Marine Pollution Bulletin 64 (2012) 2146–2150
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Rapid assessment of the bryozoan, Zoobotryon verticillatum (Delle Chiaje, 1822) in marinas, Canary Islands Dan Minchin ⇑ Marine Organism Investigations, Caragh, Marina Village, Ballina, Killaloe, Co Clare, Ireland Coastal Research and Planning Institute, Klaipeda University, H Manto 84, LT92294, Lithuania
a r t i c l e
i n f o
Keywords: Zoobotryon Marina Alien Rapid assessment Canary Islands
a b s t r a c t A rapid assessment, using the abundance and distribution range method, was used to evaluate the status of a large branching bryozoan, Zoobotryon verticillatum attached to the immersed part of marina pontoons in the Canary Islands. Colonies were also found attached to the hulls of leisure craft berthed alongside pontoons at three marinas in Lanzarote during 2012. Low levels of abundance and distribution of the bryozoan occurred in marinas with a freshwater inﬂuence whereas in a sheltered marina lacking direct freshwater inputs colonies occurred at 2 per metre of combined pontoon length. While the occurrence of this bryozoan is recent it may be expected to occur elsewhere in Macaronesia most probably spread by leisure craft. Ó 2012 Elsevier Ltd. All rights reserved.
1. Introduction Recent studies on marinas have involved several specialists and investigations on many taxonomic groups (Pedersen et al., 2005; Cohen et al., 2005; Arenas et al., 2006; Buschbaum et al., 2010) including marine algae (Mathieson et al., 2008). While signiﬁcantly impacting species are revealed in such studies many of the species identiﬁed are of little interest to managers. Targeting a series of species (Ashton et al., 2006; Minchin, 2007) reduces sampling effort and areas can be more rapidly surveyed and reported in direct time, should they be found. This enables a direct response where this is appropriate. The approach to target species was developed by Hayes et al. (2002). They provided a list of potential species, according to perceived impact, that may arrive in Australia based on their known invasiveness elsewhere and their potential/known association with pathways and their vectors to Australia. Pathway analysis should also be part of such rapid assessments. Rapid assessment, according to Ramsar (2005) is deﬁned as: ‘‘a synoptic assessment, which is often undertaken as a matter of urgency, in the shortest timeframe possible to produce reliable and applicable results for its deﬁned purpose’’. The targeting of single species in rapid assessment surveys is a more recent approach to dealing with high impacting species of concern to society (Martin et al., 2010; Minchin and Zaiko, in press). Here it is shown how a large easily seen and clearly identiﬁable species attached to marinas can be rapidly surveyed within hours to provide an abundance and distribution range (ADR) which can provide an indication of the level of ⇑ Tel.: +353 866080888. E-mail address: [email protected]
0025-326X/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.marpolbul.2012.07.041
impact such a species may have on an environment and discuss how the species might have arrived. The bryozoan Zoobotryon verticillatum (Della Chiaje, 1822) is known from the Mediterranean Sea from the west coast of Italy (Zirpolo, 1924; Corriero et al., 2007) and is reported to be widespread within the Mediterranean Sea in harbour regions (Kit, 1972; Ardizzone and Riggio, 1981; Ramadan et al., 2006; Abdel-Salam and Ramadan, 2008). It has an expansive distribution in sub-tropical to tropical localities in the Atlantic, Indo-Paciﬁc (Osburn, 1927; Ganapathi and Satyanarayana Rao, 1968; Li, 1983; Abdel-Salam and Ramadan, 2008; Carlton and Eldredge, 2009; Antit et al., 2011; Knapp et al., 2011). Although established for some decades in widely separated regions it has expanded its range to the Seychelles (Ikin and Dogley, 2005), Australia (Wells and McDonald, 2010; Tilbrook, 2012), New Zealand (Cranﬁeld et al., 1998; Inglis et al., 2005) and although established in Brazil for some time (Marcus, 1937) has recently been recorded in north-eastern Brazil (Farrapeira, 2011). It has been reported from harbours and from ﬁsh farms (Ortega et al., 1993) and on mangroves and sea-grasses in Belize and on seagrasses in Florida (Winston, 1995; 2004). While in some world regions the species is considered to be cryptogenic, this bryozoan continues to expand its range to areas where it has not been previously known (McCann et al., 2007). The recent records from Macronesia, from Madeira (Wirtz and Canning-Clode, 2009) the Açores (Amat and Tempera, 2009) and Canary Islands (Olenin and Minchin, 2011) are discussed. This account documents its abundance and distribution range at three marinas on Lanzarote and its occurrence in Grand Canaria, Canary Islands. The preponderance of colonies on small craft implicates such craft in its secondary spread.
