Rob McAllen

Gill Damage to Atlantic Salmon (Salmo salar) Caused by the Common Jellyfish (Aurelia aurita) under Experimental Challenge

Background Over recent decades jellyfish have caused fish kill events and recurrent gill problems in marine-farmed salmonids. Common jellyfish (Aurelia spp.) are among the most cosmopolitan jellyfish species in the oceans, with populations increasing in many coastal areas. The negative interaction between jellyfish and fish in aquaculture remains a poorly studied area of science. Thus, a recent fish mortality event in Ireland, involving Aurelia aurita, spurred an investigation into the effects of this jellyfish on marine-farmed salmon. Methodology/Principal Findings To address the in vivo impact of the common jellyfish (A. aurita) on salmonids, we exposed Atlantic salmon (Salmo salar) smolts to macerated A. aurita for 10 hrs under experimental challenge. Gill tissues of control and experimental treatment groups were scored with a system that rated the damage between 0 and 21 using a range of primary and secondary parameters. Our results revealed that A. aurita rapidly and extensively damaged the gills of S. salar, with the pathogenesis of the disorder progressing even after the jellyfish were removed. After only 2 hrs of exposure, significant multi-focal damage to gill tissues was apparent. The nature and extent of the damage increased up to 48 hrs from the start of the challenge. Although the gills remained extensively damaged at 3 wks from the start of the challenge trial, shortening of the gill lamellae and organisation of the cells indicated an attempt to repair the damage suffered. Conclusions Our findings clearly demonstrate that A. aurita can cause severe gill problems in marine-farmed fish. With aquaculture predicted to expand worldwide and evidence suggesting that jellyfish populations are increasing in some areas, this threat to aquaculture is of rising concern as significant losses due to jellyfish could be expected to increase in the future.

The effect of salinity change on the oxygen consumption and swimming activity of the high-shore rockpool copepod Tigriopus brevicornis

Tigriopus brevicornis is the dominant member of the fauna in high-shore rockpools (above the mean high water of spring tides) that are subject to extreme environmental variation especially in salinity due to infrequent tidal inundation. The present study was designed to assess the effect of large-scale salinity change on the rate of oxygen consumption and levels of activity. Measurements of the rates of oxygen consumption (VO2) of T. brevicornis in response to simulated changes in salinity (of a magnitude that had previously been recorded in high-shore rock pools inhabited by T. brevicornis) were carried out using closed respirometry. Activity levels of T. brevicornis during exposure to three different salinities (10, 33 and 90 psu) were assessed by means of video image analysis. The study showed that T. brevicornis exhibits a reduction in activity and in oxygen consumption when exposed to higher salinities. However, individuals exposed to low salinities showed elevated rates of oxygen consumption without an associated increase in activity. The present study indicates that animals living in high-shore rockpools may incur a considerable energetic cost, due to the rapid and large-scale environmental changes that are characteristic of this habitat.

Go with the flow: tidal import and export of larvae from semi-enclosed bays

There is a growing body of evidence that suggests the effective functioning of marine reserves is dependent on the dispersal and recruitment of larvae. Enhanced production inside reserves is predicted to lead to a net larval export and increased settlement and recruitment outside reserve boundaries. However, larval retention in bays is also well documented. Since bays are increasingly being used as reserve areas, planktonic larvae of benthic marine invertebrates were sampled from two semi-enclosed marine reserves during flood and ebb tides to determine whether these bays are acting as net exporters of larvae. Neither reserve was a net importer or exporter of species richness, larval abundance or diversity, although one reserve showed a small export of species richness during the hours of darkness. Both reserves balanced the net import of some species with a net export of others, which was generally related to adult or larval abundance, although exceptions were found in one reserve. Significant effects of light were found, with the net import or export of some species occurring exclusively during either the hours of daylight or darkness. An increased understanding of larval sink-source dynamics in bays is essential for ensuring their effective use as marine reserves to meet specific conservation needs.

Behavioural effects of biofouling in a marine copepod

The impact of biofouling by the filamentous bacteria Leucothrix mucor upon the body density and swimming behaviour of the harpacticoid copepod Tigriopus brevicornis was investigated. Biofouled individuals had a greater body density than non-fouled individuals. Biofouled and non-fouled animals swam similar distances and for similar periods of time during trials, but biofouled animals engaged in fewer, but longer bouts of swimming per trial and as a result experienced a lower swimming rate. These observations imply that biofouling has significant implications for the behavioural ecology of T. brevicornis .

Increases in the abundance of the invasive barnacle Austrominius modestus on the Isle of Cumbrae, Scotland

The distribution and abundance of the Australasian barnacle Austrominius modestus around the Isle of Cumbrae, Scotland, were examined in October 2007. The species was found at all of the nineteen sites examined, which included highly exposed to highly sheltered sites. Its abundance varied from common to occasional. Over fifty years after its initial appearance as a single specimen (1954), Austrominius now appears to be well established on the island. Factors that may have influenced its spread and establishment are described, however, at this stage the relative importance of these cannot be determined. Consequently, further research is planned here, to collect quantitative data on the abundance of Austrominius and the other barnacle species that occur intertidally and how their relative abundances vary both within and between shores.

