Spatial and seasonal fluctuations of Ichthyoplankton assemblage in the Mediterranean coast of Morocco (Southwestern Alboran Sea)

Ichthyoplankton represent the first life stages of fish. The study of ichthyoplankton is crucial to understanding marine ecosystems and plays an important role in the management and durability of fisheries resources. During March and October of 2019, two oceanographic ichthyoplankton surveys were conducted in the Mediterranean Sea of Morocco from Tanger to Saadia by studying the horizontal structure of the ichthyoplankton species assemblage and its relation to environmental parameters. The average surface water temperature was (15.8°C in spring and 16.4°C in autumn). The fish eggs and larvae were more abundant in March than in October (21268 eggs/10m² and 14084 larvae/10m² in spring and 10094 eggs/10m² and 13796 larvae/10m²). In both seasons, fish eggs from the families Sternoptychidae and Sparidae were dominant (10101 eggs/10m² and 7527 eggs/10m² in spring and 4422 eggs/10m² and 3928 eggs/10m² in fall, respectively). However, Myctophidae larvae were the most abundant in the study area, reaching 7601 larvae/10m² in spring and 11021 larvae/10m² in autumn. The environmental parameters: temperature, salinity and chlorophyll-a (surface) seem to directly influence the spatial distribution of ichtyoplancton. On the other hand, it seems that predation by jellyfish (Pelagia noctiluca)was a very important factor that added to the factors that influenced the distribution of the species of fish eggs and larvae. This work represents the first survey conducted in the southwestern Alboran Sea, which studies the horizontal structure of the ichthyoplankton species assemblage and its relation to environmental factors in the spring and autumn of 2019

Mortality of early life stages of European pilchard Sardina pilchardus along the Atlantic Coast of Northwest Africa (22°30'N-26°N)

The purpose of this study was to estimate the natural mortality of embryonic and larval stages of European pilchard Sardina pilchardus along the Atlantic Coast of Northwest Africa between Cape Barbas (22°30'N) and Cape Bojador (26°N) during November 2007. Using planktonic data that were fitted to an exponential model, sardine eggs hourly mortality rate (Z) was estimated in 0.07 (per hour) corresponding to 83.5% of daily mortality rate. On the other hand, for sardine larvae, Z was estimated in 0.01 (per hour), corresponding to a daily mortality rate of 21.4%. Southward and offshore transport can be considered as causes of variability in drifting scenario and survival condition of sardine larvae. Additional analyses of time series of the early life history data of sardines and future adaptive monitoring should be conducted to better manage sardine fisheries in Morocco.El objetivo de este estudio fue estimar la mortalidad natural en los estados embrionarios y larvales de la sardina europea Sardina pilchardus a largo de la Costa Atlántica del Noroeste de África entre el Cabo Barbas (22°30'N) y el Cabo Bojador (26°N) durante noviembre de 2007. Se utilizaron datos planctónicos seleccionados de un estudio realizado en noviembre 2007 y ajustados a un modelo exponencial; el índice de mortalidad de huevos de sardina (Z) fue estimado en 0,07 (por hora), siendo el índice de mortalidad diario del 83,5%. Por otra parte, para larvas de sardina, Z fue estimada en 0,1 (por hora), correspondiente a un índice de mortalidad diario igual al 21,4%. Migraciones hacia el sur y costa afuera pueden ser consideradas como una causa de la variabilidad en la deriva y condiciones de sobrevivencia de larvas de sardina. Análisis adicionales de serie de tiempo de las primeras etapas del ciclo vital de las sardinas y la futura supervisión con programas de monitoreo adaptativo deberían ser conducidos para un mejor manejo de la industria pesquera de esta especie en Marruecos

Comparison and Validation of Ichthyoplankton DNA Extraction Methods

Ichthyoplankton is the cluster of planktonic organisms that consists of fish eggs and larvae. These planktonic stages belong to the temporary zooplankton, representing future exploitable stocks. The study of the early ontogenesis of fish plays a key role in the understanding and evaluation of these populations through the study of their abundance and their spatio-temporal distribution. To better understand and protect these fisheries resources, it is essential to identify the different stages of fish embryonic development. This identification is usually performed using the classical method, based on morphological criteria under a binocular magnifying glass; however, this methodology is not always sufficient and is time consuming and, therefore, it is necessary to rely increasingly on molecular tools. The major problem with these tools is the yield and quality of the nucleic acids extracted from ichthyoplankton, especially in the case of eggs, which are small. Several methods have been used for DNA extraction from ichthyoplankton, either automated or manual, but very often from larvae or adults. In the present work, five fish egg DNA extraction protocols were compared based on their DNA yield and extraction quality, verified by agarose gel electrophoresis and quantitative PCR amplification. The results showed that extraction by our heat-protocol for direct PCR (Hp-dPCR) presents the simplest and cheapest protocol of all the kits used in this study, providing a sufficient quantity and quality of nucleic acids to be used for PCR amplification, and being within the reach of third world laboratories that often do not have sufficiently large budgets to obtain automated kits

Short-term variation of zooplankton community in Cintra Bay (Northwest Africa)

Summary: This is the first study that describes the spatial-temporal distributions of the zooplankton community and potential control factors in Cintra Bay. Zooplankton were sampled using a bongo net, 150 μm mesh size, during two surveys, in autumn 2015 and spring 2016, extending from the coast to the open sea. Fourteen zooplankton groups were identified, where copepods represented 49.1% and 92.5% of the total abundance in autumn 2015 and spring 2016, respectively. Tintinnids accounted for 39.7% and 4.7%, respectively. The total zooplankton abundance was higher in autumn (55 992 ind m−3) than in spring (2123 ind m−3). Nineteen species of copepods, belonging to 14 families, were identified. Euterpina acutifrons and Oithona nana were the most common and abundant species. The Acartiids were represented by three species (Acartia clausi, A. tonsa and A. bifilosa) in autumn and one species in spring (A. clausi). The copepods diversity was significantly different between the two seasons showing high values at the entrance and the center of the bay in autumn 2015 and in the southern half of the bay in spring 2016. The copepod structure was characterized by 13 species at different degrees of contribution in autumn 2015. In spring 2016, only four species qualified as indicator species although their contribution was not significant. Given its large opening on the ocean, Cintra Bay benefits largely from the conditions of the oceanic environment, particularly the upwelling. This situation is likely to have an impact on the spatiotemporal variability of the composition and distribution of zooplankton, especially the copepods. Keywords: Cintra Bay, Zooplankton, Copepods, Diversity indices, Environmental parameter