Reef fish larval dispersal and population connectivity along a windward coastline

- Chelsie Counsell*, RR Coleman, SS Lal, MA McManus, M Hixon, & MJ Donahue - 

Many marine organisms have a biphasic life cycle, in which relatively sedentary benthic adults spawn pelagic larvae with high dispersal potential. This dispersal phase poses challenges for understanding the spatial ecology of marine organisms because the existence and strength of connections between local populations are difficult to observe. In this study, we investigate the connectivity of a commonly fished species in Hawai‘i, the convict surgeonfish (Acanthurus triostegus), by combining insights from ecological surveys, a particle tracking model, and genetic parentage analyses. Ecological surveys showed a higher relative abundance of juvenile A. triostegus along the windward coast of O‘ahu, Hawai'i, with the highest abundance within Kāneʻohe Bay. With a focus on this region, we employed a coupled physical-particle tracking model to simulate the transport of A. triostegus larvae in 2014 and 2015. Most of the explained variation in settlement success was accounted for by the location of larval release. The importance of spatial differences along the study region was also clear when considering the spatial distribution of where virtual larvae settled. We found that Kāneʻohe Bay acts as an effective partial retention zone, with larvae released within or entering the bay having a much higher chance of successful settlement. Simulations of virtual larvae predict high connectivity for habitats within Kāneʻohe Bay. Parentage analyses confirmed self-seeding of A. triostegus within Kāneʻohe Bay, as well as recruitment into Kāneʻohe Bay from sites along the windward coast.

Spatial and functional analysis of the fish communities of Cayo Arcas Reef, Banco de Campeche

- Enrique Nunez* & Claira Coello-Rondón - 

Cayo Arcas is a semi-isolated small reef located ca150 km from land in southern Gulf of Mexico. The objective of the study was to describe the ecological composition of fish communities, emphasizing functional aspects that explain the formation of ensamblages and co-occurrence networks of fish species. Fishes were counted and species identified along four transects, 50m long by 2m width, at each of six survey sites distributed on leeward and windward of the reef. Sixty species were registered with an average density of 1.5 ind/m2 and a mean diversity of 1.6 per site. Ward´s clustering analysis conducted over a Bray-Curtis dissimilarity matrix showed the formation of two groups of sites, sites 2, 3 and 5 exhibited the highest similarity, while sites 1 and 4 formed a group clearly dissimilar. Fish trophic structure was dominated by the category of big invertebrate feeders in terms of the number of species and by zooplankton feeders in terms of number of individuals. The co-occurrence network analysis show four main assemblages of fishes formed in terms of the relative abundance and frequency: i) typical reef residents, ii) middle size snappers and groupers, iii) low specificity species and iv) rare and lonely. Some of the representative species of the fists group were the parrotfishes (Scarus iserti, S. Taeniopteurs, S. vetula, Sparisoma aurofrenatum and S. viride), damselfishes (Stegastes planifrons, S. partitus and S. variabilis) and wrasses (Halichoeres maculipinna and Thalassoma bifasciatum). The procedure to find indicator species shows that Haemulon flavolineatum, Scarus taeniopterus and Stegastes planifrons were those with higher values as indicator species, which means that those fish species are characteristic of a living community on the surveyed sites and could be used to monitor changes in ecological variables or to help explaining biotic interactions among species at fine scale

A curious case of host preference by the generalist alien brittle star Ophiothela mirabilis in a coral reef in northeastern Brazil

- Ligia Salgado Bechara*, Thainá dos Santos S Araujo, Emiliano N Calderon, & Carlos AM Barboza - 

Ophiothela mirabilis is an alien species from the eastern Pacific, which recently colonized reefs along almost the entire south west Atlantic coast. By the number of host species reported, particularly sponges, O. mirabilis is considered a classic case of a generalist species in relation to its host. Herein we reported the first study of spatial distribution and host preference by O. mirabilis in a coral reef. Surveys occurred during February 2019 at a marine protected area in the northeastern coast, Recife de Fora Marine Park (RFMP). Seven reef locations were surveyed by scuba diving using three transects of 20 m X 2 m at depths between 1,5 m and 7,0 m. All host species were identified. Unexpected, O. mirablis was associated only to octocoral species: Phyllogorgia dilatata, Muriceopsis sulphurea, Leptogorgia punicea, Heterogorgia uatumani, Muricea flamma, Plexaurella grandiflora, Plexaurella regia. The latter three are new reports. Proportions of colonies of the most three common octocoral species hosted by O. mirabilis, M. sulphurea, P. dilatata and P. regia, were recorded. Macrofauna associated to 15 colonies of the octocoral M. sulphurea, the most common hosted species, was sampled. From 12 species of octocorals hosts species reported for the Atlantic coast, four occur in studied area but only two hosted by O. mirabilis. Despite the high diversity of sponges in the RFMP no host species was reported. Proportion of hosted colonies varied between and within locations, suggesting a patchy distribution. O. mirabilis comprised 0.87 (± 0.30) of the associated fauna of M. sulphurea, revealing significant changes in the reef associated species at a decadal scale. Our data suggests that a generalist pattern of hosts by of one of the most common alien species of the Atlantic reefs is not a rule and can be related to reef community structure.