal stress a likely contributing factor that resulted in terminal secondary bacterial infections. A marine heatwave event, which promoted blooms of algae, including C. coarctatus, was likely the primary cause of widespread marine mortalities throughout South Australia in 2013. With marine heatwaves projected to increase in frequency, duration and spatial extent, this investigation demonstrated that most at risk will be temperate species in shallow water habitats already at their upper thermal tolerance limits, particularly those with high site fidelity. This should be considered in future climate proofing strategies, including risk and impact assessments underpinning the management of marine resources, fisheries, aquaculture and ecotourism.

ACCURACY OF UNSUPERVISED CLASSIFICATION TO DETERMINE CORAL HEALTH USING SPOT-6 AND SENTINEL-2A

Abstract. Characteristics of corals spectral from different species are expected to have optically different characters. The aims of this research are to compare unsupervised classification between IsoData and K-Means methods with Lyzenga application, and to analyze the precision of SPOT-6 and Sentinel-2A satellite imagery in classsifying shallow water habitat. The image processing are atmosferic correction, cropping, masking, Depth Invariant Index, Unsupervised classification, ground truthing, reclassify, accuracy assessment, and shallow water habitat spectral reflectance analysis. Rubble and dead coral with algae were indicating as coral death due to either damaging human activity or natural death such as bleaching. The accuracy of unsupervised classification IsoData and K-Means method have the same accuracy 62.50%. The IsoData method is better detected live coral and algae. Rubble were dominant detected in K-Means method.

Foraging guild structure and niche characteristics of waterbirds wintering in selected sub-Himalayan wetlands of India

Abstract Guild structure and niche characteristics are important indicators of quantitative niche partitioning of a community. In the present study the niche structure was analyzed to determine whether resource partitioning reflected coexistence or exclusion of different waterbird species in relevant guilds at sub-Himalayan terai-dooars wetlands. Trophic guild structure and niche organization in wintering waterbirds were studied to understand why some species were rare and some were abundant and what possibly determined the diversity and abundance of multi-species waterbird communities. Two trophic components of niche partitioning, namely foraging habitat and foraging techniques, were considered in the present study. Cluster analyses based on foraging habitats and foraging techniques (i.e., two dimensions) provided bi-dimensional foraging guilds. Waterbirds precisely formed five distinct guilds, namely, medium and shallow water generalists, stalking waders, pecking waders, mud picking wader and divers. Further, a much higher diversity of waterbirds was observed from shallow and medium water habitats than deep waters which could be the outcome of higher net available trophic energy. Potential competitive interactions within intra-guild members were possibly minimized by using varied feeding techniques. The present study pointed out that the specialist guild members showed comparatively higher intra-guild niche overlap, whereas generalist guild members showed much lower niche overlap. Results indicated that waterbird communities were influenced mostly by trophic resources at a site and the birds' ability to exploit them. Waterbird guild structures and niche characteristics thus provide important ecological indicators of the ability of wetlands to support a range of species. Further, information on guild structures and niche characteristics are surely important for monitoring the biotic health of sub-Himalayan wetlands that would be important to work out effective wetland conservation strategies.

Limitations of Boulder Detection in Shallow Water Habitats Using High-Resolution Sidescan Sonar Images

Stones and boulders in shallow waters (0–10 m water depth) form complex geo-habitats, serving as a hardground for many benthic species, and are important contributors to coastal biodiversity and high benthic production. This study focuses on limitations in stone and boulder detection using high-resolution sidescan sonar images in shallow water environments of the southwestern Baltic Sea. Observations were carried out using sidescan sonars operating with frequencies from 450 kHz up to 1 MHz to identify individual stones and boulders within different levels of resolution. In addition, sidescan sonar images were generated using varying survey directions for an assessment of range effects. The comparison of images of different resolutions reveals considerable discrepancies in the numbers of detectable stones and boulders, and in their distribution patterns. Results on the detection of individual stones and boulders at approximately 0.04 m/pixel resolution were compared to common discretizations: it was shown that image resolutions of 0.2 m/pixel may underestimate available hard-ground settlement space by up to 42%. If methodological constraints are known and considered, detailed information about individual stones and boulders, and potential settlement space for marine organisms, can be derived.

