Coastal fish assemblages reflect marine habitat connectivity and ontogenetic shifts in an estuary-bay-continental shelf gradient

Bioaccumulation of chemical elements in fish from areas affected by oil on the coast of Bahia, Brazil

In 2019, the Brazilian coast was affected by the largest oil spill in its history. We assessed the levels of chemical elements in Lutjanus synagris and Haemulon aurolienatum fish from Itacaré (least affected area), Tinharé-Boipeba (most affected area) and Madre de Deus (chronically affected area). The level of metals differed between species, tissues, life cycle phases, maturation stages and between sampled locations, indicating the influence of biological and environmental aspects on bioaccumulation. Only fish in Madre de Deus showed lead contamination, while arsenic concentrations in the three areas exceeded the maximum value acceptable by Anvisa (National Health Surveillance Agency). It is suggested that the oil spill may have impacted species differently, also having an impact in fish from less affected areas. However, metal concentrations in fish in Madre de Deus stood out when compared to populations in other studied areas.

Daily age, growth rate, and pelagic larval duration of commercially important snapper species in Abrolhos National Marine Park

The age and daily growth of fish are registered through the deposition of increments in their otoliths, which are concretions formed by the precipitation of substances present in the endolymphatic fluid, mainly calcium carbonate (CaCO3). Faced with the need to fill some of the gaps in the knowledge on the occurrence and duration of the initial stages of snapper species' life cycles in the Abrolhos Bank, this study aimed to describe the growth rates, age, and period of pelagic larval duration (PLD) of three snapper species during the larval pre-settlement phase, in the Abrolhos Bank region. The post-larvae were captured using light traps. Otoliths were removed from 117 samples of snapper species; however, only 69 were viable for age estimation, of which 15 were Lutjanus analis, 25 were Lutjanus jocu, and 29 were Lutjanus synagris. Together, the samples presented individuals with total lengths ranging from 16.14 to 24.76 mm and ages from 21 to 39 days. Settlement marks were found for all three species, and the average PLD was ~25 days. The somatic growth of the snapper species was positively correlated with otolith growth. L. jocu presented the greatest daily growth compared to the other species. The three species use the Abrolhos Bank as a larval settlement site, demonstrating plasticity by using different habitats throughout their lives.

Catch assemblages in the small-scale trap fishery with relation to hydrographic features of a tropical bay in the Gulf of Thailand

Catches from the small-scale trap fishery in Bandon Bay, Suratthani, Thailand, were monitored from 14 sites around the Bay, then disturbance to aquatic communities and catch assemblage were examined. At the same time, the hydrographical features of the bay were surveyed. The study was conducted throughout 2019 except in December, when a tropical cyclone made sampling impossible. In total, 17,373 animals from 118 species or species groups of aquatic animals were collected. The main target of the fishery, blue swimming crab Portunus pelagicus, contributed about 10% of the total catch in terms of number; meanwhile, another crab, Charybdis affinis, was the most dominant species (41% of total). W-statistics of Abundance-Biomass Comparison curves ranged between -0.025 and 0.031, indicating light disturbance to the communities in this fishing ground. The catch assemblage, based on number in catch composition, were divided into three main clusters and six sub-clusters by using the self-organizing map (SOM) technique. The SOM results showed that the catch assemblages differed based largely on temporal variation. The hydrographic features of Bandon Bay at times exhibited a layered structure and had strong spatial variation. The bay's current system was governed by motion of tidal currents; meanwhile, the circulation was governed by monsoonal wind and freshwater discharges. Tidal current was strong and ranged between approximately 0.6 m to 2.2 m. Water within the bay was always warmer than the outer sea. High water temperature was observed two times during the year: during monsoon transition 1 (April to May) and transition 2 (October). Salinity showed great spatial and temporal variation, differing by more than 5-10 ppt horizontally. It was possible to use these dynamic hydrological features of Bandon Bay to explain assemblage patterns of the trap-net catches.

