From uniformity to multiplicity: development of a sub-arctic Littoral Mussel Bed in the Sea of Okhotsk

Abstract

Mussel beds are common in many intertidal and subtidal habitats, including sub-Arctic and Arctic regions. Despite their ecological importance, little is known about the demographic processes governing the development of mussel beds and particularly about the synchronization of these processes at different spatial scales. The development of a relatively compact, narrow littoral mussel bed of Mytilus trossulus, extending several hundred m along the shore of Koni Peninsula (Tauyskaya Bay, northern Sea of Okhotsk), was studied for four years during the period 2014–2017. This model bed was located along an exposed coast with a seasonal sea ice cover. It was used to test the hypothesis that small-scale synchronization exists, i.e., the changes in demographic structure of the population that occur simultaneously within a single mussel bed follow a similar pattern. This hypothesis was rejected. The size structure of the mussel population at the same tidal level changed from being uniform (2014) to being varied in 2015–2017. The course of development of the mussel population was different at the opposite ends of the bed. The cause of these differences may be unequal levels of recruitment of juveniles in the form of a gradient from one end of the bed to the other over the length of the bed. The gradient was associated with transition from one type of shore dynamic processes to another (accumulation vs. abrasion). Small-scale desynchronization may represent one of the reasons explaining the heterogeneity of mussel populations. The possibility of desynchronization of demographic processes should be taken into consideration when studying the spatial organization and dynamics of mussel beds.