Future ocean climate homogenizes communities across habitats through diversity loss and rise of generalist species.

Predictions of the effects of global change on ecological communities are largely based on single habitats. Yet in nature, habitats are interconnected through the exchange of energy and organisms, and the responses of local communities may not extend to emerging community networks (i.e., metacommunities). Using large mesocosms and meiofauna communities as a model system, we investigated the interactive effects of ocean warming and acidification on the structure of marine metacommunities from three shallow-water habitats: sandy soft-bottoms, marine vegetation, and rocky reef substrates. Primary producers and detritus-key food sources for meiofauna-increased in biomass under the combined effect of temperature and acidification. The enhanced bottom-up forcing boosted nematode densities but impoverished the functional and trophic diversity of nematode metacommunities. The combined climate stressors further homogenized meiofauna communities across habitats. Under present-day conditions metacommunities were structured by habitat type, but under future conditions they showed an unstructured random pattern with fast-growing generalist species dominating the communities of all habitats. Homogenization was likely driven by local species extinctions, reducing interspecific competition that otherwise could have prevented single species from dominating multiple niches. Our findings reveal that climate change may simplify metacommunity structure and prompt biodiversity loss, which may affect the biological organization and resilience of marine communities.

Environmental parameters of shallow water habitats in the SW Baltic Sea

Abstract. The coastal waters of the Baltic Sea are subject to high variations in environmental conditions, triggered by natural and anthropogenic causes. Thus, in situ measurements of water parameters can be strategic for our understanding of the dynamics in shallow water habitats. In this study we present the results of a monitoring program at low water depths (1–2.5 m), covering 13 stations along the Baltic coast of Schleswig-Holstein, Germany. The provided dataset consists of records for dissolved inorganic nutrient concentrations taken twice a month and continuous readings at 10 min intervals for temperature, salinity and oxygen content. Data underwent quality control procedures and were flagged. On average, a data availability of >90 % was reached for the monitoring period within 2016–2018. The obtained monitoring data reveal great temporal and spatial variabilities of key environmental factors for shallow water habitats in the southwestern Baltic Sea. Therefore the presented information could serve as realistic key data for experimental manipulations of environmental parameters as well as for the development of oceanographic, biogeochemical or ecological models. The data associated with this article can be found at https://doi.org/10.1594/PANGAEA.895257 (Franz et al., 2018).

Community structure of Harpacticoida and Canuelloida (Crustacea, Copepoda) on the Great Meteor Seamount (North-east Atlantic Ocean)

AbstractDuring the expedition POS397 ‘GroMet’ in 2010 the sediments of the Great Meteor Seamount (GMS) plateau were sampled quantitatively for the first time, allowing statistical analysis of the community structure of Harpacticoida and Canuelloida. Analysis of similarity revealed no differences between three geographic regions at family/species level. Analysis of diversity indicated slightly greater diversity in the south, with more species belonging to more genera/families. Dispersal opportunities possibly occurring at the plateau (emergence, erosion, rafting) are discussed. Of 18 investigated families 106 species were identified, but only 5.66% were already scientifically known and widely distributed. Within the investigated families, 37.74% of the species belonged to shallow-water genera, leading to the conclusion that the plateau was once connected to shallow-water habitats, perhaps functioning as a stepping stone, but is now geographically isolated. This isolation is most likely due to seafloor spreading of the Atlantic Ocean and descending of the GMS. On the plateau, six species with wider distribution ranges were present, indicating that species may arrive accidentally, but their means of settlement remains unknown. Comparisons of the identified GMS plateau fauna with that of other seamounts and mid-oceanic islands revealed similar communities at family level, but at species level the GMS shares only one species with the Seine Seamount; all other elevations had more species in common. Hence, the GMS plateau is considered to be isolated regarding benthic Copepoda but may play an important role in meiofaunal species distribution, as it represents a shallow-water habitat within the deep sea.

