Atlantic blue crab (Callinectes sapidus Rathbun, 1896) in a protected coastal lagoon in SE Spain.
-
1
Oceanographic Center of Murcia, Spanish Institute of Oceanography, Spain
-
2
Cofradía de Pescadores de San Pedro del Pinatar, Spain
Introduction
The Atlantic blue crab (Callinectes sapidus) supports an important fishery in the Western Atlantic coast, especially off the Maryland and Virginia states. Although it was detected in the Mediterranean in the 1950s, it was only recently recorded for first time in Spain, in the Mar Menor (Alos, 2005) and Delta del Ebro, 2012 (Castejón and Guerao, 2013). The blue crab has spread fast along Spain’s Mediterranean coast ever since, crossing recently the Gibraltar Strait (JA Cuesta (2018), pers. comm.). In Southeast Spain, the species has been found in a very wide salinity range, from nearly fresh water (A.A. Ramos (2018) , pers. comm.) to hypersaline environments, such as the Mar Menor coastal lagoon, which is part of a Specially Protected Area of Mediterranean Importance. Catch data are incomplete because although the artisanal fleet in the lagoon landed a few kg back in summer 2016, official catch records begun months later. Nevertheless the increased presence of blue crab in Mar Menor is clearly reflected in the available sales slips, which recorded nearly 900 kg in autumn 2018. These incipient records show a seasonal minimum in December but the overall trend is increasing.
The local Fisher’s Guild expressed their concerns, as even though the blue crab has high market value, it preys on gillnet catch and damages the gear. In addition, previous studies in other Mediterranean countries show that the blue crab is a very efficient colonizer that can effectively displace native species and alter significantly ecosystems and local economies (Carrozzo et al., 2014).
Thus a very basic and preliminary sampling scheme was implemented last year in collaboration with the fishermen. Our initial aims were threefold, to investigate i) the spatio-temporal distribution of the blue crab in the lagoon by means of stratified seasonal sampling with traps deployed by fishermen, ii) its trophic ecology, to evaluate its impact on both traditional target species and the endangered species in the lagoon that might be preyed upon, Aphanius iberus, Anguilla anguilla and Hippocampus guttulatus; and iii) its reproductive ecology, to estimate its fecundity rate.
Methods
Because we depend on fishermen to deploy the baited traps, stratification was based on fishing grounds located in different areas within the lagoon and with variable distances to the three channels opening to the Mediterranean. Catch of trapped blue crabs was meant to be used to estimate population abundance and supply samples for the trophic and reproduction studies.
However, so far we have not succeeded with neither of the two different trap designs used, and we have resorted for the time being to commercial catches to obtain samples.
Results
Samples from commercial catch have known limitations, i.e. biased length frequency and spatial distributions. In addition, not all samples have been processed yet. These caveats notwithstanding, we have observed that males and females show the same caparace length modes. Females dominate the samples in all months but May, when they are ovigerous and nearly absent. From September to December hardly any crabs are caught in the lagoon.
There are as well significant differences between length – weight relationships of males and females, with males growing to larger sizes.
With regard to blue crab diet, preliminary results show that decapods Natantia, fish and other crab species are preferred among a wide spectrum of prey species found in smaller proportions, including the endangered seahorse Hippocampus guttulatus.
Discussion
The exponential growth of commercial catch, the size frequency distribution, and the presence of mature ovigerous females suggest an established population of blue crab in the Mar Menor lagoon. Furthermore, the scarcity of females in the lagoon in May and catches of ovigerous females indicate that there are two spawning events in spring. It is very likely that females migrate to the less saline Mediterranean Sea to spawn, which would explain their absence in May. However, it must be noted that in the Eastern US Coast, female migrate towards saltier waters to spawn (Turner et al, 2003).
In origin, the Atlantic blue crab is also a seasonal fishery, with crabs migrating to deeper offshore channels in autumn, where they bury themselves in the sand until the following spring. So far we lack data to establish migration patterns in our study area, but the nearly complete absence of crabs in the commercial catch in autumn points to seasonal variations in the distribution area –or in behaviour.
Our study requires further data compilation; i.e. fishery independent sampling effort both within and outside the lagoon, as well as sampling of megalopa larvae in the channels communicating the lagoon with the Mediterranean.
Despite the urgent need for further data compilation to understand the distribution, life cycle and migration patterns of blue crab in SE Spain, present evidence suggests that for the time being a targeted fishery may be the best option to control blue crab populations in the Spanish Mediterranean. To this regard, it is unadvisable to classify Atlantic blue crab as an invasive species, since EU regulation forbids their trade.
References
Castejón D, Guerao G. A new record of the American blue crab, Callinectes sapidus Rathbun, 1896 (Decapoda: Brachyura: Portunidae), from the Mediterranean coast of the Iberian Peninsula. BioInvasion Records. 2013 Apr 1;2:141-3.
Carrozzo L, Potenza L, Carlino P, Costantini ML, Rossi L, Mancinelli G. Seasonal abundance and trophic position of the Atlantic blue crab Callinectes sapidus Rathbun 1896 in a Mediterranean coastal habitat. Rendiconti Lincei. 2014 Jun 1;25(2):201-8.
Turner HV, Wolcott DL, Wolcott TG, Hines AH. Post-mating behavior, intramolt growth, and onset of migration to Chesapeake Bay spawning grounds by adult female blue crabs, Callinectes sapidus Rathbun. Journal of Experimental Marine Biology and Ecology. 2003 Oct 28;295(1):107-30.
Keywords:
Callinectes sapidus,
Mediterranean,
Coastal lagoon,
Crab fishery,
invasion
Conference:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) , Braga, Portugal, 9 Sep - 12 Sep, 2019.
Presentation Type:
Poster Presentation
Topic:
Global Change, Invasive Species and Conservation
Citation:
Guijarro-García
E,
Vivas
M,
García
E,
Barcala
E,
Trives
M and
Muñoz
A
(2019). Atlantic blue crab (Callinectes sapidus Rathbun, 1896) in a protected coastal lagoon in SE Spain..
Front. Mar. Sci.
Conference Abstract:
XX Iberian Symposium on Marine Biology Studies (SIEBM XX) .
doi: 10.3389/conf.fmars.2019.08.00196
Copyright:
The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers.
They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.
The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.
Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.
For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.
Received:
27 Sep 2019;
Published Online:
09 Dec 2019.
*
Correspondence:
Dr. Elena Guijarro-García, Oceanographic Center of Murcia, Spanish Institute of Oceanography, Murcia, Spain, elena.guijarro@ieo.es