Changes in egg buoyancy during development and its effects on the vertical distribution of anchovy eggs

Abstract

a b s t r a c tSmall pelagic fish populations exhibit reproductive strategies resulting from past natural selection pressure, by which certain traits become more or less common in a population, allowing them to adapt and become better suited to certain habitats. One such adaptation is the buoyancy of eggs, which is observed as density changes during development. This is an important issue in fisheries and modeling science, as it affects the vertical distribution of eggs and, therefore, egg transport. Recently, individual-based models for anchovies in the Mediterranean have focused on developing adequate biological algorithms to simulate realistic spatial variations of eggs and larvae. Some models that include movements of particles according to Stokes' law also assume a constant value of egg density during egg development. However, field observations show differences in the vertical distribution of eggs when egg density during development is considered. We address the problem of egg density and its vertical distribution within a biological context. In Mediterranean waters, the incubation time for anchovy eggs during peak spawning is approximately 48-70 h; during these first hours, egg density has an influence on the horizontal and vertical trajectories of eggs, as well as their routes and hatching zones. In this study, we introduce an algorithm describing the egg density of European anchovy eggs throughout development. Egg density measurements were carried out in a density gradient column (DGC). We fitted a polynomial model that estimated egg density, as a function of time from fertilization and that was dependent on temperature. Simulations to study the vertical transport of eggs in the Mediterranean were carried out using ICHTHYOP/MARS3D. The vertical distribution of pelagic eggs was determined by a set of interacting biological and physical parameters related to eggs (density, diameter) and ambient seawater (density, viscosity, turbulence), respectively. The egg buoyancy model introduced here was validated and will provide insight for the design of anchovy egg surveys, as the vertical position of the eggs in the water column during development can be inferred by the hydrographic structure of seawater.

Reproductive output traits of the simultaneous hermaphrodite <I>Serranus scriba</I> in the western Mediterranean

“…The buoyancy of the eggs released is also an important quality measure that is often ignored. Egg buoyancy and changes in buoyancy throughout egg development can have important consequences for dispersal and survival (Ospina-Álvarez et al 2012). Recently, a numerical simulation of eggs and larval dispersal in the area of study showed that large differences in the probability of remaining in the littoral zone occurred at spatial scales of 20 km (Basterretxea et al 2012).…”

Spawning of Bluefin Tuna in the Black Sea: Historical Evidence, Environmental Constraints and Population Plasticity

“…One study [44] involved capture of live eggs and transfer to different salinities for buoyancy measurements; numerical codes for these data are shown with a “T” in panels. Symbols represent different populations within following species: Cynoscion nebulosus , spotted seatrout (lab-fertilised) [69]: 1– Matagorda Bay, Texas; 2– Upper Laguna Madre, Texas; Enchelyopus cimbrius, fourbeard rockling (all eggs captured at sea): 1 =  Baltic Sea, Gotland Basin [104], 2 =  Baltic Sea, Kiel Bay (field-captured and transfered) [44], 3 =  Conception Bay, Newfoundland, Canada [105], 4 =  Placentia Bay, Newfoundland, Canada [106] with hydrographic data from [107], 5 =  Tracadie Bay offshore, Gulf of St. Lawrence, Canada [108]; Engraulis encrasicolus, anchovy, (all eggs captured at sea): 1– Bay of Biscay [109], [110]; 2– Black Sea [20], [111] with hydrographic data from [112], 3 - Gulf of Lyons [54]; 4– NW Africa-Morocco [113], 5– Po River plume, northern Adriatic Sea [114]; Gadus morhua, cod: 1– Arcto-Norwegian cod: Lofoten (lab-fertilised) [25]; 2 - eastern Baltic (lab-fertilised) [24], [26]; 3– Baltic Sea, Gotland Basin (lab-fertilised) [25], [26]); 4 and 4-T –Baltic Sea, Kiel Bay (field-captured and transferred) [44], 5– Baltic Sea, ICES SD 23 (lab-fertilised) [26], 6– Baltic Sea, ICES SD 24 (lab-fertilised) [26], 7– Baltic Sea ICES SD 25 (lab-fertilised) [26], 9– Baltic Sea, ICES SD 26 (field-captured) [104], 10– Conception Bay, Newfoundland, Canada (field-captured) [105], 11– Gulf of St. Lawrence, Canada (field-captured) [115], 12– Grand Banks, Newfoundland, Canada (field-fertilised) [116], 13– Gullmarenfjord, Kattegat, western Sweden (lab-fertilised) [26], 14 - inshore Newfoundland, Canada (lab-fertilised) [116], 15– Norwegian coastal cod (lab-fertilised) [23]; 16– Norwegian coastal cod, Helgeland, Norway (field-captured) [117], 17- Norwegian coastal cod, Øygården, Norway (field-captured) [117], 18 - Norwegian coastal cod, Porsanger, Norway (field-captured) [117]; 19– Norwegian coastal cod, Tysfjord, Norway (field-captured) [117], 20– Tracadie Bay offshore, Gulf of...…”

Floating along buoyancy levels: Dispersal and survival of western Baltic fish eggs

“…cod 97%) compared to marine cod eggs (93%), due to the increased water uptake during final oocyte maturation which is aquaporin-mediated (Thorsen et al, 1996;Craik and Harvey, 1987;Fabra et al, 2005). Recent studies on cod (Jung et al, 2012a,b;Guðmundsdóttir, 2013) and anchovy (Ospina-Álvarez et al, 2012) found egg buoyancy increasing and decreasing towards the end of the ontogenetic development, respectively. Changes in biochemical components are likely to be the main cause that accounts for decreased specific gravity towards hatching (Jung et al, 2012b).…”

“…Changes in biochemical components are likely to be the main cause that accounts for decreased specific gravity towards hatching (Jung et al, 2012b). Several studies recommended incorporating such detailed density changes into the modeling of potential drift routes (Myksvoll et al, 2011;Jung et al, 2012a,b;Ospina-Álvarez et al, 2012). For Norwegian coastal cod, such density adjustment was applied using linear models considering development time and temperature (Myksvoll et al, 2013).…”

“…For Norwegian coastal cod, such density adjustment was applied using linear models considering development time and temperature (Myksvoll et al, 2013). For anchovy eggs a polynomial model estimating egg density as a function of temperature dependent time from fertilization was suggested (Ospina-Álvarez et al, 2012).…”