Marine Biodiversity of Eastern Tropical Pacific Coral Reefs

Seasonal occurrence and individual variability of bull sharks, Carcharhinus leucas, in a marine reserve of the southwestern Gulf of California

Background

Studying how the bull sharks aggregate and how they can be driven by life history traits such as reproduction, prey availability, predator avoidance and social interaction in a National Park such as Cabo Pulmo, is key to understand and protect the species.

Methods

The occurrence variability of 32 bull sharks tracked with passive acoustic telemetry were investigated via a hierarchical logistic regression model, with inference conducted in a Bayesian framework, comparing sex, and their response to temperature and chlorophyll.

Results

Based on the fitted model, occurrence probability varied by sex and length. Juvenile females had the highest values, whereas adult males the lowest. A strong seasonality or day of the year was recorded, where sharks were generally absent during September-November. However, some sharks did not show the common pattern, being detected just for a short period. This is one of the first studies where the Bayesian framework is used to study passive acoustic telemetry proving the potential to be used in further studies.

Evolution and environment of Caribbean coastal ecosystems

Isolation of the Caribbean Sea from the tropical Eastern Pacific by uplift of the Isthmus of Panama in the late Pliocene was associated with major, taxonomically variable, shifts in Caribbean biotic composition, and extinction, but inferred causes of these biological changes have remained elusive. We addressed this through falsifiable hypotheses about how independently determined historical changes in oceanographic conditions may have been responsible. The most striking environmental change was a sharp decline in upwelling intensity as measured from decreases in intra-annual fluctuations in temperature and consequently in planktonic productivity. We then hypothesized three general categories of biological response based upon observed differences in natural history between the oceans today. These include changes in feeding ecology, life histories, and habitats. As expected, suspension feeders and predators became rarer as upwelling declined. However, predicted increases in benthic productivity by reef corals, and benthic algae were drawn out over more than 1 Myr as seagrass and coral reef habitats proliferated; a shift that was itself driven by declining upwelling. Similar time lags occurred for predicted shifts in reproductive life history characteristics of bivalves, gastropods, and bryozoans. Examination of the spatial variability of biotic change helps to understand the time lags. Many older species characteristic of times before environmental conditions had changed tended to hang on in progressively smaller proportions of locations until they became extinct as expected from metapopulation theory and the concept of extinction debt. Faunal turnover may not occur until a million or more years after the environmental changes ultimately responsible.

Emigration patterns of motile cryptofauna and their implications for trophic functioning in coral reefs

Patterns of movement of marine species can reflect strategies of reproduction and dispersal, species' interactions, trophodynamics, and susceptibility to change, and thus critically inform how we manage populations and ecosystems. On coral reefs, the density and diversity of metazoan taxa are greatest in dead coral and rubble, which are suggested to fuel food webs from the bottom up. Yet, biomass and secondary productivity in rubble is predominantly available in some of the smallest individuals, limiting how accessible this energy is to higher trophic levels. We address the bioavailability of motile coral reef cryptofauna based on small-scale patterns of emigration in rubble. We deployed modified RUbble Biodiversity Samplers (RUBS) and emergence traps in a shallow rubble patch at Heron Island, Great Barrier Reef, to detect community-level differences in the directional influx of motile cryptofauna under five habitat accessibility regimes. The mean density (0.13-4.5 ind cm^-3) and biomass (0.14-5.2 mg cm^-3) of cryptofauna were high and varied depending on microhabitat accessibility. Emergent zooplankton represented a distinct community (dominated by the Appendicularia and Calanoida) with the lowest density and biomass, indicating constraints on nocturnal resource availability. Mean cryptofauna density and biomass were greatest when interstitial access within rubble was blocked, driven by the rapid proliferation of small harpacticoid copepods from the rubble surface, leading to trophic simplification. Individuals with high biomass (e.g., decapods, gobies, and echinoderms) were greatest when interstitial access within rubble was unrestricted. Treatments with a closed rubble surface did not differ from those completely open, suggesting that top-down predation does not diminish rubble-derived resources. Our results show that conspecific cues and species' interactions (e.g., competition and predation) within rubble are most critical in shaping ecological outcomes within the cryptobiome. These findings have implications for prey accessibility through trophic and community size structuring in rubble, which may become increasingly relevant as benthic reef complexity shifts in the Anthropocene.

