Identifying non-invasible habitats for marine copepods using temperature-dependent R 0

SEASONAL AND INTERANNUAL DYNAMICS OF THE ABUNDANCE OF THE BLACK SEA ALIEN SPECIES <i>PSEUDODIAPTOMUS MARINUS</i> SATO, 1913 (COPEPODA, CALANOIDA, PSEUDODIAPTOMIDAE) IN THE CRIMEAN COASTAL WATERS: INFLUENCE OF THE TEMPERATURE FACTOR

Observation on the occurrence of the Black Sea alien species Pseudodiaptomus marinus were initiated since this species was reported in the coastal waters of Crimea, in 2016. Current study is focused on the 170-500 µm microplankton fraction represented by nauplii and the first copepodite stages. These data were complemented by the mesoplankton fraction abundance contributed by copepodite stages II-V and adults. Samples were collected by plastic bottles at the sea surface and by Juday and Apstein plankton nets in the upper 10 m layer. Nauplial stages of P. marinus were observed during the first three years after species invasion, in September, at the sea surface temperature range from 21.1 to 25.5 C. From 2019 to 2020, specimens appeared in July, at temperatures from 25.8 to 26.0C. The presence of specimens in samples has been observed by the end of November or December, at sea surface temperature of 13.1 or 8.6C, respectively. The maximal abundance was observed in the inner part of the Sevastopol Bay. The correlation value of 0.7-0.9 was estimated between the abundance and sea surface temperature throughout the year. Inter-annual variations of the abundance were associated with an integrative indicator of temperature (in particular, the sum of active temperatures).

Temperature cycles affect colonization potential of calanoid copepods

Marine calanoid copepods colonize new habitats, and some become invasive. Their fitness, measured by intrinsic growth rate and net reproductive rate, is partially driven by biochemical processes. Thus, it is a function of ambient temperature. Biochemical processes may not be approximated well by yearly mean temperature alone when temperature cycles yearly, largely. Higher order moments may also be important. The amplitude of yearly fluctuations of monthly and seasonal sea temperatures varies dramatically across the northern temperate regions. Thus, they can impact the fitness, thereby the colonization potential of copepods migrating across such region. To investigate this, we derive approximate metrics of periodic (yearly) fitness: the yearly intrinsic growth rate, and a weighted net reproductive rate. We use them to measure the persistence and the growth of an Allee-effect free, stage-structured, fast-maturing, small population of invasive copepods that reproduces year-round in habitats with yearly temperature cycles. We show that the yearly fitness increases substantially when a population is introduced from a habitat with large amplitude to that with small amplitude yearly fluctuating temperatures, given that their mean temperatures and other environmental and ecological factors are constant. The detected range-expansion of the modeled species matches the potential fitness gradient predicted by the metrics. The study leads to the question whether the gradient of the amplitudes of temperature between habitats with similar yearly mean temperatures impacts a class of fast-maturating calanoid copepods, colonizing new habitats, and becoming invasive.

Myofibril Changes in the Copepod Pseudodiaptomus marinus Exposed to Haline and Thermal Stresses

Copepods are small crustaceans capable to survive in various aquatic environments. Their responses to changes in different external factors such as salinity and temperature can be observed at different integration levels from copepod genes to copepod communities. Until now, no thorough observation of the temperature or salinity effect stresses on copepods has been done by optical microscopy. In this study, we used autofluorescence to visualize these effects on the morphology of the calanoid copepod Pseudodiaptomus marinus maintained during several generations in the laboratory at favorable and stable conditions of salinity (30 psu) and temperature (18°C). Four different stress experiments were conducted: at a sharp decrease in temperature (18 to 4°C), a moderate decrease in salinity (from 30 to 15 psu), a major decrease in salinity (from 30 to 0 psu), and finally a combined stress with a decrease in both temperature and salinity (from 18°C and 30 psu to 4°C and 0 psu). After these stresses, images acquired by confocal laser scanning microscopy (CLSM) revealed changes in copepod cuticle and muscle structure. Low salinity and/or temperature stresses affected both the detection of fluorescence emitted by muscle sarcomeres and the distance between them. In the remaining paper we will use the term sarcomeres to describe the elements located within sarcomeres and emitted autofluorescence signals. Quantitative study showed an increase in the average distance between two consecutive sarcomeres from 2.06 +/- 0.11 μm to 2.44 +/- 0.42 μm and 2.88 +/- 0.45μm after the exposure to major haline stress (18°C, 0 psu) and the combined stress (4°C, 0 psu), respectively. These stresses also caused cuticle cracks which often occurred at the same location, suggesting the cuticle as a sensitive area for osmoregulation. Our results suggest the use of cuticular and muscle autofluorescence as new biomarkers of stress detectable in formalin-preserved P. marinus individuals. Our label-free method can be easily applied to a large number of other copepod species or invertebrates with striated musculature.

Cleft, crevice, or the inner thigh: 'another place' for the establishment of the invasive barnacle Austrominius modestus (Darwin, 1854)

The proliferation of anthropogenic infrastructure in the marine environment has aided the establishment and spread of invasive species. These structures can create novel habitats in areas normally characterised as void of suitable settlement sites. The habitat requirements of the invasive acorn barnacle Austrominius modestus (Darwin, 1854) were assessed using a novel sampling site at Crosby Beach, Liverpool. Austrominius modestus has spread rapidly around the UK since its initial introduction, becoming locally dominant in many estuarine areas including the Antony Gormley art installation, ‘Another Place’, at Crosby Beach. The installation consists of 100 replicate solid cast-iron life-size human figures, located at a range of heights on the shore. We recorded the distribution and abundance of A. modestus present on all of the statues at various positions during the summer of 2006. The positions varied in location, exposure, direction, and rugosity. Although parameters such as rugosity and exposure did influence patterns of recruitment, they were less important than interactions between shore height and direction, and specific location on the beach. The addition of a suitable substrate to a sheltered and estuarine region of Liverpool Bay has facilitated the establishment of A. modestus. Understanding the habitat requirements of invasive species is important if we are to make predictions about their spread and the likelihood of invasion success. Austrominius modestus has already become locally dominant in some regions of the UK and, with projections of favourable warming conditions and the global expansion of artificial structures, the continued spread of this species can be expected. The implications of this on the balance between native and invasive species dominance should be considered.