Sea temperature variability and Paracentrotus lividus (Echinoidea) population fluctuations

Abstract

Observations and censi of the echinoid Paracentrotus lividus over 40 y at Lough Hyne marine nature reserve have revealed population fluctuations of >4 orders of magnitude. The P. lividus population has been anomalously low since the mid 1980s. The population age–size structure has also changed considerably and is now dominated by older individuals. Sea temperature is a known and important determinant of spawning (and recruitment) in this species. In certain years sea surface temperatures (SST) may not reach critical values for P. lividus mass-spawning to be triggered. In addition, toxic dinoflagellate blooms may have been responsible for large-scale mortalities within short periods. Years of anomalously low SSTs match the timing of critical decreases in the Lough Hyne P. lividus population. Years with low maximum SSTs coincide with the timing of major El Niňo Southern Oscillation (ENSO) events. We suggest a SST and possibly ENSO link to unfished (Lough Hyne) P. lividus population changes and propose such links as potential aggravating factors in the decline of the fisheries.

A boom–bust phylum? Ecological and evolutionary consequences of density variations in echinoderms

“…Like other herbivorous echinoids, this species has important ecological functions in controlling benthic algal communities through grazing (Kitching 1987). Surveys of the populations of P. lividus in Lough Hyne (Ireland) since the 1920s indicate that this species exhibits large, longterm (decadal) variations in densities in a no-take marine reserve (Kitching 1987, Barnes et al 2001. With the exception of a recovery period in the late 1980s, this species has now consistently declined in the Lough.…”

“…Some authors (Barnes et al 2001, Verling et al 2005) link the cause for the decline to El Nin˜o Southern Oscillation (ENSO) events, which reduce the maximum sea surface temperatures below those suggested to Notes: Population event categories are: increase in population density (I), decrease (D), and fluctuations between high and low population densities (F). Habitat categories are: temperate subtidal (TS), temperate subtidal soft sediment (TSS), deep sea (DS), seagrass bed (SB), and coral reef (CR).…”

“…(B) Paracentrotus lividus in the south basin of Loch Hyne. Data were recalculated from an original graph in Barnes et al (2002), including data from Muntz et al (1965), Kitching (1987), and Barnes et al (2001).…”

Marine reserve designation, trophic cascades and altered community dynamics

“…Since designation, populations of a number of subtidal benthic invertebrates have undergone catastrophic declines in the system, without recovery. For example, the best-studied invertebrate in Lough Hyne, the purple sea urchin Paracentrotus lividus, was found to be absent from the South Basin by 2000 (Barnes et al 2001). The purple sea urchin is the subject of a long-term population study due to its importance as a primary grazer and role in regulating algal biomass, and the population is observed to fluctuate periodically.…”

“…Although P. lividus is not demonstrated to be a keystone species at Lough Hyne (Kitching 1987), it undoubtedly has a stabilising influence in the system and its loss has community level implications. Previous studies explored the drivers of population change and invoked mechanisms such as recruitment driven by sea surface temperature (Barnes et al 2001) and intrinsic population dynamical processes (Uthicke et al 2009). …”