Invading the Adriatic: spatial patterns of marine alien species across the Ionian–Adriatic boundary

Abstract

An important pathway of introduction of alien marine species in the Adriatic seems to be the northward expansion of species already established in the Ionian Sea, aided by the East Adriatic Current. We modelled the occupancy of alien marine species in the upper infralittoral zone of rocky bottoms across the Ionian-Adriatic border (Albanian and Montenegrin coastlines), based on underwater visual survey data. A method that took into account imperfect detection of the target species was applied to make unbiased occupancy estimations, based on a multi-model inference approach. A total of 6 alien species were found during the survey (in decreasing order of occupancy): Caulerpa racemosa, Percnon gibbesi, Ganonema farinosum, Lophocladia lallemandii, Asparagopsis taxiformis and Pinctada radiata. There was a general pattern of declining occupancy from northern Ionian Albanian coastal waters towards the southeastern Adriatic coastline. Possible reasons for this pattern are: (1) the invasion of some species from the northern Ionian Sea is still in progress and the limit of the current distributional range falls within or near the study area; (2) the lower temperatures in the Adriatic Sea restrict the northward expansion of thermophilic alien species; and (3) the part of Albania north of the Otranto Strait is characterized by sandy/muddy coasts, large estuarine areas and substantial freshwater input, creating a barrier for expansion of sessile species. There is a pool of 77 species established in the central Mediterranean but not yet observed in the Adriatic Sea. Among these, 14 species are present in the Greek Ionian Sea and may be considered as the most probable newcomers to the Adriatic Sea in the near future.

New Mediterranean Biodiversity Records (December 2012)

“…cylindracea was firstly registered in the central Adriatic in 2000 (Žuljević et al, 2003), while in the southern Adriatic (Montenegro) in 2004 (Mačić, 2005). In addition, for several alien species Katsanevakis et al (2011b) found a general pattern of declining occupancy from the northern Ionian Albanian coast towards the SE Adriatic. Affinity and chances of alien establishment in the Southern Adriatic will increase if sea temperature continues to increase and already established species in the central Mediterranean are in expansion.…”

“…Considering the long duration of the species' veliger stage (Emore, 2002), as well as the occurrence of northward currents along the SE Adriatic coast (Marini et al, 2010), the spread of A. dactylomela in the Adriatic Sea appears to be inevitable, as is true for many other alien species (Katsanevakis et al, 2011b). Nevertheless, A. dactylomela has already been recorded (2006) from Croatia, further north in the Adriatic Sea than the present record (Turk, 2006;Despalatović et al, 2008).…”

Chasing fish and catching data: recreational spearfishing videos as a tool for assessing the structure of fish assemblages on shallow rocky reefs

“…In the general formulation by MacKenzie et al (2002), the presence/ absence of a species at a given number of s sites is recorded K times by the same or independent observers. In the approach proposed by Katsanevakis et al (2011), and more recently applied by Issaris et al (2012) and Salomidi et al (2013), the replication of sampling through time is replaced by repeated independent observations by different observers. Detections by each single observers are considered as surveys sensu MacKenzie et al (2006), generating, for each study site, a detection history consisting of a string of 1 (detection) and 0 (nondetection).…”

“…The wrasse, Symphodus rostratus, was used as a model species, since, in contrast to most of the other species, it was not detected at all sampling sites. The occupancy of S. rostratus was modelled by following the approach proposed by Katsanevakis et al (2011), which expands the single-season procedures developed by MacKenzie et al (2002MacKenzie et al ( , 2006. In the general formulation by MacKenzie et al (2002), the presence/ absence of a species at a given number of s sites is recorded K times by the same or independent observers.…”

“…In addition, in order to show the potential use of spearfishing videos for testing broad hypotheses, we investigated how estimates of species occupancy (i.e. probability of presence in a sampling unit) can be improved by taking into account imperfect detection (the probability of correctly recording the presence of a species when present in a sampling unit; MacKenzie et al 2002, Katsanevakis et al 2011, Issaris et al 2012. In order to provide a worked example, we modelled the occupancy of a species (the wrasse Symphodus rostratus) at increasing distances from a commercial port, explicitly incorporating imperfect detectability as a function of covariates extracted from videos (video length and habitat characteristics).…”