D. Minchin / Marine Pollution Bulletin 64 (2012) 2146–2150
within 2 m unit intervals. The presence or absence of Z. verticillatum colonies within each craft size and class were scored.
2. Methods The three marinas on Lanzarote are on its more sheltered eastern side: Puerto del Carmen (28° 55’ 16’’N, 13°40’ 27’’W) with 146 berths, and 1.7 nm to the south Puerto Calera (28° 55’ 01’’N, 13° 42’ 08’’W) with 420 berths; and 8.2 nm further south by sea and Marina Rubicon (28° 51’ 25’’N, 13° 48’ 54’’W) with 500 berths, on the island’s southern side. Marinas were all within 10 nm of each other, and were examined in February 2012. Puerto del Morgan (27° 48’ 59’’N, 15° 45’ 55’’W) with 216 berths, a marina on the southwest coast of Gran Canaria was examined in February 2011 and is 130 nm to the southwest of the Marina Rubicon. Leisure craft and ﬁshing vessels are the principal craft that berth in these marinas. Local ferries also operate between marinas. These marinas have boardwalks supported with ﬂoating sections to which craft can moor alongside. These ﬂoating pontoons had either ﬁve metre long steel tubes with an approximate diameter of 50 cm or a series of heavy duty plastic coated blocks each with a side of one metre. In Marina Rubicon steel tubes were only in use, in Puerto del Carmen only one metre sided units are in use, whereas at Puerto Calera both designs were present. The numbers of visible colonies of Z. verticillatum were recorded for each pontoon examined. The sides of ﬂoats supporting the pontoon boardwalk were examined along their edge and immediate underside, using polaroid spectacles. Colonies exceeding 10 cm were easily distinguishable at a distance on account of their irregular branching and translucent-grey/brown colouration in sunlight. Under dull conditions greater care was needed to identify colonies despite clear water. Colonies were removed from the water, from time to time, to conﬁrm identity. The abundance and distribution range (ADR) was calculated for each marina based on frequency of colonies per ﬂoating unit and according to the total number of ﬂoating units examined. In addition, the estimated number of colonies per overall unit length was provided. Each marina comprised an assessment unit for February 2012. The ﬁnal calculation of the ADR was based on the method of Olenin et al. (2007) and facilitated by the on-line service BINPAS at: http://www.corpi.ku.lt/databases/index.php/binpas/. Abundance was evaluated as low where Z. verticillatum made up only a small part of a community, moderate where its abundance was frequent but less than half of the abundance of the native community and high if it exceeded half the abundance and dominated (Table 1). The distribution scales for each assessment unit range from local, where it appeared only in one place, several localities where it was present in less than half of the stations where it may be expected many localities where it was found in more than half of the available localities and all localities where almost all substrata, where it may be expected, are occupied. Combinations of abundance and distribution provide a scale that ranges from ‘A’ few individuals at one locality to ‘E’ where a species occurs in high numbers in all localities (Table 1). Craft berthed at Puerto del Carmen were examined according to their size and design. Their lengths were paced out to class them
3. Results Z. verticillatum was present at all three marinas examined in Lanzarote and at one marina studied in Gran Canaria in 2011. In all cases the underwater visibility exceeded 3 m. Colonies branched irregularly ranging from bushy growths of usually less than 1 m to extended growths exceeding 2 m in overall length occurring in very sheltered areas. Large colonies, with collapsed branches, that hung vertically in the water were easily detached when handled. Colonies were not regularly distributed throughout each marina, being more frequent in sheltered areas away from the inﬂuence of freshwater inputs and wave action. They were not seen attached to the concrete surrounding inner walls of marinas. In Puerto del Carmen some small colonies were obscured by extensive ﬁlamentous algal growths. Several species from different taxonomic groups were associated with some of these colonies. These ranged from