Rapid relative increase of crustose coralline algae following herbivore exclusion in a reef of El Salvador

The Eastern Tropical Pacific (ETP) is one of the most isolated and least studied regions in the world. This particularly applies to the coast of El Salvador, where the only reef between Guatemala and Nicaragua, called Los Cóbanos reef, is located. There is very little published information about the reef’s biodiversity, and to our knowledge, no research on its ecology and responses to anthropogenic impacts, such as overfishing, has been conducted. The present study, therefore, described the benthic community of Los Cóbanos reef, El Salvador, using the Line-Point-Intercept-Transect method and investigated changes in the benthic community following the exclusion of piscine macroherbivores over a period of seven weeks. Results showed high benthic algae cover (up to 98%), dominated by turf and green algae, and low coral cover (0–4%). Porites lobata was the only hermatypic coral species found during the surveys. Surprisingly, crustose coralline algae (CCA) showed a remarkable total cover increase by 58%, while turf algae cover decreased by 82%, in experimental plots after seven weeks of piscine macroherbivore exclusion. These findings apparently contradict the results of most previous similar studies. While it was not possible to ascertain the exact mechanisms leading to these drastic community changes, the most likely explanation is grazing on turf by small grazing macroherbivores that had access to the cages during the experiment and clearing of CCA initially covered by epiphytes and sediments. A higher CCA cover would promote the succesful settlement by corals and prevent further erosion of the reef framework. Therefore it is crucial to better understand algal dynamics, herbivory, and implications of overfishing at Los Cóbanos to avoid further reef deterioration. This could be achieved through video surveys of the fish community, night-time observations of the macroinvertebrate community, exclusion experiments that also keep out herbivorous macroinvertebrates, and/or experimental assessments of turf algae/CCA interactions.

Octocoral populations and connectivity in continental Ecuador and Galápagos, Eastern Pacific

Octocorals are important zoobenthic organisms, contributing to structural heterogeneity and species diversity on hardgrounds. Their persistence amidst global coral reef degradation and ocean acidification, has prompted renewed interest in this taxon. Octocoral assemblages at 52 sites in continental Ecuador and Galápagos (23 species, 3742 colonies) were examined for composition, size distributions within and among populations, and connectivity patterns based on ocean current models. Species richness varied from 1 to 14 species per site, with the richest sites on the continent. Three assemblage clusters were recognised based on species richness and population size, one with a mix of sites from the mainland and Galápagos (defined by Muricea fruticosa and Leptogorgia alba, Muricea plantaginea and Pacifigorgia darwinii), the second from Santa Elena in southern Ecuador (defined by M. plantaginea and L. alba) and the third from the northernmost sites on the continent, in Esmeraldas (defined by Muricea fruticosa, Heterogorgia hickmani, Leptogorgia manabiensis). Based on biophysical larval flow models with 30, 60, 90-day Pelagic Larval Duration, good connectivity existed along the South American mainland, and from the continent to Galápagos. Connectivity between Galápagos, Cocos, Malpelo and the Colombian mainland may explain the wide distribution of L. alba. Muricea plantaginea had the densest populations with the largest colonies and therewith was an important habitat provider both in continental Ecuador and Galápagos. Continental Ecuador harbours the most speciose populations of octocorals so far recorded in the southern Eastern Tropical Pacific (ETP). Most species were uncommon and possibly vulnerable to local extirpation. The present study may serve as a base line to determine local and regional impacts of future disturbances on ETP octocorals.

eDNA metabarcoding survey reveals fine-scale coral reef community variation across a remote, tropical island ecosystem

Environmental DNA (eDNA) metabarcoding, a technique for retrieving multispecies DNA from environmental samples, can detect a diverse array of marine species from filtered seawater samples. There is a growing potential to integrate eDNA alongside existing monitoring methods in order to establish or improve the assessment of species diversity. Remote island reefs are increasingly vulnerable to climate-related threats and as such there is a pressing need for cost-effective whole-ecosystem surveying to baseline biodiversity, study assemblage changes and ultimately develop sustainable management plans. We investigated the utility of eDNA metabarcoding as a high-resolution, multitrophic biomonitoring tool at the Cocos (Keeling) Islands, Australia (CKI)-a remote tropical coral reef atoll situated within the eastern Indian Ocean. Metabarcoding assays targeting the mitochondrial 16S rRNA and CO1 genes, as well as the 18S rRNA nuclear gene, were applied to 252 surface seawater samples collected from 42 sites within a 140 km² area. Our assays successfully detected a wide range of bony fish and elasmobranchs (244 taxa), crustaceans (88), molluscs (37) and echinoderms (7). Assemblage composition varied significantly between sites, reflecting habitat partitioning across the island ecosystem and demonstrating the localisation of eDNA signals, despite extensive tidal and oceanic movements. In addition, we document putative new occurrence records for 46 taxa and compare the efficiency of our eDNA approach to visual survey techniques at CKI. Our study demonstrates the utility of a multimarker metabarcoding approach in capturing multitrophic biodiversity across an entire coral reef atoll and sets an important baseline for ongoing monitoring and management.

