Abstract
BackgroundSpatio-temporal patterns on benthic molluscan macrofauna structure and function (feeding guilds) were investigated in a commercial fishing ground in Thermaikos Gulf (N Aegean Sea). Fishery management measures in this area include a trawling period of 8 months per year (October to May). Macrofauna samples were collected before and after 30 and 120 days of the commencement of the trawling period (temporal axis) along a southward transect (spatial axis) and down through the sediment profile (vertical axis).ResultsMain results revealed no recognizable changes in community diversity and structure at temporal scales. This finding can probably be attributed to the fact that the examined communities are subjected to continuous disturbances deriving from multiple natural and anthropogenic stressors acting simultaneously in Thermaikos Gulf. Molluscan assemblages were already stressed before the commencement of the trawling period, indicating that the time period in which bottom trawling is prohibited is not sufficient for the recovery of benthic communities. Significant shifts in the trophic structure of molluscan assemblages were also detected. The direct mortality of herbivorous species and the loss of filter feeding organisms may be attributed to the passage of the fishing gear and to sediment re-suspension, respectively. Trawling disturbance may have created the observed vertical patterns of the community structure since hauling induces profound changes in the geochemical profile of the sediment.ConclusionsOur findings sustained the notion that bottom trawling, alongside with other types of human induced stressors, can have considerable effects on the structure and function of the benthic domain. Therefore, our results highlighted the need of an Ecosystem Based Fishery Management (EBFM) perspective in Thermaikos Gulf to ensure both fisheries and ecosystem sustainability.Electronic supplementary materialThe online version of this article (doi:10.1186/2241-5793-21-10) contains supplementary material, which is available to authorized users.
Highlights
Spatio-temporal patterns on benthic molluscan macrofauna structure and function were investigated in a commercial fishing ground in Thermaikos Gulf (N Aegean Sea)
The present study aims to address the structure and function of macrobenthic molluscan assemblages in a heavily trawled fishing ground of the Eastern Mediterranean, Thermaikos Gulf (N Aegean Sea), along spatiotemporal axes, down through the sediment profiles
In terms of numerical dominance, the bivalve Corbula gibba accounted for 26.7% of the total abundance, whereas the gastropod Turritella communis and the bivalves Kurtiella bidentata and Thyasira biplicata accounted for 13.6%, 13.1% and 7.7% of total abundance, respectively
Summary
Spatio-temporal patterns on benthic molluscan macrofauna structure and function (feeding guilds) were investigated in a commercial fishing ground in Thermaikos Gulf (N Aegean Sea). It is well known that physical disturbance caused by bottom trawling can be classified as one of the most important sources of human induced disturbance to soft-sediment benthic communities and habitats [5,6,7] Both experimental and field studies have shown that bottom trawling modifies seabed morphology and complexity, Macrofauna is frequently used to detect bottom trawling disturbance because it is relatively easy to sample and process, is directly affected by the passage of the fishing gear as species are directly killed or damaged, and it provides information about habitat structure [2]. In intensively trawled sediments small infaunal species are expected to proliferate, since they usually exhibit higher resilience after disturbance events, whereas larger epifaunal organisms are expected to be absent [14,15]
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