David Morritt

Scaling laws of marine predator search behaviour

Many free-ranging predators have to make foraging decisions with little, if any, knowledge of present resource distribution and availability. The optimal search strategy they should use to maximize encounter rates with prey in heterogeneous natural environments remains a largely unresolved issue in ecology. Lévy walks are specialized random walks giving rise to fractal movement trajectories that may represent an optimal solution for searching complex landscapes. However, the adaptive significance of this putative strategy in response to natural prey distributions remains untested. Here we analyse over a million movement displacements recorded from animal-attached electronic tags to show that diverse marine predators—sharks, bony fishes, sea turtles and penguins—exhibit Lévy-walk-like behaviour close to a theoretical optimum. Prey density distributions also display Lévy-like fractal patterns, suggesting response movements by predators to prey distributions. Simulations show that predators have higher encounter rates when adopting Lévy-type foraging in natural-like prey fields compared with purely random landscapes. This is consistent with the hypothesis that observed search patterns are adapted to observed statistical patterns of the landscape. This may explain why Lévy-like behaviour seems to be widespread among diverse organisms, from microbes to humans, as a ‘rule’ that evolved in response to patchy resource distributions.

Species sensitivity distributions: data and model choice

Species sensitivity distributions (SSDs) are increasingly incorporated into ecological risk assessment procedures. Although these new techniques offer a more transparent approach to risk assessment they demand more and superior quality data. Issues of data quantity and quality are especially important for marine datasets that tend to be smaller (and have fewer standard test methods) when compared with freshwater data. An additional source of uncertainty when using SSDs is appropriate selection from the range of methods used in their construction. We show through examples the influence of data quantity, data quality, and choice of model. We then show how regulatory decisions may be affected by these factors.

Development of Crassostrea gigas Larvae is Affected by 4-nonylphenol

Nonylphenol is a known endocrine disrupter that is widespread in the aquatic environment. In this investigation, the Pacific Oyster, Crassostrea gigas (Thunberg), a marine invertebrate widely used in standard pollution bioassays, was exposed to a range of concentrations of 4-nonylphenol (0.1, 1, 10, 100, 1000 and 10 000 μg/l). Development of C. gigas to a particular larval stage (D-shape) was monitored over a 72 h time period at eight-hourly intervals. 4-nonylphenol delayed development to D-shape and caused a significant decrease in survival rate. In addition a growth abnormality was observed.

Plastic in the Thames: a river runs through it.

Although contamination of the marine ecosystems by plastics is becoming recognised as a serious pollution problem, there are few studies that demonstrate the contribution made by freshwater catchments. Over a three month period from September to December 2012, at seven localities in the upper Thames estuary, 8490 submerged plastic items were intercepted in eel fyke nets anchored to the river bed. Whilst there were significant differences in the numbers of items at these locations, the majority were some type of plastic. Additionally in excess of 20% of the litter items were components of sanitary products. The most contaminated sites were in the vicinity of sewage treatment works. While floating litter is visible, this study also demonstrates that a large unseen volume of submerged plastic is flowing into the marine environment. It is therefore important that this sub-surface component is considered when assessing plastic pollution input into the sea.

Can Saltwater Toxicity be Predicted from Freshwater Data

The regulation of substances discharged to estuarine and coastal environments relies upon data derived from ecotoxicity tests. Most such data are generated for freshwater rather than saltwater species. If freshwater toxicity data are related to saltwater toxic effects in a systematic and predictable way, the former can be used to predict the latter. This would have economic advantages due to a reduction in toxicity testing of saltwater species. If toxicity data are plotted as species sensitivity distributions, four theoretical relationships between freshwater and saltwater can be envisaged. Examples show that each one of these relationships is supported by empirical data. These examples show that although there is considerable potential for freshwater to saltwater prediction, species parity and representativeness need to be examined for each chemical substance to avoid bias.

Vitellogenin: a review of analytical methods to detect (anti) estrogenic activity in fish.

Vitellogenin, the fish egg yolk precursor protein, is the most common biochemical endpoint in general use for the detection of (anti) estrogen active substances in fish and other oviparous species. This review aims to cover the major methods (both protein and nucleic acid) for vitellogenin determination. Comparisons are drawn between vitellogenin and other endpoint effect levels. This review highlights strengths and weaknesses of the various techniques, concentrating on practical considerations and problems in evaluating the data they generate.

