Impact of Berm Breaching on Hyperbenthic Macroinvertebrate Communities in Intermittently Closed Estuaries

Abstract

Berm breaching of intermittently closed estuaries, either naturally or due to management practices, results in a physicochemical disturbance due to the flushing of water, material and biota into the ocean and the subsequent tidal influx. In 2007 and 2008 comparative and controlled studies were employed in three New Zealand estuaries: Sawmill Creek (46°04′S 170°12′E), Otokia Creek (45°57′S 179°20′E) and Kaikorai Lagoon (45°56′S 170°23′E), to investigate the impact of berm breaching on the hyperbenthic macroinvertebrate community in intermittently closed estuaries. Significant changes in community structure occurred in both the weekly comparative and the controlled studies (ANOSIM P<0.01). Furthermore, the catch per unit effort of both total and key invertebrate taxa significantly increased after breaching (ANOVA P<0.01). However, substantial numbers of individuals were expelled into the ocean (5,800 individuals, 20-min sample) while new taxa immigrated into the estuaries. Along with migration-related changes to community structure, berm breaches also resulted in the loss of ∼80% of inundated habitat and the concentration of existing populations. Consequently, the management of intermittent estuary connections to the ocean has implications for the ecology of individual, managed estuaries and also for regional coastal populations of epibenthic invertebrates.

Feeding ability of a fluvial habitat‐specialist and habitat‐generalist fish in turbulent and still conditions

“…The only significant effect of turbulence we identified was on the feeding of common bullies from Sawmill Creek, our coastal river pool site. This may relate to their development in a pool with minimal turbulence and little or no flow (see Lill et al 2012), thus experiencing minimal selective pressures for fluvial morphological or behavioural adaptations. The site was also located within 300 m of the sea, greatly limiting the distance of upstream migration of amphidromous juvenile common bullies to this pool.…”

Habitat‐related specialization of lateral‐line system morphology in a habitat‐generalist and a habitat‐specialist New Zealand eleotrid

“…cotidianus because of the unique conditions of the collection site, a large main‐channel pond‐like pool with no visible surface turbulence. Flow is minimal in this downstream reach of the creek as the creek's outlet to the sea is typically blocked by a naturally formed sand‐dune berm (Lill et al , ), allowing for further investigation of habitat‐specific adaptations of G . cotidianus in a still habitat within a river.…”

Juvenile Steelhead Locate Coldwater Refugia in an Intermittently Closed Estuary

“…Depending on inlet state, water quality (WQ) conditions in ICEs can vary considerably, and changes in connectivity often create stressful conditions for benthic communities and nekton (Saad et al 2002;Sloan 2006;Lill et al 2012;Moreira et al 2014). Open-inlet conditions are tidal, with dynamic marine exchange and longitudinal gradients in salinity and temperature.…”

“…On the proximate scale, populations must cope with the physiological stress brought on by immediate changes in environmental conditions while continuing to forage and minimizing predation risk. Changes in WQ can be so sudden and severe that they cause large-scale mortality (Sloan 2006;Lill et al 2012;Netto et al 2012). Fish kills associated with breaching events during the low-flow season are caused by the sudden outflow of the freshwater lens while the anoxic saline layer remains (Becker et al 2009).…”

“…Fish kills associated with breaching events during the low-flow season are caused by the sudden outflow of the freshwater lens while the anoxic saline layer remains (Becker et al 2009). After the transition period, communities reorganize relative to the salinity gradient, but they are often limited by other WQ issues, such as high temperatures and low DO concentrations (Harrison and Whitfield 2006;Lill et al 2012;Lanés et al 2015). Community reorganization includes changes in species richness, which consist of complete losses of species' populations and drastic fluctuations in population densities.…”