A comparison of inshore marine soundscapes

• Acoustic signatures differed significantly within but not between habitats.
• Unique acoustic signatures exist over different spatial ranges.
• A 2–4 kHz peak in acoustic complexity was seen in nearly all habitat patches.
• Passive listening indicated the presence of particular sounds of biological origin.
• Soundscapes were influenced by proximity to areas with high-level broadband sound.

Sound travels well through water and is capable of conveying information to any listener on both the presence of particular organisms and the quality of the environment. Many marine organisms use sounds to navigate, forage and communicate, while different marine habitats often have their own acoustical characteristics. However, there are still large gaps in our knowledge of marine soundscapes, particularly in regard to their spatial patterns. The goal of this research was to investigate passive acoustic monitoring as an ecological survey technique. The specific objectives were to compare soundscapes between and within benthic habitats and to evaluate the influence of different environmental factors. Acoustic recordings were made in Lough Hyne, Ireland during May 2012, following a nested design in three benthic habitats; Mud, Gravel and Cliff. Three patches of each habitat were selected using hydro-acoustic and underwater video surveys and within each patch five different sites were monitored (n = 45). A nested analysis of variance (ANOVA) showed that acoustic profiles differed significantly within but not between habitats, although unique acoustic signatures existed over different spatial ranges, illustrating a degree of stability at local patch level. A distinct peak (2–4 kHz) in acoustic complexity was observed in all habitat patches but one, and was caused by the presence of transient broadband pulses or snaps. These snaps were attributed to the presence of snapping shrimp (family Alpheidae), found at a particular location within the lough. Other distinctive sounds of suspected biological origin were identified in particular habitat patches (Cliff and Gravel) and suggested the presence of habitat related biophonies. Soundscape signatures of different patches were strongly correlated with proximity to the source of the high-energy snaps, indicating that location was more important than habitat in determining soundscape characteristics. Other environmental factors such as bottom type and depth were less important. It is evident that acoustical sources of high energy and broadband properties have pervasive effects over considerable distances (up to 1 km). The acoustic characteristics of a habitat patch were greatly influenced by extraneous sounds, in this case from a biological source. The high acoustic connectedness of marine habitats underlines the need for evaluating the impact of anthropogenic activities, particularly for ecosystems with unique biophonies in need of protection. There is potential for developing passive acoustic monitoring as a principal method for surveying marine habitats and observing local processes at different spatial and temporal scales.