Decadal Monitoring in Bermuda Shows a Widespread Loss of Seagrasses Attributable to Overgrazing by the Green Sea Turtle Chelonia mydas

The condition of seagrass habitat and the marine environment on the Bermuda Platform, a mid-oceanic shallow water habitat in the northwest Atlantic, has been monitored since 2006. The overall oceanic climate of the Platform is subtropical; the Platform supports communities of tropical marine seagrasses, including Thalassia testudinum, Syringodium filiforme, Halodule sp., and Halophila decipiens. At the beginning of the study, the general condition of seagrass beds at 17 permanent offshore and nearshore sites indicated that 14 were healthy, complex, and thriving communities, and three represented offshore beds, which had declined precipitously prior to the initiation of study. Over the period of the study, seagrass beds declined at all 17 sites; three beds disappeared, and there was no recovery at the sites known to have declined prior to 2006. Over the same period, there was no apparent negative change in the water quality overlying the seagrass beds. Assessments of elemental content, stable isotopic composition, and leaf morphology indicated that grazing by the green turtle (Chelonia mydas) is driving the decline of the seagrasses of Bermuda. Given the feeding behavior of these turtles on the Bermuda Platform, human intervention may be required to mitigate the decline of seagrass in Bermuda.

New taxa and revised stratigraphic distribution of the crinoid fauna from Anticosti Island, Québec, Canada (Late Ordovician-early Silurian)

AbstractEnd-Ordovician extinctions had a profound effect on shallow-water benthic communities, including the Crinoidea. Further, recovery after the extinctions resulted in a macroevolutionary turnover in crinoid faunas. Anticosti Island is the most complete Ordovician-Silurian boundary section recording shallow-water habitats. Both new taxa and changes in Anticosti Island stratigraphic nomenclature are addressed herein. New taxa includeBecsciecrinus groulxin. sp.,Bucucrinus isotaloin. sp.,Jovacrinus clarkin. sp.,Plicodendrocrinus petrykin. sp.,Plicodendrocrinus martinin. sp.,Thalamocrinus daoustaen. sp., andLateranicrinus saintlaurentin. gen. n. sp. The status ofXenocrinus rubusas a boundary-crossing taxon is confirmed, range extensions of several taxa are documented, and the distribution of crinoids with the revised stratigraphic nomenclature is documented.UUID:http://zoobank.org/19613a44-ec69-47d7-88ab-fcf88ba771f0.

Predicting important rockfish (Sebastesspp.) habitat from large-scale longline surveys for southern British Columbia, Canada

Rockfish, particularly yelloweye (Sebastes ruberrimus) and quillback (Sebastes maliger), are vulnerable to overfishing because they mature late and have affinity for shallow water (50–200 m) habitats. Because studies relating habitat characteristics with the distribution and presence of rockfishes at large scales (100s of kilometres) remain scarce, we sought to investigate the relationships between benthic characteristics with the presence–absence and abundance of rockfishes caught in longline surveys in nearshore waters of southern British Columbia. Habitat parameters were calculated from a 20 m resolution bathymetry layer. Yelloweye and quillback were examined separately and combined with 19 other rockfish species in a species aggregate (total rockfish); occurrence data were fitted with generalized linear mixed effects models, and abundance data were fitted with zero-inflated mixed effects models. The relationship between rockfish abundance with presence–absence and slope, distance to rocky habitat, and fine bathymetric position index suggests that these species prefer rocky, steep habitat. While underwater visual observation data offer measures of visual fish habitat and abundance, longline surveys may be a more cost-effective method for large-scale studies.

Shallow-Water Habitat Mapping using Underwater Hyperspectral Imaging from an Unmanned Surface Vehicle: A Pilot Study