Incised valleys drive distinctive oceanographic processes and biological assemblages within rhodolith beds

Continental shelves encompass gently sloped seascapes that are highly productive and intensively exploited for natural resources. Islands, reefs and other emergent or quasi-emergent features punctuate these shallow (<100 m) seascapes and are well known drivers of increased biomass and biodiversity, as well as predictors of fishing and other human uses. On the other hand, relict mesoscale geomorphological features that do not represent navigation hazards, such as incised valleys (IVs), remain poorly charted. Consequently, their role in biophysical processes remains poorly assessed and sampled. Incised valleys are common within rhodolith beds (RBs), the most extensive benthic habitat along the tropical and subtropical portions of the mid and outer Brazilian shelf. Here, we report on a multi-proxy assessment carried out in a tropical-subtropical transition region (~20°S) off Eastern Brazil, contrasting physicochemical and biological variables in IVs and adjacent RBs. Valleys interfere in near bottom circulation and function as conduits for water and propagules from the slope up to the mid shelf. In addition, they provide a stable and structurally complex habitat for black corals and gorgonians that usually occur in deeper water, contrasting sharply with the algae-dominated RB. Fish richness, abundance and biomass were also higher in the IVs, with small planktivores and large-bodied, commercially important species (e.g. groupers, snappers and grunts) presenting smaller abundances or being absent from RBs. Overall, IVs are unique and vulnerable habitats that sustain diverse assemblages and important ecosystem processes. As new IVs are detected by remote sensing or bathymetric surveys, they can be incorporated into regional marine management plans as conservation targets and priority sites for detailed in situ surveys.

Geographic variation in the life history of lane snapper Lutjanus synagris, with new insights from the warm edge of its distribution

Research on life-history variations in widely distributed fish species is needed to understand global warming impacts on populations and to improve fisheries management advice. The lane snapper Lutjanus synagris (Linnaeus, 1758) is commercially important to fisheries in the Western Central Atlantic, where spread information on its life-history traits is available. We studied growth, age, reproduction and mortality of lane snapper in the Guatemalan Caribbean, the warmest part of its distribution range, and collated the new information with published data in a latitudinal analysis extending between 18°S and 30°N. Longevity was estimated at 11 years, and von Bertalanffy growth parameters were asymptotic length (Linf) 45.6 and 42.2 cm for females and males, respectively, the growth coefficient (K) was 0.1 year-1 and the theoretical age at zero length (t0 ) was -4.4 years. Lane snapper grew slowest in April, prior to the rainy season, and at the onset of the reproductive season, which lasted from May to October. Fifty percent of female and male lane snappers matured at 23 and 17 cm, corresponding to 3.5 and 2.4 years of age respectively. A regional multivariate analysis found seawater temperature to be an important driver of life-history variation. Lane snapper lifespan was shorter at the warm edge of its distribution range, and maximum size and peak reproductive investment were negatively related to sea surface temperature. The trade-offs in lane snapper life-history traits and phenology likely enhance its fitness to differing environments. Interpolation from the present regional estimates to less-studied regions of the Caribbean is useful for preliminary understanding of reaction norms and harvest potentials.

Assessing the influence of sewage outfalls on seagrass meadows using nitrogen isotopes

Untreated sewage discharged increases the nutrient loads and changes ecosystem functions. It increases the values of the nitrogen isotopic signature (δ15N) of primary producers such as seagrasses. Itaparica Island (Bahia, Brazil) has undergone extensive urbanization over 50 years. Most of the island has no sewage treatment, and a bridge's construction could increase its population ten times. We evaluated the effects of sewage inputs on the δ15N of seagrass (Halodule wrightii) across Itaparica Island in 14 areas of the island with different degrees of urbanization. Average values of δ15N ranged from -3.95 ‰ (±1.04 SD) to 2.73 ‰ (±1.61). The highest human occupation site also has the highest mean value of δ15N, and seagrass shoot density. The significant correlation (p < 0.05) between δ15N values and shoot density may indicate a possible anthropogenic pressure impacting meadow abundance. Despite a positive correlation, increased anthropogenic nutrient supply can support algae growth and harm seagrass ecosystems.

Fine-scale variation in the proximity of baited remote underwater video stations (BRUVS) to rocky reefs reveals changes in the structure of temperate fish assemblages

We investigated changes in the structure of coastal fish assemblages in Northern Patagonia, Southwestern Atlantic, by using baited remote underwater video stations (BRUVS) deployed at increasing distances from rocky reefs: 0-5 m, 15-20 m and 50-60 m. We estimated species richness and abundance (total and by preferred habitat type) and searched for diagnostic species in each distance range. We recorded 14 taxa across 11 families in 19 areas surveyed. Species richness and abundance were higher on reef ledges and decreased with distance from them, at a finer spatial scale than previously reported. Acanthistius patachonicus and Sebastes oculatus were indicative of reef ledges; they were less abundant at 15-20 m and disappeared at 50-60 m. Callorinchus callorynchus and Odontesthes spp. occurred only at distances >15-20 m from the reefs, while Galeorhinus galeus was distributed homogeneously throughout the surveyed area. Our findings have practical implications for monitoring ecotone demersal habitats with BRUVS.

