Abstract
Our objective was to determine the role of two invasive bivalves on the concentration of ammonium as well as pH within intertidal surface sediments (0 - 3 and 3 - 6 cm depth) and interstitial waters, within the context of a warming environment. To meet this objective we applied both controlled laboratory (microcosm) and field (mesocosm) experiments where we varied bivalve presence and absence and sediment temperature. Mesocosm sampling was tide dependent as we attempted to capture changes in ammonium concentration and pH as related to flood and ebb tide. We focused on ammonium as this nutrient is typically a limiting nutrient in oceanic systems and its cycling is a key process that regulates biological productivity. We also determined pH because of the increasing threat of ocean acidification. Integration of laboratory and field studies suggests that bivalves significantly contribute to ammonium to the intertidal with this amount increasing with increasing temperature. This ammonium is then released from the sediment as a “pulse” to overlying seawater on the flood tide. Under laboratory conditions, increased temperature and density of bivalves decreased overlying water pH. Mesocosm studies suggested some tide dependence of pH with flood tide acting as a buffer, increasing pH on the flood tide, after sediment exposure during ebb tide. Increased numbers of invasive bivalves within a warming environment are likely to increase amounts of ammonium released as a pulse on flood tides from intertidal ecosystems making this region a source of ammonium to coastal seas. Greater numbers of non-indigenous bivalves within the intertidal could also contribute to increased acidity within these regions although the significance of such increases is unknown.
Highlights
The shallow seas of coastal zones are one of the most valued of the world’s ecosystems ranking higher than terrestrial or open ocean systems despite their smaller area, a result of their role in the storage and cycling of the nutrients nitrogen and phosphorus [1]
Varnish clams excrete ammonium directly as inorganic ammonium through urine of which the composition can range from 60% - 100% ammonium depending on the species of bivalve [16] and indirectly as organic ammonium to the water and sediment environment
Concentrations of ammonium measured in sediments and water in the sterilized treatments should be from the bivalve alone rather than that contributed by ammonification or lost through nitrification
Summary
The shallow seas of coastal zones are one of the most valued of the world’s ecosystems ranking higher than terrestrial or open ocean systems despite their smaller area, a result of their role in the storage and cycling of the nutrients nitrogen and phosphorus [1]. First reported in the early 1990s, the varnish clam, native to China and Korea, is thought to have been transported in ballast waters to Vancouver Harbour and has since spread to a northern limit in Smith Sound, BC and to Coos Bay, Oregon in the south [5]. This species can reach densities of 800 m−2, up to four times greater than those of indigenous species [6]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have