Frequency, Magnitude, and Possible Causes of Stranding and Mass-Mortality Events of the Beach Clam Tivela mactroides (Bivalvia: Veneridae)

Abstract

Stranding combined with mass-mortality events of sandy-beach organisms is a frequent but little-understood phenomenon, which is generally studied based on discrete episodes. The frequency, magnitude, and possible causes of stranding and mass-mortality events of the trigonal clam Tivela mactroides were assessed based on censuses of stranded individuals, every four days from September 2007 through December 2008, in Caraguatatuba Bay, southeastern Brazil. Stranded clams were classified as dying (closed valves did not open when forced) or dead (closed valves were easily opened). Information on wave parameters and the living intertidal clam population was used to assess possible causes of stranding. This fine-scale monitoring showed that stranding occurred widely along the shore and year-round, with peaks interspersed with periods of low or no mortality. Dead clams showed higher mean density than dying individuals, but a lower mean shell length, attributed to a higher tolerance to desiccation of larger individuals. Wave height had a significant negative relationship to the density of dying individuals, presumed to be due to the accretive nature of low-energy waves: when digging out, clams would be more prone to be carried upward and unable to return; while larger waves, breaking farther from the beach and with a stronger backwash, would prevent stranding in the uppermost areas. This ecological finding highlights the need for refined temporal studies on mortality events, in order to understand them more clearly. Last, the similar size structure of stranded clams and the living population indicated that the stranded individuals are from the intertidal or shallow subtidal zone, and reinforces the ecological and behavioral components of this process, which have important ecological and socioeconomic implications for the management of this population.

Clam population dynamics as an indicator of beach urbanization impacts

“…In this context, clams' population dynamics would be a potential good bioindicator of beach urbanization since these organisms are key ecosystem components of sandy beaches (Turra et al, 2016). Along the South West Atlantic coasts, the yellow clam Amarilladesma mactroides and the wedge clam Donax hanleyanus are the dominant infaunal bivalves of sandy beaches.…”

Peer Review #3 of "Storm effects on intertidal invertebrates: increased beta diversity of few individuals and species (v0.1)"

“…This time lag was found to show the strongest correlation between wave height/power and changes in macrobenthic species in the area (Turra et al 2016).…”

The science we need for the beaches we want: frontiers of the flourishing Brazilian ecological sandy beach research

“…Investigations on the effects of climate change focused mainly on high-intensity storms (Machado et al, 2016;Turra et al, 2016;Corte et al, 2017b;Corte et al, 2018;Oliveira and Yokoyama, 2021). Experiments to assess anthropogenic and climate change impacts are still scarce (but see Laurino et al, 2020;Izar et al, 2022;Laurino et al, 2022, Laurino et al, 2023Laurino and Turra, 2021).…”