Predominant east to west colonizations across major oceanic barriers: Insights into the phylogeographic history of the hydroid superfamily Plumularioidea, suggested by a mitochondrial DNA barcoding marker

We provide preliminary insights into the global phylogeographic and evolutionary patterns across species of the hydrozoan superfamily Plumularioidea (Cnidaria: Hydrozoa). We analyzed 1,114 16S sequences of 198 putative species of Plumularioidea collected worldwide. We investigated genetic connections and divergence in relation to present-day and ancient biogeographic barriers, climate changes and oceanic circulation. Geographical distributions of most species are generally more constrained than previously assumed. Some species able to raft are dispersed widely. Human-mediated dispersal explains some wide geographical ranges. Trans-Atlantic genetic connections are presently unlikely for most of the tropical-temperate species, but were probably more frequent until the Miocene-Pliocene transition, before restriction of the Tethys Sea and the Central American Seaway. Trans-Atlantic colonizations were predominantly directed westwards through (sub)tropical waters. The Azores were colonized multiple times and through different routes, mainly from the east Atlantic, at least since the Pliocene. Extant geminate clades separated by the Isthmus of Panama have predominantly Atlantic origin. Various ancient colonizations mainly directed from the Indian Ocean to the Atlantic occurred through the Tethys Sea and around South Africa in periods of lower intensity of the Benguela upwelling. Thermal tolerance, population sizes, dispersal strategies, oceanic currents, substrate preference, and land barriers are important factors for dispersal and speciation of marine hydroids.

Marine biodiversity baseline for Área de Conservación Guanacaste, Costa Rica: published records

The diversity of tropical marine organisms has not been studied as intensively as the terrestrial biota worldwide. Additionally, marine biodiversity research in the tropics lags behind other regions. The 43,000 ha Sector Marino of Área de Conservación Guanacaste (ACG, Marine Sector of Guanacaste Conservation Area), on the North Pacific coast of Costa Rica is no exception. For more than four decades, the terrestrial flora and fauna has been studied continuously. The ACG marine biodiversity was studied in the 1930's by expeditions that passed through the area, but not much until the 1990's, except for the marine turtles. In the mid 1990's the Center for Research in Marine Science and Limnology (CIMAR) of the Universidad de Costa Rica (UCR) initiated the exploration of the marine environments and organisms of ACG. In 2015, ACG, in collaboration with CIMAR, started the BioMar project whose goal is to inventory the species of the marine sector of ACG (BioMar ACG project). As a baseline, here I have compiled the published records of marine ACG species, and found that 594 marine species have been reported, representing 15.5% of the known species of the Pacific coast of Costa Rica. The most diverse groups were the crustaceans, mollusks and cnidarians comprising 71.7% of the ACG species. Some taxa, such as mangroves and fish parasites are well represented in ACG when compared to the rest of the Costa Rican coast but others appear to be greatly underrepresented, for example, red algae, polychaetes, copepods, equinoderms, and marine fishes and birds, which could be due to sampling bias. Thirty species have been originally described with specimens from ACG, and 89 species are not known from other localities on the Pacific coast of Costa Rica except ACG. Most of the sampling has been concentrated in a few localities in Sector Marino, Playa Blanca and Islas Murciélago, and in the nearby waters of Bahía Santa Elena. In an effort to fill this gap, CIMAR is collaborating with ACG and a private foundation to start an inventory of the marine organisms of the conservation area. The project will be assisted by two marine parataxonomists, and all samples will be catalogued, photographed, bar coded and voucher specimens deposited at the Museo de Zoología, UCR. All the information will be available through Internet. It is anticipated that the BioMar project will fill many of the knowledge gaps and significantly more marine species will be encountered. This project could become a viable model for marine biodiversity inventories in other Costa Rican Conservation Areas (Áreas de Conservación) and in other countries.