erect sponges, spirorbids, serpulids, erect bryozoa, ﬁlamentous rhodophytes, phaeophytes, small stoloniferous tunicates, caprellids, isopods, amphipods, harpactacoids, copepods and egg masses of a nudibranch. Mullet were frequently seen grazing on the underside of pontoons; but appeared to avoid Z. verticillatum. In Puerto del Carmen visible colonies were about 2 per metre of pontoon length and provided an ADR = C [medium abundance of colonies on many pontoons] (Fig. 1), whereas in Marina Rubicon and Puerto Calera both had an ADR = A value [low colony abundance on several pontoons], with <0.3 visible colonies per metre of pontoon length (Table 2). There was a preponderance of colonies attached to smaller craft (Fig. 2 and Fig. 3). Yachts of up to 12 m in length were also found with attached colonies in Marina Rubicon and Puerto Calera. In Puerto del Morgan, Gran Canaria, forty-three of sixty craft examined had attached colonies, a prevalence of 71%. In Lanzarote at Puerto del Carmen forty-ﬁve of a hundred and sixty-eight craft had one or more colonies, a prevalence of 27%. In Marina Rubicon this was 19%. Colonies were seen attached to vessels ranging from a dinghy with 14 colonies to a disused ferry of 24 m in overall length. The most frequent boat classes to be colonised were small seasonal ﬁshing vessels, angling craft, and fast sports craft including a rigid-hulled inﬂatable boat (RIB) and a jet ski. Colonies attached to hulls were clearly visible and most attached close to the waterline on a hull; although some attached at greater depths. Specimens of up to 80 cms in length attached to hulls, rudders, ladders, stabilisers, mooring lines, fenders, dinghies, cables and ﬂoats.
Table 1 Classes of abundance and distribution according to Olenin et al. (2007). Abundance
Low Medium High
Distribution scale One locality
A B B
A B C
B C D
C D E
Fig. 1. Z. verticillatum colonies attached to 1 m ﬂoating block unit.
D. Minchin / Marine Pollution Bulletin 64 (2012) 2146–2150
Table 2 Sum of the numbers of colonies per ﬂoat unit and size found on three marinas in Lanzarote. Colony numbers
Marina rubicon 5m
Puerto calera 5m
Puerto calera 1m
Puerto del carmen 1m
0 1 2 3 4 5 6 7 8 9
89 23 10 1 0 0 0 0 0 0 123 615 0.07 A
43 26 12 13 7 3 1 1 0 0 106 530 0.27 A
137 9 3 4 1 0 0 0 0 0 154 154 0.2 A
36 33 44 19 10 10 6 1 1 1 161 161 2.04 C
Total m Colonies m ADR
transparency and the obvious appearance of colonies. Such surveys are cost effective and provide sufﬁcient information at low-cost. However, the approach used here could result in a bias towards recording larger colonies >50cm in length; because these could be attached to the underside of a ﬂoat some distance away from its edge as slight water currents could displace colonies either away or into view. In addition, when scoring the numbers of colonies, their attachment points were not always clearly distinguishable as some colonies interlaced and so may not have been counted correctly. Small colonies, although not counted, frequently occurred alongside large colonies. In areas devoid of large colonies more careful examination often failed to reveal the presence of smaller colonies. Although the overall numbers of all colonies per unit length of pontoon were likely to have been underestimated, the method was unlikely to have altered the ADR assessment. The numbers of colonies at these three marinas do not represent a heavy fouling burden; but their numbers could expand to a nuisance level later in the season or at some future time. Should this happen it would be likely to take place within the most sheltered part of a marina away from the inﬂuence of freshwater discharges. Colonies are known to result in fouling of structures in Galveston Bay, USA (Gossett et al., 2004) and when abundant can ﬁlter large volumes of water (Bullivant, 1968; Hill, 2001). Growths do not appear to be grazed upon by mullet and this may relate to the bromo-alkaloids produced by colonies (Sato and Fenical, 1983) which may discourage this. Discharges of freshwater at two marina sites may suppress colony formation, however, the species is capable of surviving in hyper saline environments to salinities of 56 psu (Coleman, 1999). 4.2. Association with vessel hulls
Fig. 2. Z. verticillatum attached to the hull of a sport craft 8 m length.
