growth rate, otolith growth rate, as well as RNA, DNA, and protein content at a
given age were comparatively higher in larvae collected in the NW Mediterranean
coast (Ebro Delta). From the somatic point of view, the NW Mediterranean sardine
grew faster in body size in comparison to the Alboran Sea larvae which tended to
distribute body mass increase by means of increasing body weight, suggesting in the
latter that growth tends to build up body reserves possibly due to their dependence
on intermittent pulses of productivity caused by wind-induced upwelling.
The NW Mediterranean sardine is exposed to differentiated environmental
drivers prompting productivity, principally the Ebro river outflow that induces
hydrographic frontal structures and the upwelling resulting from the Northern
Current flow along the Catalonian coastline (Palomera et al. 2007). Therefore,
these differences in growth rates and biochemical indices were attributed to a higher
microzooplankton abundance in the NW Mediterranean, particularly in areas close
to the Ebro Delta. According to previous studies, the higher abundance of
microzooplankton in the closest areas to the Ebro Delta could also explain to some
extent the differences in nutritional condition and growth rates found in anchovy
larvae from different spawning sites located in the NW Mediterranean (García et al.
1998), although in the south of the Ebro river outlet, microzooplankton biomass has
been reported to be much lower (García et al. 2006a, b). A previous study of
Palomera and Lleonart (1989) larval mortality revealed differences between the
northern and southern spawning sites in agreement with the former study of García
et al. (1998) whereby greater growth rates were observed in the northern spawning
site, within the surroundings of the highly productive Gulf of Lions.
It is interesting to also highlight the existence of differences in the biochemical
composition of sardine larvae between different areas of the Alboran Sea. García
et al. (2006a, b) reported that sardine larvae from the Almeria Bay presented higher
carbohydrate content than sardine collected in the Malaga Bay. These differences in
carbohydrate content could not be explained by differences in microzooplankton
abundance or composition. Quite to the contrary, microzooplankton from the
Almeria Bay presented higher protein content which was not reflected in different
larval protein content. Based on these results, García et al. (2006a, b) suggested that
larvae in the Almeria Bay could feed on other preys with higher carbohydrate
content. It has been reported that sardine larvae feed actively on copepods eggs,
nauplii, and copepodites, these accounting for 78–89% of the gut content (Conway
et al. 1994; Yebra et al. 2019). However, there are also studies reporting passive
feeding of clupeid fish larvae, including sardine, on phytoplankton (Lasker 1978;
Walsh et al. 1980; Rasoanarivo et al. 1991).
Carbohydrate content of phytoplankton ranges from 14.1 to 55.8%, while protein
content seems to be more stable ranging from 50.7 to 34.1%, (Ríos et al. 1998). In
the case of zooplankton, the main constituents are proteins followed by lipids and
carbohydrates (Jo et al. 2018; Jagadeesan et al. 2010). The inclusion of phytoplankton in the diet of sardine larvae from the Almeria Bay would explain their high
carbohydrate content (García et al. 2006a, b; Mercado et al. 2007). From such
findings, we can be likewise infer that the quality of feeding resources may be as
important as the abundance of trophic resources.
506
A. García et al.
given age were comparatively higher in larvae collected in the NW Mediterranean
coast (Ebro Delta). From the somatic point of view, the NW Mediterranean sardine
grew faster in body size in comparison to the Alboran Sea larvae which tended to
distribute body mass increase by means of increasing body weight, suggesting in the
latter that growth tends to build up body reserves possibly due to their dependence
on intermittent pulses of productivity caused by wind-induced upwelling.
The NW Mediterranean sardine is exposed to differentiated environmental
drivers prompting productivity, principally the Ebro river outflow that induces
hydrographic frontal structures and the upwelling resulting from the Northern
Current flow along the Catalonian coastline (Palomera et al. 2007). Therefore,
these differences in growth rates and biochemical indices were attributed to a higher
microzooplankton abundance in the NW Mediterranean, particularly in areas close
to the Ebro Delta. According to previous studies, the higher abundance of
microzooplankton in the closest areas to the Ebro Delta could also explain to some
extent the differences in nutritional condition and growth rates found in anchovy
larvae from different spawning sites located in the NW Mediterranean (García et al.
1998), although in the south of the Ebro river outlet, microzooplankton biomass has
been reported to be much lower (García et al. 2006a, b). A previous study of
Palomera and Lleonart (1989) larval mortality revealed differences between the
northern and southern spawning sites in agreement with the former study of García
et al. (1998) whereby greater growth rates were observed in the northern spawning
site, within the surroundings of the highly productive Gulf of Lions.
It is interesting to also highlight the existence of differences in the biochemical
composition of sardine larvae between different areas of the Alboran Sea. García
et al. (2006a, b) reported that sardine larvae from the Almeria Bay presented higher
carbohydrate content than sardine collected in the Malaga Bay. These differences in
carbohydrate content could not be explained by differences in microzooplankton
abundance or composition. Quite to the contrary, microzooplankton from the
Almeria Bay presented higher protein content which was not reflected in different
larval protein content. Based on these results, García et al. (2006a, b) suggested that
larvae in the Almeria Bay could feed on other preys with higher carbohydrate
content. It has been reported that sardine larvae feed actively on copepods eggs,
nauplii, and copepodites, these accounting for 78–89% of the gut content (Conway
et al. 1994; Yebra et al. 2019). However, there are also studies reporting passive
feeding of clupeid fish larvae, including sardine, on phytoplankton (Lasker 1978;
Walsh et al. 1980; Rasoanarivo et al. 1991).
Carbohydrate content of phytoplankton ranges from 14.1 to 55.8%, while protein
content seems to be more stable ranging from 50.7 to 34.1%, (Ríos et al. 1998). In
the case of zooplankton, the main constituents are proteins followed by lipids and
carbohydrates (Jo et al. 2018; Jagadeesan et al. 2010). The inclusion of phytoplankton in the diet of sardine larvae from the Almeria Bay would explain their high
carbohydrate content (García et al. 2006a, b; Mercado et al. 2007). From such
findings, we can be likewise infer that the quality of feeding resources may be as
important as the abundance of trophic resources.
506
A. García et al.