Osmoregulation in littoral and terrestrial talitroidean amphipods (Crustacea) from Britain

Osmoregulation was investigated in both aerated seawater and on saturated sand in four species of talitrid amphipods, Talitrus saltator (Montagu), Orchestia gammarellus (Pallas), Orchestia cavimana (Heller) and Arcitalitrus dorrieni (Hunt). The Osmoregulation of one species of intertidal hyalid amphipod Hyale nilssoni (Rathke) was also investigated. Appreciable differences were demonstrated in the osmoregulatory abilities of the species. Whilst the marine supralittoral species O. gammarellus and T. saltator demonstrated the ability to hypo-regulate at higher external concentrations ( > 800 mOsm), they hyper-regulated at lower concentrations, maintaining the haemolymph concentration between 750–850 mOsm. The fresh-water and estuarine supralittoral species O. cavimana and the landhopper A. dorrieni did not have this capacity; both these species maintained the haemolymph hyper-osmotic between external concentrations of 50–900 mOsm. The intertidal H. nilssoni also demonstrated this hyper-osmotic regulation pattern. Hyper-regulation in O. cavimana between external concentrations of 15–290 mOsm was at least partially mediated by the production of hypo-osmotic urine from the antennary gland. The landhopper A. dorrieni produced isosmotic urine as did the hyper-hypo regulating O. gammarellus. There was, however, some evidence that hyper-regulating T. saltator may also produce hypo-osmotic urine. Survivals under different acclimation regimes largely reflect the original habitat of the species: the estuarine/marine supralittoral species were tolerant of a wide range of salinities in water and on sand: the freshwater species showed reduced survival at higher salinities (1200 mOsm) but higher survival than its marine relations in freshwater ( 900 mOsm) salinities were greater on sand than in water. The results are discussed in relation to the habitats of the species and in relation to the presumed evolutionary history of the group as a whole.

Evaporative water loss under desiccation stress in semiterrestrial and terrestrial amphipods (Crustacea: Amphipoda: Talitridae)

Abstract Transpiration rates were measured in both still and moving air systems in three talitrid amphipods, Orchestia gammarellus (Pallas), Talitrus saltator (Montagu), and Arcitalitrus dorrieni (Hunt). Significant differences were demonstrated between the rates of water loss in the three species. The terrestrial A. dorrieni exhibited much higher rates than the supralittoral species. In still air at 15 °C and 75% r.h., for example, the mean rate in A. dorrieni was 0.183 ± 0.008 mg·h−1· mg wet wt−1 compared with 0.111 ± 0.003 for Orchestia gammarellus and 0.106 ± 0.003 for Talitrus saltator. In moving air, regression lines plotting weight-specific rates of water loss against saturation deficit were significantly different between the three species in their slope. The regression line for Arcitalitrus dorrieni (R= - 0.0514 + 0.0481φ) was much steeper than that for Orchestia gammarellus (R = 0.0465 + 0.0187φ) and for Talitrus saltator (R = 0.033 + 0.0128φ).Arcitalitrus dorrieni therefore showed the highest rates ofwater loss, under conditions of high desiccation stress, but there was no clear difference between the species at low values of saturation deficit. Mean calculated permeabilities reflect this trend: A. dorrieni, 0.0403 ± 0.0009 mg · h−1· mg wet wt−1 · mm Hg−1, Orchestia gammarellus, 0.0247 ± 0.0008, and Talitrus saltator, 0.0188 − 0.0006. Juvenile supralittoral talitrids of approximately the same body size as Arcitalitrus dorrieni consistently showed higher weight-specific rates of water loss in still air than adults of their own species, but the rates were usually lower than those of adult A. dorrieni. The very high rates of transpiration in A. dorrieni are not explicable by purely allometric considerations. The results are discussed with reference to the ecology and natural habitats of the species investigated and in relation to the colonization of the terrestrial habitat.

A brief re-examination of the function and regulation of extracellular magnesium and its relationship to activity in crustacean arthropods

Abstract 1. 1. The magnesium ion [Mg 2+ ] plays an important role as a co-factor in enzyme systems and as a modulator of the haemocyanin of crustacean arthropods. 2. 2. Mg 2+ is actively regulated in most decapod crustaceans via the antennal gland. The degree of regulation can be correlated to some extent with the “activity” of a particular species although there are “exceptions to the rule”. 3. 3. Intraspecific studies indicate that there is a clear relationship between haemolymph [Mg 2+ ] and the level of activity in particular crustacean species. 4. 4. A plea is made for the investigation of temporal changes in the [Mg 2+ ] of the haemolymph of a number of crustaceans and for more studies of Mg 2+ homoeostasis in general.

Foraging behaviour of Patella vulgata L. in an Irish sea-lough

Abstract The foraging movements of limpets Patella vulgata L. were studied on a vertical rock face at Lough Hyne, County Cork, Ireland. Rhythms on two adjacent grids were similar, but showed some differences in timing. Distance moved and speed of movement were related to limpet size. Feeding excursions were more regular and prolonged on spring tides than on neaps. Limpets high on the shore were active ony at night, at low water, when they moved vertically up the rock face. They fed in habitats unlike those surrounding their homes, mainly on rock that was either bare, or covered by lichens. Limpets near mid-tide level did not move preferentially in any one direction, and they appeared to show no choice of feeding area. Limpets low on the shore were active near the times of low water both at night and during the day. They tended to move horizontally and, at least on some occasions, they chose areas of low barnacle density in which to feed. The feeding patterns seen at different tidal heights are discussed in relation to growth rates.