Spatio-temporal variation in stable isotope signatures (δ(13)C and δ(15)N) of sponges on the Saba Bank.
Spatio-temporal variation in stable isotope signatures (δ(13)C and δ(15)N) of sponges on the Saba Bank.
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作者：
Van Duyl FC;Mueller B;Meesters EH
海绵在珊瑚礁上无处不在，大多数都很长寿，因此能够适应不断变化的环境条件。它们以从流水中提取的有机物为食，它们可能含有微生物（内共生体），这有助于它们的营养。它们的饮食和稳定同位素（SI）分馏决定了海绵holobiont的SI签名。热带海绵δ 13 C和δ 15 N的SI特征的时空变化以及它们是否反映了环境的变化还知之甚少。我们调查了七种常见的海绵物种的SI签名与不同的功能特性和它们的潜在食物来源之间的15和32米的深度沿着的S-SE和E-NE侧的萨巴银行，东加勒比，在2011年10月和2013年10月。大多数海绵物种之间的SI签名显着不同，无论是在平均值和变化，表明不同的食物偏好和/或分馏，推断海绵物种特定的同位素生态位空间。2011年，与E-NE侧相比，S-SE侧的所有海绵物种都富含d13 C。2013年，双方海绵的SI特征没有差异，并且δ 13 C和δ 15 N总体上比2011年轻。海绵SI的时空变化不能归因于其潜在食物来源的SI特征的变化，其保持稳定，具有不同的SI特征的浮游生物（颗粒有机物（POM）：δ 13 C −24.9‰，δ 15 N +4.3 ‰）和底栖生物来源的食物（大型藻类：δ 13 C −15.4‰，δ 15 N +0.8 ‰）。2011年，S-SE侧海绵中δ 13 C的富集特征被认为是主要以底栖生物来源的C为食。2011年10月，双方在水团成分上的显著差异支持了这一解释。NO3和溶解有机物浓度的升高表明，2011年在浅滩的S-SE侧比N-NE侧的礁石上覆水中有更强的礁石信号。与2011年10月相比，2013年10月海绵中δ 13 C和δ 15 N的消耗与POM浓度的显著升高一致。同期δ 15 N的减少表明海绵主要从底栖来源的食物中获得N，其δ 15 N比浮游食物低。不同种类的海绵对可利用来源的平均摄食比例不同，底栖动物的摄食比例为20%~ 50%，浮游动物的摄食比例为50%~ 80%，假设海绵的δ 13 C营养富集因子为0.5‰ ± sd 0.5，δ 15 N营养富集因子为3‰ ± sd 0.5。我们认为，观察到的SI在海绵之间的变化，双方和年的结果是摄入的底栖和浮游生物衍生的有机物的比例的变化驱动的环境变化。我们发现，海绵SI签名反映了环境的变化在空间和时间上的萨巴银行和SI的海绵，无论其物种特异性的性状在一个类似的方向移动，以响应这些环境变化。
Sponges are ubiquitous on coral reefs, mostly long lived and therefore adaptive to changing environmental conditions. They feed on organic matter withdrawn from the passing water and they may harbor microorganisms (endosymbionts), which contribute to their nutrition. Their diets and stable isotope (SI) fractionation determine the SI signature of the sponge holobiont. Little is known of spatio–temporal variations in SI signatures of δ13C and δ15N in tropical sponges and whether they reflect variations in the environment. We investigated the SI signatures of seven common sponge species with different functional traits and their potential food sources between 15 and 32 m depth along the S-SE and E-NE side of the Saba Bank, Eastern Caribbean, in October 2011 and October 2013. SI signatures differed significantly between most sponge species, both in mean values and in variation, indicating different food preferences and/or fractionation, inferring sponge species-specific isotopic niche spaces. In 2011, all sponge species at the S-SE side were enriched in d13C compared to the E-NE side. In 2013, SI signatures of sponges did not differ between the two sides and were overall lighter in δ13C and δ15N than in 2011. Observed spatio–temporal changes in SI in sponges could not be attributed to changes in the SI signatures of their potential food sources, which remained stable with different SI signatures of pelagic (particulate organic matter (POM): δ13C −24.9‰, δ15N +4.3‰) and benthic-derived food (macroalgae: δ13C −15.4‰, δ15N +0.8‰). Enriched δ13C signatures in sponges at the S-SE side in 2011 are proposed to be attributed to predominantly feeding on benthic-derived C. This interpretation was supported by significant differences in water mass constituents between sides in October 2011. Elevated NO3 and dissolved organic matter concentrations point toward a stronger reef signal in reef overlying water at the S-SE than N-NE side of the Bank in 2011. The depletions of δ13C and δ15N in sponges in October 2013 compared to October 2011 concurred with significantly elevated POM concentrations. The contemporaneous decrease in δ15N suggests that sponges obtain their N mostly from benthic-derived food with a lower δ15N than pelagic food. Average proportional feeding on available sources varied between sponge species and ranged from 20% to 50% for benthic and 50% to 80% for pelagic-derived food, assuming trophic enrichment factors of 0.5‰ ± sd 0.5 for δ13C and 3‰ ± sd 0.5 for δ15N for sponges. We suggest that observed variation of SI in sponges between sides and years were the result of shifts in the proportion of ingested benthic- and pelagic-derived organic matter driven by environmental changes. We show that sponge SI signatures reflect environmental variability in space and time on the Saba Bank and that SI of sponges irrespective of their species-specific traits move in a similar direction in response to these environmental changes.
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