Does environmental heterogeneity explain β diversity of estuarine fish assemblages? Example from a tropical estuary under the influence of a semiarid climate, Brazil

Estuarine fish assemblages are often sensitive to environmental conditions, because fluctuation in physico-chemical conditions at different spatial and seasonal scales can directly influence species distributions. In this way, we conducted a field survey to investigate the role of estuarine gradient (environmental heterogeneity) in fish α and β diversity. The study was carried out in three zones in Mamanguape River estuary according to salinity and geomorphology features during an atypical climatic event in 2015. In total, 18,084 specimens of 125 species were captured. Additive partitioning of diversity analysis detected a higher proportion of beta diversity among estuarine zones during the rainy (β₃ = 58.6%) and dry season (β₃ = 40.94%) and were higher than expected by chance (Prop_{exp> obs} <0.001). Decomposing β-diversity analysis showed that total β-diversity (β_sor) results were more dominated by species turnover (β_sim) than nestedness (β_nes) in both seasons. Forward selection procedure and db-RDA identified salinity, coarse sand and chlorophyll-a as the main environmental variables influencing β_sor and site distance from estuary mouth and split as the main landscape variables. Variation partitioning analysis revealed more contribution to the pure fraction of environmental variables to fish species turnover, however, both pure fraction of environmental and landscape variables significantly contributed to β_sim. Our study highlighted the importance to environmental heterogeneity and connectivity to promote fish diversity across the Mamanguape River estuary. Thus, future conservation policies should focus on maintaining these two components to guarantee its nursery ground role to estuarine fish assemblages.

Marine food web perspective to fisheries-induced evolution

Fisheries exploitation can cause genetic changes in heritable traits of targeted stocks. The direction of selective pressure forced by harvest acts typically in reverse to natural selection and selects for explicit life histories, usually for younger and smaller spawners with deprived spawning potential. While the consequences that such selection might have on the population dynamics of a single species are well emphasized, we are just beginning to perceive the variety and severity of its propagating effects within the entire marine food webs and ecosystems. Here, we highlight the potential pathways in which fisheries-induced evolution, driven by size-selective fishing, might resonate through globally connected systems. We look at: (i) how a size truncation may induce shifts in ecological niches of harvested species, (ii) how a changed maturation schedule might affect the spawning potential and biomass flow, (iii) how changes in life histories can initiate trophic cascades, (iv) how the role of apex predators may be shifting and (v) whether fisheries-induced evolution could codrive species to depletion and biodiversity loss. Globally increasing effective fishing effort and the uncertain reversibility of eco-evolutionary change induced by fisheries necessitate further research, discussion and precautionary action considering the impacts of fisheries-induced evolution within marine food webs.

Radiocarbon in otoliths of tropical marine fishes: Reference Δ14C chronology for north Caribbean waters

Reef fishes support important fisheries throughout the Caribbean, but a combination of factors in the tropics makes otolith microstructure difficult to interpret for age estimation. Therefore, validation of ageing methods, via application of Δ¹⁴C is a major research priority. Utilizing known-age otolith material from north Caribbean fishes, we determined that a distinct regional Δ¹⁴C chronology exists, differing from coral-based chronologies compiled for ageing validation from a wide-ranging area of the Atlantic and from an otolith-based chronology from the Gulf of Mexico. Our north Caribbean Δ¹⁴C chronology established a decline series with narrow prediction intervals that proved successful in ageing validation of three economically important reef fish species. In examining why our north Caribbean Δ¹⁴C chronology differed from some of the coral-based Δ¹⁴C data reported from the region, we determined differences among study objectives and research design impact Δ¹⁴C temporal relationships. This resulted in establishing the first of three important considerations relevant to applying Δ¹⁴C chronologies for ageing validation: 1) evaluation of the applicability of original goal/objectives and study design of potential Δ¹⁴C reference studies. Next, we determined differences between our Δ¹⁴C chronology and those from Florida and the Gulf of Mexico were explained by differences in regional patterns of oceanic upwelling, resulting in the second consideration for future validation work: 2) evaluation of the applicability of Δ¹⁴C reference data to the region/location where fish samples were obtained. Lastly, we emphasize the application of our north Caribbean Δ¹⁴C chronology should be limited to ageing validation studies of fishes from this region known to inhabit shallow water coral habitat as juveniles. Thus, we note the final consideration to strengthen findings of future age validation studies: 3) use of Δ¹⁴C analysis for age validation should be limited to species whose juvenile habitat is known to reflect the regional Δ¹⁴C reference chronology.

