Short-term post-mortality scavenging and longer term recovery after anoxia in the northern Adriatic Sea

Abstract. The northern Adriatic Sea is one of nearly 500 areas worldwide suffering widespread mortalities due to anoxia. The present study documents post-anoxia macrofauna dynamics after experimentally inducing small-scale anoxia in 24 m depth (2 plots, each 50 cm × 50 cm). Time-lapse camera deployments examined short-term scavenging of the moribund and dead organisms (multi-species clumps consisting of sponges and ascidians) over two 3-day periods (August 2009: 71.5 h, September 2009: 67.5 h). Longer term recovery (days to 2 yr) in the same two plots was examined with an independent photo series. Scavengers arrived quickly and in a distinct sequence: demersal (Gobius niger, Serranus hepatus) and benthopelagic fishes (Diplodus vulgaris, Pagellus erythrinus), followed by hermit crabs (Paguristes eremita, showing a clear day/night rhythm in presence) and gastropods (Hexaplex trunculus). This sequence is attributed to the relative speeds and densities of the organisms. The sessile fauna was largely removed or consumed within seven (August plot) and 13 (September plot) days after anoxia, confirming our first hypothesis that decaying organisms are quickly utilised. The scavengers remained in dense aggregations (e.g. up to 33 P. eremita individuals at one time) as long as dead organisms were available. No recovery of sessile macroepibenthos macroepibenthos occurred in the experimental plots one and two years after anoxia, undermining our second hypothesis that small denuded areas are more rapidly recolonised. This study underlines the sensitivity of this soft-bottom community and supports calls for reducing additional anthropogenic disturbances such as fishing practices that further impede recolonisation and threaten benthic community structure and function over the long term.

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Short-term post-mortality predation and scavenging and longer-term recovery after anoxia in the northern Adriatic Sea

Biogeosciences Discussions ◽

10.5194/bgd-10-4367-2013 ◽

2013 ◽

Vol 10 (3) ◽

pp. 4367-4401 ◽

Cited By ~ 9

Author(s):

M. Blasnig ◽

B. Riedel ◽

M. Zuschin ◽

L. Schiemer ◽

M. Stachowitsch

Keyword(s):

Adriatic Sea ◽

Late Summer ◽

Time Lapse ◽

Hermit Crabs ◽

Small Scale ◽

Commercial Fishing ◽

Short Term ◽

Northern Adriatic Sea ◽

Northern Adriatic ◽

And Function

Abstract. In the Mediterranean, the northern Adriatic Sea shows most features known to promote late-summer hypoxia and anoxia. These features, along with anthropogenic eutrophication and marine snow events, have led to repeated benthic mortalities here. The present study was designed to document the post-anoxia macrofauna dynamics. We deployed an underwater instrument to induce small-scale anoxia in situ (total area 0.5 m2). Two time-lapse camera deployments examined short-term scavenging of the moribund and dead organisms (multi-species clumps consisting of sponges and ascidians) over a 3-day period (August 2008: 71.5 h, September 2008: 67.5 h). Longer-term recovery (2 yr) in the same two plots was examined with an independent photo-series. Predators and scavengers arrived in a distinct sequence. The first to arrive were demersal (Gobius niger, Serranus hepatus) and benthopelagic fishes (Diplodus vulgaris, Pagellus erythrinus), followed by hermit crabs (Paguristes eremita, showing a clear day/night rhythm in presence) and gastropods (Hexaplex trunculus). This sequence of arrival is attributed to the relative speeds of the organisms and their densities. The scavengers remained in dense aggregations (e.g. up to 33 P. eremita individuals at one time) as long as the dead organisms were available. The whole sessile fauna was largely removed or consumed within 7 (August plot) and 13 (September plot) days after anoxia. No macroepibenthic recovery took place in the experimental plots one and two years after anoxia. This study underlines the sensitivity of this soft-bottom community and supports calls for reducing additional anthropogenic disturbances such as damaging commercial fishing practices that impede recolonization and threaten benthic community structure and function over the long-term.

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Spatial distribution of suspended solids during short-term high river discharge in the Bay of Koper, northern Adriatic Sea

Mediterranean Marine Science ◽

10.12681/mms.2141 ◽

2018 ◽

Vol 19 (1) ◽

pp. 36 ◽

Cited By ~ 2

Author(s):

ROK SOCZKA MANDAC ◽

DUŠAN ŽAGAR

Keyword(s):

Spatial Distribution ◽

River Discharge ◽

Suspended Solids ◽

Adriatic Sea ◽

Anthropogenic Influences ◽

Short Term ◽

Northern Adriatic Sea ◽

Northern Adriatic ◽

River Flooding ◽

The Impact

The Bay of Koper (BoK) located in the Gulf of Trieste (northern Adriatic Sea) is subject to a variety of anthropogenic influences; pollutants from inland are transported to the sea by the local rivers. The impact of high river discharge on suspended solids distribution was assessed by analysing results of an extensive measurement campaign conducted during two episodes of river flooding. The spatial analysis demonstrated the area influenced by fresh water and the distribution of inorganic suspended solids (ISS). The results were then used to calibrate the PCFLOW3D model and to simulate two episodes. A correlation was identified between the measurements and short-term simulations found in the central part of the bay. The results confirm the methods and the model used in this study to be appropriate for studying complex suspended solids processes in coastal areas.

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CellTracker Green labelling vs. Rose Bengal staining: CTG wins by points in distinguishing living from dead anoxia-impacted copepods and nematodes

Biogeosciences Discussions ◽

10.5194/bgd-10-2857-2013 ◽

2013 ◽

Vol 10 (2) ◽

pp. 2857-2887 ◽

Cited By ~ 5

Author(s):

M. Grego ◽

M. Stachowitsch ◽

M. De Troch ◽

B. Riedel

Keyword(s):

Rose Bengal ◽

Adriatic Sea ◽

Staining Method ◽

Tipping Points ◽

Sediment Layer ◽

Short Term ◽

Northern Adriatic Sea ◽

Northern Adriatic ◽

Harpacticoid Copepods ◽

Sediment Layers

Abstract. Hypoxia and anoxia have become a key threat to shallow coastal seas. Much is known about their impact on macrofauna, less on meiofauna. In an attempt to shed more light on the latter group, in particular from a process-oriented view, we experimentally induced short-term anoxia (1 week) in the Northern Adriatic Sea, Mediterranean, and examined the two most abundant meiofauna taxa – harpacticoid copepods and nematodes. Both taxa also represent different ends of the tolerance spectrum, with copepods being the most sensitive and nematodes among the most tolerant. We compared two methods: CellTracker Green (CTG) – new labelling approach for meiofauna – with the traditional Rose Bengal (RB) staining method. CTG binds to active enzymes and therefore colours live organisms only. The two methods show considerable differences in the number of living and dead individuals of both meiofauna taxa. Generally, RB will stain dead but not yet decomposed copepods and nematodes equally as live ones. Specifically, RB significantly overestimated the number of living copepods in all sediment layers in anoxic samples, but not in any normoxic samples. In contrast, for nematodes, the methods did not show such a clear difference between anoxia and normoxia. Surprisingly, RB overestimated the number of living nematodes in the top sediment layer of normoxic samples, which implies an overestimation of the overall live nematofauna. For monitoring and biodiversity studies, the RB method might be sufficient, but for more fine-scaled (days, hours, tipping points) studies, especially on hypoxia and anoxia where it is necessary to resolve the course of events, CTG labelling is a better tool. Moreover, it clearly highlights the surviving species within the copepod or nematode community. As already accepted for foraminiferal research, we demonstrate that the CTG labelling is also valid for other meiofauna groups.

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