The environmental effects of salinity and temperature on the oxygen consumption and total body osmolality of the marine flatworm Procerodes littoralis

The present study examined the effect of salinity and temperature on the rate of oxygen consumption and total body osmolality of the triclad turbellarian Procerodes littoralis, a common marine flatworm normally found in areas where freshwater streams run out over intertidal areas. Extremes in environmental factors encountered by P. littoralis were recorded at the study site. These were salinity (0–44 psu), temperature (2.7–24.9 °C) and oxygen concentration (2.8–16.1 mg l−1). Respirometry experiments showed minimal oxygen consumption rates at the salinity extremes encountered by the study species (0 and 40 psu). Further experiments showed relatively constant oxygen consumption rates over the temperature range 5–20 °C and elevated consumption rates at temperatures above 25 °C. Total body osmolality of P. littoralis increased with increasing salinity. The study illustrates how a marine flatworm uses integrated physiological and behavioural mechanisms to successfully inhabit an environment that is predominantly freshwater for up to 75% of the tidal cycle.

Determination of spatial and temporal variability of pH and dissolved oxygen concentrations in a seasonally hypoxic semi-enclosed marine basin using continuous monitoring

Measurement and prediction of ocean acidification effects for nearshore marine ecosystems is currently a major objective of climate change research. This study examines the scales of pH variability in both surface waters (<10 m depth) and deeper waters associated with localised seasonal hypoxia over two years at Lough Hyne marine reserve, Cork, Ireland. Lough Hyne, a semi-enclosed marine system, experiences localised seasonal (approximately May to September each year) hypoxia and eventual anoxia below a depth of circa 25 m, due largely to its bathymetric profile. We report the relationships between pH and other environmental parameters such as dissolved oxygen (DO) and temperature at this location, and we provide data, obtained using continuous autonomous sensing technology, which demonstrates that the variability in pH measurements in the waters of Lough Hyne marine reserve are comparable to predictions of future ocean acidification. This is of interest as comparatively few directly measured time series of pH in marine waters are reported, and additionally the first pH measurements were reported from Lough Hyne over 6 decades ago in 1952. This work also measures for the first time the steep chemical gradients associated with the transition from anoxia to normoxia that result in profound pH changes at Lough Hyne, providing insight into natural variability in pH experienced by marine organisms at such locations.

Hanging on in there - position maintenance by the high-shore rockpool harpacticoid copepod Tigriopus brevicornis

The high-shore rockpool habitat of Tigriopus brevicornis is subject to considerable physical disturbance from high spring tides and storms and hence the species must deal with the potential hazard of being swept out. Scanning electron microscopy, video image analysis and flow-through chamber experimentation was used to study the micro-morphology and behaviour of T. brevicornis to understand the position maintenance capabilities of the species. Micro-serrations and forward-facing claws on the first swimming leg combined with hooks on the caudal furcae appear to be the major morphological structures used in position maintenance. Morphological comparisons are made with the subtidal sand-dwelling harpacticoid Harpacticus flexus. The ability of T. brevicornis to burrow into loose sediment is also discussed.

Behavioural responses of shallow-water benthic marine scavengers to fish carrion: a preliminary study

Abstract Observations of the behavioural responses of near-shore marine scavengers to fish carrion were made at two depths (1–2 m, 16–18 m). Gobies and juvenile whelks were the most numerous scavengers, but appeared to consume little biomass. The first scavengers to appear at carrion (seconds/minutes) were swimming forms, later (minutes) joined by fast-moving, crawling portunid crabs. Large scavengers (crabs/starfish/catsharks) arrived after tens of minutes/hours. Scavengers were ‘direct feeders’ on the bait (crabs and some fish) or ‘indirect feeders’ (gobies and whelks) on scraps generated by direct feeders. Scavengers spent little time in aggression. While fish spent relatively low proportions of their time feeding (e.g. Lipophrys pholis: 2.2–15.8%), crabs fed almost continuously (e.g. Carcinus maenas: 97.8–99.3%) before leaving baits. Crab presence depressed fish feeding. Crabs were wasteful feeders that macerated the baits, generating scraps for indirect feeders and attracting more scavengers. Large scavengers consumed most bait.

Shallow subtidal octocorals in an Irish marine reserve

Alcyonacean octocorals are anthozoans which are found in many coastal benthic habitats, where they can be sensitive to environmental and/or anthropogenic stress. As part of a two-decade monitoring study of Lough Hyne (Europe’s first marine reserve and Ireland’s only one), we documented benthic communities at rocky-shore sites. As a fully marine, semi-enclosed, tidal ‘lake’ connected to the Atlantic Ocean via tidal rapids, Lough Hyne has long been noted for its high species and habitat diversity. One of the noteworthy guilds we report here was the alcyonacean octocorals: (1) the soft coral Alcyonium hibernicum under shallow subtidal rocks at monitoring sites in the lough from 2002 to 2015 and (2) the first known records (2013 to present) of the red soft coral A. glomeratum inside the lough (above the rapids). Furthermore, in August/September 2014 and 2015, we rediscovered the stoloniferous octocoral Sarcodictyon catenatum, last reported in the lough in the 1930s. We documented the distribution and abundance of these species in shallow subtidal areas of the lough as a baseline in the face of rapidly degrading conditions due to extreme oxygen fluctuations from eutrophication.