Influence of environmental factors on different life stages of European anchovy (Engraulis encrasicolus) and European sardine (Sardina pilchardus) from the Mediterranean Sea: A literature review

Highlights

• We reviewed the literature available on how environmental factors affect anchovy and sardine.

• The studies were heterogeneously distributed.

• The most studied variables were temperature, depth, salinity and Chl-a.

• Temperature was one of the most influencing variables for both species.

• More information on the environmental effect on larvae and egg is needed.

Abstract

European anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) are two of the most important small pelagic fish species in terms of biomass and commercial interest in the Mediterranean Sea. Their populations are clearly influenced by environmental variations, making them good bio-indicators of climate-driven changes. Here, we reviewed the different environmental factors documented to affect anchovy and sardine biology by using a systematic review approach on methodologies used to study environmental effects on these species, variables identified to play a role, and relationships found between ecological variables and the environment. Our results show that available studies were heterogeneously distributed, being more abundant for anchovy adults in the Western Mediterranean. Among all the environmental factors found significant, temperature, depth, salinity and chlorophyll-a concentration were the most studied for both species. Further emphasis was placed on the effect of these four variables, with various relationships found for the different life stages and areas. This review provides a general insight of what is known about how the environment influences growth, spawning, abundance and distribution of anchovy and sardine in the Mediterranean Sea, and identifies gaps of knowledge for future research. Our study sets a knowledge baseline for future studies about climate variability and change in the Mediterranean basin.

Introduction

European anchovy (Engraulis encrasicolus) and sardine (Sardina pilchardus) are two of the most important commercial species in the Mediterranean Sea, reaching respectively up to 270,000 and 189,500 landed tons per year on average in the whole basin (FAO, 2018). These species are essential elements in the transfer of energy from lower to higher trophic level organisms (Palomera et al., 2007), coupling the Mediterranean pelagic and demersal environments. Cury et al. (2000) showed that fluctuations in small pelagic populations may modify ecosystem structure and functioning. Recent changes of anchovy and sardine have been observed in the Mediterranean Sea, in parallel with an overall increase of fishing effort (FAO, 2018).

Populations of anchovy and sardine are clearly influenced by changes in the environment (e.g. Lloret et al., 2004, Palomera et al., 2007). Environmental fluctuations can affect fish populations indirectly by controlling food quantity and quality or directly influencing annual recruitment, growth and condition of organisms (Basilone et al., 2017); with early life stages being particularly sensitive to these changes (Costalago et al., 2015). Sardine and anchovy have a relatively low position in the marine food web, and together with their short life-span and their reproductive strategy of producing large quantities of pelagic eggs, makes their populations strongly dependent on the environment (Palomera et al., 2007, Giannoulaki et al., 2013, Patti et al., 2020). This condition also makes them excellent bio-indicators of climate-driven changes in marine systems worldwide (Peck et al., 2013).

The study of the interactions of each of the two species with their environment is complex. Aspects such as interactions between both species, differences in habitat use, adaptations to the environmental change and the possible migratory movements in response to the climatic variability, pose an additional difficulty that needs to be considered and studied (Katara et al., 2011). The different studies available in the Mediterranean Sea on how environmental factors affect anchovy and sardine include different environmental variables and cover different ontogenetic stages and specific area. Therefore, the principal aim of this study was to systematically map and review information available on how environmental factors affect anchovy and sardine in the Mediterranean Sea in order to provide a general overview of what is known and identify the gaps of knowledge where future research should focus. The information extracted from the literature review is combined and discussed in terms of the relationships shown between the main environmental drivers at different life stages: egg, larvae, juveniles and adults. Since many marine resources from the Mediterranean Sea, including anchovy and sardine, are showing important declines (FAO, 2018), this review provides a step towards a better understanding on how marine species react to environmental factors, which is essential to manage marine resources sustainably under a context of climate change.