Fine-scale behavior of red snapper (Lutjanus campechanus) around bait: approach distances, bait plume dynamics, and effective fishing area

The behavior of fish around bait is poorly understood despite it being important for the fish catching process and estimating relative abundance. We used a fine-scale acoustic positioning system to quantify the movements of 26 red snapper (Lutjanus campechanus) around 120 bait deployments in 2019 at a natural reef site (~37-m deep) in North Carolina, USA. There were 39 instances of tagged red snapper approaching bait during four baiting days, some of which approached due to apparent sensory cues (28%) while most approached incidentally (72%). Tagged red snapper approached bait from initial distances of 1 to 1 147 m (median = 27 m; mean = 86 m), and took 0 – 77 min (mean = 22 min) to approach. Fish were more likely to approach bait if they were located close to, and down-current of, the bait at deployment. Our estimated effective fishing area of 2 290 m2 (within which >50% of red snapper responded to bait) could be used along with video counts and other information to estimate densities of red snapper.

The Sea Urchin Centrostephanus Tenuispinus (Clark, 1914) is an Important Bio-Eroder on a High Latitude (32o S) Coral Reef.

Sea urchins are keystone herbivores in many marine benthic habitats. They can significantly influence coral-algae phase shifts and impact on reef carbonate budgets through grazing. Hall Bank reef in Western Australia is unique among other reefs in the region being high latitude with a high hermatypic coral cover but lacking macroalgae and soft corals. Since the reef status is thought to result from high densities of the urchin Centrostephanus tenuispinus limiting the growth of macroalgae, the present study was focused on evaluating their role as bio-eroders. Monthly samples of 26 urchins were collected from 2014–2016 and gut composition was analyzed. Gut evacuation rates were calculated using 50 urchins dissected at time intervals (0, 4, 8, 16, 24, 36, 48, 60, 72 and 96 h). Reworked calcium carbonate was calculated using 30 urchins maintained in five cages in a seagrass bed adjacent to the reef site. Mean percentages for organic component, calcium carbonate and other siliceous components were 86.29 ± 3.23%, 10.32 ± 2.76% and 3.39 ± 1.52% respectively. Gut evacuation rates for autumn, winter, spring and summer were 0.70, 0.24, 0.48 and 0.72 (day− 1). Bio-erosion rates were significantly higher in Summer-16 (3.52 g CaCO3 m− 2 day− 1) and lower in winter (1.32 g CaCO3 m− 2 day− 1) (F = 101.580, p < 0.000). High erosion rates were recorded for large urchins (F = 37.789, P < 0.001. Annual urchin bio-erosion was 1017.69 g CaCO3 m− 2 a− 1. Differences in food ingestion rates in response to seawater temperature changes are thought to be the main cause for the significant differences in seasonal bio-erosion rates.

A metagenomic-based study of two sites from the Barbadian reef system

We study the microbiome of sea water collected from two locations of the Barbadian coral reefs. The two sites differ in several environmental and ecological variables including their endogenous benthic community in addition to their proximity to urban development and runoffs from inland watersheds. The composition of the microbial community was estimated using whole genome DNA shotgun sequencing. Although both sites exhibit a similar degree of richness, the less urbanized site (Maycocks reef at Hangman’s Bay) is strongly concentrated with phototrophs. In comparison, the more urbanized location (Bellairs Research Institute) is enriched for copiotrophs, macroalgal symbionts and marine-related disease-bearing organisms from taxa scattered across the tree of life. Overall, our samples and associated measurements of chemical and environmental qualities of the water are in line with previous marine microbiome profiles of warm ocean surface waters. This suggests our approach captures salient information regarding the state of each coral reef site and sets the stage for larger longitudinal studies of coral reef dynamics in Barbados.

Predation on a newly-stocked long-spined sea urchin (Diadema antillarum) by the batwing coral crab (Carpilius corallinus) on a coral reef restoration site

This photograph documents a batwing coral crab (Carpilius corallinus) preying on the sea urchin (Diadema antillarum) on a coral reef site enhanced with artificial shelter and staghorn coral. This interaction illustrates an interaction that to be better understood to develop a restoration strategy that harnesses positive ecological processes.

Population genomics of a bioluminescent symbiosis sheds light on symbiont transmission and specificity

All organisms depend on symbiotic associations with bacteria for their success, yet the processes by which specific symbioses are established and persist remain largely undescribed. To examine the ecological mechanisms involved in maintaining symbiont specificity over host generations, we examined the population genomics of a binary symbiosis involving the coral reef cardinalfish Siphamia tubifer and the luminous bacterium Photobacterium mandapamensis. Using restriction site-associated sequencing (RAD-Seq) methods we demonstrate that the facultative symbiont of S. tubifer exhibits genetic structure at spatial scales of tens of kilometers in Okinawa, Japan in the absence of physical dispersal barriers and in contrast to the host fish. These results suggest the host’s behavioral ecology help structure symbiont populations at a reef site by symbiont enrichment, consequently fostering symbiont specificity. This approach also revealed several symbiont genes that were divergent between host populations including genes known to play a role in other host-bacteria associations.