4. Discussion 4.1. Relative abundance at marinas Z. verticillatum varied in abundance between and within marinas. Each marina was surveyed within a four-hour period by a single person. Observations were facilitated by good water
The abundance of Z. verticillatum attached to pontoon ﬂotation units provide opportunities to colonise the adjacent surfaces of hulls of vessels berthed alongside. According to Floerl and Inglis (2005) the hulls of vessels gradually develop over time the same fouling communities that occur on pontoons. In this way colonies, once established on a hull, may subsequently become transported elsewhere. The appearances of Z. verticillatum in Macaronesian marinas that lie on yachting routes implicate leisure craft in its transmission. This is most likely to have happened with departures from the Mediterranean Sea. From Gibralter to Funchal in Madeira the distance is 613 nm, to Puerto Calera, 608 nm; Horta in the Azores,
Fig. 3. Frequency of Z. verticillatum attached to craft of different overall lengths (m) at Puerto del Carmen. Numbers indicate the numbers of craft with one or more colonies.
D. Minchin / Marine Pollution Bulletin 64 (2012) 2146–2150
1135 nm (Cornell, 2002). Distances between the Azores, Madeira and the Canary Islands range from 269–490 nm. The distance southwards to the Cape Verde Islands, also a destination area for yachts, is 860 nm; and Z. verticillatum might be expected to arrive there. Yachts travel at comparatively lower speeds than most other craft and under light wind conditions small attached colonies, or attached remnants of these, may be retained en route. A small number of yachts, >10 m length, with ensigns from different European states and from North America, were found to be fouled with Z. verticillatum in Puerto Calera and Marina Rubicon, whereas local craft are mainly berthed in Puerto del Carmen (Hammick, 2004). According to Geiger and Zimmer (2002) should colonies become damaged during passage, new colonies can grow from their small remaining anchoring rootlets. As a result it is possible for re-growth of surviving colonies following a voyage to distant marinas. Locally small craft movements of Z. verticillatum may be responsible for secondary spread between adjacent marinas along a coastline, a view shared by Wells and McDonald (2010) in their study in Western Australia. In the present study several colonies were found attached to such craft occurring within the most sheltered region of a marina, where colonies appear more frequently. Only small attached stages in sheltered regions along the hull are most likely to be transmitted, because large colonies are easily detached or broken. Brock (1985) noted that detachments from harbour structures were often stranded. Vessels already fouled with other biota may aid a transmission. In the Puerto Calera marina, colonies were conﬁned to the central part of the innermost pontoons where some visiting yachts were berthed. Large colonies attached to some craft indicate inactivity. Nevertheless colonies can grow rapidly and may attain a length of over a metre in a six to eight month period (Fox, 2001). The port of Arrecife, also on the island of Lanzarote, was not examined in this study. It is possible ships discharging ballast water might have released colony fragments of Z. verticillatum. However, Z. verticillatum has a short-lived free-swimming coronate larva unlikely to be transmitted in this way and for this reason hull transport would appear to be a more likely mode of spread. 4.3. Application of the method elsewhere Marinas are generally accepted as being sites where many alien species can appear. Marinas are practical sites to survey as this can take place at any tidal state and yet enable representative collections because the fouling is conﬁned within a narrow zonation when attached to pontoon ﬂoats. The rapid assessment method involving direct observation, with some selective sampling for conﬁrmation, should be suitable for scoring large organisms that protrude from marina pontoons such as the fanworm Sabella spallanzanii and the macroalga Undaria pinnatiﬁda. Sampling, to evaluate the abundance and distribution of smaller sessile species, by scraping samples from pontoon surfaces would not require clear water and would be suitable for evaluating the ADR of a wider range of organisms, although this would require more time to complete. Acknowledgements The author would like to thank S. Olenin, A. Zaiko and an anonymous reviewer for constructive criticism. References Abdel-Salam, K.H.M., Ramadan, S.H.E., 2008. Fouling bryozoa from some Alexandria harbours Egypt (I) erect species. Medit. Mar. Sci. 9 (2), 5–20. Amat, J.N., Tempera, F., 2009. Zoobotryon verticillatum Della Chiaje, 1822 (Bryozoa), a new occurrence in the archipelago of the Azores (North-Eastern Atlantic). Mar. Pollut. Bull. 58 (5), 761–764.
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