Burrowing behaviour of unionid mussels in subtropical rivers: Implications for survey guidelines

Abstract

Conservation efforts have increased in response to global mussel declines, and effective surveys are a crucial step in assessing and monitoring mussel populations and in determining their conservation status. The burrowing behaviour of mussels can affect their detectability, and a better understanding of these behaviours would help to improve survey design and guidelines. The burrowing depth of mussels may differ between seasons, habitat conditions, species, and individuals, and little is known about the burrowing behaviour of mussels in subtropical rivers. Burrowing depth variation was examined and compared at three sites in the San Marcos, Guadalupe, and San Antonio river drainages in central Texas. In addition, laboratory experiments were used to determine whether observed differences between field sites and seasons could be linked to differences in substrate type and water temperature and to examine differences between species. Seasonal variation in burrowing depth was found at all field sites, and water temperature was a significant factor for explaining variation in burrowing depth, but there was no clear relationship between burrowing depth and temperature in shorter term laboratory experiments, where individual variation was high and burrowing behaviour seemed to be solely a function of time. Mussels burrowed significantly deeper in finer substrate (sand vs. gravel) in both field and laboratory experiments. Few significant differences between species were found in the field, but no differences were found in the laboratory experiments. The results suggest that surveys may need to follow different guidelines depending on local conditions, such as substrate and water temperature. Surveys will be less efficient and may fail to detect larger proportions of populations in colder water temperatures. In addition, a larger proportion of burrowed mussels can be expected at sites with finer substrate, such as sand. Under these conditions, visual searches will not suffice, as a large part of the population or specific species may be overlooked.

Experimental evidence associates burrowing behavior of Castalia ambigua (Bivalvia: Hyriidae) with shell shape and density

“…suggesting that their burrowing behavior may be linked with their functional morphology (Hernández et al, 2021). For example, more elongated shells may allow mussels to remain buried more deeply and yet maintain their filtration apertures extended close to the sediment surface, facilitating filtration in more hydrodynamic areas.…”

“…Burrowing is an important behavioral response of many mussel species to persist during periods of high flow (Lymbery et al, 2021 ; Sansom et al, 2022 ). Morphotype I is especially associated with high hydrodynamics (Simeone et al, 2022 ), suggesting that their burrowing behavior may be linked with their functional morphology (Hernández et al, 2021 ). For example, more elongated shells may allow mussels to remain buried more deeply and yet maintain their filtration apertures extended close to the sediment surface, facilitating filtration in more hydrodynamic areas.…”

Translocation as an ultimate conservation measure for the long-term survival of a critically endangered freshwater mussel

“…Previous studies recommended permanent monitoring of translocated specimens (Dunn et al, 2000;Jourdan et al, 2019;Luzier & Miller, 2009; IUCN/ SSC, 2013). In large rivers, such as the Ebro River (Spain), this is a difficult task due to the harsh environmental conditions (high depth, poor visibility, and winter floods), an issue that can be even more complicated for species that live buried, such as freshwater mussels (Prié et al, 2018;Hernández et al, 2021). In our case, it was not possible to monitor the specimens during high water levels.…”

“…Besides the possible influence of the method used, we have identified two other possible causes of this higher percentage of non-detection: some of the specimens may have been outside the plot (washed away during floods) and/or they were totally buried at the time of monitoring. Hernández et al (2021), in their study on detectability, state that the variables that most affect the movement behavior of mussels are temperature and the type of substrate. In the Ebro River we had access to the plots only in summer, when water temperature was higher and the mussels were more active; therefore it is quite possible that many specimens were outside the plot going unnoticed.…”

Survey of freshwater mussels using high‐resolution acoustic imaging sonar and deep learning‐based object detection in Lake Izunuma, Japan

“…Although conventional survey methods such as quadrat sampling have been widely used to survey mussel distributions (Vaughn et al, 1995; Vaughn & Taylor, 1999; Metcalfe‐Smith et al, 2000; Hernández et al, 2021; Lopez et al, 2022), they are time consuming and labour intensive, and their effectiveness can be influenced by factors such as water transparency, depth and underwater topography. For instance, Randklev et al (2013) studied mussels in the Leon River in Texas, where they inspected 44 sites with lengths of 35–405 m and widths of 1.5–41.1 m. The research group had to collect living or freshly dead mussels manually, and they took 3 months to complete the survey.…”