Evaluation of metal contamination in mangrove ecosystems near oil refining areas using chemometric tools and geochemical indexes

The northern and northeastern portion of the Todos os Santos Bay (TSB) is known for the presence of an oil refinery in addition to the development of other activities with significant potential for impact on the environment. 30 samples of superficial mangrove sediment were collected in two different locations: on the banks of the São Paulo River near the Landulpho Alves Mataripe Refinery (RLAM) and at Caboto Beach, a place that was once a control point in studies of metal pollution. After the determination of potentially toxic elements (Al, As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V, Zn), the quality of the sediment was evaluated using the concentrations of these elements associated with geochemical parameters (TOC, P, S, and granulometry). In this way, the pollution indexes (EF, I_geo, P_N) were calculated in addition to the comparison with the guide values for the sediment quality (TEL, PEL, ERL, ERM). Among the elements analyzed, Cu also showed levels (92.71-97.54 mg kg^-1) very close to PEL (108 mg kg^-1). At 13 sampling points, Cr concentrations were higher (56.16-66.01 mg kg^-1) than TEL (52.3 mg kg^-1). Ba showed significant concentrations in 6 samples collected on the São Paulo River, a region close to the oil refining area. The enrichment factor (EF) showed that most elements did not show enrichment, except for Zn. Through Igeo there was a tendency towards serious pollution of Ba, Cu, and Zn; moderately polluted by Cr. Principal component analysis (PCA) and Spearman's classification showed a correlation greater than 70% between the variables. According to Nemerow Synthetic Pollution (P_N), both areas are polluted by Al, Ba, Cr, Cu, Fe, Mn, Ni, Ti, V, and Zn.

Bioaccumulation of Per- and polyfluoroalkyl substances (PFASs) in a tropical estuarine food web

The biomagnification of per- and polyfluoroalkyl substances (PFASs) was investigated in a tropical mangrove food web from an estuary in Bahia, Brazil. Samples of 44 organisms (21 taxa), along with biofilm, leaves, sediment and suspended particulate matter were analyzed. Sum (∑) PFAS concentrations in biota samples were dominated by perfluorooctane sulfonate (PFOS, 93% detection frequency in tissues; 0.05 to 1.97 ng g^-1 ww whole-body (wb)), followed by perfluorotridecanoate (PFTrDA, 57%; 0.01 to 0.28 ng g^-1 ww wb). PFOS precursors such as perfluorooctane sulfonamide (FOSA, 54%; 0.01 to 0.32 ng g^-1 ww wb) and N-ethyl perfluorooctane sulfonamide (EtFOSA; 30%; 0.01 to 0.21 ng g^-1 ww wb) were also detected. PFAS accumulation profiles revealed different routes of exposure among bivalve, crustacean and fish groups. Statistics for left-censored data were used in order to minimize bias on trophic magnification factors (TMFs) calculations. TMFs >1 were observed for PFOS (linear + branched isomers), EtFOSA (linear + branched isomers), and perfluorononanoate (PFNA), and in all cases, dissimilar accumulation patterns were observed among different trophic positions. The apparent biodilution of some long-chain PFCAs through the food chain (TMF < 1) may be due to exposure from multiple PFAS sources. This is the first study investigating bioaccumulation of PFASs in a tropical food web and provides new insight on the behavior of this ubiquitous class of contaminants.

Seagrass and rhodolith beds are important seascapes for the development of fish eggs and larvae in tropical coastal areas

In this study, the ichthyoplankton in two distinct tropical seascapes, gravelly sand with rhodolith beds (SRB) and muddy sand with seagrasses, were compared. The number of eggs was higher in the seagrass beds; however, the number of fish larvae was slightly higher in the SRB. Seagrass beds present less turbulent hydrodynamics and favor the retention of eggs and spawning. A more structured habitat provides better shelter, especially for eggs. However, as ontogeny progresses, the fish can explore areas with less shelter. This behavior was observed in this study, where the less structured SRB habitat had a high density of larvae in the later developmental stage. The dominance of earlier larval stages demonstrates a preference for more protected and less turbulent seascapes for nursery and offspring rearing. The results highlight that mapping of these seascapes (e.g., seagrass and rhodolith beds) will help to establish conservation measures to protect ecological connectivity and important tropical species.