The impacts of human activity on coastal ecosystems are becoming increasingly evident across the world. Consequently, there is a growing need to map, monitor, and manage these regions in a sustainable manner. In this pilot study, we present what we believe to be a novel mapping technique for shallow-water seafloor habitats: Underwater hyperspectral imaging (UHI) from an unmanned surface vehicle (USV). A USV-based UHI survey was carried out in a sheltered bay close to Trondheim, Norway. In the survey, an area of 176 m2 was covered, and the depth of the surveyed area was approximately 1.5 m. UHI data were initially recorded at a 1-nm spectral resolution within the range of 380–800 nm, but this was reduced to 86 spectral bands between 400-700 nm (3.5-nm spectral resolution) during post-processing. The hyperspectral image acquisition was synchronized with navigation data from the USV, which permitted georeferencing and mosaicking of the imagery at a 0.5-cm spatial resolution. Six spectral classes, including coralline algae, the wrack Fucus serratus, green algal films, and invertebrates, were identified in the georeferenced imagery, and chosen as targets for support vector machine (SVM) classification. Based on confusion matrix analyses, the overall classification accuracy was estimated to be 89%–91%, which suggests that USV-based UHI may serve as a useful tool for high-resolution mapping of shallow-water habitats in the future.

Contrasting distribution and foraging patterns of herbivorous and detritivorous fishes across multiple habitats in a tropical seascape

Understanding drivers behind patterns of functionally important groups of fishes is crucial for successful management and conservation of tropical seascapes. Herbivorous fishes are the most prominent consumers of marine primary production which can have profound effects on reef resilience. We explored environmental variables affecting distribution and foraging patterns of herbivorous and detritivorous fish assemblages (siganids, acanthurids and parrotfish) across distinct shallow-water habitats (coral reefs, macroalgae beds and seagrass meadows) during September–November 2016 at Mafia Island, Tanzania (8°00′S, 39°41′E). We performed underwater visual census to quantify fish assemblages, measured habitat features, deployed macroalgal assays and conducted inventories of grazing scars. Multi-dimensional scaling and mixed-effects linear models were used to evaluate differences in fish assemblages and environmental variables influencing abundance and foraging patterns of fishes. Fish communities of focal functional groups differed among habitats. Abundance of herbivores and detritivores as well as relative browsing and scraping was highest on coral reefs compared to macroalgae and seagrass meadows. Adult fish were more abundant on coral reefs while juveniles were abundant in macroalgal beds. Coral cover and crustose coralline algal cover had a positive effect on the abundance of fish in coral reef areas, while macroalgal cover had a negative effect. Contrastingly, in macroalgae habitats, macroalgal cover had a positive effect on the abundance of parrotfish. These results highlight the importance of considering connectivity between macroalgal beds and coral reefs through ontogenetic shifts in habitat use by primarily microphagous parrotfish and of incorporating a range of habitats within coastal management plans.

Symbiosis and host morphological variation: Symbiodiniaceae photosynthesis in the octocoral Briareum asbestinum at ambient and elevated temperatures

Intra-species morphological variation may occur in sessile organisms, such as corals, living in different habitats. Conversely, the octocoral Briareum asbestinum exhibits both encrusting and upright branching morphologies at the same shallow water habitat, enabling studying physiological differences uncoupled from habitat variation due to depth or reef location. We investigated the mutualism between endosymbiotic dinoflagellate algae, Breviolum spp. (previously clade B Symbiodinium), and these B. asbestinum morphologies at ambient and elevated temperatures. Based on msh1 gene sequences, the host morphologies were genetically similar although they differed in protein content, polyp expansion behavior, and associated Breviolum (B19 for encrusting and B21 for branching B. asbestinum). Due to colony orientation, polyps in encrusting B. asbestinum experienced irradiance levels nearly three times higher than polyps in the branching morph, which probably contributed to the lower photochemical and light absorption efficiencies of the Breviolum in encrusting fragments. The light-limited portion of photosynthesis-irradiance curves and the intracellular chlorophyll concentrations, however, indicated that Breviolum in both morphologies were acclimated to similar internal irradiances. Encrusting B. asbestinum exhibited higher Breviolum density, areal chlorophyll a, and greater photosynthetic rates cm(-2) compared to branching B. asbestinum. Notably, elevated temperature did not cause bleaching in either morphology, as Breviolum and chlorophyll densities did not differ significantly from ambient temperature, although the two morphologies adjusted some of the measured parameters, indicating coping with the stressor. In the face of continued ocean warming, the high thermal tolerance of octocorals may reinforce the shift of Caribbean reefs from scleractinian coral to octocoral dominance.