New encrusting species of Lanceoporidae (Bryozoa, Cheilostomata) from the southern Great Barrier Reef, Australia

Three new species of lanceoporids from the southern Great Barrier Reef are described. Calyptotheca trimandibulata n. sp. is recorded from inter-reefal sites, Stephanotheca bahloo n. sp. is recorded from a coral reef site, and Stephanotheca kutyeri n. sp. is recorded from inter-reefal sites and also Bass Strait and the Great Australian Bight, and is therefore unusual amongst Australian lanceoporids in occurring in both tropical and temperate locations. The known variation in morphological characters is widened for both genera: C. trimandibulata n. sp. is the only known Calyptotheca species typically having three adventitious avicularia per zooid, S. bahloo n. sp. has the most pronounced orifice dimorphism and the most transversely oval primary orifice for the genus, and S. kutyeri n. sp. is distinguished by long, narrow, slit-like pseudopores in the frontal shield. All three species have occasional dimorphic autozooids, distinguished by larger orifices resembling those of the respective ovicellate zooids, and this is documented for the first time for both genera.

Filamentous calcareous alga provides a substrate for coral-competitive macroalgae in the degraded lagoon of Dongsha Atoll, Taiwan

BackgroundThe chemically-rich seaweed Galaxaura is not only highly competitive with corals, but also provides substrate for other macroalgae. Its ecology and associated epiphytes remain largely unexplored. To fill this knowledge gap, we herein undertook an ecological assessment to explore the spatial variation, temporal dynamics, and epiphytic macroalgae of G. divaricata on patch reefs in the lagoon of Dongsha Atoll, a shallow coral reef ecosystem in the northern South China Sea, repeatedly impacted by mass coral bleaching events.MethodsTwelve spatially independent patch reefs in the Dongsha lagoon were first surveyed to assess the benthic composition in April 2016, and then revisited to determine G. divaricata percent cover in September 2017, with one additional Galaxaura-dominated reef (site 9). Four surveys over a period of 17 months were carried out on a degraded patch reef (site 7) to assess the temporal variation in G. divaricata cover. Epiphytic macroalgae associated with G. divaricata were quantified and identified through the aid of DNA barcoding.ResultsPatch reefs in the Dongsha lagoon were degraded, exhibiting relatively low live coral cover (5-43%), but high proportions of macroalgae (13-58%) and other substrates (rubble and dead corals; 23-69%). The distribution of G. divaricata was heterogeneous across the lagoon, with highest abundance (16-41%) in the southeast area. Temporal surveys from site 7 and photo-evidence from site 9 suggested that an overgrowth by G. divaricata was still present to a similar extend after 17 months and 3.5 years. Yet, G. divaricata provides a suitable substrate some allelopathic macroalgae (e.g., Lobophora sp.).ConclusionsOur study demonstrates that an allelopathic seaweed, such as G. divaricata, can overgrow degraded coral reefs for extended periods of time. By providing habitat for harmful macroalgae, a prolonged Galaxaura overgrowth could strengthen negative feedback loops on degraded coral reefs, further decreasing their recovery potential.

Assessing health status of corals at a tropical marginal reef site through bleaching and decadal change in population parameters

Scleractinian corals are key organisms in structuring reef habitats and coral cover is being lost due to local and global stressors caused and/or exacerbated by anthropogenic activities. Despite being hardly touched upon, studies of size-frequency distributions serve as snapshots of coral populations’ status and provide information on population decline or growth over time. In our study we have intermittently monitored two Brazilian scleractinians species, the endemic Mussismilia hispida and Siderastrea stellata, since 2000 in an important coral marginal reef site at Armação dos Búzios, Rio de Janeiro, Brazil. We measured length, width and arc of all colonies from both species found across transects at eleven sites. In total, over 5,000 colonies have been measured over the past 17 years. Although the frequency of small and medium colonies remained relatively constant, we observed a clear decline in the frequency of larger colonies (> 30 cm) for both species, particularly the most common S. stellata. Additionally, we have been monitoring colonies for bleaching in five of these sites throughout 2017 to assess health status. The relationship between observed bleaching prevalence/intensity and environmental variables (temperature, light availability and sedimentation) may elucidate how changes in local conditions influence coral health.