Population growth involves demographic bottlenecks that regulate recruitment success during various early life-history stages. The success of each early life-history stage can vary in response to population density, interacting with intrinsic (e.g. behavioural) and environmental (e.g. competition, predation) factors. Here, we used the common reef-building coral Acropora millepora to investigate how density-dependence influences larval survival and settlement in laboratory experiments that isolated intrinsic effects, and post-settlement survival in a field experiment that examined interactions with environmental factors. Larval survival was exceptionally high (greater than 80%) and density-independent from 2.5 to 12 days following spawning. By contrast, there was a weak positive effect of larval density on settlement, driven by gregarious behaviour at the highest density. When larval supply was saturated, settlement was three times higher in crevices compared with exposed microhabitats, but a negative relationship between settler density and post-settlement survival in crevices and density-independent survival on exposed surfaces resulted in similar recruit densities just one month following settlement. Moreover, a negative relationship was found between turf algae and settler survival in crevices, whereas gregarious settlement improved settler survival on exposed surfaces. Overall, our findings reveal divergent responses by coral larvae and newly settled recruits to density-dependent regulation, mediated by intrinsic and environmental interactions.

Settlement of invertebrates is a key process affecting the structure of marine communities and underpins the ability of benthic ecosystems to recover from disturbance. While it is known that specific crustose coralline algae (CCA) are important for settlement of some coral species, the role of algal chemical compounds versus surface microbial biofilms has long been ambiguous. Using a model system - a CCA of a genus that has been shown to induce high levels of settlement of Acropora corals (Titanoderma cf. tessellatum) and an abundant coral species (Acropora millepora)- we show that chemical effects of CCA are stronger than those from CCA surface microbial biofilms as drivers of coral settlement. Biofilms contributed to some extent to larval settlement via synergistic effects, where microbial cues were dependent on the CCA primary metabolism (production of dissolved organic carbon). We propose that optimal coral settlement is caused by complex biochemical communications among CCA, their epiphytic microbial community and coral larvae.

Crustose coralline algae (CCA), a group of calcifying red algae found commonly in benthic marine ecosystems worldwide, perform essential ecological functions on coral reefs, including creating benthic substrate, stabilizing the reef structure and inducing coral settlement. An important feature of CCA is the ability to keep their surfaces free of epiphytic algae, thereby reducing algal overgrowth and allowing them access to light. However, the mechanisms by which CCA prevent settlement of opportunistic seaweeds (fleshy macroalgae) are not fully understood, nor is whether these mechanisms vary among CCA species. In our study based on the Great Barrier Reef, we demonstrate that three common CCA species (Titanoderma pustulatum, Porolithon onkodes and Neogoniolithon sp.) have a remarkable ability to deter settlement of seaweed spores. We provide experimental evidence that the CCA use allelopathy and microbial inhibition against the settlement of spores of the brown seaweed Padina boergesenii. Methanol extracts of allelopathic compounds from T. pustulatum, Po. onkodes and Neogoniolithon sp. significantly reduced the settlement of Pa. boergesenii spores by 4.3 times, 3.0 and 3.8 times, respectively. Further, we found that microbial biofilms, while having a lower inhibitory effect than allelopathic compounds, also reduced seaweed settlement of Pa. boergesenii. Our study demonstrates that allelopathy and microbial inhibition, in addition to epithallial tissue sloughing, are mechanisms employed by CCA to prevent the settlement of epiphytic algae. Understanding the mechanisms by which CCA avoid seaweed overgrowth contributes to our understanding of the dynamics of seaweed proliferations on reefs and to the ecological knowledge of this important group of reefbuilding organisms.

No abstract

This is the first report of the presence of Penaeus monodon off the Guajira Peninsula in the Colombian Caribbean. Three specimens were collected near Cabo de la Vela and one in Punta Gallinas at the continental shelf, while trawling for shrimps.

Brachyura crustaceans composition and structure assemblage along be continental shelf of La Guajira and its variation according to depth gradient and sediment characteristics were determined. 44 bottom drag samples were taken at 10 and 50 m depth using a semi globe demersal net, during March and April 2005. 83 species belonging to 21 families were identified; the most important families due to their abundance of specimens and amount of species were Goneplacidae, Portunidae, and Mithracidae; and dominant species were Glyptoplax smithii, with, 12.53 % of total abundance; Portunus spinicarpus, 7.42 % and Nemausa cornuta, 6.84 %. The non-metric multidimensional scaling analysis (NMDS) did not show any well defined sampling station clusters, but meaningful statistical differences were found in the assemblage structure according to depth gradient and the different kinds of sediments. The ANOSIM tests and the ordination analysis (NMDS) pointed out that there is a single assemblage that varies gradually with depth, and to a lesser degree by physical sediments characteristics. The ordination (NMDS) also reveals that the assemblage is more heterogeneous at 10 m than at 50 m depth, possibly as a result of the larger environmental variability close to the coast, in comparison with the environmental stability that characterizes deeper zones.

Positive feedbacks driving habitat-forming species recovery and population growth are often lost as ecosystems degrade. For such systems, identifying mechanisms that limit the re-establishment of critical positive feedbacks is key to facilitating recovery. Theory predicts the primary drivers limiting system

Abstract. Introduction: Rehabilitation of hermatypic coral species that have declined in the Caribbean in recent decades is a priority. Production of sexual recruits is considered the best restoration method to aid affected populations. Objective: To gain knowledge of early life stages of Orbicella faveolata and to enhance production of new sexual recruits. Methods: Gamete bundles from the coral species O. faveolata were collected over three years (2016, 2018, and 2019) from Los Corales del Rosario y de San Bernardo Natural National Park, Cartagena, Colombia. Assisted fertilization, larval rearing, settlement (onto crustose coralline algae, CCA) and post settlement survival in laboratory conditions were monitored. Results: Embryonic and larval development were documented over 55 hours after the first cleavage, when larvae were fully developed and started pre-settlement behavior. Settlement began 7 days after first cleavage and after 37 days polyps had acquired zooxanthellae. Larval settlement was higher on Lythophyllum congestum and Titanoderma prototypum than in response to Porolithon pachydermum, Neogoniolithon sp., Hydrolithon sp., and Lythophyllum sp. Larvae did not settle on dead coral or on the negative control (sterilized seawater). After the first week post settlement survival was 59 % amongst O. faveolata recruits. During the second week, survival dropped to 42 %, and was further reduced to 0 % at the end of the third week. Conclusions: O. faveolata larvae require cues from certain CCA species to settle, they do not settle in absence of CCA. Increased larvae availability is possible through assisted fertilization in the laboratory, however, due to the high mortality in early post-settlement phases, additional research needs to be conducted in order to scale up larvae production and improve understanding of the cues that enhance settlement and the factors which cause post-settlement mortality.