Anthropogenic impacts and historical decline in body size of rocky intertidal gastropods in southern California

Abstract

The diverse fauna and flora of rocky intertidal ecosystems are being impacted by the activities of rapidly increasing coastal populations in many regions of the world. Human harvesting of intertidal species can lead to significant changes in body sizes of these taxa. However, little is known about the temporal trajectories of such size declines and more importantly, the long-term effects of chronic human impacts. Furthermore, it is unclear whether sizes of species not directly targeted for harvesting are also declining through indirect effects. Here we use historical (extending back to 1869) and field survey data covering 200 km of mainland southern California coast to show that human activities have led to significant and widespread declines in body sizes of rocky intertidal gastropod species over the last century. These declines, initiated several decades ago, are continuing and contrary to expectation, they are not restricted to species harvested for human consumption. Data from the only national park in this area, where conservation laws are strictly imposed, demonstrate that negative ecological impacts can be ameliorated if existing laws are enforced.

Community-level analysis of anthropogenic impacts on rocky shore communities in Sri Lanka

“…Present findings have clearly shown that zoo-benthic community are highly sensitive to corresponding human disturbances and disturbances can finally affect on zoo-benthic abundance and growth. Study on historical and field survey data of mainland southern California coast have shown, accompanying with present results that human activities have lead to significant and widespread decline in body size of rocky intertidal gastropod species over the last century (Roy et al, 2003). In contrary to zoobenthos, having lower disturbance index, macroalgae at Rumassala show the higher stress ( Figure 5).…”

Increased seasonality in the Western Mediterranean during the last glacial from limpet shell geochemistry

“…Of these, 14 shells spanning the period 40-19 kyrs BP were analysed to produce oxygen isotope profiles and 10 of these were analysed to produce Mg/Ca ratio profiles. Historical and contemporary empirical data from sites around the world have often shown reductions in body size in Patella and similar species through time (Keough et al, 1993;Roy et al, 2003). A significant, although not the sole, contributor to this observed size reduction has been the sustained exploitation of these species over time by humans for food or fish bait.…”

Evidence of size-selective evolution in the fighting conch from prehistoric subsistence harvesting

“…Archaeological middens the world over demonstrate that coastal shellfish have been harvested for hundreds of years to millennia [11][12][13] and have undergone marked changes to their ecological structure as a result [14][15][16][17][18][19]. Many (but not all) mollusc species that have a long history of subsistence harvesting have become smaller over time [14,16,20], suggestive of size-selective evolutionary change.…”

“…Many (but not all) mollusc species that have a long history of subsistence harvesting have become smaller over time [14,16,20], suggestive of size-selective evolutionary change. It is impossible, however, to convincingly establish if the causal mechanism is selection to mature at a smaller size, as described above, or if it is simply because larger individuals become less common as they are preferentially harvested, thereby lowering mean size.…”