Relationships among predatory fish, sea urchins and barrens in Mediterranean rocky reefs across a latitudinal gradient

Abstract

Previous studies conducted on a local scale emphasised the potential of trophic cascades in Mediterranean rocky reefs (involving predatory fish, sea urchins and macroalgae) in affecting the transition between benthic communities dominated by erected macroalgae and barrens (i.e., bare rock with partial cover of encrusting algae). Distribution patterns of fish predators of sea urchins (Diplodus sargus sargus, Diplodus vulgaris, Coris julis and Thalassoma pavo), sea urchins (Paracentrotus lividus and Arbacia lixula) and barrens, and fish predation rates upon sea urchins, were assessed in shallow (3-6m depth) sublittoral rocky reefs in the northern, central and southern sectors of the eastern Adriatic Sea, i.e., on a large spatial scale of hundreds of kilometres. No dramatic differences were observed in predatory fish density across latitude, except for a lower density of small D. sargus sargus in the northern Adriatic and an increasing density of T. pavo from north to south. P. lividus did not show any significant difference across latitude, whereas A. lixula was more abundant in the southern than in the central Adriatic. Barrens were more extended in the southern than in the central and northern sectors, and were related with sea urchin density. Fish predation upon adult sea urchins did not change on a large scale, whereas it was slightly higher in the southern sector for juveniles when predation rates of both urchins were pooled. Results show that: (1) assemblages of predatory fish and sea urchins, and barren extent change across latitude in the eastern Adriatic Sea, (2) the weak relations between predatory fish density and predation rates on urchins reveal that factors other than top-down control can be important over large scale (with the caveat that the study was conducted in fished areas) and (3) patterns of interaction among strongly interacting taxa could change on large spatial scales and the number of species involved.

Role of two co-occurring Mediterranean sea urchins in the formation of barren from Cystoseira canopy

“…In the Mediterranean Sea Paracentrotus lividus and Arbacia lixula are commonly found in both barren grounds and erected macroalgae assemblages (Guidetti and Dul ci c, 2007;Agnetta et al, 2013) and traditionally they have been considered a guild of herbivores (Bulleri et al, 1999(Bulleri et al, , 2002. However recent investigations have distinguished the diets and trophic positions of the two species showing that A. lixula is an omnivore tending to carnivore, while P. lividus is basically a herbivore that can turn into an omnivore both on barren and vegetated rocky areas .…”

Timing and habitat preferences for settlement of juvenile fishes in the Marine Protected Area of Torre Guaceto (south-eastern Italy, Adriatic Sea)

“…across latitudinal gradients) and time (e.g. from year to year), also considering the implications of current climate change in the Mediterranean Sea (Astraldi et al 1995;Guidetti et al 2002a;Bianchi & Morri 2003;Guidetti & Dulcic 2007;Nykjaer 2009). There is thus the need to widen the spatio-temporal scales for the assessment of distribution patterns of juvenile stages of many coastal fishes to see whether or not the information coming from the NW Mediterranean Sea is coherent at a larger scale.…”

Temperature modulates the response of the thermophilous sea urchin Arbacia lixula early life stages to CO2-driven acidification

“…It is also found on the other side of the Atlantic, but only in the Southern Hemisphere, off the coast of Brazil . It is currently one of the most abundant echinoids in shallow rocky habitats of the southern Mediterranean (Guidetti and Dulcic, 2007). This species has a considerable trophic plasticity, ranging from omnivory to strict carnivory (Wangensteen et al, 2011;Agnetta et al, 2013) and its scraping predatory behaviour can play a dominant role in driving switches between one complex state, dominated by a stratified assemblage of several erect macroalgae, to a simpler one dominated by few encrusting algae: the so-called 'barren ground' Wangensteen et al, 2012;Agnetta et al, 2013).…”

“…This species has a considerable trophic plasticity, ranging from omnivory to strict carnivory (Wangensteen et al, 2011;Agnetta et al, 2013) and its scraping predatory behaviour can play a dominant role in driving switches between one complex state, dominated by a stratified assemblage of several erect macroalgae, to a simpler one dominated by few encrusting algae: the so-called 'barren ground' Wangensteen et al, 2012;Agnetta et al, 2013). New and increasing evidence suggests that on-going warming of the Western Mediterranean results in an environment increasingly favourable for the reproduction and development of A. lixula (Francour et al, 1994;Guidetti and Dulcic, 2007;Gianguzza et al, 2011;Privitera et al, 2011;Lessios et al, 2012;Wangensteen et al, 2012).…”